Improved image quality at 256-slice coronary CT angiography in patients with a high heart rate and coronary artery disease: comparison with 64-slice CT imaging

Abstract

Background

The 256-slice computed tomography (CT) scanners with wider detector coverage and faster gantry rotation speed are now available. The performance of scanners that feature a rotation speed of 270 ms at coronary CT angiography (CCTA) has not been evaluated in patients with a higher heart rate.

Purpose

To evaluate the image quality of 256-slice CT with faster gantry rotation speed in patients undergoing CCTA.

Material and Methods

We enrolled 886 patients; 357(40.3%) underwent study on a 64-slice CT at a rotation speed of 420 ms, the other 529 (59.7%) were examined using a 256-slice CT scanner at 270 ms. Two observers judged the image quality of 2658 imaged coronary arteries on a 4-point scale.

Results

The mean image quality score was significantly higher for the 256 - than the 64-slice CT scans (3.94 ± 0.28 vs. 3.73 ± 0.61; P < 0.01). There was no significant difference in the image quality scores between 64 - and 256-slice scans in patients whose heart rate (HR) was <60 bpm. However, in patients whose HR exceeded 60 bpm these scores were significantly higher for 256-slice CT images (P < 0.01).

Conclusion

CCTA performed on the 256-slice CT scanner yielded significantly better image quality in patients with an HR exceeding 60 bpm.

Keywords

Coronary CT angiography image quality 256-slice CT rotation speed heart rate computed tomography (CT)

Introduction

Coronary computed tomography angiography (CCTA) facilitates non-invasive, accurate evaluation for the confirmation or exclusion of significant coronary artery stenosis (1 –3). Although the gantry rotation time is faster on advanced scanners (4,5), a high heart rate (HR) increases motion artifacts of the coronary arteries and this limits the diagnostic image quality (4). New 256-slice CT scanners with wider detector coverage and a faster gantry rotation speed (270 ms/rotation) are now available. The single-cycle temporal resolution of the 256-slice CT instruments is 135 ms; it is 165–210 ms for 64-slice CT scanners. Klass et al. (6) whose study population included only patients with a stable HR below 65 bpm suggested that CCTA performed on a 256-slice CT scanner yields significantly improved and more stable image quality than 64-slice CT. To our knowledge, the effect of using 256-slice CT for CCTA in patients with a high HR has not been thoroughly assessed.

The purpose of this study was to clarify the effect of the faster gantry rotation speed and wider detector coverage of 256-slice CT scanners on the image quality at CCTA in high HR patients and to compare the results with images acquired on a 64-slice CT scanner.

Material and Methods

This retrospective study was approved by our institutional review board; patient informed consent was waived.

Study population

We reviewed 1014 consecutive series of ECG-gated CCTA studies performed at our institute during the year 2011. A total of 128 patients with inadequate breath-holding during scanning and patients with atrial fibrillation, coronary artery bypass grafting, and aged less than 16 years were excluded. Consequently, 886 patients (591 men, 295 women; mean age, 70.3 ± 10.3 years; age range 32–91 years) were included. All were referred for CCTA for clinical reasons based on guidelines promulgated by the American College of Cardiology (7). Of the 886 patients, 357 (40.3%) underwent scanning on a 64-slice CT scanner (Brilliance 64, Philips Healthcare, Cleveland, OH, USA) between January and May 2011. In June 2011 we replaced that machine with a 256-slice CT scanner (Brilliance iCT, Philips Healthcare, Cleveland, OH, USA) and assessed the other 529 patients (59.7%) seen thereafter on the new scanner.

The characteristics of our patients are summarized in Table 1. The mean HR of all patients during data acquisition was 60.7 ± 9.4 bpm (range, 38–113 bpm); and 60.4 ± 8.8 bpm (range, 40–103 bpm) and 60.9 ± 9.9 bpm (range, 38–113 bpm) in patients subjected to 64 - and 256-slice CCTA, respectively (P = 0.51). The patients were assigned to different groups based on their average HR during data acquisition: (group 1: HR< 60 bpm, n = 424; group 2: 60 bpm ≤ HR <70 bpm, n = 325; group 3: 70 bpm ≤ HR <80 bpm, n = 105; group 4: 80 bpm ≤ HR, n = 32).

Table 1.

Patient characteristics.

	64-slice CT	256-slice CT	P value
Patients (n)	357	529	–
Group 1: HR <60	174	250	–
Group 2: 60 ≤ HR <70	131	194	–
Group 3: 70 ≤ HR <80	42	63	–
Group 4: 80 ≤ HR	10	22	–
Age (years)	71.1 ± 10.1	69.7 ± 10.1	0.69
Female/male	119 / 238	174 / 355	0.62
Body weight (kg)	54.5 ± 10.9	55.7 ± 10.4	0.47
Average heart rate (bpm)	60.4 ± 8.8	60.9 ± 9.9	0.51
Calcium score (Agatston score)	326.4 ± 454.0	397.2 ± 460.2	0.55
Hypertension	171 (48%)	237 (45%)	0.36
Hyperlipidemia	142 (40%)	191 (36%)	0.27
Diabetes mellitus	47 (13%)	59 (11%)	0.37

Data are the mean ± SD.

HR, heart rate.

CCTA acquisition

The parameters for 64-slice CT scanning were: detector collimation, 64 × 0.625 mm; tube rotation time, 420 ms; helical pitch (beam pitch), 0.20; tube voltage, 120 kVp; tube current-time product, 800–900 mAs. The calculated volume CT dose index (CTDI_vol) was 52.8 mGy. The parameters for 256-slice CT scanning were: detector collimation, 2 × 128 × 0.625 mm with dynamic z-focal spot; tube rotation time, 270 ms; helical pitch (beam pitch), 0.16; tube voltage, 120 kVp; tube current-time product, 800–1000 mAs. The CTDI_vol was 51.5 mGy. We did not use the ECG-dependent tube current modulation technique with either protocol.

If the baseline HR was ≥65 bpm we intravenously (i.v.) injected the beta-blocker landiolol hydrochloride (6–10 mg, Corebeta; Ono Pharmaceutical, Osaka, Japan) 4–7 min before CCTA or administered propranolol hydrochloride (10–20 mg, Inderal; AstraZeneca, Osaka, Japan) orally 60 min before CCTA. Each patient received nitroglycerin (0.3 mg, Nitropen; Nippon Kayaku, Tokyo, Japan) sublingually 5 min before data acquisition to dilate the coronary arteries. Using a double-head power injector (Autoenhance A-250; Nemoto Kyorindo, Tokyo, Japan), iopamidol (iodine concentration 370 mg/mL; Iopamiron-370; Bayer HealthCare, Osaka, Japan) was given to each patient via a 20-gauge catheter inserted into an antecubital vein. The amount of contrast material, adjusted to the body weight of each patient (350 mgI/kg for 64-slice CT, 300 mgI/kg for 256-slice CT), was injected at a fixed injection duration of 14 s (64-slice CT) and 12 s (256-slice CT). We then injected 40 mL of a saline solution at the same rate as the contrast medium. The start time of data acquisition was determined with a computer-assisted bolus-tracking program (Bolus Pro Ultra; Philips Medical Systems) (8); the trigger threshold was 100 Hounsﬁeld units (HU) in the ascending aorta and data acquisition started 6 s after triggering. Axial images (section thickness and interval 0.67 and 0.33 mm) were reconstructed using a medium cardiac kernel (XCB). Initially, a single dataset was reconstructed during the mid-diastolic phase (75% of the R-R interval). In cases with unsatisfactory image quality, image reconstruction of the raw data was performed from 0% to 95% of the R-R interval in 5% steps to improve the image quality of all available coronary segments. Depending on the patient HR, for both 64 - and 256-slice CT a single- or multi-segment (2–5 segments) reconstruction algorithm was used; this resulted in a temporal resolution ranging from 210 to 42 ms (64-slice CT) and from 135 to 27 ms (256-slice CT). Our acquisition parameters are summarized in Table 2.

Table 2.

Imaging and contrast material parameters of helical CCTA at 64- and 256-slice CT.

	64-slice CT	256-slice CT
Imaging parameters
Detector collimation (mm)	64 × 0.625	2 × 128 × 0.625
Dynamic z focal spot	No	Yes
Gantry rotation time (ms)	420	270
Tube voltage (kVp)	120	120
Tube current–time product (mAs)	900	800
Beam pitch	0.20	0.16
ECG synchronization	Retrospective ECG gating	Retrospective ECG gating
Imaging duration (s)	Approximately 8.5	Approximately 3.5
Reconstructed slice thickness(mm)	0.67	0.67
Slice overlap (mm)	0.33	0.33
Reconstruction kernel	Medium cardiac kernel (XCB)	Medium cardiac kernel (XCB)
Contrast material parameters
Iodine concentration (mgI/mL)	370	370
Volume (mgI/kg)	350	300
Injection duration (s)	14	12
Bolus tracking threshold (HU)	100	100
Post-threshold delay (s)	6	6

Image analysis

All images were reviewed and interpreted on PACS workstations (EV Insite, PSP Corp., Tokyo, Japan). The available images included axial source images and multiplanar- and curved multiplanar reconstructions. For viewing, images acquired on the two CT systems were intermixed. Two radiologists with 4 and 8 years of experience in CCTA who were blinded to the CT systems used, consensually assessed the images with respect to motion artifacts of the right coronary artery (RCA), the left main to the left anterior coronary artery (LMA-LAD), and the left circumflex coronary artery (LCX). They used a 4-point scale (Fig. 1) where: 4 (excellent) = no motion artifacts, useful diagnostic information; 3 (good) = some motion artifacts, sufficient diagnostic information; 2 (fair) = motion artifacts present, partially limited diagnostic information, and 1 (poor) = too much motion artifacts, no diagnostic information. A total of 2658 coronary arteries were assessed. Image quality scores below 2 (fair) were considered non-diagnostic. We compared the image quality scores of the two CT systems and also compared the scores assigned to patients grouped by their HR.

Fig. 1.

Angiographic examples of the image quality. (a) Poor image quality (score = 1). There are too many motion artifacts. No diagnostic information. (b) Fair image quality (score = 2). There are motion artifacts. Diagnostic information is somewhat limited. (c) Good image quality (score = 3). There are some motion artifacts. Diagnostic information is sufficient. (d) Excellent image quality (score = 4). There are no motion artifacts and the information is diagnostically useful.

Radiation dose

The machine-generated CTDI_vol (mGy) per examination during CCTA imaging was recorded. The method averages the radiation dose over the center slice of a CT examination consisting of multiple parallel slices. The dose length product (DLP) was calculated on the basis of the CTDI_vol and data acquisition range. The effective radiation dose to the chest was obtained by using the equation (9): effective radiation dose = DLP × 0.014.

Effect of oral and i.v. beta-blockers on HR

In 349 of the 886 patients (39.4%) the baseline HR was ≥65 bpm and they received oral (n = 251) or i.v. beta blockers (n = 98). Before CCTA the effect of the beta blockers on HR was assessed; the HR before beta blocker administration and also the mean HR during CCTA scanning were recorded. There was no significant difference in the age (P = 0.73) and gender distribution (P = 0.61) of patients treated with oral or i.v. beta blockers.

Statistical analysis

Numerical data were expressed as the mean ± SD. Patient demographics and image quality scores obtained at 64- and 256-slice CT were compared. We also assessed the DLP and the effective radiation dose delivered under the two protocols. Differences in the mean values obtained at 64- and 256-slice CT for normally and non-normally distributed data were determined with the two-tailed independent t-test and the Mann-Whitney U test, respectively. All statistical analyses were with commercially available software (SPSS; SPSS version 15.0, SPSS, Chicago, IL, USA) and P values <0.05 were considered to indicate significant differences.

Results

Image quality analysis

The mean image quality score for all coronary arteries and the individual scores for the RCA, LMA-LAD, and LCX were significantly higher for 256-slice than 64-slice CCTA (P < 0.01; Table 3). In patients where the HR was less than 60 bpm there was no significant difference between 256- and 64-slice CCTA with respect to the mean image quality scores of all coronary arteries. On the other hand, when we compared the other groups categorized by the HR (60 bpm ≤ HR <70 bpm, 70 bpm ≤HR <80 bpm, and 80 bpm ≤HR) we found that the mean image quality scores were significantly higher for 256- than 64-slice CCTA (P < 0.01). The 256-slice CCTA images of 1566 of 1587 coronary arteries (98.7%) were of diagnostic quality as were the images of 983 of 1071 coronary arteries (91.8%) scanned at 64-slice CCTA (Table 4). The difference between the two systems with respect to diagnostic images of the coronary arteries was statistically significant (P < 0.01). The reconstruction cardiac phases on the 64- and 256-slice CT scanner are summarized in Table 5.

Table 3.

Comparison of the coronary image quality grade at 64- and 256-slice CT.

Heart rate (bpm)	Coronary	64-slice CT	256-slice CT	P value
<60	RCA	3.94 ± 0.26	3.99 ± 0.09	0.44
	LMA-LAD	3.96 ± 0.20	4.00 ± 0.00	0.48
	LCX	3.93 ± 0.32	4.00 ± 0.00	0.33
	Total	3.94 ± 0.26	3.99 ± 0.05	0.16
60 ≤ HR <70	RCA	3.68 ± 0.65	3.96 ± 0.22	<0.01
	LMA-LAD	3.84 ± 0.46	3.99 ± 0.07	0.07
	LCX	3.86 ± 0.44	4.00 ± 0.00	0.10
	Total	3.79 ± 0.53	3.98 ± 0.14	<0.01
70 ≤ HR <80	RCA	2.71 ± 0.89	3.68 ± 0.62	<0.01
	LMA-LAD	2.88 ± 0.86	3.83 ± 0.46	<0.01
	LCX	3.09 ± 0.79	3.79 ± 0.45	<0.01
	Total	2.90 ± 0.86	3.77 ± 0.52	<0.01
80≤HR	RCA	2.40 ± 0.84	3.68 ± 0.62	<0.01
	LMA-LAD	2.80 ± 0.92	3.83 ± 0.46	<0.01
	LCX	2.71 ± 0.95	3.79 ± 0.45	<0.01
	Total	2.63 ± 0.89	3.48 ± 0.79	<0.01
All	RCA	3.66 ± 0.70	3.92 ± 0.34	<0.01
	LMA-LAD	3.76 ± 0.58	3.95 ± 0.23	<0.01
	LCX	3.77 ± 0.56	3.96 ± 0.22	<0.01
	Total	3.73 ± 0.61	3.94 ± 0.28	<0.01

Data are the mean ± SD.

HR, heart rate; LAD, left anterior coronary artery; LCX, left circumflex coronary artery; LMA, left main coronary artery; RCA, right coronary artery.

Table 4.

Number of diagnostic coronary artery images obtained on 64- and 256-slice CT.

Heart rate (bpm)	Diagnostic coronary arteries for 64-slice CT	Diagnostic coronary arteries for 256-slice CT	P value
<60	518/522 (99.2%)	750/750 (100%)	0.02
60 ≤ HR <70	372/393 (94.7%)	581/582 (99.8%)	<0.01
70 ≤ HR <80	77/126 (61.1%)	181/189 (95.8%)	<0.01
80 ≤ HR	16/30 (53.3%)	54/66 (81.8%)	<0.01
Total	983/1071 (91.8%)	1566/1587 (98.7)	<0.01

Data are the mean ± SD.

HR, heart rate.

Table 5.

Reconstruction cardiac phases on 64- and 256-slice CT.

	64-slice CT		256-slice CT
Heart rate (bpm)	Systolic phase (%)	Diastolic phase (%)	Systolic phase (%)	Diastolic phase (%)
<60	2/174 (1.1%)	172/174 (98.9%)	1/250 (0.4%)	249/250 (99.6%)
60 ≤ HR <70	9/131 (6.9%)	122/131 (93.1%)	7/194 (3.6%)	187/194 (96.4%)
70 ≤ HR <80	13/42 (31.0%)	29/42 (69.0%)	17/63 (27.0%)	46/63 (73.0%)
80 ≤ HR	7/10 (70.0%)	3/10 (30.0%)	17/22 (77.3%)	5/22 (22.7%)
Total	31/357 (8.7%)	326/357 (91.3%)	42/529 (7.9%)	487/529 (92.1%)

HR, heart rate.

Radiation dose

At 64-slice CCTA, the estimated radiation dose was 14.5 ± 2.6 mSv (range, 11.8–20.6 mSv); it was 15.1 ± 2.9 mSv (range, 12.2–21.0 mSv) at 256-slice CCTA (P = 0.41).

Effect of oral and i.v. beta-blockers on the heart rate

The mean HR reduction obtained with the oral and the i.v. beta-blockers was –19.0 ± 10.1 and –18.8 ± 10.9, respectively (P = 0.53). No major adverse reactions were observed.

Discussion

We demonstrate that in patients with an HR of 60 bpm or higher the 256-slice CT scanner yielded significantly better image quality than the 64-slice scanner. This was primarily attributed to the improved gantry rotation speed (270 ms) of the 256-slice CT scanner and the shorter imaging time required for helical acquisition at wider detector coverage. The increased coverage shortens the acquisition time for the cardiac anatomy and lowers the sensitivity to HR variations.

At CCTA, the 256-slice CT scanner yields a temporal resolution of 135 – 27 ms depending on the patient HR; at 64-slice CT it is 210 – 42 ms. At an HR of 60 bpm or higher, the image quality of 64-slice CT scans deteriorated; this may be explicable by the lower temporal resolution. On the other hand, at 256-slice CCTA the image quality was robust even at higher HR and the temporal resolution was better.

When multi-segment reconstruction algorithms are used, the image quality may suffer due to a broadening of the time sensitivity profile because of inconsistencies of subsequent heart cycles. As the cardiac motion pattern varies with each beat, spatial inconsistencies and blurring occur if data for a single transverse image are sampled from several heartbeats. Segmented reconstruction algorithms assume periodicity of consecutive cardiac cycles, however, data from several subsequent cardiac cycles with slightly different R-R interval lengths are derived from slightly different cardiac phases (10). As this timing shift is averaged out during the reconstruction of each transverse image, blurring within individual images is increased. Theoretically, such spatial inconsistencies impair diagnostic accuracy for stenosis detection and grading. The improved temporal resolution of 256-slice CT can increase the HR range over which single-segment image reconstruction is obtained, thereby avoiding the need for multi-segment reconstruction and excessive image blurring.

Klass et al. (6) who compared the image quality of CCTA performed on 64- and 256-slice CT systems in patients with a stable HR below 65 bpm concluded that CCTA using 256-slice CT yielded significantly better and more stable image quality and attributed this, as we did, primarily to their faster gantry rotation speed. Ours is the first comparative evaluation of 64- and 256-slice CT in patients with a high HR undergoing CCTA. According to Khan et al. (11), at CCTA the image quality was significantly better with 320-row than 64-slice CT. We posit that this is attributable to the reduction in the image acquisition time at 320-row CT because the gantry rotation time was 350 ms for both systems. We suggest that not only the shorter acquisition time but also the faster rotation time improve subjective image quality at CCTA.

At dual-source CT the temporal resolution is 83 ms. Wang et al. (12) compared the image quality at single- and dual-source CT. They reported similar results in patients with a lower HR but in patients with an HR in the range of 70–79 bpm, dual-source CT yielded better image quality, suggesting that faster temporal resolution is a prerequisite for successful CCTA in patients with a high HR.

The higher the HR, the greater is the likelihood of motion artifacts that can considerably diminish the diagnostic accuracy of CCTA scans (13,14). Bamberg et al. (15) evaluated a total of 6253 coronary segments and found that the odds for non-evaluable segments were 1.35 per 10 bpm. According to current guidelines, the ideal HR is below 60 bpm for optimal image quality (16).

Reducing the HR with beta blockers has been recommended in most patients referred for CCTA (16 –19). Variability in the HR, which also affects the image quality, was considerably lower in patients treated with beta blockers before CCTA (2.45 bpm ± 1.53 vs. 4.29 bpm ± 2.25) (20). There was no significant difference in the HR reduction after the oral or i.v. delivery of beta blockers and no adverse reactions were elicited in our patients. Maffei et al. (21) reported that the desired effect was obtained much faster with the i.v. than the oral delivery of beta blockers. To avoid prolongation of pre- and post CCTA care we now routinely deliver the beta blocker landiolol hydrochloride i.v. to patients with a high HR who are scheduled for CCTA.

Earlier studies that used 64- and 256-slice CT systems reported that the coronary image quality was equivalent and that the radiation dose could be reduced by 73–77% at prospective compared to helical CCTA (22,23). Thus, in select patients with a regular, low HR, prospective ECG-gated CCTA should be used. However, this technique cannot be applied in patients with an irregular or high HR. Moreover, with prospective gating, cardiac images are acquired during only a small portion of the R-R interval and functional information on cardiac valve and wall motion is not available. Therefore, helical acquisition remains important in patients with an irregular or high HR and when functional information of the heart wall and heart valves must be obtained.

The study population in this retrospective study consisted of 886 patients seen during the period from January to December 2011. During that period we routinely used retrospective ECG-gated scanning to evaluate not only the coronary arteries but also left ventricular function, myocardial ischemia, and the cardiac valves (24 –26) and to avoid unexpected motion artifacts. However, we recognize that the radiation exposure was much higher at retrospective than prospective ECG-gated scanning. Hou et al. (23) compared the image quality and radiation dose for CCTA obtained with a prospectively gated and a retrospectively gated technique using a 256-slice CT scanner with a 270-ms gantry rotation speed, the same system we employed in our study. They concluded that a prospectively gated technique was applicable in patients with a stable HR below 75 bpm. With respect to radiation exposure, we should have used a prospectively gated technique in our patients with a stable HR below 75 bpm, and a retrospectively gated technique with ECG-dependent dose modulation in patients whose HR was 75 bpm or higher.

Our study has some limitations. First, we did not consider segment bias in our evaluations. The effect of temporal resolution may be different in each coronary segment even in the same coronary artery. Second, we evaluated the image quality subjectively and did not perform quantitative measurements to assess diagnostic accuracy and the signal-to-noise and the contrast-to-noise ratios. Third, ours is a retrospective study of patients imaged on two different systems. Repeat image acquisition in each patient for prospective studies using both 64- and 256-slice CT systems facilitates patient-specific image quality comparisons but is prohibited by dose-exposure considerations. Fourth, we did not use radiation dose reduction techniques such as prospective ECG-gated scanning and ECG-dependent dose modulation in our CCTA protocol.

In conclusion, ECG-gated CCTA performed on a 256- rather than a 64-slice CT scanner yields significantly better image quality in patients whose HR is 60 bpm or higher. Our findings suggest that 256-slice CCTA is a viable non-invasive option for cardiac imaging in patients with a high HR.

Footnotes

Conflict of interest

None declared.

Funding

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

References

Mowatt

Cook

Hillis

. 64-Slice computed tomography angiography in the diagnosis and assessment of coronary artery disease: systematic review and meta-analysis. Heart 2008; 94: 1386–1393.

Miller

Rochitte

Dewey

. Diagnostic performance of coronary angiography by 64-row CT. N Engl J Med 2008; 359: 2324–2336.

Meijer

O YL Geleijns

. Meta-analysis of 40- and 64-MDCT angiography for assessing coronary artery stenosis. Am J Roentgenol 2008; 191: 1667–1675.

Muenzel

Noel

Dorn

. Step and shoot coronary CT angiography using 256-slice CT: effect of heart rate and heart rate variability on image quality. Eur Radiol 2011; 21: 2277–2284.

Wicky

Rosol

Hoffmann

. Comparative study with a moving heart phantom of the impact of temporal resolution on image quality with two multidetector electrocardiography-gated computed tomography units. J Comput Assist Tomogr 2003; 27: 392–398.

Klass

Walker

Siebach

. Prospectively gated axial CT coronary angiography: comparison of image quality and effective radiation dose between 64- and 256-slice CT. Eur Radiol 2010; 20: 1124–1131.

Taylor

Cerqueira

Hodgson

. ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac Computed Tomography. A Report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, the Society of Cardiovascular Computed Tomography, the American College of Radiology, the American Heart Association, the American Society of Echocardiography, the American Society of Nuclear Cardiology, the North American Society for Cardiovascular Imaging, the Society for Cardiovascular Angiography and Interventions, and the Society for Cardiovascular Magnetic Resonance. Circulation 2010; 122: e525–555.

Cademartiri

Nieman

van der Lugt

. Intravenous contrast material administration at 16-detector row helical CT coronary angiography: test bolus versus bolus-tracking technique. Radiology 2004; 233: 817–823.

Jessen

Shrimpton

Geleijns

. Dosimetry for optimisation of patient protection in computed tomography. Appl Radiat Isot 1999; 50: 165–172.

10.

Halliburton

Stillman

Flohr

. Do segmented reconstruction algorithms for cardiac multi-slice computed tomography improve image quality? Herz 2003; 28: 20–31.

11.

Khan

Khosa

Nasir

. Comparison of radiation dose and image quality: 320-MDCT versus 64-MDCT coronary angiography. Am J Roentgenol 2011; 197: 163–168.

12.

Wang

. Dose performance and image quality: dual source CT versus single source CT in cardiac CT angiography. Eur J Radiol 2009; 72: 396–400.

13.

Hoffmann

Shi

Manzke

. Noninvasive coronary angiography with 16-detector row CT: effect of heart rate. Radiology 2005; 234: 86–97.

14.

Dewey

Vavere

Arbab-Zadeh

. Patient characteristics as predictors of image quality and diagnostic accuracy of MDCT compared with conventional coronary angiography for detecting coronary artery stenoses: CORE-64 Multicenter International Trial. Am J Roentgenol 2010; 194: 93–102.

15.

Bamberg

Abbara

Schlett

. Predictors of image quality of coronary computed tomography in the acute care setting of patients with chest pain. Eur J Radiol 2010; 74: 182–188.

16.

Abbara

Arbab-Zadeh

Callister

. SCCT guidelines for performance of coronary computed tomographic angiography: a report of the Society of Cardiovascular Computed Tomography Guidelines Committee. J Cardiovasc Comput Tomogr 2009; 3: 190–204.

17.

Shim

Kim

Lim

. Improvement of image quality with beta-blocker premedication on ECG-gated 16-MDCT coronary angiography. Am J Roentgenol 2005; 184: 649–654.

18.

Budoff

Achenbach

Blumenthal

. Assessment of coronary artery disease by cardiac computed tomography: a scientific statement from the American Heart Association Committee on Cardiovascular Imaging and Intervention, Council on Cardiovascular Radiology and Intervention, and Committee on Cardiac Imaging, Council on Clinical Cardiology. Circulation 2006; 114: 1761–1791.

19.

Jacobs

Boxt

Desjardins

. ACR practice guideline for the performance and interpretation of cardiac computed tomography (CT). J Am Coll Radiol 2006; 3: 677–685.

20.

Leschka

Wildermuth

Boehm

. Noninvasive coronary angiography with 64-section CT: effect of average heart rate and heart rate variability on image quality. Radiology 2006; 241: 378–385.

21.

Maffei

Palumbo

Martini

. “In-house” pharmacological management for computed tomography coronary angiography: heart rate reduction, timing and safety of different drugs used during patient preparation. Eur Radiol 2009; 19: 2931–2940.

22.

Shuman

Branch

May

. Prospective versus retrospective ECG gating for 64-detector CT of the coronary arteries: comparison of image quality and patient radiation dose. Radiology 2008; 248: 431–437.

23.

Hou

Yue

Guo

. Prospectively versus retrospectively ECG-gated 256-slice coronary CT angiography: image quality and radiation dose over expanded heart rates. Int J Cardiovasc Imaging 2012; 28: 153–162.

24.

Seneviratne

Truong

Bamberg

. Incremental diagnostic value of regional left ventricular function over coronary assessment by cardiac computed tomography for the detection of acute coronary syndrome in patients with acute chest pain: from the ROMICAT trial. Circ Cardiovasc Imaging 2010; 3: 375–383.

25.

Nagao

Matsuoka

Kawakami

. Detection of myocardial ischemia using 64-slice MDCT. Circ J 2009; 73: 905–911.

26.

Chen

Manning

Frazier

. CT angiography of the cardiac valves: normal, diseased, and postoperative appearances. Radiographics 2009; 29: 1393–1412.