ROLE OF HIGH-RESOLUTION PINHOLE TOMOGRAPHY IN THE EVALUATION OF THYROID ABNORMALITIES

The present study was undertaken to evaluate the contribution of pinho le-single photon emission computed tomography (P-SPECT) to scintigraph y of the thyroid gland. Thirty-six patients, referred for thyroid scin tigraphy because of palpatory or ultrasonographic findings, were studi ed after intravenous administration of technetium-99m pertechnetate (2 22 MBq) using a rectilinear scanner and a single-headed rotating gamma camera equipped with a pinhole collimator. P-SPECT study was acquired on a 128 x 128 matrix, in 30 projections over 180 degrees and an acqu isition time of 40 seconds per step. After transaxial reconstruction, coronal slices were compared with planar views obtained by the scanner . The size of the thyroid gland obtained by P-SPECT matched the life-s ize image of a rectilinear scan, and it clearly delineated the shape a nd borders of two huge multinodular glands. Its major contribution was in its improved resolution. Pinhole-SPECT identified 21 foci not visu alized on planar views, 19 cold lesions, and 2 ''warm'' nodules embedd ed in normal tissue of 13 patients. Furthermore, it clearly delineated 18 discrete ill-defined nodules of 13 patients, (single in 4 patients and multiple in 9 patients): 16 cold lesions, and 2 hot foci. When a distinct palpable nodule was present, whether cold (22 lesions) or hot (2 foci), SPECT was of no additional diagnostic value. However, when the palpable nodule was a toxic one, the contralateral suppressed lobe was visible on SPECT only. Two ultrasonographic findings, of 3- and 5 -mm in diameter, were neither identified on planar views nor on P-SPEC T. In conclusion, P-SPECT of the thyroid gland improves delineation of huge multinodular glands and detection of small nodules (within the r esolution of the camera) that could otherwise have been overlooked on planar views of a thyroid scanner. It allows for definition of tracer uptake in tiny discrete nodules and in multinodular goiter, and is a b etter guide to the physician in fine-needle aspiration of the cold are as.