Showing papers by "Ravinder Reddy published in 1998"
TL;DR: In vivo sodium MRI of human patellar articular cartilage provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritis in vivo, and the process of optimizing imaging time and signal‐to‐noise ratio is discussed.
Abstract: Preliminary results from in vivo sodium MRI of human patellar articular cartilage are presented. Sodium images generated of an in vitro bovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage. This provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritis in vivo. The process of optimizing imaging time and signal-to-noise ratio, as well as potential implications in the detection of osteoarthritic change, are discussed.
212 citations
TL;DR: Findings are indicative of an impaired antioxidant defense system, not attributable to neuroleptic treatment, and lend further support to the notion that oxidative stress may have a pathophysiological role in schizophrenia.
161 citations
TL;DR: It is suggested that haloperidol may not have direct regulatory effect on AODS enzyme activities and that SOD and GSH-Px activities may change in response to other factors such as change in symptom severity.
129 citations
Journal Article•
TL;DR: Images of magnetic flux density, generated by uniform and nonuniform current flow, and the current density image of a uniform current flow are given and current density levels as low as 1A=mm 2 are measured.
Abstract: In this study, images of nonuniform and uniform electric current density in conductor phantoms, which contain magnetic resonance active nuclei, are produced using Magnetic Resonance Imaging (MRI). A standard spin echo pulse sequence is used, with the addition of a bipolar current pulse. The flux density parallel to the main magnetic eld, generated by the current pulse, is encoded in the phase of the complex MR image. The spatial distribution of magnetic flux density is extracted from the phase image. Current density is calculated using the magnetic flux density. This fairly recent technique is known as Magnetic Resonance Current Density Imaging (MRCDI). In this paper, images of magnetic flux density, generated by uniform and nonuniform current flow, and the current density image of a uniform current flow are given. Current density levels as low as 1A=mm 2 are measured. Eects of current density on k-space data are also discussed.
38 citations
TL;DR: The signal‐to‐noise ratios of T1ρ‐weighted images are significantly better than comparable T2‐ Weighted images, allowing for improved visualization of tissue contrast, and the feasibility of proton T 1ρ‐dispersion imaging for detecting intravenous H217O on a live mouse brain is demonstrated.
Abstract: Detection of H2(17)O with proton T1rho-dispersion imaging holds promise as a means of quantifying metabolism and blood flow with MRI. However, this technique requires a priori knowledge of the intrinsic T1rho dispersion of tissue. To investigate these properties, we implemented a T1rho imaging sequence on a 1.9-T Signa GE scanner. A series of T1rho images for different locking frequencies and locking durations were obtained from rat brain in vivo and compared with 5% (wt/vol) gelatin phantoms containing different concentrations of (17)O ranging from .037% (natural abundance) to 2.0 atom%. Results revealed that, although there is considerable T1rho-dispersion in phantoms doped with H2(17)O, the T1rho of rat brain undergoes minimal dispersion for spin-locking frequencies between .2 and 1.5 kHz. A small degree of T1rho dispersion is present below .2 kHz, which we postulate arises from natural-abundance H2(17)O. Moreover, the signal-to-noise ratios of T1rho-weighted images are significantly better than comparable T2-weighted images, allowing for improved visualization of tissue contrast. We have also demonstrated the feasibility of proton T1rho-dispersion imaging for detecting intravenous H2(17)O on a live mouse brain. The potential application of this technique to study brain perfusion is discussed.
27 citations
TL;DR: Off‐resonance proton T1p dispersion imaging shows promise as a safe, sensitive technique for generating 17O‐based T1P contrast without exceeding SAR limitations.
Abstract: Proton T1rho dispersion imaging is a recently described method for indirect detection of 17O. However, clinical implementation of this technique is hindered by the requirement for a high-amplitude spin-locking field (gammaB1 > 1 kHz) that exceeds current limitations in specific absorption rate (SAR). Here, a strategy is offered for circumventing high SAR in T1rho dispersion imaging of 17O through the use of low-amplitude off-resonance spin-locking pulses (gammaB1 < 300 Hz). Proton spin-lattice relaxation times in the off-resonance rotating frame were measured in H2(17)O-enriched tissue phantoms. On- and off-resonance T1rho dispersion imaging was implemented at 2 T using a spin-locking preparatory pulse cluster appended to a standard spin-echo sequence. On- and off-resonance dispersion images exhibited similar 17O-based image contrast. Magnetization transfer effects did not depend on 17O concentration and had no effect on image contrast. In conclusion, off-resonance proton T1rho dispersion imaging shows promise as a safe, sensitive technique for generating 17O-based T1rho contrast without exceeding SAR limitations.
26 citations
TL;DR: In this article, a 2D, fast gradient-echo sequence with a nominal constant flip angle of 12 degrees was used to visualize the paranasal sinuses and the nasal cavity.
Abstract: In this study, MRI of hyperpolarized 3He gas in human paranasal sinuses is presented. Helium images were obtained at 1.5 T, using a surface coil and a 2D, fast gradient-echo sequence with a nominal constant flip angle of 12 degrees. Coronal images of 20-mm thick slices were generated and compared with proton images of the corresponding sections. The images enable visualization of the paranasal sinuses and the nasal cavity, suggesting a potential use of this method not only in identifying the anatomical configuration of these pneumatic spaces, but also in assessing sinus ventilation.
20 citations
TL;DR: It was found that the residual quadrupolar interaction was reduced in the compressed samples, and changes in the ordering of collagen fibers may be responsible for the observed effect.
Abstract: The effects of mechanical compression on the multiple quantum coherences generated from sodium ions in articular cartilage were investigated. Cartilage samples obtained from bovine patellae were studied during compression at 0.7 MPa (100 psi) for 1 hour. The double quantum filtered spectra showed marked lineshape changes in the compressed samples. Compression did not seem to influence the lineshapes of the single quantum and triple quantum filtered spectra significantly. We found that the residual quadrupolar interaction was reduced in the compressed samples. Changes in the ordering of collagen fibers may be responsible for the observed effect.
9 citations
Journal Article•