White matter imaging of ethanol-fixed rat brain by phase-contrast X-ray computed tomography.

ABSTRACT

BACKGROUND: Phase-contrast X-ray computed tomography imaging (PCI) based on crystal X-ray interferometry can detect minute density differences within biological soft tissues without contrast agents. Ethanol fixation yields increased tissue-background density differences due to the dehydrating and delipidifying effects of ethanol. PURPOSE: To obtain high image contrast of cerebral white matter structures in PCI, tissue fixation using ethanol and routinely used formalin have been examined. MATERIAL AND METHODS: Ethanol-fixed (EF) (n = 4) and formalin-fixed (FF) (n = 4) rat brains were imaged by crystal X-ray interferometry-based PCI. Tissue staining/microscopy was also performed for histological comparison and myelin density evaluation. Three-dimensional white matter tract images were reconstructed. RESULTS: Superior image contrast was obtained in the images of EF brains (EF images) compared to those of formalin-fixed brains (FF images), particularly for white matter structures. Significant density differences between the white matter structures and hippocampus (P < 0.01)/thalamus (P < 0.001) were observed in the EF, but not FF, images. Ethanol fixation enhanced the image contrast of white matter tracts by approximately sixfold compared to formalin fixation, and close agreement (r2 = 0.97; P < 0.05) between the density values on the CT images and the myelin density values in histological images was observed for the EF brains. Three-dimensional reconstruction of the white matter tracts was possible from the EF images, but not FF images. CONCLUSION: Ethanol fixation resulted in marked contrast enhancement of cerebral white matter structures in PCI. Thus, high-resolution PCI using ethanol for tissue fixation could be valuable for experimental neurological studies and postmortem neuropathology evaluation.