[The most suitable parameter to distinguish brain tumor using 201Tl-chloride and SPECT].

: We performed 201Tl single photon emission CT (SPECT) studies on 62 patients with brain tumors prior to any therapy for the tumor. Ten lesions of open-scar and 17 patients without brain tumor were also studied. The SPECT imaging were initiated 5 min (early image) and 4 hours (delayed image) after injection with 74 MBq of 201Tl-chloride. For a semi-quantitative analysis, we used the ratio of delayed count density to the early count density of the tumor (Td/Te), the ratio of tumor to normal brain tissue (Te/B(e)) on the early SPECT and the index of T/B ((Td/Te)/(Bd/B(e))). Delay to early ratio of 34 normal brain tissue (Bd/B(e)) was 1.22 +/- 0.15 and tended to decrease with the age. The Td/Te ratio of meningioma and region of operation scar was about 0.75 which was less than that of normal brain tissue. In 31 patients with astrocytic tumor, Td/Te ratio was clearly higher in poorly differentiated tumor than in well differentiated one. The index of Td/Te ratio was superior to Te/B(e) or T/B ratio for differentiating brain tumor and grading astrocytic tumor.