小兒低劑量全脊椎攝影影像處理之研究

Study of Image Processing for Low Dose Whole-Spine Examination in Pediatric

龔永權(Yung-Chuan Kung)

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(2018年)

https://doi.org/10.6840/cycu201800055

摘要

脊椎側彎，顧名思義就是脊椎構造不對稱，形成向側面彎曲的現象。好發於青少年，主要診斷方式為身體理學檢查或影像檢查。影像檢查以全脊椎X光攝影檢查為主，對於需長期追蹤接受輻射曝露檢查的青少年而言，會擔心接受輻射劑量的多寡。本研究之目的，尋找較佳之曝露參數及影像處理模式，在合理抑低的原則下，有效的降低輻射劑量。
本研究利用小兒類人形假體依臨床現行條件為基礎下，來建立調降條件參數，調降與輻射劑量影響關係較大之mAs為主。並輔以影像處理技術(含Log值轉換、直方圖等化、中值濾波器等技術)優化影像以提升影像品質，現行條件約為75kVp、25mAs，研究以不同攝影曝露參數及儘可能最低的情況下且不影響醫師診斷，所建立之條件約可降至70kVp、10mAs。以所建立之調降條件參數，實際運用於70位臨床病人攝影檢查來獲得X光影像。評估方面，除了比較其調降輻射劑量外，並藉由歐盟出版之小兒放射診斷影像品質評估準則之影像品質分數(IQS)及主觀特徵評估(VGA)進行定性評估及定量評估之工作，再加上比較影像處理前後之訊雜比，以瞭解本研究之實用性。
研究結果顯示，於調降條件前、後在脊椎側彎角度量測方面並無明顯差異。假體在不同曝露參數模式下及調降參數至儘可能最低的情況下，處理後之影像與原始影像比較，整體平均對比訊雜比提升分別約20.5%及11%，影像優值於處理前後最大差異百分比分別達49.38%及32.20%。實驗所建立之攝影參數及影像處理模型，應用於假體及臨床病人，所得到之影像與原始影像比較，結果顯示影像品質評估皆無統計上明顯差異。定量評估方面所有調降條件之影像整體平均對比訊雜比值及整體平均優值皆比現行條件之影像優值來的高。輻射劑量方面調降條件後劑量由0.303mSv降為0.201mSv，整體輻射曝露劑量減少33.66%。
由結果顯示本研究經由調降攝影條件參數及影像處理優化後之影像，並不會影響臨床醫師診斷，且能夠降低病人所接受到的輻射曝露劑量及輻射風險。研究結果所得之曝露參數及影像處理技術加以整合後，應可以運用於臨床檢查使用，未來影像處理的系統如能更成熟應用及整合，輻射曝露劑量的下降幅度空間應該可以在更大。

關鍵字

全脊椎攝影 ； 輻射劑量 ； 影像處理 ； 影像品質

並列摘要

Scoliosis usually occurs in young people, and is defined as the asymmetry of spine structure, and consisting of a lateral curvature. Physical examination and radiographic examination are the two current medical methods for diagnosing of scoliosis. As for the radiographic examination, whole spine radiography is usually performed. Scoliosis patients of young age may need long-term follow-up by the whole spine radiography during their treatment periods, and radiation doses coming from the repeated studies will be the concern. In this study, we provide suitable exposure techniques and image processing algorithms to further reduce the radiation dose as low as reasonably achievable without compromising clinical diagnosis.
The study was aimed to expose the pediatric anthropomorphic phantom with current routine clinical protocols first (75 kVp, 25 mAs), and then progressively reduced the exposure parameters (mainly mAs) to the lowest to acquire X-ray images. After acquiring images with lower dose, image processing algorithms including log transformation, histogram equalization, and median filter were performed to further improve image quality. From this investigation, we modifying the exposure parameters and reducing the exposures parameters, and found that the lowest possible dose without compromising image interpretation is 70 kVp and 10 mAs. We further served as this exposure parameter as the basis to perform the whole spine radiographic examinations on 70 patients. Comparisons of radiation dose, image quality score (IQS), visual grading analysis (VGA) were performed before (routine protocol) and after exposure parameter modifications. In addition, comparisons of contrast-to-noise ratios (CNRs) and figure of merits (FOMs) for the images before and after applying image processing were also performed to investigate the feasibility of this study.
The results showed that there were no significant difference of the spinal angulation measurements between the images acquired using exposure parameters before and after modification. For the assessments of the feasibility of applying image processing algorithms on the lower dose images, CNRs were increased as compared to the images without image processing (20.5% and 11% increased for modifying exposure parameters and reducing the dose to the lowest, respectively). And FOMs were also increased after image processing as compared to the images without image processing (maximum of 49.38% and 32.20% increased for modifying exposure parameters and reducing the dose to the lowest, respectively). There was no significant difference of the qualitative image quality with image processing between the images acquired using exposure techniques before and after modifications for both phantom and patients. For qualitative evaluation, both CNR and FOM were higher for the image acquired using exposure techniques after modification. As for the radiation dose investigations, averaged effective dose was significantly reduced from 0.303 mSv to 0.201 mSv, with the reduction of 33.66 % of the dose of the current protocol.
In conclusion, exposure doses for the whole spine radiography can be reduced without compromising clinical diagnosis when reducing exposure parameters and applying suitable image processing algorithms. If image processing algorithms develop further well and integrate well into clinical applications, radiation dose may be further reduced in the future.

並列關鍵字

whole spine radiography ； radiation dose ； image processing ； image quality

參考文獻

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