1. NUCLEAR IMAGING Prepared By: Muhammad Yaseen Trainee Med.
Physicist Radiology Department Mail: [email protected]
2. Contents Introduction Advantages Of Nuclear Imaging
Radiography Vs Nuclear Imaging Radioisotopes used in NM
Radiopharmaceuticals Gamma Camera SPECT Safety Summary
3. INTRODUCTION DEFINITION: Nuclear imaging is a method of
producing images by detecting radiation from different parts of the
body after a radioactive tracer material is administered. The
images are recorded on computer and on film. The nuclear imaging
physician interprets the images to make a diagnosis. Radioactive
tracers used in nuclear medicine are, in most cases, injected into
a vein.
4. Advantages Of Nuclear Medicine Target tissue function is
investigated. All similar target tissues can be examined during one
investigation, e.g. the whole skeleton can be imaged during one
bone scan. Computer analysis and enhancement of results are
available.
5. Radiographic Vs Nuclear ImagingRadiographic Imaging Nuclear
ImagingTransmission Type Image Emission Type Of ImageMorphologic
Imaging Functional ImagingHigh Resolution Low ResolutionUse X-rays
Use Gamma RaysShort Time Long Time
6. Radioisotopes Used In Conventional Nuclear Medicine An ideal
radionuclide has following properties: - A short half life. - Emits
-rays. - Capable of binding to a variety of biomolecules. Examples
of radionuclides together with their target tissues or target
diseases: - Technetium (99mTc) Salivary glands, thyroid, bone,
blood, liver, lung & heart. - Iodine (131I ) Thyroid - Gallium
(67Ga) Tumors & inflammation
7. For Imaging Technetium Is Used Extensively, As It Has
Following PropertiesA. Technetium is a gamma emitter. This is
important as the rays need to penetrate the body so the camera can
detect them.B. It has a short half life of 6 1/2 hours. Thus the
amount of radioactive exposure is limited.C. It is readily attached
to a variety of different substances that are concentrated in
different organs, e.g. - Tc + MDP (methylene disphosphonate) in
bone - Tc + sulphur colloid in the liver and spleen.D. It is easily
produced, as and when required, on site.
8. Tc-99m
9. Main Indications Of Nuclear Imaging Nuclear imaging
technique is used for assessing function of: - Salivary gland as
salivary scans - Brain - Thyroids - Heart - Lungs -
Gastro-intestinal system It is also used for diagnosis of: -
Metastatic diseases - Bone tumors as bone scans
10. Principle Of Nuclear Imaging Technique THE STEPWISE
PROCEDURE OF NUCLEAR IMAGING:Radionuclides are administered via
vein or mouthThey distribute in the body according to their
strength for particular tissues so called target tissues.
Radionuclides emit gamma radiations. Detected by -scintillation
cameraWhich forms images showing location of radionuclides in the
body.
14. GAMMA CAMERA A gamma camera, also called a scintillation
camera or Anger camera, is a device used to image gamma emitting
radioisotopes, a technique known as scintigraphy. These cameras
capture photons and convert them to light and then to a voltage
signal. These signals are reconstructed to an image that shows
distribution of radionuclide in the patient.
15. Gamma Camera Components Collimator Crystal PM Tubes Analog
To Digital Convertor X And Y Positioning Circuits A Visual Display
With Display Electronics
16. Collimator The collimator can be made from lead foil. The
collimator stops about 99.9% of the available photons. The walls of
each channel in the collimator are called septa, and if a photon
manages to penetrate the wall, it is called septal
penetration.
18. Parallel Hole Collimator LEGP (low energy general purpose)
or LEAP (low energy all purpose). To increase the resolution,
smaller diameter holes are needed. To increase sensitivity, the
holes need to be wider.
19. Parallel Hole Collimator To image higher energy isotopes
such as Ga-67 or I-131, the collimator needs to have thicker septa
in order to stop penetration. This produces a heavier collimator
with lower sensitivity.
21. Crystal (NaI) The -rays that pass through the collimator
then strike scintillation crystal. Made up of sodium iodide with
trace amount of thallium. This crystal shows florescence when it
absorbs -rays. These flashes of light are detected by
photomultiplier tubes coupled to the crystal.
22. Photo Multiplier Tube Extremely sensitive detector of light
in the ultraviolet, visible and near infrared Multiplies the signal
produced by incident light by as much as 108 single photons can be
resolved High gain, low noise, high frequency response, and large
area of collection A tiny and normally undetectable current becomes
a much larger and easily measurable current
23. Components Of PMT Made of a glass vacuum tube Photocathode
Several dynodes One anode
24. How It Works
25. Analog To Digital Convertor The signals from
photomultiplier tubes go through an analog to digital converter
(ADC) This component is used to convert the analogue information
produced by the imaging system so that it is coded in the form of
binary numbers. In this way the analog signal is digitalized &
used to produce image by computer
26. X And Y Position Circuit
27. Further Developments in Radioisotope Imaging Techniques
Include SPECT (single photon emission computed tomography) And PET
(Positron emission tomography)
28. Single Photon Emission Computed Tomography SPECT is a
method of acquiring tomographic slices through a patient. Most
gamma cameras have SPECT capability. In this technique either a
single or multiple gamma cameras is rotated 360 degrees about the
patient. Image acquisition takes about 30 45 min.
29. Applications of SPECT Heart Imaging Brain Imaging Tumor
detection SPECT can be used to detect tumors in cancer patients in
the early stages. Bone Scans
30. Advantages of SPECT Better detailed resolution Enhanced
contrast Localization of defects is more precise and more clearly
seen. Extend and size of defects is better defined.
31. Limitation Of Nuclear Medicine Poor image resolution only
minimal information of target tissue is obtained. The radiation
dose to the whole body can be relatively high. Images are not
usually disease-specific. Difficult to localize exact anatomical
site of source of emission. Facilities are not widely
available.
32. Safety Precautions Injected patient should avoid to keep
away from everyone but specially from children and pregnant women
Only authorized users are allowed to handle the source. Do not look
directly into bore hole of the source holder or cover it with any
part of your body. Use Lead Apron, lead goggles and lead thyroid
shield
33. Summary
34. References Medical instrumentation by : Jennifer Prekeges
The essential physics of medical imaging by: Bush Berg