64 切多層切面電腦斷層掃描螢幕顯示值與掃描照野劑量探討

The Correlation between Dose Report and SFOV on 64-slice Computed Tomography

丁雲龍(Yung-Long Ting) ； 李美容(Mei-Jung Li) ； 宋成龍(Thomas C. Soong)

《北市醫放雜誌》 3卷1期 (2013/12) Pp. 7-12

https://doi.org/10.6663/TPART.2013.3.1.7

摘要

多層切面電腦斷層(Multi-slice computed tomography, MSCT)至今多年，螢幕顯示值是很重要的劑量參考依據。臨床上使用參數設定（Protocol）與螢幕顯示劑量報告（Dose report）來控制病人受檢輻射劑量。螢幕顯示值隨著掃描照野(Scan field of view, SFOV)參數設定改變呈現出的劑量會有所不同。成人與小孩掃描參數設定劑量差異甚大。本研究的目的是使用不同的掃描照野與劑量間的相關性。本研究使用螺旋式64 切MSCT，利用電腦斷層頭部、軀幹劑量假體以筆型游離腔分別進行成人腹部、頭部參數設定與小孩腹部、頭部參數設定，評估量實測值和螢幕顯示值。結果顯示螢幕顯示值會隨著掃描照野不同而變化。使用成人腹部參數設定，用大掃描照野(Large body)改變為小孩掃描照野(Ped body)時，電腦斷層劑量指標(Volume computed tomography index, CTDI_(vol))預期值減少16 %、實測值減少64 %；用Large body 改變為成人頭部掃描照野(Adult head)時，CTDI_(vol) 預期值增加120 %、實測值沒有增加；用Large body 改變為小孩頭部掃描照野(Ped head)時；CTDI_(vol) 預期值減少15 %、實測值減少64 %；用小孩掃描照野(Ped body)改變為Adult head 時，CTDI_(vol) 預期值沒有增加、實測值減少0.6 %；用Ped body 改變為Large body 時，CTDI_(vol) 預期值減少50 %、實測值減少2 %。因此臨床執行檢查時應注意掃描照野，避免將成人掃描照野用於小孩掃描照野則劑量與螢幕顯示值劑量會比預期來得高。

關鍵字

多層切面電腦斷層 ； 劑量報告 ； 掃描照野

並列摘要

Up to now, MSCT (multiple -slice computed tomography) has been a valued imaging modality in clinical routine. The dose report was used to study the influence of technical parameters on radiation dose. In clinical routine, CT dosimetry will depend strongly on scan protocols. Protocols would be taken into account on disease (clinical question), size, weight, and age. Dose report changed with SFOV (scan field of view). There was a much different from adult protocols and pediatric protocols. Our aim was explore the correlation between different SFOVs and dose report. The phantoms of 16 and 32cm diameters were used to simulate head and abdominal scans for pediatric and adult, respectively with seven different SFOVs, including large, medium, small, head, body, small head, pediatric head. In addition, the pencil ionization chamber was used to measure radiation dose. We would compare radiation dose from the pencil ionization chamber with from dose report. The results showed dose repot changed with different SFOVs. Also, SFOVs were related to software on the CT scanner. The radiation dose of head and abdominal scans for pediatric and adult from the phantoms of the diameter of 16 and 32 cm were changed with different SFOVs. We found the radiation dose from either dose report and the pencil ionization chamber would be higher than expected values when SFOV for adult was applied to the SFOV for pediatric. When setting protocols for pediatric and adult, we should pay attention to the choices of SFOV.

並列關鍵字

multi-slice computed tomography ； dose report ； scan field of view