Rationale and Objectives
The aim of this study was to evaluate the effect of mean heart rate (HR) and HR variability on image quality in low-dose computed tomographic coronary angiography (CTCA) using prospective electrocardiographic (ECG) triggering.
Materials and Methods
One hundred thirty-six consecutive patients were scheduled for low-dose CTCA using prospective ECG triggering. The image quality of all coronary segments was rated on a 5-point scale by two independent readers (scores of 1–3 were considered diagnostic, and scores of 4 and 5 were considered nondiagnostic). Intravenous β blockers were administered targeting HR < 65 beats/min before scanning, but not if HR increased during scanning.
Results
After the exclusion of seven patients because of arrhythmia ( n = 4) or mean HRs > 65 beats/min despite using β blockers ( n = 3), 129 patients underwent computed tomographic scanning. The estimated mean effective radiation dose was 2.2 ± 0.7 mSv (range, 1.1–3.5). The mean HR during scanning was 58.4 ± 6.6 beats/min (range, 44.2–80.1), with a variability of 1.6 ± 1.0 beats/min (range, 0.2–5.3). Mean HR ( r = 0.49, P < .001) but not mean HR variability ( r = 0.14) was related to image quality. Nondiagnostic image quality on CTCA was found in 5% of the coronary segments in 21 of 129 patients. However, on receiver-operating characteristic analysis, a cutoff HR of 62 beats/min was determined, below which nondiagnostic segments were significantly less frequent (2% vs 14%, P < .001).
Conclusion
Prospective triggering allows low-dose CTCA but requires a low HR. Because a low HR offers a prolonged diastole, widening the optimal phase for scanning, HR variability seems to have a negligible impact on image quality.
The implementation of multidetector computed tomography (MDCT) for coronary angiography allows fast imaging as well as increased temporal and spatial resolution ( ). However, motion artifacts caused by a higher heart rate (HR) or HR variability remain an issue, because they affect image quality. In four-slice and 16-slice MDCT, a higher HR has shown to cause a relevant degradation of image quality ( ). With 64-slice MDCT, the influence of HR and HR variability on image quality remains controversial, with such an effect reported by some authors ( ) but not by others ( ).
Despite further technical refinements and the introduction of dual-source computed tomographic (CT) coronary angiography (CTCA), leading to better temporal resolution, there still appears to be a negative influence of HR variability ( ) or both HR and HR variability ( ) on image quality. To minimize motion artifacts resulting from high HR or HR variability, images are usually reconstructed at the phase of near quiescence in mid-diastole called diastasis ( ). Scanning protocols using a spiral acquisition mode offer the opportunity for image reconstruction at any given point throughout the cardiac cycle, allowing the retrospective selection of any phase in the RR interval ( ) and the use of multisegment reconstructions for improving temporal resolution. With the introduction of prospective electrocardiographic (ECG) triggering ( ), radiation is administered at only one predefined time point in the cardiac cycle. This substantially reduces the effective radiation dose ( ) but in turn provides only a single data set for image reconstruction, achieving diagnostic image quality.
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Material and methods
Patients
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CT Data Acquisition and Postprocessing
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CT Image Analysis
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Statistical Analysis
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Results
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Image Quality of Coronary Artery Segments
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Table 1
Image Quality Scoring of All Segments
Coronary Artery Image Quality Score 1 2 3 4 5 ( n = 755) ( n = 635) ( n = 253) ( n = 56) ( n = 38) RCA Mean 176 173 107 23 11 Segment 1 50 50 16 9 3 Segment 2 22 32 55 12 7 Segment 3 51 44 27 2 1 Segment 4 53 47 9 0 0 LAD Mean 354 263 87 12 13 Segment 5 81 39 7 0 1 Segment 6 71 39 15 0 1 Segment 7 63 49 10 3 3 Segment 8 32 50 38 5 4 Segment 9 60 46 7 3 2 Segment 10 47 40 10 1 2 CX Mean 225 199 59 21 14 Segment 11 68 44 8 6 3 Segment 12 44 36 8 3 3 Segment 13 45 49 19 7 4 Segment 14 42 44 19 3 3 Segment 15 5 6 3 1 1 Segment 16 21 20 2 1 0
CX, circumflex coronary artery; LAD, left anterior descending coronary artery; RCA, right coronary artery.
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Impact of Mean HR on Image Quality
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Table 2
Correlations
Image Score Mean HR Mean HR Variability_r__P__r__P_ All arteries 0.49 <.001 0.17 NS RCA 0.59 <.001 0.14 NS LAD 0.37 <.001 0.17 NS CX 0.37 <.001 0.10 NS
CX, circumflex coronary artery; HR, heart rate; LAD, left anterior descending coronary artery; NS, not significant; RCA, right coronary artery.
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Impact of Mean HR Variability on Image Quality
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Discussion
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