Semi-quantitative analysis is used to evaluate the degree of tracer binding to the striatum in dopamine transporter (DaT) single-photon emission computed tomography (SPECT). In DaT SPECT, it is difficult to evaluate the accurate tracer accumulation due to the partial volume effect (PVE). In this study, we propose a novel semi-quantitative approach for measuring the amount of accumulation by examining the approximate image. Using the striatal phantom, we verified the validity of a newly proposed method that can accurately evaluate the tracer accumulations in the caudate and putamen, separately.
The left and right caudate/putamen regions, and the whole brain region as the background (BG) region were identified in computed tomography (CT) images obtained by SPECT/CT imaging, and the positional information of each region was obtained. The SPECT-like images were generated by assigning assumed accumulation amounts to the left and right caudate/putamen and BG regions based on the positional information. By changing the assumed accumulation amounts assigned to each region, the SPECT-like image, which was approximated to the image obtained by the SPECT imaging, was examined. The accumulation amounts assumed, when the generated SPECT-like image approximated the most to the image actually obtained by the SPECT imaging, were determined as the accumulation amounts in each region. We evaluated the correlation between the count density calculated by the proposed method and the actual count density of 123I solution filled into the striatal phantom, and verified the validity of the proposed method. In addition, the specific binding ratio (SBR) and caudate-putamen ratio (CPR) computed by the proposed method were compared with the theoretical SBR and CPR calculated by the count density of the 123I solution filled into the striatal phantom.
The count density calculated by the proposed method and the count density of 123I solution filled in the striatal phantom had an extremely strong positive correlation (r=0.997, p < 0.001). The SBRs computed by the proposed method were overestimated. However, the obtained CPRs were very similar to the theoretical CPRs.
The proposed method was able to compute the accurate accumulation amounts in the caudate and putamen, considering the PVE.