Preparation of a 99mTc wipe standard for survey instrument calibration in nuclear medicine.
A method was developed for the preparation of a standard source to satisfy the U.S. Nuclear Regulatory Commission requirement for calibration of wipe-assay procedures used in nuclear medicine laboratories. An essential element of this standard was that a locally prepared calibration wipe could be used with thin-window Geiger-Muller detectors that detect 99mTc conversion electrons with high sensitivity. This proposed calibration wipe was evaluated with both a NaI(Tl) well counter and a thin-window Geiger-Muller pancake probe. Average detector sensitivities of 1,540 and 160 counts min-1 per 2000 disintegrations min-1, respectively, were found for 99mTc. An analysis of the errors for each step of the procedure showed most to be less than 3% (95% confidence level). The nuclear medicine dose calibrator, used to assay the activity from which the wipe was prepared, was estimated to contribute a 9% absolute calibration error. Use of the pancake probe contributed a 12% geometry-reproducibility error. The total error associated with the use of the calibration wipe standard to calibrate a typical 99mTc wipe-assay procedure, exclusive of the count-dependent error associated with the number of counts acquired, was found for the NaI(Tl) well counter to be given by a percentage of 2 SD = 10% and for the thin-window Geiger-Muller pancake probe, percentage 2 SD = 16%. Coating of the calibration wipe with an acrylic spray, to prevent it from contaminating instruments during use, was evaluated. This coating was effective while it reduced the detectability of the wipe activity by a negligible degree.
Eubig
C
C
Department of Radiology, Medical College of Georgia, Augusta 30912-3950.
Lodhi
L M
LM
Trueblood
J H
JH
D002138:Calibration / Q000592:standards; D004866:Equipment Contamination; D009683:Nuclear Medicine / Q000295:instrumentation*; D011874:Radiometry / Q000295:instrumentation*; D012015:Reference Standards; D013667:Technetium
D013667:Technetium