Rationale and Objectives
Prospective electrocardiogram (ECG) triggering allows coronary computed tomography angiography (CCTA) scanning with low radiation dose but requires heart rates below 63 beats/min. We assessed the impact of a novel vendor-specific motion-correction algorithm on image quality and interpretability of low-dose CCTA acquired despite insufficient heart rate control.
Materials and Methods
In 40 patients undergoing CCTA for the assessment of known or suspected coronary artery disease who did not reach the target heart rate below 63 beats/min despite β-blockade before prospective low-dose scanning, the temporal acquisition window was increased (80 ms additional padding). The new algorithm detects and integrates vessel path and velocity from adjacent cardiac phases for motion correction. Two blinded observers assessed image quality on a 4-point Likert scale (1, nonevaluative; 2, reduced but evaluative; 3, good; and 4, excellent) and the fraction of interpretable segments (score 2 or more) using motion correction versus standard reconstruction.
Results
Image reconstruction with motion correction resulted in an increased median coronary artery image quality score (excellent interobserver agreement, κ = 0.85) compared to standard reconstruction (3.4 vs. 3.0, P < .001). Consequently, motion-corrected reconstruction significantly improved the overall interpretability of coronary arteries (from 78% to 88%, P < .001). Estimated mean effective radiation dose was 2.3 ± 0.8 mSv.
Conclusions
A novel, vendor-specific, motion-corrected, reconstruction algorithm improves image quality and interpretability of prospectively ECG-triggered low-dose CCTA despite insufficient heart rate control.
Coronary computed tomography angiography (CCTA) is an established noninvasive tool for the evaluation of coronary artery disease (CAD) in daily clinical routine with high accuracy compared to invasive coronary angiography in a large variety of patients .
Despite impressive technical improvements of CT technology over the past years such as increased temporal resolution and growing number of detectors, motion artifacts remain an important limitation of CCTA. Specifically, when using prospective electrocardiogram (ECG)–triggering protocols for achieving low radiation dose CCTA, a low and stable heart rate is crucial as these protocols are prone to motion artifacts because of insufficient heart rate control . Although dual source CT offers a superior temporal resolution, currently scanning with low heart rate is preferred to allow taking full advantage of the high pitch scanning capability . An opening of the padding, that is, adding surrounding X-ray beam time to the middiastolic window or even conventional spiral scanning with retrospective gating has often been suggested to overcome motion-induced image degradation. However, this is associated with a substantial increase in radiation dose exposure to the patient and does not necessarily improve image interpretability . Many studies have shown a negative correlation of image quality score and heart rate or heart rate variability . Therefore, heart rate control for CCTA is essential before the scan and currently recommended by the guidelines of the Society of Cardiovascular Computed Tomography .
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Materials and methods
Study Population
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CT Acquisition
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CT Image Reconstruction
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CT Image Analysis
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Radiation Dose Estimation
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Statistical Analysis
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Results
Patient Characteristics
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Table 1
Patient Characteristics ( n = 40)
Characteristic Value Age (mean ± SD, y) 60 ± 12 Male (%) 70 BMI (mean ± SD, kg/m 2 ) 27 ± 4 Cardiovascular risk factors (prevalence, %) Hypertension 38 Dyslipidemia 28 Smoking 48 Diabetes 25 Positive family history 33 History of CAD (prevalence, %) Prior PCI 15 Prior CABG 3 Intravenous β-blockade (mean ± SD, mg metoprolol) 21 ± 7 HR during scan (mean ± SD, beats/min) 69 ± 9 HR variability during scan (mean ± SD, beats/min) 3 ± 5 Mean maximum HR during scan (mean ± SD, beats/min) 73 ± 11 Dose–length product (mean ± SD, mGycm) 163 ± 57 Radiation dose (mean ± SD, mSv) 2.3 ± 0.8
BMI, body mass index; CABG, coronary artery bypass grafting; CAD, coronary artery disease; HR, heart rate; PCI, percutaneous coronary intervention; SD, standard deviation.
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Image Quality and Interpretability
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Table 2
Image Quality and Interpretability: Motion-Corrected Versus Standard Reconstructions
Parameter Motion Correction Standard_P_ Value Overall Image quality Per-artery 3.4 (2.7–4.0) 3.0 (2.4–4.0) <.001 Per-patient 3.3 (2.6–3.6) 3.0 (2.5–3.4) <.001 Overall interpretability Per-segment, % 93 (453/488) 86 (421/488) <.001 Per-artery, % 88 (140/160) 78 (125/160) <.001 Interpretability by artery LM, % 100 (40/40) 100 (40/40) 1.0 LAD, % 83 (33/40) 73 (29/40) .125 LCX, % 83 (33/40) 73 (29/40) .219 RCA, % 85 (34/40) 68 (27/40) .016
LAD, left anterior descending artery; LCX, left circumflex artery; LM, left main artery; RCA, right coronary artery.
Image quality values are given as median and interquartile range. Interpretability is given in percentage, whereby the numbers in brackets indicate the ratio of interpretable divided by all segments and coronaries, respectively.
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Impact of Mean Heart Rate and Mean Heart Rate Variability on Image Quality
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Discussion
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Acknowledgments
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