ASSOCIATION OF (82)RUBIDIUM AND C-11 METHIONINE UPTAKE IN BRAIN-TUMORS MEASURED BY POSITRON EMISSION TOMOGRAPHY

Positron emission tomography (PET) studies have indicated that alterat ion of active transport contributes to increased net amino acid accumu lation into human brain tumors. We compared the uptake of C-11-methion ine (MET) and the K+ analog (82)Rubidium (RUB) in 30 patients sufferin g from various brain tumors using PET. MET and RUB accumulated rapidly in tumor tissue and remained on average at a stable level thereafter from which normalized uptake values were calculated (tissue radioactiv ity over injected radioactivity x body weight (NU)). K1 (RUB) and K1, k2, k3 (MET) were also estimated using non-linear rate constant fittin g in 17/30 patients. NU and K1 values were significantly correlated fo r MET (Spearman Rank p<0.005) and RUB (p<0.001). NU and K1 values for MET and RUB were higher in meningiomas compared to gliomas and were si gnificantly correlated for the whole spectrum of tumors (p<0.001). Whe n meningiomas were excluded, the correlation was maintained. K3 values for MET (metabolic rate) in tumors were in the range of normal brain. No correlation between RUB and MET was found for normal brain. With i ncreasing RUB uptake, the ratio of NU MET over NU RUB approached the v alue of 1.0. These results suggest that apart from active transport, a lso passive diffusion across the blood-brain barrier (BBB) may account for MET uptake from blood into tumor tissue. This probably limits the use of MET in the differential diagnosis of brain lesions where BBB d isruption is present.