With the growing popularity of 64-Multidetector CT (MDCT) and DSCT, CTCA has gained a wide spectrum of applications due to its simplicity, non-invasiveness and high accuracy in detecting significant stenoses in patients with regular and low (<65 bpm) heart rates. β-blockers are commonly administered prior to CTCA to lower the heart rate, thereby reducing the number of image-degrading motion artifacts. DSCT scanners provide an improved temporal resolution compared with single-source CT equipment and may eliminate the need for prescan β-blockers (16
). However, in previous studies, the number of patients with increased heart rate (>80 bpm) was small and patients with arrhythmias were excluded from the majority of studies (3
). Heart rate modulation by oral or intravenous administration of β-blockers was not required prior to the scanning procedure in the present study. The present technique of the CorAdSeq demonstrated high image quality, even in a number of patients with arrhythmias (). No correlation was identified between the image quality and MHR or HRV.
Figure 4. Male, 65-year-old patient with atrial fibrillation, BMI=22.54 kg/m2. HRV was 11 bpm during scanning; MHR and heart rate range were 101 and 54–146 bpm, respectively. Image quality score was 5 points. CT coronary angiograms show cross-sections (A–D) (more ...)
A small number of studies have investigated the effect of HRV on image quality and diagnostic performance. However, in these studies the HRVs were defined as the standard deviation of the MHR during CTCA. A sudden change in heart rate may cause several problems in the acquisition of CTCA since artifacts are created due to differences in the image reconstruction phases between consecutive heart beats. Previous studies did not perform CTCA in patients with arrhythmias. In the present study, 7.9% (54/683) patients had a heart rate >100 bpm during scanning and 119 patients (17.4%) had arrhythmias. Diagnostic image quality was obtained for all patients on the basis of adaptive prospective CorAdSeq, even patients with severe HRV. This finding indicates that CorAdSeq is a robust technique and may be used in all patients undergoing CTCA.
DSCT uses two mutually perpendicular tubes, one rotation of which significantly increases the covered area and scan speed. Using a 0.33 sec gantry rotation time, the time resolution is one quarter (1/4) of the rotation time, i.e. 83 msec (17
). In the present study group, the gantry rotation time was reduced to 0.28 sec and the time resolution was increased to 75 msec. Such a time resolution was enough for coronary CT scans without the need to control heart rates. By contrast, conventional perspective CorAdSeq scanning requires more strict control of heart rate and rhythm (heart rate <70 bpm) and heart rate fluctuation <10 times/min (3
). Therefore, the conventional technique may only be applied to patients with a regular rhythm and low heart rate. Furthermore, the time phase cannot be changed when restructuring and split images are likely to appear if the heart rate change is abrupt, thereby affecting the image quality. CorAdSeq scanning selects appropriate reconstruction phases to control the exposure to X-rays using the heart rate monitoring by ECG. This has the advantage of increasing the scanning speed and lowering radiation dose as the X-ray exposure only occurs in selected phases rather than in the whole cardiac cycle. If arrhythmia occurs, the patient table stops in the original position without scanning and data collection. Only when the next R-R wave becomes rhythmic is the patient table moved to the appropriate position and scanning and data acquisition restarted. Since the examination bed does not move, there is no data gap in the cardiac cycle before and after arrhythmia. A high overall diagnostic performance was observed for DS CTCA in the detection of significant coronary artery stenosis with a sensitivity of 99% and an NPV of 99% on a per-patient basis. These results were obtained without excluding any segments or patients on the basis of non-diagnostic image quality. No significant differences were observed in image quality between the two groups regardless of MHR and HRV. Despite high heart rates (maximal 171 bpm and MHR 78.8±13.6 bpm) and large heart rate fluctuations (22.2±23.4 bpm) during scanning in the patients, 98.2% (671/683) yielded high quality images. No coronary segments were considered non-diagnostic due to elevated MHR or HRV, indicating that the image quality obtained by CorAdSeq scanning was not significantly affected by increased heart rate or arrhythmia. In the present study, the overall average image score for all the patients was 4.80±0.41.
Numerous factors affect CTCA radiation dose, including scan length, scan speed and tube voltage (18
). The biggest difference between CorAdSeq and DSCT retrospective ECG-gated spiral scanning is CordAdSeq’s CARE Dose 4D technique. CARE Dose 4D is based on the approach of modulating the tube current and keeping the image noise constant from patient to patient and over the whole scan. The reference current is adjusted automatically according to the anatomy of the patient’s body and organs. In slim patients, the CARE Dose 4D automatically reduces the current in the CTCA scanning. In obese patients, it increases the current when CTCA scanning and so is able to further reduce the radiation dose. SAS CTCA has attracted interest as a technique for reducing radiation exposure while preserving diagnostic image quality. However, SAS CTCA is currently limited to selected patients with low and regular heart rates only (9
). The present findings confirm and corroborate those of previous reports (7
) investigating prospective ECG gating and demonstrate the clinical feasibility of the technique as an effective method for reducing radiation exposure without affecting image quality. It should, however, be emphasized that these results were obtained in a selected groups of patients. If the prospective gating technique is applied to patients with low (<70 bpm) and regular heart rates, that would only demonstrate that this technology is applicable to such patients. More significantly, the radiation dose of such a method remains higher. Under the same conditions, in the present study of patients with a BMI <25.0 kg/m2
, the ED of was 2.57 mSv±1.01, while for those with a BMI ≥25.0 kg/m2
, the ED was 6.36 mSv±1.88, although the average DLP and ED were slightly lower than in relevant studies (10
) and significantly reduced compared with retrospective ECG-gated scanning or 64-MDCT (19
The present study had certain limitations. Firstly, the classification of the subgroups was arbitrary and was not categorized according to MHR and HRV. Secondly, evaluation was not performed between the image quality and diagnostic accuracy. The association between the two should be the subject of further studies.
In conclusion, using CTCA with the new generation DSCT adaptive perspective CorAdSeq is feasible in patients without heart rate control. This greatly widens the scope of its applications with increased image quality and reduced radiation exposure in coronary artery imaging.