A non-contrast CMR index for assessing myocardial fibrosis

Abstract

Purpose: Safe, sensitive, and non-invasive imaging methods to assess the presence, extent, and turnover of myocardial fibrosis are needed for early stratification of risk in patients who might develop heart failure after myocardial infarction. We describe a non-contrast cardiac magnetic resonance (CMR) approach for sensitive detection of myocardial fibrosis using a canine model of myocardial infarction and reperfusion. Methods: Seven dogs had coronary thrombotic occlusion of the left anterior descending coronary arteries followed by fibrinolytic reperfusion. CMR studies were performed at 7 days after reperfusion. A CMR spin-locking T1ρ mapping sequence was used to acquire T1ρ dispersion data with spin-lock frequencies of 0 and 511 Hz. A fibrosis index map was derived on a pixel-by-pixel basis. CMR native T1 mapping, first-pass myocardial perfusion imaging, and post-contrast late gadolinium enhancement imaging were also performed for assessing myocardial ischemia and fibrosis. Hearts were dissected after CMR for histopathological staining and two myocardial tissue segments from the septal regions of adjacent left ventricular slices were qualitatively assessed to grade the extent of myocardial fibrosis. Results: Histopathology of 14 myocardial tissue segments from septal regions was graded as grade 1 (fibrosis area, <20% of a low power field, n = 9), grade 2 (fibrosis area, 20–50% of field, n = 4), or grade 3 (fibrosis area, >50% of field, n = 1). A dramatic difference in fibrosis index (183%, P < 0.001) was observed by CMR from grade 1 to 2, whereas differences were much smaller for T1ρ (9%, P = 0.14), native T1 (5.5%, P = 0.12), and perfusion (−21%, P = 0.05). Conclusion: A non-contrast CMR index based on T1ρ dispersion contrast was shown in preliminary studies to detect and correlate with the extent of myocardial fibrosis identified histopathologically. A non-contrast approach may have important implications for managing cardiac patients with heart failure, particularly in the presence of impaired renal function.

MR extracellular volume mapping and non-contrast T1ρ mapping allow early detection of myocardial fibrosis in diabetic monkeys

“…However, mFI values were significantly different between animals with mild DD and animals with moderate DD as well as between HCs and animals with mild DD. A recent animal study [14] provided additional evidence that mFI has a greater sensitivity for detecting diffuse types of myocardial fibrosis as compared with T1ρ in dogs with myocardial infarction.…”

“…The magnitude of the increase is modulated by the chemical shifts and exchange rates of the macromolecules. The higher sensitivity of mFI to the changes in collagen content may be due to the cancelation of intrinsic T2, thereby resulting in an amplified effect of the chemical exchange during the relaxation times, when water protons to exchange are locked without dephasing [14]. It was noted previously that mFI represents the subtraction of two T1ρ images.…”

“…In one study, a positive correlation between T1ρ and ECV was observed in 20 patients with dilated cardiomyopathy [12]. In addition, to improve the sensitivity of T1ρ mapping for myocardial fibrosis assessment, T1ρ dispersion contrast has been adopted [13, 14]. There is a real need for non-contrast techniques for patients with renal dysfunction or for whom contrast is otherwise contraindicated [15].…”

Fast myocardial T1ρ mapping in mice using k-space weighted image contrast and a Bloch simulation-optimized radial sampling pattern

“…Compared to other native quantification techniques, T 1ρ improves the contrast ratio between diseased and healthy myocardial tissue [16][17][18]. In experimental models as well as in vivo, T 1ρ has already been shown to be a sensitive marker for the detection of several tissue damages like edema, ischemia, fibrosis and myocardial infarction [19][20][21][22]. Moreover, T 1ρ gives the possibility for dispersion measurements by manipulation of the effective SL pulse amplitude, enabling additional contrast mechanisms and further improved tissue characterization [11].…”

“…Moreover, T 1ρ gives the possibility for dispersion measurements by manipulation of the effective SL pulse amplitude, enabling additional contrast mechanisms and further improved tissue characterization [11]. In this context it could already be shown that T 1ρ dispersion quantification can be used as a myocardial biomarker for the classification of different stages of fibrosis [19]. This dispersion behavior is of great interest and might be highly beneficial not only in basic research in various animal models, but also in various scenarios in clinical practice [23][24][25].…”