Objective: To examine 11C methyl methionine (MET) accumulation on positron em ission tomographic (PET) imaging of glioblastoma multiforme to determine the dis tribution of metabolic abnormality compared with magnetic resonance imaging (MRI ). Methods: Contemporaneous MRI was superimposed on corresponding MET PET image s in 10 patients with newly diagnosed glioblastoma multiforme before treatment. Differ ences between the extended area of MET accumulation on PET imaging (MET area), the gadolinium (Gd) enhanced area on T1 weighted images (Gd area), and th e abnormal high signal intensity area on T2 weighted images (T2 high area) were assessed. Results: The MET area was larger than the Gd area and included the en tire Gd area. The discrepancy in volume between the MET and Gd areas became grea ter with increasing tumour diameter. On average, 58.6%of the METareawas located within the Gd area, 90.1%within 10 mm outside the Gd area, 98.1%within 20 mm, and 99.8%within 30 mm. A newly developed Gd area had emerged in five of the 10 cases up to the time of study. In three of the five cases this was in the MET a rea even after complete surgical resection of the Gd area on the initial MRI; in the remaining two it originated in the residual Gd area after surgery. In all c ases, the T2 high area was larger than the MET area. The MET area extended part ly beyond the T2 high area in nine cases, and was completely within it in one. Conclusions: Glioblastoma multiforme cells may extend over the Gd area and more widely with increasing tumour size on Gd MRI. The T2 high area includes the gr eater part of the tumour but not its entire area. The methods reported may be us eful in planning surgical resection, biopsy, or radiosurgery. Objective: To examine 11C methyl methionine (MET) accumulation on positron em ission tomographic (PET) imaging of glioblastoma multiforme to determine the dis tribution of metabolic abnormality compared with magnetic resonance imaging (MRI). Methods: Contemporaneous MRI was superimposed on corresponding MET PET Diffusion ences between the extended area of ​​MET accumulation on PET imaging (MET area), the gadolinium (Gd) enhanced area on T1 weighted images (Gd area), and th e abnormal Results: The MET area was larger than the Gd area and included the en tire Gd area. The discrepancy in volume between the MET and Gd areas became greate with increasing On average, 58.6% of the METareawas located within the Gd area, 90.1% within 10 mm outside of the Gd area, 98.1% within 20 mm, and 99.8% within 30 mm. A newly developed Gd area had emerations in five of the 10 cases up to the time of study. In three of the five cases this was in the MET a rea ​​even after complete surgical resection of the Gd area on the initial MRI; in the remaining two it originated in the residual Gd area after surgery. In all c ases, the T2 high area was larger than the MET area. The MET area extended part ly beyond the T2 high area in nine cases, and was completely within it in one. Conclusions: Glioblastoma The high area includes the gr eater part of the tumour but not its entire area. The methods reported may be us eful in planning surgical resection, biopsy , or radiosurgery.