We have declared that no competing interests exist.
Conceived and designed the experiments: YW HX ZJ. Performed the experiments: ZW YC LK. Analyzed the data: ZW JC SL. Contributed reagents/materials/analysis tools: ZW YC YW. Wrote the paper: ZW YW HX.
To evaluate the image quality and radiation dose of combined heart, head, and neck CT angiography (CTA) using prospectively electrocardiography (ECG)-triggered high-pitch spiral scan protocol, compared with single coronary CTA.
151 consecutive patients were prospectively included and randomly divided into three groups. Group 1 (n = 47) underwent combined heart, neck, and head CTA using prospectively ECG-triggered high-pitch spiral (Flash) scan protocol with a single-phase intravenous injection of iodinated contrast and saline flush; Group 2 (n = 51) underwent single coronary CTA with Flash scan protocol; and Group 3 (n = 53) underwent single coronary CTA with prospective sequence scan protocol. All patients were examined on a dual source CT (Definition FLASH). The image quality was determined for each CT study.
Patients of scanning protocol Group 1, 2, and 3 showed no significant differences in age, sex, heart rates, and BMI. Evaluation of coronary artery image quality showed comparable results in the three scanning protocol groups on a per patient-based analysis. In group 1, image quality was found to be sufficient to be diagnostic in all arterial segments of carotid arteries. The mean dose-length product (DLP) for group 1 was 256.3±24.5 mGy×cm and was significantly higher in comparison with group 2 (93.4±19.9 mGy×cm; p < 0.001). However, there was no significant difference of DLP between group 1 and group 3 (254.1±69.9 mGy×cm).
The combined heart, neck, and head arteries scan using prospectively electrocardiography (ECG)-triggered high-pitch spiral scan protocol in 1 single examination resulted in an excellent opacification of the aorta, the carotid arteries, and the coronary arteries and provided a good image quality with low radiation dose.
Cardio-cerebral vascular disease is the leading cause of mortality worldwide
The second generation of the dual-source 128-slice CT system (Definition Flash, Siemens Healthcare, Forcheim, Germany) provides a wider coverage of 38.4 mm; this, along with faster gantry rotation, have improved temporal resolution to 75 milliseconds, allowing spiral acquisitions to be performed at a pitch as high as 3.4
The purpose of this randomized study is to evaluate the image quality and radiation dose of a combined heart, neck, and head CTA using a high-pitch scan protocol with a low contrast media dose in comparison with both coronary-only high-pitch cCTA and prospective ECG-trigger cCTA.
This study was approved by Peking Union Medical College Hospital ethics committee. Written informed consent was obtained from all patients. Between June 2012 and September 2012, 219 patients were clinically referred for cCTA at our institution. Patients who had a history of percutaneous intervention (n = 27) or bypass surgery (n = 11) were not eligible for our study and were excluded. Patients with known allergy to iodinated contrast material (n = 5), impaired renal function (serum creatinine level, >120 μmol/L; n = 9), or persistent arrhythmias (n = 11) were excluded. Thus, 156 consecutive patients were eligible for inclusion in this study.
Study patients were randomly divided into three groups. Patients in Group 1 (n = 49) received a combined heart, neck, and head prospective ECG-triggered high-pitch CTA; Group 2 (n = 54) underwent high-pitch cCTA, and Group 3 (n = 53) underwent prospective ECG-triggered sequence scan cCTA. All patients received nitroglycerin (0.4 mg per dose) sublingually just prior to the CT scan. All patients with a heart rate above 65 beats per minute, in the absence of contraindications, received a single dose of 100 mg metoprolol (AstraZeneca, China) 1 hour prior to scanning. A heart rate greater than 65 beats per minute with contraindications to β-blockers or patients not properly responding to the administered β-blocker were excluded. Finally, 151 patients were eligible for analysis (
All CTs was performed using a 128-slice DSCT system (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany). Detector collimation is 2×64×0.6 mm. A z-axis flying focal spot is applied with an acquisition of 2×128 slices per rotation. Both tubes were operated at 120 kV. Scout-based automatic tube current modulation (CareDose 4D, Siemens healthcare, Forcheim, Germany) was used with the reference tube current–time product set at 320 mAs per rotation. The pitch was 3.2 for group 1, and 3.4 for group 2. For all protocols, patients were positioned supine on the CT table with both arms along the chest. Contrast media (Ultravist 370 mgI/ml, Bayer Schering) and saline chaser were administered at 5 mL/s using a dual-head power injector (Empower, ACIST) into an antecubital vein through an 18-gauge catheter. Heart rate and ECG trace were recorded during examinations.
A test bolus scan was performed to determine the transit time. An injection of 15 mL of iodinated contrast media was followed by a 30 mL saline chaser. The time until the peak opacification in the proximal ascending aorta was measured and this time added 3 seconds was considered to represent the transit time of contrast agent. Sixty-five mL of contrast agent were injected, followed by a 50 mL saline chaser. The scan was initiated with a delay according to the transit time. The scan was performed in a caudocranial direction, starting above the diaphragm, just below all cardiac structures, and ending at the apex of the skull.
Fifty-five milliliters of contrast media followed by a 50 mL saline chaser were administered. with bolus tracking using a region of interest (ROI) in the ascending aorta. The scan was automatically triggered when the tracking ROI reached a threshold of 100 Hounsfield units (HU) above baseline attenuation. Scan direction was craniocaudal, starting above the coronary ostia and ending at the diaphragm below all cardiac structures. In the high-pitch spiral mode (Group 2), prospective ECG-triggering was used to obtain a complete dataset in a single heart beat
Axial sections for the entire dataset (1.0 mm, increment 0.6 mm) were reconstructed using a medium-soft convolution kernel (B26). Datasets for coronary arteries were reconstructed with a slice thickness of 0.6 mm, an increment of 0.4 mm, a field of view of 180 mm, a medium-soft convolution kernel (B26) and additionally a sharp convolution kernel (B46) in patients exhibiting coronary calcium.
All reconstructed images were transferred to a dedicated workstation (MMWP, Siemens Healthcare, Forchheim, Germany). Axial images, multiplanar reformations, and maximum intensity projections were used to evaluate arteries.
Coronary artery segments were classified according to a modified American Heart Association 17-segment model
Subjective image quality was also evaluated by two independent readers (each with more than 5 years of CT head and neck angiographic experience) for carotid arteries using a four-point scale
Objective evaluation of image quality of the coronary arteries was measured as image noise, attenuation (measured in Hounsfield Units, HU), and contrast of the coronary lumen, as well as signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR)
Quantitative evaluation of carotid artery image quality was likewise evaluated. For each Group 1 examination, attenuation was measured for ROIs placed in the bifurcation of the left and right common carotid arteries (CCA), as well as for ROIs in the internal carotid arteries (ICA) at the level of C7. To determine vessel contrast enhancement, the CT attenuation in the sternocleidomastoid muscle (at the same level of the vessel measurements) was measured. Image noise was defined as the standard deviation of attenuation in the sternocleidomastoid muscle. SNR and CNR were measured at the level of the CCA bifurcation. Attenuation values of the internal jugular veins (IJV) at the level of the CCA bifurcations were also measured for the evaluation of contamination. The area of the ROI was kept constant (0.11–0.13 cm2) during all measurements.
Measurements of CNR and SNR were performed in a single session. Readers were blinded to the CT protocol used as the images were read in an anonymized fashion. In addition, readers were completely blinded to the clinical -condition of the patients and the indication for examination.
CT Dose Index (CTDIvol) and dose-length product (DLP) were obtained for all scans using the dose exposure record generated by the scanner console.
All variables are expressed as mean value ± SD. Statistical analyses were performed using commercially available software (SPSS, version 16.0, Chicago, IL, USA). Differences in patient characteristics, radiation dose, and image quality parameters (image quality, attenuation, contrast enhancement, image noise, SNR, and CNR) were compared using an ANOVA test and Student’s t test for parametric data, Kruskal-Wallis test for non parametric data, as appropriate. The agreement between the two observers in assessing image quality was calculated by means of Cohen’s kappa statistics. Kappa results were interpreted as being either poor (κ < 0.20), fair (κ = 0.21–0.40), moderate (κ = 0.41–0.60), good (κ = 0.61–0.80), very good (κ = 0.81–0.90), or excellent (κ≥0.91). A P-value of less than 0.05 was considered significant.
In all eligible patients, CTA examinations were carried out successfully. No complications, side effects, or technical failures occurred. Scan times were 1.31±0.06, 0.38±0.01, and 0.42±0.02 seconds and scan range were 504±28, 133.5±11, and 135.5±12 mm for Group 1, 2 and 3, respectively.
Patients from Groups 1, 2 and 3 showed no significant differences in age, sex, or BMI, heart rate (
Characteristics | Group1 | Group2 | Group3 | p |
No. of patients | 47 | 51 | 53 | |
No. of women | 20 | 23 | 24 | NS |
Age (y) | 56.6±9.9 | 62.2±10.2 | 59.9±10.0 | NS |
Heart rate (bpm) | 58.9±4.9 | 57.6±5.3 | 57.0±5.0 | NS |
BMI (kg/m2) | 23.6±6.6 | 24.7±3.4 | 24.8±2.7 | NS |
NS = Not significant.
For Group 1, Group 2 and Group 3: mean attenuation of the aortic root was 445.7±68.4, 376.5±50.0, and 402.0±51.8 HU, mean image noise was 29.0±4.7, 23.0±3.5, and 23.9±2.6 HU, and SNR was 15.7±3.5, 16.7±3.2, and 17.0±3.0, respectively. No significant difference in SNR was observed among the three groups.
The image quality of the LM and proximal RCA did not significantly differ between groups (
Parameter | Group1 | Group2 | Group3 | P |
Mean image quality of coronary arteries | 1.07±0.31 | 1.06±0.38 | 1.04±0.26 | 0.753 |
SNR (AO) | 15.7±3.5 | 16.7±3.2 | 17.0±3.0 | 0.238 |
SNR(LM) | 15.8±3.2 | 16.5±3.4 | 17.3±3.5 | 0.239 |
SNR(RCA) | 15.6±3.3 | 16.7±3.2 | 17.4±3.4 | 0.100 |
CNR(LM) | 17.9±3.6 | 19.2±4.3 | 20.3±4.3 | 0.073 |
CNR(RCA) | 18.5±3.7 | 20.2±3.7 | 20.4±3.9 | 0.084 |
CTDIvol (mGy) | 4.6±0.4 | 5.2±1.1 | 19.0±4.9 | <0.01 |
DLP (mGy×cm) | 256.3±24.5 | 93.4±19.9 | 254.1±69.9 | <0.01 |
Note-Data are mean±SD. NS = Not significant, SNR = Signal-to-noise ratio, CNR = Contrast-to-noise ratio.
There were 722 coronary artery segments available for interpretation in Group 1, 789 segments in Group 2, and 824 segments in Group 3 (Figs.
(a) VRT reconstruction of the whole arteries and MIP reconstructions of the coronary arteries of anterior descending(b) and carotid arteries (c), all with good opacification and definition, without artifacts. DLP was 242 mGy×cm (Scan time: 1.39s; Scan range: 538.5 cm; heart rate: 55 bpm; BMI: 25.4 kg/m2).
(a) MIP reconstruction of the coronary arteries revealed significant stenosis of proximal anterior descending and mild stenosis of proximal right coronary artery. (b)MIP reconstruction of left carotid arteries revealed calcification of proximal ICA. DLP was 242 mGy×cm (Scan time: 1.26s; Scan range: 490.0 cm; heart rate: 59 bpm; BMI: 23.1 kg/m2).
The k statistic for interobserver agreement on the image quality for per-coronary-segment analysis was 0.79. Whereas the k statistic for intraobserver agreement was 0.85. The overall interobserver agreement on a per-patient-based analysis was good (κ = 0.73).
In all cases, the carotid arteries were 100% diagnostic (rated good or excellent) in all arterial segments (Fig2, 3). The mean attenuation values at the left and right CCA bifurcation were 542.4±112.5 HU and 531.1±119.3 HU, respectively. The mean attenuation of the C7 segments of the left and right ICA were 462.0±100.2 HU and 444.8±120.5 HU, respectively. The mean SNRs at the level of the left and right CCA bifurcation were 38. 3±16.0 and 38.5±16.8, respectively. The mean CNRs at the level of the left and right CCA bifurcation were 34.1±18.3 and 35.4±17.6, respectively. The mean attenuation values of left and right IJV at the level of the carotid bifurcation were 156.2±84.1HU and 128.7±83.7 HU respectively. The mean image quality of MCA was 1.11±0.31.
The mean DLP for Group 1 was 256.3±24.5 mGy•cm, significantly higher than that of Group 2 (93.4±19.9 mGy•cm; p<0.001). However, there was no significant difference of DLP between Group 1 and Group 3 (254.1±69.9 mGy•cm).
This is the first study demonstrating feasibility of high-pitch CTA for the combined evaluation of coronary and carotid arteries. Our results confirm that high-pitch CTA can properly assess in a single examination coronary, epiaortic, and intracranial vessels and demonstrate high diagnostic IQ, excellent interreader variability. Most importantly, this protocol used a low dose of contrast media while delivering a minimal amount of radiation. This protocol could be of significant clinical benefit to patients at risk of concomitant coronary and carotid atherosclerosis.
In the study of Bjerrum
The feasibility of the combined cardiac and carotid CTA has been previously investigated in a similar study conducted on patients with suspected stroke
The extremely fast acquisition provides excellent intravascular enhancement at a contrast media dose of 65 mL. In particular the mean vascular attenuation fulfilled the requisites for diagnostic studies as previously reported for the coronary
The major limitation in our study is the lack of a direct comparison with a gold standard, such as invasive angiography, for the assessment of diagnostic accuracy in stenosis detection. However, the performance of high-pitch cCTA has been previously established as reliable in CAD detection
The combined heart, neck, and head artery examination using a low contrast, prospectively ECG-triggered high-pitch CTA resulted in excellent vessel enhancement for high quality images at a low radiation dose. This protocol could be of significant clinical benefit to patients at risk of concomitant coronary and carotid atherosclerosis.