超音波により計測された弾性率分布を用いた動脈壁絤織分類に関する研究

摘要

本研究グループでは，動脈壁の局所弾性率の計rn測による組織性状の診断を目指している．これまrnでの研究により動脈壁各組織の弾性率分布（弾性ラrnイブラリ）が得られており，弾性ライブラリを用rnいて弾性率断層像を軟らかい組織と硬い組織へ分rn類することが可能となった．しかし，弾性率分布rnが酷似している組織については，弾性率に単純にrn閾値を設けて分類することは困難である．%Pathological changes in arterial walls significantly influence their mechanical properties. We have developed a correlation-based method, the phased tracking method, for measurement of the regional elasticity of the arterial wall. Using this method, elasticity distributions of lipids, blood clots, fibrous tissue, and calcified tissue were measured by in vitro experiments for excised arteries (mean ± SD: lipid 89 ± 47 kPa, blood clot 131 ± 56 kPa, fibrous tissue 1022 ± 1040 kPa, calcified tissue 2267 ± 1228 kPa). We previously proposed a tissue classification method using the elasticity distribution in each small region. In this method, the elasticity distribution of each small region of interest (ROI) (not a single pixel) in an elasticity image is used to classify lipids, blood clots, fibrous tissue, and calcified tissue by calculating the likelihood function for each tissue. In the present study, the optimum size of the ROI and threshold T_(o,i)(R_(m,n)) for the likelihood function L_i(m,n) were investigated to improve the tissue classification. By setting the ROI whose size is larger than resolution of ultrasound (800 μm× 600 μm) and the threshold T_(o,i)(R_(m,n)) determined by the variance in measurement of the radial strain, the tissue classification of the arterial wall was improved.