New normal ranges for the radioiodine uptake study.

attached to an external detector system, the thyroid uptake of iodine was measured at 6 and 24 hr. The external detector consisted of a 1Â1⁄4x 1 in. NaI(Tl) scintillation crystal and a flat-field lead collimator. A Lucite extension of the collimator was shaped to fit the neck and assure good geometry with a neck-to crystal distance of 20 cm. A standard neck phantom was used with standard capsules containing doses identical to those given to the subjects.