Quantification of Myocardial Extracellular Volume Fraction with Cardiac MR Imaging in Thalassemia Major

Purpose: To quantify myocardial extracellular volume (ECV) by using cardiac magnetic resonance (MR) imaging in thalassemia major and to investigate the relationship between ECV and myocardial iron overload. Materials and Methods: With institutional review board approval and informed consent, 30 patients with thalassemia major (mean age +/- standard deviation, 34.6 years +/- 9.5) and 10 healthy control subjects (mean age, 31.5 years +/- 4.4) were prospectively recruited (clinicaltrials.gov identification number NCT02090699). Nineteen patients (63.3%) had prior myocardial iron overload (defined as midseptal T2* < 20 msec on any prior cardiac MR images). Cardiac MR imaging at 1.5 T included cine steady-state free precession for ventricular function, T2* for myocardial iron quantification, and unenhanced and contrast material-enhanced T1 mapping. ECV was calculated with input of the patient's hematocrit level. Peak systolic global longitudinal strain by means of speckle tracking was assessed with same-day transthoracic echocardiography. Statistical analysis included use of the two-sample t test, Fisher exact test, and Spearman correlation. Results: Unenhanced T1 values were significantly lower in patients with prior myocardial iron overload than in control subjects (850.3 +/- 115.1 vs 1006.3 +/- 35.4, P<.001) and correlated strongly with T2* values (r = 0.874, P<.001). Patients with prior myocardial iron overload had higher ECV than did patients without iron overload (31.3% +/- 2.8 vs 28.2% +/- 3.4, P=.030) and healthy control subjects (27.0% +/- 3.1, P=.003). There was no difference in ECV between patients without iron overload and control subjects (P=.647). ECV correlated with lowest historical T2* (r = -0.469, P=.010) but did not correlate significantly with left ventricular ejection fraction (r = -0.216, P=.252) or global longitudinal strain (r = -0.164, P=.423). Conclusion: ECV is significantly increased in thalassemia major and is associated with myocardial iron overload. These abnormalities may potentially reflect diffuse interstitial myocardial fibrosis. (C) RSNA, 2015