心电图调制电流对于容积CT心脏扫描图像质量及曝光剂量影响的评估

Evaluation on the influence of electrocardiograph modulated milliampere on image quality and exposure dosage of volume CT heart scan

目的评估容积 CT(VCT)心脏扫描时,开启或关闭心电图(ECG)调制电流(mA)技术对图像质量是否有影响,并判断 ECG 调制 mA 技术是否能有效降低曝光剂量。方法将跳动心脏模具设定为高、中、低不同速率的稳定心率,采用与不同速率稳定心率相匹配的重组算法,开启 ECG 调制 mA,对心脏模具进行扫描,扫描同时记录各扫描序列的曝光剂量,在采集到的图像中选取结构均匀的部位,测量该部位的 CT 值及不同部位 CT 值的差值,并记录图像测量部位的标准差(s)值;关闭ECG 调制 mA,重复上述扫描并记录曝光剂量,对采集到的图像进行相同测量和记录。将2次扫描所测得的数据进行统计学分析。结果在同样心率条件下,ECG 调制开启时比关闭时曝光剂量有明显减低,在每分钟搏动数(bpm)为50、60、75和95的4种心率条件下,曝光剂量分别减少了48.0%、44.0%、37.0%和37.7%;2组图像的数据分析差异无统计学意义(P>0.05)。结论 VCT 心脏扫描时,开启 ECG 调制 mA 技术能够有效降低曝光剂量,同时对图像质量无明显影响。

Objective To find out whether the use of ECG modulated current （mA） will influence image quality and to decide whether the electrocardiograph （ECG） modulated mA will effectively reduce the exposure dosage. Methods The cardiac pulsating phantom was set at three speed levels, i.e. high, medium, and low speed so as to simulate different heart rates. The phantom was scanned with ECG modulated mA turned on and off, and the exposure dosage of each scan sequence was documented. The images were reconstructed with reconstruction algorithm that matched the different levels of heart rate. CT values and their corresponding standard deviations at uniform areas on the images and the variation of the CT values at different locations were measured. The results from the two groups with and without ECG modulated mA were analyzed. Results Under the same level of heart rate, the exposure dosage was remarkably reduced when the ECG modulated mA was on than when it was off. Statistical analysis showed no significant difference （P 〉 0. 05） between the images from the two groups. Conclusion When scanning the heart with volume CT （ VCT）, the application of ECG modulated mA can effectively reduce the exposure dosage without sacrificing the image quality.