Showing papers by "Brian A. Wandell published in 2014"

Lifespan maturation and degeneration of human brain white matter.

Abstract: Properties of human brain tissue change across the lifespan. Here we model these changes in the living human brain by combining quantitative magnetic resonance imaging (MRI) measurements of R1 (1/T1) with diffusion MRI and tractography (N=102, ages 7-85). The amount of R1 change during development differs between white-matter fascicles, but in each fascicle the rate of development and decline are mirror-symmetric; the rate of R1 development as the brain approaches maturity predicts the rate of R1 degeneration in aging. Quantitative measurements of macromolecule tissue volume (MTV) confirm that R1 is an accurate index of the growth of new brain tissue. In contrast to R1, diffusion development follows an asymmetric time-course with rapid childhood changes but a slow rate of decline in old age. Together, the time-courses of R1 and diffusion changes demonstrate that multiple biological processes drive changes in white-matter tissue properties over the lifespan.

Evaluation and statistical inference for human connectomes

Abstract: Diffusion-weighted imaging coupled with tractography is currently the only method for in vivo mapping of human white-matter fascicles. Tractography takes diffusion measurements as input and produces the connectome, a large collection of white-matter fascicles, as output. We introduce a method to evaluate the evidence supporting connectomes. Linear fascicle evaluation (LiFE) takes any connectome as input and predicts diffusion measurements as output, using the difference between the measured and predicted diffusion signals to quantify the prediction error. We use the prediction error to evaluate the evidence that supports the properties of the connectome, to compare tractography algorithms and to test hypotheses about tracts and connections.

The vertical occipital fasciculus: A century of controversy resolved by in vivo measurements

Abstract: The vertical occipital fasciculus (VOF) is the only major fiber bundle connecting dorsolateral and ventrolateral visual cortex. Only a handful of studies have examined the anatomy of the VOF or its role in cognition in the living human brain. Here, we trace the contentious history of the VOF, beginning with its original discovery in monkey by Wernicke (1881) and in human by Obersteiner (1888), to its disappearance from the literature, and recent reemergence a century later. We introduce an algorithm to identify the VOF in vivo using diffusion-weighted imaging and tractography, and show that the VOF can be found in every hemisphere (n = 74). Quantitative T1 measurements demonstrate that tissue properties, such as myelination, in the VOF differ from neighboring white-matter tracts. The terminations of the VOF are in consistent positions relative to cortical folding patterns in the dorsal and ventral visual streams. Recent findings demonstrate that these same anatomical locations also mark cytoarchitectonic and functional transitions in dorsal and ventral visual cortex. We conclude that the VOF is likely to serve a unique role in the communication of signals between regions on the ventral surface that are important for the perception of visual categories (e.g., words, faces, bodies, etc.) and regions on the dorsal surface involved in the control of eye movements, attention, and motion perception.

White matter consequences of retinal receptor and ganglion cell damage.

Abstract: PURPOSE Patients with Leber hereditary optic neuropathy (LHON) and cone-rod dystrophy (CRD) have central vision loss; but CRD damages the retinal photoreceptor layer, and LHON damages the retinal ganglion cell (RGC) layer. Using diffusion MRI, we measured how these two types of retinal damage affect the optic tract (ganglion cell axons) and optic radiation (geniculo-striate axons). METHODS Adult onset CRD (n = 5), LHON (n = 6), and healthy controls (n = 14) participated in the study. We used probabilistic fiber tractography to identify the optic tract and the optic radiation. We compared axial and radial diffusivity at many positions along the optic tract and the optic radiation. RESULTS In both types of patients, diffusion measures within the optic tract and the optic radiation differ from controls. The optic tract change is principally a decrease in axial diffusivity; the optic radiation change is principally an increase in radial diffusivity. CONCLUSIONS Both photoreceptor layer (CRD) and retinal ganglion cell (LHON) retinal disease causes substantial change in the visual white matter. These changes can be measured using diffusion MRI. The diffusion changes measured in the optic tract and the optic radiation differ, suggesting that they are caused by different biological mechanisms.

27.2: Distinguished Paper: Modeling Visible Differences: The Computational Observer Model

Abstract: We describe a new approach to the design of visible difference metrics that is based on calculating the information available at different points in the visual pathway and determining whether an ideal linear classifier can use this information to reliably predict the difference between two stimuli. This approach, referred to as the computational observer model, establishes a near upper bound on performance by assessing whether the information necessary to make discrimination is present in the visual system. We describe the implementation of a software framework that embodies the computational observer and illustrate how this framework can be used to address specific questions about display design.

Automating the design of image processing pipelines for novel color filter arrays: local, linear, learned (L3) method

Abstract: The high density of pixels in modern color sensors provides an opportunity to experiment with new color filter array (CFA) designs. A significant bottleneck in evaluating new designs is the need to create demosaicking, denoising and color transform algorithms tuned for the CFA. To address this issue, we developed a method(local, linear, learned or L3) for automatically creating an image processing pipeline. In this paper we describe the L3 algorithm and illustrate how we created a pipeline for a CFA organized as a 2×2 RGB/Wblock containing a clear (W) pixel. Under low light conditions, the L3 pipeline developed for the RGB/W CFA produces images that are superior to those from a matched Bayer RGB sensor. We also use L3 to learn pipelines for other RGB/W CFAs with different spatial layouts. The L3 algorithm shortens the development time for producing a high quality image pipeline for novel CFA designs.

A Predominantly Visual Subdivision of The Right Temporo-Parietal Junction (vTPJ)

Abstract: A multiplicity of sensory and cognitive functions has been attributed to the large cortical region at the temporo-parietal junction (TPJ). Using functional MRI, we report that a small region lateralized within the right TPJ responds robustly to certain simple visual stimuli (“vTPJ”). The vTPJ was found in all right hemispheres (n= 7), posterior to the auditory cortex. To manipulate stimuli and attention, subjects were presented with a mixture of visual and auditory stimuli in a concurrent block design in 2 experiments: (1) A simple visual stimulus (a grating pattern modulating in mean luminance) elicited robust responses in the vTPJ, whether or not the subject attended to vision and(2) a drifting low-contrast dartboard pattern of constant mean luminance evoked robust responses in the vTPJ when it was task-relevant (visual task), and smaller responses when it was not (auditory task). The results suggest a focal, visually responsive region within the right TPJ that is powerfully driven by certain visual stimuli (luminance fluctuations), and that can be driven by other visual stimuli when the subject is attending. The precise localization of this visually responsive region is helpful in segmenting the TPJ and to better understand its role in visual awareness and related disorders such as extinction and neglect.

Visualization of heart wall tissue

Abstract: Various aspects of the instant disclosure are directed to imaging tissue. As may be implemented in accordance with one or more embodiments, aspects of the present disclosure are directed to apparatuses and methods involving the following. A light source includes an array of light emitters that illuminate a tissue region of a heart wall with light at different wavelength ranges. A light collector collects multispectral images including respective images collected at each of the different wavelength ranges at which the tissue region is illuminated. A catheter positions the light source and light collector proximate the tissue region of the heart wall for respectively illuminating the tissue region and collecting the multispectral images. A display circuit collects and displays one or more images depicting a condition of the health of heart wall tissue, based on the respective images collected at the different ones of the wavelength ranges.

Spectral Optics Simulation for Rapid Image Systems Prototyping: Ray-tracing, Diffraction and Chromatic Aberration

Abstract: We describe a software tool that models multicomponent spherical lenses, and calculates the spectral irradiance and depth maps for three-dimensional scenes. Combined with image systems simulations, this tool allows for the rapidly prototyping of imaging systems.