CMR for myocardial iron overload quantification. Calibration curve from the MIOT Network

R2${}^{\ast }$ cardiac magnetic resonance (CMR) allows the non-invasive measurement of myocardial iron. We calibrated cardiac R2${}^{\ast }$ values against myocardial tissue–measured iron concentration by using a segmental approach and we assessed the iron distribution. Five hearts of thalassemia patients were donated after death/transplantation to the CoreLab of the Myocardial Iron Overload in Thalassemia Network. A multislice multiecho R2${}^{\ast }$ approach was adopted. After CMR, used as guidance, the heart was cut in three short-axis slices and each slice was cut into different equiangular segments according to AHA segmentation and differentiated into endocardial and epicardial layers. Tissue iron concentration was measured by atomic absorption spectrometer technique. Fifty-five samples were used since only for two hearts all the 16 samples were analyzed. Mean iron concentration was 4.71 ± 4.67 mg/g dw. Segmental iron levels ranged from 0.24 to 13.78 mg/g dw. The coefficient of variability of iron for myocardial segments ranged from 8.08 to 24.54% (mean 13.49 ± 6.93%). Iron concentration was significantly higher in the epicardial than in the endocardial layer (5.99 ± 6.01 vs 4.84 ± 4.87 mg/g dw; p = 0.042). Four different circumferential regions (anterior, septal, inferior, and lateral) were defined. A circumferential heterogeneity was noted, with more iron in the anterior region, followed by the inferior region. The direct nonlinear fitting of R2${}^{\ast }$ and [Fe] data led to the calibration curve: [Fe] = 0.0022 ∙ (R2*-ROI)${}^{1.462}$ (R-square = 0.956). Our data further validate R2${}^{\ast }$ CMR using a segmental approach as a sensitive and early technique for quantifying iron distribution in the current clinical practice.