ドパミントランスポー夕シンチグラフィにおけるSBR算出のための参照領域決定法の検討

摘要

ドパミントランスポータシンチグラフィでは，ドパミントランスポータを介して取り込まれる~(123)I-N-ω-fluoropropyl-2β-carbomethoxy-3β- (4-iodophenyl) nortropane (~(123)LFP-CIT)を静注し，single photon emission computed tomography(SPECT)を施行して線条 体の集積を評価する.さまざまなパーキンソン症候群やレビー小体型認知症において，ドパミン系のシ ナプス前機能障害を反映した集積低下がみられ，これ らの疾患の診断や病態把握に用いられる.%The specific binding ratio (SBR) was first reported by Tossici-Bolt et al. for quantitative indicators for dopamine transporter (DAT) imaging. It is defined as the ratio of the specific binding concentration of the striatum to the non-specific binding concentration of the whole brain other than the striatum. The non-specific binding concentration is calculated based on the region or interest (ROI), which is set 20 mm inside the outer contour, defined by a threshold technique. Tossici-Bolt et al. used a 50% threshold, but sometimes we couldn't define the ROI of non-specific binding concentration (reference region) and calculate SBR appropriately with a 50% threshold. Therefore, we sought a new method for determining the reference region when calculating SBR. We used data from 20 patients who had undergone DAT imaging in our hospital, to calculate the non-specific binding concentration by the following methods, the threshold to define a reference region was fixed at some specific values (the fixing method) and reference region was visually optimized by an examiner at every examination (the visual optimization method). First, we assessed the reference region of each method visually, and afterward, we quantitatively compared SBR calculated based on each method. In the visual assessment, the scores of the fixing method at 30% and visual optimization method were higher than the scores of the fixing method at other values, with or without scatter correction. In the quantitative assessment, the SBR obtained by visual optimization of the reference region, based on consensus of three radiological technologists, was used as a baseline (the standard method). The values of SBR showed good agreement between the standard method and both the fixing method at 30% and the visual optimization method, with or without scatter correction. Therefore, the fixing method at 30% and the visual optimization method were equally suitable for determining the reference region.