摘要
電腦斷層掃瞄(computed tomography scanning)的廣泛被使用，儼然成為放射診斷中的一大利器，尤其在頭部或是腹部的病變上，已大量取代傳統的X光影像，在治療方面影像的利用更加是別種影像技術無法取代的，成為一種不可或缺的放射診斷技術。然而，使用電腦斷層的同時，金屬假影卻可能隨時影響影像的品質，因此，如何減少金屬假影的影響，進而增進電腦斷層影像的可信度，變成了現今的一大問題。本實驗提出一個從影像介面上，去減少金屬假影的矯正法。可以將金屬假影的高CT值(CT number)降低而低CT值提高，以減少金屬假影的對比差異。首先根據金屬假影的線條設定閥值去尋找放射中心，透過放射中心去對整張影像做360度的切割，再計算每個切割後區塊的比重因子，然後對於影像中想要補強的區塊加以圈選，接著利用比重因子分別對每個區塊做補強。在校正影像的選取方面，我們選用一張內部插入一顆直徑4公釐的鋼球Rando假體的頭部影像，以及一張臨床腹部的電腦斷層影像來做修正。並藉由修正的金屬影像討論金屬假影在臨床上的影響。

Abstract
Computed tomography has been used successfully in many clinical imaging applications recently. A major problem with X-ray computed tomography(CT) is metal artifact, distortion or error in the image cause by the metal objects. The artifacts seriously degrade image quality, particularly near the metal surfaces. The purpose of this research is to reduce the effect from metal artifacts via minimizing the contrast of the metal artifacts. We have selected a metal artifact radiation center to divided the image into 360 parts, and calculated the ratio of the mean of the whole image to the part to produce a weighting factor. Correct the parts of the image by weighting factor to lower the high CT numbers of the bright lines and higher the dark lines. We have utilized this method to correct both the Rando phantom and clinical patient CT images and discussed the effect of the metal artifacts.

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