J Nucl Med 2002 Jan;43(1):21-6
Direct comparison of spatially normalized PET and SPECT scans in Alzheimer's
disease.
Herholz K, Schopphoff H, Schmidt M, Mielke R, Eschner W, Scheidhauer K, Schicha
H, Heiss WD, Ebmeier K.
Hexamethylpropyleneamine oxime (HMPAO) SPECT and 18F-FDG PET depict similar
aspects of perfusion and metabolic abnormalities in Alzheimer's disease (AD),
but the correspondence between them is not known in detail. We therefore used
statistical parametric mapping to detect and compare abnormal brain areas
objectively and quantitatively. METHODS: Twenty-six patients with probable AD
(mean age +/- SD, 66 +/- 9 y; mean Mini-Mental State Examination score, 22.5 +/-
4.2) and 6 nondemented healthy volunteers (mean age, 63 +/- 11 y) were studied
with HMPAO SPECT and 18F-FDG PET. All images underwent the same processing
steps, including 12-mm gaussian smoothing, spatial normalization, and z
transformation with respect to normal average and SD. Thresholding of z maps was
used to detect abnormal voxels. RESULTS: The overall correlation between PET and
SPECT across the entire brain was significant but not close (average r = 0.43).
The best correspondence was found in the temporoparietal and posterior cingulate
association cortices. There, the number of abnormal voxels for PET correlated
strongly with the number for SPECT (r = 0.90 at a z threshold of -2.25), but
tracer uptake reductions were significantly more pronounced for PET than for
SPECT. Discordant findings were most frequently seen in the temporobasal and
orbitofrontal areas (PET low, SPECT high) and in the cerebellum, parahippocampal
cortex, and midcingulate cortex (PET high, SPECT low). The correlation between
dementia severity and the number of abnormal voxels was closer for PET than for
SPECT. Separation of patients from healthy volunteers by counting the number of
abnormal voxels was possible over a much wider range of z thresholds with PET
than with SPECT. CONCLUSION: Correspondence between 18F-FDG PET and HMPAO SPECT
is limited to the main finding of temporoparietal and posterior cingulate
functional impairment in mild to moderate AD. The distinction between healthy
volunteers and patients is less sensitive to threshold selection with PET than
with SPECT, and findings in the frontal, temporobasal, and temporomesial
cortices and in the cerebellum may differ between the 2 techniques.
