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Biomedical subjects

S J Gibbs

Publications and source records attributed to S J Gibbs.

At least 19 recordsLinked to original sources
PubMed1999

Xenon-131 surface sensitive imaging of aerogels in liquid xenon near the critical point.

In recent years, optically pumped xenon-129 has received a great deal of attention as a contrast agent in gas-phase imaging. This report is about the other NMR active xenon isotope (i.e., xenon-131, S = 32) which exhibits distinctive features for imaging applications in material sciences that are not obtainable from xenon-129 (S = (1/2)). The spin dynamics of xenon-131 in gas and liquid phases is largely determined by quadrupolar interactions which depend strongly on the surface of the surrounding materials. This leads to a surface dependent dispersion of relaxation rates, which can be substantial for this isotope. The dephasing of the coherence due to quadrupolar interactions may be used to yield surface specific contrast for imaging. Although optical pumping is not practical for this isotope because of its fast quadrupolar relaxation, a high spin density of liquid xenon close to the critical point (289 K) overcomes the sensitivity problems of xenon-131. We report the first xenon-131 magnetic resonance images and have tested this technique on various meso-porous aerogels as host structures. Aerogels of different densities and changing levels of hydration can clearly be distinguished from the images obtained.

Gels↗
PubMed1998

Rapid MRI and velocimetry of cylindrical Couette flow.

A narrow-gap, temperature-controlled Couette flow rheometer has been developed to study fluid velocities within the annular gap between two concentric cylinders by nuclear magnetic resonance (NMR) imaging and velocimetry. Alternative pulsed-field-gradient-based nuclear magnetic resonance imaging strategies which may be used for measurement of velocity within the Couette flow device have been evaluated. These include two-dimensional (2-D) imaging techniques with acquisition times of several minutes and a one-dimensional (1-D) projection method which exploits the symmetry of the device to reduce overall measurement time to less than 1 min. Velocity measurements made using each technique are presented for a Newtonian fluid undergoing Couette flow at shear rates of approximately 20 and 60 s(-1).

Blood Flow Velocity↗
PubMed1998

A protocol for magnetic resonance imaging of the temporomandibular joints.

The complex concepts and procedures of magnetic resonance imaging (MRI) are unfamiliar to many dentists. Similarly, many radiologists lack understanding of the clinical requirements of the dentist for accurate assessment of TMJ abnormalities. Thus, TMJ imaging procedures may be inadequate or incomplete, may vary from facility to facility, and sometimes from patient to patient in a given facility. A protocol for TMJ imaging is presented which meets dental requirements and is rapidly performed in the MRI facility. The protocol may be copied and attached to the prescription to the imaging center. It may be modified or expanded to accommodate specific patient requirements or equipment performance.

Clinical Protocols↗
PubMed1997

Initial TMJ disk recapture with anterior repositioning appliances and relation to dental history.

Fifty-eight consecutive patients in a referral based practice seeking treatment for complex chronic painful temporomandibular joint (TMJ) disease were enrolled in a prospective study to assess the recapture of displaced disks by anterior repositioning appliances (ARA) and the improvement in disk position in those disks that did not fully recapture. After standard clinical workup, including assessment of pain, maxillary and mandibular ARAs were constructed which repositioned condyles to the Gelb 4/7 position as determined by cephalometrically-corrected linear tomograms. Multi-planar magnetic resonance imaging (MRI) was performed immediately before and after insertion of the mandibular ARA, showing three-dimensional recapture of disks in 85% and improved disk position in 6% of reducing displacements. Disk position was improved in 28% of nonreducing joints, but none were totally recaptured. Recapture or improvement was achieved in 91% of reducing, 28% of nonreducing, and 63% of all joints with internal derangements. Initial disk position, reduction on opening and recapture by ARA were statistically independent of patient age, number of teeth missing, number of third molars missing, malocclusion (Angle's class), overjet, overbite, prosthetic appliances, and previous orthodontic treatment. It was concluded that ARA therapy provided effective recapture of displaced TMJ disks that reduce upon mouth opening. In this population of patients with chronic TMJ pain, previous dental treatment had no statistically significant effect on the incidence of internal derangement or on disk recapture by ARA therapy. There was no evidence of adverse effect from orthodontics, prosthetics, or any other dental care.

Adult↗
PubMed1996

Studies of soil-water transport by MRI.

Sequential spin-echo spin-warp MRI pulse sequences have been used to study soil-water transport processes including infiltration, redistribution, and drainage of water in soil columns. Those images provide a means for monitoring and quantifying spatial and temporal changes of soil-water distributions and the movement of wetting fronts. In addition, temporal-geometric changes of unstable wetting fronts during water redistribution were estimated from 2D images and the temporal development of the longest length of finger was described by a fractal relation t approximately L1.38. Bulk dispersion-time-dependent displacement and velocity spectra, as well as 2D maps of flow velocities and dispersion coefficients in soil macropores during saturated steady-state flow, were reconstructed from data obtained using the alternating-pulsed-field-gradient (APFG) pulse sequences.

Fractals↗
PubMed1996

A pilot study to evaluate the cost-effectiveness of ondansetron and granisetron in fractionated total body irradiation.

The duration of the antiemetic effect of granisetron was examined in a pilot study of patients (n = 26) undergoing a standard emetogenic stimulus in the form of total body irradiation fractionated over 3-4 days, in a randomized comparison with twice-daily ondansetron. A single intravenous dose of granisetron at the onset of therapy was effective over the entire follow-up period in 50% (6/12) of patients, compared with 77% (10/13) prescribed twice-daily oral ondansetron for 3 or 4 days. The response rate within the first 24 hours from the start of irradiation was 67% (8/12) for granisetron and 77% (10/13) for ondansetron. Granisetron and ondansetron were therefore of similar efficacy within the first 24-hour period, but granisetron was less efficaceous more than 24 hours after the onset of therapy. Patients who required a second dose of granisetron did so at intervals of 12, 42, 47 and 48 hours following the first fraction of radiotherapy. The cost per patient in this study was pound 48 for granisetron and pound 54 for ondansetron, but the dose scheduling we used cannot be recommended in view of the lower effectiveness of granisetron.

Administration, Oral↗
PubMed1996

Long-term follow-up of modified condylotomy for internal derangement of the temporomandibular joint.

OBJECTIVES: The purpose of this study was to evaluate disk position and patient response 10 years after modified condylotomy for symptomatic reducing disk displacement. STUDY DESIGNS: Questionnaires and invitations to return for examination and temporomandibular joint magnetic resonance imaging were mailed to 39 consecutive patients 10 years after modified condylotomy. RESULTS: On a 10-point scale the mean pain experienced by the 17 respondents (27 joints) to the questionnaire was 2.0. Ninety percent of 20 joints (12 patients) examined were free of tenderness to palpation. Magnetic resonance imaging in 10 patients (17 joints) showed disk reduction in 59%, displacement with reduction in 29%, and displacement without reduction in 12%. Eighty-five percent of the joints met American Association of Oral and Maxillofacial surgeons criteria for a successful therapeutic outcome. CONCLUSIONS: The study suggests a role for modified condylotomy in the long-term management of symptoms associated with reducing disk displacement. Further, modified condylotomy can frequently reverse an internal derangement and seems to protect against the natural progression of osteoarthrosis.

Adult↗
PubMed1996

Radiology: closing a century, opening a millennium.

As we close the file on the first century of radiology, we honor the pioneers and reflect on the progress they started. We also open a new file, not just a new century, but a new millennium of opportunity. The dramatic technologic advances in diagnostic imaging within recent decades have provided the foundation for expanding our activities in Oral and Maxillofacial Radiology. We are no longer just dental radiology; we can no longer rest on the teaching and practice of conventional dental radiography. We can summarize in one word the direction our efforts must take in opening the millennium: research. Only with research at the fundamental as well as clinical level we can continue to expand our service to the public, to our patients, and to our colleagues.

Germany↗
PubMed1995

Disk position before and after modified condylotomy in 80 symptomatic temporomandibular joints.

OBJECTIVE: Our primary objective was to determine the frequency of disk reduction after modified condylotomy and whether the type of displacement affected outcome. DESIGN: We classified reducing disk displacements from magnetic resonance images of 80 symptomatic temporomandibular joints before modified condylotomy. Disk position was reassessed after surgery. RESULTS: The disk and condyle typically move in reciprocal directions. The disk was reduced by surgery in 79% of the joints. The rate of reduction varied by the type of displacement, but the differences between the groups were not statistically significant. CONCLUSION: This finding reaffirms that modified condylotomy has a high rate of disk reduction. The unexpected observation that the increase in joint space resulting from the surgery typically permitted a variable degree of spontaneous movement of the disk has implications for the nature of osteoarthrosis and internal derangement and for surgical treatments intended to reduce the risk.

Adolescent↗
PubMed1995

Recapture of temporomandibular joint disks using anterior repositioning appliances: an MRI study.

Thirty consecutive patients seeking treatment for painful temporomandibular joint (TMJ) disease were enrolled in a prospective study to assess the relationship between the recapture of displaced disks by anterior repositioning appliances (ARA) and the relief of symptoms. After standard clinical workup including assessment of pain, maxillary and mandibular ARAs were constructed that repositioned condyles to the Gelb 4/7 position. Magnetic resonance imaging (MRI) was performed before and immediately after the insertion of ARAs. Initial MRI findings showed 26 joints with reducing disk displacements in 17 patients, seven partially-reducing joints in four patients, 14 nonreducing joints in 11 patients, and 13 normal joints in eight patients. Postinsertion MRI showed recapture of disks in 25 of 26 reducing displacements (96%), but no recapture in partially-reducing or nonreducing joints. All but one of the normal joints remained unchanged. Pain assessment showed significant relief of symptoms in all three categories. The degree of pain relief was significantly greater in recaptured reducing disks than the other categories (p < 0.05). ARA therapy provides effective pain relief regardless of disk status, although a greater degree of relief may be achieved in recaptured reducing internal derangements.

Facial Pain↗
PubMed1995

Brain proton magnetic resonance spectroscopy studies in recently abstinent alcoholics.

Chronic alcohol-dependent patients have reduced brain volumes and concomitant neurobehavioral deficits that may recover during abstinence. In 10 chronic alcoholic patients, using localized proton magnetic resonance spectroscopy, we found reliable increases during the first 3-4 weeks of abstinence in the concentrations within the superior cerebellar vermis of choline (Cho)-containing compounds relative to the neuronal marker, N-acetylaspartate (NAA). Lesser changes were observed following 1 month of abstinence, and in one of the patients studied longitudinally over 3 months, a marked reduction in the Cho/NAA ratio was associated with relapse. After detoxification, the Cho/NAA ratio correlated with a composite clinical impression of brain functions. The lowest Cho/NAA was observed in a patient with persisting alcoholic dementia, in striking contrast to reduced relative concentrations of NAA reported in dementia of the Alzheimer's type. Possible molecular explanations for these brain metabolic changes are discussed.

Adult↗
PubMed1994

Pore geometry information via pulsed field gradient NMR.

Studies of echo attenuation at long diffusion times in pulsed field gradient NMR experiments on a variety of rock core samples are interpreted in the light of recent theoretical analysis of the effect of pore geometry and surface relaxation. This study is motivated by the need to test the applicability of that theory to real rock systems.

Calcium Carbonate↗