電腦斷層掃描定義與決定冠狀動脈開口之 最佳投影角度演算法：與傳統血管造影之比較

Abstract

心血管疾病是僅次於癌症的全球第二大死因，而心導管手術為近年來廣泛用來檢查與治療冠狀動脈粥狀病變。因每位病人的生理結構不盡相同，手術時必須調整系統儀器的角度，來得到較佳的手術視野，以增加心導管進行的時間。若遇到開口處病變的患者，更需要適當的觀察角度去判斷支架放置的位置。故本研究的目的為提供心導管手術時，左、右冠狀動脈開口的手術視野之最佳投影角度，並開發了一套電腦輔助系統，用來幫助醫師支架放置的準確性，以及節省手術的時間。 根據病患手術前的電腦斷層影像，找出開口處的幾何結構特徵做分析，並利用三維曲率、血管寬度與血管表面結構等來定義開口處位置，再採用最小平方誤差近似法(least squares approximation method)擬合開口處的切平面。採用阻擋距離(overlap length)與血管縮短比例(vessel foreshortening ratio)當作投影角度最佳化的判斷條件，當阻擋距離為零時，血管縮短比例最小即是最佳投影角度。依照開口切平面的法向量與血管中心線方向的外積結果，再隨平面旋轉一圈後，便可利用梯度下降法(gradient descent manner)取得最佳投影角度。 結果顯示，在目前累積的二十筆案例中，與常用投影角度的結果比較下，最佳投影角度可以得到更好的血管縮短比例。為解決因儀器的限制而無法達成的最佳投影角度，本研究使用全範圍最佳化圖譜，能同時提供阻擋距離與血管縮短比例的資訊，並能迅速地找出次要的最佳投影角度。經由統計二十筆結果後發現，左冠狀動脈之最佳投影角度都多集中在特定範圍內，而右冠狀動脈之最佳投影角度則因為不同的人體生理結構，分成兩區域的落點。 因此，本研究的結果能輔助醫師在進行心導管手術時，更精確判斷支架放置的位置，並進而節省手術的時間。

The purpose of this study was to assist doctors in achieving a more efficient placement of coronary stents. Because of the inter-patient difference and special cases like coronary ostial stenosis, it usually takes time to attain the informative projection angles (PA) during cardiac catheterization. Based on the preoperative CT scans, a computer aided cardiac catheterization (CACC) system was adopted to assess the conventional projection angle (CPA) as well as to provide the optimal projection angle (OPA) during the procedure. The study focused on the geometric properties of the aorto-ostial plane around the coronary ostium, including curvature, vessel diameter, and surface structure, etc. An aorto-ostial plane, which defined the section of the aorta and a coronary artery, is derived by least squares approximation method to a plane with the intersecting contour points of a vascular structure and the aorta. The intersecting contour points are selected as the points of the intersecting contour of the aorta, and then a fifth order polynomial surface fits to the surface structure. The terms of the overlap length (OL) and the vessel foreshortening ratio (VFR) are defined as the two main factors of the optimality of the PA. The OPA can be found by rotating the viewing direction starting from the cross product of vessel center line direction and the normal vector of the aorto-ostial plane in a gradient descent manner. Twenty five cases have been analyzed using the CACC system with the computed OPAs and the CPAs for both left coronary artery (LCA) and right coronary artery (RCA). It is evident that the performance of OPAs is clearly superior to those attained by the CPAs. To facilitate the selection of a suboptimal PA in few cases which affected by practical constraints, a full-range optimality map has been developed to signify the OLs and the VFRs for all possible PAs within the operable range of an intraoperative angiography system. It was found in the scatter diagram of OPA for all cases that the OPA of LCA is pointed to a specific range of the operable area. However, the OPA of RCA is grouped into two types because of the different physical conditions within people. The results of the study revealed that the OPA provided by CACC system may greatly facilitate stent placement for treating coronary ostial lesions and thus help spend less time in one surgical procedure.