Early diffusion evidence of retrograde transsynaptic degeneration in the human visual system (original) (raw)

In vivo diffusion tensor imaging of the human optic nerve: Pilot study in normal controls

Magnetic Resonance in Medicine, 2006

Diffusion tensor imaging (DTI) of the optic nerve (ON) was acquired in normal controls using zonally oblique multislice (ZOOM) DTI, which excites a small field of view (FOV) using a fast sequence with a shortened EPI echo train. This combines the benefit of low sensitivity to motion (due to the single-shot acquisition used), with the additional advantage of reduced sensitivity to magnetic field susceptibility artifacts. Reducing the bright signal from the fat and cerebrospinal fluid (CSF) surrounding the nerve are key requirements for the success of the presented method. Measurements of mean diffusivity (MD) and fractional anisotropy (FA) indices were made in a coronal section of the middle portion of the optic nerve (ON) in the right (rON) and left (lON) ONs. The average values across 10 healthy volunteers were FA rON ‫؍‬ 0.64 ؎ 0.09 and FA lON ‫؍‬ 0.57 ؎ 0.10, and MD rON ‫؍‬ (1173 ؎ 227) ؋ 10 -6 mm 2 s -1 and MD lON ‫؍‬ (1266 ؎ 170) ؋ 10 -6 mm 2 s -1 . Measurements of the principal eigenvalue of the DT and its orthogonal component were also in agreement with those expected from a highly directional structural organization. Magn Reson Med 56:446 -451, 2006.

Diffusion tensor imaging in acquired blind humans

Neuroscience Letters, 2006

Retinal implants as a future possible therapy of blindness rely on an intact neural transmission from the retina to the primary visual cortex. By now it remains unknown, in how far the absence of afferent input in blindness affects also the organization of the optic radiation. Using diffusion tensor imaging (DTI), the non-invasive evaluation of large fiber tracts including the optic radiation has become possible. This method is sensitive to changes of the axonal state such as wallerian degeneration. We have compared DTI data from 6 acquired blind patients with those of a group of 11 healthy control subjects. Neither the relative anisotropy quotient of the visual fiber tract and the pyramidal tract showed a statistically significant difference between the blind patients and the control group nor did the absolute values of the relative anisotropy in the pyramidal tract and the visual fiber tract. There was no axonal degeneration of the optic radiation in late onset acquired blindness. With the optic pathways remaining intact, transmitting electric signals of retinal implants to the visual regions of the human brain seems to be possible even after decades of acquired blindness.

Diffusion Tensor Imaging in Acute Optic Neuropathies

Archives of Neurology, 2012

Diffusion tensor imaging of visual pathways in patients with acute and chronic optic neuritis

International Eye Research

AIM: To investigate diffusion tensor imaging (DTI) evaluations of visual pathways in patients with acute and chronic optic neuritis (ON), and investigate the correlations between visual disability, retinal nerve fiber layer thickness (RNFLT) and diffusion index changes. METHODS: We performed DTI in 26 patients and 13 healthy controls. Patients had acute ON in 17 eyes, chronic ON in 20 eyes and 15 unaffected eyes. In all participants, the visual afferent system was evaluated with neuro-ophthalmological examinations, optical coherence tomography (OCT), visual evoked potential (VEP), orbital and cranial MRI. RESULTS: Fractional anisotropy (FA) in the optic nerves was lower in patients with acute ON and chronic ON than controls (P=0.28). Mean diffusivity (MD) in the optic nerves, was higher in patients with acute and chronic ON than the unaffected eyes of patients and controls (P<0.01). Retinal nerve fiber layer thickness, P100 amplitude and latency and visual acuity (VA) were signif...

Cerebral white matter damage in frontotemporal dementia assessed by diffusion tensor tractography

Neuroradiology, 2008

Introduction We used diffusion tensor imaging (DTI) to study white matter integrity in patients with frontotemporal dementia (FTD). Methods The subjects comprised 20 patients (9 men, 11 women) with FTD and 17 age-matched healthy controls (9 men, 8 women). Based on the data obtained from DTI, we performed tractography of the major cerebral pathways, including the pyramidal tracts, genu and splenium of the corpus callosum (CC), bilateral arcuate fasciculi (AF), inferior longitudinal fasciculi (ILF) and uncinate fasciculi (UF). We measured the values of fractional anisotropy (FA) in each fiber and statistically compared the findings in patients with those in controls.

Assessing optic nerve pathology with diffusion MRI: from mouse to human

NMR in Biomedicine, 2008

Optic nerve is often affected in patients with glaucoma and multiple sclerosis (MS). Conventional MRI can detect nerve damage but it does not accurately assess the underlying pathologies. Mean diffusivity and diffusion anisotropy indices derived from diffusion tensor imaging (DTI) have been shown to be sensitive to a variety of central nervous system (CNS) white matter pathologies. Despite being sensitive, the lack of specificity limits the ability of these measures to differentiate the underlying pathology in CNS white matter tissues. Directional (axial and radial) diffusivities, measuring water diffusion parallel and perpendicular to the axonal tracts, have been shown to be specific to axonal and myelin damages in mouse models of optic nerve injury, including retinal ischemia and experimental autoimmune encephalomyelitis (EAE). The progression of Wallerian degeneration has also been detected using directional diffusivities after retinal ischemia. However, translating these findings to human optic nerve is technically challenging. The current status of human optic nerve diffusion MRI, including the imaging sequences and protocols, are summarized herein. Despite lacking a consensus of the optimal sequence or protocol among different groups, increased mean diffusivity and decreased diffusion anisotropy has been observed in injured optic nerve from chronic optic neuritis patients. Decreased λ ∥ , correlating with visual function and recovery, was observed recently in acute optic neuritis patients in a pilot study, suggesting the specificity of λ ∥ to axonal injury. From different mouse models of optic nerve injuries to the emerging studies on optic neuritis patients, directional diffusivities demonstrate great potential to be specific biomarkers for axonal and myelin injury.

Diffusion tensor imaging of the optic radiations after optic neuritis

2011

Trans-synaptic degeneration could exacerbate neurodegeneration in multiple sclerosis (MS). We aimed to assess whether anterograde trans-synaptic degeneration could be identified in the primary visual pathway in vivo. Diffusion tensor imaging (DTI) was used to assess the optic radiations in 15 patients with previous optic nerve inflammation and 9 healthy volunteers. A probabilistic atlas of the optic radiations was created from healthy diffusion tractography data. Lengthwise profiles for DTI parameters (axial [k || ], radial [k ? ] and mean diffusivity [MD], fractional anisotropy [FA] and the angle of deviation of the principal eigenvector [a]) were analyzed for patients and controls. Patients also underwent multifocal visual evoked potential (mfVEP) assessments to characterize the latency and amplitude of cortical potentials. Correlations were performed between mfVEP latency and amplitude in the left and right visual hemi-fields and DTI parameters in the contra-lateral optic radiations. Patients displayed a significant decrease in k || within the body of both optic radiations, which significantly correlated with loss of mfVEP amplitude. Abnormal k ? and FA were detected bilaterally throughout the optic radiations in patients but the abnormality was not associated with amplitude reduction or latency prolongation of the mfVEP. An abnormal a value was observed in the left optic radiations of patients, and the a value in the body of the optic radiations also correlated with mfVEP amplitude loss. The assocation between bilateral DTI abnormalities within the optic radiations and loss of afferent electrical activity could indicate anterograde trans-synaptic degeneration occurs following optic neuritis. Hum Brain Mapp 00:000-000, 2011. V

Diffusion Tensor Imaging in Acute Optic Neuropathies: Predictor of Clinical Outcomes

2012

Objective-To evaluate directional diffusivities within the optic nerve in a first event of acute optic neuritis to determine whether decreased axial diffusivity (AD) would predict 6-month visual outcome and optic nerve integrity measures. Design-Cohort study. Setting-Academic multiple sclerosis center. Patients-Referred sample of 25 individuals who presented within 31 days after acute visual symptoms consistent with optic neuritis. Visits were scheduled at baseline, 2 weeks, and 1, 3, 6, and 12 months. Main Outcome Measures-Visual acuity, contrast sensitivity, visual evoked potentials (VEPs), and thickness of the retinal nerve fiber layer (RNFL). Results-An incomplete 6-month visual recovery was associated with a lower baseline AD (1.50 μm 2 /ms [95% confidence interval {CI}, 1.36-1.64 μm 2 /ms for incomplete recovery vs 1.75 μm 2 / ms [95% CI, 1.67-1.83 μm 2 /ms] for complete recovery). Odds of complete recovery decreased by

Visualization of human optic nerve by diffusion tensor mapping and degree of neuropathy

PLOS ONE

Diffusion-weighted magnetic resonance imaging of the human optic nerve and tract is technically difficult because of its small size, the inherent strong signal generated by the surrounding fat and the cerebrospinal fluid, and due to eddy current-induced distortions and subject movement artifacts. The effects of the bone canal through which the optic nerve passes, and the proximity of blood vessels, muscles and tendons are generally unknown. Also, the limited technical capabilities of the scanners and the minimization of acquisition times result in poor quality diffusion-weighted images. It is challenging for current tractography methods to accurately track optic pathway fibers that correspond to known anatomy. Despite these technical limitations and low image resolution, here we show how to visualize the optic nerve and tract and quantify nerve atrophy. Our visualization method based on the analysis of the diffusion tensor shows marked differences between a healthy male subject and ...

Visualization of human optic nerve and tract by diffusion tensor mapping and degree of neuropathy

2022

Diffusion-weighted magnetic resonance imaging of the human optic nerve and tract is technically difficult because of its small size, the inherent strong signal generated by the surrounding fat and the cerebrospinal fluid, and due to eddy current-induced distortions and subject movement artifacts. In addition, the effects of the bone channel through which the optic nerve passes, and the proximity of blood vessels, muscles and tendons are generally unknown. Furthermore, the limited technical capabilities of the scanners and the minimization of acquisition times result in poor quality diffusion-weighted images. It is challenging for current tractography methods to accurately track optic pathway fibers that correspond to known anatomy and to produce a reasonable fraction of decussating fibers. Despite these technical limitations and low image resolution, here we show how to visualize the optic nerve and tract and quantify nerve atrophy. Our visualization method based on the analysis of ...

Early diffusion evidence of retrograde transsynaptic degeneration in the human visual system (original) (raw)

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