A diagnostic method for suspected Alzheimer's disease using (H2O)-O-15 positron emission tomography perfusion Z score

We developed cerebral perfusion Z score map (Z map) images using (H2O)-O-15 and positron emission tomography (PET), and examined their use in diagnosi ng Alzheimer's disease (AD). Cerebral blood flow (CBF) images were obtained using the PET and (H2O)-O-15 autoradiographic method. The best region for normalising the CBF value to remove individual variantion was determined. T hen CBF images were transformed to Talairach's standard space, and each pix el value of an individual's image set was normalized to the mean value of t he sensorimotor area. Based on the CBF images of 20 normal volunteers, norm ative mean and standard deviation (SD) CBF images were constructed. Then, e ach pixel value of the axial CBF images in 28 patients with probable AD and 10 further normal volunteers was converted to a Z score (Z = [normal mean - individual value]/normal SD). A Z map, showing pixels exceeding a thresho ld of Z score > 2 on MRI of standardised anatomical space was demonstrated. These 38 Z maps were interpreted by four radiologists. When regions in the temporoparietal area were found with Z scores > 2, the subject was diagnos ed as having AD. A receiver operating characteristic (ROC) analysis was per formed to compare the conventional CBF images and Z maps. The diagnostic pe rformance of the Z map was superior to that of visual inspection of convent ional CBF images (mean areas under the ROC curve of the four radiologists w ere 0.946 and 0.584, respectively). These results indicate that a Z map obt ained in this way is superior to conventional PET for diagnosing AD.