VOLUMETRIC-ANALYSIS OF CEREBRAL HYPOPERFUSION ON SPECT - VALIDATION AND RELIABILITY

A method of volumetric analysis of hypoperfusion on Tc-99m-labeled hex amethylpropylene amine oxime SPECT has been developed. This analysis i ntegrates both the size and severity of perfusion reduction, yielding an equivalent volume of cortical tissue having zero brood flow, or the effective hypoperfusion volume. This study aimed to Validate the meth odology in vitro using the Hoffman brain phantom and two different cam era systems, to examine the relationship between spatial resolution an d accuracy of volume measurement and to assess the interobserver varia bility in SPECT studies of stroke patients. Methods: Simulated cortica l lesions of three different sizes were sequentially incorporated into the Hoffman brain phantom and imaged using both single-and triple-hea d camera systems, For each system and for each lesion size, successive acquisitions were performed using three progressively larger radii of camera rotation. The hypoperfusion volume for each study was measured three times by a blinded observer, and the percentage difference from the true lesion Volume was then calculated. SPECT studies of 32 strok e patients were independently analyzed by two blinded observers. Resul ts: At the smallest radii of rotation, mean (s.d.) percentage differen ce between observed and true Volumes was 0.90% (4.80%) for the triple- head and 4.50% (11.58%) for the single-head system. The degree of over estimation was similar for both systems. Percentage overestimation was strongly associated with radius of rotation (B = 0.71 +/- 0.32, p = 0 .04 for the triple-head system; B = 1.26 +/- 0.55, p = 0.03 for the si ngle-head system) but not with lesion size. The mean difference betwee n hypoperfusion volumes of stroke patients obtained by two observers w as 0.045 (3.240) cm(3), which was not significant. Conclusion: This st udy has shown that this technique of volumetric analysis of regional h ypoperfusion on SPECT is both highly accurate and reproducible between two different camera systems. The degree of overestimation chiefly re lates to diminishing spatial resolution. Despite some element of subje ctivity, the interobserver variability is negligible.