目的 探讨极低剂量扫描联合 迭代模型重建(IMR)技术在下肢CTA成 像中的可行性。方法 60例患者接受下 肢CTA检查，随机分为常规剂量(RD) 组和低剂量(LD)组，每组各30例。扫 描方案RD组：管电压120kV，管电流采 用自动管电流调控技术(DoseRight， Philips Healthcare)，图像指数设 为12；LD组：管电压80kV，管电流 20mAs。RD组图像采用常规FBP重建，LD 组图像采用IMR重建。比较下肢血管不 同位置(主动脉分叉，髂动脉分叉，股 动脉近端，股动脉中端以及腘动脉近 端)图像质量客观评价指标[血管内CT 值，图像噪声，信噪比(SNR)和对比噪 声比(CNR)]，和不同分段(主-髂动脉 段，股-腘动脉段及小腿段)主观评价 指标(血管对比度，图像噪声，图像伪 影及诊断信心)。结果 辐射剂量LD组 较RD组下降91.40%(0.16mSv±0.01， 1.86mSv±0.51，t=-18.229，P ＜0.05)。相较RD组，LD组在不同位置的 血管内CT值、SNR和CNR均显著增高，而 图像噪声则显著降低(P＜0.05)。主-髂 动脉段噪声和伪影以及股-腘动脉段、小 腿段的各项主观指标LD组均高于RD组(P ＜0.05)，余无差异。结论 结合模型迭 代技术，极低剂量下肢CTA在降低高达 91.40%的辐射剂量时，仍具有满足诊断 要求的图像质量。

Objective To investigate the feasibility of lower extremity CT angiography with extreme low radiation dose by using iterative model reconstruction (IMR) algorithm. Methods Lower extremity CT angiography scans were acquired using a 256-slice MSCT for 60 patients: 30 patients were scanned with routine dose (RD) protocol, 120kVp, automatic tube current modulation (ACTM) with image quality index of 12 (DoseRight, Philips Healthcare), and the other 30 patients were scanned with low dose (LD) protocol, 80 kVp, 20 mAs. Images from RD-group and LD-group were reconstructed with filtered back projection (FBP) and IMR algorithms respectively. CT attenuation, image noise, SNR and CNR of 5 positions including aortic bifurcation, iliac bifurcation, proximal femoral artery, middle femoral artery, proximal popliteal artery were calculated. Subjective image quality (intravascular contrast, noise, artifacts, and diagnostic confidence) of aortoiliac, femoropopliteal and lower leg segments were assessed by two radiologists using a 4-point scale. Results Radiation dose was reduced 91.0% in LD-group compared RD-group (0.16mSv±0.01, 1.86mSv±0.51, t=-18.229, P<0.05). Higher mean intravascular attenuation, SNR and CNR as well as lower image noise were obtained in LD-group compared to RD-group (all, P<0.05). Higher subjective image quality scores were observed in LD-group compared to RD-group (P<0.05), except intravascular contrast and diagnostic confidence of aortoiliac segment. Conclusion By using of IMR, lower extremity CTA allows for a radiation dose reduction up to 91.40% meanwhile without compromising image quality.