Alcohol-fixed specimens for high-contrast post-mortem MRI

Abstract

• Increased contrast between soft tissues in MRI of alcohol-fixed specimens. • Superior contrast in MRI of methanol-fixed murine brain. • High quality MRI images of alcoholic samples by saturation of redundant NMR signals. • Formaldehyde-fixed specimens can be transferred to methanol for better MRI contrast. • Novel contrast in result of interplay of cross-links with coagulation of tissues. MRI of alcohol-fixed mouse specimens, so far unappreciated because of multiple 1 H NMR signals, should be considered as a valuable research strategy due to the possibility of obtaining images with increased contrast between the soft tissues. Moreover, the poor contrast in MRI images of specimens fixed with formaldehyde solutions can be increased by transferring the specimens to a methanol solution. In this work mice fixed with 5%-formaldehyde, 70%-ethanol, 70%-methanol solutions, and also specimen transferred from 5%-formaldehyde to 70%-methanol solution and not fixed specimens were imaged using 9.4 T MRI scanner to obtain T 1 - and T 2 -weighted images as well as T 1 and T 2 maps. For samples containing alcohol saturation of redundant (not of methyl group) 1 H NMR signals, originating from the alcohol and water present in the samples, allowed to obtain high quality MRI images. The optimal distribution of values of T 1 and T 2 was obtained for the methanol-fixed specimen, leading to high-contrast MRI images. Transferring the specimen from formaldehyde to methanol solution resulted in an unfamiliar spatial distributions of T 1 and T 2 of the brain tissues and, consequently, a novel contrast in the MRI images. Presented findings reveal hidden potential of the MRI of wet-fixed specimens.