64层螺旋CT低剂量左心室功能分析的可靠性研究

Assessment of the Left Ventricular Function with Low-dose 64-MSCT

目的通过动态心脏模具研究低剂量CT左心室功能分析的价值和可靠性.方法采用64排GELightSpeed VCT扫描可模拟左心室运动的心脏模具,模具射血分数选择25%和40%两种,50、60、70、90和120 bpm 5种心率条件,扫描剂量设定:A.关闭ECG管电流调制技术,扫描参数为120 kV、500 mA;B.开启ECG管电流调制技术,电流调制范围设定在250～500 mA,调制期相80%～90%和30%～90%两种;C.电流调制范围100～500 mA,其它同B.计算各个扫描条件下的有效剂量以及各组数据中的最高噪声指数.测量收缩末期容积(ESV)、舒张末期容积(EDV)并计算射血量(EF),统计分析不同心率和低剂量条件下的ESV、EDV和EF变化.统计冠脉的解剖学图像质量,综合评价低剂量心室功能合并冠脉检查的有效性.结果相比常规模式,ECG调制技术下低管电流采用250 mA,最多可降低20%的剂量,如低管电流采用100 mA则最多能够节约近39%的射线剂量,差异有统计学意义(P<0.05);常规剂量下,射血分数值表现为与心率呈负相关变化(25%:r=-0.961,40%:r=-0.948),但与标准理想射血分数相比均无明显统计学差异(P>0.05),同时标准射血量的不同不会影响实际测得的射血分数与标准值相似性(25%组:92.1%,40%组:91.8%);ECG调制组,不同心率下对应组图像所测得的EDV、ESV、EF值,结果差异均无统计学意义,噪声使分析时间相应增加,对分析结果影响小;ECG调制时相的选择会对冠脉解剖分析产生影响.结论不同心率条件下的低剂量ECG调制CT扫描技术进行心室分析可行并可靠,但考虑冠脉检查的需要,电流调制的期相范围要根据心率情况合理设置,以期低剂量检查做到行之有效.

Objective To evaluate the role of low- dose 64- slice computed tomography in assessing left ventricular function on dynamic cardiac phantom.Methods The cardiac phantom that simulated motion of LV was scanned with 25% and 40% EF,and five heart rates including 50,60,70,90,120 bpm were used.The scan parameters was set as：A.Standard 120 kV,500mA without electrocardiograph （ECG） modulated current （mA）.B. 250～500 mA with ECG modulated mA technique, and two different phases were set：80%～90% and 30 % ～90% .C.100 ～500 mA with ECG modulated mA technique.The exposure dosage of each scan sequence was documented.And 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 with and without ECG modulated mA were analyzed.Statistical analysis was performed among ESV,EDV,EV,coronary image quality at different heart rate and dosage level.Results The exposure dosage with 250～500 mA and 100～500 mA ECG modulated mA was maximized decreased by 20% and 39% respectively,compared to that of without ECG modulated mA, indicating significant statistical difference （P0.05）.The negative relationship between EF and heart rate was found without ECG modulated mA （25%：r=- 0.961,40%： r=- 0.948）,but no significant statistical difference was found compared with standard EF （P0.05）.EDV, ESV,EF with ECG modulated mA showed no significant difference, and ECG modulated mA affected the image quality at high heart rate. Conclusion Our result indicates that it is reliable to assess global LV function with low- dose 64- MSCT. Functional analysis in additional to anatomical evaluation may increase the clinical efficacy of MSCT,but ECG modulated mA must be set rationally according to heart rates.