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At least 253 records · Page 14Linked to original sources
PubMed1993

Optical transducer for reception of ultrasonic waves.

A new optical transducer for the detection of acoustic pressure in the diagnostic ultrasound frequency range is described. This transducer is based on the modulation of an evanescent light field by the incident acoustic energy. Theoretical design considerations are presented for the purpose of developing the most sensitive transducer. Based on these considerations an experimental transducer was constructed. Although less sensitive than predicted this device was capable of transducing ultrasonic pulses with a 1.0-MHz center frequency at diagnostic ultrasound amplitude levels. The techniques developed here are applicable for two-dimensional transduction and may prove a viable alternative to piezoelectric array transducers.

Acoustics↗
PubMed1996

A parametric study of the concentric-ring transducer design for MRI guided ultrasound surgery.

Noninvasive surgery using high-powered, focused ultrasound transducers in conjunction with magnetic resonance imaging has been shown to be feasible in previous studies. For clinical treatments, the geometry of standard MRI equipment limits the space available for ultrasound surgical equipment. This space requirement can be reduced in one dimension by using phased arrays to control the focal depth, thus eliminating the space required for the motion of a fixed focus transducer. Because of its symmetry, an annular array is ideal for changing the focal depth. Previous works have simulated, built, and characterized various concentric-ring transducers; however, no study has thoroughly examined the potential and limitations of the concentric-ring design for MRI guided ultrasound surgery. The present work is a systematic examination of the capabilities of the concentric-ring array, using numerical simulations to predict the power field, temperature distribution, and accumulated thermal dose. The results presented here illustrate the effects of ring size, center-to-center spacing configurations, number of rings, and radius of curvature on transducer performance. A 10-cm radius of curvature transducer with 14 evenly spaced rings has been built and characterized in order to verify the accuracy of the numerical simulations. The pressure-squared fields produced by this transducer are in excellent agreement with the simulated fields.

Equipment Design↗
PubMed2004

Artificial neural network based soft estimator for estimation of transducer static nonlinearity.

In this work, the development of an Artificial Neural Network (ANN) based soft estimator is reported for the estimation of static-nonlinearity associated with the transducers. Under the realm of ANN based transducer modeling, only two neural models have been suggested to estimate the static-nonlinearity associated with the transducers with quite successful results. The first existing model is based on the concept of a functional link artificial neural network (FLANN) trained with mu-LMS (Least Mean Squares) learning algorithm. The second one is based on the architecture of a single layer linear ANN trained with alpha-LMS learning algorithm. However, both these models suffer from the problem of slow convergence (learning). In order to circumvent this problem, it is proposed to synthesize the direct model of transducers using the concept of a Polynomial-ANN (polynomial artificial neural network) trained with Levenberg-Marquardt (LM) learning algorithm. The proposed Polynomial-ANN oriented transducer model is implemented based on the topology of a single-layer feed-forward back-propagation-ANN. The proposed neural modeling technique provided an extremely fast convergence speed with increased accuracy for the estimation of transducer static nonlinearity. The results of convergence are very stimulating with the LM learning algorithm.

Algorithms↗
PubMed1981

An improved transducer for measurement of cardiac dimensions with sonomicrometry.

Although pulse-transit sonomicrometry is an accurate and sensitive technique for measuring cardiac dimensions, transducer directionality has been a significant problem in certain applications. Construction of an improved ultrasonic dimension transducer is described for the measurement of global cardiac diameters. The transducer consists of a hemispheric piezoelectric crystal with a quarter-wavelength impedance matched faceplate. The in vitro acoustic characteristics of this transducer reveal a substantially improved beam pattern compared to the flat piezoceramic transducer commonly used. This improvement in transducer design greatly facilitates sonic alignment, enhances tracking throughout the cardiac cycle, and allows the measurement of more complex cardiac dimensions.

Acoustics↗
PubMed1993

Some problems in using a polyvinylidene fluoride transducer for the intra-articular determination of joint contact stress.

A piezoelectric transducer and associated instrumentation were developed and evaluated as a means of experimentally determining joint contact stress. Each transducer, fabricated from a polyvinylidene fluoride film, comprised four discrete sensing elements. Following dynamic calibration of all sensing elements, in vitro evaluations were performed with transducers positioned in canine tibio-femoral joints. Quantitative measurements of contact stress as a function of time were obtained using these transducers, the magnitudes of which ranged between 0.01 and 7.99 MPa. Limitations associated with the transducer material and its use in this specific application included calibration variability and temporal phase shift of the transducer output signal relative to the applied load.

Animals↗
PubMed2004

Reliability and validity of a linear position transducer for measuring jump performance.

This study determined the reliability and validity of a linear position transducer to measure jump performance by comparing the mean force, peak force, and time-to-peak force measurements with data obtained simultaneously with a force platform. Twenty-five men performed squat, countermovement, and drop jumps with the linear transducer connected from a waist belt and base, which were placed upon a force platform. The Pearson correlation coefficients across the 3 jumps for the mean force (r = 0.952-0.962), peak force (r = 0.861-0.934), and time-to-peak force (r = 0.924-0.995) were high, providing evidence that the linear-transducer and force-platform measurements were similar. The trial-to-trial reliability of the jumps measured by the linear position transducer gave an intraclass correlation coefficient of 0.924-0.975 for mean force, 0.977-0.982 for peak force, and 0.721-0.964 for time-to-peak force. The coefficients of variation were 2.1-4.5% for mean force, 2.5-8.4% for peak force, and 4.1-11.8% for time-to-peak force. Our findings showed that the calculations derived from the linear transducer were very similar to those of the force platform and hence provided evidence of the validity of this method. The data from the linear transducer were also shown to be reliable. Therefore, this method of calculating force may provide a cost-effective alternative to the force platform for measuring this variable.

Adult↗
PubMed1977

[An extraluminal strain gage force transducer: its construction and implantation (author's transl)].

1. Extraluminal strain gage force transducers have been designed and constructed in this laboratory. This device was originally developed to measure contractile force of the heart by Walton et al in 1950, however, we concentrated our effort upon durability and waterproof of the transducer in the present study. 2. Strain gages which were made for measuring large strain were prepared and bonded onto the both surfaces of CuBe strips with epoxy lesin. Water proof was then made by applying silicone (KE 45 RTV), which was excellent in waterproof, insulation and flexibility. The silicone was also found no significant influence upon the surrounding tissues as a foreign body. 3. The transducer constructed in this way had useful life for 3-6 months after implantation. Chronically implanted transducer units offer several advantages: they provide prolanged observation of gastrointestinal mechanical activity directly in conscious animals. They can be sutured on the outer surface of the gastrointestinal tract and do not interfere flow of intraluminal contents. They can measure separate contractile force of the circular and longitudinal muscle layers. 4. Major limination of the transducer is difficulty to determine if a given sequence of movements are mixing or propulsion of the contents. Application of these transducers is currently limited in animal only.

Animals↗
PubMed1993

High-frequency air conduction audiometry. Testing of a new low impedance circumaural transducer system in normal young persons.

A new circumaural transducer was tested in the frequency range 125 Hz to 20 kHz. The new transducer has a low acoustic impedance and loads the ear closely to free-field conditions, thus ensuring that sensitivity to different positions of the transducer around the ear is reduced compared to conventional audiometric headphones. The transducer was tested on 57 individuals (114 ears) in the age range 10 to 20 (median age 17.0 years). The results, showing a fairly good accordance with the ISO standard free-field thresholds values, seem to confirm that the new transducer system loads the ears similarly to free-field conditions. The results were also compared with the threshold values from other high-frequency investigations using different transducer systems. In order to verify the reliability of the system, a test-retest was carried out on 12 inexperienced normal individuals (24 ears) (median age 26.5 years; range values from 22 to 44 years). The standard deviations of the test-retest ranged from 2.8dB to 6.6dB. A comparison of these values with the results from other high-frequency test-retests is of dubious value, as such retests have often been performed and estimated in different ways. International standards for high-frequency audiometry threshold and international standards for test-retest procedure are needed. The increasing administration of cytotoxic drugs in the treatment of malignant diseases will increase the need for reliable high-frequency audiometry equipment.

Adult↗
PubMed1976

Chronic measurement of epidural pressure with an induction-powered oscillator transducer.

An induction-powered oscillator transducer (IPOT) was designed for the chronic measurement of epidural pressure. The transducer was completely implantable so all pressure measurements were made through the intact skin. The IPOT had a linear pressure range from -50 to +200 cm H2O, was sensitive to 1 mm H2O and had a zero drift of less than 1 mm H2O/day under full load. Zero drift was minimized by using a hermetically-sealed metal bellows transducing element which was chemically treated to prevent corrosion and creep. The correlation between epidural pressure and intraventricular pressure was determined during the first 24 hours after implantation in six dogs. Epidural pressure was found to be a linear function of intraventricular fluid pressure. Epidural pressure and intraventricular pressure were essential equal provided the epidural wedge pressure was minimized by proper insertion of the transducer. The correlation between epidural pressure and intraventricular pressure was determined after chronic implantation in five dogs. Epidural pressure was a linear function of intraventricular pressure in the chronically implanted dogs, but epidural pressure was not equal to intraventricular pressure. After chronic implantation, the epidural pressure transducer was not responsive to changes in intraventricular pressure because of mechanical changes in the dura. The dura became stiff and non-compliant. Maximum correlation between epidural pressure and intraventricular fluid pressure in chronic implantations will depend on judicious material selection and mechanical design at the transducer-dura interface.

Animals↗
PubMed2001

Methods of experimental and clinical assessment of the relative measurement accuracy of an intracranial pressure transducer. Technical note.

The assessment of the actual measurement accuracy of an intracranial pressure (ICP) transducer is imperative but still very difficult in practice. The authors tested the Codman MicroSensor ICP transducer experimentally. Additionally, a bedside test for assessment of measurement accuracy was used before and after clinical monitoring. For laboratory testing, seven new transducers were examined for measurement accuracy at increasing pressures ranging from 0 to 75 mm Hg. Drift was evaluated for 10 days at six different pressure levels ranging from 0 to 50 mm Hg. Temperature drift was assessed over a temperature range from 20 to 45 degrees C. The percentage absolute difference was used in the assessment of measurement accuracy. For clinical testing, measurement accuracy was assessed intraoperatively just before the insertion of the transducer and in an open water bath after its explantation, at 10 cm H2O both times. The maximum percentage absolute difference was 9% at a pressure of 10 mm Hg, and declined toward 2.3% at a pressure of 75 mm Hg. The maximum drift over 10 days was -4 mm Hg. Within the range of 30 to 40 degrees C, temperature drift was negligible. Over a period of 2 years, between June 1997 and June 1999, 40 ICP transducers were implanted in 35 patients by one surgeon. Of these devices, a malfunction was detected in two of them by testing them in a water bath before insertion. Experimental and clinical results indicate that this miniature strain-gauge transducer measures accurately; however, control readings for the probe by means of measurement in an open water bath just before insertion are strongly recommended.

Equipment Design↗
PubMed1998

Ultrasonographic detection of living adult Wuchereria bancrofti using a 3.5-MHz transducer.

Adult Wuchereria bancrofti can be readily detected by ultrasound in the lymphatic vessels of the spermatic cord with a 7.5-MHz transducer, but most ultrasound machines in developing countries are equipped with 3.5-MHz transducers. To assess the potential for ultrasound as a tool for diagnosis and epidemiologic assessment in lymphatic filariasis, we compared the performance of 3.5-MHz and 7.5-MHz transducers in 61 men in Recife, Brazil. All men had three ultrasound examinations using a 3.5 MHz transducer and an examination with a 7.5-MHz probe. Using the 7.5-MHz transducer, adult W. bancrofti were detected in 41 men; 81 adult worm nests were detected. Sixty-four (79%) nests were detected with the 3.5-MHz probe, each on all three examinations. The 3.5-MHz probe correctly identified 35 (85.4%) of 41 men as infected; sensitivity increased with lymphatic vessel diameter. Ultrasonographic examination with a 3.5-MHz transducer is a sensitive method for detection of adult W. bancrofti in men and merits consideration as a tool for rapid epidemiologic assessment.

Adolescent↗
PubMedDate not supplied

Transducers for myocardial research.

Seven miniaturized transducers to measure force, displacement, and thickness--singly and in combination--in animal experiments are described. The transducers are lightweight and during an open-chest procedure can be inserted within a heartbeat, removed, and reinserted, with minimum trauma. Six or more transducers of various kinds can be used simultaneously without artifacts. For closed-chest experiments a combination force-displacement transducer can be catheter-borne. A trifunctional transducer was used successfully to measure force-displacement thickness in a small area. A single conductor can be added for ECG measurement in the area where the transducer is implanted.

Animals↗
PubMed1993

A technique for the high-speed characterization of ultrasonic transducer insertion loss performance.

A characterization technique has been developed to address the problems associated with calibrating very-high frequency (i.e., > 50 MHz) ultrasound transducers. The technique is based on using a pc-controlled network analyzer to acquire the through-transmission voltage transfer function spectrum from a pair of ultrasound transducers which are closely spaced in water. This spectrum, which includes electrical feed-through noise and multiple reflection artifacts, is then corrected for the water's attenuation and the transfer response of the electronics system. An inverse Fourier transform is then performed, to produce the time domain response of the transducers. The portion of the response which corresponds to the first acoustic arrival is then gated out of this response, and a Fourier transform is performed to compute the transducers' true transfer function (insertion loss) spectrum. A pc-controlled automated calibration system based on this technique has been developed and numerous transducer pairs have been tested. Excellent agreement has been shown between this method and the conventional tone-burst technique for accurately characterizing insertion loss spectra. In this paper, a detailed description of the technique, actual transducer test results, and comparisons with the conventional tone-burst method are presented in detail.

Calibration↗
PubMed1995

Brain-derived neurotrophic factor-transduced fibroblasts: production of BDNF and effects of grafting to the adult rat brain.

Local delivery of brain-derived neurotrophic factor (BDNF) by genetically modified cells provides the unique opportunity to examine the effects of BDNF on adult dopaminergic and cholinergic neurons in vivo. Primary rat fibroblasts were genetically engineered to produce BDNF. Conditioned media from BDNF-transduced fibroblasts supported embryonic chick dorsal root ganglion neurons as well as rat fetal mesencephalic neurons. BDNF-transduced fibroblasts grafted to the rat brain survived and showed continued mRNA production for at least 2 weeks. The effects of BDNF-transduced fibroblast grafts on the dopaminergic and cholinergic systems were then assessed. BDNF-transduced fibroblasts grafted into the normal intact substantia nigra induced sprouting of tyrosine hydroxylase- and neurofilament-immunoreactive fibers into the graft. Fibroblast grafts implanted into the normal intact striatum and midbrain as well as the 6-hydroxydopamine-lesioned brain did not induce sprouting of dopaminergic fibers; neither did they affect drug-induced rotational behavior. BDNF-transduced fibroblasts did, however, significantly increase the homovanillic acid/dopamine ratio when grafted into the normal midbrain. Following transection of the fimbriafornix, BDNF-transduced fibroblasts grafted into the septum were unable to rescue the septal cholinergic population, as did nerve growth factor-producing fibroblast grafts. Genetically modified fibroblast grafts may provide an effective, localized method of BDNF delivery in vivo to test biological effects of this factor on the central nervous system.

Animals↗
PubMed2003

Sonographic evaluation of the anterior liver surface in chronic liver diseases using a 7.5-MHz annular-array transducer: correlation with laparoscopic and histopathologic findings.

PURPOSE: We studied the sonographic appearance of the anterior liver surface using an ultrasound scanner equipped with a 7.5-MHz annular-array transducer to determine the accuracy of this imaging modality in monitoring the course of chronic liver diseases. METHODS: We prospectively evaluated patterns of the liver surface in the sonograms of 77 consecutive patients with chronic liver diseases who had undergone sonographic examination with a 7.5-MHz annular-array transducer and a 3.75-MHz convex-array transducer over a 2-year period and compared these findings with those of laparoscopy (using previously described categories) and histopathology. RESULTS: Histopathologically confirmed disease prevalences for inactive chronic hepatitis, active chronic hepatitis, liver cirrhosis, and others were 10% (8/77), 56% (43/77), 29% (22/77), and 5% (4/77), respectively. The sonographic appearance of the liver surface with the 3.75-MHz transducer was classified as either a regular or an irregular pattern. The regular pattern corresponded to 69% (34/50) of the cases in laparoscopic category 200 or 300 and the irregular pattern with 85% (23/27) of the cases in category 400 or 500. The sonographic appearance of the liver surface with the 7.5-MHz transducer was classified as regular, unevenly irregular, diffusely irregular, or nodular. These 4 patterns detected 75% (24/32), 78% (14/18), 52% (12/23), and 75% (3/4) of the cases of laparoscopic categories 200, 300, 400, and 500, respectively. In a comparison of the sonographic patterns of the liver surface with the differential histopathologic findings, the regular sonographic pattern corresponded to 88% (7/8) of the cases of inactive chronic hepatitis, the unevenly irregular pattern with 35% (15/43) of the cases of active chronic hepatitis, and the diffusely irregular and nodular patterns (considered as 1 group) with 68% (15/22) of the cases of liver cirrhosis. CONCLUSIONS: Our results suggest that sonographic evaluation of the liver surface with a 7.5-MHz annular-array transducer using this classification provides detailed information on the evolution of chronic liver diseases that correlates with the laparoscopic and histopathologic findings and thus is a useful noninvasive method for monitoring the disease course to cirrhosis.

Biopsy, Needle↗
PubMed2006

Mixed hematopoietic molecular chimerism results in permanent transgene expression from retrovirally transduced hepatocytes in mice.

BACKGROUND: Cytotoxic immune elimination of transduced hepatocytes may limit gene therapy for inherited liver diseases. Using beta-galactosidase as a marker gene, we studied whether creation of mixed beta-galactosidase molecular hematopoietic chimerism could induce tolerance to beta-galactosidase-transduced hepatocytes. METHODS: Molecular hematopoietic chimerism was established in irradiated recipient mice by transplantation of either a mixture of wild-type and beta-galactosidase-transgenic bone marrow or autologous bone marrow stem cells that were transduced with beta-galactosidase lentiviral vectors. After transplantation, mice were hepatectomized and injected with beta-galactosidase recombinant retroviruses to transduce regenerating hepatocytes. We monitored the presence of beta-galactosidase-expressing hepatocytes as well as the appearance of anti-beta-galactosidase antibodies during the time. RESULTS: In control animals, anti-beta-galactosidase antibodies and cytotoxic T-lymphocyte (CTL) response developed as early as 3 weeks after gene transfer. Transduced hepatocytes disappeared concomitantly. In bone marrow transplanted mice, tolerance could be observed in a significant proportion of animals. Tolerance resulted in permanent liver transgene expression and was absent unless a chimerism above 1% was achieved, demonstrating a threshold effect. CONCLUSIONS: Creation of a molecular hematopoietic chimerism can result in transgene tolerance and evade immune rejection of retrovirally transduced hepatocytes. This strategy may be useful for hepatic inherited diseases in which the transgene product behaves as a non-self protein.

Animals↗
PubMed1999

GM-CSF-transduced B16 melanoma cells are highly susceptible to lysis by normal murine macrophages and poorly tumorigenic in immune-compromised mice.

Granulocyte-macrophage colony-stimulating factor (GM-CSF)-transduced B16-F10 murine melanoma cells had lower tumorigenicity in both syngeneic and nude mice than parental or LacZ-transduced (control) cells. The subcutaneous (s.c.) tumors producing GM-CSF were densely infiltrated with macrophages, whereas the control tumors were not. In vitro studies showed that GM-CSF-transduced B16 cells were susceptible to lysis mediated by nonactivated murine macrophages, whereas control B16 cells were not. Macrophage-mediated cytotoxicity against GM-CSF-transduced B16 cells was independent of the presence of NO, H2O2, O2-, tumor necrosis factor alpha, and matrix metalloproteinase. Coculture experiments using GM-CSF-producing and -nonproducing B16 cells demonstrated that GM-CSF produced by the transduced B16 cells activated macrophages to kill the bystander non-GM-CSF-producing tumor cells. The results suggest that GM-CSF released by tumor cells can induce macrophage-mediated cytotoxicity, which in turn can inhibit the in vivo growth of GM-CSF-transduced tumor cells.

Animals↗
PubMed2002

Retroviral transduction and engraftment ability of primate hematopoietic progenitor and stem cells transduced under serum-free versus serum-containing conditions.

The ability to efficiently transduce hematopoietic stem and progenitor cells under serum-free conditions would be desirable for safety and standardization of clinical gene therapy protocols. Using rhesus macaques, we studied the transduction efficiency and engraftment ability of CD34-enriched SCF/G-CSF mobilized progenitor cells (PBSC) transduced with standard amphotropic marking vectors under serum-free and serum-containing conditions. Supernatants were collected from producer cells 16 hours after serum-free medium or medium containing 10% fetal calf serum was added. Vector titers were approximately two- to threefold higher when producer cells were cultured in serum-containing medium. However, retroviral transduction of rhesus CFU-GM was improved using serum-free vector-containing medium. For analysis of engraftment with transduced cells, three macaques had CD34+ peripheral blood stem cells split into two fractions for transduction. One fraction was transduced using serum-free vector-containing medium, and the other fraction was transduced using standard serum-containing medium. The two fractions were re-infused simultaneously following total body irradiation. In all three animals, there was equivalent marking from both vectors for 7-9 months post-transplantation. These data are encouraging regarding the removal of serum-containing medium from clinical hematopoietic cell transduction protocols, given the lack of a detrimental effect on transduction and engraftment with transduced cells.

Animals↗