減少臨床電腦斷層假牙假影之最佳方式探討

背景與目的現今放射線診斷盛行，不論是急診或門診病患皆時常需要接受放射線診斷，電腦斷層檢查便是其一，如今電腦斷層攝影檢查儀器已進展至雙能量掃描模式，然後並非每家醫院皆能提高經費更新儀器，因此此研究之目的是針對一般螺旋式電腦斷層掃描儀器之金屬假影做探討，利用自製水假體並搭配鋁金屬條做掃描，研究中更改掃描參數及影像重建後處理方式來找出降低金屬物品所造成假影的最佳方法。方法與材料在掃描參數中固定 FOV 及 rotation time，以原廠設定之機器掃描參數下去做調整，原廠設定之頭部掃描參數為 120kVp 和 180mAs，再分別固定 kVp 調整 mAs 以及調整 kVp 固定 mAs，kVp 使用三個數值分別為 100、120、135;mAs 使用三個數值分別為 200、250、300。 IX 結果使用較高的 kVp 降低圖像對比度可以減少假影，當 kVp 值固定而增加 mAs 時，影像假影相對減少，但調高兩項掃描參數皆會造成病人劑量提高。討論研究發現調整掃描參數之影響不大，雖然肉眼可看見細微差異，但假影指標數值(Artifact Index value)顯示差距不大，要降低金屬假影最原始也最好的方式便是檢查之前就將金屬物品移除，此些調整參數與重建後處理方法僅能些微減少假影對影像的影響，但相對的代價是病人劑量提高。

關鍵字

電腦斷層；金屬假影；假體

並列摘要

Background and Purpose Today's radiological diagnosis is prevalent. Whether it is emergency or outpatients, radiological diagnosis is often needed. Computed tomography is one of them. Nowadays, computed tomography instruments have progressed to dual-energy scanning mode, but not every hospital can raise funds updated, so this study was to investigate the metal artifacts of the general spiral in computed tomography instrument. The self-made water phantom was used with the aluminum metal strip for scanning. In the study, the scan parameters were changed and the image reconstruction method was used to find out the best way on reduction artifacts. Method and Material We fixed the FOV and rotation time in the scan parameters, and adjust the scan parameters set by the factory. The original scan parameters are 120kvp and 180mAs, then fix kVp to adjust mAs and adjust kVp fixed mAs respectively. The kVp values are 100, 120, and 135 respectively; the mAs use five values of 200, 250 and 300 respectively. Result We found that when the kVp value is fixed and the mAs is increased, the image artifact is relatively reduced, but the patient dose is relatively increased. Discussion The study found that adjust of scan parameters have little effect. The best way to reduce the metal artifacts is to remove the metal objects before the scanning. These adjustments and reconstruction methods can only slightly reduce the effect of artifacts on the image.