Scatter and attenuation correction for brain SPECT using attenuation distributions inferred from a head atlas

Sequential transmission scanning (TS)/SPECT is impractical for neurological ly impaired patients who are unable to keep their heads motionless for the extended duration of the combined scans. To provide an alternative to TS, w e have developed a method of inferring-attenuation distributions (IADs), fr om SPECT data, using a head atlas and a registration program. The validity of replacing TS with IAD was tested in 10 patients with mild dementia. Meth ods: TS was conducted with each patient using a collimated Tc-99m line sour ce and fanbeam collimator; this was followed by hexamethyl propyleneamine o xime-SPECT. IAD was derived by deformably registering the brain component o f a digital head atlas to a preliminary SPECT reconstruction and then apply ing the resulting spatial transformation to the full head atlas. SPECT data were reconstructed with scatter and attenuation correction. Relative regio nal cerebral blood flow was quantified in 12 threshold-guided anatomic regi ons of interest, with cerebellar normalization. SPECT reconstructions using IAD were compared with those using TS (which is the "gold standard") in te rms of these regions of interest. Results: When we compared all regions or interest across the population, the correlation between IAD-guided and TS-g uided SPECT scans was 0.92 (P < 0.0001), whereas the mean absolute differen ce between the scans was 7.5%. On average, IAD resulted in slight underesti mation of relative regional cerebral blood flow; however, this underestimat ion was statistically significant for only the left frontal and left centra l sulcus regions (P = 0.001 and 0.002, respectively). Error analysis indica ted that approximately 10.0% of the total error was caused by IAD scatter c orrection, 36.6% was caused by IAD attenuation correction, 27.0% was caused by discrepancies in region-of-interest demarcation from quantitative error s in IAD-guided reconstructions, and 26.5% was caused by patient motion thr oughout the imaging procedure. Conclusion: SPECT reconstructions guided by IAD are sufficiently accurate to identify regional cerebral blood flow defi cits of 10%, which are typical in moderate and advanced dementia.