Detection of cortical architecture of rat brain using high-resolution 7.0 T manganese-enhanced MRI in vivo

Objective: To study the role of manganese-enhanced MRI (MEMRI) in the depiction of cortical architecture of rat brain after systemic administration of Mn2+ through caudal vein and compare the effects of normal or opened blood-brain barrier on the manganese-enhanced MRI. Methods: Fifteen SD rats were randomly divided into three groups according to ranked list of random. Blood-brain barrier was opened in short time by the injection of 30% mannitol via the right internal carotid artery in group A, then 100 mmol/L MnCl2 physiologic saline solution was delivered through vena caudalis, and MRI was performed 12 hours later.. In group B, 100 mmol/L MnCl2 physiologic saline solutions was administrated through vena caudalis, following normal saline injection into the right internal carotid artery, and MRI was performed 12 hours later. The group C served as normal control group. All images were acquired with a 7.0 T micro MR scanner. Signal-to-noise ratios (SNR) in regions of interest were measured by Paravision 4.0 and the differences of three groups were compared by using one-way ANOVA. The differences of SNR on both sides of hemispheres were compared by using paired t test. Results: MEMRI could show the gray matter and white matter of rat brain and the anatomy borders between somatosensory cortex and motor cortex clearly. Periventricular structures such as hippocampus, dentate gyrus, habenula united, and olfactory bulb could also be showed clearly. Symmetrical enhancement on both sides of the cortex and banded structures was shown clearly in group B. The SNR increased and t he differences were significant in right cerebral cortex, both sides of cerebellar cortex, hippocampus and pituitary among three groups (right cerebral cortex 35.2 ± 7.0, 30.1 ± 2.4, 26.6 ± 2.8, F=4.36, P=0.038; left cerebellar cortex 27.1 ± 5.2, 29.4 ± 3.8, 19.4 ± 4.5, F=6.66, P=0.011; right cerebellar cortex 27.8 ± 3.8, 28.5 ± 4.2, 20.4 ± 4.8, F=5.84, P=0.017; left hippocampus 34.5 ± 4.9, 38.1 ± 5.3, 24.5 ± 3.6, F=11.38, P=0.002; right hippocampus 35.3 ± 5.5, 37.6 ± 4.7, 25.6 ± 3.0, F=9.93, P=0.003; pituitary 39.5 ± 3.8, 52.6 ± 9.1, 26.2 ± 4.2, F=22.80, P=0.001) after systemic administration of Mn2+. Asymmetric enhancement on two sides of cortex was shown in group A. The mannitol-infused side was enhanced obviously but displayed blurring banded structures. However, the SNR differences of both sides of hemispheres in group A and B were not significant (P>0.05). Conclusions: After systemic administration ofMnCl2 through vena caudalis, MEMRI could map the laminar architectures and the anatomy border of functional zone of somatosensory cortex specifically. High concentration of mannitol could open blood brain barrier (BBB) effectively and have distinct impacts on the architectures displayed in MEMRI. Opening or maintaining BBB in MEMRI had respective characteristics, and it should be selected according to practical needs. (authors)