48 Questions
What is the main limitation of conventional planar gamma imaging?
Loss of depth information and reduced contrast
What is the purpose of using a parallel hole collimator in SPECT?
To improve the resolution of the image
How many views are taken in a SPECT scan?
60 views
What is the total scanning time required for a SPECT scan?
30 minutes
How many counts are acquired in a SPECT scan?
3 million counts
What are the two methods of emission tomography?
SPECT and PET
What is the benefit of using a dual- or triple-headed camera in SPECT?
Halved image acquisition time or improved sensitivity
What is the purpose of using an elliptical orbit in SPECT?
To reduce the gap between the collimator and the patient
What is a useful rotation option in cardiac tomography in SPECT?
180°
What is a major use of SPECT?
Thallium studies of myocardial infarctions and ischaemia
How can SPECT studies be presented?
Either as a series of slices or as a three-dimensional display
What is the effect of persistence of vision in SPECT image display?
Reduces image noise
What is the purpose of testing for radionuclide purity in radiopharmaceuticals?
To prevent unnecessary dose to the patient
How is the patient administered a radiopharmaceutical in planar imaging?
Intravenously, through an injection
What is the ideal function of a radiopharmaceutical in planar imaging?
To concentrate in the organ or tissues of interest
What is the purpose of testing for radiochemical purity in radiopharmaceuticals?
To detect free pertechnetate in a labelled compound
What is the purpose of testing for chemical purity in radiopharmaceuticals?
To detect the presence of alumina
What is the purpose of the dose calibrator in radiopharmaceuticals?
To measure the activity of the radiopharmaceutical
What percentage of nuclides in the world are stable?
Nearly 100%
What is the main reason for innovation in nuclear medicine diagnostic imaging over the last century?
Development of new equipment and techniques
What is the significance of Röntgen’s discovery of X-rays?
It started the innovation in diagnostic imaging
What is the requirement for practicing nuclear medicine safely?
Clear understanding of the behavior and principles of radiation sources and radiation detection
What is unique about the nucleus of ordinary hydrogen?
It has a single proton
What is the general trend in the composition of stable lighter nuclei?
They have nearly equal numbers of protons and neutrons
What is the result of forcing an additional neutron into a stable nucleus?
A neutron excess
What is the result of a positive beta particle coming to the end of its range?
It combines with a negative electron
What is the purpose of a cyclotron in producing radionuclides?
To accelerate positively charged ions
What is the energy of each photon emitted during the annihilation of a positive and negative electron?
511 keV
What is the characteristic of the half-lives of radionuclides produced in a cyclotron?
Short-lived, ranging from less than a minute to a couple of hours
What type of radiation is emitted when an electron from an outer shell fills a created vacancy in the K-shell?
X-ray radiation
Why are medical minicyclotrons designed to be located near hospital sites?
To enable the use of short-lived radionuclides in medical imaging
What is the result of forcing an additional proton into a stable nucleus?
An increase in atomic number
What is the characteristic of gamma rays emitted during radioactive decay?
A line spectrum of specific energies
What is the process by which a nuclide with a neutron deficit decays?
K-electron capture
What is the total number of known radionuclides?
More than 2700
What is the result of the combination of a positive and negative electron?
The neutralization of opposite charges
What is the decay process in which a radionuclide with a neutron excess loses energy and becomes stable?
Beta minus decay
What is the name of the radionuclide that is produced from the decay of Molybdenum-99?
Technetium-99m
What is the energy of the gamma ray emitted during the decay of Technetium-99m to Technetium-99?
140 keV
What is the change in the atomic number of Iodine-131 during its decay to Xenon-131?
Increases by one
What is the process by which a radionuclide in an excited state returns to its ground state with the emission of a gamma ray?
Isomeric transition
What is the name of the radionuclide that is produced from the decay of Germanium-68?
Gallium-68
What is the result of adding a neutron to the nucleus of Molybdenum-98?
The atomic number of the nucleus remains unchanged, but its mass increases by one
What happens when an additional proton is forced into a stable nucleus in a cyclotron?
A neutron is knocked out of the nucleus, resulting in a neutron deficit
What is a characteristic of radionuclides produced in a cyclotron?
They have short half-lives, ranging from less than a minute to a couple of hours
What is a medical application of radionuclides produced in a cyclotron?
They are used in medical imaging, such as in the production of fluorine-18
What is a method of producing radionuclides?
Extracting radioactive fission products from spent fuel rods of nuclear reactors
What is a characteristic of radionuclides obtained from generator systems?
They are daughter products obtained from a longer-lived radioactive parent
Study Notes
Image Acquisition and SPECT
- Image acquisition time can be halved or sensitivity improved by using a dual- or triple-headed camera.
- The camera must move on a sufficiently large circular orbit to avoid the patient's shoulders.
- An elliptical orbit can be used to minimize the gap between the collimator and the patient, improving resolution.
- A 180° rotation is a useful option, especially in cardiac tomography.
SPECT Studies and Display
- SPECT studies can be presented as a series of slices or as a 3D display.
- The 3D display is particularly effective when rotated continuously on the computer screen, reducing the effect of image noise.
Applications of SPECT
- Thallium studies of myocardial infarctions and ischaemia are major uses of SPECT.
- SPECT can be used in dynamic imaging where short exposure times are necessary, accepting poorer resolution.
Collimators
- Medium-energy collimators have thicker septa (1.4 mm) and fewer holes, resulting in lower sensitivity.
- They are used up to 400 keV, e.g., with 111In, 67Ga, and 131I.
Tomography with Radionuclides
- Conventional planar gamma imaging produces a 2D projection of a 3D distribution of a radiopharmaceutical.
- The images of organs are superimposed, losing depth information and reducing contrast.
- Emission tomography addresses these deficiencies.
Types of Emission Tomography
- There are two methods of emission tomography: Single-Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET).
SPECT Process
- In its simple form, a gamma camera with a parallel hole collimator rotates slowly in a circular orbit around the patient.
- Every 6°, the camera halts for 20-30s and acquires a view of the patient.
- 60 views are taken from different directions, each with fewer counts than in conventional static imaging.
SPECT Scanning
- Approximately 3 million counts are acquired in an overall scanning time of around 30 minutes.
- This technology reduces the radiation exposure of the staff.
Radiopharmaceuticals and Quality Control
- Quality control includes testing for:
- Radionuclide purity
- Radiochemical purity
- Chemical purity
- Response of the radionuclide calibrator
Radiation and Decay
- Radionuclides with a neutron excess may lose energy and become stable by a neutron changing into a proton plus an electron.
- The electron is ejected from the nucleus with high energy and is referred to as a negative beta particle.
- Isomeric transition can occur in some radionuclides, where the gamma ray is not emitted until an appreciable time after the emission of the beta particle.
Introduction to Nuclear Medicine
- The technologies used in nuclear medicine for diagnostic imaging have improved over the last century.
- Each decade has brought innovation in the form of new equipment, techniques, radiopharmaceuticals, advances in radionuclide production, and better patient care.
- All such technologies have been developed and can only be practiced safely with a clear understanding of the behavior and principles of radiation sources and radiation detection.
Learn about the techniques used in Single-Photon Emission Computed Tomography (SPECT) imaging, including camera orbit and rotation options to improve image acquisition and resolution.
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