VOLUME MEASUREMENT IN VIVO USING POSITRON TOMOGRAPHY.

The high density avalanche chamber (HIDAC) positron camera has been used for tomographic imaging of the human thyroid in vivo. Images are made seven and twenty-four hours after oral adminstration to the patient of the positron-emitting radionuclide **1**2**4I. As a consequence of the high spatial resolution of the camera (2. 5 mm fwhm), the functional volume of the thyroid may be estimated from the tomographic images to within about 12%. This paper discusses some of the studies performed to ensure reconstructed images free from artifacts and distortions, and, as illustration of the technique, two typical patient cases are presented.