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Tc-99m MIBI imaging was performed in 34 patients with histopathologically proven malignant tumors. The study was performed in two steps. In the first step, only Tc-99m MIBI imaging was performed (Group 1). In the second step, both Tc-99m MIBI and Tl-201 imaging were performed for comparison (Group 2). Seventeen patients were studied in each step. The size of the smallest primary tumor (breast cancer) was 15 x 10 mm, and that of the largest (lung cancer) was 145 x 130 mm. Of the 34 patients, 26 showed Tc-99m MIBI uptake at the tumor site. In Group 1, 12 patients showed Tc-99m MIBI tumor uptake, but no uptake was detected in five patients (squamous cell carcinoma of the esophagus, teratoma of the testis, nonHodgkin's lymphoma, and squamous cell carcinoma of the lung). In Group 2, 13 patients showed both Tc-99m MIBI and Tl-201 uptake at the tumor site, but one patient with breast cancer showed only Tc-99m MIBI uptake, and three patients showed no Tc-99m MIBI and Tl-201 uptake (embryonal cell carcinoma of the testis, hepatocellular carcinoma). The overall sensitivity of Tc-99m MIBI imaging was 76.4%. In Group 2, the sensitivity was 82.3% for Tc-99m MIBI and 76.4% for Tl-201. Our preliminary clinical experience suggests that Tc-99m MIBI can be helpful in localizing malignant tumors and that its sensitivity is slightly higher than Tl-201.

A patient with pulmonary actinomycosis who unexpectedly showed focal uptake of technetium-99m-hexakis-2-methoxy isobutyl isonitrile and thallium-201 is presented. The appearance of the lesion on the chest radiograph and x-ray CT scan resembled a mediastinal tumor. The diagnosis of pulmonary actinomycosis was achieved by histopathologic examination of the surgically removed mass.

The case of a patient with giant lymph node hyperplasia of the mediastinum who unexpectedly showed focal uptake of technetium 99m hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI) is presented in this article. The patient was included in our research programme of tumor imaging with 99mTc-MIBI because the appearance of the mass on the chest radiogram and CT scan resembled a mediastinal tumour. Final diagnosis of giant lymph node hyperplasia was achieved through histopathological examination of the surgically removed lymph node.