Potential Sources of Error Leading to Erroneous Thyroid Uptake Measurements
| 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 |