ILLUSTRATIONS Fig. 1 Comparative spectra of iodine~123 and technetium-99m obtained with the use of a 2 x 2 inch sodium fodide crystal. The source of radioactivity was placed in an IAEA neck phantom used to measure thyroidal uptake of radioiodine. Fig. 2 BNL Neg. #11-513-73 Residual thyroid tissue in the neck following previous thyroidectomy and radioiodine for carcinoma. The iodine-123 image (below) is clearly superfor to the technettum-99m image. : BNL Neg. #12-106-71 Fig. 3 Substernal nodular goiter. The technetium image (above) does not clearly delineate the gland but only suggests a functioning nodule in the left upper pole. extension. There is no clear evidence of substernal The radioiodine image (below) more clearly demonstrates multiple functioning nodules and definite substernal extension. Reproduced with permission of the American Journal of Roentgenology, Radium Therapy and Nuclear Medicine (Ref. 15) BNL Neg. #12-661-71. Fig. 4 The cold nodule along the left inferior portion of the thyroid is somewhat obscured by background activity in the technetium image (above) but clearly seen in the iodine image (below). Reproduced with permission of the American Journal of Roentgenology, Radium Therapy and Nuclear Medicine (Ref. 15) BNL Neg. #12-425-71 Fig. 5 A comparison of the thyroidal uptake of radioiodine at 24 hours following intravenous (!23z) and oral (99™Tc) administration in 29 patients. BNL Neg. #11-514-73 ‘ || 5901309