Assessment of myocardial fibrosis with cardiovascular magnetic resonance

Abstract

Diffuse interstitial or replacement myocardial fibrosis is a common feature of a broad variety of cardiomyopathies. Myocardial fibrosis leads to impaired cardiac diastolic and systolic function and is related to adverse cardiovascular events. Cardiovascular magnetic resonance (CMR) may uniquely characterize the extent of replacement fibrosis and may have prognostic value in various cardiomyopathies. Myocardial longitudinal relaxation time mapping is an emerging technique that could improve CMR's diagnostic accuracy, especially for interstitial diffuse myocardial fibrosis. As such, CMR could be integrated in the monitoring and therapeutic management of a large number of patients. This review summarizes the advantages and limitations of CMR for the assessment of myocardial fibrosis.

Figure 1

Etiophysiopathology of Myocardial Fibrosis. Myocardial fibrosis is a complex process that involves each cellular component of the myocardial tissue. The myocardial fibroblast has a central position in this process by increasing the production of collagen and other extracellular matrix components under the influence of various factors (renin-angiotensin system, myocyte apoptosis, pro-inflammatory cytokines, reactive oxygen species).

Figure 2

Diabetic cardiomyopathy: mild myocardial interstitial fibrosis stained in blue with Masson trichrome (white arrow) in a patient with long-duration type 1 diabetes mellitus at autopsy, with perivascular fibrosis (A) and mild fibrosis between myocytes (B). Reprinted with permission Konduracka et al. (80)

Figure 3

A) T₁ map Construction. T₁ map after 15 minutes of gadolinium administration in a inferior infarct case. This is the modified look-locker inversion recovery sequence that uses 17 heart-beats to reconstruct 11 images with different inversion times during mid-diastole. It is necessary to combine all images to generate the final T1 map. For that, it is necessary to apply algorithms to define the best fitting curve over the 11 acquired initial voxels linking for the same location. Those fitting algorithm are very sensitive to motion and image quality/artifacts. The result is a T1 map imaging where the T1 time for the global or segmented LV can be assessed. B) T₁ Recovery Graph after Contrast Administration. Graph showing the recovery of absolute myocardial T₁ value in a healthy heart (short-axis, mid-ventricle) at different time points prior and after contrast administration (0, 2, 4, 6, 8, 10, 15 and 20 minutes). T₁ values are expressed as means ± standard deviations. The global and regional mean T₁ values will vary significantly significantly with the time of assessment. The standard deviation of T₁ value is more significant prior to contrast administration. Reprinted with permission, from Messroghli et al. (70)

Figure 3

A) T₁ map Construction. T₁ map after 15 minutes of gadolinium administration in a inferior infarct case. This is the modified look-locker inversion recovery sequence that uses 17 heart-beats to reconstruct 11 images with different inversion times during mid-diastole. It is necessary to combine all images to generate the final T1 map. For that, it is necessary to apply algorithms to define the best fitting curve over the 11 acquired initial voxels linking for the same location. Those fitting algorithm are very sensitive to motion and image quality/artifacts. The result is a T1 map imaging where the T1 time for the global or segmented LV can be assessed. B) T₁ Recovery Graph after Contrast Administration. Graph showing the recovery of absolute myocardial T₁ value in a healthy heart (short-axis, mid-ventricle) at different time points prior and after contrast administration (0, 2, 4, 6, 8, 10, 15 and 20 minutes). T₁ values are expressed as means ± standard deviations. The global and regional mean T₁ values will vary significantly significantly with the time of assessment. The standard deviation of T₁ value is more significant prior to contrast administration. Reprinted with permission, from Messroghli et al. (70)

Figure 4

T₁ maps of the myocardium at the mid-ventricular short axis level in a healthy volunteer, a) Pre-contrast, b) post gadolinium contrast (0.15 mmol/kg) at 12 minutes c) and 25 minutes acquired with the MOLLI sequence. The mean T₁ value for the left ventricle (LV) can be obtained at each time after tracing the endocardial and epicardial countours of the LV (a).

Figure 5

Comparison of late gadolinium enhanced studies with corresponding T₁ maps and T₁ values distribution histograms in different cardiomyopathies: A) Chronic inferior myocardial infarction; B) Cardiac amyloïdosis; C) Non Ischemic Dilated Cardiomyopathy. In each example, the short axis late gadolinium images shows images with different patterns of enhancement, transmural localized in the case of a myocardial infarction scar (A1), sub-endocardial diffuse in the case of cardiac amyloïdosis (B1) or sub-epicardial and heterogeneous in the case of dilated cardiomyopathy. In the middle panel are the corresponding T₁ maps (A2, B2, B3) obtained after MOLLI acquisitions. From those T₁ maps, a mean left ventricular (LV) T₁ value can be obtained. This information can also be processed more precisely through the analysis of the distribution histogram of the LV T₁ values. Very distinct patterns of distributions can be seen on those examples, but this has to be shown in further larger clinical studies. This might also be a new way to assess and quantify myocardial fibrosis.