The Experimental Study On Magnetic Resonance Imaging Of Optic Nerve

Optic nerve is an important part of central nervous system, it connects the eyeball and optic chiasma. The visual signal is transferred to visual cortex via optic nerve. Traumatic optic neuropathy is an important cause of permanent vision loss. The commonly used clinical examinations such as visual acuity, visual field examination, computed tomography(CT) and visual evoked potentials may not be sufficient for the direct and comprehensive assessment of the location and extent of optic nerve damage in patients with optic nerve injury. Previous methods used for nerve tract study relied on methods that required the sacrifice of the animal, preventing their use for longitudinal studies or their eventual use in humans. Because of its merits of excellent soft-tissue resolution, multiple sequence parameters and multiple plane imaging, magnetic resonace imaging(MRI) should be regarded as the first choice to visualize the optic nerve and anatomy characters of the eyes. The optic nerve travels tortuously in intraorbital segment, and is encircled with the sinus. These structures and involuntary movement can cause the chemical shift and motion artifacts of MRI examination. MRI examination of optic nerve still faces challenges. Basic studies should be strengthened to display the structures and function of optic nerve with MRI scanners.In the research, we studied the gross anatomy and MRI of the rabbit optic nerve. Topical administration of Mn Cl2 for rabbit managnese enhanced magnetic resonance imging(MEMRI) was conducted with 3.0 Tesla systems. Topically loaded MEMRI could be used to visualize the visual system in rabbits, and detect the optic nerve injury. To investigate the distribution of Mn2+ after topical administration of Mn Cl2, dynamic images of eyes were conducted and assays were performed using inductively coupled plasma-mass spectrometer(ICP-MS). To investigate the toxicity of Mn2+ after topical administration, histologic sections were examined with microscope in the study. Our main findings are summarized as follow:1. The optic nerve of rabbit traveled horizontally in intraorbital segment with the angle 135.5° between bilateral optic nerves. There were no separate optic canal of the optic nerves, the optic nerves paralleled in the same optic canal, and formed optic chiasma.2. MRI with high resolution well displayed the shape of rabbit optic nerve, which fits with gross anatomy, but it is still a challenge to display the details structure of the optic nerve.3. Topical administration of 1.0mol·L-1 and 1.5mol·L-1 Mn Cl2 for MEMRI could visualize the visual pathway, ocular irritation symptom was mild after 1.0mol·L-1 topically loaded. The suitable concentration of Mn Cl2 for MEMRI may be 1.0mol·L-1.4. MEMRI with topical administration of Mn Cl2 could detect optic nerve injuries in rabbits. Eye drop administration may be an easy and less invasive approach for loading Mn2+ for MEMRI analysis of the optic nerve injury.5. Mn2+ could distribute into aqueous humor rapidly after topical administration of Mn Cl2, whereas, the concentration of Mn2+ in vitreous body fluctuated in a narrow range over the course. The uptake of Mn2+ in retina may involve several different pathways.6. There were no obvious toxicity to the cornea, retina and optic nerve in rabbit eyes afer topical administration of 1.0mol·L-1 Mn Cl2.In conclusion, we studied the MRI and gross anatomy of optic nerve in rabbits, conducted topical administration of Mn Cl2 for MEMRI with traditional 3.0Tesla MRI scanner. Topically loaded Mn2+ for MEMRI visualized the normal visual pathway, and detected the optic nerve injury. Topical administration of Mn Cl2 did not cause the damge to the eyes. This research provides an easier and more noninvasive MEMRI method for optic nerve study.