Table 1.

CMR Terminology and Methods for Tissue Characterization

CMR Method or Terminology	Definition	CMR Application	Interpretation in Patients With COVID-19
T1 relaxation parametersa
T1-weighted images	Images dominated by T1 relaxation magnetic relaxation. Signal intensity is relative (not quantitative).	Typically used for depiction of myocardial anatomy. Post–gadolinium administration images depict the distribution of the intravenous contrast agent	Acute: evidence for myocardial injury Chronic: evidence for myocardial fibrosis/scar
Native T1 mapping	Pixel-by-pixel presentation of T1 values (in milliseconds) of the myocardium without a gadolinium-based contrast agent.	Increased T1 times indicate increased interstitial space (eg, collagen or amyloid deposits) or increased (intracellular or extracellular) tissue water (ie, myocardial edema). Decreased T1 times indicate intracellular lipid or iron deposition.
Late gadolinium enhancement	T1-weighted images acquired 10-15 min after intravenous administration of a gadolinium-based contrast agent.	Infarction/scar: typically subendocardial involvement in a coronary artery distribution. Nonischemic necrosis/scar: typically mid or epicardial myocardial involvement, not in a coronary artery distribution.
ECV fraction	Proportion of the ECV in the myocardium compared to total myocardial volume. Estimated using native T1 and postgadolinium T1 mapping methods	Increased ECV is present in diffuse myocardial fibrosis and myocardial inflammation. ECV may also be elevated in infiltrative disease such as amyloidosis.
T2 relaxation parametersb
T2-weighted images	Images dominated by effects of T2 magnetic relaxation. Signal intensity is relative (not quantitative).	Signal intensity is markedly increased in areas of tissue edema.	Evidence for myocardial edema may be associated with inflammation
T2 mapping	Pixel-by-pixel presentation of T2 values (in milliseconds) of the myocardium.	Increased T2 time indicates myocardial edema.

CMR = cardiac magnetic resonance; ECV = extracellular volume.

^aT₁ relaxation, or longitudinal magnetic relaxation time, in milliseconds. After a radiofrequency pulse, T₁ is the time constant for regrowth of (1 − 1/e) or approximately 63% of its initial maximum magnetic strength.

^bT₂ relaxation, or transverse magnetic relaxation time, in milliseconds. After a radiofrequency pulse, T₂ is the time constant for transverse magnetization to fall to approximately 37% (1/e) of its initial value.