The effect of heart rhythm on patient radiation dose with dual-source cardiac computed tomography

Radiation dose reduction method combining the ECG-Edit function and high helical pitch in retrospectively-gated CT angiography

INTRODUCTION

The purpose of this study was to demonstrate that dose reduction does not compromise image quality when combining high helical pitch (HP) and the ECG-Edit function during low HP retrospectively gated computed tomography angiography (CTA).

METHODS

This study made use of a pulsating cardiac phantom (ALPHA 1 VTPC). The heart rate (HR) of the cardiac phantom was changed in five intervals, every 5 beats per minute (bpm), from 40 to 60 bpm. Evaluation of a range of HR was important because data loss might occur when combining a low HR and high HP. We performed retrospectively gated CTA scans five times using a low HP (0.16) and high HP (0.24), for each of the five HR intervals, using a 64-detector row CT scanner. The CT volume dose index (CTDI_vol) was recorded from the CT console of each scan. For the images with data loss, data were repaired using the ECG-Edit function. We compared the CTDI_vol, estimated cardiac phantom volume, and the visualization of the coronary ladder phantom between HP 0.16, with or without repaired HP 0.24, using the ECG-Edit function.

RESULTS

Data loss occurred with a HR of 40 bpm and 45 bpm when using HP 0.24. The CTDI_vol was reduced by approximately 33% with HP 0.24 when compared with HP 0.16. There were no significant differences in the mean cardiac motion phantom volume and visualization scores between HP 0.16 and with and without repaired HP 0.24 using the ECG-Edit function (p < 0.05).

CONCLUSION

The ECG-Edit function is potential useful for repairing the lost data in patients with a low HR, and when combined with a high HP, it is possible to reduce the radiation dose by approximately 33%.

IMPLICATIONS FOR PRACTICE

The ECG-Edit function and high HP may be a viable option in pediatric CTA studies.

Recent advances in cardiac computed tomography dose reduction strategies: a review of scientific evidence and technical developments

Cardiac imagers worldwide are bracing for increased utilization of cardiac computed tomography (CT) in clinical practice. This expanding opportunity brings along a responsibility to produce diagnostic quality images with optimized radiation dose. The following review aims to address the dose reduction strategies in cardiac CT in light of recent scientific evidence and technical developments.

Cardiothoracic Applications of 3-dimensional Printing

Medical 3-dimensional (3D) printing is emerging as a clinically relevant imaging tool in directing preoperative and intraoperative planning in many surgical specialties and will therefore likely lead to interdisciplinary collaboration between engineers, radiologists, and surgeons. Data from standard imaging modalities such as computed tomography, magnetic resonance imaging, echocardiography, and rotational angiography can be used to fabricate life-sized models of human anatomy and pathology, as well as patient-specific implants and surgical guides. Cardiovascular 3D-printed models can improve diagnosis and allow for advanced preoperative planning. The majority of applications reported involve congenital heart diseases and valvular and great vessels pathologies. Printed models are suitable for planning both surgical and minimally invasive procedures. Added value has been reported toward improving outcomes, minimizing perioperative risk, and developing new procedures such as transcatheter mitral valve replacements. Similarly, thoracic surgeons are using 3D printing to assess invasion of vital structures by tumors and to assist in diagnosis and treatment of upper and lower airway diseases. Anatomic models enable surgeons to assimilate information more quickly than image review, choose the optimal surgical approach, and achieve surgery in a shorter time. Patient-specific 3D-printed implants are beginning to appear and may have significant impact on cosmetic and life-saving procedures in the future. In summary, cardiothoracic 3D printing is rapidly evolving and may be a potential game-changer for surgeons. The imager who is equipped with the tools to apply this new imaging science to cardiothoracic care is thus ideally positioned to innovate in this new emerging imaging modality.

Image Quality and Radiation Exposure Comparison of a Double High-Pitch Acquisition for Coronary Computed Tomography Angiography Versus Standard Retrospective Spiral Acquisition in Patients With Atrial Fibrillation

OBJECTIVE

The aim of this study was to compare image quality and radiation dose of coronary computed tomography (CT) angiography performed with dual-source CT scanner using 2 different protocols in patients with atrial fibrillation.

METHODS

Forty-seven patients with AF underwent 2 different acquisition protocols: double high-pitch (DHP) spiral acquisition and retrospective spiral acquisition. The image quality was ranked according to a qualitative score by 2 experts: 1, no evident motion; 2, minimal motion not influencing coronary artery luminal evaluation; and 3, motion with impaired luminal evaluation. A third expert solved any disagreement.

RESULTS

A total of 732 segments were evaluated. The DHP group (24 patients, 374 segments) showed more segments classified as score 1 than the retrospective spiral acquisition group (71.3% vs 37.4%). Image quality evaluation agreement was high between observers (κ = 0.8). There was significantly lower radiation exposure for the DHP group (3.65 [1.29] vs 23.57 [10.32] mSv).

CONCLUSIONS

In this original direct comparison, a DHP spiral protocol for coronary CT angiography acquisition in patients with atrial fibrillation resulted in lower radiation exposure and superior image quality compared with conventional spiral retrospective acquisition.

State-of-the-Art Updates on Cardiac Computed Tomographic Angiography for Assessing Coronary Artery Disease

OPINION STATEMENT

Cardiac computed tomographic angiography (CCTA) is a noninvasive imaging modality that is increasingly useful for the evaluation of coronary artery disease (CAD). Over the past decade, CCTA has consistently demonstrated an excellent sensitivity for the detection and exclusion of coronary atherosclerosis in patients with stable or acute chest pain symptoms. Large prospective registries have repeatedly demonstrated the prognostic significance of the presence, extent, or absence of CAD by CCTA. In response to initial concerns, technical advances have permitted a dramatic reduction in patient radiation exposure with preserved image quality. For many patients, the radiation dose of CCTA is less than half of that with conventional myocardial perfusion imaging while providing significantly more anatomic information. Furthermore, CCTA's excellent spatial resolution is increasingly being used for noninvasive assessment of coronary plaque, including the detection of higher-risk vulnerable plaque and association between plaque characteristics and ischemia. Finally, new promising techniques that incorporate physiology with anatomy, such as CT-based fractional flow reserve (FFR-CT) and CT perfusion (CTP), are allowing for the noninvasive hemodynamic assessment of coronary stenoses and improvements in the specificity of CCTA findings. Such advances augur a coming transition when CCTA will be a first-line test for the detection, exclusion, and even management of CAD in many patients.

Lidocaine bolus may facilitate computed tomographic coronary angiography in patients with frequent premature ventricular contractions

Introduction

Heart rate irregularities are the major limitations of computed tomographic coronary angiography (CTCA) due to severe motion artifacts.

Aim

To evaluate the safety and efficacy of a lidocaine intravenous bolus in preserving good image quality by the transient suppression of premature ventricular contractions (PVC) during the CTCA scan.

Material and methods

The study group comprised 67 consecutive patients with sinus rhythm and numerous PVC scheduled for CTCA. Intravenous boluses of 25–50 mg lidocaine were given after calcium score assessment and immediately before CTCA. The control group comprised 67 patients with sinus rhythm without PVC matched according to the body mass index (BMI), age, sex, and calcium score. All coronary vessel segments were assessed for image quality and presence of significant stenosis.

Results

As compared with calcium score assessment, after administration of lidocaine and during the CTCA scan PVC were completely suppressed in 22 (40%), reduced in 10 (18%), unchanged in 18 (32%), and intensified in 5 (10%) patients. Overall, there were 32 (58%) patients with sinus rhythm during CTCA as compared with only 11 (20%) patients free from PVC during calcium score assessment (p < 0.001). Image quality in 871 coronary segments including both the study group and control patients was worse in patients with PVC (p < 0.0001). However, there was no statistically significant difference in the number of patients with at least one segment of non-diagnostic quality (6% vs. 12%, p = 0.36; respectively).

Conclusions

Single lidocaine bolus given prior to CTCA is safe, may temporarily eliminate or reduce the intensity of arrhythmia, and hence results in improved quality of CTCA in patients with numerous PVC.

Weekly dose reports: the effects of a continuous quality improvement initiative on coronary computed tomography angiography radiation doses at a tertiary medical center

RATIONALE AND OBJECTIVES

Numerous protocols have been developed to reduce cardiac computed tomography angiography (cCTA) radiation dose while maintaining image quality. However, cCTA practice is highly dependent on physician and technologist experience and education. In this study, we sought to evaluate the incremental value of real-time feedback via weekly dose reports on a busy cCTA service.

MATERIALS AND METHODS

This time series analysis consisted of 450 consecutive patients whom underwent physician-supervised cCTA for clinically indicated native coronary evaluation between April 2011 and January 2013, with 150 patients before the initiation of weekly dose report (preintervention period: April-September 2011) and 150 patients after the initiation (postintervention period: September 2011-February 2012). To assess whether overall dose reductions were maintained over time, results were compared to a late control group consisting of 150 consecutive cCTA exams, which were performed after the study (September 2012-January 2013). Patient characteristics and effective radiation were recorded and compared.

RESULTS

Total radiation dose was significantly lower in the postintervention period (3.4 mSv [1.7-5.7] and in the late control group (3.3 mSv [2.0-5.3] versus the preintervention period (4.1 mSv [2.1-6.6] (P = .005). The proportion of high-dose outliers was also decreased in the postintervention period and late control period (exams <10 mSv were 88.0% preintervention vs. 97.3% postintervention vs. 95.3% late control; exams <15 mSv were 98.0% preintervention vs. 100.0% postintervention vs. 98.7% late control; exams <20.0 mSv were 98.7% preintervention vs. 100.0% postintervention vs. 100.0% late control).

CONCLUSION

Weekly dose report feedback of site radiation doses to patients undergoing physician-supervised cCTA resulted in significant overall dose reduction and reduction of high-dose outliers. Overall dose reductions were maintained beyond the initial study period.

Feasibility of aortic valve assessment with low dose prospectively triggered adaptive systolic (PTAS) cardiac computed tomography angiography

BACKGROUND

Cardiac computed tomography angiography (CTA) is feasible for aortic valve evaluation, but retrospective gated protocols required high radiation doses for aortic valve assessment. A prospectively triggered adaptive systolic (PTAS) cardiac CT protocol was recently described in arrhythmia using second-generation dual-source CT. In this study, we sought to evaluate the feasibility of PTAS CTA to assess the aortic valve at a low radiation dose.

FINDINGS

A retrospective cohort of 29 consecutive patients whom underwent PTAS protocols for clinical indications other than aortic valve assessment and whom also received echocardiography within 2 months of CT, was identified. Images were reviewed for aortic valve morphology (tricuspid/bicuspid/prosthetic) and stenosis (AS) by experienced blinded readers. Accuracy versus echocardiography and radiation doses were assessed.

CONCLUSIONS

PTAS CTA protocols using second-generation dual-source CT for aortic valve evaluation are feasible at low doses. This protocol should be investigated further in larger cohorts.

Radiation dose considerations by intra-individual Monte Carlo simulations in dual source spiral coronary computed tomography angiography with electrocardiogram-triggered tube current modulation and adaptive pitch

OBJECTIVES

To evaluate radiation dose levels in patients undergoing spiral coronary computed tomography angiography (CTA) on a dual-source system in clinical routine.

METHODS

Coronary CTA was performed for 56 patients with electrocardiogram-triggered tube current modulation (TCM) and heart-rate (HR) dependent pitch adaptation. Individual Monte Carlo (MC) simulations were performed for dose assessment. Retrospective simulations with constant tube current (CTC) served as reference. Lung tissue was segmented and used for organ and effective dose (ED) calculation.

RESULTS

Estimates for mean relative ED was 7.1 ± 2.1 mSv/100 mAs for TCM and 12.5 ± 5.3 mSv/100 mAs for CTC (P < 0.001). Relative dose reduction at low HR (≤60 bpm) was highest (49 ± 5%) compared to intermediate (60-70 bpm, 33 ± 12%) and high HR (>70 bpm, 29 ± 12%). However lowest ED is achieved at high HR (5.2 ± 1.5 mSv/100 mAs), compared with intermediate (6.7 ± 1.6 mSv/100 mAs) and low (8.3 ± 2.1 mSv/100 mAs) HR when automated pitch adaptation is applied.

CONCLUSIONS

Radiation dose savings up to 52% are achievable by TCM at low and regular HR. However lowest ED is attained at high HR by pitch adaptation despite inferior radiation dose reduction by TCM.

KEY POINTS

• Monte Carlo simulations allow for individual radiation dose calculations. • ECG-triggered tube current modulation (TCM) can effectively reduce radiation dose. • Slow and regular heart rates allow for highest dose reductions by TCM. • Adaptive pitch accounts for lowest radiation dose at high heart rates. • Women receive higher effective dose than men undergoing spiral coronary CT-angiography.