Automatic Tube Current Modulation versus Fixed Tube Current in Multi-detector Row Computed Tomography of Liver: Comparison of Image Quality and Radiation Dose

自動管電流調整與固定管電流多排層偵檢器電腦斷層肝臟攝影：影像品質及輻射劑量之比較

蘇仁沛(Jen-Pai Su) ； 趙垂勳(Twei-Shiun Jaw) ； 陳巧雲(Chiao-Yun Chen) ； 郭禹廷(Yu-Ting Kuo) ； 謝賜吉(Tsyh-Jyi Hsieh) ； 李淑惠(Shu-Huei Lee) ； 林倩仲(Chien-Chung Lin)

《中華放射線醫學雜誌》 35卷3期 (2010/09) Pp. 131-142

摘要

為比較使用自動管電流調整(ACTM)或固定管電流技術在多排層電腦斷層攝影(CT)之肝臟及CT血管攝影(CTA)的影像品質、診斷接受度及輻射劑量。我們對182位臨床轉介來評估肝腫瘤之病患依檢查時期分成四組：(1)100kVp,固定管電流350mA，(2)100kVp ACTM，(3)120kVp固定管電流350mA，(4)120 kVp ATCM，施行肝臟雙相顯影CT檢查，並記錄其身高、體重、及身體質量指數(BMI)。利用訊雜比(SNR)和對比雜訊比(CNR)來量化評估肝臟CT及CTA之影像品質。以肝臟CT橫切面影像及利用電腦後處理組成的3D CTA，由兩位不知攝影條件之腹部影像次專科醫師，採四分計點法分別評定影像品質。病人的有效劑量則採用累積劑量長度乘積值(DLP)來計算。結果顯示，ACTM組於未施打對比劑掃描平均管電流較固定管電流組減少22.7%，於動、靜脈相平均管電流在100 kVp組分別減少8.6%與8.7%，在120 kVp組皆減少44.2%。而平均有效劑量ATCM組在100 kVp或120 kVp相對於固定管電流組可分別降低6.2%及35.9%。各組之影像品質的各種量化指標基本上無統計學上有意義之差異。在100 kVp與120 kVp ATCM組其平均管電流與BMI或體重皆呈正相關。至於肝臟CT及CTA影像品質評分，四組間並無統計學上之差異，而兩位放射科專科醫師間亦無統計學差異。本研究顯示利用自動管電流調整技術能有效地降低肝臟CT檢查之輻射劑量而維持良好的肝臟CT及CTA之影像品質。

並列摘要

The purpose of this study was to compare the image quality, diagnostic acceptability, and radiation exposure between z-axis automatic tube current modulation (ATCM) and fixed tube current techniques in multi-detector row computed tomography (CT) of liver. One hundred and eighty-two patients referred for performing dual-phase contrast-enhanced CT examination to assess liver tumors were divided, according to the study periods, into four groups based on different scanning parameters: (1) 100 kVp, fixed current (350 mA); (2) 100 kVp, ATCM; (3) 120 kVp, fixed current (350 mA); (4) 120 kVp, ATCM. Patient medical records of body height, body weight and body mass index (BMI) were obtained. We used signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) to quantitatively evaluate the quality of hepatic CT images and CT angiography. Radiation dose measurements were generated automatically by the CT unit with calculation of dose-length products (DLP). The axial CT images and post-processing 3D CT angiographic images were reviewed by two subspecialist radiologists who were blinded to the CT parameters. They ranked subjective image quality using a four-point quality rating independently. Data were analyzed with statistical tests. The results showed that the averaged tube current of unenhanced images in the ATCM groups was 22.7% lower than in the fixed tube current groups. As compared with fixed tube current groups, the ATCM groups decreased 8.6% and 8.7% at 100 kVp, and 44.2% at 120 kVp on arterial and venous phases respectively. The mean effective dose of the ATCM group was lower than in the fixed tube current group by 6.2% and 35.9% at 100 kVp and 120 kVp respectively. There was basically no significant difference in the quantitatively assessment of CT and CTA image quality between the ATCM and fixed tube current groups. Both 100 kVp and 120 kVp ATCM groups showed positive correlation coefficients between the tube current and BMI or body weight (100 kVp, r=0.663, 0.724; and 120 kVp, r=0.792, 0.789 respectively). In the image quality indices of hepatic CT and CTA, no significant difference existed among the four groups or between the two radiologists. In conclusion, by using ATCM, the radiation exposure and effective radiation dose of dynamic contrast-enhanced multi-detector row CT of the liver could be effectively reduced with maintenance of the image quality.