A novel semiautomatic parenchyma extraction method for improved MRI R2* relaxometry of iron loaded liver

Purpose To propose and evaluate an automatic method of extracting parenchyma from a manually delineated whole liver for the R2* measurement of iron load. Materials and Methods In all, 108 transfusion‐dependent patients with a wide range of hepatic iron content were scanned with a multiecho gradient‐echo sequence. The R2* was measured by fitting the average signal of liver parenchyma, extracted by the proposed semiautomatic parenchyma extraction (SAPE), traditional manually delineated multiple regions‐of‐interest (mROIs), and T2* thresholding methods to the noise‐corrected monoexponential model. The R2* measurement accuracy of the SAPE method was evaluated through simulation; the intra‐ and interobserver reproducibility of SAPE, mROI, and T2* thresholding were assessed from the in vivo data using coefficient of variation (CoV). Results In the simulation, the mean absolute percentage error of R2* measurement using SAPE was 0.23% (range 0.01%–1.09%). In vivo study, the CoVs of intra‐ and interobserver reproducibility were 0.83%, 1.39% for SAPE, 3.63%, 6.28% for mROI, and 1.62%, 2.66% for T2* thresholding, respectively. Conclusion The SAPE method provides an accurate and reliable approach to assessing the overall hepatic iron content. The improved magnetic resonance imaging (MRI) R2* reproducibility using the SAPE method may lead to more accurate tissue characterization and increased diagnostic confidence. J. Magn. Reson. Imaging 2014;40:67–78 . © 2013 Wiley Periodicals, Inc .