Histologic Confirmation of High Resolution MRI Ocular Imaging

Abstract

 

Purpose

 

To test the hypothesis that increased magnetic field strength will allow visualization of ocular anatomy not resolved with conventional MR, OCT and ultrasound.

 

Methods

 

7 Tesla (7T) MR scans were obtained on a human enucleation specimen (Varian Medical Systems, Palo Alto, CA). T2 weighted Data sets were produced at a resolution of 34 µ. Diffusion-weighted sequences were acquired at b-values= 10, 250 and 750. The specimen was then sectioned and mounted to provide a histologic view which corresponded to the scan plan and location of the MR images. The histology and MR images were interpreted by an ocular pathologist (DRS).

 

Results

 

7 Tesla MR scanning of the eye can display ocular anatomy down to 34 µ resolution in all parts of the eye. Specific areas of interest include the ciliary body, peripheral retina.retro-laminar optic nerve, posterior chamber and iris. The attached image reveals schlemm's canal. Individual ciliary processes are seen. The posterior surface of the iris and the posterior chamber are both identified. In the retro-laminar optic nerve the mylination of the nerve fibers is clear. The location of the central retinal artery in the anterior portion of the optic nerve is visible and the episclera is imaged.

 

Conclusions

 

7 Tesla MR scanning provides 34 µ resolution ocular anatomy which is an order of magnitude higher than 3 tesla MR scans. High frequency ocular ultrasound (20 - 50 MHz) provide high resolution of the eye, however, only the anterior portion of the globe can be imaged. The 5 - 10 MHz probes used for the posterior segment are significantly lower resolution. Spectral domain OCT give very high resolution images, however OCT is light based and depends on clear media and only displays the superficial anatomy of the posterior pole of the eye. This suggests that 7T MR may be superiorfor imaging the retro-laminar optic nerve, the posterior chamber the episclera, and the retina and choroid anterior to the equator.

 

 

This figure shows the light microscopic image on the left and the 7T MR image on the right. The area of regard is the ciliary body and anterior chamber angle, (note schlemm's canal).

 

Keywords: 550 imaging/image analysis: clinical • 599 microscopy: light/fluorescence/immunohistochemistry • 636 pathobiology