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Biomedical subjects

S W Smith

Publications and source records attributed to S W Smith.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1988

Properties of acoustical speckle in the presence of phase aberration. Part II: Correlation lengths.

In recent years, analysis of the second order statistics of ultrasound speckle has led to accurate prediction and measurements of the average speckle size in the transducer focal zone. In this paper, that work has been extended to the average speckle size as determined by the normalized autocovariance in the presence of transducer phase aberrations. In general, a phase aberration causes a narrowing of the main lobe of the normalized autocovariance in the lateral direction. However, the lateral speckle autocovariance also showed significant side lobes in the presence of phase aberrations, indicating that individual speckles in a region of interest are not independent but are correlated so that less information is present for the task of signal detection when a transducer phase aberration exists. The same evidence of correlated speckle was found in the near field of a transducer in the region of fine speckle texture. This explanation satisfies the quandary of poor detectability in the near field region where the speckle is fine but the lateral resolution is quite degraded. The axial speckle in the presence of phase aberrations showed a small increase in main lobe widths and no evidence of side lobes. Beginning in 1978, the analysis of the second order statistics of speckle images for the purpose of spatial compounding led to accurate measurement and prediction of the cross-correlation curve as a function of transducer aperture translation for purposes of spatial compounding. In this paper, that work has been extended to the presence of transducer phase aberrations. The existence of transducer phase aberrations causes significant increases in the rate of decorrelation of speckle interference patterns as a transducer is translated. This indicates that spatial compounding will result in quite significant improvements in area-wise SNR and low contrast lesion detection for the case of severe random aberrators or focal point errors.

Humans↗
PubMed1988

The Maltese cross processor: speckle reduction for circular transducers.

A new online signal processing technique is described to reduce speckle noise in ultrasound images. In the imaging system, a focused piston transducer is divided into thirty-two sectors. In the receive mode, parallel signal processing arranges the sectors into eight maltese crosses. The rf signals of the perpendicular arms of each cross are multiplied in a phase sensitive process. The orthogonal receive mode multiplication is designed to reduce side lobes resulting from the sector shapes while maintaining lateral resolution through the use of the full aperture diameter. The signals from the crosses are then combined via postdetection summation. Six of the eight crosses perform successfully. The six maltese crosses show decorrelated signals equivalent to four independent samples of the speckle noise which decreases noise contrast by a factor of two with no measureable loss of spatial resolution. Post summation compression is included to retain the conventional signal dynamic range. Parallel signal processing maintains the normal image line rate. Images of tissue-mimicking phantoms including speckle targets show improved detectability of simulated lesions.

Humans↗
PubMed1988

Multiple, annular, erythematous lesions of the oral mucosa.

Benign migratory stomatitis is a relatively rare entity, but because of its benign nature and clinical characteristics, it should be easily recognized by the general practitioner. Biopsy is usually not indicated and treatment consists of reassuring the patient that the lesions are benign even though they may disappear, reappear, and change location; the patient should report back for periodic follow-up.

Diagnosis, Differential↗
PubMed1988

The CD5+ B cell: a B cell lineage with a central role in autoimmune disease?

It is apparent that B cells are heterogeneous with respect to, for example, the antigens they express on their surface, and the stimuli to which they can respond. It is still unclear to what extent these differences relate to the stage of differentiation (eg. virgin B cells differing from activated B cells or memory cells), or whether distinct developmental lineages might exist. It has been proposed by some authors that, in the mouse, B cells expressing the ly-1 antigen constitute a separate lineage. In man also, a minor population of B cells expresses detectable levels of the CD5 antigen, but far less information is available about these cells. Interest in the CD5+ and ly-1+ B cell subpopulations has been further stimulated by the suggestion that these cells might play a special role in autoimmune disease. Although, in mouse, ly-1+ B cells differ in several respects from ly-1- B cells, the main evidence that they form a separate lineage derives from experiments in which ly-1+ B cells could not be reconstituted with adult bone marrow. It should be borne in mind that the situation is quite different in humans where, following bone marrow transplantation, CD5+ B cells are rapidly restored. Moreover, in the irradiated mice, at least in some of the experiments ly-1+ B cells were in fact reconstituted by adult bone marrow. Furthermore, at least in humans, expression of CD5 can sometimes be induced. There is, as yet, no good evidence that human CD5+ B cells form a distinct lineage, and it is possible that CD5 expression depends upon microenvironmental influences acting on the B cell during its differentiation. Several interesting properties have been attributed to ly-1+ B cells, including the ability to provide help to other B cells, and the secretion of autocrine factors. However there is also evidence that these features are not exclusive to B cells expressing ly-1. It has also been suggested that ly-1+ B cells might be long-lived. It is not yet known whether some of the properties of ly-1+ B cells might be a direct result of their expressing this antigen; this may become more clear when the function of CD5 is elucidated. The suggestion that the repertoire of ly-1+ B cells might be biased towards the expression of certain V genes is very interesting. Many of the hybridomas from neonatal mice produce antibodies which are multi-specific, and therefore well suited to form a first line of defence against potential pathogens.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Marketing strategies of nurse practitioners in New York State.

As competition within the health care field increases, marketing strategies are becoming more important for all members of the health care team, including nurse practitioners. The purpose of this research was to identify marketing strategies being used by nurse practitioners in New York state. A total of 285 practitioners responded to a survey containing questions related to marketing techniques traditionally used in the business world: service differentiation, market segmentation and practice promotion. A majority of respondents did not report using many of the marketing strategies contained in the survey, although most nurse practitioners did report identifying themselves as primary care providers in one-on-one interactions with clients. Significantly higher marketing scores were found for nurse practitioners who attended a workshop or seminar on marketing strategies, had three or more years of experience, or who practiced in private outpatient settings.

Adult↗
PubMed1987

Dosage, timing, and route of administration of cyclosporin A and nonimmunosuppressive derivatives of dihydrocyclosporin A and cyclosporin C against Schistosoma mansoni in vivo and in vitro.

The prophylactic and therapeutic effects of cyclosporin A (CsA) against percutaneous Schistosoma mansoni infection in MF1 mice were dose related and dependent on the temporal relationship between drug administration and infection. Antischistosomal activity, assessed by worm recovery from the host 6 weeks after infection, was most effective (complete worm elimination) when CsA was administered at the time of infection. Oral administration of CsA was less effective than subcutaneous injection, and no prophylactic activity was demonstrated by the former route. Derivatives of dihydrocyclosporin A and cyclosporin C, which have been reported to exert only poor immunosuppressive activity, exhibited efficacy against S. mansoni similar to that of CsA and were also less effective when given orally. Subcutaneous, but not oral CsA reduced cercarial skin penetration and transformation success; the derivative of dihydrocyclosporin A, however, was without effect. Moreover, CsA, but not the derivative of dihydrocyclosporin A, reduced the number of worms established after intraperitoneal injection of cercariae. These data provide further insight into the antischistosomal activity of cyclosporins, which appears to be distinct from their immunomodulatory properties, since parasite killing was retained both in immunologically disparate mice and with poorly immunosuppressive cyclosporin derivatives.

Animals↗
PubMed1987

In vitro ultrasonic imaging of flow through prosthetic heart valves.

A rapid, inexpensive, portable technique has been developed for the qualitative and semiquantitative evaluation of in vitro flow characteristics through prosthetic heart valves. The technique combines a cardiac pulse duplicator and any diagnostic, linear sequential array, ultrasonic imaging system. The pulse duplicator has been modified to include an acoustically transparent aortic section which contains the prosthetic valve to be evaluated. The acoustically transparent section is fabricated from Rho-c rubber and enables direct flow-imaging for several centimeters on both sides of the prosthesis. Aerated tap water is used as a contrast medium. Forward and reverse flow, laminar flow complex eddy patterns, regurgitation, and jets are easily observed in real time over a wide field of view. Time-exposure photography of sequential images and subsequent off-line calculations enable point-by-point determinations of flow velocities. This work allowed preliminary evaluations of four cardiac valves: Bjork-Shiley, St. Jude, caged disk, and Starr-Edwards.

Heart Valve Prosthesis↗
PubMed1986

Phased array ultrasound imaging through planar tissue layers.

Conventional ultrasound imaging devices are designed based on the assumption of a homogeneous tissue medium of constant acoustic velocity = 1540 m/sec. However, the body consists of tissue layers of varying thicknesses and velocities which range from 1470 m/sec in fat to 3200 m/sec in skull bone. Refraction effects from these layers degrade ultrasound image quality. In this paper, pulse-echo ultrasound imaging is modeled as imaging an organ of interest through an intervening planar tissue layer, such as liver through fat in the abdomen or brain through skull bone in the adult head. Refraction effects from planar tissue layer interfaces are analyzed using Snell's law and measured using phantoms. We also introduce an on-line phased array correction technique based on planar tissue layers to restore ultrasound image quality. We conclude that fat/organ planar interfaces do not degrade image quality significantly. However, refraction effects at a skull/brain planar interface degrades resolution and target acquisition and introduces geometric distortion. Our plane layer phased array correction technique significantly improves image quality in phantoms through lucite aberrators and improves adult cephalic ultrasound image quality when used through the top of the adult skull. The correction technique is robust even in the presence of inaccurate estimates of skull thickness.

Adipose Tissue↗
PubMed1986

Role of calcium and calmodulin in release of kallikrein and tonin from rat submandibular gland.

We investigated the role of calcium and calmodulin as intracellular mediators of kallikrein and tonin release induced by norepinephrine (NE). We studied the secretion rate of kallikrein and tonin from submandibular gland of rat in response to NE in the presence or absence of calcium, two calcium blockers, and four different calmodulin antagonists. Submandibular gland slices were incubated in vitro, and glandular kallikrein and tonin secreted into the incubation medium were determined by direct radioimmunoassays and expressed as nanograms per minute per milligram tissue. NE (10(-5) and 10(-4) M) increased the kallikrein secretion from the control value of 8.2 +/- 2.6 to 134.9 +/- 41.4 (P less than 0.05) and to 191.2 +/- 62.7 (P less than 0.05), and the release of tonin from a basal rate of 3.5 +/- 0.6 to 51.5 +/- 9.1 (P less than 0.05) and to 64.4 +/- 13.7 (P less than 0.05). The deletion of calcium and addition of EGTA into the incubation medium significantly attenuated the secretion of kallikrein and tonin induced by NE. Nifedipine, at concentrations which inhibit voltage-dependent calcium channels, did not affect the release of kallikrein and tonin, and only a high concentration (10(-4) M) reduced the release. TMB-8, a blocker of intracellular calcium, had no effect either. Phenothiazines, triflupromazine (10(-6) M) and trifluoperazine (10(-4) M), decreased significantly the kallikrein release elicited by 10(-5) M NE.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

A quantitative approach to speckle reduction via frequency compounding.

Coherent speckle is a source of image noise in ultrasonic B-mode imaging. The use of multiple imaging frequencies has been suggested as a technique for speckle contrast reduction. This technique involves the averaging of images whose speckle patterns have been modified by a change in the spectrum of the transmitted or received acoustical pulse. We have measured the rate of this speckle pattern change in ultrasonic images as a function of the change in center frequency of the transmitted acoustical pulse. This data is used to quantitatively describe the trade-off of resolution loss versus speckle reduction encountered when frequency compounding is employed and to derive the optimal method of frequency compounding. These results are then used as a basis for describing the overall advisability of frequency compounding in ultrasonic imaging systems. Our analysis indicates that simple frequency compounding is counterproductive in improving image quality.

Humans↗
PubMed1985

A plane layered model to estimate in situ ultrasound exposures.

Determination of in situ ultrasound exposures in experimental animals and patients is necessary to assess any potential hazard of ultrasound implied by reported biological effects in animals. A layered model was used to calculate total attenuation of ultrasound pulses as they passed through tissue layers to an organ site, thus enabling calculation of in situ intensities from free-field transducer emissions. The model assumes plane homogeneous layers of tissue of known thickness, attenuation and acoustic impedance. Calculations based on the model, compared with in situ measurements in a human cadaver specimen, were accurate to within approximately +/- 3 dB. We then calculated in situ clinical exposures using published obstetric B-scans. Total attenuation to the fetus averaged approximately 11 dB at 3.5 MHz.

Cadaver↗