CLINICAL UTILITY OF TC-99M METHOXISOBUTYLISONITRILE IMAGING IN DIFFERENTIATED THYROID-CARCINOMA - COMPARISON WITH THALLIUM-2O1 AND I-131 NASCINTIGRAPHY, AND SERUM THYROGLOBULIN QUANTITATION

Recently, technetium-99m methoxyisobutyl-isonitrile (Tc-99m-MIBI) has been used to image thyroid carcinoma, A prospective study was performe d to compare the efficacy of Tc-99m-MIBI to thallium-201 (Tl-201) scin tigraphy in patients with differentiated thyroid carcinoma. The clinic al utility of all radionuclide imaging modalities, i.e., Tc-99m-MIBI, Tl-201 and iodine-131 Na (I-131-Na), as well as serum thyroglobulin es timation, was evaluated. Thirty-four post-thyroidectomy patients (age range: 26-76 years) underwent 45 studies. Histopathologies studied inc luded fourteen papillary, eight papillary-follicular, ten follicular, one Hurthle cell, and one medullary carcinoma of the thyroid. Followin g optimal stimulation of endogenous thyroid stimulating hormone (i.e, TSH greater than or equal to 50 mU/ml), the patients underwent Tl-201 and Tc-99m-MIBI scintigraphy. Concomitant I-131-Na scintigraphy was pe rformed and serum thyroglobulin levels were measured. Sixteen scan set s were performed prior to I-131-Na ablation therapy. Twenty-nine scan sets were performed following I-131-Na ablation therapy. The presence or absence of thyroid cancer was established by clinical, biochemical, radiologic, and/or biopsy findings. There was no significant differen ce in sensitivity and specificity of Tl-201 scintigraphy versus Tc-99m -MIBI scintigraphy in pre- and postablation studies. I-131-Na scintigr aphy with determination of thyroglobulin level was sufficient in preab lation studies. Among postablation patients, the addition of Tc-99m-MI BI or Tl-201 offered a higher diagnostic yield. Between the Tl-201 and Tc-99m-MIBI studies, there was a concordance of 69% in preablation an d 97% among postablation patients (P=0.027). It is concluded that Tc-9 9m-MIBI is a suitable alternative to Tl-201 scintigraphy in thyroid ca rcinoma, especially following thyroidectomy and I-131-Na therapy. I-13 1-Na scintigraphy with serum thyroglobulin is adequate in both pre- an d postablation patients, Among the post-I-131-Na ablation patients, Tc -99m-MIBI or Tl-201 is extremely valuable for tumor localization, espe cially when the I-131-Na whole-body scan is negative. The combination of Tc-99m-MIBI or Tl-201 scintigraphy with I-131-Na and serum thyroglo bulin offers the highest diagnostic yield.