Clinical correlative evaluation of an iterative method for reconstruction of brain SPECT images

Background: Brain SPECT and PET investigations have showed discrepancies in Alzheimer's disease (AD) when considering data deriving from deeply locate d structures, such as the mesial temporal lobe, These discrepancies could b e due to a variety of factors, including substantial differences in gamma-c ameras and underlying technology. Mesial temporal structures are deeply loc ated within the brain and the commonly used Filtered Back-Projection (FBP) technique does not fully take into account either the physical parameters o f gamma-cameras or geometry of collimators. In order to overcome these limi tations, alternative reconstruction methods have been proposed, such as the iterative method of the Conjugate Gradients with modified matrix (CG). How ever, the clinical applications of these methods have so far been only anec dotal. The present study was planned to compare perfusional SPECT data as d erived from the conventional FBP method and from the iterative CG method, w hich takes into account the geometrical and physical characteristics of the gamma-camera, by a correlative approach with neuropsychology. Methods: Correlations were compared between perfusion of the hippocampal re gion. as achieved by both the FBP and the CG reconstruction methods, and a short-memory test (Selective Reminding Test, SRT), specifically addressing one of its function. A brain-dedicated camera (CERASPECT) was used for SPEC T studies with Tc-99m-hexamethylpropylene-amine-oxime in 23 consecutive pat ients (mean age: 74.2 +/- 6.5) with mild (Mini-Mental Status Examination sc ore greater than or equal to 15, mean 20.3 +/- 3), probable AD. Counts from a hippocampal region in each hemisphere were referred to the average thala mic counts. Results: Hippocampal per-fusion significantly correlated with the MMSE scor e with similar statistical significance (p < 0.01) between the two reconstr uction methods. Correlation between hippocampal perfusion and the SRT score was better with the CG method (r = 0.50 for both hemispheres, p < 0.01) th an with the FBP method (r = 0.37 and 0.43, respectively for the right and l eft hemisphere, p < 0.05 and p < 0.02). The bootstrap procedure showed that such correlation indexes were statistically different both in the right (p < 0.01) and in the left (p < 0.05) hemisphere. Conclusion: These results are interpreted as a better performance of the CG reconstruction method in correctly detecting counts from hippocampal ROI. By using the same gamma-camera or collimator, alternative methods for brain SPECT reconstruction may improve quality of data and then help SPECT diagn ostic accuracy, (C) 2001 Elsevier Science Inc. All rights reserved.