PET-CT 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. Benefits 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 surgery. 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. Risks 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 exam. 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. Limitations 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 scanner. 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 braces. 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 test. 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 intercom. 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. Advantages 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. Disadvantages 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 osteoporosis. 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 agent. Benefits 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. Risks 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. Limitations 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. Hemodialysis 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 dialysis. 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 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. Pulse 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 transducer. Transducer 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. Echo 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 neck. 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 time. Procedure 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 prostate. 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. Benefits Most ultrasound scanning is noninvasive (no needles or injections) and is usually painless. Ultrasound is widely available, easy-to-use and less expensive than other imaging methods. 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. Limitations 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 Definition 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. Purpose 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. Precautions 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. Description 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 include: 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. Preparation 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 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 Complications 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. Results 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 particles. 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). Advantages 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. Disadvantages 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 Definition 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. Purpose 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. Description 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. Preparation 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, Risks 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. SINGLE PHOTON EMISSION COMPUTED 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 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 defibrillator. 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 threshold. 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 adults. 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 settings. 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. Placement 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. PACEMAKER 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 death. 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 lifestyle. 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. Overview 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 heartbeats. 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 heartbeats. 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 day. Echocardiogram 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 flow. 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 surgery. 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 electrocardiogram. 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.