Metal Artefact Reduction for Orthopaedic Devices Using Monoenergetic Extrapolation from Dual-energy Computed Tomography
JCY Lee, CK Shiu, KC Lai, MK Chan
Hong Kong J Radiol 2017;20:34-40
DOI: 10.12809/hkjr1716423
Objectives: To assess the diagnostic performance and clinical efficacy of metal artefact reduction using monoenergetic imaging with dual-energy computed tomography (DECT).
Materials: A total of 30 patients with 32 metal device regions were examined using the DECT protocol with 100 kVp and 140 kVp spectra. Specific post-processing software was used to generate optimised monoenergetic images and standard combined images by filtered back projection. Two independent observers subjectively graded the degree of artefact and diagnostic quality of the two sets of images on a five-point rating scale. The beam-hardening artefact (mean density of the most pronounced streak 1 cm from the device) was compared between both groups. Qualitative assessment by type of device (internal or external device) was performed.
Results: A total of 32 examinations with 19 internal, 10 external, and 3 internal + external implanted metal devices were performed. Monoenergetic imaging was rated superior for artefact reduction in 75% cases and for diagnostic quality in 78% cases, compared with standard combined imaging by filtered back projection (p < 0.001). The mean density of beam hardening artefacts improved from -725.22 HU in standard combined imaging to -519.02 HU using monoenergetic imaging (p = 0.025). The presence of an external metal device adversely affected the artefact reduction performance of monoenergetic imaging (p = 0.045), without significantly affecting diagnostic quality.
Conclusion: Monoenergetic extrapolation using DECT can significantly reduce metal artefact and improve diagnostic quality compared with filtered back projection. Its performance was adversely affected by the presence of an external device.
Authors’ affiliation:
JCY Lee, CK Shiu, KC Lai, MK Chan: Department of Radiology and Imaging, Queen Elizabeth Hospital, Jordan, Hong Kong
中文摘要
使用單能量外推法在雙能量電腦斷層掃描時減少骨科矯形裝置的金屬物偽影
李俊賢、蕭俊傑、黎國忠、陳文光
目的：評估使用雙能量電腦斷層掃描（DECT）的單能量成像來減少金屬物偽影的診斷性能和臨床效果。
材料：30名裝上32個金屬裝置的患者接受100 kVp和140 kVp光譜的DECT檢查。使用特別後處理軟件來濾波反投影並產生優化單能量成像和標準組合圖像。兩個獨立的觀察者用五點評分量表去比較這兩組圖像的診斷質量和金屬物偽影程度，包括束硬化偽影（距離裝置1cm的最明顯條紋的平均密度）。根據內部矯形裝置或外部矯形裝置進行了定性評估。
結果：共32次檢查包括19個內部、10個外部和3個內部+外部金屬植入物。與濾波反投影標準組合成像相比，75﹪單能量成像被評定為較能減少偽影，而78%單能量成像被評定為有較佳診斷質量（p < 0.001）。束硬化偽影的平均密度從標準組合成像中的-725.22HU改善至單能量成像中的-519.02HU（p = 0.025）。外部金屬裝置的存在不利於單能量成像偽影的減少（p = 0.045），但不顯著影響診斷。
結論：與濾波反投影相比，使用DECT的單能外推法可顯著減少金屬偽影並提高診斷質量，但其性能會受到外部金屬裝置的不利影響。