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NUCLEAR MEDICINE IMAGING
Prof Jasmina Vujic Department of Nuclear
Engineering U C Berkeley
Pictures from www.ge.com
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Nuclear Medicine, X-Rays, CT, and MRI

• Nuclear medicine began approximately 50 years ago
  and has evolved into a major medical specialty
  for both diagnosis and therapy of serious
  disease. More than 3,900 hospital-based nuclear
  medicine departments in the United States
  perform over 10 million nuclear medicine imaging
  and therapeutic procedures each year. Despite its
  integral role in patient care, nuclear medicine
  is still often confused with other imaging
  procedures, including general radiology, CT, and
  MRI.
• Nuclear medicine studies document organ and
  function and structure, in contrast to
  conventional radiology, which creates images
  based upon anatomy. Many of the nuclear medicine
  studies can measure the degree of function
  present in an organ, often times eliminating the
  need for surgery. Moreover, nuclear medicine
  procedures often provide important information
  that allows the physician to detect and treat a
  disease early in its course when there may be
  more success. It is nuclear medicine that can
  best be used to study the function of a damaged
  heart or restriction of blood flow to parts of
  the brain. The liver, kidneys, thyroid gland, and
  many other organs are similarly imaged.

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General Radiology

• The image, or a x-ray film, is produced when a
  small amount of radiation passes through the body
  to expose sensitive film on the other side. The
  ability of x-rays to penetrate tissues and bones
  depends on the tissue's composition and mass. The
  difference between these two elements creates the
  images.
• The chest x-ray is the most common radiological
  examination. Contrast agents, such as barium, can
  be swallowed to highlight the esophagus, stomach,
  and intestine and are used to help visualize an
  organ or film.

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Computed Tomography

• Computed tomography or CT, shows organs of
  interest at selected levels of the body. They are
  visual equivalent of bloodless slices of anatomy,
  with each scan being a single slice. CT
  examinations produce detailed organ studies by
  stacking individual image slices. CT can image
  the internal portion of organs and separate
  overlapping structures precisely. The scans are
  produced by having the source of the x-ray beam
  encircle or rotate around the patient. X-rays
  passing through the body are detected by an array
  of sensors. Information from the sensors is
  computer processed and then displayed as an image
  on a video screen.

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Magnetic Resonance Imaging

• Like CT, MRI produces images, which are the
  visual equivalent of a slice of anatomy. MRI,
  however, is also capable of producing those
  images in an infinite number of projections
  through the body. MRI use a large magnet that
  surrounds the patient, radio frequencies, and a
  computer to produce its images.
• As the patient enters a MRI scanner, his body is
  surrounded by a magnetic field up to 8,000 times
  stronger than that of the earth. The scanner
  subjects nuclei of the body's atoms to a radio
  signal, temporarily knocking select ones out of
  alignment.
• When the signal stops, the nuclei return to the
  aligned position, releasing their own faint
  radio frequencies from which the scanner and
  computer produce detailed images of the human
  anatomy.
• Patients who cannot undergo a MRI examination
  include those people dependent upon cardiac
  pacemakers and those with metallic foreign bodies
  in the brain or around the eye.

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What is Nuclear Imaging ? The process involves
injecting into the body a small amount of
chemical substance tagged with a short lived
radioactive tracer. Depending on the chemical
substance used, the radiopharmaceutical
concentrates in the part of the body being
investigated and gives off gamma rays. A gamma
camera then detects the source of the radiation
to build a picture. These are called scans.
Radioisotope Treatments or Therapy Radiotherapy
using external beam treatment is used commonly
for treatment of cancers (see Oncology). However
the use of unsealed, liquid sources in the
treatment of disease is important in a few,
specialized situations. For example Iodine-131 is
taken orally to treat overactive thyroid and
cancer of the thyroid.
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Lung Cancer
WHAT CAN WE VISUALIZE ?
Lymphoma
Colon Cancer
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Typical dynamic image of a heart
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Nuclear Imaging Scans

• Brain Scans These investigate blood circulation
  and diseases of the brain such as infection,
  stroke or tumor. Technetium is injected into the
  blood so the image is that of blood patterns.
• Thyroid Uptakes and Scans These are used to
  diagnose disorders of the thyroid gland. Iodine
  131 is given orally , usually as sodium iodide
  solution. It is absorbed into the blood through
  the digestive system and collected in the
  thyroid.
• Lung Scans These are used to detect blood clots
  in the lungs. Albumen, which is part of human
  plasma, can be coagulated, suspended in saline
  and tagged with technetium.

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Brain and Liver Tomographic Reconstruction and 3D
Rendering
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Nuclear Imaging Scans

• Cardiac Scans These are used to study blood flow
  to the heart and can indicate conditions that
  could lead to a heart attack. Imaging of the
  heart can be synchronised with the patient's ECG
  allowing assessment of wall motion and cardiac
  function.
• Bone Scans These are used to detect areas of bone
  growth, fractures, tumors, infection of the bone
  etc. A complex phosphate molecule is labeled with
  technetium. If cancer has produced secondary
  deposits in the bone, these show up as increased
  uptake or hot spots.

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Liver Sagittal, Coronal and Transaxial Slices.
3D Rendering
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Radioisotopes Used in Nuclear Medicine

• For imaging Technetium is used extensively, as it
  has a short physical half life of 6 hours.
  However, as the body is continually eliminating
  products the biological half life may be shorter.
  Thus the amount of radioactive exposure is
  limited.
• Technetium is a gamma emitter. This is important
  as the rays need to penetrate the body so the
  camera can detect them.
• Because it has such a short half life, it cannot
  be stored for very long because it will have
  decayed. It is generated by a molybdenum source
  (parent host) which has a much greater half life
  and the Tc extracted on the day it is required.
  The molybdenum is obtained from a nuclear reactor
  and imported. For treatment of therapy, beta
  emitters are often used because they are absorbed
  locally.

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HOW IS TECHETIUM USED FOR A HEART SCAN

• The technetium heart scan is a nuclear heart
  scan, which means that it involves the use of a
  radioactive isotope that targets the heart and a
  radionuclide detector that traces the absorption
  of the radioactive isotope. The isotope is
  injected into a vein and absorbed by healthy
  tissue at a known rate during a certain time
  period. The radionuclide detector, in this case a
  gamma scintillation camera, picks up the gamma
  rays emitted by the isotope.
• The technetium heart scan uses technetium Tc-99m
  stannous pyrophosphate (usually called
  technetium), a mildly radioactive isotope which
  binds to calcium. After a heart attack, tiny
  calcium deposits appear on diseased heart valves
  and damaged heart tissue. These deposits appear
  within 12 hours of the heart attack. They are
  generally seen two to three days after the heart
  attack and are usually gone within one to two
  weeks. In some patients, they can be seen for
  several months.
• The technetium heart scan is not dangerous. The
  technetium is completely gone from the body
  within a few days of the test. The scan itself
  exposures the patient to about the same amount of
  radiation as a chest x ray. The patient can
  resume normal activities immediately after the
  test.

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HOW IS TECHETIUM USED FOR A HEART SCAN

• After the technetium is injected into a blood
  vessel in the arm, it accumulates in heart tissue
  that has been damaged, leaving "hot spots" that
  can be detected by the scintillation camera. The
  technetium heart scan provides better image
  quality than commonly used radioactive agents
  such as thallium because it has a shorter half
  life and can thus be given in larger doses.
• During the test, the patient lies motionless on
  the test table. Electrocardiogram electrodes are
  placed on the patient's body for continuous
  monitoring during the test. The test table is
  rotated so that different views of the heart can
  be scanned. The camera, which looks like an x-ray
  machine and is suspended above the table, moves
  back and forth over the patient. It displays a
  series of images of technetium's movement through
  the heart and records them on a computer for
  later analysis.

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HOW IS TECHETIUM USED FOR A HEART SCAN

• The test is usually performed at least 12 hours
  after a suspected heart attack, but it can also
  be done during triage of a patient who goes to a
  hospital emergency room with chest pain but does
  not appear to have had a heart attack. Recent
  clinical studies demonstrate that technetium
  heart scans are very accurate in detecting heart
  attacks while the patient is experiencing chest
  pain. They are far more accurate than
  electrocardiogram findings.
• The technetium heart scan is usually performed
  in a hospital's nuclear medicine department but
  it can be done at the patient's bedside during a
  heart attack if the equipment is available. The
  scan is done two to three hours after the
  technetium is injected. Scans are usually done
  with the patient in several positions, with each
  scan taking 10 minutes. The entire test takes
  about 30 minutes to an hour. The scan is usually
  repeated over several weeks to determine if any
  further damage has been done to the heart. The
  test is also called technetium 99m pyrophosphate
  scintigraphy, hot-spot myocardial imaging,
  infarct avid imaging, or myocardial infarction
  scan.

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General-Purpose Circular Detector
High-Performance Circular Detector
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The Gamma CameraWhat is about ?
The modern gamma camera consists of- multihole
collimator - large area (e.g 5 cm ) NaI(Tl)
(Sodium Iodide - Thallium activated)
scintillation crystal - light guide for optical
coupling array (commonly hexagonal) of
photo-multiplier tubes - lead shield to minimize
background radiation
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A crucial component of the modern gamma camera is
the collimator. The collimator selects the
direction of incident photons. For instance a
parallel hole collimator selects photons incident
OS the normal. Other types of collimators include
pinhole collimator often used in the imaging of
small superficial organs and structures (e.g
thyroid,skeletal joints) as it provides image
magnification. Fan beam (diverging) and cone
beam (converging) collimators are often used for
whole body or medium sized organ imaging. Such
collimators are useful because they increase the
detection efficiency because of the increased
solid angle of photon acceptance.
The action of a parallel hole collimator
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Detail of the pin-hole collimator
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Features and parameters

• The following are the typical features of the
  scintialltion crystal used in modern gamma
  cameras
• most gamma cameras use thallium-activated NaI
  (NaI(Tl))
• NaI(Tl) emits blue-green light at about 415 nm
• the spectral output of such a scintillation
  crystal matches well the response of standard
  bialkali photomultipliers (e.g SbK2Cs )
• the linear attenuation coefficient of NaI(Tl) at
  150 KeV is about 2.2 1/cm . Therefore about 90
  of all photons are absorbed within about 10 mm
• NaI(Tl) is hyrdoscopic and therefore requires
  hermetic encapsulation

• NaI(Tl) has a high refractive index ( 1.85 )
  and
  thus a light guide is used to couple the
  scintillation crystal to the photomultiplier tube
  
• the scintillation crystal and associated
  electronics are surrounded by a lead shield to
  minimize the detection of unwanted radiation
• digital and/or analog methods are used for
  image capture

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DST-XLi DSXi   Digital Long Axis Nuclear
Medicine Systems http//www.smvnet.com/
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POSiTRACE   Dual Mode PET/CT Oncology System
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Siemens gamma cameras
The e.cam family of gamma cameras offers total
flexibility in matching system requirements to
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and easy adaptability to your future clinical
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autocontour, whole body planar and SPECT as well
as dual-head configurations. The benefits of
the e.cam family Superior image quality from true
energy-independent HD3 detectors and ultra-thin
pallet Open gantry is
clinically versatile and provides easy access
High system reliabilityand clinical flexibility
Easy and convenient operation Easy
expandability and upgradeability www.siemens.com
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ECAT ART PET Scanner
The ECAT ART is the first cost-effective PET
scanner with bismuth germanate (BGO) detectors.
The system is designed to be installed in
existing nuclear medicine departments, with space
requirements comparable to a multidetector
single photon emission computed tomography
(SPECT) camera. The ECAT ART achieves its
economical price and clinical utility by applying
several key innovations continuous rotation of
two sections of BGO detectors through the use of
slip-ring technology, 3D acquisition and
reconstruction, and unique integrated circuit
electronics.