Biomedical subjects

Greg J Stanisz

Publications and source records attributed to Greg J Stanisz.

10 recordsLinked to original sources

PubMed2006

An MRI evaluation of carpal tunnel dimensions in healthy wrists: Implications for carpal tunnel syndrome.

BACKGROUND: Deviated wrist postures and pinch grip use have been linked to the development of carpal tunnel syndrome and are likely related to the size and shape of the carpal tunnel. The purpose of this study was to quantify carpal tunnel dimensions with changes in wrist posture and pinch grip. METHODS: Eight healthy volunteers (4 male, 4 female) underwent magnetic resonance imaging of their dominant wrists under seven conditions which included: 30 degrees wrist extension, neutral and 30 degrees flexion (with and without a 10 N pinch force) and a fist with a neutral wrist. Cross-sectional area of the carpal tunnel and its contents were calculated at 3mm increments along the length of the tunnel and integrated to calculate volumes. Ratios were calculated between the contents of the tunnel to the tunnel itself for area and volume. FINDINGS: The use of a correction factor significantly reduced volume and distal carpal tunnel area in flexed and extended wrists. Carpal tunnel areas were largest in neutral and smallest at the distal end with wrist flexion. An extended wrist resulted in the smallest carpal tunnel and content volumes as well as the smallest carpal tunnel content volume to carpal tunnel volume ratios. While men had significantly larger areas and volumes than women for both the carpal tunnel and it contents, there were no differences in ratios between the contents and tunnel size. INTERPRETATION: A simple correction factor for non-perpendicular magnetic resonance images proved useful in relating volume changes to known pressure changes within the carpal tunnel. More inclusive and detailed evaluation of the carpal tunnel and its contents is required to fully understand mechanisms for median nerve compression in the carpal tunnel.

Biomechanical Phenomena↗

PubMed2006

Effects of temperature and aldehyde fixation on tissue water diffusion properties, studied in an erythrocyte ghost tissue model.

Ex vivo biological sample imaging can complement in vivo MRI studies. Since ex vivo studies are typically performed at room temperature, and samples are frequently preserved by fixation, it is important to understand how environmental and chemical changes dictated by ex vivo studies alter the physical and MR properties of a sample. Diffusion and relaxation time measurements were used to assess the effects of temperature change and aldehyde fixation on the biophysical and MR properties of a model biological tissue comprised of erythrocyte ghosts suspended in buffer or agarose gel. Sample temperature was varied between 10 degrees C and 37 degrees C. Diffusion MRI data were analyzed with a biophysically appropriate two-compartment exchange model. Temperature change resulted in a complex alteration of water diffusion properties due to the compartmental nature of tissues and alteration in membrane permeability. Formaldehyde, Karnovsky's solution, and glutaraldehyde all caused statistically significant changes to the biophysical and MR properties of the samples. Fixation caused large decreases in water proton T2, which was restored to near prefixation values by washing free fixative from the samples. Water membrane permeability was also significantly altered by fixation. This study demonstrates that relating in vivo MR data to chemically fixed ex vivo data requires an understanding of the effects of sample preparation.

Analysis of Variance↗

PubMed2005

MR microscopy of rat hippocampal slice cultures: a novel model for studying cellular processes and chronic perturbations to tissue microstructure.

Brain slices provide a useful nervous tissue model to investigate the relationships between magnetic resonance imaging (MRI) contrast mechanisms and tissue microstructure; yet, these acutely isolated tissues remain viable for only 10-12 h. To study slower biological processes, this work describes the first MRI microscopy characterization of organotypic rat hippocampal slice cultures that can be maintained for several weeks. Diffusion-weighted images of slice cultures acquired with a 14.1-T magnet demonstrated the laminar anatomy of the hippocampus with relatively high signal-to-noise ratios. Diffusion data analyzed using a two-compartment model with exchange indicated that cultured slices had a comparable microstructure to acute brain slices and to in vivo brain. Immunohistochemistry indicated that slice cultures tolerated the conditions required for MRI study well. MRI of cultured tissue slices is highly amenable to correlative microscopy techniques and offers great promise for future MRI investigations of pathological tissue reorganization, molecular imaging and stem cell therapies.

Animals↗

PubMed2005

T1, T2 relaxation and magnetization transfer in tissue at 3T.

T1, T2, and magnetization transfer (MT) measurements were performed in vitro at 3 T and 37 degrees C on a variety of tissues: mouse liver, muscle, and heart; rat spinal cord and kidney; bovine optic nerve, cartilage, and white and gray matter; and human blood. The MR parameters were compared to those at 1.5 T. As expected, the T2 relaxation time constants and quantitative MT parameters (MT exchange rate, R, macromolecular pool fraction, M0B, and macromolecular T2 relaxation time, T2B) at 3 T were similar to those at 1.5 T. The T1 relaxation time values, however, for all measured tissues increased significantly with field strength. Consequently, the phenomenological MT parameter, magnetization transfer ratio, MTR, was lower by approximately 2 to 10%. Collectively, these results provide a useful reference for optimization of pulse sequence parameters for MRI at 3 T.

Animals↗

PubMed2005

MR properties of excised neural tissue following experimentally induced demyelination.

Changes in the magnetic resonance (MR) parameters of demyelinated neural tissue were measured in vitro using an experimental animal model. A tellurium (Te) diet was applied to weanling rats to induce the demyelination process in the sciatic nerve. The quantitative MR parameters, such as T(1), T(2) relaxation time constants and magnetization transfer (MT) were measured each day after applying the Te diet (up to 7 days) and were found to be substantially different from those of normal nerves. An increase in the average T(1) and T(2) was observed along with a decrease in the MT ratio (MTR) and the quantitative MT parameter M(0B), which describes the semisolid pool of protons. Most of the MR parameters correlated very well with the myelin fraction of neural tissue evaluated by quantitative histopathology. The T(2) relaxation spectrum provided the most efficient quantitative assessment of changes in neural tissue microstructure and its analysis resulted in a powerful tool to distinguish the processes of demyelination and inflammation. In comparison, the MT measurements were less successful.

Animals↗

PubMed2005

Histological and magnetic resonance analysis of sciatic nerves in the tellurium model of neuropathy.

Ingestion of tellurium (Te), a toxic element, produces paralysis of the hind limbs in weanling rats that is due to temporary, segmental demyelination of the sciatic nerves bilaterally. Weanling rats were fed a 1.1% elemental Te diet and sacrificed at various time points for histological and magnetic resonance (MR) analysis of the sciatic nerves. No controls exhibited impairments of the hind limbs, whereas Te-treated animals became progressively impaired with increased Te exposure. Toluidine blue-stained nerve sections of Te-treated animals showed widened endoneurial spaces, disrupted myelin sheaths, swollen Schwann cells, and a few instances of axonal degeneration. Te decreased healthy myelin by 68% and increased percent extracellular matrix by 45% on day 7. MR experiments showed a decrease in the area of the short T2 component, an increase in average T1, and an increase in the position of the intermediate T2 component in Te-treated nerves. The correlation coefficient for healthy myelin and average T1 was 0.88 and that for healthy myelin and the area underneath the short T2 component was 0.77. The area of the short T2 component has been postulated as the best measure of the process of demyelination.

Animals↗

PubMed2004

MR properties of excised neural tissue following experimentally induced inflammation.

Changes in the MR parameters of inflamed neural tissue were measured in vitro. Tumor necrosis factor-alpha (TNF-alpha) was injected into rat sciatic nerves to induce inflammation with negligible axonal loss and demyelination. The MR parameters, such as T1/T2 relaxation and magnetization transfer (MT), were measured 2 days after TNF-alpha injection and were found to be substantially different from those of normal nerves. The average T1/T2 relaxation times increased, whereas the MT ratio (MTR) and the quantitative MT parameter M0B (which describes the semisolid pool of protons) decreased. The MR parameters correlated very well with the extracellular volume fraction (EM) of neural tissue evaluated by quantitative histopathology. The multicomponent T2 relaxation was shown to provide the best quantitative assessment of changes in neural tissue microstructure, and allowed us to distinguish between the processes of inflammation and demyelination. In comparison, the MT measurements were less successful due to competing contributions of demyelination and pH-sensitive changes in the MT effect.

Animals↗

PubMed2003

Is multicomponent T2 a good measure of myelin content in peripheral nerve?

Multicomponent T(2) relaxation of normal and injured rat sciatic nerve was measured. The T(2) relaxation was multiexponential, indicating the multicompartmental nature of T(2) decay in nerve tissue. The size of the short, observed T(2) component correlated very well with quantitative assessment of myelin using computer-assisted histopathological image analysis of myelin. Specifically, the size of the short T(2) component reflected the processes of myelin loss and remyelination accompanying Wallerian degeneration and regeneration following trauma. However, it represented all myelin present in the sample and did not distinguish between intact myelin and myelin debris. Other changes in T(2) spectra were also observed and could be correlated with axonal loss and inflammation. The study also questions the validity of previously offered interpretations of T(2) spectra of nerve.

Animals↗

PubMed2002

Why does MTR change with neuronal depolarization?

T1 and T2 relaxation, and magnetization transfer (MT) of the rat brain were measured during experimentally induced spreading depression (SD). All measured MR parameters changed during SD: T1 relaxation increased by approximately 13%, whereas the T2 increase was substantially larger (88%). MT results showed an MT ratio (MTR) decrease of 9%. The lack of change in the MT exchange rate indicated that the MT processes between water and macromolecular protons are not affected by neuronal depolarization. The observed decrease in MTR was only caused by changes in T1 and T2 relaxation.

Animals↗

PubMed2002

Human erythrocyte ghosts: exploring the origins of multiexponential water diffusion in a model biological tissue with magnetic resonance.

A tissue model composed of erythrocyte ghosts was developed to study the effects of compartmentation on the MR signal acquired from biological tissues. This simple and flexible model offers control over the biophysical parameters that contribute to multicomponent signals arising from cellular systems. Cell density, size, intra- and extracellular composition, and membrane permeability can be independently altered. The effects of cell density and cell size on water diffusion properties were assessed. The data demonstrate non-monoexponential water diffusion in ghost cell suspensions of 17-67% cell density. Data were analysed with the widely employed two-compartment (biexponential) model, and with a two-compartment model that accounted for exchange between compartments. Water exchange between the intra- and extracellular compartments appeared to be significant over the range of diffusion times studied (7-35 ms). The biexponential fit to the ghost data appeared to be underparameterised as the ADCs and relative fractions of the fast and slow components were dependent on the experimental acquisition parameters, specifically the diffusion time. However, both analysis methods proved effective at tracking changes in the ghost model when it was perturbed. This was demonstrated with cell density variation, cell swelling and shrinkage experiments, and reduction of membrane water permeability using a water channel blocker (pCMBS). We anticipate that this model system could be used to investigate compartmental diffusion effects to simulate a range of pathologies, especially ischemic stroke.

4-Chloromercuribenzenesulfonate↗