目的探讨超低辐射剂量条件 下全模型迭代重建(IMR)技术在冠状动 脉CTA中的应用价值。方法 回顾性分析 27例心率小于65 bpm的患者冠状动脉资 料，所有检查均采用了基于管电流调制 技术的回顾性心电门控螺旋扫描模式。 常规组(A组)采用常规辐射剂量(舒张 末期)联合iDose4 (L4)重建，低剂量组 (B～F组)采用低辐射剂量(收缩末期)联 合不同重建算法重建[iDose4 (L4、L7)和 IMR(L1、L2、L3)]。比较每组图像的CT 值、图像噪声、SNR、CNR和图像主观质 量评分。采用单因素方差分析和独立样 本t检验比较图像客观指标的差异，采用 Kruskal-Wallis非参数检验比较图像主 观指标的差异。结果 常规组理论辐射剂 量为(9.77±2.72)msv，低剂量组理论辐 射剂量为(1.95±0.54)msv，两组辐射 剂量比较差异有统计学意义(F=19.02， P<0.01)。常规组与低剂量组(联合IMR重 建组)图像主观质量间比较差异无统计学 意义(P均>0.01)。结论 应用IMR重建技术 可显著降低图像噪声，改善图像质量,可 在大幅度降低辐射剂量后依然保持与常规 剂量条件下iDose4 重建时的冠状动脉图像 质量水平。

Objective To investigate the value of knowledge-based iterative modal reconstruction(IMR) technology for coronary computed tomography on 256-slice spiral CT with radiation dose reduced to 80%. Methods Retrospective analysis coronary artery data of 21cases patients with heart rate is less than 65bpm, all patients underwent CCTA with retrospective ECG tagging with cardiac dose right helical scan. The data acquisition time window centered at the 75% of the R-R cycle, including a phase tolerance of 4-5％. The images were divided into four groups according to the phase and reconstruction algorithm. Data acquisition at End-systolic phase with iDose4 (group A), data acquisition at End-systolic phase with IMR (group B); data acquisition at mid-diastolic phase with iDose4 (group C), data acquisition at mid-diastolic phase with IMR (group D).then, the image noise(SD), signal-to-noise ratio(SNR) and contrast-to-noise ratio(CNR) of ascending aortic root were measured. Objective measurements were compared with one way analysis of variance, and subjective assessments were compared with Kruskal-Wallis H test. Results A total of 21 cases of image reconstruction were completed in the Endsystolic phase and mid-diastolic phase. Image noise of group C were significantly higher than other groups [(33.0±8.9)HU, (22.4±4.1)HU, (89.6±53.9)HU and (27.7±6.1) HU]. Group C compare to other groups, the difference was statistical significance (P <0.01), SNR[(25.4±8.2), (21.4±4.7), t=-2.92, -10.85] and CNR[(37.4±13.3), (36.5±18.1), t=-2.37, -5.60] of proximal coronary arteries in IMR were significantly higher than iDose4 which used the same radiation dose, and there was no significant difference between the group A and group D in SNR[(19.0±6.0) vs.(21.4±4.7), t=- 1.48] and CNR[(29.5±7.7) vs.(36.5±18.1), t=-1.64](all P>0.05).there were significant differences for four groups [(3.95±0.22), 4.0,(19.5±0.67), (3.81±0.4), H=69.12, P<0.05]in mean score, and with no significant differences for group A, B and D(H=5.56, P>0.05). Conclusion IMR can significantly reduce image noise, increase SNR and CNR, and improve image quality. The image quality of coronary artery can still be maintained at iDose4 after reconstruction with a significant reduction in radiation dose.