PubMed Health⌕ Search

Biomedical subjects

R Buxton

Publications and source records attributed to R Buxton.

At least 19 recordsLinked to original sources
PubMed2000

Noninvasive pulmonary perfusion imaging by STAR-HASTE sequence.

The STAR-HASTE sequence has been shown to be useful for perfusion imaging in areas that are plagued by magnetic susceptibility artifacts. Pulmonary perfusion imaging with this technique was attempted in this study. Quantitative analysis was also conducted, using an appropriate kinetic model in one subject. In six healthy subjects, gradual enhancement was observed in pulmonary artery to distal lung parenchyma when inflow time was increased. Our initial results suggest that noninvasive evaluation of pulmonary perfusion by magnetic resonance imaging without administration of an exogenous agent is possible.

Adult↗
PubMed1999

Understanding Down's syndrome: a review.

Each year, one child in every 800 births in the U.S. is born with Down's syndrome. It is the most prevalent chromosomal abnormality found in humans. Of the approximately four million births in the U.S. per year, 5,000 newborns with Down's syndrome can be expected. All health care providers should understand the unique features of this condition. Likewise, dental hygienists should be cognizant of its specific oral manifestations to provide optimum oral care for these clients.

Dental Care for Persons with Disabilities↗
PubMed1998

fMRI of monkey visual cortex.

While functional magnetic resonance imaging (fMRI) is now used widely for demonstrating neural activity-related signals associated with perceptual, motor, and cognitive processes in humans, to date this technique has not been developed for use with nonhuman primates. fMRI in monkeys offers a potentially valuable experimental approach for investigating brain function, which will complement and aid existing techniques such as electrophysiology and the behavioral analysis of the effects of brain lesions. There are, however, a number of significant technical challenges involved in using fMRI with monkeys. Here, we describe the procedures by which we have overcome these challenges to carry out successful fMRI experiments in an alert monkey, and we present the first evidence of activity-related fMRI signals from monkey cerebral cortex.

Animals↗
PubMed1997

Hemispheric asymmetries in global and local processing: evidence from fMRI.

Functional magnetic resonance imaging (fMRI) was used to explore the brain substrate associated with global and local processing of visuospatial patterns. Systematic differences in activation, consistent with differences observed in reaction time data collected under conditions of visual hemifield presentation, were found in occipitotemporal regions of the right and left hemispheres. Within the right hemisphere, area of activation and fractional signal changes were greater under conditions of global processing than under local processing conditions. In the left hemisphere, activation to global and local input was high and comparable.

Adult↗
PubMed1997

LDS hospital, a facility of Intermountain Health Care, Salt Lake City, Utah.

On-line documentation by nurses and a comprehensive text management system are functional in several facilities of intermountain Health Care (IHC). The following articles detail factors in the design and implementation of this computerized network as experienced at LDS Hospital, part of the IHC system. Areas discussed are the system's applications for medical decision support, communication, patient classification, nurse staffing versus cost, emergency department usage, patient problem/event recording, clinical outcomes, and text publication. Users express satisfaction with the time saving, consistency of reporting, and cohesiveness of these applications.

Decision Support Techniques↗
PubMed1996

Magnetic resonance detection of acute pulmonary emboli in a canine model with pathologic correlation.

RATIONALE AND OBJECTIVES: The authors evaluated the accuracy of magnetic resonance (MR) imaging in depicting acute pulmonary emboli at the lobar, segmental, and subsegmental levels. METHODS: The authors induced 29 autologous emboli in five dogs and confirmed their location with angiography and anatomic dissection. MR images obtained with four sequences were independently evaluated by two radiologists to detect emboli in each vascular segment. Sensitivities, specificities, and accuracies were calculated at segmental and lobar levels. RESULTS: The fast short-tau inversion-recovery images provided the greatest conspicuity and highest overall accuracy (reader 1 = 74.3%, reader 2 = 80%). Accuracy of two-dimensional fast multiplanar spoiled gradient-recalled-echo images was limited by spatial resolution (reader 1 = 71.4%, reader 2 = 74.3%). The fast spin-echo T2-weighted and spin-echo T1-weighted sequences were intermediate in their depiction of acute emboli. Similar results were seen at the lobar level. CONCLUSION: MR images depict acute pulmonary embolism at the segmental and lobar levels with reasonable accuracy. Fast short-tau inversion-recovery sequences provided the greatest sensitivity and accuracy.

Acute Disease↗
PubMed1995

Computerized support of pressure ulcer prevention and treatment protocols.

Pressure ulcer prevention and treatment protocols were developed and implemented at LDS Hospital. While the protocols were initially implemented "on paper", compliance was not optimum until the hospital's information system was modified to support the clinician in following the new protocols. Preliminary results indicate a significant reduction in the incidence of pressure ulcers.

Clinical Protocols↗
PubMed1994

Contrast induced myocardial signal reduction: effect of lanthanide chelates on ultra high speed MR images.

The myocardial MR signal reduction associated with an intravenous bolus of Gd-DTPA and Dy-DTPA was studied in a canine model. Imaging was performed with a high speed echo-planar type imaging system (Instascan, Advanced NMR Systems, Inc.). Gated spin-echo images were obtained with TE of 30 ms, which permits image acquisition in approximately 40 ms. The gated TR was dependent on the heart rate, with an average TR of 2.4 s. After 0.1 mmol/kg of contrast was injected, 70 images were acquired, which showed in an 80-image data set a reduction in myocardial signal with a gradual return to normal. After dipyridamole infusion, the signal loss was significantly more pronounced, and earlier than in the control data set. There was no significant difference between Gd-DTPA and Dy-DTPA in these imaging studies despite the theoretical prediction of better Dy signal reduction, possibly due to physiological variability during the course of a study or between studies. The cause of enhanced contrast effect after dipyridamole infusion is discussed, as is the basis for dipyridamole enhancement, and the possible role of contrast enhanced MR imaging in the detection of cardiac disease.

Animals↗
PubMed1994

Myocardial extraction of 1-[11C] betamethylheptadecanoic acid.

UNLABELLED: Betamethylheptadecanoic acid (BMHA) is a branched chain fatty acid analog that is transported into myocardial cells by the same long chain fatty acid carrier protein mechanism as natural fatty acids, but cannot be completely catabolized and accumulates in the tissue. Thus, 11C-labeled BMHA is a useful tracer for the noninvasive evaluation of myocardial fatty acid utilization by positron emission tomography (PET). METHODS: As a prelude to PET studies, the metabolism of BMHA was studied by classical techniques. We measured the net extraction fraction (En) of 1-[11C]-beta-R,S-methylheptadecanoic acid (1-[11C]BMHA) and compared it to that of natural fatty acids in dogs, using arterial/venous measurements and a mathematical model. Two groups of conditioned dogs were studied. In the first group, measurements were made under fasting (normal control) conditions and in the second group, measurements were made during glucose and insulin infusion. Myocardial blood flow, and the extraction/utilization of other substrates (glucose, oxygen and lactate) were also measured. RESULTS: For natural fatty acids in the basal state, En(FA) was 0.335. After glucose/insulin infusion, this value decreased to 0.195. The 1-[11C]BMHA showed a similar decrease in En(BMHA) from 0.220 in the control group to 0.100 in the group treated with glucose/insulin infusion. Preliminary PET studies with 1-[11C]BMHA verified the validity of performing these measurements noninvasively. CONCLUSION: The results of these studies indicate that rates of fatty acid metabolism in the myocardium can be determined from steady-state concentrations of 1-[11C]BMHA.

Animals↗
PubMed1992

Expression, glycosylation and secretion of yeast acid phosphatase in hamster BHK cells.

The gene PHO5 coding for one of the repressible acid phosphatases of the yeast Saccharomyces cerevisiae has been expressed at high efficiency in the baby hamster kidney (BHK) cell line. The expression vector was constructed from PHO5 driven by the human beta-actin promoter and was transfected into BHK cells by the calcium phosphate method. The recombinant APase (r-APase) which was secreted in active form from the cells was estimated by SDS/polyacrylamide gel electrophoresis to have molecular mass M(r) = 62,000, indicating substitution of the polypeptide moiety by 2-3 asparagine-linked glycans. Analysis by sequential lectin affinity chromatography of glycopeptides obtained from r-APase with Pronase showed that the glycans are predominantly of the 2.2.4 triantennary and tetraantennary complex-type. These data suggest that the extensive glycosylation of yeast APase, which contains eight polymannose substituents, is not essential for secretion and expression of enzymatic activity of the transfected gene product.

Acid Phosphatase↗
PubMed1991

Fatty infiltration of the liver: quantification with phase-contrast MR imaging at 1.5 T vs biopsy.

Quantification of hepatic fat content by application of MR phase-contrast imaging (Dixon method) at 1.5 T was compared with results of biopsy in 16 patients with a variety of liver abnormalities. Motion artifact was suppressed by employing six or eight averages of short TR in-phase (echo offset, 0 msec), out-of-phase (echo offset, 1.1 msec), and in-phase (echo offset, 2.2 msec) spin-echo pulse sequences. The 360 degree out-of-phase sequence was used to assess the impact of T2* decay on this method of estimating fat fraction. A standard two-echo long TR sequence also was obtained in all patients. Histologic preparations from the biopsy specimens were examined by a pathologist who had no knowledge of the MR results and were graded according to overall visual assessment as belonging to one of four categories of fat fraction. Results of the MR-calculated apparent fat fraction were compared directly with biopsy category and were also placed in MR fat fraction categories, allowing estimation of the statistical correlation between the biopsy and MR grading systems. Eight of eight patients with biopsy categories indicating a fat fraction of less than 0.25 were computed by MR to have a fat fraction of less than 0.1. Seven of eight patients with biopsy categories indicating a fat fraction of greater than 0.25 were computed by MR to have a fat fraction of at least 0.24. The MR-calculated apparent fat fraction category correlated significantly with the histologic biopsy category (r = .86, p less than .01). When compared with the in-phase image, decreased signal from liver was visually apparent on the 180 degree out-of-phase images in all cases in which the fat fraction was at least 0.24, but there was no indication of fatty liver on the standard T1- or T2-weighted images. Calculated T2 also showed no correlation with degree of fatty deposition. Correction for T2* decay by using the 360 degree out-of-phase acquisition in addition to the standard 0 degree and 180 degree out-of-phase images had little effect on fat fraction computation. Phase-contrast MR is a promising noninvasive method for quantitative assessment of fatty deposition in the liver.

Adult↗
PubMed1986

Projective MRI angiography and quantitative flow-volume densitometry.

Projective MR images of vascular anatomy and flow are performed at 0.14 T by using phase contrast to suppress the signal contribution of the stationary background. The source of the contrast is the distinctive phase evolution of moving protons under the influence of the read-out gradient of a conventional two-dimensional Fourier transform (2D FT) spin-echo pulse sequence. By using short echo times, small phase shifts may be obtained. When phase shifts are less than about 45 degrees, the phase contrast assumes a simple and useful form. The flow image intensity at any pixel becomes proportional to the net flux or flow volume of protons which cross the corresponding voxel. This proportionality is demonstrated in images of flow phantoms as is the reproducibility of measured flow volume under a variety of transformations of imaging conditions and of the subject. Projective images gated in vivo produce angiographic views of arteries and veins, in systole and diastole, in the neck of a dog and in the lower extremities of a human subject.

Animals↗
PubMed1986

Rapid MR imaging with suspended respiration: clinical application in the liver.

The authors demonstrate that it is possible to obtain highly T1-weighted images of the abdomen using a suspended respiration partial saturation (SRPS) method in a breath-holding interval. T2*-weighted images, which reflect tissue T2 as well as variations in the static magnetic field, can also be rapidly obtained. The authors studied five healthy subjects and 19 patients with a variety of liver abnormalities, including benign and malignant hepatic neoplasms, fatty liver infiltration, ascites, and hematoma. On T1-weighted multisection acquisitions, the entire liver can be screened for mass lesions in a single 20-second breath-holding interval. Phase-contrast SRPS images are sensitive to fatty infiltration of the liver. SRPS images are more sensitive to variations in magnetic susceptibility than spin-echo images are, which has been proved to be of value in the detection of hemorrhage. With continued pulse sequence development and clinical study, this method has the potential to become the method of choice for evaluation of the upper abdomen.

Adult↗
PubMed1985

Chemical shift imaging of bone marrow: preliminary experience.

A phase-contrast method of chemical shift imaging was used to evaluate bone marrow in normal volunteers and in patients with metabolic, inflammatory, traumatic, and neoplastic disorders. Five normal volunteers were examined in order to obtain preliminary data on normal patterns of signal intensity in hematopoietic and fatty marrow using both conventional magnetic resonance imaging and proton chemical shift imaging. Normally, hematopoietic marrow yields low signal intensity on phase-contrast images; pathologic conditions affecting hematopoietic marrow typically result in increased signal intensity due to either accumulated lipid or water. Because of its high fat content, yellow marrow normally yields high signal intensity on phase-contrast images, whereas abnormal conditions usually result in decreased phase-contrast signal intensity due to increased tissue water. Proton chemical shift imaging is likely to be a valuable supplement to standard magnetic resonance imaging techniques in the study of bone marrow in vivo.

Adult↗
PubMed1979

Were you knocked out?

In the period 1970-75 inclusive 5152 patients were admitted to an accident hospital after an uncomplicated injury to their head. This group was compared with the 116 patients who needed craniotomy in the same period. It is suggested that precautionary admission of patients with minor head injuries is excessive.

Adolescent↗