[en] Pulse pile-up is a fundamental problem that limits the ability of a gamma camera to produce high quality images at high count rates. Pulse pile-up results in loss of events and spatial distortions in the image. The question asked in this study is how well do some of the test procedures for measuring count rate performance in gamma cameras compare. In four gamma cameras we compared measurements of spectral fraction, count-rate curve, pulse-pair resolution, deadtime, maximum count rate, full width at half maximum of the line spread function, and misplaced event count rate. The results indicated that no one technique provides a complete description of the count-rate effects in gamma cameras. The misplaced-event measurements provided the most information

[en] The authors developed a new dual photon absorptiometry (DPA) technique that is designed to simultaneously measure mineral, soft-tissue, and fat thicknesses at each point of a scan. To test the technique, a feasibility study was performed with known thicknesses of aluminum (simulating bone), lucite (simulating tissue), and polyethylene (simulating fat). Excellent results were obtained for a variety of thicknesses of each material. Correlations between actual and measured thicknesses were better than 0.999. The rms error was 0.5 mm, and the typical coefficient of variation was 3.4%. Special considerations for applying the method to the analysis of human subjects are addressed

[en] This paper experimentally evaluates two DEXA instruments in terms of precision, accuracy, spatial resolution, and x-ray dose. Methods and materials are described and results are offered

[en] The authors have now completed 15 years using neutron activation to measure total body calcium in patients with bone wasting disease. In the past year they have performed 88 patient irradiations. Two therapeutic regimes were under test. Under the first regime, patients were treated with 1,25 dihydroxy calciferol (vitamin D). Under the second regime, patients who had been treated with disodium chlodronate were followed after withdrawal of the drug. In both studies, an equal number of untreated control subjects were followed and many other tests were performed as well as neutron activation. Since June, 1982 the authors have also been measuring the bone mineral in the lumbar spine by the dual photon absorption technique developed by Mazess of the University of Wisconsin and applied extensively by Wahner and Riggs of the Mayo Clinic

[en] A portable computer system and phantom set for measuring performance parameters of scintillation cameras is being developed. The system design and typical applications are discussed

[en] Measurements of total body calcium by neutron activation (TBC) in 94 normal individuals and 86 osteoporotic patients are reported. The ability of TBC to discriminate normal from osteoporotic females was evaluated with decision analysis. Bone mineral content (BMC) by single-photon absorptiometry was also measured. TBC was higher in males (range 826 to 1363 gm vs 537 to 1054 in females) and correlated with height in all normals. In females over age 55 there was a negative correlation with age. Thus, for normals an algorithm was derived to allow comparison between measured TBC and that predicted by sex, age, and height (TBCp). In the 28 normal females over age 55, the TBC was 764 +/- 115 gm vs. 616 +/- 90 in the osteoporotics. In 63 of the osteoporotic females an estimated height, from tibial length, was used to predict TBC. In normals the TBC/TBCp ratio was 1.00 +/- 0.12, whereas in osteoporotic females it was 0.80 +/- 0.12. A receiver operating characteristic curve showed better discrimination of osteoporosis with TBC/TBCp than with wrist BMC. By using Bayes' theorem, with a 25% prevalence of osteoporosis (estimate for postmenopausal women), the posttest probability of disease was 90% when the TBC/TBCp ratio was less than 0.84. The authors conclude that a low TBC/TBCp ratio is very helpful in determining osteoporosis

No abstract available

[en] An investigation of the use of asymmetric energy windows with a scintillation camera equipped with an energy correction system has been carried out. Improvements in qantitative and qualitative low contrast performance are demonstrated

No abstract available

[en] Measurements of exhaled ³⁷Ar produced by total-body neutron irradiation of ⁴⁰Ca were used to determine total-body calcium in 16 human subjects. There was a good correlation between body calcium using the 30-min postirradiation breath sample of ³⁷Ar and body calcium determined by measurement of ⁴⁹Ca. (U.S.)