  99m-Tc Ethyl-Cysteinate-Dimer SPECT and MR imaging play a significant role in
diagnosing anosmia. In this study, two-tissue class and three-tissue class
attenuation maps (2C-MR and 3CMR) obtained from MR images were compared with
CT-based attenuation correction (CTAC). Afterward, the presence of
hypo-perfusion in brain lobes was evaluated in SPECT images. The 2C-MRAC map
was generated through segmentation of T1-W MR images into air and soft-tissue,
while in the 3C-MRAC map, the cortical bone was also considered. For
investigating MRAC approaches, the difference between activity concentration
(ACC) values was estimated in 144 volumes of interest. Ten normal and fourteen
anosmic patients were compared by calculating the average normalized count and
standard uptake value ratio parameters in the brain lobes. The comparison
between attenuation correction strategies represented that MRAC images resulted
in underestimation of the ACC values which was more substantial in the cortical
area rather than in central regions (maximum 9% vs. 6% for 2C-MR and maximum
5.5% vs. 3.5% for 3C-MR). Nevertheless, there was a strong correlation between
the MRAC and CTAC methods with a correlation coefficient of 0.7 for both 2C-MR
and 3C-MR. The statistical analysis between normal and affected groups
indicated the hypoperfusion in the cortex of Lh_frontal, Rh and Lh_temporal
lobes with p-values < 0.05. Using MRAC resulted in underestimation of activity
concentration which was partly eliminated by considering the cortical bone in
the 3C-MR attenuation map. Hypo-perfusion was perceived in Frontal and Temporal
lobes in SPECT-MRAC images of the anosmic group.
