Biomedical subjects

Henning U Voss

Publications and source records attributed to Henning U Voss.

7 recordsLinked to original sources

PubMed2006

A quantitative synchronization model for smooth pursuit target tracking.

We propose a quantitative model for human smooth pursuit tracking of a continuously moving visual target which is based on synchronization of an internal expectancy model of the target position coupled to the retinal target signal. The model predictions are tested in a smooth circular pursuit eye tracking experiment with transient target blanking of variable duration. In subjects with a high tracking accuracy, the model accounts for smooth pursuit and repeatedly reproduces quantitatively characteristic patterns of the eye dynamics during target blanking. In its simplest form, the model has only one free parameter, a coupling constant. An extended model with a second parameter, a time delay or memory term, accounts for predictive smooth pursuit eye movements which advance the target. The model constitutes an example of synchronization of a complex biological system with perceived sensory signals.

Attention↗

PubMed2006

Monitoring the effects of BCNU chemotherapy Wafers (Gliadel) in glioblastoma multiforme with proton magnetic resonance spectroscopic imaging at 3.0 Tesla.

Carmustine wafers (Gliadel Wafer) are implanted at resection in some patients with high-grade gliomas. Studies suggest that proton magnetic resonance spectroscopic imaging ((1)H MRSI) demonstrates early changes predictive of future failure or response to systemic chemotherapy. This study explores (1)H MRSI as a means to assess peri-tumoral tissue response post-resection and Gliadel((R)) implantation in patients with high-grade gliomas. Pilot (1)H MRSI data are presented that demonstrate noninvasive, serial monitoring of metabolic changes at the tumor site following Gliadel implantation. Three patients with newly diagnosed glioblastoma multiforme (GBM) underwent MRI and (1)H MRSI at 3.0 Tesla prior to resection and at 3-5 and > or =12 weeks post-operatively. Baseline MRS spectra of tumor tissue from all patients were characterized by marked increases of choline (CHO) and lactate (LAC), and a decrease of N-acetylaspartate (NAA), typical of GBM compared with normal contra-lateral brain tissue. Post-operatively, spectra were analyzed from the resection cavity and peri-tumoral regions and compared with normal tissue from the contra-lateral brain at baseline. In 2 of 3 patients, peri-tumoral NAA/CRE increased and CHO/NAA decreased compared to contra-lateral brain at 3-5 weeks compared with baseline following Gliadel therapy and surgery but prior to radiotherapy. This study indicates that (1)H MRSI has the ability to localize regions of heterogeneous response following Gliadel treatment. Although data are limited, these results suggest that metabolic indicators of outcome can be successfully monitored pre- and post-surgical resection and Gliadel implantation with (1)H MRSI. Additional study of patients receiving Gliadel Wafers using (1)H MRSI may serve to aid clinicians in assessing tumor regression and gauging efficacy of this chemotherapy treatment.

Aged↗

PubMed2006

Analyzing fMRI experiments with structural adaptive smoothing procedures.

Data from functional magnetic resonance imaging (fMRI) consist of time series of brain images that are characterized by a low signal-to-noise ratio. In order to reduce noise and to improve signal detection, the fMRI data are spatially smoothed. However, the common application of a Gaussian filter does this at the cost of loss of information on spatial extent and shape of the activation area. We suggest to use the propagation-separation procedures introduced by Polzehl, J., Spokoiny, V. (2006). Propagation-separation approach for local likelihood estimation. Probab. Theory Relat. Fields, in print. instead. We show that this significantly improves the information on the spatial extent and shape of the activation region with similar results for the noise reduction. To complete the statistical analysis, signal detection is based on thresholds defined by random field theory. Effects of adaptive and non-adaptive smoothing are illustrated by artificial examples and an analysis of experimental data.

Algorithms↗

PubMed2006

Fiber tracking in the cervical spine and inferior brain regions with reversed gradient diffusion tensor imaging.

Diffusion tensor echo planar magnetic resonance imaging of the inferior brain regions and the spinal cord suffers from tissue-air and tissue-bone interfaces, which cause severe susceptibility-induced artifacts. These artifacts consist of image distortions in the phase encode direction and also affect signal intensity. To correct for these distortions, we used the reversed gradient method. We find that most in-plane voxel displacements in the inferior brain regions and the cervical spine can be corrected, yielding a good match of white matter fiber tracts with anatomical reference images. Furthermore, uninterrupted white matter fiber tracts going from the cervical spine up to cortical areas, derived from data acquired in a single acquisition, are presented.

Artifacts↗

PubMed2006

Functional MR imaging at 3.0 T versus 1.5 T: a practical review.

This article reviews and discusses recent findings in functional MRI at 1.5 and 3.0 T magnetic field strengths, in research and clinical applications. Particular attention is paid to comparative studies and to an explanation of the physical and biological dependencies leading to potential gains and tradeoffs of functional scanning at magnets with a high field strength.

Artifacts↗

PubMed2006

High-pass two-dimensional ladder network resonators for magnetic resonance imaging.

A novel two-dimensional ladder network resonator design is introduced for signal transmission and detection in magnetic resonance imaging. It is shown that planar structures consisting solely of inductively coupled elements have a high-pass eigenmode spectrum and exhibit eigenfunctions which can be used for magnetic resonance imaging, including quadrature operation. Two 5 x 5 element prototypes, a planar surface coil and a volume head coil, are presented to demonstrate the suitability of the design for imaging at 3.0 Tesla.

Computer-Aided Design↗

PubMed2006

Possible axonal regrowth in late recovery from the minimally conscious state.

We used diffusion tensor imaging (DTI) to study 2 patients with traumatic brain injury. The first patient recovered reliable expressive language after 19 years in a minimally conscious state (MCS); the second had remained in MCS for 6 years. Comparison of white matter integrity in the patients and 20 normal subjects using histograms of apparent diffusion constants and diffusion anisotropy identified widespread altered diffusivity and decreased anisotropy in the damaged white matter. These findings remained unchanged over an 18-month interval between 2 studies in the first patient. In addition, in this patient, we identified large, bilateral regions of posterior white matter with significantly increased anisotropy that reduced over 18 months. In contrast, notable increases in anisotropy within the midline cerebellar white matter in the second study correlated with marked clinical improvements in motor functions. This finding was further correlated with an increase in resting metabolism measured by PET in this subregion. Aberrant white matter structures were evident in the second patient's DTI images but were not clinically correlated. We propose that axonal regrowth may underlie these findings and provide a biological mechanism for late recovery. Our results are discussed in the context of recent experimental studies that support this inference.

Adolescent↗