目的 探讨320排容积CT“Target CTA（Computed Tomography Angiography）扫描模式”在心率低于75 次/min的患者 行冠脉CT血管成像的可行性。方法 收集拟行冠状动脉CT血管成像且静息状态下心率低于75 次/min的患者78例为研究对 象，并进行随机分组：A组39例采用传统的前瞻性心电门控采集模式，曝光时间窗（R-R间期的35%~85%）；B组39例采 用第二代320排容积CT所自带的Target CTA采集模式，Target Phase设置为R-R间期的75%时间点。主观图像质量采用4分制 进行分级和评估。客观图像质量采用主要分支血管CT值、图像噪声、信噪比（Signal-to-Noise Ratio，SNR）、对比噪声比 （Contrast to Noise Ratio，CNR）进行评估，并统计有效辐射剂量（Effective Dose，ED）。结果 采用第二代320排容积 CT Target CTA采集模式比传统的前瞻性心电门控采集模式减少了66.1%的ED值[（5.9 ± 1.0）mSv vs. （2.0 ± 0.7） mSv]，差 异有统计学意义（t=-15.175，P<0.05）。A组和B组扫描模式下的噪声、SNR和CNR差异及图像质量主观评分比较，差异均 无统计学意义（均P>0.05）。结论 第二代320排容积CT Target CTA扫描模式对于心率低于75 次/min的患者行冠脉CT血管成 像，可以在保证图像质量的前提下，大幅度降低辐射剂量。

Objective To investigate the feasibility of 320-row volume CT ‘Target CTA (computed tomography angiography) scan mode’ for coronary CT angiography in patients with heart rate less than 75 times/min. Methods A total of 78 patients with resting heart rate less than 75 times/min who were to undergo coronary angiography were collected and randomly divided into two groups: 39 cases in group A received the traditional default prospective ECG gated acquisition mode with exposure time window (35%-85% of R-R interval); 39 cases in group B received the target CTA acquisition mode of the second-generation 320-row volume CT, and the Target Phase was set as 75% of the R-R interval as the center. The subjective image quality was evaluated and graded based on a 4-point scale. The objective image quality was evaluated by CT value of main branch vessels, image noise, signal to noise ratio (SNR) and contrast to noise ratio (CNR), and the effective dose (ED) was calculated. Results Using the second generation 320-row volume CT target CTA acquisition mode reduced the radiation dose by 66.1% compared with the traditional prospective electrocardio-gated acquisition mode [(5.9±1.0) mSv vs. (2.0±0.7) mSv], and the difference was statistically significant (t=-15.175, P<0.05). There were no statistically significant differences in noise, SNR and CNR, and subjective score of image quality between group A and group B (all P>0.05). Conclusion The second-generation 320-row volume CT target CTA scanning mode can significantly reduce radiation dose while ensuring image quality for coronary CT angiography in patients with heart rate below 75 times/min.