Comparative analysis of in situ and ex situ postmortem brain MRI: Evaluating volumetry, DTI, and relaxometry

Dominique Neuhaus; Thomas Rost; Tanja Haas; Maria Janina Wendebourg; Katja Schulze; Regina Schlaeger; Eva Scheurer; Claudia Lenz

doi:10.1002/mrm.30264

Comparative analysis of in situ and ex situ postmortem brain MRI: Evaluating volumetry, DTI, and relaxometry

Magn Reson Med. 2024 Sep 9. doi: 10.1002/mrm.30264. Online ahead of print.

Authors

Dominique Neuhaus^{1

2}, Thomas Rost², Tanja Haas³, Maria Janina Wendebourg^{4

5}, Katja Schulze², Regina Schlaeger^{4

5}, Eva Scheurer^{1

2}, Claudia Lenz^{1

2}

Affiliations

¹ Institute of Forensic Medicine, Department of Biomedical Engineering, University of Basel, Basel, Switzerland.
² Institute of Forensic Medicine, Health Department Basel-Stadt, Basel, Switzerland.
³ Division of Radiological Physics, Department of Radiology and Nuclear Medicine, University Hospital Basel, Basel, Switzerland.
⁴ Neurology Clinic and Policlinic, Department of Clinical Research, University Hospital Basel, University of Basel, Basel, Switzerland.
⁵ Translational Imaging in Neurology (ThINk), Department of Biomedical Engineering, University of Basel, Basel, Switzerland.

PMID: 39250425
DOI: 10.1002/mrm.30264

Abstract

Purpose: To compare postmortem in situ with ex situ MRI parameters, including volumetry, diffusion tensor imaging (DTI), and relaxometry for assessing methodology-induced alterations, which is a crucial prerequisite when performing MRI biomarker validation.

Methods: MRI whole-brain scans of five deceased patients with amyotrophic lateral sclerosis were performed at 3 T. In situ scans were conducted within 32 h after death (SD 18 h), and ex situ scans after brain extraction and 3 months of formalin fixation. The imaging protocol included MP2RAGE, DTI, and multi-contrast spin-echo and multi-echo gradient-echo sequences. Volumetry, fractional anisotropy, mean diffusivity, T₁, T₂, and $T_{2}^{*}$ have been assessed for specific brain regions.

Results: When comparing ex situ to in situ values, the following results were obtained. Deep gray matter as well as the thalamus and the hippocampus showed a reduced volume. Fractional anisotropy was reduced in the cortex and the whole brain. Mean diffusivity was decreased in white matter and deep gray matter. T₁ and T₂ were reduced in all investigated structures, whereas $T_{2}^{*}$ was increased in the cortex.

Conclusion: The results of this study show that the volumes and MRI parameters of several brain regions are potentially affected by tissue extraction and subsequent formalin fixation, suggesting that methodological alterations are present in ex situ MRI. To avoid overlap of indistinguishable methodological and disease-related changes, we recommend performing in situ postmortem MRI as an additional intermediate step for in vivo MRI biomarker validation.

Keywords: DTI; MRI; amyotrophic lateral sclerosis; postmortem; relaxometry; volumetry.

Abstract

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