The usefulness of Tc-99m MIBI for evaluating brain tumors - Comparative study with TI-201 and relation with P-glycoprotein

Purpose: This study was undertaken to determine the usefulness of Tc-99m me thoxyisobutylisonitrile (MIBI) in brain tumors compared with Tl-201 imaging . The authors evaluated the correlation between MIBI uptake and the presenc e of P-glycoprotein, and also the relation between MIBI uptake in response to combined radiotherapy and chemotherapy in glioblastoma. Materials and Methods: Thirty-four brain tumors composed of 15 glioblastoma multiforme (GBM), 5 anaplastic astrocytomas, 5 low-grade astrocytomas, and 9 metastases were evaluated. Early and delayed images were obtained for MI BI and Tl-201 scintigraphy. P-glycoprotein status in all GEM, 2 anaplastic astrocytomas, 2 low-grade astrocytomas, and 2 metastases were evaluated imm unohistochemically. Patients with GEM were divided into an effective and a noneffective group according to the change in tumor size. MIBI uptake indic es were compared for these two groups. Results: Both radiopharmaceuticals accumulated in all GEM and anaplastic as trocytomas. In low-grade astrocytomas, only one case showed tracer uptake. In metastasis, two cases showed high uptake on early images and marked wash out on delayed images. Uptake ratio values (early uptake ratio and delayed uptake ratio) in all tumors were significantly higher in MIBI than in Tl-20 1. Immunohistochemical studies showed that the metastases were positive for P-glycoprotein but the GEM were not, in low-grade astrocytomas, a few cell s were positively stained. In relation to the therapeutic outcome of GEM, b oth the early and delayed uptake ratios of MIBI were significantly greater in the noneffective group. Conclusions: Although diagnostic ability was comparable in MIBI and Tl-201, the imaging quality was better in MIBI. Both radiopharmaceuticals are usef ul in differentiating low-grade glioma from high-grade glioma. MIBI delayed imaging could also reflect the presence of P-glycoprotein. intense MIBI up take was also predictive of a poor clinical outcome in GBM.