測顱術是應用頭顱上有定義的界標點以測量顱顏相關距離與角度資料，在齒顎矯正與顏面整型相當重要，過去醫師通常是利用二維的正面與側面測顱片進行測顱分析，現今由於牙科用電腦斷層掃描系統迅速發展，三維測顱分析逐漸變成一重要課題，本研究的主要目的在於研發醫學影像處理技術，建立一個三維頭顱界標自動定位與測量系統。本系統首先需要使用者以徒手方式標記出兩點界標點(Por與N)，然後系統會自動執行影像校正；接著系統會在所欲分析的三維頭顱上自動搜尋51個自行定義的對位標記點，再將系統預建的通用界標模型利用影像對位的方式建立兩者最佳的座標轉換關係，然後進行設定邊界條件或縮小搜尋範圍做自動定位八點界標點。此外使用者也透過操作界面在三維頭顱影像中自行給定界標點和測量所有相關距離與角度，以進行臨床分析與評估。本研究影像資料是擷取現有錐形X-光束電腦斷層掃描系統，同一個案重複自動界標定位十五次，從實驗結果顯示，x軸最大的標準差0.27 mm，y軸最大的標準差0.17 mm，z軸最大的標準差0.81 mm，故本系統之界標自動定位相當精確；將定位結果與一位醫師所點的界標點相比較，在八個界標點中最大誤差的距離為4 mm。

Cephalometry utilizes the defined landmarks for measuring the associated distances and angels of craniofacial structure. It is very important in orthodontics and plastic surgery. In the past, two-dimensional postero-anterior view and lateral view of cephalograms are usually used by the doctors to perform the cephalometric analysis. To date, due to the rapid development of dental CT, three dimensional cephalometric analysis becomes an important issue. The major purpose of this study is to develop a three-dimensional landmarking and cephalometric system using the medical image processing technology. Firstly, user needs to manually locate two landmarks (Por and N) for the proposed system to do the image calibration. Then, 51 points are searched and registered to the pre-built generic landmarks model. Afterwards, the best coordinate transformation between the target skull and the generic model is found to set up the boundary conditions or narrow down the searching region. Eight landmarks are then automatically located by the proposed system. The image data set for this study is acquired from the cone-beam CT. The landmarking for one case is repeated in fifteen times. From the experimental results, the standard deviations along the x-axisis, y-axis, and z-axis are less than 0.27 mm, 0.17mm, and 0.81mm, respectively. The landmarking of the proposed system is demonstrated to be very precise. In comparison with the landmarks manually located by an experienced orthodontist for five cases, the maximal distance error of all the landmarks is about 4 mm.

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