體厚變化對線型及扇型雙能量X光吸收儀骨質密度結果之影響

Simulated increases body fat with phantom in bone mineral density measurements by fan /pencil beam DXA

洪凱羿(Kai-Yi Hung)

指導教授 ： 邵佳和

中山醫學大學/醫學科技學院/生物醫學科學學系碩士班/碩士(2016年)

摘要

研究目的：
在過去的其他研究中，發現在體厚變化下使用雙能X線吸收儀(dual-energy X-ray absorptiometry, DXA)測量的骨質密度（bone mineral density, BMD）會產生影響，但過去其他研究中的受試者都是成年人，並沒有進一步討論對幼兒的影響。然而，幼兒的受試者會有施行上的醫學倫理考量，因此我們使用幼兒假體來避免上述的困難。本研究希望觀察使用幼兒及成人假體實施腰椎骨密檢查時，偵測區域厚度變化及不同機組下是否影響BMD的準確性。
材料及方法：
本研究利用bolus模擬體厚，將未加bolus的BMD當作基準值，之後每層增加0.5cm掃描4次取平均值，來觀察體厚的變化對線型和扇型DXA兩種機型及5歲、10歲和成人假體兩種假體的差異，並使用最小顯著差異(least significant change, LSC)來觀察受到體厚變化的BMD影響程度。同時利用熱發光劑量計(thermal-luminescent dosimeter , TLD) 置入3種假體內觀察兩種機型下的器官劑量及有效劑量是否有所差異。

結果：
線型和扇型DXA於5歲假體的BMD與體厚變化其R平方值分別是0.8554和0.1535，10歲假體其R平方值分別是0.2543和0.6341，而成人假體的R平方值則分別是0.9596和0.9641。在劑量方面，線型和扇型DXA測量5歲假體的全身有效劑量為14.79和26.23μSv，10歲假體是6.94和14.89μSv，而成人假體則是6.12和45.97μSv。
結論：
體厚變化對兩種機型測量的BMD都有產生影響，但線型DXA比起扇形DXA受到的影響程度比較小。在劑量方面，兩種機型實施四次DXA檢測的劑量仍小於自然背景輻射，但扇型DXA比起線型DXA具有較高的全身有效劑量。

關鍵字

雙能量X光吸收儀 ； 骨質密度 ； 線型射束 ； 扇型射束

並列摘要

Purpose
In the past other studies we found changes in body thickness will have an impact to bone mineral density (BMD) measurement by dual-energy X-ray absorptiometry (DXA). But those studies subjects are all older adult, the effect of body thickness in child still not clear.
Materials and Methods
This study we simulated body fat by bolus to observe the effect of fat layering on BMD measurements in 5 y/o , 10 y/o and adult phantom by fan and pencil beam DXA. Also we measured effective dose by Thermolummescent detectors (TLD) to observe the different of fan and pencil beam DXA.
Results
In pencil beam DXA, associations between body fat thickness and BMD is 0.8554(5y/o) , 0.2543(10y/o) and 0.9596(adult). In fan beam DXA, associations between body fat thickness and BMD is 0.1535 (5y/o) , 0.6341 (10y/o) and 0.9641 (adult). The fan beam DXA BMD measurement effective dose were higher than pencil beam(effective dose: 26.23vs14.79μSv(5y/o) , 14.89 vs 6.93 μSv(10y/o) and 45.97 vs 6.12(adult)).
Conclusion
Pencil and fan beam DXA BMD measurement both affected by body thickness change. Pencil beam DXA had smaller effect by body thickness change in both phantom. Effective dose from pencil and fan beam DXA can not separate from natural background radiation, but fan beam had higher effective dose than pencil beam.

並列關鍵字

DXA ； BMD ； pencil beam ； fan beam

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