Novel high-performance low-field MRI technology offers several opportunities for MRI-guided cardiovascular interventions. We developed a prototype MRI system that pairs a lower field (0.55T) with modern hardware and contemporary imaging methods, and commercial variants of contemporary low-field systems are now available. We have demonstrated high-quality cardiac imaging and consistent clinical interpretation between 0.55T and 1.5T in patient cohorts with our prototype system. The opportunities and challenges of contemporary low-field MRI for MRI-guided cardiovascular interventions are described here.
There are several advantages of this platform for MRI-guided cardiovascular interventions. Since device heating scales quadratically with field strength, our contemporary 0.55T system offers 7.5-fold lower heating than 1.5T and 30-fold lower heating than 3T. We have demonstrated the use of off-the-shelf metallic guidewires and catheters for MRI-guided catheterization in patients, paired with standard bSSFP real-time imaging, using this system. Furthermore, we have developed "active” MRI devices, leveraging the reduced heating to simplify the device design, demonstrated lesion imaging capabilities, performed MRI-guided pressure-volume loop analysis, and illustrated the improved ECG morphology. Low-field MRI also offers new opportunities for lung imaging, which can be used to study cardiopulmonary interactions paired with MRI-guided hemodynamic characterization.
Several challenges are also associated with MRI-guided interventions at 0.55T. Lower SNR can be combated using advanced data sampling and image reconstruction techniques. Efficient imaging, such as spiral imaging, performs well at this field strength due to the long T2*, enabling high-efficiency data sampling. Additionally, constrained imaging reconstruction techniques and denoising methods can be applied to improve images. Reduced susceptibility artifacts result in reduced visualization of off-the-shelf metallic devices, which can be a safety concern for guidewires and catheters.
Overall, contemporary low-field MRI is attractive for MRI-guided cardiovascular interventions. Ongoing technical developments and clinical evaluations will continue to improve the applicability of this methodology in the future.