Non-invasive MRI Assessments of Tissue Microstructures and Macromolecules in the Eye upon Biomechanical or Biochemical Modulation

Ho, Leon C.; Sigal, Ian A.; Jan, Ning-Jiun; Yang, Xiaoling; Merwe, Yolandi van der; Yu, Yu; Chau, Ying; Leung, Christopher Kai-Shun; Jin, Tao; Wu, Ed X.; Kim, Seong Gi; Wollstein, Gadi; Schuman, Joel S.; Chan, Kevin C.

doi:10.1038/srep32080

Cited by 33 publications

(24 citation statements)

References 70 publications

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“… 24 – 26 , 34 However, analysis of this effect is outside the scope of this article. Also, recent studies 40 , 41 have shown the presence of the magic angle effect in the corneoscleral shell in MRI, where fibrous microstructure of the sclera is resolved at the magic angle. We did not observe this effect in our images, likely because of the relatively low in-plane and slice resolutions (1 × 1 × 8 mm 3 ) of our scans causing T2* intravoxel dephasing, point spread function (PSF) broadening, as well as partial voluming.…”

Section: Discussionmentioning

confidence: 97%

Dynamic Imaging of the Eye, Optic Nerve, and Extraocular Muscles With Golden Angle Radial MRI

Sengupta

Smith

et al. 2017

Invest. Ophthalmol. Vis. Sci.

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PurposeThe eye and its accessory structures, the optic nerve and the extraocular muscles, form a complex dynamic system. In vivo magnetic resonance imaging (MRI) of this system in motion can have substantial benefits in understanding oculomotor functioning in health and disease, but has been restricted to date to imaging of static gazes only. The purpose of this work was to develop a technique to image the eye and its accessory visual structures in motion.MethodsDynamic imaging of the eye was developed on a 3-Tesla MRI scanner, based on a golden angle radial sequence that allows freely selectable frame-rate and temporal-span image reconstructions from the same acquired data set. Retrospective image reconstructions at a chosen frame rate of 57 ms per image yielded high-quality in vivo movies of various eye motion tasks performed in the scanner. Motion analysis was performed for a left–right version task where motion paths, lengths, and strains/globe angle of the medial and lateral extraocular muscles and the optic nerves were estimated.ResultsOffline image reconstructions resulted in dynamic images of bilateral visual structures of healthy adults in only ∼15-s imaging time. Qualitative and quantitative analyses of the motion enabled estimation of trajectories, lengths, and strains on the optic nerves and extraocular muscles at very high frame rates of ∼18 frames/s.ConclusionsThis work presents an MRI technique that enables high-frame-rate dynamic imaging of the eyes and orbital structures. The presented sequence has the potential to be used in furthering the understanding of oculomotor mechanics in vivo, both in health and disease.

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Section: Discussionmentioning

confidence: 97%

Dynamic Imaging of the Eye, Optic Nerve, and Extraocular Muscles With Golden Angle Radial MRI

Sengupta

Smith

et al. 2017

Invest. Ophthalmol. Vis. Sci.

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“…Additionally, we have used micro-MRI, with in-plane resolution under 30 μm, to examine the collagen microstructure of the optic nerve head and lamina cribrosa using magic angle enhancement (Ho et al, 2014b). More recently, we used a multi-modal MRI approach, consisting of T2-weighted MRI, diffusion tensor MRI and magnetization transfer MRI to study the effects of glycosaminoglycan content and IOP in rat eyes (Ho et al, 2016). This study is the first to demonstrate the use of high-field MRI for measuring whole globe deformations and local deformation of the scleral canal during a controlled inflation test and from a single scan in a large animal model.…”

Section: Discussionmentioning

confidence: 99%

“…IOP was varied by changing the height of PBS in a gravity perfusion system as previously described (Ho et al, 2016; Ho et al, 2014b) and monitored by a pressure transducer designed for MRI applications with a sensitivity of 1 mmHg (BIOPAC Systems, Goleta, CA, USA). Eyes were suspended in hydrogel in an open container, as we have described previously, to prevent the application of external forces (Ho et al, 2016). The same eyes were scanned serially under increasing levels of IOP: 0 mmHg, 10 mmHg, 20 mmHg, or 40 mmHg.…”

Section: Methodsmentioning

confidence: 99%

“…MRI offers practically unlimited penetration depth for ocular imaging (Duong et al, 2008; Langner et al, 2010), and with improvements in MRI field strength it is now possible to obtain μm-resolution scans without contrast agents (Ho et al, 2016; Ho et al, 2014b). In fact, we recently demonstrated that MRI can be used to image the microstructure of the sclera and lamina cribrosa (Ho et al, 2014b).…”

Section: Introductionmentioning

confidence: 99%

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Whole-globe biomechanics using high-field MRI

Voorhees

Jan

et al. 2017

Experimental Eye Research

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The eye is a complex structure composed of several interconnected tissues acting together, across the whole globe, to resist deformation due to intraocular pressure (IOP). However, most work in the ocular biomechanics field only examines the response to IOP over smaller regions of the eye. We used high-field MRI to measure IOP induced ocular displacements and deformations over the whole globe. Seven sheep eyes were obtained from a local abattoir and imaged within 48 hours using MRI at multiple levels of IOP. IOP was controlled with a gravity perfusion system and a cannula inserted into the anterior chamber. T2-weighted imaging was performed to the eyes serially at 0 mmHg, 10 mmHg, 20 mmHg and 40 mmHg of IOP using a 9.4 Tesla MRI scanner. Manual morphometry was conducted using 3D visualization software to quantify IOP-induced effects at the globe scale (e.g. axial length and equatorial diameters) or optic nerve head scale (e.g. canal diameter, peripapillary sclera bowing). Measurement sensitivity analysis was conducted to determine measurement precision. High-field MRI revealed an outward bowing of the posterior sclera and anterior bulging of the cornea due to IOP elevation. Increments in IOP from 10 to 40 mmHg caused measurable increases in axial length in 6 of 7 eyes of 7.9±5.7% (mean±SD). Changes in equatorial diameter were minimal, 0.4±1.2% between 10 and 40 mmHg, and in all cases less than the measurement sensitivity. The effects were nonlinear, with larger deformations at normal IOPs (10–20mmHg) than at elevated IOPs (20–40mmHg). IOP also caused measurable increases in the nasal-temporal scleral canal diameter of 13.4±9.7% between 0 and 20 mmHg, but not in the superior-inferior diameter. This study demonstrates that high-field MRI can be used to visualize and measure simultaneously the effects of IOP over the whole globe, including the effects on axial length and equatorial diameter, posterior sclera displacement and bowing, and even changes in scleral canal diameter. The fact that the equatorial diameter did not change with IOP, in agreement with previous studies, indicates that a fixed boundary condition is a reasonable assumption for half globe inflation tests and computational models. Our results demonstrate the potential of high-field MRI to contribute to understanding ocular biomechanics, and specifically of the effects of IOP in large animal models.

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“…In this study, we hypothesize that the visual pathway is altered in the early stage of STZ–induced experimental diabetes, and such alterations can be revealed non-invasively by in vivo multi-modal magnetic resonance imaging (MRI). In vivo MRI has been increasingly employed at high magnetic field strengths to evaluate the rodent eye and brain's visual system in health and disease [ 19 – 26 ]. In this study, we used diffusion tensor MRI (DTI) at 7 Tesla to evaluate the white matter integrity along the visual pathway [ 25 , 27 , 28 ] of STZ-induced diabetic rats and sham control rats.…”

Section: Introductionmentioning

confidence: 99%

In Vivo Evaluation of the Visual Pathway in Streptozotocin-Induced Diabetes by Diffusion Tensor MRI and Contrast Enhanced MRI

et al. 2016

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Visual function has been shown to deteriorate prior to the onset of retinopathy in some diabetic patients and experimental animal models. This suggests the involvement of the brain's visual system in the early stages of diabetes. In this study, we tested this hypothesis by examining the integrity of the visual pathway in a diabetic rat model using in vivo multi-modal magnetic resonance imaging (MRI). Ten-week-old Sprague-Dawley rats were divided into an experimental diabetic group by intraperitoneal injection of 65 mg/kg streptozotocin in 0.01 M citric acid, and a sham control group by intraperitoneal injection of citric acid only. One month later, diffusion tensor MRI (DTI) was performed to examine the white matter integrity in the brain, followed by chromium-enhanced MRI of retinal integrity and manganese-enhanced MRI of anterograde manganese transport along the visual pathway. Prior to MRI experiments, the streptozotocin-induced diabetic rats showed significantly smaller weight gain and higher blood glucose level than the control rats. DTI revealed significantly lower fractional anisotropy and higher radial diffusivity in the prechiasmatic optic nerve of the diabetic rats compared to the control rats. No apparent difference was observed in the axial diffusivity of the optic nerve, the chromium enhancement in the retina, or the manganese enhancement in the lateral geniculate nucleus and superior colliculus between groups. Our results suggest that streptozotocin-induced diabetes leads to early injury in the optic nerve when no substantial change in retinal integrity or anterograde transport along the visual pathways was observed in MRI using contrast agent enhancement. DTI may be a useful tool for detecting and monitoring early pathophysiological changes in the visual system of experimental diabetes non-invasively.

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Non-invasive MRI Assessments of Tissue Microstructures and Macromolecules in the Eye upon Biomechanical or Biochemical Modulation

Cited by 33 publications

References 70 publications

Dynamic Imaging of the Eye, Optic Nerve, and Extraocular Muscles With Golden Angle Radial MRI

Dynamic Imaging of the Eye, Optic Nerve, and Extraocular Muscles With Golden Angle Radial MRI

Whole-globe biomechanics using high-field MRI

In Vivo Evaluation of the Visual Pathway in Streptozotocin-Induced Diabetes by Diffusion Tensor MRI and Contrast Enhanced MRI

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