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What is PET-CT?

PET/CT is a new imaging tool that combines two scan techniques in one exam - a PET scan
and a CT scan. PET/CT is mainly used for diagnosis, staging or restaging malignant disease
and metastases and evaluation of treatment response. It may also be used to differentiate
dementia verses Alzheimer's disease. The two procedures together provide information about
the location, nature of and the extent of the lesion. In other words, it answers questions like:
Where is the tumour, how big is it, is it malignant, benign or due to inflammatory change,
and has the cancer spread?

How does PET-CT work?

PET/CT combines or merges a PET scan and a CT scan into one set of images.

How does CT work?

CT stands for Computerized Tomography (commonly known as a CAT scan). During the CT
scan, the scanner emits X-rays, which go through the patient to detectors. The computer uses
this information to generate cross-sectional images of anatomical structures. Your body will
not come in contact with the scanner itself. You will be lying on a narrow table, which will
move through the scanner or dectors. Each cross-sectional picture or slice gives detailed
anatomic location and changes in the anatomy. The use of oral and IV contrast agents can
enhance the details by highlighting the gastrointestinal tract (filled by oral contrast) and other
organs and blood vessels (filled with IV contrast).

How does PET work?

PET stands for Positron Emission Tomography. PET scans measure metabolic activity and
molecular function by using a radioactive glucose injection. The F-18 FDG is injected into
the patient. The PET scanner detects the radiation emitted from the patient, and the computer
generates three-dimensional images of tissue function or cell activity in the tissues of your
body. These functional images can detect disease earlier than the anatomic information
gained from CT alone. Like the CT scanner, your body will never come in contact with
scanner itself. There are no side effects from this injection and procedure.

All cells use glucose as an energy source. However, cancer cells grow faster than normal
healthy cells and they use glucose at much higher rate than normal cells. This is the basis of
imaging with F-18 FDG for cancer detection in PET scan.


Nuclear medicine examinations offer information that is unique—including details on both
function and structure—and often unattainable using other imaging procedures.

For many diseases, nuclear medicine scans yield the most useful information needed to make
a diagnosis or to determine appropriate treatment, if any.

Nuclear medicine is less expensive and may yield more precise information than exploratory

By identifying changes in the body at the cellular level, PET imaging may detect the early
onset of disease before it is evident on other imaging tests such as CT or MRI.

Greater detail with a higher level of accuracy; because both scans are performed at one time
without the patient having to change positions, there is less room for error

Greater convenience for the patient who undergoes two exams (CT & PET) at one sitting,
rather than at two different times.


Because the doses of radiotracer administered are small, diagnostic nuclear medicine
procedures result in low radiation exposure, acceptable for diagnostic exams. Thus, the
radiation risk is very low compared with the potential benefits.

Nuclear medicine diagnostic procedures have been used for more than five decades, and there
are no known long-term adverse effects from such low-dose exposure.

The risks of the treatment are always weighed against the potential benefits for nuclear
medicine therapeutic procedures. You will be informed of all significant risks prior to the
treatment and have an opportunity to ask questions.

Allergic reactions to radiopharmaceuticals may occur but are extremely rare and are usually
mild. Nevertheless, you should inform the nuclear medicine personnel of any allergies you
may have or other problems that may have occurred during a previous nuclear medicine

Injection of the radiotracer may cause slight pain and redness which should rapidly resolve.

Women should always inform their physician or radiology technologist if there is any
possibility that they are pregnant or if they are breastfeeding.

Nuclear medicine procedures can be time consuming. It can take hours to days for the
radiotracer to accumulate in the part of the body under study and imaging may take up to
several hours to perform, though in some cases, newer equipment is available that can
substantially shorten the procedure time.

The resolution of structures of the body with nuclear medicine may not be as high as with
other imaging techniques, such as CT or MRI. However, nuclear medicine scans are more
sensitive than other techniques for a variety of indications, and the functional information
gained from nuclear medicine exams is often unobtainable by other imaging techniques.

PET scanning can give false results if chemical balances within the body are not normal.
Specifically, test results of diabetic patients or patients who have eaten within a few hours
prior to the examination can be adversely affected because of altered blood sugar or blood
insulin levels.

Because the radioactive substance decays quickly and is effective for only a short period of
time, it is important for the patient to be on time for the appointment and to receive the
radioactive material at the scheduled time. Thus, late arrival for an appointment may require
rescheduling the procedure for another day.

A person who is very obese may not fit into the opening of a conventional PET/CT unit.
                                         MRI SCAN

    What is MRI?
    Magnetic resonance imaging (MRI), nuclear magnetic resonance imaging (NMRI), or
    magnetic resonance tomography (MRT) is a medical imaging technique used in radiology to
    visualize internal structures of the body in detail. MRI makes use of the property of nuclear
    magnetic resonance (NMR) to image nuclei of atoms inside the body.
    MRI provides good contrast between the different soft tissues of the body, which makes it
    especially useful in imaging the brain, muscles, the heart, and cancers compared with other
    medical imaging techniques such as computed tomography (CT) or X-rays. Unlike CT scans
    or traditional X-rays, MRI does not use ionizing radiation
    An MRI scan, or Medical Resonance Imaging Scan, is one of the most common types of
    scans ordered for injuries and serious medical conditions. These scans are done for a variety
    of reasons, including muscular/skeletal problems, head injuries, and even cancer. The scans
    have been performed since the 1980s, yet many patients do not know what is happening when
    they are sent into the MRI tube.
    An MRI is a giant, extremely strong magnet that uses magnetic fields and radio waves to
    produce images of the body. Magnets are measured in a unit known as the gauss. This is
    more understandable when you note that the earth has a 0.5-gauss magnetic field. Large
    magnets are measured in a unit called a tesla, which equals 10,000 gauss. An MRI has a
    magnet that creates magnetic field of .5 to 2.0 tesla. When a patient receives an MRI, he is
    sent into the bore of the magnet, which is the hole in the middle, on a special movable table.
    The area of the body being scanned is placed into the exact center of the magnetic field
    before the scan begins.
   The Science Behind MRI Scans
    The MRI scan takes advantage of the fact that the body is made of a lot of water. This water
    contains oxygen and hydrogen molecules. Since hydrogen molecules have a natural magnetic
    spin, the MRI can change the alignment of the atoms' nuclei using the magnetic field and a
    radio-frequency wave burst. Once they are aligned, another pulse of radio-frequency waves
    will cause them to resume their normal position. When the hydrogen molecules move in this
    manner, the atoms themselves send out radio waves, which are recorded and mapped by the
    The time it takes for these molecules to regain their natural alignment varies depending on
    the type of tissue being scanned. The computer will record the amount of time the molecules
    take to realign themselves, and this allows the scan to detect different types of tissue as it
    makes a map of the body.
   What MRI Scans Show?
   MRI scans are able to show most body tissues. Tissues, like bones, that do not have much
    water in them, and therefore do not have much hydrogen, will appear dark on the scan. Other
    tissues will appear brighter. The scan will deliver two-dimensional pictures of the body,
    allowing the doctor to look layer by layer at the area being scanned. This can be turned into
    three-dimensional models on the computer that can be manipulated, allowing the doctor to
    see even more detail about the tissue before planning treatment. Blood flow can also be
    measured using an MRI scan, without the need for a contrast injection as other imaging
    techniques require.

    How To Prepare

    Before your MRI test, tell your doctor and the MRI technologist if you:

   Are allergic to any medicines. The contrast material used for MRI does not contain iodine. If
    you know that you are allergic to the contrast material used for the MRI, tell your doctor
    before having another test.
   Are or might be pregnant.
   Have any metal implanted in your body. This helps your doctor know if the test is safe for
    you. Tell your doctor if you have:
o   Heart and blood vessel devices such as a coronary artery stent, a pacemaker, an ICD
    (implantable cardioverter-defibrillator), or a metal heart valve.
o   Metal pins, clips, or metal parts in your body, including artificial limbs and dental work or
o   Any other implanted medical device, such as a medicine infusion pump or a cochlear implant.
o   Cosmetic metal implants, such as in your ears, or tattooed eyeliner.
   Had recent surgery on a blood vessel. In some cases, you may not be able to have the MRI
   Have an intrauterine device (IUD) in place. An IUD may prevent you from having the MRI
    test done.
   Become very nervous in confined spaces. You need to lie very still inside the MRI magnet, so
    you may need medicine to help you relax. Or you may be able to have the test done with open
    MRI equipment. It is not as confining as standard MRI machines.
   Have any other health conditions, such as kidney problems or sickle cell anemia, that may
    prevent you from having an MRI using contrast material.
   Wear any medicine patches. The MRI may cause a burn at the patch site.

    You may need to arrange for someone to drive you home after the test, if you are given a
    medicine (sedative) to help you relax.

    For an MRI of the abdomen or pelvis, you may be asked to not eat or drink for several hours
    before the test.

    You may need to sign a consent form that says you understand the risks of an MRI and agree
    to have the test done. Talk to your doctor about any concerns you have regarding the need for
    the test, its risks, how it will be done, or what the results will mean. To help you understand
    the importance of this test, fill out the medical test information form.

    How It Is Done

    A magnetic resonance imaging (MRI) test is usually done by an MRI technologist. The
    pictures are usually interpreted by a radiologist. But some other types of doctors can also
    interpret an MRI scan.
    You will need to remove all metal objects (such as hearing aids, dentures, jewelry, watches,
    and hairpins) from your body because these objects may be attracted to the powerful magnet
    used for the test.

    You will need to take off all or most of your clothes, depending on which area is examined
    (you may be allowed to keep on your underwear if it is not in the way). You will be given a
    gown to use during the test. If you are allowed to keep some of your clothes on, you should
    empty your pockets of any coins and cards (such as credit cards or ATM cards) with scanner
    strips on them because the MRI magnet may erase the information on the cards.

    During the test you usually lie on your back on a table that is part of the MRI scanner. Your
    head, chest, and arms may be held with straps to help you remain still. The table will slide
    into the space that contains the magnet. A device called a coil may be placed over or wrapped
    around the area to be scanned. A special belt strap may be used to sense your breathing or
    heartbeat. This triggers the machine to take the scan at the right time.

    Some people feel nervous (claustrophobic) inside the MRI magnet. If this keeps you from
    lying still, you can be given a medicine (sedative) to help you relax. Some MRI machines
    (called open MRI) are now made so that the magnet does not enclose your entire body. Open
    MRI machines may be helpful if you are claustrophobic, but they are not available
    everywhere. The pictures from an open MRI may not be as good as those from a standard
    MRI machine. See pictures of a standard MRI machine and an open MRI machine.

    Inside the scanner you will hear a fan and feel air moving. You may also hear tapping or
    snapping noises as the MRI scans are taken. You may be given earplugs or headphones with
    music to reduce the noise. It is very important to hold completely still while the scan is being
    done. You may be asked to hold your breath for short periods of time.

    During the test, you may be alone in the scanner room. But the technologist will watch you
    through a window. You will be able to talk with the technologist through a two-way

    If contrast material is needed, the technologist will put it in an intravenous (IV) line in your
    arm. The material may be given over 1 to 2 minutes. Then more MRI scans are done.

    An MRI test usually takes 30 to 60 minutes but can take as long as 2 hours.

    The main advantages of magnetic resonance imaging scans are that :

   They do not involve exposure to radiation, so they can be safely used in people who might be
    particularly vulnerable to the effects of radiation, such as pregnant women and babies.
   They are particularly useful for showing soft tissue structures, such as ligaments and
    cartilage, and organs such as the brain , heart, and eyes.
   They can provide information about how the blood moves through certain organs and blood
    vessels, allowing problems with blood circulation, such as blockages, to be identified.

    The main disadvantages of magnetic resonance imaging scans are listed below:

   MRI scanners are very expensive, a single scanner can cost over a million pounds.
   The combination of being put in an enclosed space and the loud noises that are made by the
    magnets can make some people feel claustrophobic while they are having a MRI scan.
   MRI scanners can be affected by movement, making them unsuitable for investigating
    problems such as mouth tumours because of coughing, or swallowing, can make the image
    that are produced less clear.
                                       CT SCAN

What is a CT scan?

Computerized (or computed) tomography, and often formerly referred to as computerized
axial tomography (CAT) scan, is an X-ray procedure that combines many X-ray images with
the aid of a computer to generate cross-sectional views and, if needed, three-dimensional
images of the internal organs and structures of the body. Computerized tomography is more
commonly known by its abbreviated names, CT scan or CAT scan. A CT scan is used to
define normal and abnormal structures in the body and/or assist in procedures by helping to
accurately guide the placement of instruments or treatments.

A large donut-shaped X-ray machine or scanner takes X-ray images at many different angles
around the body. These images are processed by a computer to produce cross-sectional
pictures of the body. In each of these pictures the body is seen as an X-ray "slice" of the
body, which is recorded on a film. This recorded image is called a tomogram. "Computerized
axial tomography" refers to the recorded tomogram "sections" at different levels of the body.

Imagine the body as a loaf of bread and you are looking at one end of the loaf. As you
remove each slice of bread, you can see the entire surface of that slice from the crust to the
center. The body is seen on CT scan slices in a similar fashion from the skin to the central
part of the body being examined. When these levels are further "added" together, a three-
dimensional picture of an organ or abnormal body structure can be obtained.

Why are CT scans performed?

CT scans are performed to analyze the internal structures of various parts of the body. This
includes the head, where traumatic injuries, (such as blood clots or skull fractures), tumors,
and infections can be identified. In the spine, the bony structure of the vertebrae can be
accurately defined, as can the anatomy of the intervertebral discs and spinal cord. In fact, CT
scan methods can be used to accurately measure the density of bone in evaluating

Occasionally, contrast material (an X-ray dye) is placed into the spinal fluid to further
enhance the scan and the various structural relationships of the spine, the spinal cord, and its
nerves. Contrast material is also often administered intravenously or through other routes
prior to obtaining a CT scan. CT scans are also used in the chest to identify tumors, cysts, or
infections that may be suspected on a chest X-ray. CT scans of the abdomen are extremely
helpful in defining body organ anatomy, including visualizing the liver, gallbladder,
pancreas, spleen, aorta, kidneys, uterus, and ovaries. CT scans in this area are used to verify
the presence or absence of tumors, infection, abnormal anatomy, or changes of the body
caused by trauma.

The technique is painless and can provide extremely accurate images of body structures in
addition to guiding the radiologist in performing certain procedures, such as biopsies of
suspected cancers, removal of internal body fluids for various tests, and the draining of
abscesses which are deep in the body. Many of these procedures are minimally invasive and
have markedly decreased the need to perform surgery to accomplish the same goal.

How does it work?
Computed Tomography Imaging works on the same basis of an x-ray. As the x-ray beams
pass through the body, they are absorbed at different levels and a profile is created of x-rays
beams of different strengths. These are recorded on film as an image or in the case of an x-
ray, resembling a shadow. The use of a computer in CT
scanning is what differs from a conventional x-ray. A
CT scanner consists of a table on which the patient lies
which moves in through the ring shaped scanner. A
moveable ring located is on the edge of the scanner
which contains the x-ray tube and its associated
detectors. A CT scan involves the movable ring
revolving around the patient with fine fan of x-ray
beams being passed through the body from all angles
into their associated detectors, with the information from
each detector relating to a particular part of the body.
All this information from the detectors must be
compiled into a detailed image of the particular slice of
the body by the computer. Every time the movable ring
makes a 360 degree rotation, a slice has been acquired.
These slices give such detailed images of the internal
structures of the body that they have become widely used in radiology, in both the diagnosis
of diseases, checking of bodily structures such as the brain, heart, liver, lungs and kidneys
and also in trauma to check for injury.

The CT Scan:
Preparation for a CT scan is similar to x-rays and MRI scans. Most radiology clinics provide
patients with a hospital gown, but otherwise all jewellery and items such as hats, belts, clips,
and glasses must be removed as some objects have a detrimental effect on the image when
scanned. In some cases contrast agents are administered to image particular tissues more
effectively. Many contrasts agents do contain iodine, which can provoke an allergic reaction
in some patients. If you have an allergy to iodine or any other allergies, notify the nurse,
    technician or radiologists before the administration of the contrast agent. If you suspect you
    may be pregnant or you are pregnant, you must notify your doctor before the CT scan as this
    procedure does involve radiation and can be dangerous to a developing foetus. A CT scan is
    very similar to a MRI scan.
    You will be asked to lie on the table in a still position and the table will move into the tunnel.
    During the scan, the table will move a small distance every few seconds to reposition you for
    the next scan. During the scanning, the machine may make buzzing or click sounds as it
    moves. You will be alone in the scanning room, but the radiologist conducting the scan will
    be able to see you through a window into the room and communicate with you via intercom.
    The scan can last from 30-90 minutes, during which you will be asked to lie very still in the
    scanner which for some can cause anxiety or claustrophobia. If you suffer from a fear of
    small spaces (claustrophobia), inform your doctor and the radiologists and a sedative can be
    administered in appropriate conditions. After the scan, the details of the results may be shared
    by the radiologist or referred back to your doctor. Your day can continue as normal however
    it is recommended if you were given a contrast agent to drink water to flush your body of the

    Benefits of CT include more effective medical management by:

   determining when surgeries are necessary
   reducing the need for "exploratory" surgeries
   improving cancer diagnosis and treatment
   reducing the length of hospitalizations
   guiding treatment of common conditions such as injury, cardiac disease and stroke
   improving patient placement into appropriate areas of care, such as intensive care units

    In an emergency room, patients can be scanned quickly so doctors can rapidly assess their
    condition. Emergency surgery might be necessary to stop internal bleeding. CT shows the
    surgeons exactly where to operate. Without this information, the success of surgery is greatly
    compromised. The risk of radiation exposure from CT is very small compared to the benefits
    of a well-planned surgery.

    CT provides medical information that is different from other imaging examinations, such as
    ultrasound, MRI, SPECT, PET or nuclear medicine. Each imaging technique has advantages
    and disadvantages. The principal advantages of CT are:

    CT provides medical information that is different from other imaging examinations –
    ultrasound, MRI, SPECT, PET or nuclear medicine. Each imaging technique has advantages
    and disadvantages. The principal advantages of CT are:

1. Very rapid acquisition of images
2. A wealth of clear and specific information
3. A view of a large portion of the body

    No other imaging procedure combines these advantages into a single session.


    There is no conclusive evidence that radiation at amounts delivered by a CT scan causes
    cancer. Large population studies have shown a slight increase in cancer from larger amounts
    of radiation, such as from radiation therapy. Thus, there is always concern that this risk may
    also apply to the lower amounts of radiation delivered by a CT exam. When a CT scan is
    recommended by your doctor, the expected benefit of this test outweighs the potential risk
    from radiation. You are encouraged to discuss the risks versus the benefits of your CT scan
    with your doctor, and to explore whether alternative imaging tests may be available to
    diagnose your condition.

   The effective radiation dose for this procedure varies. Women should always inform their
    physician and x-ray or CT technologist if there is any possibility that they are pregnant. CT
    scanning is, in general, not recommended for pregnant women unless medically necessary
    because of potential risk to the baby.
   Manufacturers of intravenous contrast indicate mothers should not breastfeed their babies for
    24-48 hours after contrast medium is given. However, both the American College of
    Radiology (ACR) and the European Society of Urogenital Radiology note that the available
    data suggest that it is safe to continue breastfeeding after receiving intravenous contrast.
   The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare,
    and radiology departments are well-equipped to deal with them.
   Because children are more sensitive to radiation, they should have a CT exam only if it is
    essential for making a diagnosis and should not have repeated CT exams unless absolutely
    necessary. CT scans in children should always be done with low-dose technique.


    Soft-tissue details in areas such as the brain, internal pelvic organs, and joints (such as knees
    and shoulders) can often be better evaluated with magnetic resonance imaging (MRI). In
    pregnant women, while CT can be performed safely, other imaging exams not involving
    radiation, such as ultrasound or MRI, is preferred if they are likely to be as good as CT in
    diagnosing your condition.

                               DIALYSIS MACHINE
    What is Dialysis

    The kidneys are responsible for filtering waste products from the blood. Dialysis is a
    procedure that is a substitute for many of the normal duties of the kidneys. The kidneys are
    two organs located on either side of the back of the abdominal cavity. Dialysis can allow
    individuals to live productive and useful lives, even though their kidneys no longer work
    adequately. In the United States, there are over 200,000 people who use dialysis techniques
    on an ongoing basis.

    Dialysis helps the body by performing the functions of failed kidneys. The kidney has many
    roles. An essential job of the kidney is to regulate the body's fluid balance. It does this by
    adjusting the amount of urine that is excreted on a daily basis. On hot days, the body sweats
    more. Thus, less water needs to be excreted through the kidneys. On cold days, the body
    sweats less. Thus, urine output needs to be greater in order to maintain the proper balance
    within the body. It is the kidney's job to regulate fluid balance by adjusting urine output.

    Another major duty of the kidney is to remove the waste products that the body produces
    throughout the day. As the body functions, the cells use energy. The operation of the cells
    produces waste products that must be removed from the body. When these waste products are
    not removed adequately, they build up in the body. An elevation of waste products, as
    measured in the blood, is called "azotemia." When waste products accumulate they, cause a
    sick feeling throughout the body called "uremia."

    How Do Dialysis Machines Work?
   Dialysis machines work on the principle of diffusion of solutes through a semi-permeable
    membrane. A semi-permeable membrane is one that only lets some solutes through, and the
    solutes in this case are things that are dissolved in the blood, specifically waste products. The
    dialysis membrane has two sides. One side faces the blood, which is flowing in one direction.
    The other side is facing a specially made dialysis liquid flowing in the opposite direction. The
    membrane has holes that are small enough to let small solutes (like waste products) and fluid
    flow through them but not bigger things like blood cells and sugars. The flow of the dialysis
    liquid in the opposite direction helps to ensure that there is maximum diffusion of solutes
    from the blood to the dialysis fluid. As a result, certain solutes that are abnormally high in the
    blood, such as urea, potassium and calcium, will be removed, helping the blood to maintain
    healthy levels of these solutes. The things that are present in the dialysis solution can be
    altered to fit the individual needs of the patient.
    Types of Dialysis
    There are two main types of dialysis: "hemodialysis" and "peritoneal dialysis." Hemodialysis
    uses a special type of filter to remove excess waste products and water from the body.
    Peritoneal dialysis uses a fluid that is placed into the patient's stomach cavity through a
    special plastic tube to remove excess waste products and fluid from the body.

    During hemodialysis, blood passes from the patient's body through a filter in the dialysis
    machine, called a "dialysis membrane." For this procedure, the patient has a specialized
    plastic tube placed between an artery and a vein in the arm or leg (called a "gortex graft").
    Sometimes, a direct connection is made between an artery and a vein in the arm. This
    procedure is called a "Cimino fistula." Needles are then placed in the graft or fistula, and
blood passes to the dialysis machine, through the filter, and back to the patient. In the dialysis
machine, a solution on the other side of the filter receives the waste products from the patient.

Peritoneal Dialysis
Peritoneal dialysis uses the patients own body tissues inside of the belly (abdominal cavity) to
act as the filter. The intestines lie in the abdominal cavity, the space between the abdominal
wall and the spine. A plastic tube called a "dialysis catheter" is placed through the abdominal
wall into the abdominal cavity. A special fluid is then flushed into the abdominal cavity and
washes around the intestines. The intestinal walls act as a filter between this fluid and the
blood stream. By using different types of solutions, waste products and excess water can be
removed from the body through this process.

Advantages and Disadvantages

Each of the two types of dialysis, hemodialysis and peritoneal dialysis, has advantages and
disadvantages. It is up to the patient to decide which of these procedures is best by
considering her/his life style, other medical conditions, support systems, and how much
responsibility and participation in the treatment program he/she desires. Each patient must
view the two types of dialysis procedures from her/his own perspective.

Regardless of which type of dialysis is chosen , patients have certain responsibilities such as
following a diet program, watching their fluid intake and taking special vitamins and other
medicines to control blood pressure and calcium and phosphorus balance.

For many patients, the major advantage of hemodialysis is minimal participation in the
treatment. However, patients are required to adhere to a specific schedule and travel to the
dialysis unit. Hemodialysis also requires stricter diet control and fluid control than peritoneal

For those patients preferring more independence, peritoneal dialysis allows for more flexible
scheduling and can be performed at home. The patient still must undergo a certain amount of
dialysis each day, but can alter the exact timing of the dialysis procedure. On the other hand,
peritoneal dialysis must be done every day of the week.

The major problem with peritoneal dialysis is infection. The patient has a plastic tube that
goes from the peritoneal cavity to the outside of the body and this is a potential site for the
entry of bacteria into the body. Great emphasis is placed on cleanliness and technique during
the training sessions.
                              ULTRASOUND SCAN

    Ultrasound is a cyclic sound pressure wave with a frequency greater than the upper limit of
    human hearing. Ultrasound is thus not separated from "normal" (audible) sound based on
    differences in physical properties, only the fact that humans cannot hear it. Although this
    limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy,
    young adults. The production of ultrasound is used in many different fields, typically to
    penetrate a medium and measure the reflection signature or supply focused energy. The
    reflection signature can reveal details about the inner structure of the medium, a property also
    used by animals such as bats for hunting. The most well known application of ultrasound is
    its use in sonography to produce pictures of fetuses in the human womb. There are a vast
    number of other applications as well
    Ultrasound scanning is a tool used in a wide range of fields ranging from other areas of the
    medical field to the industrial workplace. This technology works on the basis of pulse and
    echo to locate specific types of substances and map out their exact locations.
   Ultrasound scanning works by producing very high-pitched sound waves. These sound waves
    are so high that humans are unable to hear them. In fact, most ultrasound scanner equipment
    emits sounds waves between 3-10 MHz. Most humans can only hear between 20 and 20,000
    MHz. To get an image, these sound waves are projected into the subject being tested using a
   A transducer is a piece of equipment that is placed between the sound waves and the subject
    being tested. The transducer converts ultrasound waves into ultrasonic waves.

   Once the ultrasonic waves are directed into the body, they travel through the substance being
    tested. For example, when an ultrasound is being done on a human, the ultrasonic waves
    penetrate the tissues of the body. Once the waves hit a different acoustic nature or even a
    different texture, the waves are immediately bounced back to the imaging equipment. The
    ultrasound scanning equipment can then interpret the reflected signal, and use it to create a
    map of whatever is being scanned.
   Principle
          When a sound wave strikes an object, it bounces back, or echoes. By measuring these
           echo waves, it is possible to determine how far away the object is and its size, shape
           and consistency (whether the object is solid, filled with fluid, or both).
          In medicine, ultrasound is used to detect changes in appearance of organs, tissues, and
           vessels or detect abnormal masses, such as tumors.
          In an ultrasound examination, a transducer both sends the sound waves and
           receives/records the echoing waves. When the transducer is pressed against the skin, it
           directs small pulses of inaudible, high-frequency sound waves into the body. As the
           sound waves bounce off of internal organs, fluids and tissues, the sensitive
           microphone in the transducer records tiny changes in the sound's pitch and direction.
           These signature waves are instantly measured and displayed by a computer, which in
           turn creates a real-time picture on the monitor. One or more frames of the moving
           pictures are typically captured as still images. Small loops of the moving “real time”
           images may also be saved.
          Doppler ultrasound, a special application of ultrasound, measures the direction and
           speed of blood cells as they move through vessels. The movement of blood cells
           causes a change in pitch of the reflected sound waves (called the Doppler effect). A
           computer collects and processes the sounds and creates graphs or color pictures that
           represent the flow of blood through the blood vessels.

   Doppler ultrasound
    Doppler ultrasound is a special ultrasound technique that evaluates blood flow through a
    blood vessel, including the body's major arteries and veins in the abdomen, arms, legs and
    There are three types of Doppler ultrasound:
          Color Doppler uses a computer to convert Doppler measurements into an array of
           colors to visualize the speed and direction of blood flow through a blood vessel.
          Power Doppler is a newer technique that is more sensitive than color Doppler and
           capable of providing greater detail of blood flow, especially when blood flow is little
           or minimal. Power Doppler, however, does not help the radiologist determine the
           direction of blood flow, which may be important in some situations.
          Instead of displaying Doppler measurements visually, Spectral Doppler displays
           blood flow measurements graphically, in terms of the distance traveled per unit of


    For most ultrasound exams, the patient is positioned lying face-up on an examination table
    that can be tilted or moved.

    A clear water-based gel is applied to the area of the body being studied to help the transducer
    make secure contact with the body and eliminate air pockets between the transducer and the
    skin that can block the sound waves from passing into your body. The sonographer
    (ultrasound technologist) or radiologist then presses the transducer firmly against the skin in
    various locations, sweeping over the area of interest or angling the sound beam from a farther
    location to better see an area of concern.

    Doppler sonography is performed using the same transducer.
When the examination is complete, the patient may be asked to dress and wait while the
ultrasound images are reviewed.

In some ultrasound studies, the transducer is attached to a probe and inserted into a natural
opening in the body. These exams include:

      Transesophageal echocardiogram. The transducer is inserted into the esophagus to
       obtain images of the heart.
      Transrectal ultrasound. The transducer is inserted into a man's rectum to view the
      Transvaginal ultrasound. The transducer is inserted into a woman's vagina to view
       the uterus and ovaries.

Most ultrasound examinations are completed within 30 minutes to an hour.


      Most ultrasound scanning is noninvasive (no needles or injections) and is usually
      Ultrasound is widely available, easy-to-use and less expensive than other imaging
      Ultrasound imaging does not use any ionizing radiation.
      Ultrasound scanning gives a clear picture of soft tissues that do not show up well on
       x-ray images.
      Ultrasound is the preferred imaging modality for the diagnosis and monitoring of
       pregnant women and their unborn babies.
      Ultrasound provides real-time imaging, making it a good tool for guiding minimally
       invasive procedures such as needle biopsies and needle aspiration.


      Ultrasound waves are disrupted by air or gas; therefore ultrasound is not an ideal
       imaging technique for air-filled bowel or organs obscured by the bowel. In most
       cases, barium exams, CT scanning, and MRI are the methods of choice in this setting.
      Large patients are more difficult to image by ultrasound because greater amounts of
       tissue attenuates (weakens) the sound waves as they pass deeper into the body.
      Ultrasound has difficulty penetrating bone and, therefore, can only see the outer
       surface of bony structures and not what lies within (except in infants). For visualizing
       internal structure of bones or certain joints, other imaging modalities such as MRI are
       typically used.

Sterilization techniques include all the means used to completely eliminate or destroy living
microorganisms on any object, including tools used to test or treat patients.
The term microorganism, or microbe, refers to any single-celled living organism, including
bacteria, viruses, and fungi. (Though viruses are not true single-celled organisms, medical
    science still usually classifies them as microorganisms.) Microbes can be transferred by direct
    contact or indirectly through a vehicle (like a surgical tool) or via the air the patient breathes.
    If favourable conditions for growth exist in the new host, microbes reproduce and establish
    colonies. Many of these microscopic organisms are normal inhabitants of the human body
    (called microflora). For example, varieties of the bacterium Staphylococcus are normal
    inhabitants of the skin and nasal passages, and many different species of bacteria live in the
    small and large intestine, aiding in the process of digestion.
    However, many types of microorganisms are pathogenic (considered foreign to the host
    body) and, upon entering the body, cause infection when they either damage cells directly or
    release toxins that will eventually cause damage. The prevention of disease-causing microbes
    in a patient-care environment is generally accomplished through aseptic or sterile techniques.
    The goal is to create as germ-free an environment as possible, primarily through sterilization
    and the maintenance of sterile/nonsterile barriers.
    Like foods sold in the grocery store, sterile medical and surgical solutions and some other
    equipment have expiration dates indicating when the product is no longer considered sterile.
    Although many hospitals consider sterile, prepackaged disposable materials to be sterile
    indefinitely if the packaging is undamaged, sterile goods must be examined carefully to
    ensure that there are no breaks in the integrity of the packaging or that the package has not
    gotten wet. Microbes are able to enter sterile goods through either breaks in the wrapping (the
    sterile barrier) or moisture. If the wrapper is no longer intact, or has been wet, sterile goods
    must be repackaged and resterilized.
    Patients having invasive medical or surgical procedures are at risk for infection primarily
    from four sources:
   Infection is transferred from other people, including patients and health care providers. Such
    infection is called direct transmission, which usually occurs as a result of direct contact with
    skin or bodily fluids, including saliva, coughing, and spitting.
   Infection results from equipment or other objects that come in contact with the patient. This is
    called vehicle-borne infection because the microbe is transported from another place on some
    object or vehicle and introduced through a break in the skin or mucosal membranes. Primary
    examples are food poisoning caused by contaminated food items or infection caused by the
    use of non-sterile equipment in an invasive pro cedure like bronchoscopy or phlebotomy.
   Infection arises from the patient's own body, such as the possible contamination of a surgical
    site during intestinal resection if the patient's own fecal material contaminates the abdominal
    cavity contents.
   The air transports microbes. An example of air-borne infection is tuberculosis, in which
    bacteria are transmitted on air currents to others through coughing or spitting.
A technician operates a steam pressure sterilizer.
Managing as germ-free an environment as possible is necessary for surgical procedures and
even minor medical treatments normally done in a doctor's office, such as suturing a
laceration. Patients with conditions or under treatments that cause the immune system to be
compromised are sometimes treated in an artificially created environment called reverse
isolation. Leukemia patients, especially those on aggressive chemotherapy who receive bone
marrow transplants and people with immunodeficiency disorders (which can lead to little or
no natural defense against infection), are all potential candidates for reverse isolation
procedures. Patients with AIDS(acquired immune deficiency syndrome) may be treated in an
environment of isolation, both direct and reverse isolation for their protection, as well as the
protection of caregivers. An extreme example of reverse isolation is the use of a sterilized
plastic tent with filtered air circulation called an isolator. (Premature infants may be placed
in special sterile plastic bassinets called an isolette.)
Aseptic technique
It has been known since the days of Florence Nightingale that clean surroundings are
definitely less conducive to the growth of microorganisms than unclean ones. The creation of
sterile environments always includes scrupulous cleanliness. The use of disinfectants in
washing furniture, walls and floors, as well as in soaking medical equipment or other patient-
care items is another important measure. Disinfectants are harsh chemical compounds
described as bactericidal (capable of killing bacteria), or bacteriostatic (capable of stopping
the growth or reproduction of bacteria). Some of these disinfectants may also be antiviral
agents or antifungal. Disinfectants are usually too toxic to tissue to be used directly on the
body. Antiseptics are chemical compounds that are also either bactericidal or bacteriostatic.
But these are usually more diluted solutions and can safely be used in direct contact with
human tissues. Common antiseptics include iodine, hydrogen peroxide, and thimerosal.
The importance of hand washing before and after the care of any patient cannot be over-
stressed. It remains the simplest and most effective means of preventing infection. The Center
for Disease Control (CDC) estimates that hospitals produce two million hospital-borne
infections (known as nonsocomial infections) each year, and approximately one-quarter of
these are postoperative surgical incision infections. Postoperative infections result from
    breaks in sterile technique during surgery or breaks in aseptic technique during wound care.
    Further, CDC studies have shown that the average compliance with hand washing by health
    care providers from 1981 to 1999 has never risen above 50%. Proper procedure is for health
    care personnel to scrub their hands prior to and immediately after performing any procedure
    on a patient, regardless of whether latex gloves were worn or not. Gloves, as a barrier, can be
    breached via holes the size of pinpoints.
    For both surgery and reverse isolation, staff are usually required to wear presterilized gloves,
    hair nets, masks, and gowns, with clean shoe coverings. Insertion of a urinary catheter,
    changing a surgical drain, cleaning a tracheotomy tube or doing a sterile dressing are all
    instances when health care providers wear gloves. They also create what is termed a sterile
    field or area that has been prepared with antiseptics or covered with impenetrable sterile
    drapes to reduce the likelihood of organism transfer.
    Before surgical procedures, the operative site skin area is cleansed with an antiseptic solution,
    and sterile drapes are applied to the periphery. In the case of bowel surgery, laxatives and
    enemas are given prior to the surgery to remove as much faecal material as possible, thus
    limiting the amount of contamination from faeces. When the bowel is clamped shut, all
    instruments, drapes, and sponges that may have come in contact with the patient are removed
    and replaced with sterile equipment before proceeding any further. In both surgical suites and
    in reverse isolation patients' rooms, air is passed through a special ventilation system that
    filters out microorganisms.
    Five means are commonly used to sterilize objects in the patient's environment. These
   Moist heat is used via steaming or autoclaving (steaming under high pressure). Much like a
    pressure cooker used to can food at home and destroy bacteria, an autoclave circulates steam
    at temperatures of 260°F (120°C) at sustained pressure of 20 pounds per square inch for
    designated periods of time. All equipment used in carrying out medical or surgical procedures
    such as instruments, tubings (including catheters), bandages, and linens used for drapes are
    sterilized, usually in an autoclave.
   Ionizing and non-ionizing radiation is sometimes used. Ultraviolet light is a type of non-
    ionizing radiation used for items sensitive to heat.
   The passage of liquids through a filter sufficiently fine so as to trap microbes.
   Gas sterilization, usually using ethylene oxide, interferes with the metabolism and therefore
    the development of microorganisms and inhibits the growth of spores. It is effective in the
    sterilization of heat-sensitive items and penetrates deeply, but it has to be used with care since
    it is poisonous.
   Strong disinfectants are used primarily for instruments, such as thermometers and scopes that
    could not survive autoclaving. Medical equipment soaked in disinfectants to destroy microbes
    should be rinsed off prior to use due to the toxicity of many of the compounds used for
    disinfecting. Certain gasses such as ethylene oxide used for sterilization are extremely toxic
    to human beings and
    should be used with care.
    In general, preparations include standard sterilization techniques for the patient, health care
    staff, and environment. Surgery patients requiring reverse isolation procedures should be told
    about the actions of microorganisms, including the ways they gain entry into the human body,
    the diseases that can be caused, and how sterilization techniques work to prevent infection.
    Hair is no longer routinely removed from the site of the surgical incision prior to surgery as
    the skin is a natural barrier to infection and shaving it often produces small skin breaks.
    Aftercare following use of sterilized or surgically clean equipment would include monitoring
    patients for the signs and symptoms of infection, which usually occur within 48 to 71 hours.
    Signs and symptoms of infection include:
   fever
   inflammation, or redness and swelling at the site of infection, often accompanied by edema
    and erythema
   purulent or pus-like drainage from wounds
   abnormally elevated white blood count
   pain at the site of infection
    There should be no complications from using proper sterilization and aseptic techniques. An
    allergy to any of the various antiseptics used to sterilize skin prior to surgery may produce
    dermatitis or irritation. If disinfectants used to clean instruments are not properly rinsed
    before use, an inflammatory response similar to a first-degree burn may result on surfaces
    contacted by the solution.
    Proper sterilization techniques result in the prevention of infection. Sterilization techniques
    must be monitored and continually improved upon.
                                      CATH LAB
A catheterization laboratory or cath lab is an examination room in a hospital or clinic with
diagnostic imaging equipment used to support the catheterization procedure. A catheter is
inserted into a large artery, and various wires and devices can be inserted through the body
via the catheter which is inside the artery. The artery most used is the femoral artery.
However, the femoral artery is associated with local complication in up to 3% of patients and
hence, more interventional physicians are moving towards the radial (wrist) artery, as an
alternative site. Disadvantages of the radial artery include small vessel caliber and a different
"learning curve" for physicians used to the femoral (groin) access.
Most catheterization laboratories are "single plane" facilities, those that have a single X-ray
generator source and an image intensifier. Older cath labs used cine film to record the
information obtained, but since 2000, most new facilities are digital. The latest digital cath
labs are biplane (have two X-ray sources) and digital, flat panel labs.
Biplane laboratories achieve two separate planes of view with the same injection and thus
save time and limit contrast dye, limiting kidney damage in susceptible patients
Catheterization laboratories are usually staffed by a multidisciplinary team including a
Physician (normally either a cardiologist or radiologist), an Anaesthetist, a Cardiac
Physiologist, a Nurse and a Radiographer.

Cardiac Procedures
A number of cardiac diagnostic and therapeutic procedures can be performed in a
catheterization laboratory. These typically include angiograms, percutaneous coronary
interventions, closure of some congenital heart defects, treatment of stenotic heart valves, and
pacemaker implantations. Many modern cath labs have facilities for performing
electrophysiological studies, where in catheters and wires passed into the heart through blood
vessels are used in diagnosing and treating arrhythmias. Most cath lab procedures are
performed under local anesthesia. General anesthesia may often be necessary in small
children in whom longer procedure times are anticipated.
A coronary angiography is performed when the physician suspects the existence of
coronary artery disease, a condition characterized by significant stenoses in the coronary
arteries of the heart. The procedure is typically performed through the femoral (groin) artery
or the radial (wrist) artery. Pre-shaped or steerable catheters are passed through the arterial
access under fluoroscopic guidance and are used to cannulate the openings (ostia) of the
coronary arteries. Small quantities of a radiographic contrast medium ('dye') are injected into
the coronary arteries through the catheters. The dye passes through the coronary arteries into
the coronary venous circulation. During its passage, which typically takes a few cardiac
cycles, the anatomy of the coronary arterial tree can be visualized under fluoroscopy due to
the radio-opacity of the dye. The X-ray tube is rotated so as to provide specific views
(projections) to enable complete visualization of the coronary arterial tree.
                                LINEAR ACCELERATOR

Linear accelerator (linac) was originally developed as a tool for smashing atoms and first
adopted to medical applications by Varian in 1960. The normal definition of Linear
accelerator is ions are accelerated along a linear path by voltage differences on electrodes
along the path. On the other hand, the medical definition is a machine that creates high-
energy radiation to treat cancers, using electricity to form a stream of fast-moving subatomic

How Does Linear Accelerator Work

A linear accelerator generates high energy X-Rays radiation through the acceleration of
electrons that are extracted of the surface of a heated metal disk. A beam of electrons is
generated and accelerated though a waveguide that increases their energy to the keV and
MeV ranges. The electrons are accelerated through a vacuum chamber (waveguide) by
microwaves to nearly the speed of light, an action that greatly boosts their energy levels. The
speeding electrons bombard a metal target, usually tungsten. As a result of these collisions,
high energy X-Rays are scattered from the target. X-Rays are high energy photon and are
radiation in the form of electromagnetic form.

Based on Plank’s theory, each photon has an amount of energy equal to Palnk’s Constant (h)
multiplied by the frequency (f)of the generated light (E = h*f). A portion of these X-Rays is
collected and then shaped to form different shapes of beams. The geometry of each shape is
configured to match the patient’s tumor. Usually doctors with the help of other medical
equipment (PET and CAT scans), will determine the best shape to deliver the beam. It is
worth mentioning that the light beam is more intense in the middle than its periphery. This is
an important concept during cancer treatment. When the beam is centered at the middle of
tumor so most beam energy (radiation) is fired to the cancer cells while minimizing the effect
on the peripheries (healthy tissues). Since the shape is controlled precisely in modern linear
accelerator, the amount of radiation to surrounding is minimal. The linear accelerator is also
equipped with electron-beam-capabilities. To produce an electron beam, the tungsten is
moved away from the path of the beam. The original electron beam that was aimed at the
tungsten target is now the electron beam used for treatment. Electrons have become a viable
option in treating superficial tumour up to a depth of about 5 cm. while photons are used for
deep treatment.

Linear Accelerator and its Usage
Usually the room is located below ground so earth can provide extra shielding during
treatment even though the amount of radiation is minimal. The room is equipped with a
camera to monitor the patient. Also, the beam intensity is calibrated every morning before
usage to equipment traced to national standards.

Linear accelerator is used in radiation therapy for Cancer treatment as a source of radiation
(High Level of X-Rays). Radiation at high level destroys DNA of cells and stops their ability
to divide and grow. Both normal and cancer cells are affected, but radiation treatment is
designed to maximize tumor effect and minimize normal tissue effect. Maximizing tumor
effect is one reason radiation therapy is given in series of treatment rather than one treatment.
It is important to note that the tumor receives radiation at different angles with the aid of
linear accelerator. The maximum time waiting for cancer treatment using linear accelerator is
almost two weeks with minimum body discomfort if post-dose care is properly taken.

The dose of radiation absorbed correlates directly with the energy of the beam. Gray is the
basic unit of radiation absorbed dose. It is the amount of energy (joules) absorbed per unit
mass (kg). When a beam of energy photons strikes a cancer cell, its water molecules interact
with the highly energized photons and produce ions or free radicals that damage DNA. When
a photon collides with a free electron, one is not tightly bound to an atom, the electron begin
to ionize with energy given to it by the photon. The photon can then continue to undergo
additional interaction. Cancer cells often have faulty repair mechanisms and thus lose the
ability to replicate. However, healthy cells can repair themselves to a degree and continue to
mobilize. Repeated exposure to high energy X-Rays eventually impairs and kills cells. As a
result, the tumor is eradicated. The intensity of an X-Ray is governed by the inverse square
law. This law states that the radiation intensity from a point source is inversely proportional
to the square of the distance away from the radiation source (1/d2).

Linacs of appropriate design are capable of accelerating heavy ions to energies exceeding
those available in ring-type accelerators, which are limited by the strength of the magnetic
fields required to maintain the ions on a curved path. High power linacs are also being
    developed for production of electrons at relativistic speeds, required since fast electrons
    traveling in an arc will lose energy through synchrotron radiation; this limits the maximum
    power that can be imparted to electrons in a synchrotron of given size. Linacs are also
    capable of prodigious output, producing a nearly continuous stream of particles, whereas a
    synchrotron will only periodically raise the particles to sufficient energy to merit a "shot" at
    the target. (The burst can be held or stored in the ring at energy to give the experimental
    electronics time to work, but the average output current is still limited.) The high density of
    the output makes the linac particularly attractive for use in loading storage ring facilities with
    particles in preparation for particle to particle collisions. The high mass output also makes the
    device practical for the production of antimatter particles, which are generally difficult to
    obtain, being only a small fraction of a target's collision products. These may then be stored
    and further used to study matter-antimatter annihilation.


   The device length limits the locations where one may be placed.
   A great number of driver devices and their associated power supplies are required, increasing
    the construction and maintenance expense of this portion.
   If the walls of the accelerating cavities are made of normally conducting material and the
    accelerating fields are large, the wall resistivity converts electric energy into heat quickly. On
    the other hand superconductors have various limits and are too expensive for very large
    accelerators. Therefore, high energy accelerators such as SLAC, still the longest in the world
    (in its various generations), are run in short pulses, limiting the average current output and
    forcing the experimental detectors to handle data coming in short bursts.
                                    STRESS TEST
A stress test is primarily used to identify coronary artery disease. It requires patients
to exercise on a treadmill or exercise bicycle while their heart rate, blood pressure,
electrocardiogram (ECG), and symptoms are monitored.


The body requires more oxygen during exercise than at rest. To deliver more oxygen during
exercise, the heart has to pump more oxygen-rich blood. Because of the increased stress on
the heart, exercise can reveal coronary problems that are not apparent when the body is at
rest. This is why the stress test, though not perfect, remains the best initial non invasive
practical coronary test.

The stress test is particularly useful for detecting ischemia (inadequate supply of blood to the
heart muscle) caused by blocked coronary arteries. Less commonly, it is used to determine
safe levels of exercise in people with existing coronary artery disease.


A technician affixes electrodes to the patient's chest, using adhesive patches with a special gel
that conducts electrical impulses. Typically, electrodes are placed under each collarbone and
each bottom rib, and six electrodes are placed across the chest in a rough outline of the heart.
Wires from the electrodes are connected to an ECG, which records the electrical activity
picked up by the electrodes.

The technician runs resting ECG tests while the patient is lying down, then standing up, and
then breathing heavily for half a minute. These baseline tests can later be compared with the
ECG tests performed while the patient is exercising. The patient's blood pressure is taken and
the blood pressure cuff is left in place so that blood pressure can be measured periodically
throughout the test.

The patient begins riding a stationary bicycle or walking on a treadmill. Gradually the
intensity of the exercise is increased. For example, if the patient is walking on a treadmill,
then the speed of the treadmill increases and the treadmill is tilted upward to simulate an
incline. If the patient is on an exercise bicycle, then the resistance or "drag" is gradually
increased. The patient continues exercising at increasing intensity until reaching the target
heart rate (generally set at a minimum of 85% of the maximal predicted heart rate based on
the patient's age) or experiences severe fatigue, dizziness, or chest pain. During the test, the
patient's heart rate, ECG, and blood pressure are monitored.

Sometimes such other tests, as echocardiography or thallium scanning, are used in
conjunction with the exercise stress test. For instance, recent studies suggest that women have
a high rate of false negatives (results showing no problem when one exists) and false
positives (results showing a problem when one does not exist) with the stress test. They may
benefit from another test, such as exercise echocardiography. People who are unable to
exercise may be injected with such drugs, as adenosine, which mimic the effects of exercise
on the heart, and then given a thallium scan. The thallium scan or echocardiogram are
particularly useful when the patient's resting ECG is abnormal. In such cases, interpretation
of exercise-induced ECG abnormalities is difficult.

    Patients are usually instructed not to eat or smoke for several hours before the test. They
    should be advised to inform the physician about any medications they are taking, and to wear
    comfortable sneakers and exercise clothing.

    After Care

    After the test, the patient should rest until blood pressure and heart rate return to normal. If all
    goes well,


    There is a very slight risk of myocardial infarction (a heart attack) from the exercise, as well
    as cardiac arrhythmia (irregular heart beats), angina, or cardiac arrest (about one in 100,000).
    The exercise stress test carries a very slight risk (one in 100,000) of causing a heart attack.
    For this reason, exercise stress tests should be attended by health care professionals with
    immediate access to defibrillators and other emergency equipment.

    Patients are cautioned to stop the test should they develop any of the following symptoms:

   unsteady gait
   confusion
   skin that is greyish or cold and clammy
   dizziness or fainting
   a drop in blood pressure
   angina (chest pain)
   cardiac arrhythmias (irregular heart beat)

    Normal Results

    A normal result of an exercise stress test shows normal electrocardiogram tracings and heart
    rate, blood pressure within the normal range, and no angina, unusual dizziness, or shortness
    of breath.

    A number of abnormalities may appear on an exercise stress test. Examples of exercise-
    induced ECG abnormalities are ST segment depression or heart rhythm disturbances. These
    ECG abnormalities may indicate deprivation of blood to the heart muscle (ischemia) caused
    by narrowed or blocked coronary arteries. Stress test abnormalities generally require further
    diagnostic evaluation and therapy.
Patient education
Patients must be well prepared for a stress test. They should not only know the purpose of the
test, but also signs and symptoms that indicate the test should be stopped. Physicians, nurses,
and ECG technicians can ensure patient safety by encouraging them to immediately
communicate discomfort at any time during the stress test.
                              GAMMA CAMERA

A gamma camera, also called a scintillation camera or Anger camera, is a device used to
image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The
applications of scintigraphy include early drug development and nuclear medical imaging to
view and analyse images of the human body or the distribution of medically injected, inhaled,
or ingested radionuclides emitting gamma rays.

The Gamma Camera is used to measure the distribution of radioactivity in a subject. The
subject ingests, breathes in or is injected with a radioactive compound. These compounds are
designed to reflect bodily function, such as circulation, and are often directed to a particular
organ. In the heart or brain, such an image could indicate the location of damage due to a
heart attack or stroke. In a bone scan, tumors can be visualized. The urinary track, lungs, liver
and thyroid, for example, may also be imaged. A single camera, such as we will study,
produces a projection of the radioactivity. Cross-sectional images can be produced by
imaging at many angles and reconstructing the cross-section from the projections.

Construction and Working
 It consists of a large diameter NaI(Tl) scintillation crystal which is viewed by a large number
of photomultiplier tubes.
A block diagram of the basic components of a gamma camera is shown below:

The crystal and PM Tubes are housed in a cylindrical shaped housing commonly called
the camera head and a cross-sectional view of this is shown in the figure. The crystal can be
between about 25 cm and 40 cm in diameter and about 1 cm thick. The diameter is dependent
on the application of the device. For example a 25 cm diameter crystal might be used for a
camera designed for cardiac applications while a larger 40 cm crystal would be used for
producing images of the lungs. The thickness of the crystal is chosen so that it provides good
detection for the 140 keV gamma-rays emitted from 99mTc - which is the most common
radioisotope used today.
Scintillations produced in the crystal are detected by a large number of PM tubes which are
arranged in a two-dimensional array. There is typically between 37 and 91 PM tubes in
modern gamma cameras. The output voltages generated by these PM tubes are fed to a
position circuit which produces four output signals called ±X and ±Y. These position signals
contain information about where the scintillations were produced within the crystal. In the
most basic gamma camera design they are fed to a cathode ray oscilloscope (CRO).
The position signals also contain information about the intensity of each scintillation. This
intensity information can be derived from the position signals by feeding them to a
summation circuit (marked ∑ in the figure) which adds up the four position signals to
generate a voltage pulse which represents the intensity of a scintillation. This voltage pulse is
commonly called the Z-pulse which following pulse height analysis (PHA) is fed as
the unblank pulse to the CRO.
               TOMOGRAPHY (SPECT)
What is Spect?
Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a
nuclear medicine tomographic imaging technique using gamma rays. It is very similar to
conventional nuclear medicine planar imaging using a gamma camera. However, it is able to
provide true 3D information. This information is typically presented as cross-sectional slices
through the patient, but can be freely reformatted or manipulated as required.

How does a SPECT scan work?
A SPECT scan integrates two technologies to view your body: computed tomography (CT)
and a radioactive material (tracer). The tracer is what allows doctors to see how blood flows
to tissues and organs.

Before the SPECT scan, you are injected with a chemical that is radiolabled, meaning it emits
gamma rays that can be detected by the scanner. The computer collects the information
emitted by the gamma rays and translates them into two-dimensional cross-sections. These
cross-sections can be added back together to form a 3D image of your brain.

The radioisotopes typically used in SPECT to label tracers are iodine-123, technetium-99m,
xenon-133, thallium-201, and fluorine-18. These radioactive forms of natural elements will
pass safely through your body and be detected by the scanner. Various drugs and other
chemicals can be labeled with these isotopes.

The type of tracer used depends on what your doctor wants to measure. For example, if your
doctor is looking at a tumor, he or she might use radiolabled glucose (FDG) and watch how it
is metabolized by the tumor.

The test differs from a PET scan in that the tracer stays in your blood stream rather than being
absorbed by surrounding tissues, thereby limiting the images to areas where blood flows.
SPECT scans are cheaper and more readily available than higher resolution PET scans.

What does a SPECT scan show?

A SPECT scan is primarily used to view how blood flows through arteries and veins in the
brain. Tests have shown that it might be more sensitive to brain injury than either MRI or CT
scanning because it can detect reduced blood flow to injured sites.
SPECT scanning is also useful for presurgical evaluation of medically uncontrolled seizures
(Fig. 1). The test can be performed between seizures (interictal) or during a seizure (ictal) to
determine blood flow to areas where the seizures originate.

A SPECT scan of a patient with uncontrolled complex partial seizures. The temporal lobe on
the left side of the brain shows less blood flow than the right, confirming for the surgeon the
nonfunctioning area of the brain causing seizures.

This type of scanning is also useful in diagnosing stress fractures in the spine (spondylolysis),
blood deprived (ischemic) areas of brain following a stroke, and tumors.

Who performs the test?
A specially trained nuclear medicine technologist will perform the test in the Nuclear
Medicine department of the hospital, or at an outpatient imaging center.

How should I prepare for the test?
Wear comfortable clothing and be prepared to stay for 1 to 2 hours.

What happens during the test?

First, you will receive an injection of a small amount of radioactive tracer. You'll be asked to
rest for about 10-20 minutes until the tracer reaches your brain. Next, you'll lie comfortably
on a scanner table while a special camera rotates around your head. Be sure to remain as still
as possible so that the machine can take accurate pictures.

Once the scan is complete, you can leave. Be sure to drink plenty of fluids to flush out any
tracer left in your body.

What are the risks?
The amount of radiation your body is exposed to is less than you receive during a chest X-ray
or CT scan. Women who are pregnant or nursing should not undergo a SPECT scan.

Defibrillator - What is a Defibrillator?

Defibrillation is the definitive treatment for the life-threatening cardiac arrhythmias,
ventricular fibrillation and pulse less ventricular tachycardia. Defibrillation consists of
delivering a therapeutic dose of electrical energy to the affected heart with a device called a
defibrillator. This depolarizes a critical mass of the heart muscle, terminates the arrhythmia,
and allows normal sinus rhythm to be re-established by the body's natural pacemaker, in the
sinoatrial node of the heart.

Defibrillators can be external, transvenous, or implanted, depending on the type of device
used or needed. Some external units, known as automated external defibrillators (AEDs),
automate the diagnosis of treatable rhythms, meaning that lay responders or bystanders are
able to use them successfully with little, or in some cases no training at all.

Defibrillation was first demonstrated in 1899 by Prevost and Batelli, two physiologists from
University of Geneva, Switzerland. They discovered that small electric shocks could induce
ventricular fibrillation in dogs, and that larger charges would reverse the condition.

The first use on a human was in 1947 by Claude Beck, professor of surgery at Case Western
Reserve University. Beck's theory was that ventricular fibrillation often occurred in hearts
which were fundamentally healthy, in his terms "Hearts are too good to die", and that there
must be a way of saving them. Beck first used the technique successfully on a 14 year old
boy who was being operated on for a congenital chest defect. The boy's chest was surgically
opened, and manual cardiac massage was undertaken for 45 minutes until the arrival of the
defibrillator. Beck used internal paddles on either side of the heart, along with procainamide,
an antiarrhythmic drug, and achieved return of normal sinus rhythm.

These early defibrillators used the alternating current from a power socket, transformed from
the 110-240 volts available in the line, up to between 300 and 1000 volts, to the exposed
heart by way of 'paddle' type electrodes. The technique was often ineffective in reverting VF
while morphological studies showed damage to the cells of the heart muscle post mortem.
The nature of the AC machine with a large transformer also made these units very hard to
transport, and they tended to be large units on wheels.
Defibrillator Types
Manual internal defibrillator

These are the direct descendants of the work of Beck and Lown. They are virtually identical
to the external version, except that the charge is delivered through internal paddles in direct
contact with the heart. These are almost exclusively found in operating theatres, where the
chest is likely to be open, or can be opened quickly by a surgeon.

Automated external defibrillator (AED)

The AED box has information on how to use it in Japanese, English, Chinese and Korean,
and station staff are trained to use it.

These simple-to-use units are based on computer technology which is designed to analyze the
heart rhythm itself, and then advise the user whether a shock is required. They are designed to
be used by lay persons, who require little training to operate them correctly. They are usually
limited in their interventions to delivering high joule shocks for VF (ventricular fibrillation)
and VT (ventricular tachycardia) rhythms, making them generally limited for use by health
professionals, who could diagnose and treat a wider range of problems with a manual or
semi-automatic unit.

The automatic units also take time (generally 10–20 seconds) to diagnose the rhythm, where
a professional could diagnose and treat the condition far more quickly with a manual unit.
These time intervals for analysis, which require stopping chest compressions, have been
shown in a number of studies to have a significant negative effect on shock success. This
effect led to the recent change in the AHA defibrillation guideline (calling for two minutes of
CPR after each shock without analyzing the cardiac rhythm) and some bodies recommend
that AEDs should not be used when manual defibrillators and trained operators are available.
The unit monitors the patient 24 hours a day and will automatically deliver a biphasic shock
if needed. This device is mainly indicated in patients awaiting an implantable defibrillator.
Currently only one company manufactures these and they are of limited availability.

Modelling Defibrillation

The efficacy of a cardiac defibrillator is highly dependent on the position of its electrodes.
Most internal defibrillators are implanted in octogenarians, but a few children need the
devices. Implanting defibrillators in kids is particularly difficult because children are small,
will grow over time, and possess cardiac anatomy that differs from that of adults. Recently,
researchers were able to create a software modeling system capable of mapping an
individual’s thorax and determining the optimal position for an external or internal cardiac

With the help of pre-existing surgical planning applications, the software uses myocardial
voltage gradients to predict the likelihood of successful defibrillation. According to the
critical mass hypothesis, defibrillation is effective only if it produces a threshold voltage
gradient in a large fraction of the myocardial mass. Usually, a gradient of three to five volts
per centimeter is needed in 95 % of the heart. Voltage gradients of over 60 V/cm can damage
tissue. The modeling software seeks to obtain safe voltage gradients above the defibrillation
Early simulations using the software suggest that small changes in electrode positioning can
have large effects on defibrillation, and despite engineering hurdles that remain, the modeling
system promises to help guide the placement of implanted defibrillators in children and

Recent mathematical models of defibrillation are based on the bidomain model of cardiac
tissue. Calculations using a realistic heart shape and fiber geometry are required to determine
how cardiac tissue responds to a strong electrical shock.

How to use a Defibrillator

The most well-known type of electrode (widely depicted in films and television) is the
traditional metal paddle with an insulated (usually plastic) handle. This type must be held in
place on the patient's skin while a shock or a series of shocks is delivered. Before the paddle
is used, a gel must be applied to the patient's skin, in order to ensure a good connection and to
minimize electrical resistance, also called chest impedance (despite the DC discharge). These
are generally only found on the manual external units.

Newer types of resuscitation electrodes are designed as an adhesive pad. These are peeled off
their backing and applied to the patient's chest when deemed necessary, much the same as
any other sticker. These electrodes are then connected to a defibrillator. If defibrillation is
required, the machine is charged, and the shock is delivered, without any need to apply any
gel or to retrieve and place any paddles. These adhesive pads are found on most automated
and semi-automated units, and are gradually replacing paddles entirely in non-hospital

Both solid- and wet-gel adhesive electrodes are available. Solid-gel electrodes are more
convenient, because there is no need to clean the patient's skin after removing the electrodes.
However, the use of solid-gel electrodes presents a higher risk of burns during defibrillation,
since wet-gel electrodes more evenly conduct electricity into the body.

Some adhesive electrodes are designed to be used not only for defibrillation, but also for
transcutaneous pacing and synchronized electrical cardioversion.

In a hospital setting, paddles are generally preferred to pads, due to the inherent speed with
which they can be placed and used. This is critical during cardiac arrest, as each second of
nonperfusion means tissue loss. However, in cases in which cardiac arrest is suspected,
patches placed prophalacticaly are superior,as they provide appropriate EKG tracing without
the artifact visible from human interference with the paddles. Adhesive electrodes are also
inherently safer than the paddles for the operator of the defibrillator to use, as they minimize
the risk of the operator coming into physical (and thus electrical) contact with the patient as
the shock is delivered, by allowing the operator to stand several feet away. Adhesive patches
also require no force to remain in place and deliver the shock appropriately, whereas paddles
require approximately 25 lbs of force to be applied while the shock is delivered.


Resuscitation electrodes are placed according to one of two schemes. The anterior-posterior
scheme is the preferred scheme for long-term electrode placement. One electrode is placed
over the left precordium (the lower part of the chest, in front of the heart). The other electrode
is placed on the back, behind the heart in the region between the scapula. This placement is
preferred because it is best for non-invasive pacing.

The anterior-apex scheme can be used when the anterior-posterior scheme is inconvenient or
unnecessary. In this scheme, the anterior electrode is placed on the right, below the clavicle.
The apex electrode is applied to the left side of the patient, just below and to the left of the
pectoral muscle. This scheme works well for defibrillation and cardioversion, as well as for
monitoring an ECG.

What Is a Pacemaker?

A pacemaker is a small device that's placed in the chest or abdomen to help control abnormal
heart rhythms. This device uses electrical pulses to prompt the heart to beat at a normal rate.

Pacemakers are used to treat arrhythmias (ah-RITH-me-ahs). Arrhythmias are problems with
the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too
slow, or with an irregular rhythm.

A heartbeat that's too fast is called tachycardia (TAK-ih-KAR-de-ah). A heartbeat that's too
slow is called bradycardia (bray-de-KAR-de-ah).

During an arrhythmia, the heart may not be able to pump enough blood to the body. This can
cause symptoms such as fatigue (tiredness), shortness of breath, or fainting. Severe
arrhythmias can damage the body's vital organs and may even cause loss of consciousness or

A pacemaker can relieve some arrhythmia symptoms, such as fatigue and fainting. A
pacemaker also can help a person who has abnormal heart rhythms resume a more active

Understanding the Heart's Electrical System

Your heart has its own internal electrical system that controls the rate and rhythm of your
heartbeat. With each heartbeat, an electrical signal spreads from the top of your heart to the
bottom. As the signal travels, it causes the heart to contract and pump blood.

Each electrical signal normally begins in a group of cells called the sinus node or sinoatrial
(SA) node. As the signal spreads from the top of the heart to the bottom, it coordinates the
timing of heart cell activity.

First, the heart's two upper chambers, the atria (AY-tree-uh), contract. This contraction
pumps blood into the heart's two lower chambers, the ventricles (VEN-trih-kuls). The
ventricles then contract and pump blood to the rest of the body. The combined contraction of
the atria and ventricles is a heartbeat.

For more information about the heart's electrical system and detailed animations, go to the
Health Topics How the Heart Works article.

Faulty electrical signaling in the heart causes arrhythmias. Pacemakers use low-energy
electrical pulses to overcome this faulty electrical signaling. Pacemakers can:

      Speed up a slow heart rhythm.
      Help control an abnormal or fast heart rhythm.
      Make sure the ventricles contract normally if the atria are quivering instead of beating
       with a normal rhythm (a condition called atrial fibrillation).
      Coordinate electrical signaling between the upper and lower chambers of the heart.
      Coordinate electrical signaling between the ventricles. Pacemakers that do this are
       called cardiac resynchronization therapy (CRT) devices. CRT devices are used to treat
       heart failure.
      Prevent dangerous arrhythmias caused by a disorder called long QT syndrome.

Pacemakers also can monitor and record your heart's electrical activity and heart rhythm.
Newer pacemakers can monitor your blood temperature, breathing rate, and other factors.
They also can adjust your heart rate to changes in your activity.

Pacemakers can be temporary or permanent. Temporary pacemakers are used to treat short-
term heart problems, such as a slow heartbeat that's caused by a heart attack, heart surgery, or
an overdose of medicine.

Temporary pacemakers also are used during emergencies. They might be used until your
doctor can implant a permanent pacemaker or until a temporary condition goes away. If you
have a temporary pacemaker, you'll stay in a hospital as long as the device is in place.

Permanent pacemakers are used to control long-term heart rhythm problems. This article
mainly discusses permanent pacemakers, unless stated otherwise.

Doctors also treat arrhythmias with another device called an implantable cardioverter
defibrillator (ICD). An ICD is similar to a pacemaker. However, besides using low-energy
electrical pulses, an ICD also can use high-energy pulses to treat life-threatening arrhythmias.

Who Needs a Pacemaker?

Doctors recommend pacemakers to patients for a number of reasons. The most common
reason is when a patient's heart is beating too slow or there are long pauses between

A pacemaker may be helpful if:

      Aging or heart disease damages your sinus node's ability to set the correct pace for
       your heartbeat. Such damage can make your heart beat too slow, or it can cause long
       pauses between heartbeats. The damage also can cause your heart rhythm to alternate
       between slow and fast.
      You need to take certain heart medicines (such as beta blockers), but these medicines
       slow down your heartbeat too much.
      The electrical signals between your heart's upper and lower chambers are partially or
       completely blocked or slowed down (this is called heart block). Aging, damage to the
       heart from a heart attack, or other heart conditions can prevent electrical signals from
       reaching all the heart's chambers.
      You often faint due to a slow heartbeat. For example, this may happen if the main
       artery in your neck that supplies your brain with blood is sensitive to pressure. In you
       have this condition, just quickly turning your neck can cause your heart to beat slower
       than normal. When that happens, not enough blood may flow to your brain, causing
       you to faint.
      You have had a medical procedure to treat an arrhythmia called atrial fibrillation. A
       pacemaker can help regulate your heartbeat after the procedure.
      You have heart muscle problems that cause electrical signals to travel through your
       heart muscle too slow. (Your pacemaker will provide cardiac resynchronization
       therapy for this problem.)

To decide whether a pacemaker will benefit you, your doctor will consider any symptoms
you have of an irregular heartbeat, such as dizziness, unexplained fainting, or shortness of
breath. He or she also will consider whether you have a history of heart disease, what
medicines you're currently taking, and the results of heart tests.

A pacemaker won't be recommended unless your heart tests show that you have irregular

Tests That Help Determine Whether You Need a Pacemaker

A number of tests are used to detect an arrhythmia. Your doctor may recommend some or all
of these tests.

EKG (Electrocardiogram)

This simple and painless test detects and records the electrical activity of the heart. An EKG
shows how fast the heart is beating and the heart's rhythm (steady or irregular). It also records
the strength and timing of electrical signals as they pass through each part of the heart.

Holter Monitor

A Holter monitor, also called an ambulatory EKG, records the electrical signals of your heart
for a full 24- or 48-hour period. You wear small patches called electrodes on your chest that
are connected by wires to a small, portable recorder. The recorder can be clipped to a belt,
kept in a pocket, or hung around your neck.

During the 24 or 48 hours, you do your usual daily activities and keep a notebook, noting any
symptoms you have and the time they occur. You then return both the recorder and the
notebook to your doctor to read the results. Your doctor can see how your heart was beating
at the time you had symptoms.

The purpose of a Holter monitor is to record heart signals during typical daily activities and
while sleeping, and to find heart problems that may occur for only a few minutes out of the


This test uses sound waves to create a moving picture of your heart. An echocardiogram
shows the size and shape of your heart and how well your heart is pumping blood. The test
can identify areas of heart muscle that aren't contracting normally or getting enough blood

Electrophysiology Study

For an electrophysiology study, your doctor threads a small, flexible wire from a blood vessel
in your arm or leg to your heart. The wire electrically stimulates your heart to see how your
heart's electrical system responds. The electrical stimulation helps to find where the heart 's
electrical system is damaged.

Stress Test

Some heart problems are easier to diagnose when your heart is working harder and beating
faster than when it's at rest. During stress testing, you exercise to make your heart work
harder and beat faster while heart tests, such as an EKG or echocardiogram, are performed.

How Does a Pacemaker Work?

A pacemaker consists of a battery, a computerized generator, and wires with electrodes on
one end. The battery powers the generator, and a thin metal box surrounds both it and the
generator. The wires connect the generator to the heart.

The pacemaker's generator sends the electrical pulses that correct or set your heart rhythm. A
computer chip figures out what types of electrical pulses to send to the heart and when those
pulses are needed. To do this, the computer chip uses the information it receives from the
wires connected to the heart. It also may use information from sensors in the wires that detect
your movement, blood temperature, breathing, or other factors that indicate your level of
physical activity. That way, it can make your heart beat faster when you exercise.

The computer chip also records your heart's electrical activity and heart rhythms. Your doctor
will use these recordings to set your pacemaker so it works better at making sure you have a
normal heart rhythm. Your doctor can program the computer in the pacemaker without
having to use needles or directly contacting the pacemaker.

The wires in your pacemaker send electrical pulses to and from your heart and the generator.
Pacemakers have one to three wires that are each placed in different chambers of the heart.

      The wires in a single-chamber pacemaker usually carry pulses between the right
       ventricle (the lower right chamber of your heart) and the generator.
      The wires in a dual-chamber pacemaker carry pulses between the right atrium and the
       right ventricle and the generator. The pulses help coordinate the timing of these two
       chambers' contractions.
      The wires in a triple-chamber pacemaker are used for heart muscle weakness and
       carry pulses between an atrium and both ventricles and the generator. The pulses help
       coordinate the timing of the two ventricles with each other.

What To Expect During Pacemaker Surgery

Placement of a pacemaker requires minor surgery, which is usually done in a hospital or
special heart treatment laboratory. You will be given medicine right before the surgery that
will help you relax and may make you fall nearly asleep. Your doctor will give you a local
anesthetic so you won't feel anything in the area where he or she puts the pacemaker.
First, your doctor will place a needle in a large vein, usually near the shoulder opposite your
dominant hand. The doctor will then use the needle to thread the pacemaker wires into a vein
and to the correct location in your heart.

An x-ray "movie" of the wires as they pass through your vein and into your heart will help
your doctor place the wires. Once the wires are in place, your doctor will make a small cut
into the skin of your chest or abdomen. He or she will then slip the pacemaker
generator/battery box through the cut, place it just under your skin, and connect it to the wires
that lead to your heart.

Once the pacemaker is in place, your doctor will sew up the cut. The entire surgery takes a
few hours.

What To Expect After Pacemaker Surgery

Expect to stay in the hospital overnight so your heartbeat can be monitored and your doctor
can make sure your pacemaker is working properly. You probably will have to arrange for a
ride to and from the hospital because your doctor may not want you to drive yourself.

For a few days to weeks after surgery, you may have pain, swelling, or tenderness in the area
where your pacemaker was placed. The pain is usually mild and often relieved by over-the-
counter medicines. Consult with your doctor before taking any pain medicines.

Your doctor also may ask you to avoid any vigorous activities and heavy lifting for about a
month. Most people return to normal activities within a few days of having pacemaker

What Are the Risks of Pacemaker Surgery?

Your chance of having any problems from pacemaker surgery is less than 5 percent. These
problems may include:

      Swelling, bleeding, bruising, or infection in the area where the pacemaker was placed
      Blood vessel or nerve damage
      A collapsed lung
      A bad reaction to the medicine used to make you sleep during the procedure
      Infections that can become difficult to treat
                          ELECTROGRAM (ECG)
What Is an Electrocardiogram (ECG, EKG)?

The electrocardiogram (ECG or EKG) is a diagnostic tool that is routinely used to assess the
electrical and muscular functions of the heart. While it is a relatively simple test to perform,
the interpretation of the ECG tracing requires significant amounts of training. Numerous
textbooks are devoted to the subject.

The heart is a two stage electrical pump and the heart's electrical activity can be measured by
electrodes placed on the skin. The electrocardiogram can measure the rate and rhythm of the
heartbeat, as well as provide indirect evidence of blood flow to the heart muscle.

A standardized system has been developed for the electrode placement for a routine ECG.
Ten electrodes are needed to produce 12 electrical views of the heart. An electrode lead, or
patch, is placed on each arm and leg and six are placed across the chest wall. The signals
received from each electrode are recorded. The printed view of these recordings is the

By comparison, a heart monitor requires only three electrode leads – one each on the right
arm, left arm, and left chest. It only measures the rate and rhythm of the heartbeat. This kind
of monitoring does not constitute a complete ECG.

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