Myocardial inflammation and energetics by cardiac MRI: a review of emerging techniques

Abstract

The role of inflammation in cardiovascular pathophysiology has gained a lot of research interest in recent years. Cardiovascular Magnetic Resonance has been a powerful tool in the non-invasive assessment of inflammation in several conditions. More recently, Ultrasmall superparamagnetic particles of iron oxide have been successfully used to evaluate macrophage activity and subsequently inflammation on a cellular level. Current evidence from research studies provides encouraging data and confirms that this evolving method can potentially have a huge impact on clinical practice as it can be used in the diagnosis and management of very common conditions such as coronary artery disease, ischaemic and non-ischaemic cardiomyopathy, myocarditis and atherosclerosis. Another important emerging concept is that of myocardial energetics. With the use of phosphorus magnetic resonance spectroscopy, myocardial energetic compromise has been proved to be an important feature in the pathophysiological process of several conditions including diabetic cardiomyopathy, inherited cardiomyopathies, valvular heart disease and cardiac transplant rejection. This unique tool is therefore being utilized to assess metabolic alterations in a wide range of cardiovascular diseases. This review systematically examines these state-of-the-art methods in detail and provides an insight into the mechanisms of action and the clinical implications of their use.

Keywords: Cardiovascular magnetic resonance (CMR); Magnetic resonance spectroscopy (MRS); Ultrasmall superparamagnetic particles of iron oxide (USPIO).

Fig. 1

a Patient 1 week post left anterior descending artery infarction with extensive, anterior wall, transmural, mid-ventricle late gadolinium enhancement (LGE) on T1-weighted images (left column), homogeneous myocardial T2 ∗ values before erumoxytol (middle column), but intense dark ferumoxytol uptake in the region of the infarction 24 h post ferumoxytol infusion (right column). b Same patient with anteroapical, transmural LGE, again homogeneous T2 ∗ myocardial values at base, but clear ferumoxytol uptake on T2 ∗ scanning in the region of the LGE 24 h after ferumoxytol infusion. Image reproduced with permission from Merinopoulos et al. [10]

Fig. 2

An example of a patient with acute myocarditis showing sub-epicardial LGE, inferiorly and inferolaterally on 4-chamber and 3-chamber views (left) but no evidence of ferumoxytol uptake within the regions displaying LGE 24 h following infusion (right). CMR = cardiac magnetic resonance; LGE = late gadolinium enhancement. Image reproduced with permission from Merinopoulos et al. [10]

Fig. 3

Classification of aneurysms based on uptake of ultrasmall superparamagnetic particles of iron oxide (USPIO). MRI is performed at baseline then 24 h following intravenous administration of USPIO. USPIO causes a reduction in T2* and can be quantified by comparing co-registered T2* images pre- and post- USPIO administration, presented as change in T2* represented as colour maps (as above). 'Positive uptake' of USPIO is denoted by the red colour (thresholded at change in T2* of at least 71% between pre-and post-USPIO administration), whereas blue denotes areas of no positive uptake. Of note, ‘significant’ uptake (i.e. USPIO positive) is defined as at least one focal area of USPIO uptake corresponding to 10 or more contiguous voxels of positive signal change at the aneurysm wall; USPIO uptake at the periluminal area is not thought to be clinically significant. Image courtesy of Dr Rachel Forsythe, University of Edinburgh

Fig. 4

Rest and exercise myocardial 31P-MR spectra in a healthy volunteer (top row) and a T2D patient, suggesting a pre-existing energy deficit in the diabetic heart. Image reproduced with permission from Levelt et al. [47].