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Quality control focuses on detection of errors performance changes of gamma camera systems which may adversely affect nuclear medicine interpretation (Technical Standards Subcommittee, 1999:1). Based on already prescribed baseline conditions, routine checks are conducted to ensure that the camera operated within the allowable limits. There are quite a number of factors which may contribute to final imaging quality of a gamma ray camera.
These include resolution (intrinsic and energy), uniformity, collimation and the device for hard copy (Technical Standards Subcommittee, 1999:1).
Additionally, various studies have suggested like other factors like count rate ability also affect image quality of gamma ray camera. Daily QC operations are often limited to monitoring of parameters that are considered most sensitive to the performance of the system and those that are likely to affect nuclear medicine studies. This experimental review focuses on critical quality control areas of gamma camera systems. These are background/contamination check, flood field uniformity and spatial resolution (intrinsic/extrinsic) and finally the whole body scan resolution.
The quality control is assisted by a SIEMENS ECAM gamma camera at the nuclear medicine department of Prince Wales Hospital. Background/contamination check This check aims to examine the gamma camera/scanning room contamination. It is recorded from the routine gamma camera QC tests. It is important to note that radionuclide contamination is not observable using naked human eye (NEMA, 1994). Such could result into the patient and the technician’s subjection to increased and unnecessary radiation doses. Contamination results from an array of factors including container leakage, patient secretion and general accidents.
Additionally, increased background radiation levels may result from “hot” patient’s proximity to unshielded radiation from imaging devices (Busemann, Kugi & Bergmann, 1993:896). Potential penetration through the neck of the camera is also possible in such instances where high energy agents are used. When of sufficient intensity ? 500, it could potentially sacrifice imaging quality (Busemann, Kugi & Bergmann, 1993:896). Various researches have suggested that backgrounds with moderate elevation could potentially compromise intrinsic uniformity and other measurements. Results: The results from the practical put the background intensity at ?
200-400 cps (monitor observation) The result falls within the accepted limits thus significantly represented good environment for quality imaging assuming all the other factors are unaffected. Uniformity Uniformity QC checks aims at ensuring that detector’s responses to uniform radiation are kept uniform within specified limits. This is one of the basic QC tests in gamma camera applications. This is based on the fact that the camera is operated on the principle that observed differences originate from patient tracer distribution and thus the gamma camera induces no differences (NEMA, 1994).
Defects in uniformity may be marked and focal for instance when photomultiplier tubes fail, and as a result of general uniformity degradation across the view field due to distorted spatial linearity/corrections for energy (Cranage & Peake, 1979: 81). When uniformity is checked using a collimator, it is referred to as an extrinsic uniformity check while in such instances when a collimator is not used, it is referred to as extrinsic uniformity check (Cranage & Peake, 1979: 81).
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