ASIR提高低剂量CT结肠成像息肉检出率有效性的体模研究

The Efficacy of Adaptive Statistical Iterative Reconstruction in Detecting Polyps with Reduced dose CT Colonography:A Phantom Study

目的评价应用不同水平自适应统计迭代重建技术(adaptive statistical iterative reconstruction,ASIR)在低剂量CT结肠成像中提高结肠息肉检出率的有效性。材料与方法选用一段离体猪结肠通过结扎法获得20枚1～10 mm(≤5 mm 10枚,>5 mm 10枚)连续的模拟息肉,运用宝石高分辨CT在不同剂量(120 kVp,10、20、30、40、50及100 mAs)下扫描,并分别应用6种不同ASIR水平(0、10%、30%、50%、70%及100%)进行数据重建,获得CT仿真内镜、多平面重组(MPR)和虚拟分割(VD)图像。由两名有经验的影像科医师采用盲法对不同采集条件、不同ASIR水平的图像进行客观和主观评价,测量并比较平均噪声、平均信噪比(signal to noise ratio,SNR)及平均对比噪声比(contrast noise ratios,CNR)和息肉检出率。结果结肠模拟息肉模型研究显示不同管电流-时间下噪声随应用ASIR水平升高而降低,SNR及CNR随应用ASIR水平升高而增高(P<0.05)。>5 mm结肠息肉在低剂量扫描时应用ASIR对提高检出率具有统计学意义(P<0.05);而≤5 mm的结肠息肉,其检出率会随着剂量水平的增高而明显提高,应用高水平ASIR时息肉检出率无明显提高(P>0.05)。结论离体模型研究表明在低剂量CT结肠成像中,应用ASIR可以显著降低图像噪声,提高SNR及CNR;在低剂量时可提高>5 mm结肠息肉的检出率,但不会明显提高≤5 mm结肠息肉的检出率。

Objective To evaluate the efficacy of adaptive statistical iterative reconstruction（ASIR） to detect phantom colonic polyps using a reduced radiation dose CT colonography（CTC）.Materials and Methods A series of twenty artificial polyps sized from 1mm to 10mm（each 10 polys with diameter smaller than 5mm and bigger than 5mm） were established by ligation in an isolated segment of porcine colon.Volume data were acquired on High Definition CT scanner at different doses（10,20,30,40,50 and 100 mAs at 120 KVp） using six different ASIR levels at 0,10%,30%,50%,70% and 100%.CT virtual endoscopy,multiplanar reformation and virtual dissection models were reconstructed.Two radiologists assessed images blinded to the polys＇location,radiation dose and ASIR level.Average noise level,average signal to noise ratio（SNR）and average contrast to noise ratios（CNR） as well as detecting rates of the polyps were calculated and compared statistically among different acquisitions.Results The phantom study revealed a tendency that SNR and CNR was increasing and the noise was decreasing with a higher percentage of ASIR at every dose level（P〈0.05）.The detecting rates of colonic polyps were increase significantly with a higher dose especially for those polyps less than 5mm（P〈0.05）;however,the detecting rates had no significant increase with a higher ASIR level（P〉0.05）.Conclusion ASIR could significantly reduce image noise and increase SNR and CNR in low dose CT colonography.It succeed in improving the detecting rates of artificial polyps over 5mm but fail in those polyps smaller than 5 mm.