T2-weighted cardiovascular magnetic resonance in acute cardiac disease

Abstract

Cardiovascular magnetic resonance (CMR) using T2-weighted sequences can visualize myocardial edema. When compared to previous protocols, newer pulse sequences with substantially improved image quality have increased its clinical utility. The assessment of myocardial edema provides useful incremental diagnostic and prognostic information in a variety of clinical settings associated with acute myocardial injury. In patients with acute chest pain, T2-weighted CMR is able to identify acute or recent myocardial ischemic injury and has been employed to distinguish acute coronary syndrome (ACS) from non-ACS as well as acute from chronic myocardial infarction.T2-weighted CMR can also be used to determine the area at risk in reperfused and non-reperfused infarction. When combined with contrast-enhanced imaging, the salvaged area and thus the success of early coronary revascularization can be quantified. Strong evidence for the prognostic value of myocardial salvage has enabled its use as a primary endpoint in clinical trials. The present article reviews the current evidence and clinical applications for T2-weighted CMR in acute cardiac disease and gives an outlook on future developments."The principle of all things is water"Thales of Miletus (624 BC - 546 BC).

Figure 1

Possible effects of myocardial edema induced by ischemia and reperfusion on myocardial function and survival. Adapted with permission obtained from the Oxford University Press ^© Garcia-Dorado et al. Cardiovasc Res 1993, 27: 1555-63.

Figure 2

A simplified schematic view of edema evolution in ischemic injury to the myocardium. A: Normal equilibrium. B: Early phase of injury: intracellular edema. C: Late phase of injury: interstitial edema. Adapted with permission obtained from the Nature Publishing Group ^© Friedrich MG. Nat Rev Cardiol 2010, 3: 385-7.

Figure 3

Myocardial edema in a patient with active myocarditis. A: T2-weighted CMR image showing subepicardial edema in the anteroseptal segment. B: Computer-aided signal intensity analysis of the T2-weighted image with color-coded display of relative signal intensity, normalized to skeletal muscle. Blue indicates a signal intensity ratio of myocardium/skeletal muscle of ≥2.0, indicating edema, green indicates normal signal intensity (1.4-1.9). C: Contrast-enhanced image (late gadolinium enhancement) showing a high signal intensity in the same region indicating necrosis. D: Computer-aided signal intensity analysis of the necrosis image with color-coded display of relative signal intensity, normalized to remote myocardium. Red indicates a signal intensity of >5 standard deviations above remote myocardium.

Figure 4

CMR Findings in a Patient With Stress-Induced Cardiomyopathy Takotsubo. There is characteristic apical contractile dysfunction (A, B) in the absence of late gadolinium enhancement (C). T2-weighted images showing normal signal intensity of the basal myocardium (D), but global edema in the apical and midventricular myocardium matching the distribution of the LV wall motion abnormalities (E, F).

Figure 5

Assessment of myocardial salvage after acute, reperfused myocardial infarction. A: T2-weighted CMR showing high signal intensity of the anterior, anteroseptal and inferoseptal segments (area at risk). B: Computer-aided signal intensity analysis of the T2-weighted image normalized to normal, uninjured myocardium. Red indicates a signal intensity of >2 standard deviations above remote, uninjured myocardium. C: Contrast-enhanced image (late gadolinium enhancement) showing high signal intensity reflecting increased contrast accumulation in necrotic myocardium. D: Computer-aided signal intensity analysis of the late gadolinium enhancement image with color-coded display of relative signal intensity, normalized to remote myocardium. Red indicates a signal intensity of >5 standard deviations above remote, uninjured myocardium. The comparison of edema (panels A, B) with necrosis (panels C, D) shows myocardial edema in areas without necrosis, indicating major myocardial salvage.

Figure 6

T2 weighted imaging for detection of intramyocardial hemorrhage. A: T2 images showing a hypointense core indicating intramyocardial hemorrhage within the area of myocardial edema (arrow). Asterisks refer to inadequately suppressed blood signal ("slow flow artefact") B: Computer aided signal intensity analysis normalized to normal myocardium and to skeletal muscle (C). Contrast-enhanced image showing a transmural necrosis with a core of late microvascular obstruction (arrow) (D).