IDENTIFICATION OF TASK-SPECIFIC RCBF CHANGES IN INDIVIDUAL SUBJECTS -VALIDATION AND APPLICATION FOR PET

Objective: A method for identification and quantitative evaluation of task-specific changes of the regional cerebral blood flow (rCBF) measu red with PET in activation studies of individual subjects is presented . The method is based on the statistical distributions of the quantita tive and spatial information of regions of interest in rCBF subtractio n images. Methods: For validation, a cylindrical phantom of 20 cm diam eter containing six spheres of 10-30 mm in diameter was used. The sphe res representing the specific signals were filled with F-18, while one -tenth of this activity concentration was filled into the background c ompartment of the phantom representing ''noise.'' Of a sequence of dyn amically recorded frames, subtraction images with different signal-to- noise ratios were calculated. Results: In these subtraction images, ou r method allowed us to identify the larger spheres accurately and to q uantify the signals. Comparison with t map analysis in averaged subtra ction images revealed a high correspondence with the results obtained by our method in individual subtraction images. Based on this phantom validation, the method was applied for mapping of rCBF changes in huma ns. The rCBF was measured with [O-15]butanol in four subjects during u nilateral somatosensory discrimination and during rest. Conclusion: Th e method proved to be capable of identifying task-specific rCBF change s in the contralateral motor, premotor, and sensory cortex accurately and with high quantitative and anatomical precision in each subject.