Association of 82 Rubidium and 11C-methionine uptake in brain tumors measured by positron emission tomography

Abstract

Positron emission tomography (PET) studies have indicated that alteration of active transport contributes to increased net amino acid accumulation into human brain tumors. We compared the uptake of 11C-methionine (MET) and the K+ analog 82Rubidium (RUB) in 30 patients suffering 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 calculated (tissue radioactivity over injected radioactivity x body weight (NU). K1 (RUB) and K1, k2, k3 (MET) were also estimated using non-linear rate constant fitting in 17/30 patients. NU and K1 values for MET and RUB were higher in meningiomas compared to gliomas and were significantly correlated for the whole spectrum of tumors (p < 0.0001). When 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 increasing rub intake the ratio of Nu MET over Nu RUB approached the value of 1.0. These results suggest that apart from active transport, also 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 disruption is present.

Analysis of11C-methionine Uptake in Low-Grade Gliomas and Correlation with Proliferative Activity

“…13,[29][30][31] In malignant gliomas with BBB damage, passive diffusion also contributes to total uptake of MET. 32 We hypothesize that the MET uptake, especially in DAs without BBB disruption, may be closely associated with tumor viability, which itself is dependent on increased amino acid transport. There was no correlation between MET uptake and Mib-1 LI in ODs and OAs, which may be because of the different mechanisms of MET uptake in these tumors compared with DA.…”

Diagnostic and Prognostic Value of11C-Methionine PET for Nonenhancing Gliomas

“…Some reports have claimed that FDG-PET is better for grading and prognostication than MET PET, 26,[28][29][30] while others have claimed otherwise. 27,[31][32][33] In theory, accumulation of MET is influenced not only by specific carrier-mediated uptake but also by passive diffusion in areas with a disrupted blood-brain barrier, [34][35][36] while background normal cortical uptake of the tracer markedly interferes with accumulation of FDG in brain tumors. One possible reason for the abovementioned controversy could be the patient populations analyzed in those studies, in which both enhancing and nonenhancing tumors were analyzed together.…”

Diagnostic Accuracy of 11C-Methionine PET for Differentiation of Recurrent Brain Tumors from Radiation Necrosis After Radiotherapy

“…They reported that some necrotic tissues showed a high level of 82 Rb accumulation, indicating a disrupted BBB (17). Because 11 C-MET is thought to accumulate in tissue with a disrupted BBB (13,28), the level of 11 C-MET uptake in necrotic tissue should be elevated. Such a disadvantage of 11 C-MET was previously described by Roelcke et al (28).…”