Browsing by Author "Wasserman, H. J."
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- ItemThe elimination of errors caused by prior technetium-99m scintigraphy on iodine-131 thyroid uptake measurements.(Health & Medical Publishing Group, 1987) Wasserman, H. J.; Muller, C.; Klopper, J. F.Coincidence summing of technetium-99m (99mTc) pulses may disturb iodine-131 (131I) thyroid uptake measurements if these are obtained after 99mTc thyroid scintigraphy performed on the same day. The magnitude of the error was assessed in 26 patients. It was found that when pre-dose measurements were subtracted, the 6-hour and 24-hour 131I uptakes could be falsely decreased by up to 137 percentage points using a lower discriminator level of 250 keV and by up to 35 percentage points with a discriminator level of 300 keV. When pre-dose measurements from 99mTc were ignored, there was a general increase in 131I uptake values at 6 hours. Increases of up to 22 and 9 percentage points occurred when 250 keV and 300 keV lower discriminator levels respectively were used. These errors may be eliminated by performing 131I uptake measurements through a 1 mm lead filter.
- ItemFirst-pass determination of the right ventricular ejection fraction using two regions of interest and the right anterior oblique view(HMPG, 1984) Wasserman, H. J.; Otto, A.The right ventricular ejection fraction (RVEF) was determined on the right anterior oblique view in 9 patients during the first pass of a bolus of technetium-99m employing a gamma camera with high count-rate capability. The RVEF was calculated by using: (i) a fixed end-diastolic region of interest (ROI); and (ii) an end-diastolic and end-systolic ROI. Because of the movement of the tricuspid plane the first of these methods often gave low values, and agreement between the first two peaks was not as good as that when the second method was used. The mean for the second method was in agreement with that in a previous study using a gated first pass technique and two ROIs but was somewhat higher than those reported by workers using either one ROI or the anterior view.
- ItemQuantifying the risks of radiation exposure(Health & Medical Publishing Group, 1986-09) Wasserman, H. J.The considerations leading to the recommendation of dose-equivalent limits by the International Commision for Radiological Protection are outlined. The dose-equivalent limits are based on radiation risk factors estimated from effects of radiation observed over many decades. These limits are designed to ensure that radiation exposure does not entail a greater risk than that experienced in other safe occupations or accepted by the general public in everyday life. The risk factors should, however, not be used to assess the risk to patients from diagnostic procedures.