比较两种低剂量CT迭代重建法与常规剂量滤波反投影重建法的图像质量

目的 对比低剂量腹部和盆腔增强扫描自适应统计迭代重建（ASIR）和基于模型的迭代重建（MBIR）与常规剂量下传统的滤波反投影（FBP）重建的图像质量和剂量减低率。方法 31例患者接受腹部和盆腔增强常规剂量CT扫描、FBP重建；复查时，接受增强低剂量扫描、40%ASIR和MBIR。由2名医师通过锐利度、噪声、伪影和诊断接受度对图像进行评分，并测量噪声值和CT值，计算SNR。记录每例患者每次检查的剂量长度乘积（DLP）和CT剂量指数（CTDIvol），计算剂量减低率。结果 低剂量扫描的DLP值和CTDI值分别为（328.95±206.35）mGy/cm和（7.96±4.30）mGy，而常规剂量FBP重建的DLP值和CTDI分别为（689.27±339.63） mGy/cm和（16.81±7.19） mGy。对于腹部和盆腔脏器，低剂量MBIR图像比低剂量40%ASIR图像和常规剂量FBP图像有更低噪声值和更高SNR （P均<0.0167）。低剂量40%ASIR图像和常规剂量FBP图像的客观评价结果相似（P>0.0167）。MBIR和40%ASIR可以提高图像的密度分辨力，降低硬化伪影，且MBIR比40%ASIR图像有更低噪声和伪影，主观评价结果更佳。结论 在保证图像质量的前提下，相比常规剂量扫描、FBP重建，低剂量扫描MBIR和ASIR可以明显降低扫描剂量；相比ASIR法，MBIR法能提供更佳图像质量，具有进一步降低扫描剂量的潜力。

Comparison on image quality of two kinds of low-dose CT reconstruction and routine-dose CT filtered back projection reconstruction

Objective To evaluate dose reduction and image quality characteristics of abdominal low-dose CT reconstructed with model-based iterative reconstruction (MBIR) and adaptive statistical interactive reconstruction (ASIR) compared with routine-dose CT reconstructed and filtered back projection (FBP). Methods Thirty-one patients underwent contrast-enhanced abdominal-pelvis low-dose CT reconstructed with 40%ASIR and MBIR after contrast-enhanced abdominal-pelvis routine-dose CT reconstructed with FBP. Two radiologists assessed the images blindly according to the sharpness, image noise, diagnostic acceptability and artifacts. Image noise and SNR of abdominal organs relative to abdominal fat were assessed. The volume CT dose index (CTDIvol), dose-length product (DLP) and dose reduction rate were also obtained. Results CTDIvol and DLP for low-dose CT were (7.96±4.30)mGy and (328.95±206.35)mGy/cm, of routine-dose CT with FBP were (16.81±7.19)mGy and (689.27±339.63)mGy/cm, respectively. Low-dose MBIR images had significantly lower objective image noise, higher SNR than low-dose 40%ASIR images and routine-dose images (all P<0.0167). The low-dose 40%ASIR and routine-dose images had similar objective and subjective results (all P>0.0167). MBIR had better subjective scores than 40%ASIR and FBP in noise, sharpness and artifacts. Meanwhile, MBIR and ASIR could not only improve the density resolution, but also c decrease the hardening artifacts of images. Conclusion Under the premise of same image quality, low-dose CT reconstruction can decrease radiation dose significantly compared to routine-dose CT reconstruction. Image quality of low-dose CT MBIR is better than that of 40% ASIR, which has potential for further reducing radiation dose.