Diffusion Method to Image Normal Human Optic Nerve
Lazar Fleysher1, Matilde Inglese1,2,3, Mark J Kupersmith, MD2,4, and Niels Oesingmann5

1Radiology, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 2Neurology, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 3Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 4Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 5Siemens Healthcare, USA, New York, NY, United States

### Synopsis

In this work we demonstrate an application of a single-shot EPI diffusion sequence with outer-volume suppression to optic nerve imaging. The advantage of this approach is that it is simple and is available on clinical systems. This paves a way to a routine diffusion-encoded clinical examinations of the optic nerve

### Introduction

The optic nerve, optic chiasm and optic tract comprise a vision transmission system for the brain. A critical amount of functioning axons of the optic nerve is required to provide vision, pupillary function, motor and circadian rhythm control and other functions. The optic nerve is subject to a wide range of pathology including congenital anomalies, ischemic, inflammatory, neurodegenrative, metabolic and neoplastic diseases. Unfortunately, routine opthalmologic examination usually can only reveal abnormalities of the fundus oculi and optic nerve head. Visual evoked potential recording can provide indirect measure of functional integrity of the visual system via the electrophysiological changes, but it cannot accurately pinpoint the location of the optic nerve abnormality. Consequently, MRI is needed to study the vast number of disorders that injure the optic nerve and/or reduce retinal processing and the effects of neuroprotection and restoration. Nevertheless, MRI of the human optic nerve remains a challenge[1-4] due to its size, movement and surrounding CSF. The goal of this study is to establish a feasibility of routine diffusion-based MR imaging of the optic nerve using vendor-provided software and hardware.

### Methods

Three healthy volunteers (one female) were studied. Images were acquired with 3T Siemens Skyra MRI scanner (Siemens, Erlangen, Germany) equipped with a vendor-provided 32 channel head coil and with 45mT/m imaging gradients. Diffusion-encoded data were acquired using vendor provided 2D single-shot DTI-EPI sequence with 21 contiguous 2mm slices and 164x 48.2 mm FOV with 102x30 imaging matrix. Such a short EPI echotrain allowed significant reduction of image distortions associated with the magnetic field inhomogeneities. The slice package was positioned perpendicular to the optic nerve posterior to the globe. Diffusion-encoding direction was set along the slice-encode direction. During the scan, the subjects were instructed to fixate on a cross presented on the stimulus display. Other sequence parameters were TR=6000ms TE=84ms and 15 b-values randing from 0 to 1000 s/mm2 with 4 averages each. Fat suppression was “on”, CSF suppression was “off”. To avoid the wrap-around artefact in phase-encode direction (L/R), outer volume suppression was employed.

### Results

Apparent diffusion coefficient along the nerve was computed on 4 slices posterior to the globe with clear spacial separation between CSF and the nerve. The obtained values (mean $\pm$ std) for the optical nerve was $1.63\ \pm\ 0.19 \mu m^{2}/ms$ and for the CSF $2.79\ \pm\ 0.10 \mu m^{2}/ms$. These values are inline with those obtained previously using specially-developed MRI sequences[1-4].

### Conclusions

In this work we demonstrate an application of a single-shot EPI diffusion sequence with outer-volume suppression to optic nerve imaging. The advantage of this approach is that it is simple and is available on clinical systems. This paves a way to a routine diffusion-encoded clinical examinations of the optic nerve.

### Acknowledgements

No acknowledgement found.

### References

1. Wheeler-Kingshott et.al. MRM 2006;56:446

2. Trip et.al. NeuroImage 2006;30:498

3. Bodanapally et.al. AJNR 2015;36:1536

4. Xu et.al. NMR Biomed 2008;21:928

### Figures

Twenty-one contiguous diffusion slices overlayed on the sagittal and axial localizers.

Nine b=0 contiguous slices of left optic nerve (top) demonstrate good image quality and SNR. (SNR is about 15 in gray and white matte and reaches 80 in CSF). Corresponding ADC maps (bottom) .

Diffusion weighted signal as a function of diffusion-encoding.

Slice #4 with all 15 b-values demonstrating good SNR even for high (upto 1000s/mm2) b-values.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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