320-detector row CT coronary angiography: effects of heart rate and heart rate variability on image quality, diagnostic accuracy and radiation exposure

Objectives

To evaluate the effects of heart rate and heart rate variability on image quality, patient dose and diagnostic accuracy of 320-detector row CT.

Methods

94 patients were prospectively enrolled. Heart rate was defined as the mean value of different intervals elapsing between two consecutive R waves in an electrocardiogram (R–R intervals) and the heart rate variability was calculated as the standard deviation from the average heart rate. The image quality was evaluated by four grades, according to motion artefacts (“step artefacts” and “blurring artefacts”). The diagnostic accuracy was analysed in 43 patients who were scheduled for invasive coronary angiography (ICA). The coeffects of heart rate and heart rate variability on image quality, radiation dose and diagnostic accuracy were evaluated by multivariate regression.

Results

The mean image quality score was 1.2±0.5 and the mean effective dose was 14.8±9.8 mSv. The results showed that heart rate (74.0±11.2 beats per minute) was the single factor influencing image quality (p<0.001) and radiation dose (p<0.001), while heart rate variability (3.7±4.6) had no significant effect on them (p=0.16 and p=0.47, respectively). For 43 patients who underwent ICA, heart rate and heart rate variability showed no influence on the accuracy (p=0.17 and p=0.12, respectively). Overall sensitivity was 97.4% (37/38), specificity was 99.4% (351/353), positive predictive value was 94.9% (37/39) and negative predictive value was 99.7% (351/352).

Conclusion

320-detector row CT, with improved longitudinal coverage of detector, resolves step artefact and high patient dose caused by irregular heart rate. However, it is still recommended to control heart rate to a lower level to eliminate blurring artefact and radiation dose.As the clinical application of 4-detector CT to scan the coronary arteries by a non-invasive procedure, CT coronary angiography has emerged as an attractive, diagnostic modality for detecting coronary artery disease. However, motion artefact by rapid movement throughout the cardiac cycle and blooming artefact caused by calcified plaque represent the major challenges for artefact-free coronary CT angiography. Generally, “step artefacts” and “blurring artefacts” are two kinds of motion artefact influencing the quality of coronary artery image. To improve image quality, CT scanners with higher spatial resolution, temporal resolution and wider detector array were developed.The Discovery™ CT750 HD (GE Healthcare, Waukesha, WI) improves spatial resolution and decreased calcium blooming artefact significantly 1]. Dual-source CT (DSCT), with two X-ray sources and a temporal resolution of 83 ms, has improved blurring artefacts caused by high heart rate (HR) 2-4]. Nevertheless, as the coverage of the detectors is limited, step artefacts caused by heart rate variability (HRv) is still an inverse factor influencing the image quality 2,3]. Just as the improved temporal resolution should resolve the problem of high HR, the longitudinal coverage of the detector should be expanded further to resolve the influence of HRv 5-8]. 320-detector row dynamic volume CT (DVCT) can cover the whole heart within one heartbeat, which enables DVCT to have the potential to resolve the impact of HRv 9].A previous study has shown that DVCT reliably provides high diagnostic accuracy without HR control 9]. The aim of our study was to evaluate the influence of degree of HR and HRv on image quality, radiation dose and diagnostic accuracy in patients undergoing DVCT.