Application of Small Animal MRI System in the Evaluation of Brain Injury in Rats

Small-animal magnetic resonance imaging (MRI) is a powerful non-invasive tool for detecting a wide range of pathological changes.

A new generation of compact, high-performance small-animal MRI platforms employs innovative magnet design and application-driven methods to reduce the cost and complexity of traditional systems. These platforms are mobile and self-shielded, suitable for most research facilities, with no need for cryogens or specialised infrastructure. Compared with conventional MRI systems, their key advantage lies in delivering clear, three-dimensional digital morphological images of entire target organs with ease.

In small-animal MRI analysis, relaxation times such as spin–lattice (T1) and spin–spin (T2) are often encountered. Their baseline values differ across organs, tissues, and fluids. When brain injury is induced in rats, tissue changes lead to corresponding alterations in T1 and T2 signals. Variations in these weighted images allow detection of induced brain injury.

Pilocarpine, a muscarinic cholinergic agonist, is widely used to induce seizures and morphological neuronal injury in rat brains. In this neuronal-damage model, pronounced histological lesions can be observed in regions such as the piriform cortex, lateral dorsal thalamic nucleus, hippocampus, and substantia nigra.

Small-animal MRI analysis

Figure 1 presents T1- and T2-weighted MRI images. Compared with controls, pilocarpine-treated rats showed high T1 signals in the piriform cortex, lateral thalamic nucleus, periventricular thalamic posterior nucleus, and hypothalamic posterior nucleus (Fig. 1a and b). In T2-weighted images, the piriform cortex exhibited low T2 signal corresponding to the high T1 area (Fig. 1c and d). The other three high-T1 regions displayed T2 intensities comparable to controls (moderate intensity) (Fig. 1c and d).

Today’s user-friendly compact small-animal MRI systems are highly applicable to preclinical toxicological pathology studies of pilocarpine-induced brain injury in rats. High T1 and low T2 signals reveal evident neuronal damage, even though histopathological analysis remains more sensitive.