雙能量電腦斷層虛擬肝未含對比劑影像和去金屬假影之影像評估：假體研究

隨著醫療設備的改進，雙管球電腦斷層(dual source computed tomography, DSCT)的雙能量技術可以在單次掃描下同時採用高能量和低能量管電壓進行掃描，經由電腦快速運算後得到兩種不同能量的影像，以及重組後雙能量融合的診斷影像，可以更有效的分辨不同器官組織的衰減特性。在雙能量影像後處理技術中，可從有對比劑增強的影像消除病灶內的碘劑，取得虛擬未含對比劑(virtual unenhanced)影像，如此可使病患減少實際未顯影相的掃描，降低接受到的輻射劑量；另外對於體內有植入金屬材質物質的病患，在進行常規檢查時容易產生金屬假影(metal artifact)而影響附近病灶診斷，可使用虛擬單能譜(monoenergy)影像減少或去除金屬假影的影響，同時減少臨床診斷的不確定性。對此本研究觀察虛擬未含對比劑影像的可行性並評估輻射劑量的降幅程度；並觀察假牙和脊椎內固定最合適的單能譜影像和建議使用的材質物質；並搭配臨床常規的濾波反投影法(FBP)和疊代法(IR)之選擇。去除碘劑方面：將模擬二種體型並同時內嵌有不同類型的含碘及未含碘模擬病灶之雙能量假體，經由動脈相雙能量掃描後進行虛擬影像的重組，觀察虛擬影像的可行性，並於Rando假體內填入熱發光劑量計評估肝三相檢查的輻射劑量；去除金屬假影方面：在Rando假體下顎齒列附近分次填放五種臨床常用的假牙材質物質，以及於模擬二種體型的腹部假體內之模擬脊柱中分次填放不鏽鋼或鈦金屬，分別使用頭部和脊椎雙能量掃描後重組單能譜影像。經由客觀性的分析結果，雙能量動脈相產生之虛擬未含對比劑影像，亦會對未含對比劑的器官或病灶有減贅上的影響，因此仍無法取代常規無對比劑增強影像，若未包含實際未顯影相掃描時劑量降幅達24%；虛擬單能譜影像對於假牙或脊椎內固定材質造成之金屬假影能夠有效的去除，使得影像整體價值提高；在影像重建方法方面建議使用IR方法。

關鍵字

雙管球電腦斷層；雙能量；虛擬未含對比劑；單能譜；金屬假影

並列摘要

With the improvement of medical equipment. Dual-source computed tomography (DSCT) operate by two x-ray tubes with low and high kilovoltage settings at same time, which allows for dual-energy CT (DECT) scanning. This technology can be utilized for tissue characterization based on dual energy image sets. DECT allows the generation of virtual unenhanced images by subtracting iodine from contrast enhanced images which can replacing the true non-contrast scan to reduce the radiation dose. In addition, patients with metallic implants, the detectability of lesions near the implants may affect by the metal artifact. DECT also allows the generation of monoenergetic images to reduce metal artifact. In this study was to assess the feasibility of virtual non-contrast images and to evaluate the potential dose reduction by omitting true non-contrast scan. And to investigate the optimal monoenergy strategy for fixed prosthesis and spinal implants respectively. Moreover, comparing between FBP and IR images to analysis image quality. In the part of virtual unenhanced images, dual energy phantom which contains different kinds of simulation lesions was scanned by arterial protocol. The Rando phantom which was placed TLD inside was scanned by the protocol of liver three phase examination that can obtain the effective dose of liver examination. In the part of reduce metal artifact, Rando phantom and abdomen phantom was placed metallic implants of fix prosthesis and spinal, respectively. Then scanned by the head and spine protocol separately. the dual energy images were loaded into the post-processing software to produce monochromatic images. Based on the result of objective analysis. Virtual non-contrast images cannot represent true non-contrast images, because of limitations in some material subtraction. Dose reduction achieved by omitting the true non-contrast acquisition is 24%. Monoenergetic application can reduce metal artifact and using the optimal keV setting for each implants can improving image quality. The image reconstruction method applied IR images.

並列關鍵字

dual-source CT ； dual energy ； virtual unenhanced ； monoenergy ； metal artifact

參考文獻

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雙能量電腦斷層虛擬肝未含對比劑影像和去金屬假影之影像評估：假體研究

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