Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R2* Analysis: First Experience

Abstract

Purpose MR transverse relaxation rate R2* has been shown to be useful for monitoring liver iron overload. A sequence enabling acquisition of the whole liver in a single breath hold is now available, thus allowing volumetric hepatic R2* distribution studies. We evaluated the feasibility of computer-assisted whole liver segmentation of 3 D multi-gradient-echo MRI data, and compared whole liver R2* determination to analyzing only a single slice. Also, segmental R2* differences were studied. Materials and Methods The liver of 44 patients, investigated by multi-gradient echo MRI at 1.5 T, was segmented and divided into nine segments. Segmental R2* values were examined for all patients together and with respect to two criteria: average R2* values, and reason for iron overload. Correlation of single-slice and volumetric data was tested with Spearman’s rank test, segmental and group differences were evaluated by analysis of variance. Results Whole-liver R2* values correlated excellent to single slice data (p < 0.001). The lowest R2* occurred in segment 1 (S1), differences of S1 with regard to other segments were significant in five cases and highly significant in two cases. Patients with high average R2* showed significant differences between S1 and segments 2, 6, and 7. Disease-related differences with respect to S1 were significant in segments 3 to 5 and 7. Conclusion Our results suggest inhomogeneous hepatic iron distribution. Low R2* in S1 may be explained by its special vascularization. Key Points Citation Format

Segmental quantification of hepatic lipid content based on volumetric MRI data in patients with suspected iron overload

“…The resulting liver iron overload is measured by the transverse relaxation rate R 2 *. R 2 * distribution deviated from PDFF distribution: R 2 * is lowest in segment 1 and highest in segment 7 [8,10]. Since relative segmental MR-PDFF values do not correspond to relative segmental R 2 *, we conclude that our method determines these values independently from each other.…”

“…The larger group receiving blood transfusions could be spit up further into patients with additionally increased iron resorption (thalassemia) and iron overload predominantly caused by blood transfusion (sickle cell disease, Diamond-Blackfan anemia and other forms of anemia). Interestingly, despite segmental R 2 * values differing between these groups [8], there were no significant segmental MR-PDFF differences between the subgroups (data not shown).…”

“…After approval by the university's ethics committee and according to the Declaration of Helsinki (last revision 2013, Fortaleza, Brazil), patients referred to our institution between May 2017 and April 2018 for noninvasive liver iron quantification were included after written informed consent of the patients and/or their parents. Participants were examined on a 1.5 T MRI scanner (MAGNETOM Avanto, Siemens Healthcare, Erlangen, Germany) with a volumetric multi-gradient echo research sequence (6 echoes, TEs 1.2-9 ms) as previously published [8,10]. The entire liver was acquired in a single breath hold with a field of view (FoV) of 400x300x224 mm 3 at a matrix of 160x84x56 voxels and a voxel size of 2.5x2.5x4 mm 3 .…”

“…Liver segmentation was performed using the Liverhealth software tool, a part of the Intellispace Portal (ISP, Philips, Hamburg, Germany) which was described previously [8,10]. The liver contour on axial slices as well as coronal and sagittal reconstructions was checked after an initial automatic segmentation and corrected manually if necessary.…”

“…One of these tools allows users to divide the liver into its anatomical segments on the basis of manually placed landmarks and to analyze individual segments separately. Using this method, segmental differences in hepatic iron overload, reflected by segmental R 2 * differences, have been found [8].…”