Results for a gamma-camera with a new 511-keV collimator.
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Gamma Cameras↗
Biomedical subjects
W K Kübler
Publications and source records attributed to W K Kübler.
Non-uniformity measurements in PET.
To gain practical experience with the procedures suggested by the EEC task group on performance evaluation of positron tomographs, the non-uniformity of the Scanditronix PC 2048-7WB positron tomograph was measured. The test was performed using both a cylindrical head phantom and the EEC body phantom. According to the recommendation of the task group, 2 million counts were collected in each emission scan as a standard. As to be expected, non-uniformity decreased when more counts were collected or a wider reconstruction filter was used. Non-uniformity increased when going from the head phantom to the body phantom leaving all parameters unchanged. It was concluded that this effect was caused by increased noise due to the larger attenuation lengths but not to attenuation correction. The preliminary results of this study show that counting statistics dominates non-uniformity in the count range of about 2 million counts per image. Measured non-uniformity values are in the range of +/- 30%.
Equipment Design↗
Measured attenuation correction methods.
Accurate attenuation correction is a prerequisite for the determination of exact local radioactivity concentrations in positron emission tomography. Attenuation correction factors range from 4-5 in brain studies to 50-100 in whole body measurements. This report gives an overview of the different methods of determining the attenuation correction factors by transmission measurements using an external positron emitting source. The long-lived generator nuclide 68Ge/68Ga is commonly used for this purpose. The additional patient dose from the transmission source is usually a small fraction of the dose due to the subsequent emission measurement. Ring-shaped transmission sources as well as rotating point or line sources are employed in modern positron tomographs. By masking a rotating line or point source, random and scattered events in the transmission scans can be effectively suppressed. The problems of measured attenuation correction are discussed: transmission/emission mismatch, random and scattered event contamination, counting statistics, transmission/emission scatter compensation, transmission scan after administration of activity to the patient. By using a double masking technique simultaneous emission and transmission scans become feasible.
Humans↗