RT Journal Article
SR Electronic
T1 Thyroid Uptake Exceeding 100%: Causes and Prevention
JF Journal of Nuclear Medicine Technology
JO J. Nucl. Med. Technol.
FD Society of Nuclear Medicine
SP 153
OP 160
DO 10.2967/jnmt.121.262719
VO 50
IS 2
A1 Dhrumil Naik
A1 Sarah Ternan
A1 Rene Degagne
A1 Wanzhen Zeng
A1 Ran Klein
YR 2022
UL http://tech.snmjournals.org/content/50/2/153.abstract
AB Measurements of radionuclide uptake by the thyroid gland reflect its metabolic activity. Thyroid uptake is measured as a percentage of radioactivity retained by the gland at a specified time versus the activity administered to the patient; thus, uptake measurements must fall between 0% and 100%. Here, through a case study, we reviewed sources of error that can lead to uptake of more than 100%, and we describe a novel quality control (QC) indicator to improve the accuracy of uptake measurements in the clinic. Methods: Probe efficiency is determined as the ratio between the dose counts of the probe and the independent dose calibrator activity readings. The nominal probe efficiency value (M) was calculated as the mean of readings (n ≥ 20), and variance was characterized using the SD. Warning levels were set at M ± (1.96 × SD), and error levels were set at M ± (2.58 × SD). In subsequent routine clinical use, before a capsule is administered, the probe efficiency is calculated and compared with the warning and error limits. We derived M for 3 pairs of probe and dose calibrator devices using several doses and measured independently by several nuclear medicine technologists. Results: The recorded data indicated when technologists were made aware of the expected efficiency value, nominal efficiency was statistically different between our old device and the one that replaced it (P = 0.01), but coefficient of variation ([SD/M] × 100%) was not (P = 0.42). Using efficiency measurements acquired on the replacement device for the first 20 patients, we derived new QC values (M = 910, SD = 36). In 22 patients measured at our sister site, with the same device models but with the technologists unaware of the QC initiative, the derived QC values were an M of 1,025 and an SD of 116, demonstrating a significant difference between the nominal values of individual devices (P < 0.001). Furthermore, variability was significantly lower (P < 0.001) when QC was applied than when it was not. Conclusion: Adding probe efficiency as a QC indicator during thyroid uptake measurement is simple, can produce more precise clinical measurements, and can help mitigate operator and instrumentation errors.