ABSTRACT
Tc-99m d. The position of an incident gamma photon in the camera crystal is
determined by a few large photomultiplier tubes e. A photomultiplier transforms light photons into electrons which
can be read as an electrical signal that represents light intensity
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14. that are 3 mm thick small NaI phosphor
crystals coalesced into one c. Ideally patients should be situated a few metres from the crystal
to reduce photon divergence d. Photomultipliers are used to increase the intensity of the light
photon emitted by the crystal e. The use of a divergent hole collimator enables a larger field of
view (FOV)
15. The gamma camera: a. The collimator is used to reduce scatter from the patient b. The NaI crystal is entirely covered in aluminium on all sides to
prevent light entry c. A typical flash from a gamma photon would release in the
order of 500 light photons d. The photomultiplier tube contains a series of dynodes at
increasing positive potentials e. The pulse height analyser (PHA) rejects any signals that do not
fall within set limits
16. Concerning the pulse height analyser (PHA): a. Scattered gamma rays will always be rejected by the PHA b. Pulse height is inversely proportional to the photon energy c. The sensitivity of the examination is increased by reducing the
PHA window d. Multiple PHA windows may be used e. Pulses with energies of +30% of the photo peak are normally
allowed through
17. Collimators, spatial resolution and sensitivity: a. A collimator with more and smaller holes will increase
sensitivity b. A collimator with more and smaller holes will improve spatial
resolution c. A convergent hole collimator may be used for small organs and
children d. The sensitivity of a typical collimator is only in the region
of 20-30% e. It is not possible to have maximum sensitivity and maximum
spatial resolution using the same collimator
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18. computed
b. Measures gamma rays released from the annihilation of
positrons c. Employs a rotating gamma camera(s) to analyse emissions from
the patient d. Multiple axial sections are created simultaneously from one
gamma camera e. Uses a continuously rotating gamma camera which takes
measurements in one-degree increments around the patient
19. Regarding the gamma camera images: a. Spatial resolution is increased by using a thinner crystal b. The spatial resolution of a gamma image is similar to that of a
10 mm slice CT scan c. Signal to noise ratio (SNR) is increased by using a high resolution
collimator d. SPECT images typically have a spatial resolution of 15-20 mm e. Filtered back projection is used when reconstructing SPECT
images
20. Image quality in SPECT: a. The smallest detail resolvable is around 20 mm b. Quality control will ensure that gamma camera count rate
sensitivity does not vary by more than 20% c. Resolution is worse for organs at depth d. Patient movement is not a problem due to the speed of gamma
rays in air e. Multiple camera heads can improve resolution
21. Regarding PET: a. It commonly uses fluorodeoxyglucose b. The radionuclide used decays by electron capture c. The gamma photons released will always be of the same energy
regardless of the radionuclide used to produce them d. Anatomic detail is high e. Patient dose is increased with longer scan times
22. PET: a. In a PET-CT scan the low dose CT scan is performed simply to
enable anatomical correlation with the PET image b. F-18 is an unstable nucleus with a neutron excess c. Bismuth germinate solid-state scintillation detectors are used
because of their long decay time and high detection efficiency d. Two detectors on opposite sides of the detector ring must register
a photon at the same time for the event to be recorded e. Scan acquisition time is approximately 30 min for a body
PET-CT
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23. detectors surrounds
b. Each detector has only one ‘line of response’; that is with the
detector directly opposite c. Photons detected within 1029 sec of each other are considered
simultaneous d. Time of flight PET improves image contrast e. 3D acquisition improves sensitivity
24. Image formation in PET: a. Is possible with detectors covering a 1808 arc over the patient b. The activity measured in each detector is plotted as a sine curve
to create a composite sinogram for all the data in each slice c. Uses filtered back projection d. Due to the duality of data acquisition, PET image reconstruction
does not need to take account of tissue attenuation e. Data acquired in two-dimensions (2D) cannot be used for
3D imaging
25. Quality assurance in gamma imaging: a. Spatial resolution may be tested using a line source or a sheet
source with a bar test pattern b. An area of persistently high or low counts using flood field
testing could indicate photomultiplier defect c. A linear defect in the image may represent a cracked NaI crystal d. Persistently high count readings on all camera orientations may
indicate contamination of the camera e. Collimators can be tested separately to determine its point
spread function and modulation transfer function (MTF)
26. Dose: a. The organ absorbed dose depends on several factors including
activity administered, fraction taken up by the organ, half-life of the radiopharmaceutical, energy and type of radiation and the length of scan time
b. Effective dose for a Tc-99m lung ventilation and perfusion scan is in the region of 1.5 mSv
c. A bone scan using Tc-99m will incur an effective dose of approximately 5 mSv
d. Effective dose for a thallium 2-methoxy isobutyl isonitrile (MIBI) heart scan is in the region of 18 mSv
e. Effective dose for an F-18 fluorodeoxyglucose (FDG) brain scan is in the region of 1 mSv
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27. will deposit its energy in
b. Most of the gamma rays released within the patient
are detected c. Scan time does not affect dose d. A target organ will receive a lower dose than a source organ e. Staff can reduce their dose by holding radionuclides at arm’s
length and delivering them promptly
28. Regarding the safety and handling of radionuclides: a. The activity of a radionuclide dose is measured using an
ionization chamber which is situated between the patient and the gamma camera
b. The current measured in the ionization chamber of a radionuclide calibrator is dependent on the vessel in which the radionuclide is housed
c. Vials containing Tc-99m radiopharmaceuticals should be stored in Perspex pots
d. All spillages should be reported to the Health and Safety Executive (HSE)
e. Doubling your distance from a syringe containing a radiopharmaceutical will reduce the dose by 50%
29. Safety, accidents and disposal: a. Gloves should be worn when handling radiopharmaceuticals as
they provide protection from the gamma rays b. Radioactive material should be handled for the minimum
amount of time c. A radiopharmacy should be classified as a controlled area
under Ionising Radiation Regulations (IRR99) d. Pregnant patients and patients who are breastfeeding should
never receive radiopharmaceuticals e. Vomiting and incontinence are treated as radioactive spills
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1a. False This is mostly true for light nuclei, except hydrogen. Heavy stable nuclei have an excess of neutrons; for example, those with atomic numbers greater than that of calcium (Z ¼ 20) have more neutrons than protons. Also, not all isotopes with equal numbers are stable; F-18 used in PET scanning has nine protons and nine neutrons.
