Measurements of hepatic iron concentration (HIC) are important predictors of transfusional iron burden and long-term outcome in patients with transfusiondependent anemias. The goal of this work was to develop a readily available, noninvasive method for clinical HIC measurement. The relaxation rates R2 (1/ T2) and R2* (1/ T2*) measured by magnetic resonance imaging (MRI) have different advantages for HIC estimation. This article compares noninvasive iron estimates using both optimized R2 and R2* methods in 102 patients with iron overload and 13 controls. In the iron-overloaded group, 22 patients had concurrent liver biopsy. R2 and R2* correlated closely with HIC (r 2 > .95) for HICs between 1.33 and 32.9 mg/g, but R2 had a curvilinear relationship to HIC. Of importance, the R2 calibration curve was similar to the curve generated by other researchers, despite significant differences in technique and instrumentation. Combined R2 and R2* measurements did not yield more accurate results than either alone. Both R2 and R2* can accurately measure hepatic iron concentration throughout the clinically relevant range of HIC with appropriate MRI acquisition techniques. (Blood.

Purpose: To optimize R2*(1/T2*) measurements for cardiac iron detection in sickle cell and thalassemia patients. Materials and Methods:We studied 31 patients with transfusion-dependent sickle cell disease and 48 patients with thalassemia major; myocardial R2* was assessed in a single midpapillary slice using a gated gradient-echo pulse sequence. Pixel-wise maps were coregistered among the patients to determine systematic spatial fluctuations in R2*. The contributions of minimum TE, echo spacing, signal-decay model, and region-of-interest (ROI) choice were compared in synthetic and acquired images.Results: Cardiac relaxivity demonstrated characteristic circumferential variations regardless of the degree of iron overload. Within the interventricular septum, a gradient in R2* from right to left ventricle was noted at high values. Pixel-wise and ROI techniques yielded nearly identical values. Signal decay was exponential but a constant offset or second exponential term was necessary to avoid underestimation at high iron concentration. Systematic underestimation of R2* was observed for higher minimum TE, limiting the range of iron concentrations that can be profiled. Fat-water oscillations, although detectable, represented only 1% of the total signal. Conclusion:Clinical cardiac R2* measurements should be restricted to the interventricular septum and should have a minimum TE Յ 2 msec. ROI analysis techniques are accurate; however, offset-correction is essential.

Iron-induced cardiac dysfunction is a leading cause of death in transfusion-dependent anemia. MRI relaxation rates R 2 (1/T 2 ) and R* 2 (1/T* 2 ) accurately predict liver iron concentration, but their ability to predict cardiac iron has been challenged by some investigators. Studies in animal models support similar R 2 and R* 2 behavior with heart and liver iron, but human studies are lacking. To determine the relationship between MRI relaxivities and cardiac iron, regional variations in R 2 and R* 2 were compared with iron distribution in one freshly deceased, unfixed, iron-loaded heart. R 2 and R* 2 were proportionally related to regional iron concentrations and highly concordant with one another within the interventricular septum. A comparison of postmortem and in vitro measurements supports the notion that cardiac R* 2 should be assessed in the septum rather than the whole heart. These data, along with measurements from controls, provide bounds on MRI-iron calibration curves in human heart and further support the clinical use of cardiac MRI in iron-overload syndromes. Magn Reson Med 56: 681-686, 2006.