正、側面測顱片被廣泛的應用於齒顎矯正及正顎手術的診斷及評估治療成效。雖然這些二維的影像可提供臨床醫師許多資訊，卻仍存在正、側面資訊無法整合成真正的立體關係與二維資訊在成像過程中造成誤差的缺點。特別是對於顏面不對稱病患的分析與診斷，光靠傳統的二維資訊很難清楚呈現畸形的型態與程度。目前較常使用於頭骨三維重建的方法為電腦斷層和雷射掃瞄。這些方法雖可建構出精確的三維資訊，但卻因輻射暴露量高與價格昂貴等因素而大大限制其臨床應用性。而兩張拍攝交角成90度的片子可經由空間幾何關係推演出的程式換算得到界標點的空間座標，故本研究的目的即利用此原理將兩張拍攝交角互成90度的正、側面測顱片做界標點的三維重構並比較與二維分析的差異。整個實驗的流程為： (1)找出可同時出現於正、側面側顱片的界標點 (2)頭顱拍攝斷層掃描以建立將來驗證換算程式準確度的標準值，驗證程式的準確度 (3)重構後三維分析與傳統二維分析準確度的比較 (4)分析選點的精確度及建立一套準則 (5)應用於實際病例。結果如下：(1)在本實驗中共找出15個界標點可同時於正、側面測顱片上呈現。(2)藉由比較由斷層掃描及兩張測顱片重建的資料，得知此三維重建方法的準確度為98.8%，足以應用到臨床。(3)二維影像上因投射造成測量值的誤差可藉由三維重建來校正。(4)在評估選點誤差的實驗中,共六位測試者，各測試者在選取頭顱X光片界標點時的再現性都相當好，但準確度方面只有兩位測試者較好。這兩位測試者於選取病人X光片界標點時的再現性於OrR, OrL, Me, GoR 和GoL這些界標點較差，但若將X光片先行描繪再選點時則再現性相當好；然而這兩位測試者選點的差異則不論直接在X光片上選點或經描繪後選點皆大於1mm。(5)可將此三維分析應用於一顏面歪斜之實際病例。結論為利用兩張正交投影法的正、側面測顱片可藉由三維重構作出較二維分析準確的三維分析，並實際運用於臨床病例。

　Postero-anterior and lateral cephalograms have been widely used in diagnosis and assessment of treatment results in orthodontics and orthognathic surgery. Although the two views can provide plenty clinical information in two dimensions, they cannot accurately demonstrate the anatomic structures in 3 dimensional aspects and may cause measurement errors due to the distortion of 2D films. The aims of this study were to reconstruct 3D model by using biplanar cephalograms with orthogonal projection and to compare the differences between 3D and 2D analyses. The procedures were summarized as following: (1) To identify landmarks which could be used for 3D reconstruction, (2) To construct the norms of spatial information of the skull based on the error estimation from 3D reconstruction through computed tomography (CT), (3) To compare the differences between conventional 2D and 3D analyses, (4) To analyze the accuracy of the point selection procedure, and (5) To apply in clinics. We explored fifteen clear landmarks on both films and used them in this study. By comparing the data from CT and biplanar cephalograms, we found that the accuracy in this 3D reconstruction method was 98.8%, which was good enough for clinical application. The projection errors resulting from measurements on 2D films could be corrected successfully by 3D reconstruction with biplanar cephalograms. All of six examiners could precisely identify landmarks on films from a dry skull, but only two of them showed good accuracy in identifying landmarks on the same films. These two examiners showed poor precision in identification on films from clinical patients for landmarks such as OrR, OrL, Me, GoR and GoL, but good precision on tracing papers from the same films. On the other hand, the mean differences of landmark identification between the two examiners are greater than 1mm whether the observation is made directly on films or on papers through tracing. The study indicates that biplanar cephalograms with orthogonal projection can provide a clinically useful 3D analysis.

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