牙科電腦斷層對植牙前骨質密度之評估

在植牙方面，牙科電腦斷層(dental computed tomography; dental CT)已逐漸取代傳統電腦斷層，但在植牙時會依據牙槽骨之骨密度評估植牙的成功率。牙科電腦斷層屬於錐形電腦斷層系統(cone-beam computed tomography; CBCT)，可取得組織之間密度變化，但錐形電腦斷層影像的HU值並不等於物理密度，且CBCT會有影像週圍密度失真的問題發生。本研究旨在使用牙科電腦斷層影像，將影像後處理，取得病人牙槽骨之骨密度。　　本研究使用iCAT掃描水假體，使用MATLAB R2008a計算每個像素的加權值，再分析整體分佈，得到加權中心點與加權公式。利用中心點與公式模擬出CBCT的加權圖，透過Gammex 467假體取得各介質密度的HU，與物理密度做迴歸分析。　　研究結果顯示，加權值分析中心點為(85.4, 74.4) ，公式為y=5.449*10^-5*x^2-9.099*10^-7*x+0.903。校準結果可將影像均勻度提升，並且可將影像邊緣密度失真校準回來，此方法適用於各種不同的矩陣，可處理dental CT不同矩陣的影像。物理密度與HU關聯公式依不同的FOV影響而得到兩組公式，分別為密度 = 1409.5 × HU − 1724.8及密度 = 1856.3 × HU − 2150。

關鍵字

骨密度； HU(hounsfield unit) ；牙科電腦斷層

並列摘要

In the dental implant, the dental computed tomography (CT) has gradually replaced the traditional CT. The alveolar bone density is so important when the dentist assesses the success rate of implants. Dental CT belongs to cone beam computed tomography (CBCT) system which can achieves the density changes between tissue, but the HU shown in the CBCT does not mean the electron density. Sometimes the image distortion will be the problem. This study aims to use the post-processing technique of dental CT images to get the bone mineral density of alveolar bone. Water phantom was scanned by the iCAT dental CT. Then, using MATLAB R2008a to calculate the weighting factor for each pixel in the image, and analyzing the overall distribution to obtain the weighted center and weighted factor formula. Then, the weighted formula was applied to the image of Gammex 467 phantom in the CBCT system, and obtained the relationship between density and CT number. In this study, the weighted value of the center was (85.4, 74.4), and the formula was y=5.449*10^-5*x^2-9.099*10^-7*x+0.903. Calibration results can improve the image uniformity and the image distortion can be calibrated. This method was suitable for a variety of matrices, which can handle dental CT images of different matrix. According to the physical density and the HU regression formula by the different FOV influence, there showed two formulas: Density=1409.5× HU − 1724.8; Density= 1856.3 × HU − 2150.

並列關鍵字

HU(hounsfield unit) ； bone density ； cone beam computed tomography (CBCT)

參考文獻

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牙科電腦斷層對植牙前骨質密度之評估

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