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1NUCLEAR MEDICINE IMAGING
Prof Jasmina Vujic Department of Nuclear
Engineering U C Berkeley
Pictures from www.ge.com
2Nuclear 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.
3General 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.
4Computed 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.
5Magnetic 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.
6What 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.
7Lung Cancer
WHAT CAN WE VISUALIZE ?
Lymphoma
Colon Cancer
8Typical dynamic image of a heart
9Nuclear 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.
10Brain and Liver Tomographic Reconstruction and 3D
Rendering
11Nuclear 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.
12Liver Sagittal, Coronal and Transaxial Slices.
3D Rendering
13Radioisotopes 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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15HOW 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.
16HOW 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.
17HOW 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.
18General-Purpose Circular Detector
High-Performance Circular Detector
19The 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
20A 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
21Detail of the pin-hole collimator
22Features 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
23DST-XLi DSXi Digital Long Axis Nuclear
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24POSiTRACE Dual Mode PET/CT Oncology System
25Siemens gamma cameras
The e.cam family of gamma cameras offers total
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26ECAT 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
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(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.