Automated stereotactic standardization of brain SPECT receptor data using single-photon transmission images

Intra- or intersubject registration of anatomically poorly defined SPECT da ta, such as in neuroreceptor imaging, is important for longitudinal or grou p analysis. However, accurate registration is difficult with only emission CT (ECT) data. We investigated fully automated registration using transmiss ion CT (ECT) data as an intermediary image set. Methods: The accuracy of TC T registration was compared to that of ECT registration for four types of d ata: gray-matter distribution (with [Tc-99m]ethylcysteinate dimer (ECD)), n eocortical distribution (with [I-123]R91150, a highly specific 5-HT2a recep tor ligand), and striatal distribution of the D-2-receptor ligand (with [I- 123]iodobenzamide (IBZM)) and the dopamine transporter ligand (with [I-123] 2 beta -carbomethoxy-3 beta-(4-fluorophenyl)tropane (CIT)). In total, 10 da tasets of the various study types were used, all collected on a Toshiba GCA 9300 gamma camera with super-high-resolution fanbeam collimators and 3 x 37 0 MBq of Gd-153 transmission sources (4-min sequential TCT scanning for rec eptor studies and 20-min simultaneous scanning for [Tc-99m]ECD studies). Pe r dataset, 15 random misalignments of 9 rigid-body parameters (translation, rotation, and anisotropic scaling) were conducted. All coregistrations wer e done twice, both to the subject's original scan and to a study-specific t emplate. This was done manually by two independent experienced observers an d with three automated voxel similarity algorithms: mutual information (M.I .), count difference (C.D.), and uniformity index (U.I.). As an outcome mea sure, the impact of misregistration on semiquantification for the various s tudy types was established. Results: TCT matching allowed registration with in 3.3 mm, 2.4 degrees, and 1.2% scaling (mean squared values for all direc tions) with an overall accuracy decrease in the following order: C.D. > M.I . > manual > U.I. For [Tc-99m]ECD and [I-123]IBZM, TCT registration was as accurate as ECT registration, while it was far superior for the other recep tor data types, especially for abnormal studies. The automated TCT registra tion accuracy corresponded to average quantification errors of 2.9% ([Tc-99 m]ECD), 4.2% ([I-123]IBZM), 5.7% ([I-123]R91150), and 6.1% ([I-123]beta -CI T). Conclusion: Fully automated registration through intermediary TCT image s is clinically feasible, fast, and accurate. In addition to nonuniform att enuation correction, TCT scanning therefore allows coregistration for group comparisons of SPECT receptor data on a standardized or pixel-by-pixel bas is.