低管电压结合迭代重建腹部CT低剂量扫描的体模研究

摘要

目的:评价低管电压结合适应性统计迭代重建(ASIR)对腹部体模低剂量扫描图像质量的影响,探讨适合临床应用的腹部低剂量扫描方案.方法:采用100 kVp、120 kVp分别对体模进行重复扫描,应用自动管电流调节(ATCM)技术,100 kVp扫描时预设噪声指数(NI)分别为11、12、13、14、15、16、17、18、19、20,每组图像均进行30％、50％、70％、90％ ASIR重建.120 kVp组为常规剂量组,扫描时预设NI为11,30％ ASIR重建,测量不同扫描条件下肝脏、脊柱的CT值、客观噪声,并计算信噪比(SNR),记录不同扫描条件下的CT容积剂量指数(CTDIvol).由两位高年资医师采用盲法对所有序列图像进行主观评价.结果:100 kVp条件下,随着NI增大,CTDIvol明显下降;同一NI条件下随着ASIR比例增加,图像噪声减少,SNR增加;NI≥17时图像质量下降,无法满足临床诊断要求;NI=15、70％ ASIR组图像噪声、SNR与120 kVp常规组差异无统计学意义(P＞o.05),主观评分相当,但辐射剂量较常规组下降43.8％.NI=15、90％ ASIR组及NI=16、90％ASIR组的图像噪声及信噪比优于常规组(P＜0.05),但图像质量主观评分下降.结论:低管电压结合ASIR可以在降低辐射剂量的同时保证图像质量满足临床诊断要求.辐射剂量明显降低时,需要增加ASIR在图像重建中的权重.%Objective:To evaluate the influence of the image quality of low-dose abdominal CT scanning,a phantom was used,and low tube voltage in combination with adaptive statistical iterative reconstruction (ASIR) technique was adapted,in order to investigate the clinical applicable protocol for low-dose abdominal CT scanning.Methods:An abdominal phantom was scanned repeatedly with tube voltage as 100kVp and 120kVp,respectively.Automatic tube current modulation (ATCM) technique was used.For 100kVp groups,the noise index (NI) was set at 11,12,13,14,15,16,17,18,19 and 20;images were reconstructed with 30 ％ ASIR,50 ％ ASIR,70 ％ ASIR and 90 ％ ASIR,respectively.For the 120kVp group (routine standard dose group),NI was set as 11 and images were reconstructed with 30％ ASIR.Of the groups using different scanning techniques,the CT value and objective noise level of liver and vertebra were measured,the signal to noise ratio (SNR) was calculated,and the computcd tomography dose index volumes (CTDIvol) was recorded.Subjective image score was evaluated by two senior radiologists.Results:AT 100kVp,the CTDIvol decreased significantly with increase of NI.While,with the same N1,as the increase of ASIR,there was reduce of image noise and increase of SNR.The image quality was not acceptable for clinical application as NI≥17.There were no significant difference in the tissue noise level and SNR between the 70 ％ ASIR group (NI=15) and the routine standard group (P＞0.05).There was a 43.8 ％ reduction of radiation exposure in the 70 ％ ASIR group (NI =15) compared with the routine group,however,subjective image score was comparable with the routine group.The tissue noise level and SNR of the 90％ ASIR group (NI=15 or NI=16) were superior to the routine group,respectively (P＜0.05),yet subjective image score was inferior as compared to the routine group.Conclusion:Low tube voltage in combination with ASIR can ensure comparable image quality with routine standard group while the radiation dosage is significantly reduced.With significant reduce of radiation dosage,increase of ASIR is needed.