Single photon emission computed tomography of the thyroid

Single photon emission computed tomography (SPECT) entails imaging at multiple positions along an arc and computed-assisted reconstruction of transaxial, coronal, and sagittal images. To determine if SPECT imaging of the thyroid augments information provided by planar imaging, both SPECT and pinhole planar scans were performed in 52 patients with thyroid disease. After ¹²³I (n = 45), Tc^99m (n = 5), or thallium-201 (n = 2) administration, images were acquired at 30 intervals along a 180° arc. Nodules that were hypofunctioning on planar scans (n = 4) were equally well shown on SPECT images. SPECT analysis of ¹²³I uptake by 5 palpable nodules with completely normal ¹²³I planar scans demonstrated the nodular tracer uptake was increased (n = 1), equivalent (n = 3), or decreased (n = 1) in comparison with that of extranodular tissue. In 6 of 12 multinodular goiters, transaxial SPECT images showed tracheal compression, which was confirmed by neck x-ray, flow volume loops, or surgery. A neck phantom study was performed to assess the accuracy of SPECT-determined functional thyroid volume. SPECT-estimated volumes (30-173 mL; n = 11) correlated well with true volumes (r = 0.996; P <; 0.001). Our observations suggest that SPECT is a useful adjunct to planar imaging in 1) estimating functional volume for ¹³¹I dosimetry; 2) evaluating the size, extension, and tracheal compression of multinodular goiter; and 3) determining the functional properties of palpable nodules with normal ¹²³I planar pinhole images.