Acta Radiolégica M. BRucER 142 curacy, if the AB formula and a properly designed phantom are used. It is felt that this +5 percentage points of accuracy in the thyroid uptake measurementis sufficient for all clinical conditions. A standardized technique is therefore recommended for all routine thyroid uptake measurements. This standardized technique is the measurement of thyroid uptake with the AB formula system and a standard phantom at a distance of 10 inches. With any instrumentation it is pos- sible to measure thyroid uptake within = 5 percentage points of the correct figure in a patient with any thyroid uptake and with any body background Two restrictions are put on this statement: the thyroid must be eclipsed by a 4” by 4” “B-filter” and must be in a known position. It should be noted here that the calibra- tion program is so far concerned only with the physical measurements. When the art of measuring the radioiodine actiyity in the thyroid gland has progressed to the point where physicians all over the world are talking the same physical language, then it will be necessary to extend the investigations to the much more difficult problem of the biological sources of error. Eventually, there will have to be considered the more serious problem of the clinical interpretation of thyroid uptake measurements. SUMMARY This paper is a report on the survey and the extension of the work carried out by the Thyroid Radioiodine Uptake Calibration Committee of the Oak Ridge Institute of Nuclear Studies toward a method of cali- Dration. The variation in thyroid uptake measurements among laboratories is significant be- cause of the use of different combination of standards, instruments, distances, techni- ques and formulas. It was felt that a clinical intercalibration Interamericana procedure adaptableto all the various techniques in use was necessary. The program of the Committee presented three phases: 1) Determination of the variation in thy- roid radioiodine uptake measurement. 2) Determination of why there was a variation, of what factors influenced the measurements and of whether it 1s possible to set up an intercalibration program that could be fairly universally followed and would be acceptable to most workers in the field. 3) To initiate an intercalibration program for the Radioiodine Uptake Measurement. RESUMEN Se presenta un informe de la revisién y extension del trabajo realizado por la Comision del Instituto de Estudios Nucleares de Oak Ridge para la Medicién de la Captacion Tirdidea del Yodo Radioactivo. La variacién existente entre las medidas obtenidas por diferentes laboratorios es notable, debido al empleo de distinta combinacion de ‘standards’, instrumentos, distancias, técnicas y formulas. Se sintid la necesidad de hallar un procedimiento clinico de calibracién adaptable a todas las técnicas en uso. El programa de la Comisidn tenia tres fases: 1) Determinacién de la variacién en la medicién de la captacién tirdidea del yodo radioactivo. 2) Determinacidn de las causas de la va- riacion, qué factores influenciaban estas mediciones y la posibilidad de establecer un programa decalibracién que pueda ser aplicado lo mas universalmente posible y que sea aceptable para la mayoria de los que trabajan en este campo.