牙科立體影像模擬重建技術之探討

The Simulation Study of Reconstruction Techniques for Three-dimensional Dental Image

張惠茹(Huei-Ru Chang)

指導教授 ： 蘇振隆

中原大學/工學院/生物醫學工程研究所/碩士(2016年)

https://doi.org/10.6840/cycu201600931

摘要

影像重建技術應用，在醫學上從電腦斷層攝影(computed tomography, CT)開始發展並應用至MRI、PET等方面上。在掃描器部分，已發展到多切片CT掃描器，但射源仍是以扇形射束為主。現今科技蓬勃發展，出現了專為口腔頭頸部設計的錐束電腦斷層攝影(cone beam computed tomography, CBCT)為近年來逐漸普遍用於牙科的立體放射影像技術，重建法之誤差可能影響及診斷。本研究主要目的透過Shepp-Logan假體以及牙科常見病例建立兩種實驗虛擬假體，再以在扇形射束演算法進行影像模擬及了解其誤差。
本研究主要分為：實驗假體建立、投影之模擬、不同方式之影像重建及建構立體影像。透過實驗建立Shepp-Logan假體，並設定不同之投影條件，而獲得128張投影數據，而透過反投影法、濾波反投影、二維傅立葉轉換及FDK分別進行影像重建，立體影像部分，則是用影像堆疊方式建構出三維影像，最後比較重建之結果與實驗假體之差異來進行重建法之分析。在差異分析與評估的部分，使用均方根誤差(RMSE)、結構相似度指數(SSIM)並探討其可行性。
從重建後之影像結果得知，明顯看出反投影法效果最差；濾波反投影跟FDK之重建結果比較接近原始影像，其中以FDK更能顯示假體內部影像之細節；濾波反投影使用兩種濾波器進行重建，發現高通濾波器比低通濾波器效果較好。利用4張原始切面影像進行評估，從結果得知影像複雜度越高、所花費的時間較多、其重建後之影像品質越低，其影像結構相似度也就越低。
本研究已初步完成CBCT演算法之分析探討。其結果可以提供未來選用CBCT演算法之參考。

關鍵字

Shepp-Logan Phantom ； 電腦斷層掃描 ； 牙科CT ； 扇形射束 ； FDK ； 影像重建

並列摘要

Image reconstruction technique in medicine began to develop and to apply the terms of MRI, PET, etc. from the computer tomography (computed tomography, CT). In the scanner, it has been developed to multi-slice CT scanner, but still based on the fan beam radiation source.
Technology is booming, there has been designed specifically for oral head and neck on Cone - beam computed tomography (cone beam computed tomography, CBCT) imaging technology for the stereotactic radiosurgery become increasingly common in recent years for dentistry, the error of reconstruction method that may affect the diagnosis.
The main purpose of this study, create two virtual experiments prosthesis through Shepp-Logan prosthesis and dental prosthesis of common case, then the fan beam algorithm for image simulation and understand their errors.
This study is mainly divided into: Establish experimental prosthesis, the simulation projection, in different ways of image reconstruction and construction of three-dimensional images.
Through experiments establish Shepp-Logan prosthesis, and set different conditions of the projection, the projection data is obtained 128, and through the back projection method, the filtered back projection, the two-dimensional Fourier transform and FDK for image reconstruction respectively. Finally, the difference with the results of image reconstruction and the difference between the experimental prosthesis into analyze reconstruction method.
In Part variance analysis and evaluation, using the root mean square error (RMSE) and structural similarity index (SSIM) into explore its feasibility.
Results from the Image after the reconstruction informed, it is clear that back-projection method is the worst, filtered back projection reconstruction results with the FDK close to the original image, which FDK more details of the interior of the prosthesis image display. Filtered back projection reconstruction using two kinds of filters, effect of the high pass filter found better than the low-pass filter.
In this study, use four original slice images to evaluate. From the results that higher the extent of complexity of the image, it takes more time, the lower the image quality of image reconstruction, and structural similarity of image is also lower.
This study is a preliminary analysis of algorithms CBCT complete discussion. As a result, the choice of the future can provide the reference CBCT algorithms.

並列關鍵字

CT ； Dental CT:Image Reconstruction ； Shepp-Logan Phantom ； FDK ； Fanbeam.

參考文獻

[10] 蔡迪姍、黃耀德、章浩宏、李伯訓、陳木熊，《錐束電腦斷層在阻生齒治療上的優勢》，台灣醫學 2012 年 16 卷 6 期，第 587-593頁。

[15] 吳鴻謙、史天元、劉榮寬，《以小波理論進行影像壓縮之三種實現比較》，航測及遙測學刊 第十卷 第三期 第305-314頁，2005。

[2] L. A. Shepp and B. F. Logan, "The Fourier Reconstruction of a head section", IEEE Transactions on Nuclear Science, vol. NS-21, pp. 21-43, 1974.

[8] Gengsheng Lawrence Zeng , Medical Image Reconstruction, Springer, NY, 2009.

[9] Avinash C.Kak and Malcolm Slaney, Principles of Computerized Tomographic Imaging, published by IEEE Press. 1998, NY.