Advanced diffusion-weighted imaging in patients with optic neuritis deficit – value of reduced field of view DWI and readout-segmented DWI

Abstract

The objective of this article is to evaluate advanced techniques of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) measurements of the optic nerve in patients with optic neuritis. Methods: In this prospective and institutional review board-approved trial, we examined 15 patients with acute visual loss and clinical signs of optic neuritis including thin-slice multi-shot segmented readout of long variable echo trains (rs-EPI, RESOLVE) DWI and reduced field-of view DWI using a parallel transmit system (rFOV-EPI). Conventional single-shot echo-planar DWI (ss-EPI) of the whole brain was available in 13 patients. Subjective image quality was compared using a four-point scale and objective ADC measurements were performed in comparison with the non-affected side. Results: In the intraorbital segment, subjective image quality was significantly higher in rFOV-EPI (score 3.3 AE 0.8) compared with rs-EPI (score 2.1 AE 0.8) and ss-EPI (score 0.9 AE 0.8). Diagnosis was hampered in the canalicular segment (n ¼ 3) and the intracranial segment (n ¼ 1) in all applied DWI techniques. ADC measurements of the affected side differed significantly in all DWI sequences ss-EPI (sensitivity 54%, accuracy 77%), rs-EPI (sensitivity 71%, accuracy 86%), and rFOV-EPI (sensitivity 73%, accuracy 87%). Conclusion: Optic neuritis in the intraorbital segment can be detected with high sensitivity without the need for contrast application. Using rFOV-EPI improves subjective image quality compared with rs-EPI and ss-EPI. Due to its higher spatial resolution, rFOV-EPI was the preferred technique in our study and can ensure the diagnosis in the intraorbital segment. However, artefacts occur in the canalicular and intracranial segment of the optic nerve, therefore contrast-enhanced T1-weighted images must still be considered as the gold standard.

Apparent Diffusion Coefficient Variabilities of the Optic Nerve in Multiple Sclerosis: Optic nerve head and Intraorbital segment

“…Despite several number of studies that investigated the relationship between MS and optic nerve disruption on DWI have been conducted (6,16,(21)(22)(23)29), there have not been any previous study in the literature that investigated the changes at the optic nerve head/intraorbital segment in patients with MS. With DWI, there can have difficulties in evaluating the canalicular and intracranial segments of the optic nerve due to anatomical localization, but intraorbital segment and the optic nerve head can be examined with higher precision (30). Seeger et al (30) reported that it is possible to detect optic neuritis, with high sensitivity, in the intraorbital segment without the need for contrast. This study revealed that the ADC values increased in MS patients without optic neuritis when compared to the ADC values of the control group, suggesting subclinical optic neuritis in MS. Optical coherence tomography may be used to assess the damage in the optic nerve caused by the thickness of the optic nerve fiber layer.…”

Recent advances in magnetic resonance imaging of optic neuritis

“…Diffusion-based forms of imaging (DWI and DTI) result in signal-deficient sequences, so higher spatial resolution is essential to compensate for this deficiency. So-called "ZOOM" [40,41] sequences can be used to reduce the length of echo-train imaging by reducing the field-of-view to rule out undesired tissue, thus reducing image distortion and improving spatial resolution. Hickman [40] reported that using ZOOM, the mean ADC was significantly associated with clinical and electrophysiological parameters in the chronic phase of ON.…”

“…Hickman [40] reported that using ZOOM, the mean ADC was significantly associated with clinical and electrophysiological parameters in the chronic phase of ON. Compared with conventional DWI, this preferable technique [41] can improve image quality in the orbital segment of the optic nerve. It has also been used in DTI [42].…”

“…Field-of-view optimized and constrained undistorted single-shot DWI is a promising method for reducing geometric distortion and improving image quality [41] by reducing the field-of-view in the phase-encoded direction via a 2D spatially selective echo-planar radiofrequency excitation pulse and a 180° refocusing pulse. The use of ADCs derived from field-of-view optimized and constrained undistorted single-shot-DWI for evaluating the chiasma and optic nerve in acute ON is superior [46] to using conventional DWI.…”

Combining SENSE and reduced field-of-view for high-resolution diffusion weighted magnetic resonance imaging

“…To increase in-plane resolution without pronounced geometric distortion, reduced field-of-view (FOV) imaging has been developed by reducing the FOV along the phase-encoding (PE) direction and thus shortening the echo train length [ 3 – 8 ]. This technique is especially useful for high resolution diffusion imaging of specific anatomical structures like prostate [ 9 – 11 ], spinal cord [ 4 , 12 – 16 ], optic nerve [ 17 – 19 ] and etc. For this goal further, an intuitive strategy is to combine parallel imaging with reduced FOV, which has been successfully applied in 7 T applications [ 20 – 22 ].…”