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					VCE Physics
     Unit 1
    Topic 3

Medical Physics
                       Unit Outline
• This unit covers the following topics
•   applications of radioisotopes to medical diagnosis and treatment;
•   the operation of optical fibres as endoscopes and other applications
    for diagnosis and treatment;
•   the use of laser treatments considering a laser as an intense energy
•   processes of medical imaging using two or more of ultrasound, X-
    rays, CT and PET
•   make simple interpretations of images of the human body produced
    by ultrasound, X-rays, CT, PET and MRI.
   Chapter 1

Nuclear Medicine:
         1.0 Nuclear Medicine –
             A Little History
            Medical uses of radioactive elements had its
            beginnings in the work of the Curies, Pierre
            (1859 – 1906) and his wife Marie (1867 – 1934).

            Together they discovered two highly radioactive
            elements Polonium (400 times more radioactive
            than Uranium) and Radium (900 times more

              The first recorded medical use of a radioactive substance
              occurred in France in 1901 when radium was used as a cancer
              The first recorded radium use in Australia was by a Melbourne
              dermatologist in 1903.

The first diagnostic use of a radioisotope was in 1924
when a decay product of Radium was injected into the
bloodstream and its movement through the body was
recorded with a geiger counter.
                 1.1 Radioisotopes
               Radioisotopes (sometimes called radionuclides) are
               unstable atoms which, in searching for stability, emit either
               energy (in the form of gamma rays), or matter (in the form
               of neutrons, alpha or beta particles).

Radioisotopes can be naturally occuring, eg Carbon-14 (14C) or man made, eg
Cobalt-60 (60Co).
Man made radionuclides are manufactured in either a Cyclotron (a particle
accelerator) or in a nuclear reactor which, in Australia’s case, is located at
Lucas Heights, just south of Sydney.

Radioisotopes are used in many areas:
In Agriculture - to investigate plant growth and fertiliser take up.
In Industry - to check important welds in pipes etc, and to
measure metal thickness.
In Archaeology - to carbon date ancient objects.
In Sewage Disposal - to trace water flows.
In Medicine – to detect and treat disease.
         1.2 Medical Radioisotopes
     When used in Medicine, radioisotopes          A representative list of
     fall into one of two groups:                  medical radioisotopes
      1. Diagnostic Radionuclides                  is shown in the table
      2. Therapeutic Radionuclides

       Radioisotope                    Half Life                  Uses

Sodium – 24 (24Na)         15 Hours                    Study of general biological
Iron – 59 (59Fe)           46.3 Days                   Diagnosis of Blood Disease

Technetium - 99m (99mTc)   6 Hours                     Diagnosis of various
Cobalt - 60 (60Co)         5.3 Years                   Treatment of Cancer

Strontium - 90 (90Sr)      27.7 Years                  Treatment of Tumors

Iodine – 131 (131I)        2.6 Minutes                 Treatment of thyroid cancers
   1.3 Diagnostic Radioisotopes
To be useful as a diagnostic tool, a radioisotope must meet
   certain criteria. It must:
    (a) have a short half life, ideally about the same as the time
        required to perform the diagnosis.
    (b) not emit alpha or beta radiation, because they would be
        trapped inside the patient and could not be detected
    (c) emit gamma radiation which is energetic enough to allow
        its exact source to be identified.
    (d) be energetic enough to provide useful clinical information
        but not so energetic as to be dangerous to the patient.
                 From a field of more than 2300 radioisotopes, only a
                 handful come close to satisfying the criteria for use
                 as diagnostic tools.
                 Of these, the reactor produced Technetium – 99m,
                 is by far the best, being used in more that 80% of all
                 nuclear diagnostic tests performed.
                 Note: the m in the symbol 99mTc means this is the
                 “metastable” form of Tc, which radiates gamma
                 rays and low energy electrons.
               1.4 Technetium 99m
The radioisotope most widely used in medicine is
It is an isotope of the reactor-produced element
technetium and it has almost ideal characteristics for a
nuclear medicine scan.
                        These are:
                         a. It has a half-life of six hours which is long enough to
                            examine metabolic processes yet short enough to
                            minimise the radiation dose to the patient.
                         b. Technetium-99m decays by an "isomeric" process
                            which emits gamma rays and low energy electrons.
                            Since there is no high energy beta emission the
                            radiation dose to the patient is low.
                         c. The low energy gamma rays it emits easily escape
                            the human body and are accurately detected by a
                            gamma camera. Once again the radiation dose to the
                            patient is minimised.
                         d. The chemistry of technetium is so versatile it can
                            form tracers by being incorporated into a range of
                            biologically-active substances to ensure that it
                            concentrates in the tissue or organ of interest.
  1.5 Technetium Delivery
Technetium generators are popularly known as
“technetium cows” because they can be “milked” of
technetium as needed.

          The generator consists of a lead pot enclosing a glass
          tube containing the radioisotope, is supplied to
          hospitals from the nuclear reactor where the isotopes
          are made.

          It contains molybdenum-99, with a half-life of 66 hours,
          which progressively decays to technetium-99m.

          The Tc-99m is washed out of the lead pot by saline
          solution when it is required.

          The generator is exhausted after approximately two
          weeks and returned for recharging.
         1.6 The Gamma Camera
             Once produced, 99mTc is linked to chemical compounds which
             permit specific physiological processes to be scrutinised.

   It can be given by injection, inhalation or orally.

The gamma ray photons are detected by                    Gamma Camera
a gamma camera which can view
organs from many different angles.

The camera builds up an image from the
points from which radiation is emitted.

This image is enhanced by a computer
and viewed by a physician on a monitor
for indications of abnormal conditions.
                  1.7 Diagnosis
Positioning of the radiation source within the body
is the fundamental difference between nuclear
medicine imaging and other imaging techniques
such as x-rays.
Gamma imaging provides a view of the position and
concentration of the radioisotope within the body.
             Organ malfunction can be indicated if the isotope is either
             partially taken up in the organ (cold spot), or taken up in
             excess (hot spot).
             A series of images are taken over a period of time that
             show unusual patterns or rates of isotope movement could
             indicate malfunction in the organ.
A distinct advantage of nuclear imaging over x-ray
techniques is that both bone and soft tissue can be
imaged very successfully.
This has led to its common use in developed countries
where the probability of anyone having such a test is
about one in two and rising.
  1.8 Therapeutic Radioisotopes
   Rapidly dividing cells are particularly sensitive to damage by
   For this reason, some cancerous growths can be controlled or
   eliminated by irradiating the area containing the growth.
                  External irradiation can be carried out using a gamma
                  beam from a radioactive cobalt-60 source, though in
                  developed countries the much more versatile linear
                  accelerators are now being utilised as a high-energy x-ray
                  source (gamma and x-rays are much the same).

Internal radiotherapy is by administering or planting a small
radiation source, usually a gamma or beta emitter, in the
target area.
Iodine-131 is commonly used to treat thyroid cancer, probably
the most successful kind of cancer treatment.
Iridium-192 implants are used especially in the head and
They are produced in wire form and are introduced through a catheter to the
target area. After administering the correct dose, the implant wire is removed
to shielded storage. This procedure gives less overall radiation to the body, is
more localised to the target tumour and is cost effective.
      1.9 A Cure for Anything !
At present, approximately 35 radioisotopes
are commonly used in the detection and
treatment of illness or disease. Those used
for treatment include:

         Radioisotope                         Use
         Cobalt – 60:             External cancer radiation
         Dysprosium-165:          Treatment, arthritis
         Iodine-125:              Treatment, cancer of prostate, brain
         Iodine-131:              Treatment, cancer of thryoid
         Phosphorus-32:           Treatment, excess red blood cells
         Rhenium-188:             Treatment, coronary artery disease
         Samarium-153:            Treatment, breast, prostate cancers
         Boron – 10:              Treatment, brain tumours
     Chapter 2

Optical Instruments:
                    2.0 Endoscopes
The name endoscope is derived from two Greek
words: endom (within) and skopein (view).
The endoscope is an optical instrument used for
viewing internal organs through natural openings
(ear, throat, rectum, etc.) or through a small
incision in the skin.

There are 2 basic types of endoscopes: Rigid and Flexible

                           In rigid endoscopes the image is conveyed by a
                           relay of lenses.
                           The classical rigid endoscopes have a number of
                           periscopic and field lenses in order to convey the
                           image from distal end to the eyepiece.
                           Generally, a flexible endoscope is referred to as a
                           In flexible endoscopes, a bundle of precisely
Various rigid & flexible   aligned flexible optical fibres is used.
2.1 Endoscopes – Some History
                     The concept of endoscopy originated in
                     the early 19th century.
                     Philip Bonzini, an Italian doctor, is
                     credited with the first use of a rigid
                     endoscope in humans in the early
In 1930, German medical student, Heinrich
Lamm was the first person to assemble a
bundle of optical fibres to carry an image.
Lamm's goal was to look inside
inaccessible parts of the body.
During his experiments, he reported
transmitting the image of a light bulb.
However the image was of poor quality.

                       The first endoscope made of optical fibres (fibrescope)
                       was used for viewing the stomach and esophagus at
                       the University of Michigan School of Medicine in 1957.
                       Since then, there has been rapid progress in
                       endoscope development.
   2.2 Principles of Optical Fibres
Total internal reflection (TIR) is the most important phenomenon for the guiding of
light in optical fibres.
With TIR light can be completely reflected at the optical fibre surface without any
reflective coating.
TIR can only occur for light travelling from a more dense to a less dense medium.
Thus, in the diagram, the refractive index of the actual optical fibre n1 is greater
than that of the cladding n2 .
For TIR to occur the angle of incidence (θ) must be greater than the critical

                   Lost Light                                     n1 > n2    n2 Cladding
         θ1 θ1                    θC                  θ2 θ2
                                                                             n1 Optical Fibre
      Some Reflected Light      Critical Angle         All Light Reflected

         θ1< θC                                       θ2> θC                 n2 Cladding

 For light with with θ < θC , much of the light is refracted out of the optical fibre
 For light with θ = θC , all light is refracted so it just grazes the surface of the fibre
 For light with θ > θC , light is totally internally reflected and will continue to do
 so whenever it strikes the fibre’s surface.
    2.3 Optical Fibre Construction
Usually optical fibres are      Fibre Type     Cross Section     Refractive Index Profile
flexible, thin, cylindrical
and made of transparent                                            RI
materials such as glass           Step                       r n1
and plastic.                     Index          n2  n1          n2
The most abundant and                                                                     r
widespread material used
to make optical fibre is                                           RI
glass and most often this                                       n1
                                 Graded                      r
is an oxide glass based on         Index        n2  n1
silica (SiO2) with some
The required properties for an optical fibre are:
optical quality, mechanical strength, and flexibility.
For these reasons, plastic optical fibres have been made with polymethylmeth-
acrylate (PMMA). They have a “tighter turning circle” than glass fibres.
In general, optical fibres have a cylindrical core and are surrounded by a cladding.
If both Refractive Indexes, (n1) and (n2) are uniform across their cross sections,
the fibre is called a STEP INDEX FIBRE (SI) .
If (n1) varies with the core radius (i.e., (n1) gradually decreases from the centre of
the core to n2 at the outer radius), it is a GRADED INDEX FIBRE (GRIN).
            2.4 Step vs Graded Fibres
                                                            In SI fibre, the light
                                   Cladding   Core
                                                            rays zigzag between
                                                            the core/cladding on
                                                            each side of the fibre
Accptance                                                   axis.
                                                            The Fibre Acceptance
                                                            Cone represents the
                                                            range of angles for
                              Step Index Fibre              which the incidence
                                                            angles are greater
                                                            than the critical angle
In GRIN fibre, the
gradient in the                                           Core
refractive index
gradually bends the
rays back toward the     Fibre
axis.                    Cone

                                                     Graded Index Fibre
                   2.5 Fibre Bundles
  It is impossible for a single fibre to transmit an image.
  An individual fibre can transmit only a spot of a certain color and intensity.
  To transmit an image, a large number of single fibres must be aligned and
  fused together.
  This means assembly of optical fibres in which the fibres are ordered in
  exactly the same way at both ends of the bundle to create an image.
  This type of fibre bundle is called a Coherent Bundle

(a) is a low power endoscope
                                        Object seen by           Image projected to
(b) is a high power endoscope            endoscope                   eyepiece
Incoherent Bundles are
groups of fibres which are
not ordered at both ends.
They are used as light pipes
to bring light from an
external source down the
                                        Object seen by           Image projected to
endoscope to illuminate the                                          eyepiece
area under view.
2.6 Endoscope Construction
    Fibre Optic Endoscopes
       have a number of
       basic components:
    1. A Coherent Bundle for
       bringing the image to
       the eyepiece (or video
                                                  A piece of dried
    2. An Incoherent Bundle
                                                pork crackling stuck
       for taking an external                     in oesophagus
       light source down the
       endoscope to            A Ball Bearing
       illuminate the viewing   lodged in the
       area.                     oesophagus
    3. Optional tubes or
       channels for the
       passage of air, water,
       as well as remote                           A coin in the
       control implements                            stomach
       such as biopsy
       forceps or cytology
       brushes.               Stomach Ulcer
              2.7 Endoscope Man
An incredible number of
endoscopes have been
developed for both diagnosis
and treatment.
Some of the more common are
shown on “Endoscope Man”
Ultra thin endoscope for
investigating blood vessels


Famous in “Aussie Rules” for
investigating knee injuries

     Typical Rigid Endoscope
                                             Most commonly used
                                             endoscope in general
   Chapter 3

    Lasers &
Laser Treatments
                            3.0 Laser Basics
 "Laser" is an acronym for Light Amplification by
 Stimulated Emission of Radiation.
Although there are many types of lasers, all have
certain common features.
In explaining laser operation, the common ruby laser
will be used as an example.                               Typically, very intense
                     In a laser, the lasing medium (the   flashes of light from a flash
      Ruby Crystal   ruby crystal) is so called           tube (or from an electrical
                     “pumped” to get the electrons of     discharge pump) enter the
       Ruby Atoms    the ruby atoms into an excited       lasing medium and create a
                     state.                               large collection of excited-
       Flash Tube      These excited electrons then       state atoms (atoms with
                       release their excess energy        higher- energy electrons).
         Mirror        as photons of red light.
         Ruby Atoms
Partially silvered mirror
These red photons
rush back and forth
finally exiting the
tube as a coherent
                       3.1 Laser Types
Since their development in 1960, lasers used in
medicine and surgery have evolved, and while
medical lasers have never become the "magic ray"
that some had hoped, they have become powerful
and indispensable tools in clinical practice.
                                                        Letters etched on a human
There are many medical laser systems available
                                                        hair using an Eximer Laser
today, but they all use the principal of selective
photothermolysis which means getting the right          Note: YAG = Yttrium-
amount of the right wavelength of laser energy to the   Aluminium- Garnett
right tissue to damage or destroy only that tissue,     KTP = potassium-titanyl-
and nothing else.                                       phosphate


                         Some of the many medical and surgical lasers in use.
3.1 Laser Types & Treatments
  Laser       Wavelength                             Use
CO2             10,600     Surgery (used as a “scalpel”)
Er: YAG         2940       “Shaving” of skin to remove wrinkles
Ho: YAG         2070       Shaving bones (eg, arthroscopes), kidney stone remov
Nd: YAG         1064       Blue/black ink tattoo removal; hair removal
Diode         800 to 900   Hair removal; dental surgery
Alexandrite      755       Blue/black ink tattoo removal; hair removal
Ruby             694       Treatment and removal of moles, freckles, birthmarks
Pulsed Dye    577 to 585   Treatment of port wine birthmarks and spider veins
KTP              532       Cutting tissue, red/yellow tattoo ink removal
Argon         488 to 514   Retinal and ear surgery, removal of birthmarks
Eximer           193       Laser eye correction

                           Tattoo removal using
                               Nd:YAG laser
Chapter 4

            4.0 Ultrasound Basics
Definition of Ultrasound
Sound consists of travelling pressure waves
Speed of sound waves in human tissue: ~ 1500 ms-1.
Frequency range: between 2 MHz and 10 MHz
Ultrasound is produced using piezo-electric transducers,
crystals which change shape under the action of an electric
Quartz is the most commonly known piezo-electric material.
                                                The disk is placed between 2
                                             electrodes and applying a voltage
                                                causes the crystal to vibrate.
Better performing piezo –
electric materials (such                                           Variable frequency
as BARIUM TITANATE or                                                 A.C Voltage:
LEAD ZIRCONATE) is                                                  V = VoCos 2π ft
formed into disks.

      The crystal will vibrate at the same frequency   The crystal’s vibrations set up
     as the supply voltage, producing sound waves      Ultrasonic sound waves in the
         with frequencies between 2 and 10 MHz         medium around the crystal
                   4.1 Echo Location
Ultrasound or ultrasonography is a medical imaging technique that uses high
frequency sound waves and their echoes.
The technique is similar to the echolocation used by bats, whales and dolphins,
as well as SONAR used by submarines.

The ultrasound signals
generated as previously
described leave the handpiece
and are reflected back from
various tissues and bones.

                            These reflected waves strike the handpiece causing
                            the piezo electric crystal to contract and expand.
                            This change in shape causes a voltage to be
                            generated which is then processed into a “picture”.
            4.2 Ultrasonic Speeds
When ultrasonic waves are applied to various body tissues they travel at
varying speeds from a low of 1450 ms-1 through fat to a high of 4080 ms-1
through skull bone.

                                                         Ultrasound image of
                                                         yolk sac and fetus at 6
                                                         week gestation.
       4.3 Sound Intensity Profile
                                          Field Zones

                                          Near Field - the region of a sound
                                          beam in which the beam diameter
                                          decreases as the distance from the
                                          transducer increases. This zone is
                                          called the Fresnel (Fra-nel, the s is
                                          silent) zone.

                                          Focal Zone - the region where the
                                          beam diameter is most concentrated
Beam Properties:                          giving the greatest degree of focus.

Longitudinal Waves - the wave in which    Far Field - the region where the
the particle motion is parallel to the    beam diameter increases as the
direction of the wave travel.             distance from the transducer
A series of longitudinal waves make up    increases. This zone is called the
the ultrasound beam.                      Fraunhoffer zone
The best ultrasound images are produced with the transducer operating in the
Focal Zone.
     4.4 An Ultrasound Examination
     In ultrasound examination, the following
     events happen:
                                                     Below is an Ultrasound image of a
1.   High-frequency sound pulses are
                                                     growing fetus (approximately 12
     transmitted into your body using a probe.       weeks old) inside a mother's
2.   The waves travel into your body and hit a       uterus.
     boundary between tissues (e.g. between          This is a side view of the baby,
     fluid and soft tissue, soft tissue and bone). showing:
3.   Some of the sound waves get reflected
     back to the probe, while some travel on
     further until they reach another boundary
     and get reflected.
4.   The reflected waves are picked up by the
     probe and relayed to the machine.
5.   The machine calculates the distance from
     the probe to the tissue or organ
     (boundaries) using the speed of sound in
     tissue and the time of the each echo's
     return (usually on the order of millionths of
     a second).                                    Legs
                                                                   Neck Head
6.   The machine displays the distances and
     intensities of the echoes on the screen,           Torso
     forming a two dimensional image.
             4.5 Ultrasound in 3D

In the past few years,
ultrasound machines
capable of three-
dimensional imaging have
been developed.
In these machines, several   3-D ultrasound images Photo courtesy Philips Research
two-dimensional images
are acquired by moving       The same computer technology is used to
the probes across the          produce the famous “dancing babies”
body surface or rotating                      images
inserted probes.
The two-dimensional
scans are then combined
by specialized computer
software to form 3-D
             4.6 Doppler Ultrasound
Doppler ultrasound is based upon the Doppler Effect.
When the object reflecting the ultrasound waves is moving, it
changes the frequency of the echoes, creating a higher
frequency if it is moving toward the probe and a lower
frequency if it is moving away from the probe.

                                        How much the frequency is changed
                                        depends upon how fast the object is
                                        Doppler ultrasound measures the
                                        change in frequency of the echoes to
                                        calculate how fast an object is
                                        Doppler ultrasound has been used
                                        mostly to measure the rate of blood
                                        flow through the heart and major
Chapter 5

 X Rays
  Wilhelm Conrad
Roentgen (1845-1923)        5.0 X rays
                 Roentgen found that, if the discharge tube is enclosed in a
                 sealed, thick black carton to exclude all light, and if he worked
                 in a dark room, a paper plate covered on one side with the
                 compound barium platinocyanide placed in the path of the
                 rays became fluorescent (gave out a greenish light) even when
                 it was as far as two metres from the discharge tube
                                               Following this discovery, he
                                               asked his wife to hold her hand in
In 1895 Röntgen was studying                   the path of rays between the tube
what happened when an electric                 and a photographic plate.
current was passed through a gas               He observed, after developing the
of extremely low pressure in                   plate, an image of his wife's hand
apparatus called Crooke’s Tubes.               which showed the shadows
                                      The      thrown by the bones of her hand
                                 “first X ray” and that of a ring she was
                                Because the nature of the new rays was then
                                unknown, he gave them the name X-rays.
                                Later it was shown that they are of the same
                                electromagnetic nature as light, but differ from it
                                only in the higher frequency of their vibration.
               5.1 X Ray Production
An x-ray machine, like
that used in a doctor's
or a dentist's office, is   X-rays are just like any other kind
really very simple.         of electromagnetic radiation.
                            They are produced in parcels of
                            energy called photons, just like      Individual Photon
                            There are two different atomic
                            processes that can produce x-
                            ray photons.
Inside the machine is an x- 1. The first is called
ray tube.                   Bremsstrahlung, which is a
An electron gun inside the fancy German name meaning
tube shoots high energy     "braking radiation."
electrons at a target made
of heavy atoms, such as
tungsten.                                          2. The other is called K-shell
X-rays come out because of                         emission. They can both occur
atomic processes induced                           in heavy atoms like tungsten.
by the energetic electrons
shot at the target.
                5.2 Types of X Rays
1. Bremsstrahlung. This form of X     2. K Shell. The K-shell is the lowest energy
radiation occurs when the velocity    state of an atom.
of electrons fired towards the
tungsten nucleus changes.

                                     The incoming electron can give the K shell
                                     electron enough energy to knock it out of its
This electron slows down after       energy state.
swinging around the nucleus of a Then, a tungsten electron of higher energy
tungsten atom and loses energy by (from an outer shell) can fall into the K-shell.
radiating x-rays.                    The energy lost by the falling electron
In this process, a lot of photons of shows up in an emitted x-ray photon.
different wavelengths are            Meanwhile, higher energy electrons fall into
produced, but none of the photons the vacated energy state in the outer shell,
has more energy than the electron and so on.
had to begin with.                   K-shell emission produces higher-intensity
After emitting the spectrum of x-    x-rays than Bremsstrahlung, and the x-ray
ray radiation the original electron  photon comes out at a single wavelength.
is slowed down or stopped.
            5.3 X Ray Diagnostics
X rays are most
commonly used       Steel spikes
for investigation     in wrist
of the skeleton,
the diagnosis of
broken bones                       Shotgun Pellets
and the display
of the effects of
trauma on the

                                   Shattered Femur
                    Broken Femur
Chapter 6

CT Scans
   6.0 CT Scans
                      CT or Computerised Tomography, also
One of the first      know as CAT or Computerised Axial
dedicated head CT
                      Tomography Scans use an X-ray
scanners, in 1974
                      source coupled with an X-ray detector
                      on the opposite side of the body, which
                      are rotated together to give a cross-
                      sectional picture of the body at one
                      level or cut.
                      CT scans are of greatest value for
                      showing physical changes in tissue,
                      although small tumours may be
                      missed if absorption properties are
                      like those of normal tissue.
                       COMPUTED AXIAL TOMOGRAPHY

                    CAT Scan of the
                    Pelvic Region
                    • Images the body using X-rays.
                    • Initial research: 1960s
                    • Applied research: 1970s-80s
                    • X-rays are sent through the body at
                    various angles, resulting in cross-sectional
                       6.1 CT - History
Tomography is from the Greek
                                       CT image of a normal brain using
word "tomos" meaning "slice"
                                       a state-of-the-art CT system and a
or "section" and graphia               512 x 512 matrix image.
meaning "describing".
CT was invented in 1972 by           The first clinical CT scanners were installed
British engineer Godfrey             between 1974 and 1976. The original systems
Hounsfield of EMI                    were dedicated to head imaging only, but "whole
Laboratories, England, and           body" systems with larger patient openings
independently by South               became available in 1976.
African born physicist Allan         CT became widely available by about 1980.
Cormack of Tufts University,         There are now 30,000 installed worldwide.
Massachusetts.                       The first CT scanner took several hours to
                                     acquire the raw data for a single scan or "slice"
                                     and took days to reconstruct a single image
                                     from this raw data.
                                     The latest multi-slice CT systems can collect up
                                     to 4 slices of data in about 350 ms and
                                     reconstruct a 512 x 512-matrix image from
Original CT image from scanner       millions of data points in less than a second. An
circa 1975. This image is a coarse   entire chest (forty 8 mm slices) can be scanned
128 x 128 matrix, showing a slice of in five to ten seconds using the most advanced
the brain
                                     multi-slice CT system.
Chapter 7

PET Scans
                         7.1 PET Scans
Positron Emission                                         Human Brain Performing
Tomography, or PET,     A PET scan provides a
scanning is an          color-coded image of a
imaging technique       body organ in function
that uses radioactive   rather than its structure.
                        During a PET scan, a
positrons (positively
charged particles) to
                        radioisotope called a
detect subtle changes
                        tracer is either injected
in the body's
                        into a vein or inhaled as
metabolism and
                        a gas.
chemical activities.
                           This tracer is typically a chemical that is normally
       PET Scanner
                           found in the body (carbon, nitrogen, oxygen) that has
                           been altered to allow it to emit positrons.
                           Once the tracer enters the body, it travels through the
                           bloodstream to a specific target organ, such as the
                           brain or heart.
 There the tracer emits positrons, which collide with electrons (negatively
 charged particles), producing gamma rays (similar to X-rays).
 These gamma rays are detected by a ringed-shaped PET scanner and
 analyzed by a computer to form an image of the target organ's metabolism or
 other functions.
Chapter 8

MRI Scans
         8.0 MRI - Basic Operation
   Typical MRI Scanner         MRI (Magnetic Resonance Imaging) started out as
                               a tomographic imaging (CT) technique, that is, it
                               produced an image of a thin slice through the
                               human body.
                               MRI has advanced beyond a tomographic imaging
                               technique to a volume imaging technique.
The human body is primarily                           In the absence of an external
fat and water.                                        magnetic field, these
Both fat and water have many                          hydrogen atoms are not
hydrogen atoms which make                             lined up in any particular
the human body roughly 63%                            direction.
hydrogen atoms.
                                    When those atoms are placed in a
MRI takes advantage of the fact
                                    strong magnetic field, their nuclei
that the nuclei of certain atoms,
                                    align the axis of spin either with
hydrogen and phosphorous, in
                                    or against the direction of the
particular, behave like a
When the field is turned-off, the
                                                            These emissions are
nuclei against the field spin and
                                                            collected and fed into a
release a characteristic radio-
                                                            computer which
frequency photon emission.
                                                            produces the MRI image.
                         8.1 MRI Scans
 MRI scanners are good at looking at the
 non-bony parts or "soft tissues" of the
 In particular, the brain, spinal cord and
 nerves are seen much more clearly with
 MRI than with regular x-rays and CAT
 Also, muscles, ligaments and           Knee MRI
 tendons are seen quite well so        Colour Enhanced

 that MRI scans are commonly
 used to look at knees and                               The Magnetic Fields used by
 shoulders following injuries.                           MRI’s are about 1 million times
An advantage of MRI is the radio waves used are a        stronger than the Earth’s field.
trillion times less energetic (and potentially less      So beware funny things can
damaging) than X rays.                                   happen when these machines
                        Neck                             are switched on !
                                                          A disadvantage of MRI is it’s
                                                          higher cost compared to a
                                                          regular x-ray or CAT scan.

    Brain                             Kidneys
     Chapter 9

Image Interpretation
         9.1 Image Interpretation:
                 X Rays
                   Bullet lodged
                    in shoulder
                               Coin lodged in
                            child’s oesophageus

                                          Needle in
                                         child’s foot

Broken Ulna Bone
    in forearm
          9.2 Image Interpretation:
                 CT Scans
   Brain Scan                                         Liver Scan
                                      Cuts due
                                       to MVA

                    Stroke – Bleeding
                        into brain

                                                      Brain Scan

Calf (Lower Leg) Scan     Sub Dural Haematoma –
                          Bleeding inside skull due
                          to head injury from MVA

                        DVT (Deep Vein Thrombosis)
                         Economy Class Syndrome
         9.3 Image Interpretation:
                                                      Knee Scan
   Brain Scan                     Ruptured Cruciate
                   Brain Tumor

                             Heart Scan

     Spinal Scan
                                                      Breast Scan

                        Ruptured Disc

Actual       Colour                       Cancer
          9.4 Image Interpretation:
Whole Body
                PET Scans scan – growing child
                  Brain Scan

                                     Shows the remarkable increase in
              These days, scans
                                     brain activity during the 1st year of life
              are “colour coded”
              making them much      Brain
              easier to “read”.

              Scans comparing
              brain activity
Dark Spots
              during various
are cancers
              activities with the
              same brain in its
              resting state.
9.5 Image Interpretation:

     Twins shown in colour
     enhanced scan

                             3-D scan of fetus
                             with a Clubfoot
Information sources:
•Uranium Information Centre (UIC)
•     Ollie Leitl 2003

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