Cardiac magnetic resonance fingerprinting: Trends in technical development and potential clinical applications

Abstract

Quantitative cardiac magnetic resonance has emerged in recent years as an approach for evaluating a range of cardiovascular conditions, with T₁ and T₂ mapping at the forefront of these developments. Cardiac Magnetic Resonance Fingerprinting (cMRF) provides a rapid and robust framework for simultaneous quantification of myocardial T₁ and T₂ in addition to other tissue properties. Since the advent of cMRF, a number of technical developments and clinical validation studies have been reported. This review provides an overview of cMRF, recent technical developments, healthy subject and patient studies, anticipated technical improvements, and potential clinical applications. Recent technical developments include slice profile and pulse efficiency corrections, improvements in image reconstruction, simultaneous multislice imaging, 3D whole-ventricle imaging, motion-resolved imaging, fat-water separation, and machine learning for rapid dictionary generation. Future technical developments in cMRF, such as B₀ and B₁ field mapping, acceleration of acquisition and reconstruction, imaging of patients with implanted devices, and quantification of additional tissue properties are also described. Potential clinical applications include characterization of infiltrative, inflammatory, and ischemic cardiomyopathies, tissue characterization in the left atrium and right ventricle, post-cardiac transplantation assessment, reduction of contrast material, pre-procedural planning for electrophysiology interventions, and imaging of patients with implanted devices.

Keywords: Cardiac MRI; Magnetic Resonance Fingerprinting; Multiparametric MRI; Quantitative MRI; Relaxometry.

Figure 1.. Overview of the cardiac Magnetic Resonance Fingerprinting (cMRF) approach.

A previously reported 16-heartbeat sequence [13] is used as an example. (a) Components of the cMRF sequence are shown in a representative pulse diagram. Preparation modules include a magnetization preparation pulse (e.g. inversion, INV) followed by a spoiler gradient and delay time before an acquisition block. The acquisition block is composed of an excitation pulse (EXC), spiral gradient trajectory and readout, and gradient spoiler. (b) cMRF employs variable flip angles of the excitation pulses to impart sensitivity to T₁ relaxation. Variable repetition time for the acquisition blocks can also be used, but typically short, constant TR is employed for efficient data collection. (c) The non-Cartesian gradient trajectory, e.g. variable density spiral, is used to impart “noise-like” incoherent undersampling artifact through time. (d) Accelerated images are reconstructed and coil-combined to produce a time series of image data. The cMRF signal for a voxel (yellow box) is measured and compared to a dictionary of signal evolutions for different tissue properties (e.g. T₁, T₂) to find the best match by maximizing the complex inner product. This procedure is repeated for each voxel to obtain T₁, T₂, and M₀ maps (units: T₁ and T₂ (ms), M₀ (arbitrary units)). (e) Stylized, hypothetical healthy and pathologic sub-voxel myocardial tissues are shown to demonstrate the physiological factors that contribute to cMRF signals and are of interest in myocardial tissue characterization. Shown are: intravascular space (red, e.g. capillary), extracellular space (yellow), intracellular space (pink, e.g. cardiomyocytes), and pathologic proteins (blue, e.g. amyloid fibrils). Alterations to intracellular, extracellular, intravascular, or protein deposition patterns can influence magnetic relaxation times and thus may be characterized by cMRF.

Figure 2.

Representative comparison of cMRF-derived T₁ and T₂ maps in a healthy subject and patient with diagnosed light-chain cardiac amyloidosis (AL). Myocardial T₁ and T₂ values were elevated in the AL patient (average T₁: 1592 ms vs 1261 ms, average T₂: 46.3 ms vs 31.7 ms). Additionally, thickening of the left ventricular myocardium is evident in the AL patient as compared to the healthy subject.