Discrepancy between lesion distributions on methionine PET and MR images in patients with glioblastoma multiforme -insight form a PET and MR fusion images study

Purpose: 11C-methyl methionine (MET) accumulation on positron emission tomography (PET) imaging of glioblastomaPmultiforme (GBM) was examined to determine the distribution of metabolic abnormality of this tumour. This distribution was compared with the abnormal tumour signal intensity of GBM on MRI to evaluate the discrepancy between lesion distributions yielded by these methods. Methods: MET-PET was performed for 10 patients with newly diagnosed GBM before treatment. At the same time, MRI was performed and superimposed on corresponding MET-PET images using a SUN workstation. The differences between the extended area of MET accumulation on PET imaging (MET area), that of the gadolinium (Gd)-enhanced area on T1-weighted images (Gd area), and that of the abnormal high signal intensity area on T2-weighted images (T2-high area) were assessed. Results: The MET area was distinctly larger than the Gd area and included the entire Gd area. The discrepancy in volume between the MET area and the Gd area became larger with increasing tumour diameter. On average, 58.6% of the MET area was located within the Gd area, 90.1% within 10 mm outside of the Gd area, 98.1% within 20 mm of the Gd area and 99.8% within 30 mm of the Gd area. A newly developed Gd area has emerged in 5 of the 10 cases in their clinical courses until the time of this study. The newly developed Gd area was demonstrated even in the MET area after completely surgical resection of Gd area in the initial MRI in 3 of the 5 cases, and originated in the residual Gd area after surgery in the remaining 2 cases. In all cases, the T2-high area was larger than the MET area. The MET area extended partly beyond the T2-high area in 9 cases, and the MET area was completely within the T2-high area in one case. Conclusion: Previous PET studies on GBM have reported that the MET area corresponds well with the area of tumour extension. The results of our study show that GBM cells may extend over the Gd area and more widely with increasing tumour size on Gd-MRI. The T2-high area includes the greater part of GBM, but does not completely show the entire area of GBM. GBM cells are strongly suggested to extend partly beyond the T2-high area. The T2-high area beyond the MET area is suspected to show mainly peritumoural oedema. The methods reported here may be useful in the planning of surgical resection, biopsy, or radiosurgery for GBA. (authors)