| As a low dose scan protocol, prospectively electrocardiogram-triggered(ECG) high-pitch spiral acquisition(flash spiral) mode of dual-source CT(DSCT) can accomplish coronary angiography in one single cardiac cycle. It takes about 250 ms and radiation dose can be reduced to about 1 m Sv. The flash spiral mode is adequate for patients with regular low heart rates. Although some scholars have improved the image qualities of coronary computed tomography angiography(CCTA) by using 20%-30% of the R-R interval as exposure windows, the failure rate is still high in patients with high rates(HR≥70 bpm). The propose of the research is to improve image qualities and the success rate of flash spiral mode of DSCT coronary angiography by exploring the characteristic changes of left ventricular volume in the cardiac cycle and finding the proper exposure windows in patients with high heart rates. Part One:Study on the characteristic changes of left ventricular volume and the proper exposure windows on flash spiral mode of DSCT coronary angiographyObjectiveTo explore the characteristic changes of left ventricular volume in the cardiac cycle by using the second generation DSCT coronary angiography, to find the proper exposure window on flash spiral mode of DSCT in patients with high heart rates(HR≥ 70 bpm).MethodsThrough prospective analysis 68 patients who were suspected of having coronary artery disease have been conduct retrospective ECG-triggered coronary angiography using DSCT. All patients were divided into five groups by heart rate. CT images were reconstructed into 21 phase images with 5%R-R period as time interval. The left ventricular volumes were obtained using cardiac function evaluation software and the volume-time curves were plotted. By calculating the average rate of changes in left ventricular volume in 250 ms, the proper exposure windows on flash spiral mode of DSCT coronary angiography in patients with different heart rates were found.ResultsThe volume-time curves and the rate of changes-time curves of the five groups had regular patterns, the higher the heart rates were, the smaller of the RR-interval for the proper exposure windows on flash spiral mode of the DSCT coronary angiography. For patients with HR<70 bpm?70 to 79bpm?80 to 89bpm?90 to 99 bpm and≥100bpm, the proper exposure windows on flash spiral mode of the DSCT coronary angiography were 60. 0%?30.5%?25.8%?23%?16.7% RR-interval respectively.ConclusionThe characteristic changes of left ventricular volume in the cardiac cycle provide the instruction in finding the proper exposure window on flash spiral mode of DSCT coronary angiography.Part Two: Study on the modified flash spiral mode coronary computed tomography angiography in patients with high heart ratesObjectiveTo conduct the modified flash spiral mode CCTA in patients with high heart rates(HR≥ 70 bpm) by comparing the image qualities and radiation doses with prospectively electrocardiography-gated step-and-shoot(SAS) mode which was used conventionally by DSCT.Methods106 patients who met criteria were divided into two groups: Group A underwent flash spiral mode coronary angiography,the start phase of image acquisition of the most cranial slice was according to the results of Part One. Group B underwent SAS mode CCTA. The image qualities and radiation doses of the two groups were assessed.Results1. There were no significant differences in sex, age, BMI and constituent ratio of HR between the two groups(P=0.556,0.164,0.124, 0.859).2. Image qualities: According to the heart rates, the two group divided into four group respectively. For patients with HR from 70 bpm to79 bpm and from 80 bpm to 89 bpm, the image qualities had no significant difference between group A and group B(P=0.883, 0.617). For patients with HR from 90 bpm to 99 bpm and ≥100 bpm, the image qualities had significant differences between group A and group B(P=0.048,0.044), the image qualities of group B were better than those of group A.3. Radiation doses: The dose length product and the effective doses were significant difference between the two groups(P<0.001 both), the radiation doses of group A were significantly lower than those of group BConclusionFor patients with HR from 70 bpm to 89 bpm, the image qualities of coronary angiography performed by the flash spiral mode are similar with those of SAS mode CCTA, but the effective radiation doses are significantly reduced to about 1m Sv. For patients with irregular heart rhythms or with heart rate≥90 bpm, the image qualities of coronary angiography detected by the flash spiral mode are not good enough, SAS mode CCTA is suggested. |
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