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Dual-Source CT: Effect of Heart Rate, Heart Rate Variability, and Calcification on Image Quality and Diagnostic Accuracy¹

¹ From the Departments of Diagnostic Radiology (H.B., I.T., A.R., C.D.C., M.H., A.F.K.) and Cardiology (C.B., S.S.), Eberhard-Karls-University, Hoppe-Seyler-Str 3, 72076 Tübingen, Germany. Received May 24, 2007; revision requested July 31; revision received September 9; accepted October 9; final version accepted October 29. Address correspondence to H.B. (e-mail: h.brodoefel{at}t-online.de)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Purpose: To prospectively evaluate the effect of heart rate, heart rate variability, and calcification on dual-source computed tomography (CT) image quality and to prospectively assess diagnostic accuracy of dual-source CT for coronary artery stenosis, by using invasive coronary angiography as the reference standard.

Materials and Methods: This study had local Ethics Committee approval; all patients gave informed consent. Patients who underwent bypass surgery were excluded; patients with coronary artery stent-grafts were included. One hundred patients (20 women, 80 men; mean age, 62 years ± 10 [standard deviation]) known to have or suspected of having coronary artery disease underwent dual-source CT and invasive coronary angiography. Image quality was assessed. Accuracy of dual-source CT in depiction or exclusion of significant stenosis (50%) was evaluated on a per-segment and per-patient basis. Effects of heart rate, heart rate variability, and calcification on image quality and accuracy were analyzed by using multivariate regression and were analyzed between subgroups of predictor variables. Simple regression was performed to calculate thresholds for adequate image quality.

Results: Mean heart rate was 64.9 beats per minute ± 13.2, mean variability was 23.6 beats per CT examination ± 36.2, and mean Agatston score was 786.5 ± 965.9. Diagnostic image quality was obtained in 90.2% of segments. Sensitivity, specificity, and positive and negative predictive values for the presence of significant stenosis were, respectively, 91.1%, 92.0%, 75.4%, and 97.5% by segment and 100%, 81.5%, 93.6%, and 100% by patient. Image quality was significantly related to heart rate variability (P = .015) and calcification (P < .001); the number of nondiagnostic segments was significantly affected by calcification only. Calcification was the single factor with significant impact on diagnostic accuracy (P = .001).

Conclusion: While dual-source CT resulted in heart-rate independent image quality, image quality remained prone to heart rate variability and calcification.

© RSNA, 2008

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
In the field of noninvasive coronary artery imaging, motion and blooming artifacts have been recognized as the essential challenges to image quality and accurate detection of vessel stenosis (1,2). While cardiac motion is mainly a concern at elevated or irregular heartbeat, blooming artifacts are caused by severe calcification which may, at its worst, lead to obscuration of the entire vessel lumen.

In the past few years, advances in spatial and temporal resolution translated into better image quality and improved accuracy for the detection of high-grade stenosis (3–12). Thereby, 16- and 64-section computed tomographic (CT) technology had the potential to extend acceptable image quality to higher heart rates and likewise reduce blooming artifacts related to heavy calcification (13–16). However, even with 64-section CT, with its superior gantry rotation speed of 330 msec and isotropic spatial resolution of 0.4 mm³, elevated and irregular heartbeats were found to cause relevant degradation of image quality (16–20). Moreover, severe calcification has persistently been linked to a decrease in diagnostic accuracy (12,21).

Recently, a CT system equipped with two tubes and corresponding detectors in a 90° geometry has been designed and provides temporal resolution of approximately a quarter of its 330-msec gantry rotation time (22). This approach thus allows a temporal resolution of 83 msec, which is independent of the patient's heart rate and eliminates the need for dual-segment reconstruction algorithms. Results of pilot studies on cardiac applications of this dual-source CT system have been promising, and results of a feasibility study have shown excellent accuracy for detection of coronary artery disease in an unselected patient cohort (23–25). However, to date, effects of heart rate and heart rate variability on diagnostic accuracy have not been systematically assessed in a larger patient cohort to our knowledge.

The aim of our study was to prospectively evaluate the effect of heart rate, heart rate variability, and calcification on dual-source CT image quality and to prospectively assess the diagnostic accuracy of dual-source CT for coronary artery stenosis, by using invasive coronary angiography as the reference standard.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Study Patients
Our study protocol was approved by the local Ethics Committee, with radiation dose information having been supplied to that Committee. All patients provided informed consent for participation in the study after having been informed of radiation dose information.

From September 2006 to March 2007 we screened 119 patients who were scheduled to undergo invasive coronary angiography because they were suspected of having coronary artery disease or because progression of known coronary artery disease was suspected. Exclusion criteria were renal insufficiency (serum creatinine level > 1.5 mg/dL [132.6 µmol/L]), hyperthyroidism (basal thyroid-stimulating hormone < 0.03 µL/L), known allergic reaction to iodinated contrast medium, and inability to follow breath-hold commands. Patients who underwent bypass surgery were excluded from this study, while patients with coronary artery stent grafts were not. Eight patients could not be enrolled because of refusal or withdrawal of consent. Two patients were excluded because of impaired renal function, seven were excluded because of previous bypass surgery, and one was excluded because of acute coronary syndrome necessitating immediate invasive coronary angiography. After coronary CT angiography, one patient declined to undergo invasive coronary angiography. Thus, the ultimate study population comprised 100 patients (20 women, 80 men; mean age, 62 years ± 10). Seventy-five of these patients were taking a beta-blocker as part of their baseline medication. Additional beta-blocker medication was not administered. All dual-source CT studies were performed the day prior to invasive coronary angiography.

Coronary CT Angiography
CT studies were performed with a dual-source scanner (Somatom Definition; Siemens Medical Solutions, Forchheim, Germany) in all patients and were performed without complications. Prior to acquisition of the topogram, patients received a single dose of 2.5 mg of isosorbiddinitrate (Isoket; Schwarz Pharma, Monheim, Germany).

Total calcium burden was assessed by using an initial unenhanced CT scan with the following parameters: collimation, 32 x 0.6 mm; section acquisition, 64 x 0.6 mm with the z-flying focal spot technique; gantry rotation time, 330 msec; pitch, 0.2–0.39, depending on heart rate; tube current, 80 mAs per rotation; and tube voltage, 120 kV.

For contrast material–enhanced studies, vessel opacification was achieved by using automated injection (CT2; Medtron, Saarbrücken, Germany) of 80 mL of iomeprol (Imeron 400; Altana, Konstanz, Germany) at a flow rate of 5 mL/sec and a 60-mL chaser bolus. Estimation of individual circulation time was based on the test-bolus technique, by using a 20-mL bolus and dynamic evaluation software (Dyn Eva; Siemens).

For coronary CT angiography, collimation was 32 x 0.6 mm; section acquisition was 64 x 0.6 mm with the z-flying focal spot technique; gantry rotation time was 330 msec; pitch was 0.20–0.43, adapted to heart rate; tube voltage was 120 kV; and maximum tube current was 400 mAs per rotation. For dose reduction, prospective tube current modulation was applied. Thereby, at heart rates less than 60 beats per minute, full tube current was applied from 60% to 70% of the cardiac cycle; at heart rates 60–70 beats per minute, from 50% to 80% of the cardiac cycle; and at heart rates higher than 70 beats per minute, from 30% to 80% of the cardiac cycle.

For data reconstruction, a single-segment reconstruction algorithm was applied, which used the data of a quarter rotation of both detectors for image reconstruction.

For calcium scoring, the standard reconstruction window was set at 60% of the R-R interval by using nonoverlapping images with 3-mm effective section thickness and a medium-sharp convolution kernel (B35f).

For CT angiography, an initial reconstruction window was based on the results of a test series that were obtained in a transverse plane at the level of segment 2 and that displayed reconstruction window offsets by 5% of the entire cardiac cycle. In case of motion artifacts in the initial reconstruction, further reconstructions were performed in 5% increments of the cardiac cycle until all individual arteries could be visualized at optimal image quality.

In case of arrhythmia, R-wave indicators were manually adapted to improve the quality of synchronization.

Effective section thickness was 0.75 mm, with a reconstruction increment of 0.4 mm. Data sets were filtered with a medium-soft convolution kernel (B26f).

Image Analysis
CT data were referred to an offline workstation (Leonardo; Siemens) and were interactively assessed by two readers (H.B. and A.R., each with 4 years of experience in cardiovascular radiology) who were blinded to the results of invasive coronary angiography and to clinical information. Decisions were reached with consensus reading.

The Agatston score was assessed on unenhanced images with a detection threshold of 130 HU by using semiautomated software (Syngo Calcium Scoring; Siemens).

Contrast-enhanced dual-source CT was evaluated by using thin-slab maximum intensity projection, along with curved-planar reformation and three-dimensional volume rendering.

For the rating of image quality and stenosis detection, a modified model of the coronary tree with 13 segments was employed (26): For the right coronary artery, segment 1 was considered proximal; 2, middle; 3, distal; and 4, combined posterior descending and posterolateral branches. Segment 5 was considered the left main stem artery. For the left anterior descending artery, 6 was considered proximal; 7, middle; 8, distal; 9, first diagonal; and 10, second diagonal. For the left circumflex artery, 11 was considered proximal; 12, marginal branches; and 13, combined distal American Heart Association segments 13, 14, and 15.

Image quality was classified for each segment as being excellent (absence of artifacts related to motion or coronary calcification), as indicated with a score of 1; good (minor artifacts), score of 2; moderate (considerable artifacts but maintained visualization of arterial lumen), score of 3; or poor (nondiagnostic because of severe motion artifacts or extensive wall calcification), score of 4.

Segments were visually scored for the presence of significant stenosis (50% narrowing in luminal diameter). In the case of multiple lesions per segment, the segment was classified by using the worst stenosis.

Invasive Coronary Angiography
Conventional coronary angiography was performed by two experienced cardiologists (C.B. and S.S., with 7 and 13 years of experience, respectively) according to standard procedures by using the transfemoral or transradial Judkins technique. To visualize the right coronary artery, at least two projections were obtained; for the left coronary artery, at least six projections were obtained. Stenosis severity was evaluated by using quantitative coronary analysis (QCA, version 3.3; Philips, Eindhoven, the Netherlands).

All invasive coronary angiograms were evaluated by a single observer (C.B.) who was blinded to CT results. Segmental disease was analyzed in each vessel by using the same 13-segment model employed for dual-source CT analysis. Lesions with a stenosis 50% or more in diameter were considered to be significant. Stenosis severity was classified on the projection with maximal luminal diameter stenosis.

Statistical Analysis
Statistical analysis was performed with software (JMP, version 6, SAS Institute, Cary, NC; GraphPad Prism, version 4.00, GraphPad Software, San Diego, Calif; Stata, version 9.2, StataCorp, College Station, Tex). A P value of less than .05 indicated a statistically significant difference.

Quantitative variables were expressed as means ± standard deviations; categoric variables were expressed as frequencies or percentages. Values of image quality are given in means ± standard deviations. Impact of heart rate, heart rate variability, or calcification on mean image quality per patient was tested by using multivariate linear regression analysis and effect testing. Thereby, heart rate was defined as mean heart rate during examination; heart rate variability refers to the maximal spread of heart rate during examination. Calcification is quantified by Agatston score. Interaction between variables was checked by including multiplicative terms in the initial model; colinearity of x variables was ruled out by calculating the variance inflation factor. In case of skewed distribution, logarithmic transformation of x variables was performed (log₁₀). Simple linear regression was performed to plot effects of the above parameters against image quality, and thresholds were calculated by using a linear regression equation.

Image quality and the number of nondiagnostic segments in subgroups of the predictor variables were compared by using Mann-Whitney or Kruskal-Wallis statistics with Dunn multiple-comparison test.

The diagnostic performance of dual-source CT for the detection of significant stenosis is presented as sensitivity, specificity, positive predictive value, negative predictive value, and accuracy. Comparison between dual-source CT and coronary angiography was performed on a per-segment and per-patient basis (presence or absence of at least one significant coronary artery stenosis).

The impact of heart rate, heart rate variability, or calcification on the accuracy for all segments was tested by using multivariate logistic regression analysis. The per-segment accuracy across subgroups of predictor variables was compared by using univariate logistic regression. For both tests, we took into account the clustered nature of the data by using a generalized estimating equation population-averaged model.

Retrospective power calculations were performed for nonsignificant results in between-subgroup comparisons for image quality and diagnostic accuracy. For image quality, power was calculated as a function of a .05 significance level, the given data structure (sample size and standard deviation), and a clinically meaningful effect size. For accuracy, power was calculated by simulation analyses with 1000 replications according to the observed intrapatient correlation, the distribution between subgroups, and clinically meaningful effect sizes.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Study Patients
Evaluation of both image quality and diagnostic accuracy was based on a total of 1229 segments among 100 patients (Table 1, Fig 1). Sixty-six segments were excluded from analysis because of stent-graft placement; five segments were nonaccessible because of variations in coronary anatomy (n = 3) or small vessel diameter (n = 2). Agatston score was 400 or less in 53 patients and more than 400 in 47 patients. Median calcium score was 370 (mean score, 787).

View larger version (18K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Chart of patient flow and outcome for CT angiography (CTA) and the reference standard, invasive coronary angiography (ICA). Abnormal result and target are defined as significant coronary artery stenosis per segment or per patient. ACS = acute coronary syndrome.

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 2a: CT angiographic images show good image quality despite mean heart rate of 98 beats per minute. On curved-planar reconstructions, the (a) right coronary artery, (b) left anterior descending artery, and (c) circumflex artery are displayed in their entire length without motion artifacts.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 2b: CT angiographic images show good image quality despite mean heart rate of 98 beats per minute. On curved-planar reconstructions, the (a) right coronary artery, (b) left anterior descending artery, and (c) circumflex artery are displayed in their entire length without motion artifacts.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 2c: CT angiographic images show good image quality despite mean heart rate of 98 beats per minute. On curved-planar reconstructions, the (a) right coronary artery, (b) left anterior descending artery, and (c) circumflex artery are displayed in their entire length without motion artifacts.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 3a: (a) Curved-planar CT reconstruction and (b) conventional CT angiogram of left anterior descending artery in a 72-year-old patient with Agatston score of 379, heart rate of 61 beats per minute, and heart rate variability of 45 beats per examination. Dual-source CT imaging resulted in moderate image quality, and soft-plaque stenosis in segment 7 (arrow in a) is suspected. Angiographic results confirm high-grade stenosis in mid left anterior descending artery (arrow in b). At the same time, significant stenosis was ruled out for mixed plaque in segment 6, which suggests difficulty with coronary calcification.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 3b: (a) Curved-planar CT reconstruction and (b) conventional CT angiogram of left anterior descending artery in a 72-year-old patient with Agatston score of 379, heart rate of 61 beats per minute, and heart rate variability of 45 beats per examination. Dual-source CT imaging resulted in moderate image quality, and soft-plaque stenosis in segment 7 (arrow in a) is suspected. Angiographic results confirm high-grade stenosis in mid left anterior descending artery (arrow in b). At the same time, significant stenosis was ruled out for mixed plaque in segment 6, which suggests difficulty with coronary calcification.

View larger version (140K): [in this window] [in a new window] [Download PPT slide]   Figure 4a: (a) Maximum intensity CT projection, (b) curved-planar CT reconstruction, and (c) conventional angiogram of right coronary artery in a 58-year-old patient with Agatston score of 417, heart rate of 88 beats per minute, and heart rate variability of 26 beats per examination. Dual-source CT imaging resulted in good image quality despite elevated heart rate and considerable variability of heartbeat. High-grade stenosis (arrow) in segment 2 is confirmed at angiography.

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 4b: (a) Maximum intensity CT projection, (b) curved-planar CT reconstruction, and (c) conventional angiogram of right coronary artery in a 58-year-old patient with Agatston score of 417, heart rate of 88 beats per minute, and heart rate variability of 26 beats per examination. Dual-source CT imaging resulted in good image quality despite elevated heart rate and considerable variability of heartbeat. High-grade stenosis (arrow) in segment 2 is confirmed at angiography.

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 4c: (a) Maximum intensity CT projection, (b) curved-planar CT reconstruction, and (c) conventional angiogram of right coronary artery in a 58-year-old patient with Agatston score of 417, heart rate of 88 beats per minute, and heart rate variability of 26 beats per examination. Dual-source CT imaging resulted in good image quality despite elevated heart rate and considerable variability of heartbeat. High-grade stenosis (arrow) in segment 2 is confirmed at angiography.

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   Figure 5a: Images of false-positive finding in a 65-year-old patient with Agatston score of 510, heart rate of 68 beats per minute, and heart rate variability of 39 beats per examination. (a) Maximum intensity CT projection and (b) curved-planar CT reconstruction show poor image quality in segment 7 due to extensive calcification and motion artifacts (arrow); (c) assumption of high-grade stenosis was not confirmed at angiography.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 5b: Images of false-positive finding in a 65-year-old patient with Agatston score of 510, heart rate of 68 beats per minute, and heart rate variability of 39 beats per examination. (a) Maximum intensity CT projection and (b) curved-planar CT reconstruction show poor image quality in segment 7 due to extensive calcification and motion artifacts (arrow); (c) assumption of high-grade stenosis was not confirmed at angiography.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 5c: Images of false-positive finding in a 65-year-old patient with Agatston score of 510, heart rate of 68 beats per minute, and heart rate variability of 39 beats per examination. (a) Maximum intensity CT projection and (b) curved-planar CT reconstruction show poor image quality in segment 7 due to extensive calcification and motion artifacts (arrow); (c) assumption of high-grade stenosis was not confirmed at angiography.

The significant effect of calcification was confirmed for all arteries, while the effect of heart rate variability proved true for all vessels except the left main artery. Heart rate independence of image quality was likewise established for the entire vessel tree.

Heart Rate and Image Quality
Mean image quality and the total number of motion-degraded segments were not significantly different in patients with heart rates more than 70 beats per minute compared with patients with heart rates 70 or fewer beats per minute (P = .13 and .37, respectively) (Table 2). Given the sample size of 100 patients and the observed standard deviations in our subgroups for image quality, this analysis had 94% power to detect a difference between the means of image quality of 0.50.

View larger version (6K): [in this window] [in a new window] [Download PPT slide]   Figure 6: Linear regression plot of mean image quality of all coronary segments (excluding segments nondiagnostic because of calcification) against mean heart rate during CT examination. Slope is not significantly different from zero (P = .12). Dashed lines = 95% confidence limits. According to linear correlation, the x-intercept is 95.2 beats per minute when y is 2.0.

View larger version (7K): [in this window] [in a new window] [Download PPT slide]   Figure 7: Linear regression plot of mean image quality of all coronary segments (excluding segments nondiagnostic because of calcification) against the logarithm of heart rate variability during CT examination. On the x-axis, corresponding raw values of logarithms are denoted in parentheses. Slope is significantly different from zero (P = .004). Dashed lines = 95% confidence limits. According to linear correlation, the x-intercept is 29.9 beats per examination when y is 2.0.

View larger version (6K): [in this window] [in a new window] [Download PPT slide]   Figure 8: Linear regression plot of mean image quality of all coronary segments against Agatston score. Slope is significantly different from zero (P < .001). Dashed lines = 95% confidence limits. According to linear correlation, x-intercept is at Agatston score of 375.8 when y is 2.0. Ca = calcium.

Diagnostic Accuracy and Heart Rate, Heart Rate Variability, or Calcification
According to a multivariate logistic regression analysis considering the effect of heart rate, heart rate variability, and calcium score on the accuracy of lesion detection, calcification was the single factor with a significant influence (P = .002). At the same time, there was a significant difference between accuracies among the three subgroups of Agatston score (Table 4) (P < .001).

According to multivariate regression analysis, heart rate and heart rate variability showed no impact on accuracy of lesion detection (P = .95 and .56, respectively). Accuracies were equal among subgroups of these predictor variables (Tables 2, 3) (P = .73 for heart rate, P = .09 for heart rate variability). Given the observed data structure, the analyses had 85% power to detect absolute differences in accuracy by subgroups of heart rate and heart rate variability of 8% each.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Our primary study findings are threefold: First, in a patient population that is unselected for heart rate, arrhythmias during the examination, and calcification, dual-source CT resulted in good image quality and high diagnostic accuracy, both of which were independent of patient heart rate. Second, while inconsistency of heartbeat during examination does exert a considerable effect on image quality, there is no translation of such effect into deterioration of diagnostic accuracy. Finally, excessive calcification was found to pose a serious limitation to image quality and was linked to a significant reduction in diagnostic accuracy.

The overall accuracy that was found for dual-source CT in our patient group is comparable to previously reported data on the use of 64-section scanners (9,10,12). Nevertheless, in contrast to these studies, our data were obtained in an unselected patient group with excessive Agatston scores and without an additional beta-blocker premedication for heart rate control or minimization of intercycle variability.

The benefit of improved temporal resolution with dual-source CT is evident from results of multivariate regression analysis, which showed heart rate to have no effect on image quality and diagnostic accuracy. This finding was true on a segmental and arterial basis and was confirmed with an additional investigation of two subgroups for heart rate.

According to linear regression analysis performed for heart rate against image quality, dual-source CT results in good image quality at heart rates up to 95.2 beats per minute.

Interestingly, with regard to 64-section CT systems, a conceivable effect of heart rate on diagnostic accuracy has been controversially discussed. While Raff et al (12) found a significant degradation of accuracy in subgroups of elevated heart rate, such inverse correlation was less obvious according to results of other investigations (7–9,11). By contrast, almost all studies on 64-section CT revealed a persistent significant impact of heart rate on image quality (16,17,19,20).

Our data suggest a superior stability of dual-source CT in the setting of elevated heart rate. The finding of heart-rate independent image quality may represent another milestone in cardiac CT.

Interexamination heart rate variability results in unpredictability of R-R intervals and subsequent impairment of electrocardiographically gated image-reconstruction technique. Interestingly, results of a recent study (16) on 64-section CT showed heart rate variability as a major determinant of image quality while, in the same collective, heart rate itself was ruled out as a significant predictor variable.

Likewise, in our investigation on dual-source CT, heart rate variability was proved to have significant effect on image quality of all included segments or individual coronary arteries. Of note, in our unselected patient collective, mean interexamination variability was excessive and considerably exceeded changeability findings in the above cited analysis on 64-section CT (16). Indeed, according to our linear regression analysis, dual-source CT may result in good image quality until a variability of 29.9 beats per examination.

It is of special interest that effects of heart rate changeability on image quality did not translate into a loss of diagnostic accuracy. The most likely explanation is that deterioration of global image quality was predominantly caused by a shift of excellent toward good or good toward moderate image quality; the number of motion-degraded, nondiagnostic segments proved equal in both subgroups of heart rate variability. This preservation of diagnostic image quality reflects the improved temporal resolution of dual-source CT. As with 64-section CT, arrhythmia still necessitates a thorough manual repositioning of R-wave indicators in case of inadequate automatic synchronization. Yet, enhanced stability in the setting of irregular heartbeat represents a major advantage over previous CT generations and may eventually extend the application of noninvasive coronary angiography to patients known to have arrhythmia.

According to our multivariate regression analysis, vessel calcification was a serious challenge to accurate assessment of coronary arteries. Given a median Agatston score of 370 (mean, 787), overall calcium burden in our study was comparatively high and, indeed, effects on image quality and diagnostic accuracy were highly significant. A total of 100 (8.1%) segments that were considered nondiagnostic because of abundant calcification suggest that calcium burden remains a fundamental problem of coronary CT angiography and is certainly not addressed by exclusive increase of temporal resolution. In fact, according to linear regression analysis, there is a persistent threshold for adequate image quality at an Agatston score around 400. This finding is in agreement with previous data (12) on 64-section CT, which likewise show a significant loss of accuracy in a subgroup for patients with a calcium score more than 400.

Our study had limitations. As all patients were referred to our center for catheterization, there was a considerable patient selection bias with a prevalence of coronary artery disease of 73%. At the same time, our study excluded patients with acute coronary syndromes, and further investigations are needed to determine diagnostic accuracy in such patients.

The study design has a lack of direct comparison with previous CT generations; hence, the benefit of increased temporal resolution may not be quantified, and differences in results may potentially be attributed to different population variables. The evaluation of coronary artery stenosis was performed with consensus reading instead of independent reading, and quantification was performed by using visual assessment.

Because the primary focus of our study was on image quality and accuracy as functions of multiple predictors, the outcome variable was kept as homogeneous as possible and stents were excluded from the analysis.

In conclusion, we demonstrated that improved temporal resolution with dual-source CT provides heart-rate independent image quality within a wide range of patient heart rates. While interexamination variability has a persistent impact on global image quality, there is a large cutoff for good image quality and no translation of effect into deterioration of accuracy. Such findings have important implications for the administration of beta-blockers or exclusion of patients with arrhythmia and may eventually broaden the clinical indications for coronary CT angiography. With further increase of temporal resolution, calcification emerges as the primary cause of degraded image quality and continues to pose a fundamental challenge to diagnostic accuracy.

	ADVANCES IN KNOWLEDGE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 

• Results of multifactor logistic regression analysis show that dual-source CT results in good image quality that is independent of heart rate.
  
• Despite a persistent inverse correlation of image quality to heart rate variability with dual-source CT, there is no translation of such effect into deterioration of accuracy.
  
• With dual-source CT, calcification emerges as the primary cause of degraded image quality and continues to pose a fundamental challenge to diagnostic accuracy.
  

	IMPLICATION FOR PATIENT CARE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 

• Our findings have potential implications on administration of beta-blockers or exclusion of patients with arrhythmia and may eventually broaden the clinical indications for coronary CT angiography.
  

	ACKNOWLEDGMENTS

 
The authors thank Jacqueline Buros from the PERFUSE Core Laboratory and Data Coordinating Center at Harvard Medical School for her substantial contribution to the statistical analysis of our data.

	FOOTNOTES

 
Author contributions: Guarantors of integrity of entire study, H.B., C.B., A.F.K.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, H.B., A.F.K.; clinical studies, C.B., I.T., A.R., M.H.; statistical analysis, H.B.; and manuscript editing, H.B., C.B., S.S., C.D.C., M.H., A.F.K.

Authors stated no financial relationship to disclose.

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 

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