Metabolic imaging to follow stereotactic radiation of gliomas -: the role of 1H MR spectroscopy in comparison to FDG-PET and IMT-SPECT

Purpose: To evaluate the clinical value of 1H MR spectroscopy (1 H MRSI) for follow-up of irradiated glioma compared to posi-. tron emission tomography (PET) with [18F]-2-fluoro-deoxy-D-glucose (FDG-PET) and single photon emission tomography with [1231]-a-methyl-L-tyrosine (IMT-SPECT). Materials and Methods: Twenty-four patients with irradiated gliomas were examined using 1H MRSI (2D spectroscopic imaging; PRESS; TE=135 msec; 1.5T Magnetom Vision, Siemens; Voxel size 9 x 9 x 15 mm(3)). MR spectra (n = 233) were evaluated in areas suspicious of tumor (n = 86) as well as in healthy appearing brain tissue (n = 147). Relative signal intensity ratios of choline (Cho), creatine (Cr) and N-acetyl-aspartate (NAA) were calculated. PET. scans (n = 19) were performed with 200 - 250 MBq FDG, IMT-SPECT examinations (n = 14) with 200 - 250 mBq IMT. Based on clinical and MRI/CT, follow-up lesions were classified as either neoplastic [PIT] or non-neoplastic [nPT]. Results: True positive results for the diagnosis of PT/nPT were 88/89% (1H MRSI), 73/100 % (PET) and 100/75 % (SPECT). Cho/Cr showed highly significant changes for PT. Determinating a correlation between Cho, Cr, NAA and IMT-SPECT as well as FDG-PET was not possible because of different location of maximum tracer uptake and acquired 2D I H MRSI. Conclusion: IMT-SPECT seems to be superior to detect tumor progression in irradiated gliomas. 1 H MRSI was more suitable than FDG-PET to differentiate between recurrence and radiation-induced changes. FDG-PET plays a role as sensitive method for detecting high-grade tumors. PET and SPECT allowed the examination of the entire tumor including surrounding brain tissue with higher spatial resolution than the acquired 2D 1H MRSI. A main limitation of our study was that only 2D 1 H MRSI was used, with only parts of the tumor evaluated. The use of 3D MR spectroscopic imaging may further increase the diagnostic accuracy.