Usefulness of non-contrast-enhanced MRI with two-dimensional balanced steady-state free precession for the acquisition of the pulmonary venous and left atrial anatomy pre catheter ablation of atrial fibrillation: Comparison with contrast enhanced CT in cl

ACR Appropriateness Criteria® Preprocedural Planning for Left Atrial Procedures in Atrial Fibrillation

This document summarizes the relevant literature for the selection of preprocedural imaging in three clinical scenarios in patients needing endovascular treatment or cardioversion of atrial fibrillation. These clinical scenarios include preprocedural imaging prior to radiofrequency ablation; prior to left atrial appendage occlusion; and prior to cardioversion. The appropriateness of imaging modalities as they apply to each clinical scenario is rated as usually appropriate, may be appropriate, and usually not appropriate to assist the selection of the most appropriate imaging modality in the corresponding clinical scenarios. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Atrial fibrillation cardiac radioablation target visibility on magnetic resonance imaging

Magnetic resonance imaging (MRI) guided cardiac radioablation (CR) for atrial fibrillation (AF) is a promising treatment concept. However, the visibility of AF CR targets on MRI acquisitions requires further exploration and MRI sequence and parameter optimization has not yet been performed for this application. This pilot study explores the feasibility of MRI-guided tracking of AF CR targets by evaluating AF CR target visualization on human participants using a selection of 3D and 2D MRI sequences.MRI datasets were acquired in healthy and AF participants using a range of MRI sequences and parameters. MRI acquisition categories included 3D free-breathing acquisitions (3D_acq), 2D breath-hold ECG-gated acquisitions (2D_ECG-gated), stacks of 2D breath-hold ECG-gated acquisitions which were retrospectively interpolated to 3D datasets (3D_interp), and 2D breath-hold ungated acquisitions (2D_real-time). The ease of target delineation and the presence of artifacts were qualitatively analyzed. Image quality was quantitatively analyzed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and non-uniformity. Confident 3D target delineation was achievable on all 3D_interp datasets but was not possible on any of the 3D_acq datasets. Fewer artifacts and significantly better SNR, CNR and non-uniformity metrics were observed with 3D_interp compared to 3D_acq. 2D_real-time datasets had slightly lower SNR and CNR than 2D_ECG-gated and 3D_{interp n} datasets. AF CR target visualization on MRI was qualitatively and quantitatively evaluated. The study findings indicate that AF CR target visualization is achievable despite the imaging challenges associated with these targets, warranting further investigation into MRI-guided AF CR treatments.

Interleaved, undersampled radial multiple-acquisition steady-state free precession for improved left atrial cine imaging

PURPOSE

Balanced steady-state free precession (bSSFP) left atrial (LA) cine suffers from off-resonance artifacts, particularly in the pulmonary veins (PVs). Linear combination or multiple-acquisition SSFP (MA-SSFP) effectively removes banding but greatly increases scan time. We hypothesized that MA-SSFP with interleaved radial undersampling, where each phase-cycling is acquired with an interleaved set of radial projections, would improve image quality of LA cine with a small increase of scan time and streak artefacts.

METHODS

Undersampled radial MA-SSFP with and without interleaving was compared with fully sampled radial bSSFP by means of simulations, phantoms, and in vivo imaging. Ten healthy subjects were imaged on a 3T scanner, with bSSFP and MA-SSFP cine of the left atrium, and B0-mapping. Images were assessed (1 = worst, 5 = best) by 2 independent readers, with respect to 5 qualitative criteria and apparent signal-to-noise ratio.

RESULTS

In healthy subjects, off-resonance differed from the right inferior PVs to the LA cavity by 163 Hz ± 73 Hz at 3T. Compared with fully sampled radial bSSFP, interleaved radial MA-SSFP significantly improved image quality with respect to off-resonance artifacts (3.8 ± 0.6 versus 2.3 ± 1.0; P = 0.005), PV conspicuity (2.8 ± 1.0 versus 4.3 ± 0.5; P = 0.005), and the number of visualized PVs (1.7 ± 0.4 versus 0.9 ± 0.7; P = 0.008), although with greater streak artifacts (3.4 ± 0.4 versus 4.9 ± 0.2; P = 0.004) and lower measured apparent signal-to-noise ratio (24 ± 9 versus 69 ± 36; P = 0.002). Flow artifacts were similar. Interleaved radial MA-SSFP reduced streaking artifacts and increased apparent signal-to-noise ratio versus noninterleaved radial.

CONCLUSIONS

Interleaved radial MA-SSFP cine reduces banding artifacts with an acceptable increase of scan time and streak artifacts. The proposed technique improves the LA and PV visualization in bSSFP cine imaging.

Influence of longitudinal position on the evolution of steady-state signal in cardiac cine balanced steady-state free precession imaging

Background

Emerging quantitative cardiac magnetic resonance imaging (CMRI) techniques use cine balanced steady-state free precession (bSSFP) to measure myocardial signal intensity and probe underlying physiological parameters. This correlation assumes that steady-state is maintained uniformly throughout the heart in space and time.

Purpose

To determine the effects of longitudinal cardiac motion and initial slice position on signal deviation in cine bSSFP imaging by comparing two-dimensional (2D) and three-dimensional (3D) acquisitions.

Material and Methods

Nine healthy volunteers completed cardiac MRI on a 1.5-T scanner. Short axis images were taken at six slice locations using both 2D and 3D cine bSSFP. 3D acquisitions spanned two slices above and below selected slice locations. Changes in myocardial signal intensity were measured across the cardiac cycle and compared to longitudinal shortening.

Results

For 2D cine bSSFP, 46% ± 9% of all frames and 84% ± 13% of end-diastolic frames remained within 10% of initial signal intensity. For 3D cine bSSFP the proportions increased to 87% ± 8% and 97% ± 5%. There was no correlation between longitudinal shortening and peak changes in myocardial signal. The initial slice position significantly impacted peak changes in signal intensity for 2D sequences (P < 0.001).

Conclusion

The initial longitudinal slice location significantly impacts the magnitude of deviation from steady-state in 2D cine bSSFP that is only restored at the center of a 3D excitation volume. During diastole, a transient steady-state is established similar to that achieved with 3D cine bSSFP regardless of slice location.

Almanac 2015: atrial fibrillation research in Heart

Atrial fibrillation continues to attract interest in the cardiovascular community and in Heart. Over 60 original research and review papers published in Heart in 2014–2015 cover various aspects of atrial fibrillation, from associated conditions and precipitating factors to new approaches to management. Here, we provide an overview of articles on atrial fibrillation published in Heart in 2014–2015, highlighting new developments, emerging concepts and novel approaches to treatment.