本研究目的在建立具有三軸頭顱位置監測裝置之電腦系統以自動化正面測顱片界標定位，減低病患拍攝測顱片時因頭顱旋轉所造成的投影誤差。首先應用霍氏轉換與直線擬合方法，從描軌圖影像擷取具代表性的頭顱形態特徵參數，應用模糊分類法將描軌圖依據特徵參數進行分類，分別將各類描軌圖影像透過最小平方誤差法加以疊印，建立頭顱樣板與統計出包含界標點的區域範圍；其次，測顱片透過影像強化與霍氏轉換擷取與描軌圖樣板相同的特徵參數，可以找出最相似的樣板，接著應用形態特徵參數與影像處理技術可以獲得測顱片的界標位置。在三軸頭顱位置監測裝置部份，利用雙軸加速度計與電子羅盤以即時量測頭顱旋轉角度，藉由Zigbee無線傳輸技術，讓齒顎矯正醫生得以將頭顱旋轉角度變化作為參考。本研究中，對一百三十張描軌圖進行分類，共分成八類，每類包含十張以上的描軌圖，其界標點座標分布的標準差在4 mm以下；在界標定位結果上，對二十二位病患的測顱片作處理，比較本系統和人工定位數據之間的誤差情形，整體而言，本系統定位的平均誤差小於4 mm；在三軸頭顱位置監測系統的部份，由實驗可得知在拍攝過程中頭顱旋轉約-2到3度左右，醫師可以依據此裝置所量測出的頭顱旋轉角度以矯正拍攝時的誤差。

In this study, the computerized system with a 3D head position monitoring device for automated landmarking of PA cephalogram is developed to reduce the projection error caused by head rotation. Firstly, the morphological feature parameters for craniofacial structure are obtained from the tracing images using Hough transform and linear regression. Then based on these parameters, the tracings are clustered using fuzzy c-means. For each class, the template and the ranges of landmarks distribution are computed from the superimposed tracings with least-square-error method. Secondly, the image enhancement and Hough transform are applied to cephalogram for obtaining the corresponding morphological features parameters. A template with the shortest distance is found and overlapped for landmarking. Through the morphological information and image processing technique, the actual positions of landmark are located. For the 3D head position monitoring device, a two-axis digital accelerometer and a digital compass are integrated to monitor the head position in real time. Via the Zigbee wireless module, the angle information is obtained for the orthodontist’s reference. In this study, a data set of 130 tracings is acquired and clustered into eight classes. Each class contains more than ten tracings. For the same class, the landmark distributions are all within 4 mm. Twenty two cephalograms are tested for evaluating the performance of proposed system. In comparison with the manual measurements, the average error of the automated landmarking system is less than 4 mm. For the head position measurement, the range of head rotation is from -2 to 3 degree during radiography. The orthodontist can measure the angles of head rotation to reduce the error of cephalometric radiography.

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