FIG 2. A (above), Perfusion MR shows marked increase of regional cerebral blood volume (rCBV) and regional cerebral blood flow (rCBF) within the solid component of the lesion (arrow). Note that there is no interhemispheric difference in mean transit time (MTT). A total of 12 mL of gadopentate dimeglumine was administered (4 mL/s) and a T2*-weighted gradient-echo sequence with multishot echo-planar sequences 0.8/10/90 (TR/TE/flip angle) was obtained, followed by image postprocessing with maps of rCBV, MTT, rCBF, and time to peak.

B (facing page), Single-photon emission CT images obtained 120 minutes after administration of 94 MBq 201-thallium (TI) shows ncreased 201-TI uptake within the solid part of the residual LDD (arrow). This area corresponds to the zone of increased rCBV and rCBF shown in A. Images were aquired with a rotating gamma camera (Siemens ZLC 370/750, Germany) 5 minutes and 120 minutes after intravenous administration of 97 MBq 201-TI. Data acquisition was completed after 32 minutes by using a 128 x 128 matrix. Butterworth and Ramp filters were used to reconstruct images. Ratios of regions of interest compared with contralateral cerebellum were calculated.

C (facing page), 18-FDG-PET with 3D MR imaging overlay shows the increased 18-FDG uptake is within the solid component of the LDD (arrow) and corresponds to the zone of increased rCBV and increased 201-TI uptake (see A and B). A Siemens CTI ECAT EXACT tomograph scanner (Germany) was used with a 10.8-cm field of veiw and 6.8-mm full width half maximum. The images were acquired 30 minutes after injection of 185 MBq 18-FDG. Images with attenuation correction were reconstructed using the standard mathematical algorithm implemented in ECAT software and using filtered back-projection by Shepp-Logan filter (cut-off 0.35 cycles/pixel). Automated spatial normalization to the stereotactic Talairach space was performed using SPM96. ROIs confined to the LDD were defined in all realigned slices covering the mass lesion, and identical regions were defined for the contralateral unaffected cerebellar hemisphere. Mean values for semiquantitative analysis of each region of interest (ECAT counts per pixel per second) were normalized to individual global brain glucose metabolism to give a glucose metabolic index as region of interest over global cerebral metabolic rate of glucose