Biomedical subjects

W Scott Hoge

Publications and source records attributed to W Scott Hoge.

5 recordsLinked to original sources

PubMed2006

Collateral nerve fibers in human spinal cord: visualization with magnetic resonance diffusion tensor imaging.

Diffusion tensor magnetic resonance imaging provides structural information about nerve fiber tissue. The first eigenvector of the diffusion tensor is aligned with the nerve fibers, i.e., longitudinally in the spinal cord. The underlying hypothesis of this study is that the presence of collateral nerve fibers running orthogonal to the longitudinal fibers results in an orderly arrangement of the second eigenvectors. Magnetic resonance diffusion tensor scans were performed with line scan diffusion imaging on a clinical MR scanner. Axial sections were scanned in a human cervical spinal cord specimen at 625 microm resolution and the cervical spinal cord of four normal volunteers at 1250 microm resolution. The spinal cord specimen was fixed and stained for later light microscopy of the collateral fiber architecture at 0.53 microm resolution. Diffusion measured by MR was found to be anisotropic for both white and gray matter areas of the spinal cord specimen; the average fractional anisotropy (FA) was 0.63 +/- 0.09 (diffusion eigenvalues lambda1 0.38 +/- 0.05 micros/mm2, lambda2 0.14 +/- 0.03 micros/mm2, lambda3 0.10 +/- 0.03 micros/mm2) in white matter and 0.27 +/- 0.04 (lambda1 0.36 +/- 0.04 micros/mm2, lambda2 0.28 +/- 0.03 micros/mm2, lambda3 0.21 +/- 0.04 micros/mm2 in gray matter. The normal-volunteer FA values were similar, i.e., 0.66 +/- 0.04 (lambda1 1.66 +/- 0.14 micros/mm2, lambda2 0.55 +/- 0.02 micros/mm2, lambda3 0.40 +/- 0.01 micros/mm2) in white matter and 0.35 +/- 0.03 (lambda1 1.14 +/- 0.07 micros/mm2, lambda2 0.70 +/- 0.03 micros/mm2, lambda3 0.58 +/- 0.02 micros/mm2) in gray matter. The first eigenvector pointed, as expected, in the longitudinal direction. The second eigenvector directions exhibited a striking arrangement, consistent with the distribution of interconnecting collateral nerve fibers discerned on the histology section. This finding was confirmed for the specimen by quantitative pixel-wise comparison of second eigenvector directions and collateral fiber directions assessed on light microscopy image data. Diffusion tensor MRI can reveal non-invasively and in great detail the intricate fiber architecture of the human spinal cord.

Adult↗

PubMed2006

Extension of the UNFOLD method to include free breathing.

Unaliasing by Fourier-encoding the overlaps using the temporal dimension (UNFOLD) is a method to reduce the data acquisition burden in dynamic MRI. The method works by forcing aliased signals to behave in specific ways through time, so that these unwanted signals can be detected and removed. Unexpected events in time, such as displacements caused by breathing, have the potential to disturb the temporal strategy and may affect UNFOLD's ability to suppress aliasing artifacts. This work presents an extension of the UNFOLD method to accommodate temporal encoding disruptions. While the main type of disruption considered here comes from respiratory motion, other types of disruption can be envisioned, such as departures from the usual UNFOLD k-space sampling scheme. This extended version of UNFOLD was incorporated into UNFOLD-sensitivity encoding (UNFOLD-SENSE), and should also be applicable to closely related methods such as temporal SENSE (TSENSE), k-t Broaduse Linear Acquisition Speed up Technique (k-t BLAST), and k-t SENSE. Five patients were imaged with a modified version of a myocardial-perfusion sequence, and UNFOLD was used either alone or in conjunction with SENSE to obtain an acceleration of 2.0 (in three patients) or 3.0 (in two patients). In both cases this extended version of UNFOLD was able to suppress artifacts caused by the presence of breathing motion.

Algorithms↗

PubMed2006

Generalized encoding through the use of selective excitation in accelerated parallel MRI.

Selective RF excitation is employed in magnetic resonance imaging (MRI) to achieve a variety of effects, such as slice selection. More elaborate transverse magnetization patterns can be realized via tailored RF excitation pulses, useful for example to image any specific region geometry within the field of view, or, to acquire non-Fourier encoded samples of the underlying magnetization distribution. In this manuscript, we review prior work on the combination of selective RF excitation with parallel MRI acquisition techniques. This combination can be used both to advantageously manipulate the numerical conditioning of the reconstruction problem, as well as to compact the information content of the acquired data so as to improve the achievable acceleration rate. With the latter application it is possible to also consider the acceleration provided by parallel imaging alone as a compaction of information content, which in certain cases can be used to reduce the length of the selective excitations. The main contribution of this review is to show how the combination of selective excitation with parallel imaging provides the latter an added flexibility that can be used to either enhance image quality, increase imaging speed, or both.

Algorithms↗

PubMed2005

Identification of translational displacements between N-dimensional data sets using the high-order SVD and phase correlation.

This paper presents an extension of the phase correlation image alignment method to N-dimensional data sets. By the Fourier shift theorem, the motion model for translational shifts between N-dimensional images can be represented as a rank-one tensor. Through use of a high-order singular value decomposition, the phase correlation between two N-dimensional data sets can be decomposed to independently identify translational displacements along each dimension with subpixel resolution. Using three-dimensional MRI data sets, we demonstrate the effectiveness of this approach relative to other N-dimensional image registration methods.

Algorithms↗

PubMed2004

Non-Fourier-encoded parallel MRI using multiple receiver coils.

This paper describes a general theoretical framework that combines non-Fourier (NF) spatially-encoded MRI with multichannel acquisition parallel MRI. The two spatial-encoding mechanisms are physically and analytically separable, which allows NF encoding to be expressed as complementary to the inherent encoding imposed by RF receiver coil sensitivities. Consequently, the number of NF spatial-encoding steps necessary to fully encode an FOV is reduced. Furthermore, by casting the FOV reduction of parallel imaging techniques as a dimensionality reduction of the k-space that is NF-encoded, one can obtain a speed-up of each digital NF spatial excitation in addition to accelerated imaging. Images acquired at speed-up factors of 2x to 8x with a four-element RF receiver coil array demonstrate the utility of this framework and the efficiency afforded by it.

Calibration↗