iNAV-Based 3D Whole-Heart Coronary MRA at 0.55T: Clinical Feasibility (RF_FR_290)

Coronary artery disease (CAD) is the leading cause of morbidity and mortality in the developed world.¹ Interest in low-field (< 1.0T) scanners is growing, due to low installation and running costs, environmental advantages due to low helium and a wide bore in the latest generation of commercial low-field scanners, making it more acceptable to claustrophobic and bariatric patients.^2,3 Recently, we were able to demonstrate the feasibility of high-resolution free-breathing coronary magnetic resonance angiography (CMRA) in healthy subjects at 0.55T⁴. In this study we sought to investigate the feasibility of 0.55T low-field CMRA imaging in a series of patients with suspected cardiovascular disease.



Methods:

Nine patients with a range of cardiovascular conditions were recruited and scanned at 0.55T (MAGNETOM Free.Max, Siemens Healthcare, Forchheim, Germany). The sequence consists of an ECG-triggered, 3x under-sampled, free-breathing 3D whole-heart bSSFP acquisition with a variable density spiral-like Cartesian (VD-CASPR) trajectory and the following parameters: FoV = 312x312x88-108 mm³, TR/TE = 4.87/2.20 ms, isotropic spatial resolution=1.5 mm³, bandwidth = 801 Hz/Px. A T2 preparation pulse (60 ms duration, MLEV-4 refocusing scheme) was applied to enhance blood pool contrast. Low-resolution 2D image navigators (iNAV)⁵were incorporated into the sequence at each heartbeat to enable 100% respiratory scan efficiency and predictable scan times. Non-rigid motion-corrected reconstruction with patch-based low-rank denoising⁶ was performed directly in the scanner software. Image acquisition was performed in diastole when heartrate (HR) < 70 beats-per-minute (bpm) or systole otherwise. Qualitative image quality analysis using a  4-point Likert scale (1: uninterpretable images, 2: poor image quality, 3: acceptable image quality, 4: excellent image quality) was performed by a clinical expert to analyse the quality of the images.

Results:

All patients (7 males, average age=57 years, average HR= 63 bpm) were successfully scanned using the described technique with an average scan time of 8.4±1.4 min. One patient was acquired in systole due fast heart rate ( >70 bpm). The average image quality score for each vessel was, LAD: 3.1 (SD=0.8); LCx: 2.8 (SD=0.8); RCA: 3.5 (SD=0.5). An example patient diagnosed with anomalous origin of the right coronary artery (RCA) is shown in Fig. 1. A second patient with CAD displaying coronal, axial and a reformat of the RCA is shown in Fig. 2.



Conclusion:

In this study, we demonstrate the feasibility of performing CMRA at 0.55T low-field strength in patients with cardiovascular disease, with a predictable scan time of ~8 min. Despite a lower signal-to-noise ratio compared with higher-field scanners², we were able to accurately depict the proximal and mid-sections of the coronary arteries in a variety of patients. As demonstrated in one patient with coronary anomaly, we were able to demonstrate the coronary origins clearly and thus detect interarterial course of RCA. Future work will focus on acquiring images in patients with coronary artery disease to assess the suitability of the technique for detecting significant coronary stenoses.