Emerging MRI techniques for molecular and functional phenotyping of the diseased heart

Figures

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  FIGURE 1. Emerging cardiac MRI (CMR) techniques for molecular and functional characterization of the diseased heart.

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  FIGURE 2. Comparison of a potential future workflow for MRI of microvascular dysfunction to conventional workflow. Instead of injecting a vasoactive drug to induce vasoreactivity, breathing elevated levels of CO2 is proposed as a safer, more repeatable vasoactive alternative. Furthermore, traditional assessment of perfusion change in response to stress via a double gadolinium injection protocol is replaced with a single-injection, blood-pool contrast imaging protocol that permits higher accuracy and specificity.

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  FIGURE 3. Illustration of hypercapnic vasoactive stimulus and single-injection, steady-state blood-pool imaging assessment of microvascular response. (A) Myocardial perfusion maps show the equivalency of gas challenge vs. pharmacological agents for inducing vasodilation. Global myocardial perfusion is shown in a representative subject at baseline, during hypercapnic stimuli, and during adenosine stress [this research was originally published in Pelletier-Galarneau et al. (9)]. (B) Blood-pool steady-state imaging for the assessment of microvascular reactivity. (Left) Vasodilation and vasoconstriction induced by a succession of hypercapnic maneuvers on a rat administered Ablavar. On T1-weighted images, the microvasculature of the renal cortex is seen to constrict (low contrast) on exposure to 20% CO2 but rapidly vasodilate (bright contrast) upon return to 5% CO2. [This research was originally published in Ganesh et al. (6). (Right) A patient with progressive angina presents a large, reversible inferior wall perfusion defect. Ferumoxytol-enhanced T1 map shows rest hypoperfusion in the inferior wall (arrows). At peak stress, ferumoxytol-enhanced T1 reactivity is 6% in the hypoperfused inferior…

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  FIGURE 4. Comparison of targeted imaging of myocardial fibrosis to conventional late gadolinium enhancement. (Upper panel) Late gadolinium enhancement (LGE) in an acute setting does not mean definitive fibrosis, as LGE at 1 week after onset of acute myocarditis disappeared at 6-month follow-up [this research was originally published in Aquaro et al. (79)]. (Lower panel) Myocardial scar injected with a fibrosis-targeted agent, EP-3533, is not visible pre-contrast but is clearly visible 40 min after contrast injection [this research was originally published in Caravan et al. (16)].

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  FIGURE 5. Potential applications of strain cardiac MRI. Strain MRI is suggested for deeper phenotyping of diseases affecting different heart chambers. Note that each list is intended to highlight potential applications and may contain diseases that are not exclusive to a particular chamber.

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  FIGURE 6. 31P MR spectroscopy of myocardial energetics, challenges, and potential applications. (Upper left panel) CMR images of a patient with heart failure with preserved ejection fraction (HFpEF), corresponding localized 31P MR spectra from the left ventricle, and individual PCr/gamma-ATP ratio in patients with HFpEF and in control subjects [this research was originally published in Phan et al. (48)].

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  FIGURE 7. Deep learning-assisted cardiac MRI acceleration. Despite having demonstrated an ability to reconstruct high-quality cardiac MRI from undersampled k-space datasets, deep learning-assisted MRI acceleration face important challenges that must be addressed to ensure flexible, reliable, and widespread adoption.