Chemical Shift Artifact on Steady-State Free Precession Cardiac Magnetic Resonance Sequences as a Result of Lipomatous Metaplasia: A Novel Finding in Chronic Myocardial Infarctions

Abstract Background Because balanced steady-state free precession (SSFP) sequences are opposed-phase gradient echo techniques, linear low signal due to chemical shift artefact is observed at fat-water interfaces. We observed that some patients with chronic myocardial infarctions had linear low signal along the inner myocardial wall in areas of infarction, which we postulated was due to chemical shift artefact, as a result of lipomatous metaplasia. The purpose of this retrospective review was to evaluate whether subendocardial low signal on SSFP, likely related to chemical shift artifact, could be used to identify chronic myocardial infarctions. Methods Of 128 patients who underwent cardiac magnetic resonance, 79 with myocardial infarctions were included in this retrospective study. Results Of the 79 patients, 35 (44%) demonstrated areas of linear subendocardial decreased signal. In 16 of those 35 (46%), the infarcts were confirmed as fatty by correlation with CT. In 29 of 35 (83%) of these patients, the infarcts were likely chronic based on fixed wall thinning to less than 4 mm. In 3 patients, chemical shift artifact due to lipomatous metaplasia was also confirmed with conventional in-phase and opposed-phase T1-weighted sequences. Subendocardial chemical shift artefacts were not seen in any of the 19 patients with known, acute infarcts included in this series. Aneurysms were more common when subendocardial chemical shift artefact was present (22 of 35), in comparison to patients who did not have this finding (10 of 44, P = 0.02). Conclusions Identification of linear subendocardial chemical shift artefacts on SSFP sequences is a sign of lipomatous metaplasia in chronic myocardial infarcts and is associated with an increased incidence of ventricular aneurysms.