ABSTRACT
Background Functional magnetic resonance imaging technique based on a manganese (Mn2+) tracer makes labeling the optic nerve in vivo possible.However studies on the optimal concentration and dynamic change after injection of Mn2+ are rare.Objective This study was designed to explore the time- and dose-dependent response for Mn2+-enhanced MRI of visual pathway after intravitreal injection of MnCl2.Methods Different concentrations of MnCl2(0.5,1,2,5,10,15,20,40mmol/L) with a volume of 25μl were intravitreally injected into the left eyes of 48 pigmented rabbits and were randomly divided into eight groups according to the drug concentrations.No reagent reg was injected into the right eyes as controls.MRI was performed at 4,6,8,12,24,48,96 and 168 hours after the administration of MnCl2 to examine the imaging of the optic nerve,chiasma,optic tract,lateral geniculate body and epithalamus.The signal-noise ratio of MRI in visual pathway was calculated and the optimal concentration and best imaging time after injection of MnCl2 were assessed.The use of the animals followed the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.Results The imaging of the optical nerve in the left eyes was enhanced in comparison with the right eyes 24 hours after injection of 0.5-1 mmol/L MnCl2 with a significant difference in SNR value between these two groups (t=1.17,t=0.95,P>0.05).24 hours after the injection of 2 mmol/L MnCl2 into the left eyes,the SNR value of the optic nerve on the left side was higher than the right side t=8.43,P0.05).The strongest imaging signal in optical nerve was seen in 24 hours after the intravitreal injection of 10-40 mmol/L MnCl2 and decayed gradually from 24 to 168 hours with a transportation speed of (3.32±0.19) mm/h in rabbit visual pathway.SNR value of optic nerve showed a positive correlation with the concentrations of MnCl2 with the regression equation Y=77.786+2.467X(F=20.102,P=0.004,R2=0.770).Conclusion Manganese-enhanced MRI is a viable method for temporospatial visualization of optic never in the pigmented rabbits.The image intensity of MRI is associated with the dose of Mn2+.