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Direct Comparison of Spatially Normalized PET and SPECT Scans in Alzheimer’s Disease

¹ Neurologische Universitätsklinik, Köln, Germany
² Max-Planck-Institut für neurologische Forschung, Köln, Germany
³ Nuklearmedizinische Universitätsklinik, Köln, Germany
⁴ Department of Psychiatry, University of Edinburgh, Edinburgh, United Kingdom

View larger version (12K): [in a new window]   FIGURE 1. Scatterplot and regression line of correlation coefficients (R) between individual PET and SPECT z maps on dementia severity (MMSE). Correspondence between PET and SPECT tended to be closer in patients with more severe dementia (1 extreme additional point at MMSE = 11, r = 0.75, not included in plot; the 2 boxed points represent 2 cases each). Regression was significant (Pearson coefficient for correlation between imagewise correlation coefficients and MMSE = -0.57, r2 = 0.33, P = 0.002; corresponding Spearman rank correlation coefficient = -0.50, P = 0.01).

View larger version (78K): [in a new window]   FIGURE 2. Regional distribution of correspondence between PET and SPECT z maps. Product of PET and SPECT z scores (with both scores negative) was summed over all patients and displayed as fusion image with standard MR image for anatomic orientation. Green line delineates volume of best correspondence (VBC), defined as average z product of 1. Numbers on scale represent square roots of product of PET and SPECT z scores (with both scores negative) summed over all patients.

View larger version (53K): [in a new window]   FIGURE 3. (A) Good correspondence between PET and SPECT is shown by spatially normalized original images of AD patient (MMSE score = 19, r of z maps = 0.62), particularly with respect to reduced uptake in temporoparietal association cortex (white arrows). (B) Discordance is found in another patient (MMSE score = 21, r = 0.35), with impaired frontal uptake for PET (red arrows) but not for SPECT.

View larger version (15K): [in a new window]   FIGURE 4. Scatterplot and regression line of number of abnormal voxels for SPECT versus PET at z threshold of -2.25.

View larger version (24K): [in a new window]   FIGURE 5. Number of misclassified subjects for PET and SPECT as determined using selected z threshold to identify abnormal voxels. Number of abnormal PET voxels within VBC completely separated AD patients from healthy volunteers for all z thresholds between -1.5 and -3.5, whereas separation was less complete for other techniques.