Inter- and intra-observer reproducibility of quantitative analysis for FP-CIT SPECT in patients with DLB.

Abstract

Dopamine transporter single photon emission CT (DAT-SPECT) is useful in the evaluation of dementia with Lewy bodies (DLB). The specific binding ratio (SBR) is an index to measure DAT density. However, poorly reproducible cases are occasionally experienced in clinical practice. We hypothesized that distance-weighted histogram (DWH) may be useful to improve the reproducibility of SBR. The purpose of this study was to investigate inter- and intra-observer reproducibility of SBR with conventional and DWH methods, and to visually evaluate the precision in reference voxel of interest (VOI) definition using these methods. This study included 50 adult patients with probable DLB. They underwent brain MRI, DAT-SPECT, and cerebral blood flow SPECT with N-isopropyl-p-[123I]iodoamphetamine (I-123 IMP). SBR of the striatum was calculated using conventional and DWH method. For inter-observer reproducibility validation, conventional and DWH SBR were independently evaluated by experienced nuclear medicine physicians; these measurements were repeated by the nuclear medicine physician to investigate intra-observer reproducibility. Proper reference VOI definition was achieved in 60.0% using conventional SBR and in 98.0% with DWH SBR. Both conventional and DWH SBR demonstrated good inter- and intra-observer reproducibility, however, there were statistically significant inter- and intra-observer variations with conventional SBR measurements. Average inter- and intra-observer errors of conventional SBR were 7.9 and 6.1%, respectively. Conversely, DWH SBR errors were not observed in all patients. Moreover, average inter- and intra-observer errors were significantly higher in conventional SBR with improper reference VOI definition than in that with proper reference VOI definition. Although the reproducibility of conventional and DWH SBR was good, inter- and intra-observer bias could not be ignored in conventional SBR, particularly with improper reference VOI definition. Thus, DWH may be useful to improve inter- and intra-observer reproducibility of SBR.