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Title: MEDICAL IMAGING


1
MEDICAL IMAGING
  • Created By Shale Olagbegi
  • DOD TELEHEALTH RESEARCH TOPIC

2
What Is Medical Imaging?
  • Medical imaging is the process by which
    physicians evaluate an area of the subject's body
    that is not normally visible. This process could
    be clinical or research motivated and can also
    have scientific and industrial applications.

3
Origin of Medical Imaging
  • In its most primitive form, imaging can refer to
    the physician simply feeling an area of the body
    in order to visualize the condition of internal
    organs.
  • It remains an important step today in making
    initial assessments of potential problems,
    although additional steps are often used to
    confirm a diagnosis.
  • The primary drawback of this approach is that
    findings are subject to interpretation, and while
    a recorded image can be produced manually, in
    practice this is often not done.

4
Modern Imaging Techniques
  • Radiographs
  • Computed Tomography
  • Magnetic Resonance Imaging
  • Ultrasound
  • Mammography
  • Microwave Imaging

5
Radiography
  • This is the creation of radiographs,
    photographs made by exposing a photographic film
    or other image receptor to X-rays.
  • Since X-rays penetrate solid objects, but are
    slightly attenuated by them, the picture
    resulting from the exposure reveals the internal
    structure of the object.
  • The most common use of radiography is in the
    medical field (where it is known as medical
    imaging).

6
Theory of Radiography
  • The type of electromagnetic radiation of most
    interest to radiography is x-ray and gamma
    radiation. This radiation is much more energetic
    than the more familiar types such as radio waves
    and visible light. It is this relatively high
    energy, which makes gamma rays useful in
    radiography but potentially hazardous to living
    organisms.
  • They are produced by X-ray tubes, high energy
    X-ray equipment or natural radioactive elements,
    such as Radium and Radon, and artificially
    produced radioactive isotopes of elements, such
    as Cobalt 60 and Iridium 192. Electromagnetic
    radiation consists of oscillating electric and
    magnetic fields. It is generally pictured as a
    single sinusoidal wave.
  • It is characterized by its wavelength (the
    distance from a point on one cycle to the point
    on the next cycle) or its frequency (the number
    of oscillations per second). All electromagnetic
    waves travel at the same speed, the speed of
    light (c). The wavelength (W) and the frequency
    (?) are all related by the equation
  • W? c
  • This is true for all electromagnetic radiation.
  • Electromagnetic radiation is known by various
    names, depending on its energy . The energy of
    these waves is related to the frequency and the
    wavelength by the relationship
  • E h? hc / W
  • Where h is a constant known as Planck's Constant.
  • Gamma rays are indirectly ionizing radiation. A
    gamma ray passes through matter until it
    undergoes an interaction with an atomic particle,
    usually an electron. During this interaction,
    energy is transferred from the gamma ray to the
    electron, which is a directly ionizing particle.
    As a result of this energy transfer, the electron
    is liberated from the atom and proceeds to ionize
    matter by colliding with other electrons along
    its path.
  • For the range of energies commonly used in
    radiography, the interaction between gamma rays
    and electrons occurs in two ways. One effect
    takes place where all the gamma ray's energy is
    transmitted to an entire atom. The gamma ray no
    longer exists and an electron emerges from the
    atom with kinetic (motion in relation to force)
    energy almost equal to the gamma energy. This
    effect is predominant at low gamma energies and
    is known as the photoelectric effect. The other
    major effect occurs when a gamma ray interacts
    with an atomic electron, freeing it from the atom
    and imparting to it only a fraction of the gamma
    ray's kinetic energy. A secondary gamma ray with
    less energy (hence lower frequency) also emerges
    from the interaction. This effect predominates at
    higher gamma energies and is known as the Compton
    effect.
  • In both of these effects the emergent electrons
    lose their kinetic energy by ionizing surrounding
    atoms. The density of ions so generated is a
    measure of the energy delivered to the material
    by the gamma rays.
  • The most common means of measuring the variations
    in a beam of radiation is by utilizing its
    effects onto a photographic film. This effect is
    the same as that of light, and the more intense
    the radiation is, it will produce a darker film,
    or a more exposed film. Other methods are in use,
    such as the ionizing effect measured
    electronically, its ability to discharge an
    electro statically charged plate or to cause
    certain chemicals to fluoresce as in fluoroscopy.

7
What's an X-Ray?
  • X-rays are basically the same thing as visible
    light rays. Both are wavelike forms of
    electromagnetic energy carried by particles
    called photons.
  • The difference between X-rays and visible light
    rays is the energy level of the individual
    photons. This is also expressed as the wavelength
    of the rays.

8
Theory of X-ray
  • X rays were discovered in 1895 by W. C. Roentgen,
    who called them X rays because their nature was
    at first unknown they are sometimes also called
    Roentgen, or Röntgen, rays. X-ray line spectra
    were used by H. G. J. Moseley in his important
    work on atomic numbers (1913) and also provided
    further confirmation of the quantum theory of
    atomic structure.
  • Also important historically is the discovery of
    X-ray diffraction by Max von Laue (1912) and its
    subsequent application by W. H. and W. L. Bragg
    to the study of crystal structure.

9
Production of X Rays
  • An important source of X rays is synchrotron
    radiation. X rays are also produced in a highly
    evacuated glass bulb, called an X-ray tube, that
    contains essentially two electrodesan anode made
    of platinum, tungsten, or another heavy metal of
    high melting point, and a cathode. When a high
    voltage is applied between the electrodes,
    streams of electrons (cathode rays) are
    accelerated from the cathode to the anode and
    produce X rays as they strike the anode.
  • Two different processes give rise to radiation of
    X-ray frequency. In one process radiation is
    emitted by the high-speed electrons themselves as
    they are slowed or even stopped in passing near
    the positively charged nuclei of the anode
    material. This radiation is often called
    brehmsstrahlung Ger.,braking radiation. In a
    second process radiation is emitted by the
    electrons of the anode atoms when incoming
    electrons from the cathode knock electrons near
    the nuclei out of orbit and they are replaced by
    other electrons from outer orbits. The spectrum
    of frequencies given off with any particular
    anode material thus consists of a continuous
    range of frequencies emitted in the first
    process, and superimposed on it a number of sharp
    peaks of intensity corresponding to discrete
    frequencies at which X rays are emitted in the
    second process. The sharp peaks constitute the
    X-ray line spectrum for the anode material and
    will differ for different materials.

10
Applications of X Rays
  • Most applications of X rays are based on their
    ability to pass through matter. This ability
    varies with different substances e.g., wood and
    flesh are easily penetrated, but denser
    substances such as lead and bone are more opaque.
    The penetrating power of X rays also depends on
    their energy. The more penetrating X rays, known
    as hard X rays, are of higher frequency and are
    thus more energetic, while the less penetrating X
    rays, called soft X rays, have lower energies. X
    rays that have passed through a body provide a
    visual image of its interior structure when they
    strike a photographic plate or a fluorescent
    screen the darkness of the shadows produced on
    the plate or screen depends on the relative
    opacity of different parts of the body.
  • Photographs made with X rays are known as
    radiographs or ski graphs. Radiography has
    applications in both medicine and industry, where
    it is valuable for diagnosis and nondestructive
    testing of products for defects. Fluoroscopy is
    based on the same techniques, with the
    photographic plate replaced by a fluorescent
    screen (see fluorescence fluoroscope ) its
    advantages over radiography in time and cost are
    balanced by some loss in sharpness of the image.
    X rays are also used with computers in CAT
    (computerized axial tomography) scans to produce
    cross-sectional images of the inside of the body.
  • Another use of radiography is in the examination
    and analysis of paintings, where studies can
    reveal such details as the age of a painting and
    underlying brushstroke techniques that help to
    identify or verify the artist. X rays are used in
    several techniques that can provide enlarged
    images of the structure of opaque objects. These
    techniques, collectively referred to as X-ray
    microscopy or microradiograph, can also be used
    in the quantitative analysis of many materials.
    One of the dangers in the use of X rays is that
    they can destroy living tissue and can cause
    severe skin burns on human flesh exposed for too
    long a time. This destructive power is used in
    X-ray therapy to destroy diseased cells.

11
Medical uses
  • X-rays have been developed for their use in
    medical imaging.
  • Radiology is a specialized field of medicine that
    employs radiography and other techniques for
    diagnostic imaging.
  • The use of X-rays are especially useful in the
    detection of pathology of the skeletal system,
    but are also useful for detecting some disease
    processes in soft tissue.
  • X-ray, which can be used to identify lung
    diseases such as pneumonia, lung cancer or
    pulmonary oedema.

12
Other X-Ray Uses
  • The most important contributions of X-ray
    technology have been in the world of medicine,
    but X-rays have played a crucial role in a number
    of other areas as well.
  • X-rays have been pivotal in research involving
    quantum mechanics theory, crystallography and
    cosmology.
  • In the industrial world, X-ray scanners are often
    used to detect minute flaws in heavy metal
    equipment.
  • And X-ray scanners have become standard equipment
    in airport security, of course.

13
Cat Scan
  • (CT), also known as computed axial tomography or
    computer-assisted tomography (CAT) and body
    section roentgenography, is medical imaging
    method employing tomography where digital
    processing is used to generate a
    three-dimensional image of the internals of an
    object from a large series of two-dimensional
    X-ray images taken around a single axis of
    rotation.
  • The word "tomography" is derived from the Greek
    tomos (slice) and graphia (describing).
  • Although most common in healthcare, CT is also
    used in other fields, e.g. nondestructive
    materials testing

14
History of Cat Scan
  • The CT system was invented in 1972 by Godfrey
    Newbold Hounsfield of EMI Central Research
    Laboratories owned by Creative Technology.)
    using X-rays.
  • Allan McLeod Cormack of Tufts University
    independently invented the same process and they
    shared a Nobel Prize in Medicine in 1979. The
    first scanner took several hours to acquire the
    raw data and several days to produce the images.
    Modern multi-detector CT systems can complete a
    scan of the chest in less time than it takes for
    a single breath and display the computed images
    in a few seconds.

15
Principles of Cat Scan
  • X-ray slice data is generated using an X-ray
    source that rotates around the object X-ray
    sensors are positioned on the opposite side of
    the circle from the X-ray source. Many data scans
    are progressively taken as the object is
    gradually passed through the gantry. They are
    combined together by the mathematical procedure
    known as tomographic reconstruction.
  • Newer machines with faster computer systems and
    newer software strategies can process not only
    individual cross sections but continuously
    changing cross sections as the gantry, with the
    object to be imaged, is slowly and smoothly slid
    through the X-ray circle. These are called
    helical or spiral CT machines. Their computer
    systems integrate the data of the moving
    individual slices to generate three dimensional
    volumetric information, in turn viewable from
    multiple different perspectives on attached CT
    workstation monitors.

16
Principles of Cat Scan (contd)
  • EBT Machine
  • In conventional CT machines, an X-ray tube is
    physically rotated behind a circular shroud in
    the less used electron beam tomography (EBT)
  • The data stream representing the varying
    radiographic intensity sensed reaching the
    detectors on the opposite side of the circle
    during each sweep360 degree in conventional
    machines, 220 degree in EBTis then computer
    processed to calculate cross-sectional
    estimations of the radiographic density,
    expressed in Hounsfield units.
  • CT is used in medicine as a diagnostic tool and
    as a guide for interventional procedures.
    Sometimes contrast materials such as intravenous
    iodinated contrast is used. This is useful to
    highlight structures such as blood vessels that
    otherwise would be difficult to delineate from
    their surroundings. Using contrast material can
    also help to obtain functional information about
    tissues.

17
Principles of Cat Scan (contd)
  • Pixels in an image obtained by CT scanning are
    displayed in terms of relative radio-density. The
    pixel itself is displayed according to the mean
    attenuation of the tissue that it corresponds to
    on a scale from -1024 to 3071 on the Hounsfield
    scale. Water has an attenuation of 0 Hounsfield
    units (HU) while air is -1000 HU, bone is
    typically 400 HU or greater and metallic
    implants are usually 1000 HU.
  • Improvements in CT technology have meant that the
    overall radiation dose has decreased, scan times
    have decreased and the ability to reconstruct
    images (for example, to look at the same location
    from a different angle) has increased over time.
    Still, the radiation dose from CT scans is
    several times higher than conventional X-ray
    scans.
  • Presently, the cost of an average CT scanner is
    US1.3 million.

18
Diagnostic use of Cat Scan
  • Since its introduction in the 1970s , CT has
    become an important tool in medical imaging to
    supplement X rays and medical ultrasonography.
    Although it is still quite expensive, it is the
    gold standard in the diagnosis of a large number
    of different disease entities.
  • Cranial CT
  • Diagnosis of cerebra vascular accidents and
    interracial hemorrhage is the most frequent
    reason for a "head CT" or "CT brain". Scanning is
    done without intravenous contrast agents
    (contrast may resemble a bleed). CT generally
    does not exclude infarct in the acute stage, but
    is useful to exclude a bleed (so anticoagulant
    medication can be commenced safely).
  • For detection of tumors, CT scanning with IV
    contrast is occasionally used but is less
    sensitive than (MRI).
  • CT can also be used to detect increases in
    intracranial pressure, e.g. before lumbar
    puncture or to evaluate the functioning of a
    ventriculoperitoneal shunt.
  • CT is also useful in the setting of trauma for
    evaluating facial and skull fractures.

19
Diagnostic use of Cat Scan (contd)
  • Chest CT
  • CT is excellent for detecting both acute and
    chronic changes in the lung parenchyma. For
    detection of airspace disease or cancer, ordinary
    non-contrast scans are adequate.
  • For evaluation of chronic interstitial processes.
    For evaluation of the mediastinum and hilar
    regions for lymphadenopathy, IV contrast is
    administered.
  • CT angiography of the chest (CTPA) is also
    becoming the primary method for detecting
    pulmonary embolism (PE) and aortic dissection,
    and requires accurately timed rapid injections of
    contrast and high-speed helical scanners. CT is
    the standard method of evaluating abnormalities
    seen on chest X-ray and of following findings of
    uncertain acute significance.

20
Diagnostic use of Cat Scan (contd)
  • Cardiac CT
  • With the advent of sub second rotation combined
    with multi-slice CT (up to 64 slices), high
    resolution and high speed can be obtained at the
    same time, allowing excellent imaging of the
    coronary arteries. It is uncertain whether this
    modality will replace the invasive coronary
    catheterization.
  • Abdominal and pelvic CT
  • Many abdominal disease processes require CT for
    proper diagnosis. CT has limited application in
    the evaluation of the pelvis. For the female
    pelvis in particular, ultrasound is the imaging
    modality of choice. Nevertheless, it may be part
    of abdominal scanning (e.g. for tumors), and has
    uses is assessing fractures.

21
Extremities of Cat Scan
  • CT is often used to image complex fractures,
    especially ones around joints, because of the
    ability to reconstruct the area of interest in
    multiple planes

22
Magnetic resonance imaging
  • (MRI) - also called magnetic resonance tomography
    (MRT) - is a method of creating images of the
    inside of opaque organs in living organisms as
    well as detecting the amount of bound water in
    geological structures.

23
MRI Machine
24
MRI
  • To understand how MRI works, let's start by
    focusing on the "magnetic" in MRI. The biggest
    and most important component in an MRI system is
    the magnet.
  • The magnet in an MRI system is rated using a unit
    of measure known as a tesla. Another unit of
    measure commonly used with magnets is the gauss
    (1 tesla 10,000 gauss).
  • The magnets in use today in MRI are in the
    0.5-tesla to 2.0-tesla range, or 5,000 to 20,000
    gauss. Magnetic fields greater than 2 tesla have
    not been approved for use in medical imaging,
    though much more powerful magnets -- up to 60
    tesla -- are used in research. Compared with the
    Earth's 0.5-gauss magnetic field, you can see how
    incredibly powerful these magnets are.

25
MRI (contd)_
  • Numbers like that help provide an intellectual
    understanding of the magnetic strength, but
    everyday examples are also helpful.
  • The MRI suite can be a very dangerous place if
    strict precautions are not observed. Metal
    objects can become dangerous projectiles if they
    are taken into the scan room. For example,
    paperclips, pens, keys, scissors, hemostats,
    stethoscopes and any other small objects can be
    pulled out of pockets and off the body without
    warning, at which point they fly toward the
    opening of the magnet (where the patient is
    placed) at very high speeds, posing a threat to
    everyone in the room. Credit cards, bank cards
    and anything else with magnetic encoding will be
    erased by most MRI systems.

26
Purpose Of MRI
  • To obtain two-dimensional views of an internal
    organ or structure, especially the brain and
    spinal cord.
  • To assess response to treatment, especially
    cancer chemotherapy or radiation therapy.
  • To assess sports-related injury to bones and
    joints.

27
How it works
  • MRI uses a powerful magnetic field and radio
    waves to alter the natural alignment of hydrogen
    atoms within the body.
  • Computers record the activity of the hydrogen
    atoms and translate that into images.

28
Preparation
  • All jewelry, hair clips, and other metal objects
    must be removed.
  • Some facilities ask patients to disrobe and put
    on a hospital gown others allow patients to wear
    clothing so long as it doesn't have metal parts.
  • A contrast medium may be injected before some
    studies (e.g., gadolinium may be injected before
    an MRI study of the brain) people who are
    claustrophobic or have difficulty lying still may
    be given a sedative. Otherwise, no special
    preparation is required.

29
Test procedure
  • You will be instructed to lie as still as
    possible on a narrow table that slides into a
    tubelike structure that holds the magnet (see
    figure).
  • A loud thumping or hammering noise will be heard
    during the test you may request earplugs or
    listen to music with earphones to reduce the
    noise level.
  • At certain points during the test, the noise will
    stop and you will be able to hear instructions
    from the doctor or technician administering the
    test.

30
FIGURE Magnetic Resonance Imaging
  • Variations Echoplanar MRI is a new technique
    that allows for rapid accumulation of data such
    as cardiac motion.
  • After the test You can resume your pretest
    activities immediately.
  • Factors affecting results Movement, extreme
    obesity, and the presence of metal objects can
    all affect results.
  • Interpretation A radiologist or other medical
    specialist interprets the results.

31
FIGURE Magnetic Resonance Imaging (contd)
  • Advantages
  • MRI offers increased-contrast resolution,
    enabling better visualization of soft tissues.
    Also, it allows for multiplanar imaging, as
    opposed to CT, which is usually only axial.
  • It provides highly detailed information without
    exposing the body to radiation. In many
    instances, it provides more useful images than CT
    scanning and ultrasound.
  • Disadvantages
  • It is an expensive procedure and not available in
    many small hospitals and rural areas.
  • It also cannot be used for patients with
    implanted pacemakers and certain other metal
    objects.
  • MRI systems are very, very expensive to purchase,
    and therefore the exams are also very expensive.

32
Ultrasound
  • This is a technique that uses sound waves to
    study and treat hard-to-reach body areas. In
    scanning with ultrasound, high-frequency sound
    waves are transmitted to the area of interest and
    the returning echoes recorded.

33
Ultrasound equipment and test
34
What is an Ultrasound Test?
  • An ultrasound test is a radiology technique,
    which uses high-frequency sound waves to produce
    images of the organs and structures of the body.
    The sound waves are sent through body tissues
    with a device called a transducer. The transducer
    is placed directly on top of the skin, which has
    a gel applied to the surface. The sound waves
    that are sent by the transducer through the body
    are then reflected by internal structures as
    "echoes." These echoes return to the transducer
    and are transmitted electrically onto a viewing
    monitor. The echo images are then recorded on a
    plane film and can also be recorded on videotape.
    After the ultrasound, the gel is easily wiped
    off.
  • The technical term for ultrasound testing and
    recording is "sonography." Ultrasound testing is
    painless and harmless. Ultrasound tests involve
    no radiation and studies have not revealed any
    adverse effects.

35
Major Uses of Ultrasound
  • Ultrasound has been used in a variety of clinical
    settings, including obstetrics and gynecology,
    cardiology and cancer detection.
  • The main advantage of ultrasound is that certain
    structures can be observed without using
    radiation.
  • Ultrasound can also be done much faster than
    X-rays or other radiographic techniques.

36
Here is a short list of some uses for ultrasound
  • Obstetrics and Gynecology
  • measuring the size of the fetus to determine the
    due date
  • determining the position of the fetus to see if
    it is in the normal head down position or breech
  • checking the position of the placenta to see if
    it is improperly developing over the opening to
    the uterus (cervix)
  • seeing the number of fetuses in the uterus
  • checking the sex of the baby (if the genital area
    can be clearly seen)
  • checking the fetus's growth rate by making many
    measurements over time
  • detecting ectopic pregnancy, the life-threatening
    situation in which the baby is implanted in the
    mother's Fallopian tubes instead of in the uterus
  • determining whether there is an appropriate
    amount of amniotic fluid cushioning the baby
  • monitoring the baby during specialized procedures
    - ultrasound has been helpful in seeing and
    avoiding the baby during amniocentesis (sampling
    of the amniotic fluid with a needle for genetic
    testing). Years ago, doctors use to perform this
    procedure blindly however, with accompanying use
    of ultrasound, the risks of this procedure have
    dropped dramatically.
  • seeing tumors of the ovary and breast
  • Cardiology
  • seeing the inside of the heart to identify
    abnormal structures or functions
  • measuring blood flow through the heart and major
    blood vessels
  • Urology
  • measuring blood flow through the kidney
  • seeing kidney stones
  • detecting prostate cancer early

37
For what purposes are ultrasounds performed?
  • Ultrasound examinations can be used in various
    areas of the body for a variety of purposes.
    These purposes include examination of the chest,
    abdomen, blood vessels (such as to detect blood
    clots in leg veins) and the evaluation of
    pregnancy.
  • In the chest, ultrasound can be used to obtain
    detailed images of the size and function of the
    heart. Ultrasound can detect abnormalities of the
    heart valves, such as mistral valve prolapse,
    aortic stenosis, and infection.
  • Ultrasound is commonly used to guide fluid
    withdrawal aspiration) from the chest, lungs, or
    around the heart.

38
For what purposes are ultrasounds performed? contd
For what purposes are ultrasounds performed?
  • Ultrasounds also commonly used to examine
    internal structures of the abdomen. Ultrasound
    can detect fluid, cysts, tumors or abscess in the
    abdomen or liver. Impaired blood flow from clots
    or arteriosclerosis in the legs can be detected
    by ultrasound. Aneurysms of the aorta can also be
    seen. Ultrasound is also commonly used to
    evaluate the structure of the thyroid gland in
    the neck.
  • During pregnancy, an ultrasound can be used to
    evaluate the size, gender, movement, and position
    of the growing baby. The baby's heart is usually
    visible early, and as the baby ages, body motion
    becomes more apparent. The baby can often be
    visualized by the mother during the ultrasound,
    and the gender of the baby is sometimes
    detectable.

39
How do patients prepare for an ultrasound?
  • Preparation for ultrasound is minimal. Generally,
    if internal organs such as the gallbladder are to
    be examined, patients are requested to avoid
    eating and drinking with the exception of water
    for six to eight hours prior to the examination.
    This is because food causes gallbladder
    contraction, minimizing the size, which would be
    visible during the ultrasound.
  • In preparation for examination of the baby and
    womb during pregnancy, it is recommended that
    mothers drink at least four to six glasses of
    water approximately one to two hours prior to the
    examination for the purpose of filling the
    bladder. The extra fluid in the bladder moves
    air-filled bowel loops away from the womb so that
    the baby and womb are more visible during the
    ultrasound test.

40
What is Mammography
  • This is a specific type of imaging that uses a
    low-dose x-ray system for examining the breasts.
  • The images of the breasts can be viewed on film
    at a view box or as soft copy on a digital
    mammography work station.
  • Most medical experts agree that successful
    treatment of breast cancer often is linked to
    early diagnosis.
  • Mammography plays a central part in early
    detection of breast cancers because it can show
    changes in the breast up to two years before a
    patient or physician can feel them.

41
A mammography unit
42
Procedures involved
  • A mammography unit is a rectangular box that
    houses the tube in which x-rays are produced. The
    unit is a dedicated equipment because it is used
    exclusively for x-ray exam of the breast, with
    special accessories that allow only the breast to
    be exposed to the x-rays. Attached to the unit is
    a device that holds and compresses the breast and
    positions it so images can be obtained at
    different angles.
  • The breast is exposed to a small dose of
    radiation to produce an image of internal breast
    tissue. The image of the breast is produced as a
    result of some of the x-rays being absorbed
    (attenuation) while others pass through the
    breast to expose either a film (conventional
    mammography) or digital image receptor (digital
    mammography). The exposed film is either placed
    in a developing machineproducing images much
    like the negatives from a 35mm cameraor images
    are digitally stored on computer

43
Uses of Mammography
  • The detection of breast cancer is X-ray imaging
    of the breasts.
  • When mammography screening is combined with a
    follow-up ultrasonic examination of those women
    whose mammographies show signs of possible cancer

44
Other common uses of the procedure
  • Mammography is used to aid in the diagnosis of
    breast diseases in women. Screening mammography
    can assist your physician in the detection of
    disease even if you have no complaints or
    symptoms.
  • Initial mammographic images themselves are not
    always enough to determine the existence of a
    benign or malignant disease with certainty. If a
    finding or spot seems suspicious, your
    radiologist may recommend further diagnostic
    studies.
  • Diagnostic mammography is used to evaluate a
    patient with abnormal clinical findings, such as
    a breast lump or lumps, that have been found by
    the woman or her doctor. Diagnostic mammography
    may also be done after an abnormal screening
    mammography in order to determine the cause of
    the area of concern on the screening exam

45
Screening mammography
  • Imaging examination of the breast by means of
    x-rays, of individuals usually without symptoms
    to detect those with a high probability of having
    breast disease.

46
Microwave Imaging
47
What is Microwave Imaging
  • The term microwave imaging covers all processes
    in which measurements of electromagnetic fields
    in the microwave region from 300 MHz to 30 GHz
    are used for creating images.

48
Processes involved in microwave imaging
  • To create images from microwave measurements, it
    is necessary to construct a microwave camera,
    which is able to transmit microwaves and measure
    the scattered waves at one or more antennas.
    Different types of microwave cameras are
    currently being used for imaging in such areas as
    ground penetrating radar and remote sensing.
    Depending on the items to be imaged, different
    types of microwave cameras are needed. These
    range from  small antennas used for near field
    measurements in ground penetrating radar to the
    large airborne systems used in remote sensing.
    There are two key issues to address when
    designing a microwave cameras. One is the
    increase of the signal to noise ratio in the
    system and the other is to assure that the system
    has a large dynamic range. The importance of both
    of these is closely related to the fact that the
    scattered signal is often very weak in comparison
    to the transmitted signal. This implies that any
    noise in the system will have a large impact on
    the image quality and that the system must be
    able to distinguish even small differences in the
    received signals. To obtain the maximum amount of
    information from the microwave measurements,
    inverse scattering techniques must be applied.

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Techniques involved in MI
  • Inverse scattering is the technique in which the
    images are created by inverting a model of the
    scattering mechanisms derived from Maxwell's
    equations.
  • The quality of the images when using inverse
    scattering for microwave imaging are determined
    by
  • The accuracy of the forward model
  • The accuracy of the inversion algorithm.
  • By using Maxwell equations, an exact solution to
    the forward scattering problem can be determined.

50
References
  • www.answers.com
  • www.colorado.edu/physics
  • www.reference.dictionary.com
  • www.medicalimaging.org
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