Effect of inversion recovery fat suppression on hepatic R2* quantitation in transfusional siderosis

OBJECTIVE. The purpose of this study is to evaluate whether the application of spectral pre-saturation inversion recovery (SPIR) fat suppression in standard multiecho gradient-echo sequences has a significant effect on hepatic R2* quantitation in patients with iron overload syndromes. MATERIALS AND METHODS. Eighty patients were scanned with a multiecho gradient-echo sequence without and with the application of SPIR. Six different postprocessing approaches were used to extract R2* values for maximum generality. RESULTS. SPIR fat suppression lowered R2* values by 3.9-7.0% (p < 0.0001 in all pairwise comparisons), independently of the postprocessing algorithm. Coefficients of variation for R2* ranged from 4.5% to 10.0%. Regardless of the size of the ROI (area of homogeneous tissue or entire liver profile in the slice), pixelwise approaches combined with an exponential-plus-constant fitting model yielded the lowest coefficients of variation (4.5% and 5.1%), whereas truncated exponential fits of the averaged signals produced the highest coefficients of variation (7.8% and 10%). For R2* values exceeding 200 Hz, a Bland-Altman analysis showed a bias that grew linearly for all postprocessing methods. CONCLUSION. SPIR fat suppression resulted in systematically lower hepatic R2* estimates. Because calibration curves were derived using images without fat suppression, these biases should be corrected when reporting liver iron concentrations estimated from fat-suppressed multiecho T2*-weighted images.