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Biomedical subjects

S W Smith

Publications and source records attributed to S W Smith.

At least 19 recordsLinked to original sources
PubMed1992

Complications encountered in the treatment of pilon fractures.

A total of 52 tibial plafond (pilon) fractures in 51 patients were retrospectively reviewed from the years 1985-1990 to define the rate of complications encountered during their management. All fractures were managed under faculty supervision at a level I trauma center and its two affiliated institutions. The follow-up period was scrutinized to determine whether or not a complicating event occurred. Major local complications, termed events, were defined as those requiring unplanned surgery due to infection, wound breakdown with subsequent flap coverage, and failure of fixation or fracture healing. Reduction accuracy and final clinical results were not specifically examined. There were 14 (27%) type I, 17 (33%) type II, and 21 (40%) type III Ruedi-Allgower fracture types. The majority (79%) of the fractures were closed and 89% were treated by open reduction and internal fixation. The overall local complication rate was 54%. A total of 21 (40%) pilon fractures (six type I, six type II, and nine type III) had major local complicating events requiring 77 additional operations. Patient follow-up time ranged from 1 week (the occurrence of a major local complication) to 200 weeks (no complication), with a mean of 67 weeks. Kaplan-Meier survivorship (K-M) analysis was utilized to statistically estimate the complication rate in this patient population accounting for the occurrence of censored events. The K-M-determined event rate was 42 +/- 7%. Ten (of 21) pilon fractures had events by 3 weeks, while only two occurred beyond 40 weeks.

Adolescent↗
PubMed1992

The haemodynamic responses to venesection and the effects of cardiovascular disease.

The haemodynamic effects of the venesection of one unit (450 ml) of blood over 9 min were measured using non-invasive techniques, in 14 healthy controls and 18 patients with coronary heart disease or hypertension. Venesection was associated with significant reductions in supine and standing systolic and diastolic blood pressure, stroke volume index and cardiac index, and increases in standing heart rate, in both patient groups. No significant differences were observed between the responses of subjects with and without cardiovascular disease. The authors conclude that, in contrast to established teaching, blood loss can be detected in its early stages by careful haemodynamic monitoring and that venesection can be performed safely without volume replacement in patients with stable cardiovascular disease.

Adult↗
PubMed1992

Phylogenetic relationships of chemoautotrophic bacterial symbionts of Solemya velum say (Mollusca: Bivalvia) determined by 16S rRNA gene sequence analysis.

The protobranch bivalve Solemya velum Say (Mollusca: Bivalvia) houses chemoautotrophic symbionts intracellularly within its gills. These symbionts were characterized through sequencing of polymerase chain reaction-amplified 16S rRNA coding regions and hybridization of an Escherichia coli gene probe to S. velum genomic DNA restriction fragments. The symbionts appeared to have only one copy of the 16S rRNA gene. The lack of variability in the 16S sequence and hybridization patterns within and between individual S. velum organisms suggested that one species of symbiont is dominant within and specific for this host species. Phylogenetic analysis of the 16S sequences of the symbionts indicates that they lie within the chemoautotrophic cluster of the gamma subdivision of the eubacterial group Proteobacteria.

Animals↗
PubMed1992

Two-dimensional arrays for medical ultrasound.

The design, fabrication and evaluation of two-dimensional transducer arrays are described for medical ultrasound imaging. A 4 x 32, 2.8 MHz array was developed to use new signal processing techniques for improved B-scan imaging including elevation focusing, phase correction and synthetic aperture imaging. Laboratory measurements from typical array elements showed 50 omega insertion loss of -56 dB, -6 dB fractional bandwidth of 43%, interelement crosstalk of -19 dB, and -6 dB pulse-echo angular response of 62 degrees. Simulations of pulse-echo beam plots have shown grating lobes 20 dB below the main lobe at +/- 7 degrees in the elevation direction. The complete 2-D array has been used for measurements of phase aberrations in breast, and the individual 32 element linear arrays have been used to obtain conventional B-scans. Several 16 x 16 arrays have also been developed for high speed volumetric imaging. These include 96 transmit elements and 32 receive channels. With a lambda/4 matching layer, laboratory measurements show 50 omega insertion loss of -72 dB, -6 dB fractional bandwidth of 63%, interelement crosstalk of -29 dB and -6 dB angular response of 25 degrees. Pulse-echo sensitivity was improved by 21 dB through the use of integrated circuit preamplifiers of high impedance mounted in the transducer handle. In vivo cardiac, abdominal, and obstetric B-scans with elevation focusing, as well as high speed C-scans, have been obtained with these 2-D arrays.

Equipment Design↗
PubMed1992

In vivo imaging using a copolymer phased array.

Phased-array images have been obtained in vivo with a steered copolymer array operating at 2.5 MHz. The array was fabricated using 28 microns copolymer film, lambda/4 resonant at 21 MHz, which was bonded to a glass ceramic backing with a thin film bond. The 32 array elements were created by laser ablation of the continuous gold electrode on one side of the film. The transducer was driven by 200 V shock excitation, and the received signal was processed by 32 custom IC preamplifiers that were mounted to the array connector. The amplifiers had a high input impedance compared to that of the array elements and their output impedance matched that of the coaxial cable that connected to the scanner. Because the copolymer transducer had a broad bandwidth, the spectrum of the pulse echo image was modified by the frequency dependent attenuation of tissue and the bandpass of the ultrasound scanner, resulting in a center frequency of 2.5 MHz. The performance of the copolymer array was compared to that of a 3 MHz, PZT array with similar dimensions. On the Duke phased-array scanner, the copolymer sensitivity was 28 dB less than that of PZT. The copolymer elements had a 6 dB pulse-echo angular response of 30 degrees, and the interelement cross-coupling was -35 dB. Phased-array images were made of the heart of a 25 year-old normal male.

Equipment Design↗
PubMed1992

Two dimensional ultrasonic beam distortion in the breast: in vivo measurements and effects.

Two dimensional arrival time data was obtained for the propagation of ultrasound across the breasts of 7 female volunteers. These profiles were extracted through the use of cross-correlation measurements and a simulated annealing process that maintained phase closure while aligning the data. The phase aberration measured in two dimensions had a larger magnitude than previously reported phase aberration measured in one dimension in the breast. A point spread function generation computer program was used to demonstrate the system response degrading effects of the measured phase aberration and the usefulness of current one dimensional phase aberration correction techniques. The results indicate that two dimensional correction algorithms are necessary to restore the system performance losses due to phase aberration.

Female↗
PubMed1991

Whole-bowel irrigation as a treatment for acute lithium overdose.

STUDY OBJECTIVE: To determine if gastrointestinal decontamination using whole-bowel irrigation (WBI) was an effective treatment for acute ingestion of sustained-release lithium. METHODS: In a two-phase, crossover protocol, ten normal volunteers ingested in each phase 0.80 mEq/kg sustained-release lithium carbonate. In the second phase, WBI was begun one hour after lithium ingestion, and 10 L of polyethylene glycol solution were administered over five hours. Serum samples were collected every half hour for six hours, every hour for an additional six hours, and then every 24 hours for as long as 72 hours after ingestion. These samples were analyzed for lithium concentration. The area under the lithium serum concentration-versus-time curve was calculated for each phase. RESULTS: The average area under the lithium serum concentration-versus-time curve in the WBI phase was 67% +/- 11% less than that in the control phase (P less than .0005 using a two-tailed Student's t test). The mean serum lithium concentration was significantly decreased (P = .03) within one hour of beginning WBI. CONCLUSION: WBI is an effective treatment for acute ingestion of sustained-release lithium. We recommend it as the decontaminant procedure of choice in this situation.

Adolescent↗
PubMed1991

Internal carotid artery occlusion: diagnostic inaccuracy of the ocular pneumoplethysmography.

The diagnosis of internal carotid artery (ICA) occlusion has serious management and prognostic consequences. The accuracy of noninvasive techniques in this setting remains questionable, with the result that contrast arteriography remains the diagnostic method of choice in patients in whom ICA occlusion is suspected. Ocular pneumoplethysmography-Gee (OPG-Gee) is one of the noninvasive methods that is still utilized extensively in the evaluation of carotid artery disease. In order to determine the real utility of OPG-Gee, the authors conducted a retrospective comparison of the results of OPG-Gee and arteriography in 26 patients (52 internal carotid arteries) who had undergone both examinations. [table: see text] With the angiography results as the standard of comparison, 4 incorrect diagnoses were obtained by OPG-Gee, thus yielding an overall accuracy of 92 for this method. However, duplex ultrasonography, also performed in the same 26 patients, correctly identified the 2 ICA occlusions defined by angiography and further demonstrated patency in the 48 arteries so shown by angiography. The authors conclude from this experience that OPG-Gee is less reliable than duplex ultrasonography in the diagnosis of ICA occlusion. Furthermore, despite the 92% overall accuracy of their results with OPG-Gee, the occurrence of both false-positive and false-negative results renders this examination modality suspect in the diagnosis of ICA occlusion.

Air↗
PubMed1990

Real time volumetric ultrasound imaging system.

A real time volumetric ultrasound imaging system has been developed for medical diagnosis. The scanner produces images analogous to an optical camera and supplies more information than conventional sonograms. Potential medical applications include improved anatomic visualization, tumor localization, and better assessment of cardiac function. The system uses pulse-echo phased array principles to steer a two-dimensional array transducer of 289 elements in a pyramidal scan format. Parallel processing in the receive mode produces 4992 scan lines at a rate of approximately 8 frames/second. Echo data for the scanned volume is presented as projection images with depth perspective, stereoscopic pairs, multiple tomographic images, or C-mode scans.

Computer Systems↗
PubMed1990

Specificities compared for a radioreceptor assay and a radioimmunoassay of atrial natriuretic peptide.

The main active form of atrial natriuretic peptide (ANP) in the circulation is alpha ANP(1-28) [gamma-ANP(99-126)], although some active and inactive metabolites are also though to be present. Some immunoassays for alpha ANP reportedly detect inactive metabolites, as determined by their comparison with results by receptor assay, which would lead to misleading results for alpha ANP(1-28) measurements. Here we compare a radioreceptor assay (RRA) and a radioimmunoassay (RIA) for alpha ANP and show that their results correlate very well with regard to specificity and that the RIA appears to detect only the active circulating form of alpha ANP(1-28).

Adrenal Glands↗
PubMed1989

New contrast-detail phantoms for improved precision in lesion detection measurements.

The previous design of our ultrasound contrast-detail (C-D) phantom is limited in its ability to evaluate the quality of diagnostic ultrasound imaging systems. There is uncertainty in the contrast-detail measurements due to the single available viewing angle for each target and the resulting single realization of the ultrasound speckle pattern. Two new contrast-detail phantom designs are described which enable many independent realizations of the speckle noise for observer C-D experiments of improved precision. In the first design, a single tissue-mimicking cone is located on the axis of a tissue-mimicking cylinder. Cross-sectional images of the cone which simulate focal lesions can be obtained from any orientation by rotating the cylinder under the transducer. In the second new design, a tissue-mimicking cone is positioned in a tissue-mimicking slurry of agar/graphite spheres. Gentle stirring of the slurry and rotation of the cone produce many independent realizations of the speckle. In both new phantoms, the lesion contrast can be specified and is frequency/transducer independent.

Equipment Design↗
PubMed1989

Anthropomorphic cardiac ultrasound phantom.

A new phantom is described which simulates the human cardiac anatomy for applications in ultrasound imaging, ultrasound Doppler, and color-flow Doppler imaging. The phantom consists of a polymer left ventricle which includes a prosthetic mitral and aortic valve and is connected to a mock circulatory loop. Aerated tap water serves as a blood simulating fluid and ultrasound contrast medium within the circulatory loop. The left ventricle is housed in a Lexan ultrasound visualization chamber which includes ultrasound viewing ports and acoustic absorbers. A piston pump connected to the visualization chamber by a single port pumps degassed water within the chamber which in turn pumps the left ventricle. Real-time ultrasound images and Doppler studies measure flow patterns through the valves and within the left ventricle.

Heart↗
PubMed1989

Phase aberration correction in medical ultrasound using speckle brightness as a quality factor.

Medical ultrasonic images are degraded by tissues with inhomogeneous acoustic velocities. The resulting phase aberration raises the off-peak response of the imaging system's point spread function (PSF), decreasing dynamic range. In extreme cases, multiple images of a single target are displayed. Phase aberration may become a limiting factor to image quality as ultrasonic frequency and aperture size are increased in order to improve spatial resolution. A method is proposed to correct for unknown phase aberration, which uses speckle brightness as a quality factor. The phase delays of a phased array transducer are modified, element by element, to maximize mean speckle brightness in a region of interest. The technique proposed is analogous to the correction technique used by Muller and Buffington [J. Opt. Soc. Am. 64 (9), 1200-1209 (1974)] to adaptively focus incoherent optical telescopes. The method is demonstrated using a computer model with several different simulated aberration profiles. With this model, mean speckle brightness is calculated using the two-dimensional PSF. Experiments have also been conducted in which speckle brightness is shown to increase as the phase delays of an ultrasonic scanner are modified in order to compensate for a rippled aberrating layer made of silicone rubber. The characteristics of the proposed method, and the possibility of employing it clinically to correct for unknown inhomogeneities in acoustic velocity, are discussed.

Computer Simulation↗
PubMed1988

Prophylactic and therapeutic effects of ciclosporin A in murine Schistosomiasis mansoni: studies on bisexual and unisexual infections and the hepatic inflammatory response.

Ciclosporin A (CsA), administered subcutaneously as 5 daily injections of 50 mg.kg-1, reduced the numbers of Schistosoma mansoni perfused from MF1 mice at 7 weeks post-infection. The timing of drug administration revealed that the antischistosomal effects were greater when CsA treatment coincided with or was within a few days of infection with the parasite. CsA exerted a clear prophylactic effect, which decreased with time and was virtually abolished by 4 months pre-infection. Adult worms treated in vivo were partially susceptible to CsA. In addition to its antiparasite action, CsA reduced hepatosplenomegaly due to schistosomiasis and diminished the granulomatous inflammatory response of mice to parasite eggs in the liver. The mode of action of CsA is not understood but evidence is presented that supports the proposition that the antiparasite effects are perhaps host-mediated.

Animals↗
PubMed1988

Properties of acoustical speckle in the presence of phase aberration. Part I: First order statistics.

The first order statistical properties of acoustical speckle patterns are studied as a function of several types of random and structured phase error. Such errors may arise from tissue velocity inhomogeneities or limitations in the acoustical imaging system. In this paper, we review the theory describing the statistical properties of speckle, describe a computer model which predicts the mean speckle brightness in the presence of phase aberrations, and report experiments in which we measure the effect of these aberrations on speckle brightness and variance. We find that the average speckle brightness is significantly reduced by even mild phase aberrations. The phase aberrations studied include focal point errors, random phase errors, and structured errors. Good agreement is found between experiment and computer simulation. We then discuss the implications of these results for imaging through aberrating media, tissue characterization and phase compensation methods.

Humans↗