Quantification of Optic Nerve Cross Sectional Area on MRI: A Novel Protocol using Fiji Software

Summary

We provided a detailed protocol for a standardized method of optic nerve assessment and quantification using MRI, utilizing a widely available imaging sequence, and open access software for image analysis. Following this standardized protocol would provide meaningful data for comparison between different patients and different studies.

Abstract

Optic nerve assessment is an important aspect of glaucoma diagnosis and follow-up. This project describes a protocol for a unified methodology of optic nerve cross-sectional assessment and quantification using 3 T MRI for image acquisition and ImageJ's Fiji software for image processing quantification. Image acquisition was performed using 3 T MRI, with proper instructions for the patient to ensure straight fixation during imaging. A T2-weighted fat suppressed sequence was used. A coronal cut taken 3 mm behind the globe and perpendicular to the optic nerve axis should be uploaded to the software. Using the threshold function, the white matter area of the optic nerve is selected and quantified, thus, eliminating inter-individual measurement bias. We also described the normal limits for the optic nerve cross-sectional area according to age, based on previously published literature. We used the described protocol to assess optic nerve of a suspected glaucoma patient. The optic nerve cross-sectional area was found to be within the normal limits, a finding further confirmed via optical coherence tomography of the optic nerve.

Introduction

Glaucoma is an optic neuropathy that is considered to be the most common cause of irreversible blindness¹. Despite that, it is still poorly understood in terms of its pathophysiology and diagnosis, with no single standard reference for establishing the diagnosis². According to the National Institute for Health and Care Excellence (NICE) the diagnosis of primary open-angle glaucoma (POAG) requires the assessment of multiple domains, including optic disc assessment on fundus exam or optical coherence tomography (OCT) imaging, visual field assessment, and intraocular pressure measurement ³. The idea ....

Protocol

The following study was approved by the research committee and institutional review board of the University of Jordan Hospital. The following protocol will describe the imaging technique used to acquire MRI images, followed by image processing and optic nerve quantification using Fiji software.

1. MRI image acquisition

NOTE: MR image acquisition was done using a 3 Tesla (3 T) MRI to perform multiplanar T2-weighted fat suppression sequence (Table of Materials).

1. Fully explain the examination to the patient. The following include instructions and explanations that need to be mentioned to....

Results

The cup to disc ratio for a 30-year-old male patient presenting for a checkup ophthalmology exam was 0.8 (Figure 1A), which is suspicious and might be suggestive of glaucoma. Upon performing an optical coherence tomography for nerve fiber layer thickness, we found that the nerve thickness was within the normal limits for age (Figure 1B). The patient was scheduled for an orbit MRI, where a coronal cut for optic nerve assessment was ordered and performed as per th.......

Discussion

We described a protocol to assess and quantify optic nerve white matter that might be used for glaucoma patient assessment. The protocol uses widely available imaging sequences for image acquisition, and it uses the open-source Fiji software for image analysis. We standardized the image parameters that were previously found to be most accurate and highly reproducible in optic nerve image acquisition, including asking the patient to fixate straight ahead, using T2 with fat suppression sequence, and capturing the cross-sec.......

Materials

Name	Company	Catalog Number	Comments
Magnetic resonance imaging (MRI) machine	Siemens Magnetom Verio	N/A	3T MRI scanner