A fully automatic parenchyma extraction method for MRI T2*relaxometry of iron loaded liver in transfusion-dependent patients

Purpose: To develop a fully automatic parenchyma extraction method for the T2* relaxometry of iron overload liver. Methods: A retrospective multicenter collection of liver MR examinations from 177 transfusion-dependent patients was conducted. The proposed method extended a semiautomatic parenchyma extraction algorithm to a fully automatic approach by introducing a modified TransUNet on the R2* (1/T2*) map for liver segmentation. Axial liver slices from 129 patients at 1.5 T were allocated to training (85%) and internal test (15%) sets. Two external test sets separately included 1.5 T data from 20 patients and 3.0 T data from 28 patients. The final T2* measurement was obtained by fitting the average signal of the extracted liver parenchyma. The agreement between T2* measurements using fully and semiautomatic parenchyma extraction methods was assessed using coefficient of variation (CoV) and Bland-Altman plots. Results: Dice of the deep network-based liver segmentation was 0.970 +/- 0.019 on the internal dataset, 0.960 +/- 0.035 on the external 1.5 T dataset, and 0.958 +/- 0.014 on the external 3.0 T dataset. The mean difference bias between T2* measurements of the fully and semiautomatic methods were separately 0.12 (95% CI: -0.37, 0.61) ms, 0.04 (95% CI: -1.0, 1.1) ms, and 0.01 (95% CI: -0.25, 0.23) ms on the three test datasets. The CoVs between the two methods were 4.2%, 4.8% and 2.0% on the internal test set and two external test sets. Conclusions: The developed fully automatic parenchyma extraction approach provides an efficient and operatorindependent T2* measurement for assessing hepatic iron content in clinical practice.