| ObjectiveTo study the main influence factors of sixteen-slice spiral CT coronary angiography, to optimize the scanning parameters and to further study the clinical value of MSCT coronary angiography.Materials and Methods1 Analysis of main influence factors on image quality of 16-slice spiral CT coronary angiography and optimization of scanning parameters: cardiac phantom study1.1 Influence of heart rate on the image quality of 16-slice spiral CT coronary angiography and optimization of scanning parameters An adjustable pulsating cardiac phantom (GE) containing predetermined simulated coronary arteries was scanned using a 16-slice spiral CT (GE Lightspeed) with cardiac pulsating rates of 40,45,50,55,60,65,70,75,80,85,90, and 95 beats per minute (bpm). The rotation speed of 0.5s and 0.6s were used respectively. The raw data were reconstructed using one-sector, two-sector and four-sector reconstruction algorithm at optimal window of the R-R interval. According to same evaluation standard of reformatted image, the image quality was scored by a radiologist and a technician. The correlation between heart rate (HR), rotation speed, reconstruction algorithm and the score of image quality (SIQ) were analyzed. Factorial analysis was applied. The SIQ as independent variable and the HR, rotation speed, reconstruction algorithm as dependent variables were analyzed by multiple linear regression analysis.1.2 Influence of fluctuation of heart rate on image quality of 16-slice spiral CT coronary angiography and optimization of scanning parameters An adjustable pulsating cardiac phantom containing predetermined simulated coronary arteries was scanned using a 16-slice spiral CT(GE Lightspeed 16) with cardiac pulsating rates of 60 and 85 beats per minute (bpm) and fluctuation amplitude of 2.5, 5 and 10 beats per minute respectively. The raw data were reconstructed using one-sector (Snapshot segment), two-sector (burst-2) and four-sector (burst-4) reconstruction algorithm at 5%-95% of the R-R interval with an increment of 10%. Reconstruction images were transmitted to workstation (ADW4.1) and post-processed using a pattern of volume rendering (VR) and multi-planar reformation (MPR). According to same evaluation standard of reformatted image, the image quality was scored by a radiologist and a technician. The correlation between heart rate (HR), fluctuation amplitude of HR, reconstruction algorithm, phase(R-R interval) and the score of image quality were analyzed.2 Thirty-six cases with suspected coronary heart disease were performed sixteen-slice spiral CT coronary angiography. They were divided into three groups according to their heart rates. Group A with heart rate≤65bpm, group B with heart rate from 66bpm to 70bpm and group C with heart rate from 71bpm to 75bpm. One-sector reconstruction algorithm were used in Group A and B, two-sector reconstruction algorithm were used in Group C. Reconstruction phase were placed at 75%R-R interval in advance and at 45%, 55%, 65% and 85%R-R interval after scanning. Reconstruction images were transmitted to workstation (ADW4.1) and post-processed using a pattern of maximum intensity projection (MIP), volume rendering (VR) and multi-planar reformation (MPR) and curved planar reformation (CPR). The demonstrated coronary artery branches were calculated and analyzed.Results1.1 The heart rate, rotation speed and reconstruction algorithm had significant influence on the SIQ(F=11.15,P<0.0001). The SIQ was higher when the heart rate was lower than 65 beats per minute; same situation was happened when rotation speed was 0.5 seconds per rotation. There was linear regression relationship between heart rate, rotation speed, reconstruction algorithm and the SIQ (P<0.0001). The equation of multiple regression was SIQ=6.92551-0.04848×HR-0.38889×rotation speed+0.39583×reconstruction algorithm. The multi-sector (namely two-sector and four-sector) reconstruction algorithm improved the image quality remarkablely than one-sector did.1.2 ANOVA suggests that all variables including HR, fluctuation amplitude of HR, reconstruction algorithm, phase (R-R interval) had significant influence on the image quality score. The average score of the 60bpm groups was much higher than that of the 85bpm groups (p<0.05). The average score of the groups (fluctuation amplitude of 2.5bpm and 5bpm) was higher than that of the groups (fluctuation amplitude of 10bpm) (p<0.05), while there was no significant difference between the former two groups (p>0.05). The average score of the two-sector and four-sector reconstruction algorithm groups was significantly higher than that of the one-sector reconstruction algorithm groups (p<0.05), while there was no significant difference between the former two groups (p>0.05). The average score of the groups whose reconstruction phase at 45% and 95% R-R interval was significantly higher than that of other groups (p<0.05), while there was no significant difference between the former two groups (p>0.05). The image quality of the groups their phase at 15% R-R interval was the worst.2 The demonstrating rate of main branches of coronary artery including RCA, LM, LAD and LCX was 100% in group A, that of group B were 91.67%,100%,100% and 91.67% respectively, and 80%,100%,90% and 70% respectively in group C. The optimal reconstruction phase for LM and LAD was at 75%R-R interval,LCX at 55% R-R interval, RCA at R-R interval.ConclusionsThe heart rate, rotation speed and reconstruction algorithm are the main influence factors on the image quality of coronary arteries, which could be evaluated with 16-slice spiral CT using a pulsating cardiac phantom. Optimization of scanning parameters could improve the image quality of coronary arteries. As a noninvasive technique, sixteen-slice spiral CT coronary angiography could demonstrate the anatomy of coronary arteries and their main branches and the characteristics of coronary artery diseases. With the development of CT technology and its increase of clinical application, MSCT would play a great role in coronary artery imaging.
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