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Biomedical subjects

I Soutar

Publications and source records attributed to I Soutar.

7 recordsLinked to original sources
PubMed1998

Photophysics of Carbazole-Containing Systems. 3 Fluorescence of Carbazole-Containing Oligoethers in Dilute Solution.

Fluorescence techniques, including quenching and anisotropy measurements, have been used to study the photophysical behavior of the carbazole-based oligoethers poly{9-(2,3-epoxypropyl)carbazole}, PEPCz, and poly{1,2-epoxy-6-(9-carbazolyl)-4-oxahexane}, PECzOH, and their model compounds, in dilute fluid solutions in THF. These compounds show no evidence of excimer formation under these conditions and their fluorescences exhibit first-order decay behavior regardless of the degree of polymerization of the oligomer. Both steady-state and time-resolved anisotropy measurements upon dilute, glassy solutions show that intramolecular energy migration occurs in the oligomers. Fluorescence quenching experiments, using both dimethylterephthalate and oxygen as quenchers, produced evidence which supports the supposition that in the absence of excimer trapping sites, intramolecular energy migration will be encouraged in dilute fluid solutions of the oligoethers. Unfortunately, the fluorescence quenching data did not permit evaluation of the extents of energy migration in the various polymers or the relative efficiencies with which migration occurs in the two different types of oligoether. This limitation would appear to be a general feature of fluorescence quenching measurements, despite their frequent adoption, in the past, in studies of energy migration in polymers.

Journal Article↗
PubMed1998

Hearing screening in Jamaica: prevalence of otitis media with effusion.

Hearing screening is well established in most developed countries, and the data extensively published. However, little information has been presented by the developing, nonwhite populations. A screening study was carried out on 2202 Jamaican children aged 5 to 7 years. This involved tympanometry and pure-tone audiometry (frequencies of 0.5, 1, and 2 kHz.) Failure was considered to have occurred if a type B or C curve was obtained or if the threshold of hearing was greater than 20 dB. These children were further evaluated by a full ear, nose, and throat examination, inclusive of pneumatic otoscopy, and audiologic testing. The prevalence of hearing impairment was 4.9%. Otitis media with effusion (OME) was present in 1.9%. The prevalence of OME in Jamaica is low when compared with that of the same age-group in the developed countries.

Acoustic Impedance Tests↗
PubMed1995

Role of equalisation mammography of dense breasts.

Parenchymal patterns characteristic of dense breasts are known to degrade the mammographic detection of small breast cancers and microcalcifications. This arises from large variations in exposure of the film, resulting in reduced image contrast over areas of suboptimal exposure. Based on sensitometric measurements of mammograms from a typical patient population, it is shown that over 60% of a typical mammogram in Wolfe's DY classification was found to be exposed suboptimally, suggesting a significant margin for improving mammography for these patients. In order to address this problem, a prototype mammographic version of scanning equalisation radiography (MSER) has been developed, which delivers a patient-specific spatially non-uniform distribution of breast exposure, adjusted to maintain optimal film exposure and contrast over the entire mammogram. Anthropomorphic phantom MSER images show a marked improvement in subjective image quality relative to conventional mammograms, while exhibiting a similar radiation risk. The detection of small microcalcifications and fibrils over clinically significant breast densities is found to be improved by factors eight and four, respectively. Such a system may be clinically practical through the use of multiple-beam equalisation methods with available X-ray tube technology.

Breast Neoplasms↗
PubMed1995

An MR compatible flow simulator for intravascular pressure simulation.

An MR compatible flow simulator is described which generates physiologically realistic pressure and flow waveforms. The simulator is based on a servomotor-driven gear pump which produces pulsatile flow by modulation of the servomotor rotation rate. Operation of the simulator is under the control of a personal computer, which executes an iterative feedback loop to minimize errors between measured and desired pressure waveforms. The simulator is totally automatic, requiring only a few minutes of iteration to generate the desired pressure waveform. Accurate sinusoidal waveforms with frequencies up to 10 Hz have been generated using the simulator, with high-frequency contamination of the measured waveform at least 80 dB below the fundamental frequency. Aortic waveforms have been produced with realistic flow rates and pressure variations. The pump assembly is mechanically straightforward and can operate at an 8-m distance from the flow phantom to allow the device to be isolated from the MR magnet room.

Biophysical Phenomena↗
PubMedDate not supplied

Errors in quantitative dynamic three-dimensional keyhole MR imaging of the breast.

Three-dimensional (3D) keyhole magnetic resonance (MR) imaging has been proposed as a means of providing dynamic monitoring of contrast agent uptake by breast lesions, with complete breast coverage and high spatial and temporal resolution. The 3D keyhole technique dynamically samples the central regions of k-space in both phase-encoding directions and provides high-frequency data from a precontrast acquisition. Errors due to data truncation with two-dimensional and 3D region-of-interest measurements are estimated from a numerical simulation of various implementations of the 3D keyhole technique. Errors were found to increase with increasing temporal resolution and reduced object size. Errors of 75% are possible for objects with a diameter approaching 1 pixel when a 3D keyhole implementation that samples 50% of phase-encoding data in each direction is used. Preliminary clinical images with this approach illustrate artifacts consistent with inadequate k-space sampling.

Artifacts↗
PubMedDate not supplied

Visualizing tissue compliance with MR imaging.

We propose a method for visualizing the mechanical properties of tissue based on the use of periodic mechanical compression in conjunction with phase-contrast MR imaging. A specialized mechanical transducer was used to provide programmable compression pulses to the surface of compliant phantoms. These compression pulses were synchronized to a spin-echo sequence with motion-sensitizing gradients to generate phase information reflecting spin displacement throughout the phantom. This sequence was tested with two agarose gel phantoms. The first was a cylinder containing three parallel layers of varying compliance and the second was composed of a semirigid sphere suspended in a uniform layer of decreased elastic modulus. Images showed complex patterns of motion throughout the phantom, which correlated with expected motion behavior of the phantom structures. This indicates that the biomechanical properties of tissues may be elucidated through the use of motion-sensitized MR imaging and suggests that a form of image contrast relating to tissue elasticity may be feasible.

Compliance↗