[H₂^(15)O] 양전자 단층촬영을 이용한 심근혈류와 혈류분포의 불균일성 측정

Abstract

심근 [H_(2)^(15)O] 동적(dynamic) 양전자 단층촬영(Positron Emission Tomography; PET) 영상에서 추적자 역학(tracer kinetic)을 이용하여 정량적인 심근 혈류측정 및 심근 혈류분포의 불균일성을 측정하고자 하였다. 우선 PET을 이용한 정량적인 혈류측정을 위해 고려해야 할 것들을 이론에서 소개하고 혈류분포의 불균일성 특성에 대하여 서술하였다. 혈류분포의 불균일한 특성을 해석하기 위하여 광물학 분석에서 쓰이는 구성불균일성(Constitution Heterogeneity; CH)의 개념을 도입하였으며, 추적자 역학의 이론을 바탕으로 혈류와 혈류분포의 불균일성을 동시에 측정할 수 있는 모델을 유도하였다. 유도한 모델을 검증하기 위하여 다양한 혈류분포를 갖는 심근조직을 구성하고 이를 컴퓨터 모의실험에 적용하였다. 이전의 연구에서 관류가능한 조직분획(perfusable tissue index; PTI)이 혈류분포의 불균일성을 나타낸다고 하였으나, 컴퓨터 모의실험 결과 PTI는 불균일성에 거의 영향을 않받고 단위 조직당 추적자의 분포를 나타내는 분배계수(partition coefficient)가 분균일성이 커짐에 따라 비선형적으로 감소하는 것을 볼 수 있었다. 이러한 이론과 방법이 임상에 적용 가능한가를 알아보기 위해 동물실험을 실시하였다. 동물실험 결과, 정상 개에 대해서는 분배계수가 정상범위 안에서 측정되었으며 색전술(embolization)을 시행한 개에서는 정상보다 낮게 측정되었다.;For the estimation of regional myocardial blood flow with O-15 water PET, a few modifications considering partial volume effect based on the single compartment model have been proposed. In this study, it is attempted to quantify the degree of heterogeneity and to show the effect of tissue flow heterogeneity on partition coefficient(λ) and to find the relation between perfusable tissue index(PTI) and λ by computer simulation using two modified models. The model Ⅱ of two models used in the computer simulation is used to a dog study. Tissue curves were simulated for the region with homogeneous and heterogeneous blood flow over a wide flow range(0.2 ~ 4.0 ml/min/g). Simulated heterogeneous tissue were composed of 4 subregions of the same or different size of subregions which have the different homogeneous flow. And the heterogeneous tissue for the case of the various distribution of blood flow and 1ml/min/g of mean flow was simulated. For each heterogeneous tissue, the index of the flow heterogeneity was presented by the constitution heterogeneity(CH). Using the model I, PTI, flow, and F_(MMF) were estimated. For the model Ⅱ, it was assumed that the partition coefficient was another variable which could represent tissue characteristics of the heterogeneity of flow distribution. Using the model Ⅱ, PTI, flow and λ were estimated. O-15 water dynamic myocardial PET scan were performed to 6 dogs at rest and dipyridamole stress. 4 of them were normal and 2 of them were infacted. To obtain the input function, ROI were drawn in the left ventricle. Total 54 paired(rest-stress) tissue time-activity curves(TACs) were obtained. 6 parameters including flow and partition coeffient, were estimated using model Ⅱ by non-linear least-square fitting. For the simulated homogeneous tissue, the estimated parameters were equal to the initial values. For the simulated heterogeneous tissue, in the model 55 I, flow and F_(MMF) were correctly estimated as CH was increased moderately. In the model Ⅱ, flow and k were decreased curvi-linearly as CH was increased. The degree of understimation of λ obtained using the model Ⅱ, was correlated with CH. The degree of the undersetimation of flow was dependent on the degree of the underestimation of λ. PTI were somewhat overestimated and not changed according to CH. In the dog study, flow and the partition coefficient for the normal dogs were estimated successively in the normal range. For the infarcted dogs, the rate of flow change between at rest and stress was less than that for the normal dogs. The partition coefficients were more less than the normal range(0.92 ~ 1). PTI were, howcever, nearly neighbour of 1 eigther in the normal or the infarcted dogs. From the result, estimated λ reflects the degree of the flow heterogeneity. The degree of underestimation of λ could be used to find the characteristics of the heterogeneity of tissue flow and to recover the underestimated flow.