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At least 163 records · Page 9Linked to original sources
PubMed1986

A new tremor balance-transducer.

A new tremor-measuring device has been developed. It is constructed as a beam balance and measures principally in a vertical direction. Both arms of the beam contain a ceramic crystal; one of the arms has an extension that rests on the object to be measured. In this way, problems associated with mounting the transducer to the object are eliminated. The balance-transducer performs a well defined rotational movement in contrast to the frequently used transducers with a single sensor which are mounted to the object. The tremor movement of the limb and/or inadequate mounting causes unknown variation in the influence of the gravity component on the sensor; this can cause substantial errors. This tremor-transducer eliminates this problem. The static load of the balance-transducer on the object can be adjusted to less than 0.5 X 10(-3) kg(0.005 N). Even in the case of finger tremor, the balance-transducer does not influence the tremor phenomenon significantly. The principle of the balance-transducer is suited to measurements of postural, intention and limited action tremor of the finger, hand, forearm and jaw.

Biomechanical Phenomena↗
PubMed1995

The effect of transducer bandwidth on ultrasonic image characteristics.

PURPOSE: This study was conducted to determine the effect of transducer bandwidth on the characteristics of ophthalmic ultrasound images. METHODS: B-scan images produced using two transducers, one with a narrow bandwidth and the other with a broad bandwidth, both having nominal center frequencies of 10 MHz, were evaluated. Comparative scans were made of a tissue-mimicking phantom, an intraocular tumor, and a vitreous hemorrhage. RESULTS: Results showed that broadband transducers gave improved resolution and finer speckle texture, but had lower sensitivity. Broadband transducers were most suitable for situations in which resolution was more important than sensitivity, such as imaging of tumors. The greater sensitivity of the narrowband probe made it most useful for evaluation of vitreous complications, such as hemorrhage and membranes. CONCLUSION: In addition to transducer frequency, bandwidth should be taken into account when choosing a transducer for a specific ophthalmic imaging application. Both broad- and narrowband transducers have relative advantages in particular applications.

Ciliary Body↗
PubMed1989

A transducer for detection of fetal breathing movements.

The paper describes a new transducer for detection of fetal movements and sounds from the maternal abdominal wall. This transducer is based on an inductive principle. The compliance of the transducer should match the compliance of the maternal abdominal wall in order to detect the very weak acoustic signal caused by individual fetal breathing movements. The contact area of the transducer is supported on a membrane, the tension of which can be adjusted so as to match the compliances of tissue and transducer. The goal of this paper is to investigate detection of fetal movements in order to monitor fetal condition and motility. The more specialized field of investigating fetal heart rate variability by studying the relationship between fetal breathing movements and fetal heart rate may become of more interest in the future. The inductive phonometer (INPHO) shows a flat (+/- 1.5 dB) frequency response between 0.2 and 200 Hz which is not affected by the compliance adjustment. Some in vivo measurements have been performed. The transducer signal is stored on a 20MB hard disk of an Olivetti M24 Personal Computer (PC) simultaneously with a control signal indicating the presence of breathing movements. Ultrasound imaging is exclusively used for verification of breathing movements. The images are stored on videotape simultaneously with control signals from the PC for synchronization of data and image. Substantial digital filtering is necessary to discriminate between actual breathing movements and other fetal activities. It is shown that optimal adjustment of the transducer's compliance to that of the maternal abdominal wall is possible and that individual breathing movements can indeed be measured.

Female↗
PubMed1996

The design of an optical fiber pressure transducer for use in the upper airways.

The development of an optical fiber transducer for use in biomedical applications has been presented. The design was targeted for use in the upper airways of patients with sleep disorders stemming from partial or total occlusion of the airway. The transducer's preliminary specification was suited for that of upper airway manometry: a resolution of 10 Pa over the range +/- 5 kPa, a single transducer being less than 0.94 mm in diameter. Amplitude modulated optical fiber sensors are susceptible to loss due to bending of the fiber core and cladding. The design of the transducer uses a series of three optical fibers, one emitting and two receiving, the combination of the two receiving optical fibers is used to reduce effects of light loss: a bend radius of 50 mm is typical for the insertion into the naso-pharynx. The transducer transduction element is a silicone gel coated with reflective titanium dioxide, the meniscus deforms under pressure and modulates the intensity of light reflected back into the receiving optical fibers. The main disadvantage of optical fiber pressure transducers is their susceptibility to temperature drift. Temperature in the airway rarely changes more than 17 degrees C. The frequency of breathing and the high thermal mass of the catheter means that temperature drift in this application is not significant, and will cause an insignificant error of 12 Pa. The transducer is inexpensive to produce, and may be deemed disposable: approximately $20 in material costs (using current manufacturing techniques this can be halved). The system has the added advantage of being electrically, magnetically, and chemically passive. The potential for miniaturization is limited only by the mechanical strength of the optical fibers as mechanical problems associated with fragile elastic membranes do not apply.

Airway Obstruction↗
PubMed1997

Cylindrical ultrasonic transducers for cardiac catheter ablation.

This study was designed to evaluate the feasibility of using cylindrical ultrasound transducers mounted on a catheter for the ablation of cardiac tissues. In addition, the effects of ultrasound frequency and power was evaluated both using computer simulations and in vitro experiments. Frequencies of 4.5, 6, and 10 MHz were selected based on the simulation studies and manufacturing feasibility. These transducers were mounted on the tip of 7-French catheters and applied in vitro to fresh ventricular canine endocardium, submerged in flowing degassed saline at 37 degree C. When the power was regulated to maintain transducer interface temperature at 90-100 degree C, the 10-, 6-, and 4.5-MHz transducers generated a lesion depth of 5.9 +/- 0.2 mm, 4.6 +/- 1.0 mm, and 5.3 +/- 0.9 mm, respectively. The 10-MHz transducer was chosen for the in vivo tests since the maximum lesion depth was achieved with the lowest power. Two dogs were anesthetized and sonications were performed in both the left and right ventricles. The 10-MHz cylindrical transducers caused an average lesion depth of 6.4 +/- 2.5 mm. In conclusion, the results show that cylindrical ultrasound transducers can be used for cardiac tissue ablation and that they may be able to produce deeper tissue necrosis than other methods currently in use.

Animals↗
PubMed2002

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials.

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO3) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO3) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 ohms for the PZT fiber composite and PbTiO3 ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO3 and PbTiO3 transducers provided better image contrast than the other materials.

Equipment Design↗
PubMed1999

Optimal configuration of multiple-focused ultrasound transducers for external hyperthermia.

External ultrasound hyperthermia is considered to be a very flexible modality for heating deep-seated tumors owing to its penetration and focusing ability. However, using this flexibility requires that many complicated, interacting decisions be made to obtain optimal treatment. This paper presents the feasibility of arranging multiple-focused ultrasound transducers to produce an appropriate heating pattern for a specific treatment, based on the optimal scan parameters obtained from an optimization algorithm. The variable scan parameters of the heating system optimized are the transducer tilt and rotation angles, focal depth, scan radius, and output acoustical power. After obtaining the optimal scan parameters, multiple transducers are systematically arranged according to these scan parameters. Three-dimensional ultrasound power deposition and temperature distribution for a specific treatment are calculated for this multiple ultrasound transducer system. A more uniform temperature distribution in the treatment region for a large, highly perfused tumor can be achieved by scanning the system with respect to the central scan axis and/or swinging the transducers inwards and outwards. The maximum heating depth of focused ultrasound transducers used in this heating system is also studied. Simulation results demonstrate that the optimal arrangement of this multiple-focused ultrasound transducer system is highly promising for heating deep, large, and highly perfused tumors.

Algorithms↗
PubMed1984

A hermetically sealed cardiac dimension transducer for long-term animal implantation.

Pulse transit sonomicrometry is a well-accepted method for assessing cardiac dimensions and function in research animals. Unfortunately, this technique has been hampered in chronic applications by a significant incidence of transducer failure secondary to leakage of corrosive biological fluids into the piezoelectric material. The fluid leakage generally occurred at the interface between the encapsulating epoxy and the bioelectric cable and resulted in progressive functional deterioration with time. In this paper, a new hemispheric ultrasonic dimension transducer is described with a mechanical hermetic seal at the bioelectric cable-transducer interface. The hermetically sealed transducers withstood 400 psi compressed air without leakage, while conventional transducers routinely leaked at 60 psi. The performance characteristics of the new transducers were similar to those previously reported with omnidirectional designs, and no failures have occurred during 3 yr of experience with repeated transducer implantations.

Animals↗
PubMed2005

Catheter ultrasound phased-array transducers for thermal ablation: a feasibility study.

The feasibility of catheter single-element ultrasound transducers for cardiac ablation has been shown previously. We describe the design and testing of catheter-sized linear phased arrays transducers for ultrasound ablation. One array has 86 PZT-4 elements operating at 8 MHz and 5 MHz. The overall array size is 14.9 mm by 3.1 mm (10 Fr). The other array has 50 PZT-5 elements operating at 4 MHz and is 17 mm by 3.1 mm (10 Fr). In order to produce the intensity needed to create lesions in heart tissue, we modified a real-time, 3D scanner to produce 100 Vpp 256-cycle transmit pulses at a pulse repetition frequency of 14.1 kHz. This made it possible for the PZT-4 and PZT-5 transducers to produce ISPTA of 3.26 W/cm2 and 142 W/cm2, respectively. When driving the transducers at high duty factor, the transmit circuitry in the scanner was damaged. A mechanically-focused transducer with the same dimensions as the PZT-4 transducer was built. When transmitting continuously at 9 MHz, it produced an ISPTA of 29.3 W/cm2. This created a lesion 5 mm across and 5 mm deep in beef tissue while raising the focal temperature 23 degrees C. Ablation is within the capabilities of a catheter phased array transducer integrated into a diagnostic ultrasound scanner.

Catheter Ablation↗
PubMed1989

The design and fabrication of high frequency poly(vinylidene fluoride) transducers.

Poly(vinylidene fluoride) (PVDF) transducers are well suited for use in high frequency pulse-echo ultrasound systems because of their high bandwidth. We analyze the design parameters of PVDF transducers operating in the 100 MHz range using the KLM transducer model. The effect of backing layers, electrode configuration, transducer surface area and tuning circuits on the insertion loss and pulse-echo response of the transducers are investigated. Using this design procedure, an experimental PVDF transducer is proposed for applications in the 100 MHz range. The transducer is built into a high frequency SMA electrical connector. Insertion loss and pulse-echo response measurements are compared with theoretical predictions.

Equipment Design↗
PubMed1995

Optimization of signal-to-noise ratio for multilayer PZT transducers.

In medical ultrasound imaging, two-dimensional (2-D) array transducers are desirable to implement dynamic focusing and phase aberration correction in two dimensions as well as volumetric imaging. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near the resonance frequency. This results in poor signal-to-noise ratio (SNR) of the array elements. It has previously been demonstrated that transducers made from multilayer PZT ceramics have lower electrical impedance and greater SNR than comparable single layer elements. A simplified circuit model has been developed to optimize the SNR for multilayer ceramic (MLC) transducers. In this model, an electronic transmitter excites the array element and in the receive mode, the element drives a coaxial cable load terminated by a high impedance preamplifier. The transducer impedance is Zt/N2, where N is the number of piezoelectric layers. Maximum transmit signal is obtained when N = Ntx such that the transducer impedance, Zt/Ntx2, is matched to the source impedance. Maximum receive signal is obtained when N = Nrx such that the transducer impedance, Zt/Nrx2, is matched to the coaxial cable reactance. For maximum pulse-echo signal, the transducer should be designed with N = square root of Ntx Nrx, the geometric mean of Ntx and Nrx. Using this optimization technique, a 1.5-D array was designed with 3 layers for maximum pulse-echo SNR. Results of simulations from the simplified circuit analysis were consistent with those of the KLM model. The 3 layer array was fabricated as well as a single layer control array. The measured transmit signal and receive signal agreed with the simulation results.

Ceramics↗
PubMed1995

Clinical evaluation of a miniature strain-gauge transducer for monitoring intracranial pressure.

In 25 patients, we evaluated the accuracy of a new miniature strain-gauge transducer developed for the measurement of intracranial pressure (ICP). The ICP in each patient was measured with the intraventricular, miniature strain-gauge transducer, and that value was compared with the ICP measured with a ventriculostomy catheter coupled to an external strain-gauge transducer. From the two monitors, 2218 simultaneous measurements of ICP were obtained. The average ICP measured with the miniature strain-gauge transducer was 15.9 +/- 10.0 mm Hg (range, -3 to 104 mm Hg). The ICP measured with the ventriculostomy-catheter transducer averaged 15.4 +/- 10.1 mm Hg (range, -9 to 104 mm Hg). A highly significant correlation was found over the wide range of pressures observed (n = 2218, r = 0.97, P < 0.001). The average difference between the two measurements of the ICP was 0.5 +/- 2.6 mm Hg, and the differences were equally positive and negative, demonstrating no consistent bias. The two values for the ICP were within 2 mm Hg of each other on 63% of the measurements and within 4 mm Hg of each other on 89% of the measurements. The average zero drift of the miniature strain-gauge transducer, measured at ambient pressure after removal of the catheter, was 0.2 +/- 0.5 mm Hg. The results indicate that this miniature strain-gauge transducer is highly accurate and stable and that it is a reliable alternative to a ventriculostomy for monitoring the ICP.

Adult↗
PubMed1984

Evaluation of transducer performance for buttock-cushion interface pressure measurements.

To assess the performance of transducers used clinically to measure pressure at the skin-cushion interface of seated patients, transducers were placed between slabs of gel and/or foam materials compressed between platens. The recorded pressures consistently exceeded the nominal pressures calculated using the surface area of the slabs. This overestimation, observed in both miniature diaphragm transducers and air cell transducers, appeared to result from preferential loading of the transducer due to insufficient structural compliance in the environs. On the other hand, air cell transducers placed at a skin-foam interface beneath the thighs of human subjects gave readings which agreed closely with subcutaneous tissue pressure measurements obtained from a wick catheter inserted at the same location. These results suggest that, although pressure measurements are prone to error due to load sharing, results obtained clinically from subjects on soft cushions are reasonably accurate because of the high compliance of human soft tissue and the foam. Under low loads these distribute the pressure equitably and avoid concentrations of load on the transducer.

Buttocks↗
PubMed1997

[Echocardiographic diagnosis of left intraventricular thrombus. A comparative study of 2.5, 3.5 and 5 MHz transducers].

The authors undertook a prospective and comparative echocardiographic study of 2.5, 3.5 and 5 MHz ultrasonic transducers for the detection of left ventricular mural thrombosis in 53 patients with left ventricular dysfunction. Thirty-three patients had advanced ischaemic heart disease following anterior myocardial infarction and 20 had dilated cardiomyopathy with a left ventricular ejection fraction of < or = 40%. Eighty-two per cent of patients had anticoagulant therapy. The diagnosis of thrombosis was based on Asinger's classification. Eleven thrombi were detected, an incidence of 21%. Using the 5 MHz transducer as a reference, the sensitivity of the 3.5 MHz transducer was 100% and much greater than that of the 2.5 MHz transducer (55%) which was associated with 4 false positive results. The specificities were respectively 97 and 86% for the 3.5 and 2.5 MHz transducers. There was no correlation between the apical Doppler flow velocities and the presence of mural thrombosis. Atrial fibrillation was significantly associated with mural thrombosis (p = 0.04). The increased sensitivity associated with transducers of higher frequency is, however, limited by the echogenicity of patients. The introduction of transducers of variable frequencies should facilitate the diagnosis and improve the sensitivity of echocardiography in detecting left ventricular mural thrombosis.

Aged↗
PubMed1976

Effect of transducer placement on echocardiographic mitral valve systolic motion.

The influence of transducer position and angulation upon the mitral systolic echo was studied in 100 presumably healthy females. Echocardiographic studies were performed from the second, third, fourth and fifth intercostal spaces (ICS). The role of the sound beam's path relative to cardiac motion was assessed by analyzing the recorded mitral valve pattern as a function of transducer orientation, independent of the absolute ICS used. With the transducer directed caudally when both mitral leaflets and left atrium were recorded, holosystolic or midsystolic posterior motion of the mitral valve leaflet echo was seen in 59% of the subjects. These patterns, recorded this way, were not related to phonocardiographic signs suggesting mitral valve prolapse. Best correlation with phonocardiographic findings was obtained when the echocardiographic examination was performed with the transducer either perpendicular to the chest in the sagittal plane, or pointing slightly cephalad ('perpendicular' position). With the transducer in 'perpendicular' position, both holosystolic and midsystolic posterior motion of the mitral systolic echo, deviating more than 2 mm from a line joining the C and D points, were highly related statistically to phonocardiographic findings suggesting mitral valve prolapse. This study demonstrates that transducer position and angulation on the chest wall are important determinants of echocardiographic appearance of mitral valve during systole. Only the 'perpendicular' transducer position should be used when analyzing echocardiograms for the presence of mitral valve prolapse.

Echocardiography↗
PubMed2005

Repair of articular cartilage defect by autologous transplantation of basic fibroblast growth factor gene-transduced chondrocytes with adeno-associated virus vector.

OBJECTIVE: To examine the effects of basic fibroblast growth factor (bFGF) gene-transduced chondrocytes on the repair of articular cartilage defects. METHODS: LacZ gene or bFGF gene was transduced into primary isolated rabbit chondrocytes with the use of a recombinant adeno-associated virus (AAV) vector. These gene-transduced chondrocytes were embedded in collagen gel and transplanted into a full-thickness defect in the articular cartilage of the patellar groove of a rabbit. The efficiency of gene transduction was assessed according to the percentage of LacZ-positive cells among the total number of living cells. The concentration of bFGF in the culture supernatant was measured by enzyme-linked immunosorbent assay to confirm the production by bFGF gene-transduced chondrocytes. At 4, 8, and 12 weeks after transplantation, cartilage repair was evaluated histologically and graded semiquantitatively using a histologic scoring system ranging from 0 (complete regeneration) to 14 (no regeneration) points. RESULTS: LacZ gene expression by chondrocytes was maintained until 8 weeks in >85% of the in vitro population. LacZ-positive cells were found at the transplant sites for at least 4 weeks after surgery. The mean concentration of bFGF was significantly increased in bFGF gene-transduced cells compared with control cells (P < 0.01). Semiquantitative histologic scoring indicated that the total score was significantly lower in the bFGF-transduced group than in the control group throughout the observation period. CONCLUSION: These results demonstrated that gene transfer to chondrocytes by an ex vivo method was established with the AAV vector, and transplantation of bFGF gene-transduced chondrocytes had a clear beneficial effect on the repair of rabbit articular cartilage defects.

Animals↗
PubMed2004

RNA-containing adenovirus/polyethylenimine transfer complexes effectively transduce dendritic cells and induce antigen-specific T cell responses.

BACKGROUND: Dendritic cells (DCs) are the most potent antigen-presenting cells in initiating primary immune responses. Given the unique properties of DCs, gene-modified DCs represent a particularly attractive approach for immunotherapy of diseases such as cancer. METHODS: Gene-modified DCs were obtained by a receptor-mediated gene delivery system using adenovirus (Ad) particles as ligand and RNA or DNA condensed by polyethylenimine (PEI). In vitro transcribed polyadenylated or non-polyadenylated RNA was used. RNA-transduced DCs were generated expressing chicken ovalbumin (OVA) or chimeric constructs thereof, and compared with DNA-transduced DCs. RESULTS: Ad/PEI transfection complexes efficiently delivered RNA into DCs. Such RNA-transduced DCs induced OVA-specific T cell responses more effectively than DNA-transduced DCs. Furthermore, DCs transduced with polyadenylated RNA were more potent in stimulating CD4(+) and CD8(+) T cell responses than DCs transduced with non-polyadenylated RNA and this was particularly important for CD4(+) T cell responses. CONCLUSIONS: Ad/PEI/RNA transfection is an efficient means for generating RNA-transduced DCs and for stimulating antigen-specific T cell responses. Polyadenylation of RNA enhances CD8(+) T cell responses and is essential for CD4(+) T cell responses.

Adenoviridae↗
PubMed2004

Sustained transgene expression by human cord blood derived CD34+ cells transduced with simian immunodeficiency virus agmTYO1-based vectors carrying the human coagulation factor VIII gene in NOD/SCID mice.

BACKGROUND: Gene therapy is being studied as the next generation therapy for hemophilia and several clinical trials have been carried out, albeit with limited success. To explore the possibility of utilizing autologous bone marrow transplantation of genetically modified hematopoietic stem cells for hemophilia gene therapy, we investigated the efficacy of genetically engineered CD34+ cell transplantation to NOD/SCID mice for expression of human factor VIII (hFVIII). METHODS: CD34+ cells were transduced with a simian immunodeficiency virus agmTYO1 (SIV)-based lentiviral vector carrying the enhanced green fluorescent protein (eGFP) gene (SIVeGFP) or the hFVIII gene (SIVhFVIII). CD34+ cells transduced with SIV vectors were transplanted to NOD/SCID mice. Engraftment of transduced CD34+ cells and expression of transgenes were studied. RESULTS: We could efficiently transduce CD34+ cells using the SIVeGFP vector in a dose-dependent manner, reaching a maximum (99.6 +/- 0.1%) at MOI of 5 x 10(3) vector genome/cell. After transducing CD34+ cells with SIVhFVIII, hFVIII was produced (274.3 +/- 20.1 ng) from 10(6) CD34+ cells during 24 h in vitro incubation. Transplantation of SIVhFVIII-transduced CD34+ cells (5-10 x 10(5)) at a multiplicity of infection (MOI) of 50 vector genome/cell into NOD/SCID mice resulted in successful engraftment of CD34+ cells and production of hFVIII (minimum 1.2 +/- 0.9 ng/mL, maximum 3.6 +/- 0.8 ng/mL) for at least 60 days in vivo. Transcripts of the hFVIII gene and the hFVIII antigen were also detected in the murine bone marrow cells. CONCLUSIONS: Transplantation of ex vivo transduced hematopoietic stem cells by non-pathogenic SIVhFVIII without exposure of subjects to viral vectors is safe and potentially applicable for gene therapy of hemophilia A patients.

Animals↗