R2* Relaxometry for the Quantification of Hepatic Iron Overload: Biopsy-Based Calibration and Comparison with the Literature

Abstract

We compared the calibration of hepatic iron based on R2* relaxometry and liver biopsy with similar studies that have already been published to investigate the transferability of published calibration curves. Materials and Methods: 17 patients with clinically suspected hepatic iron overload (HIO) were enrolled. All patients underwent liver biopsy and MRI of the liver using a multi-echo gradient echo sequence (TR = 200 ms; TE-initial 0.99 ms; Delta-TE 1.41 ms; 12 echos; flip-angle: 20°). R2* parameter maps were analyzed using manually placed regions of interest and R2* values were correlated with liver iron concentration (LIC) obtained from liver biopsy. In addition, the results of our study were compared with 6 similar, already published studies. Results: A linear relationship between R2* and LIC was found. Regression analysis yielded a correlation coefficient of 0.926, a slope of 0.024 (s mg/g) [95 % CI 0.013 -0.024] and an intercept of 0.277 (mg/g) [95 % CI -0.328 -2.49]. We found a significant correlation between the calibration curves obtained from our study in comparison to 3/6 similar studies. The other 3 studies used a different reference standard or sequence parameters which lead to a significant difference for slope, intercept or both in comparison to our data. Conclusion: Calibration curves from published studies that are based on a correlation of liver biopsy and R2* can be used for the estimation of liver iron concentration, although different scanning parameters and post-processing protocols were used. Low initial TEs might be a prerequisite for pooling data for liver iron quantification.

3D Multiecho Dixon for the Evaluation of Hepatic Iron and Fat in a Clinical Setting

“…It has to be noted that the 2D ME GRE sequence used was calibrated in an earlier study with liver biopsies and agrees well with calibration data given by Hankins et al and Wood et al…”

“…The 2D GRE sequence used as a reference in our study was calibrated based on liver biopsies . With this, a modified calibration curve for 3D MR Dixon can easily be derived based on the regression parameters of Fig.…”

“…For the evaluation of iron overload two main techniques have emerged: MR relaxometry for direct quantification of R2 or R2* and the signal‐intensity‐ratio (SIR) method . Many studies have already evaluated the different approaches and several studies addressed the calibration of these methods . Nevertheless, the clinical use is somewhat limited to specialized centers.…”

Does fat suppression via chemically selective saturation affect R2*-MRI for transfusional iron overload assessment? A clinical evaluation at 1.5T and 3T

“…It should be noted as well that Sanches‐Rocha et al evaluated only T2* rather than R2*, where potential differences might be more subtle because of the inverse relationship between T2* and R2*. Furthermore, in a very recent biopsy‐calibrated R2*‐LIC study by Henninger et al , mGRE imaging in combination with CHESS was performed. In this study, the authors did not find a significant difference in the slopes or y‐intercepts of the R2*‐LIC calibrations compared with other biopsy‐calibrated studies [eg, Wood et al and Hankins et al ], which were established via mGRE sequences without any FS technique.…”

Noninvasive MRI-Based Liver Iron Quantification: Methodic Approaches, Practical Applicability and Significance

“…This is possibly the reason for the dependence of the consistency of results on the minimum echo time as postulated by Henninger et al [36]. The attempt to substantiate the plausibility of the observed results with mathematic simulations of the MR signal [40] is of limited value since the simulation method does not take the influence of the described dephasing between the fat signal and water signal into consideration.…”