Clinical utility of technetium-99m methoxisobutylisonitrile imaging in differentiated thyroid carcinoma: comparison with thallium-201 and iodine-131 Na scintigraphy, and serum thyroglobulin quantitation

Recently, technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) has been used to image thyroid carcinoma. A prospective study was performed to compare the efficacy of^99mTc-MIBI to thallium-201 (²⁰¹T1) scintigraphy in patients with differentiated thyroid carcinoma. The clinical utility of all radionuclide imaging modalities, i.e.,^99mTc-MIBI,²⁰¹Tl, and iodine-131 Na (¹³¹I-Na), as well as serum thyroglobulin estimation, was evaluated. Thirty-four post-thyroidectomy patients (age range: 26-76 years) underwent 45 studies. Histopathologies studied included fourteen papillary, eight papillaryfollicular, ten follicular, one Hürthle cell, and one medullary carcinoma of the thyroid. Following optimal stimulation of endogenous thyroid stimulating hormone (i.e, TSH >-50 mU/ml), the patients underwent²⁰¹Tl and^99mTc-MIBI scintigraphy. Concomitant¹³¹I-Na scintigraphy was performed and serum thyroglobulin levels were measured. Sixteen scan sets were performed prior to¹³¹I-Na ablation therapy. Twenty-nine scan sets were performed following¹³¹I-Na ablation therapy. The presence or absence of thyroid cancer was established by clinical, biochemical, radiologic, and/or biopsy findings. There was no significant difference in sensitivity and specificity of²⁰¹Tl scintigraphy versus^99mTc-MIBI scintigraphy in pre- and postablation studies.¹³¹I-Na scintigraphy with determination of thyroglobulin level was sufficient in preablation studies. Among postablation patients, the addition of^99mTc-MIBI or²⁰¹Tl offered a higher diagnostic yield. Between the²⁰¹Tl and^99mTc-MIBI studies, there was a concordance of 69% in preablation and 97% among postablation patients (P=0.027). It is concluded that^99mTc-MIBI is a suitable alternative to²⁰¹Tl scintigraphy in thyroid carcinoma, especially following thyroidectomy and¹³¹I-Na therapy.¹³¹I-Na scintigraphy with serum thyroglobulin is adequate in both pre- and postablation patients. Among the post-¹³¹I-Na ablation patients,^99mTc-MIBI or²⁰¹Tl is extremely valuable for tumor localization, especially when the¹³¹I-Na whole-body scan is negative. The combination of^99mTc-MIBI or²⁰¹Tl scintigraphy with¹³¹I-Na and serum thyroglobulin offers the highest diagnostic yield.