The Future of Cardiovascular Magnetic Resonance Imaging

Matthias G. Friedrich MD

Disclosures

Eur Heart J. 2017;38(22):1698-1701. 

In This Article

Important Recent Developments Shaping the Future of Cardiovascular Magnetic Resonance

Magnetic Resonance Imaging Systems and Coils

Following improvements in magnet and helium handling technology, stronger gradient systems, and higher field strengths have allowed for an increased contrast-to-noise ratio for several applications, especially perfusion, contrast-enhanced tissue characterization, and angiography. Coil technology has benefitted from novel surface coil concepts with more channels and a massive increase of data points, which can be used for increasing spatial resolution, temporal resolution, or signal-to-noise.

Workstation and User Interface

More and more, fast Graphics Processing Units (GPU) are used for accelerated image reconstruction instead of Central Processing Units (CPU).

In comparison with other imaging modalities, magnetic resonance imaging (MRI) has many more adjustable parameters and a wider range of imaging options. Therefore, special attention must be paid to system operations. Recently, the industry has intensified the development of more intuitive user interfaces and workflows, including automated algorithms for identifying anatomical axes of the heart or even the entire scan procedure. Such advances, where used, have enabled less experienced staff to acquire diagnostically useful CMR images. Furthermore, software for a time-efficient post-processing, evaluation, and reporting of data are increasingly facilitating the work for readers.

Morphology and Function

Accelerated or parallel image acquisition such as compressed sensing can shorten scan times by a factor of 10 or more,[2] with complete 3D cine imaging of the ventricles in one single breath-hold (Figure 1)

Novel analysis methods (feature-tracking or tissue-tracking) allow for measuring strain, strain rate, torsion, and twist in post-processed regular cine images, thereby not adding additional scan time (Figure 2).

Faster computing algorithms have also facilitated handling of large flow data sets with calculation of time-resolved 3D data, also dubbed 4D flow (Figure 3). Flow patterns and quantification provide information on flow volumes, turbulence, and shunts.[3] This is especially interesting for CMR assessment in patients with complex congenital heart disease.

Protocols

Driven by the Society for Cardiovascular MR (SCMR) and partners such as the CMR Section of the European Association for Cardiovascular Imaging, protocol standards and evaluation procedures for CMR have been published and are regularly updated.[4,5] In typical clinical settings, focused protocols facilitate an efficient workflow, allowing for scan times of less than 30 min even for scans with pharmacological vasodilation.[6] In a recent landmark study performed in Bangkok, 123 CMR scans for the assessment of ventricular function and myocardial iron load were performed within 24 work hours,[7] demonstrating the potential of optimized workflows in state-of-the-art CMR.

Tissue

After more than a decade of development, parametric myocardial mapping of myocardial relaxation times is rapidly entering clinical application. The technique provides direct measurement of relaxation times instead of signal intensity values and thus further improves the capabilities of CMR to perform a non-invasive assessment of myocardial pathology in vivo.[8] For acute myocarditis, cardiac amyloidosis, iron overload, and Fabry's disease, native (i.e. without contrast agents) mapping including the measurements of the extracellular volume is already robust enough to be used for clinical decision-making. Figure 4 gives an example.

MR Fingerprinting (MRF) uses randomly acquired data points and pattern recognition algorithms to generate parametric maps for proton density images and T1/T2 maps.[9]

Optimized T1-weighted sequences have been shown to identify unstable plaques and therefore add an important missing piece to the diagnostic evaluation of coronary artery disease. While still scarce, published data indicate an outstanding potential for identifying plaques at risk.[10]

Dynamic Tissue Analysis

Native T1 mapping before and during vasodilator infusion has been successfully applied to track myocardial perfusion,[11] alleviating the need of contrast agents for perfusion imaging. Importantly, such dynamic studies using quantitative data are less sensitive to systematic confounders.

Very recently, oxygenation-sensitive CMR (OS-CMR) has emerged as a disruptive technology for monitoring changes of markers for myocardial oxygenation without the use of contrast agents.[12] The combination with CMR-derived markers for perfusion and metabolism leads to an unprecedented power to examine all levels of myocardial pathophysiology.[13] OS-CMR has also already demonstrated the ability to assess for microvascular dysfunction and for the detection of inducible myocardial ischaemia in patients with significant coronary artery stenosis (Figure 5).[14]

Interventional

Several labs in the USA and in Europe have already started using CMR for invasive vascular applications such as catheterization of the pulmonary arteries. Interventional CMR opens the door to radiation-free vascular procedures, including the quasi-simultaneous assessment of myocardial tissue characteristics via catheter-mounted receive coils during electrophysiology interventions.[15] In the future, even coronary interventions in an MRI system may become feasible.

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