THYROID UPTAKE MEASUREMENTS WITH I-123 - PROBLEMS AND PITFALLS - CONCISE COMMUNICATION

  • 1 January 1982
    • journal article
    • research article
    • Vol. 23  (8) , 667-670
Abstract
The measurement of radioiodine uptake [RAIU] is generally considered to be straightforward and accurate. However, during the past 2 decades, discrepancies in normal thyroid uptake values were noticed between Montefiore Hospital and Medical Center and the Hospital of Albert Einstein College of Medicine. These differences were attributed to differences in patient population. Further investigation revealed that the persisting uptake discrepancies arose from neck-phantom differences and variations in procedure. Differences in presumably standardized neck-phantom attenuation characteristics caused large variations in count rates from I-123 and I-131 standard capsules. The effect of high-voltage fluctuations on phantom count rates is more pronounced with I-123 than with I-131. High-energy contaminants in I-123 also affect the uptake measurements. Large errors in the measurements of thyroid uptake values may result from seemingly unimportant variations in technique. A stable high-voltage power supply, precise high-voltage adjustment, careful selection of energy window, and the use of a standardized neck-phantom with generally accepted attenuation characteristics are absolutely essential if RAIU values are to be compared and appropriate therapeutic doses are to be administered based on these measurements.

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