Article Figures & Data
Figures
- FIGURE 1.
Thyroid uptake workflow diagram. At time 0, patient ingests dose of radioiodine that was measured at a prior time using thyroid probe. At 24 h after ingestion, patient returns to department for thyroid uptake measurement using same thyroid probe. Room and patient background measurements are performed with probe at time of dose and thyroid uptake measurements, respectively, for background subtraction before uptake ratio is calculated as percentage. Optional measurement of administered dose with dose calibrator can be used to calculate probe efficiency to be used for QC.
- FIGURE 2.
99mTc-pertechnetate uptake images of patient 1 at time of investigation (baseline) and 32 mo prior to that time. Image intensities were manually normalized to have similar contrast. Biodistribution is similar, contradicting large thyroid uptake change between time points.
Tables
Dose calibrator Probe 24-h uptake Patient no. Activity (MBq) Time Count 1 (cps) Count 2 (cps) Room background counts (cps) Net capsule counts (cps) Time Room background time Probe efficiency (cps/MBq) Original (%) Adjusted (%) 1 0.420 9:16 213 210 1 211 8:26 8:23 501 139.6% 71% 2 0.435 10:35 214 216 1 214 8:29 8:23 490 34.8% 18% 3 0.388 9:08 208 206 1 206 13:24 8:23 534 47.0% 24% Original 24-h thyroid uptake results are shown along with their corresponding adjusted values after compensating for deviations in probe efficiencies from previous patients (Table 2). Time is expressed as time of day (hr:min).
- TABLE 2.
131I Capsule Activity, Probe Net Capsule Count, and Probe Efficiency Results at Clinic for Previous Patients
Dose calibrator Probe Patient no. Activity (MBq) Time Count 1 (cps) Count 2 (cps) Room background counts (cps) Net capsule counts (cps) Time Room background time Probe efficiency (cps/MBq) 4 0.370 9:22 474 477 1 475 11:33 11:16 1,287 5 0.383 10:35 466 464 1 464 13:26 11:16 1,217 6 0.310 10:45 294 294 3 291 10:43 10:16 939 7 0.290 8:42 286 281 3 281 8:39 8:06 967 8 0.350 9:20 353 349 1 350 15:20 15:18 1,009 9 0.420 13:44 410 408 3 406 10:51 10:16 962 10 0.390 9:40 389 389 4 385 9:31 8:18 987 11 0.410 9:00 362 366 4 360 8:57 8:18 878 12 0.305 10:53 265 269 4 263 10:30 10:24 862 13 0.292 10:10 280 280 3 277 10:07 9:56 949 14 0.302 9:11 271 272 4 268 9:15 8:50 886 15 0.350 11:30 346 346 3 343 10:55 10:52 979 16 0.389 10:30 402 406 3 401 10:05 9:41 1,030 17 0.360 9:02 355 348 3 349 8:59 8:35 968 Time is expressed as time of day (hr:min).
Level Lower limit Upper limit ±range Pass 808 955 8% Warning 784–807 956–978 11% Error <783 >979 — Data are cps/MBq for baseline QC (Site2Old).
- TABLE 4.
Comparison of Probe Efficiencies and Their Variability for 3 Devices (and Practices)
Device n Nominal efficiency (cps/MBq) Measured CV Comment Site2Old 29 881 4% QC limits derived with explicit test measurements that served as QC estimates for Site2New Site2New 20 910* 4% From clinical data using QC estimate from Site2Old as guideline Site1New 22 1,025* 11%* From clinical data without using any efficiency QC *P < 0.05 in comparison to Site2Old.
Error source Means to mitigation of error Operator Probe misalignment during dose assay Review efficiency against dose calibrator activity measurement; review count rate against typical values for similar dose Probe misalignment during room background assay Use phantom and probe ruler, reproducing positioning for dose assay; ensure low count rate consistent with background radiation Probe misalignment during uptake assay Palpate for thyroid location; use probe ruler, repositioning between duplicate measures to verify consistency; cross-validate with other time points; cross-validate with imaging Probe misalignment during patient background assay Use probe ruler; ensure low count rates; investigate high count rates, including patient or clothing contamination Wrong uptake time Preschedule visits according to protocol; use automated time logging by probe software; record all steps in clinical worksheet or software Wrong dose Label doses with patient identifiers; verify matching of patient using multiple identifiers; view energy spectrum to confirm correct isotope Wrong patient Confirm multiple patient identifiers against software-recorded entry or clinical worksheet; use electronic patient worklist Instrumentation System malfunction Ensure appropriate QC using quality management system; clearly label and communicate system serviceable status Clock error Configure time server synchronization Acquisition setting error Use predefined acquisition protocols; password-protect software administrator settings, including protocol settings Patient Motion Monitor patient during acquisition; repeat acquisition if patient has moved Incomplete ingestion or vomiting Monitor patient at dose administration; debrief patient before uptake acquisition Missed appointment Time-stamp all patient encounters and counting of administered dose; consider delaying or repeating procedure if there is erroneous uptake time Internal or external contamination Inspect energy spectrum for signs of other isotopes; review patient history for exposure to radionuclides (previous medical procedures and occupational or environmental exposures); apply energy windowing Changes in health Implement intake questionnaire; review adherence to preparation instructions; correlate with other medical data (1) Diet Follow societal guidelines for patient preparation, including abstinence from foods high in iodine (e.g., kelp) (1) Medication Follow guidelines for patient preparation, including extensive list of medications and iodinated contrast agents that interfere with thyroid uptake (1); review patient list of medications and medical history Environmental (background radioactivity) Remove potential sources of radiation, including from neighboring rooms (e.g., patients, x-ray equipment); use radioiodine-appropriate energy window; ensure that background is measured near time of assay, and QC for low background count rates
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