Abstract
Cardiovascular magnetic resonance imaging (CMR) has become an indispensable clinical tool for the assessment of morphology, function and structure of the heart muscle. By exploiting quantification of the effective transverse relaxation time (T2*) CMR also affords myocardial tissue characterization and probing of cardiac physiology, both being in the focus of ongoing research. These developments are fueled by the move to ultrahigh magnetic field strengths, which permits enhanced sensitivity and spatial resolution that help to overcome limitations of current clinical MR systems with the goal to contribute to a better understanding of myocardial (patho)physiology in vivo. In this context, the aim of this report is to introduce myocardial T2* mapping at ultrahigh magnetic fields as a promising technique to non-invasively assess myocardial (patho)physiology. For this purpose the basic principles of T2* assessment, the biophysical mechanisms determining T2* and (pre)clinical applications of myocardial T2* mapping are presented. Technological challenges and solutions for T2* sensitized CMR at ultrahigh magnetic field strengths are discussed followed by a review of acquisition techniques and post processing approaches. Preliminary results derived from myocardial T2* mapping in healthy subjects and cardiac patients at 7.0 Tesla are presented. A concluding section discusses remaining questions and challenges and provides an outlook on future developments and potential clinical applications.
Highlights
T2∗ Sensitized Cardiovascular Magnetic ResonanceMyocardial tissue characterization plays an important role in the diagnosis and treatment of cardiac diseases
Quantitative mapping of MR relaxation times which govern the MR signal evolution offers the potential of non-invasive myocardial tissue characterization without the need of exogenous contrast agents
By exploiting the blood oxygenation level-dependent (BOLD) effect [3], T2∗ sensitized cardiovascular magnetic resonance imaging (CMR) has been proposed as a Myocardial T2∗ Mapping at Ultrahigh Field means of assessing myocardial tissue oxygenation and perfusion
Summary
Myocardial tissue characterization plays an important role in the diagnosis and treatment of cardiac diseases. The enhanced susceptibility effects at 7.0 T may be useful to extend the dynamic range of the sensitivity for monitoring T2∗ changes and to lower their detection level Another advantage of performing T2∗ weighted imaging and mapping at ultrahigh magnetic field strengths (UHF) is that the signal-to-noise ratio (SNR) gain achieved at higher fields can be used to improve the spatial resolution [37, 38]. Transitioning to higher magnetic field strengths runs the additional benefit that the in-phase interecho time governed by the fat-water phase shift between the water and main fat peak of about 3.5 ppm is reduced from approximately 4.5 ms (223 Hz) at 1.5 T to 0.96 ms (1,043 Hz) at 7.0 T This enables rapid acquisition of multiple echoes with different T2∗ sensitization and facilitates high spatio-temporally resolved myocardial CINE T2∗ mapping of the human heart [39]. With this in mind it is fair to conclude that myocardial T2∗ mapping could be beneficial for a better understanding of cardiac (patho)physiology in vivo with the ultimate goal to support risk stratification in HCM
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