Ex vivo micro-CT imaging of rodent brain using nonionic clinical contrast media

Objectives Histologic assessment of brain structure can suffer deleterious effects from the processing and slicing of tissue. We have developed a method of contrast-enhanced, high resolution histology of intact brains using a clinically available contrast medium and micro-CT. To our knowledge this is the first report using a safe, low osmolarity, nonionic agent that is in widespread use (Iohexol; GE, Milwaukee, WI). We evaluated different dilutions of media at several bathing times in order to optimize contrast uptake and image quality.

Methods Brains from 24 normal mice were removed and immersed in solutions of Iohexol and PBS to final iodine concentrations of: 350, 263, 175, 88, 35, and 17 mg/mL. Immersion times used for each concentration of iodine were 144, 45, and 24 hours. Micro-CT images of the whole brains were acquired using a Siemens Inveon (Siemens, Knoxville, TN) instrument operating at 80 kVp and 100 µA. Images were acquired and reconstructed with 20 µm on-a-side cubic voxels and displayed using the Siemens analysis software. Qualitative and quantitative measures of image quality were performed to determine optimal tissue discrimination and image quality.

Results Images acquired of brains immersed in solutions containing 350 mg/mL iodine for 45 hours demonstrated the greatest soft tissue structure delineation. Brain structures including the hippocampus, striatum, and cerebellum were readily distinguishable, and white and gray matter contrast was also evident.

Conclusions The ability to non-destructively assess animal soft tissue structures such as the brain using high resolution CT may enhance assessment of normal anatomy and tissue defects that would otherwise be difficult to examine with standard histological methods.