Biomedical subjects

Mehmet Bilgen

Publications and source records attributed to Mehmet Bilgen.

25 records · Page 2Linked to original sources

PubMed2004

Simple, low-cost multipurpose RF coil for MR microscopy at 9.4 T.

An inductively coupled RF coil is introduced for high-resolution MR studies at 9.4 T. The coil offers the flexibility of use as an implantable coil for local imaging inside the body or as a surface coil for imaging below complex surfaces. Successful operation of this coil at strong magnetic field requires special design considerations. In this note, implementation issues of the coil are discussed in detail and practical solutions to overcome some of these difficulties are offered. Imaging performance of the coil and its versatility are demonstrated with images acquired from rat spinal cord when the coil is implanted, and mouse spine and brain when the coil is placed on the surface.

Animals↗

PubMed2004

High-resolution magnetic resonance imaging of the human median nerve.

OBJECTIVES: It is widely accepted that peripheral nerve repairs performed within 6 weeks of injury have much better outcomes than those performed at later dates. However, there is no diagnostic technique that can determine if a traumatic peripheral nerve injury requires surgical intervention in the early postinjury phase. The objective of this article was to determine whether novel, noninvasive magnetic resonance imaging techniques could demonstrate the microstructure of human peripheral nerves that is necessary for determining prognosis and determining if surgery is indicated following traumatic injury. METHODS: Ex vivo magnetic resonance imaging protocols were developed on a 9.4-T research scanner using spin-echo proton density and gradient-echo imaging sequences and a specially designed, inductively coupled radio frequency coil. These imaging protocols were applied to in situ imaging of the human median nerve in 4 fresh-frozen cadaver arms. RESULTS: Noninvasive high-resolution images of the human median nerve were obtained. Structures in the nerve that were observed included fascicles, interfascicular epineurium, perineurium, and intrafascicular septations. CONCLUSION: Application of these imaging techniques to clinical scanners could provide physicians with a tool that is capable of grading the severity of nerve injuries and providing indications for surgery in the early postinjury phase.

Echo-Planar Imaging↗

PubMed2003

Elastography imaging of small animal oncology models: a feasibility study.

To test the feasibility of applying ultrasonic elastography on small animal oncology models, experiments were performed in vitro and in situ on murine mammary lesions induced exogenously by tumor cell line 66.3. In vitro studies involved three 1-week-old excised tumors embedded in a phantom block with ultrasonic properties similar to those of soft biologic tissues. In situ studies involved five mice whose bodies were embedded in pure gelatin blocks. The data were acquired from the blocks with a clinical scanner modified to have an automated compressor assembly and processed to construct the elastograms at various imaging planes within each block. The results were analyzed both qualitatively and quantitatively to assess the merits of the elastographic imaging and its limitations for in vivo serial studies of tumors in small animal oncology models.

Animals↗

PubMed2003

Mohr diagram interpretation of anisotropic diffusion indices in MRI.

Descriptions of diffusion anisotropy in MR Diffusion Tensor Imaging are often based on scalar indices such as surface-to-volume ratio, volume ratio, fractional anisotropy and rotational anisotropy. Recently, Mohr diagram was introduced to visualize the anisotropic diffusion information, but in a graphical form. Even though both scalar indices and the Mohr diagram are derived from the elements of the diffusion tensor, so far, the relationships between these measures and the key aspects of the Mohr diagram have not been established. This paper demonstrates these relationships both qualitatively and quantitatively for two microscopically heterogeneous biologic tissues, kidney and spinal cord.

Anisotropy↗

PubMed2002

Mohr diagram representation of anisotropic diffusion tensor in MRI.

With current approaches, it is difficult to visually comprehend the complete information contained in a diffusion tensor (DT) measured from a microscopically heterogeneous biological tissue. Therefore, in this work the Mohr diagram is introduced to graphically display the key aspects of DTs and to interpret the underlying anisotropy, both qualitatively and quantitatively. Specifically, the mathematical basis for the construction of the Mohr diagram from the elements of DTs is described, the merits of the approach are illustrated with examples of DTs reported for various biological tissues, and the results are discussed in the context of relating the diffusion anisotropy to the tissue structures.

Anisotropy↗

PubMed2002

In vivo diffusion tensor imaging of rat spinal cord at 7 T.

In vivo diffusion tensor imaging of normal rat spinal cord was performed using a multi-segmented, blipped EPI sequence at 7 T field strength. At high diffusion weighting, the signal exhibited a non-monoexponential decay that was fitted to a biexponential function, associated with the fast and slow components of diffusion in the cord tissue, using a nonlinear regression analysis along with a constrained optimization procedure. From the measured tensors, the eigenvalues and the maps of invariant scalar measures (fractional anisotropy, relative anisotropy, volume ratio, and trace) were calculated and analyzed statistically. The results were combined to quantitatively characterize the anisotropic properties of the fast and slow diffusions in white- and gray matter of live spinal cords.

Animals↗

PubMed2002

In vivo assessment of blood-spinal cord barrier permeability: serial dynamic contrast enhanced MRI of spinal cord injury.

Serial in vivo dynamic contrast enhanced (DCE) MRI studies were performed on spinal cord injured rats on post-injury Days 0, 10, 20 and 30 to determine the distribution of gadopentetate-dimeglumine (Gd) concentration in injured cord tissue. A two-compartment pharmacokinetic model was fitted to the time course of the concentration data at the epicenter of injury for each post-injury day. From these fits, the rates of the Gd transport between plasma and injured cord tissue were determined as a measure of blood-spinal cord barrier (BSCB) permeability. The results indicated that Gd transport rates decrease steadily with a concomitant improvement in motor functions of the rats with post-injury time. Specifically, the rates of Gd accumulation in injured SC tissue and its clearance correlated with the neurobehavioral scores with correlation coefficients of rho = -0.96 and -0.79, respectively, suggesting a significant link between the neurobehavioral function and the restoration of BSCB integrity as a result of the ongoing repair and recovery processes within the injured cords.

Animals↗