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Magn Reson Med. 2018 Oct;80(4):1614-1625. doi: 10.1002/mrm.27112. Epub 2018 Feb 9.

Diffusion MRI monitoring of specific structures in the irradiated rat brain.

Author information

1
Center for Research in Radiotherapy, Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, Sherbrooke, Québec, Canada.
2
Plateforme d'analyse et visualisation d'images (PAVI), Centre de Recherche du Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Québec, Canada.
3
Sherbrooke Molecular Imaging Center, Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, Sherbrooke, Québec, Canada.
4
Service of Radiation Oncology, Centre Hospitalier Université de Sherbrooke, Sherbrooke, Québec, Canada.
5
Department of Pathology, Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Québec, Canada.
6
Department of Pharmacology and Physiology, Université de Sherbrooke, Sherbrooke, Québec, Canada.
7
Department of Computer Science, Université de Sherbrooke, Sherbrooke, Québec, Canada.

Abstract

PURPOSE:

The analysis of biological and mesoscopic structures properties by diffusion MRI (dMRI) in brain after radiation therapy remains challenging. In our study, we described the consequences associated with an unwanted dose to healthy tissue, assessing radiation-induced brain alterations of living rats with dMRI compared to histopathology and behavioral assays.

METHODS:

The right primary motor cortex M1 of the rat brain was targeted by stereotactic radiosurgery with a mean radiation dose of 41 Gy. Multidirectional single b-value dMRI data of the whole brain were acquired with a 7T small-animal scanner before irradiation until 110 days post-irradiation. Diffusion tensor imaging metrics, such as fractional anisotropy (FA), mean diffusivity (MD), axial (AD), and radial diffusivity (RD) were compared to brain alterations detected by immunohistochemistry and motor performances measured by a behavioral test.

RESULTS:

Between days 90 and 110, radiation necrosis was observed into the white matter spreading into M1 . Results showed a reduction of FA in the corpus callosum and in the striatum, which was driven by an increase in RD from 90 to 110 days post-irradiation, whereas only RD increased in M1 . Values of RD and AD increased in the irradiated hippocampus, while FA remained constant. Moreover, an increased MD, AD and RD was observed in the hippocampus that was probably related to inflammation as well as reactive astrogliosis after 110 days post-irradiation. Finally, rats did not exhibit locomotor deficits.

CONCLUSIONS:

dMRI metrics can assess brain damage; the sensitivity of dMRI metrics depends on the brain region.

KEYWORDS:

Gamma Knife; diffusion MRI; diffusion tensor imaging (DTI); radiation necrosis; small-animal

PMID:
29427386
DOI:
10.1002/mrm.27112

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