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PubMed1982

A note on the application and evaluation of the buckle transducer for the knee ligament force measurement.

Knee ligament forces were directly measured with buckle transducers. Given a collection of buckle transducers with adequate rigidity and a variety of sizes to accommodate different ligamentous geometries, two potential problems remain when using the buckles 1) impingement of the transducers with bone, producing a false output; 2) ligament shortening due to buckle installation, potentially altering the distribution of ligament forces around the knee. This report describes our current buckle transducer designs and installation procedures, and presents data which demonstrated that the errors due to ligament shortening and bone impingement can be assessed and reduced to acceptable levels.

Humans↗

PubMed2006

Tissue deformation induced by radiation force from Gaussian transducers.

Imaging techniques based upon the tissue mechanical response to an acoustic radiation force are being actively researched. In this paper a model for predicting steady-state tissue displacement induced by a radiation force arising from the absorption of Gaussian ultrasound beams is presented. A simple analytic expression is derived that agrees closely with the numerical quadrature of the displacement convolution integrals. The analytic result reveals the dependence of the steady-state axial displacement upon the operational parameters, e.g., an inverse proportional relationship to the tissue shear modulus. The derivation requires that the transducer radius be small compared to the focal length, but accurate results were obtained for transducer radii comparable to the focal length. Favorable comparisons with displacement predictions for non-Gaussian transducers indicate that the theory is also useful for a broader range of transducer intensity profiles.

Acoustics↗

PubMed1995

A head and transducer support system for making ultrasound images of tongue/jaw movement.

A head and transducer support system (HATS) was developed for use in ultrasound imaging of tongue movement. Ultrasound is an imaging technique that captures tongue motion during speech and thus has great appeal as a tool for speech research. However, because ultrasound systems are designed for clinical use, the transducer is hand-held and it is almost impossible to hold it completely steady under the chin when collecting tongue data. A system was needed to fix the head and support the transducer under the chin in a known position without disturbing speech. The HATS system was designed, constructed, and modified to provide valid, reliable tongue movement data by (1) immobilizing the head and (2) positioning the ultrasound transducer in a known relationship to the head.

Head↗

PubMed1982

Transoesophageal cross-sectional echocardiography with a phased array transducer system. Technique and initial clinical results.

Cardiac imaging by transthoracic two dimensional echocardiography is impaired in patients with chronic lung disease, those with obesity, and those with abnormal chest wall configuration. In order to overcome these limitations, a miniature phased array ultrasound transducer fitted to the tip of a commercially available gastroscope was developed. Transducer position and orientation can be adjusted completely by external control of vertical displacement inside the oesophagus, rotation, and angulation. Introduction and operation of the transducer gastroscope system are usually well tolerated by the patients, since no mechanical vibrations are generated and there is no need for an oil bag to secure oesophageal wall contact. Cardiac images of high quality are obtained even from structures and regions that are poorly or not at all imaged from external transducer positions.

Adult↗

PubMed1992

A novel remote-sensing isometric force transducer for micromechanics studies.

We have developed an innovative transducer for measuring force with femtonewton-to-micronewton resolution in biological systems. A magnetic microsphere is attached to the specimen being studied and is positioned between two electromagnets. Video microscopy and edge detection are used to monitor small movements of the microsphere that occur when the specimen generates force. An automatic control system adjusts the current through the electromagnets to keep the microsphere stationary. Measured force is a linear function of this current. This transducer is unique in its combination of sensitivity and isometric properties and its ability to measure force without direct connections to the specimen. That is, the transducer is "remote sensing" and can measure force through intervening membrane or tissue. The transducer is isometric at steady state to the limit at which displacement of the microsphere can be resolved, which can be as low as 19 nm. The completed system is being used to study the mechanics of interstitial connective tissue but may also be used to study molecular generation of force.

Animals↗

PubMed1979

Effect of implant duration on in vivo sensitivity of electromagnetic flow transducers.

Twenty-three electromagnetic flow transducers with lumen diameters of 3.5-6.0 mm were implanted in rhesus monkeys and baboonss for 12 h to 120 days. Each flow transducer was calibrated 1) in vitro on dialysis tubing with saline before implantation, 2) in vivo the last day of the implant period, and 3) again in vitro after the flow transducer was recovered. Three other flow transducers were implanted on femoral arteries of baboon just central to an arteriovenous Silastic shunt, and were calibrated in vivo daily for 23-47 days. In vitro sensitivity was not affected by implant durations of up to 120 days. In vivo sensitivity fluctuated unpredictably for the first 3-4 wk of implant, after which it followed a systematic course that depended on the lumen size. In vivo sensitivity at any time during implant (after the initial period) could be accurately predicted by knowing either the in vitro sensitivity or the terminal in vivo sensitivity.

Animals↗

PubMed2003

Laparoscopy-assisted intrapelvic sonography with a high-frequency, real-time miniature transducer to assess the ovary: a preliminary report.

OBJECTIVE: Our purpose was to evaluate the normal and pathologic internal textures of the ovary using laparoscopy-assisted intrapelvic sonography (LAIPS) with a specially developed 20-MHz flexible catheter-based high-resolution real-time miniature (2.4 mm in outer diameter) ultrasound transducer in patients with gynecologic disorders and infertile women. METHODS: 30 women (19 patients with gynecologic disorders and normal menstrual cycles (2 adenomyoses, 1 cervical cancer, 5 fibromyomas, 5 simple ovarian cysts, 1 endometriosis, 3 benign cystic teratomas, and 2 endometriomas), and 11 patients with infertility including 4 with polycystic ovarian syndrome, PCOS) were studied by intrapelvic sonography using a high-frequency real-time miniature transducer with pelvic saline effusion and laparoscopy. RESULTS: In the normal ovary in the mid-follicular phase, follicles were depicted more distinctly than with transvaginal sonography (TVS). In the late-follicular phase, cumulus oophorus formations were visualized in 6 of 9 patients (54.5%), but were not clear using TVS. In the luteal phase, the corpus luteum was noted in 9 of 12 patients (75%) by both TVS and LAIPS. In patients with PCOS, the thickened capsule of the ovary was distinguished clearly especially in the peripheral type, in which numerous small cysts were aligned in the subcapsular region of the ovary, whereas it could not be detected by TVS. In all 4 cases with PCOS (8 ovaries), the ovarian capsular thickness could be measured by means of LAIPS. In subjects with benign cystic teratoma, minimal high echoic lesions were depicted. In subjects with endometrioma, a diffuse coarse-granular internal texture was visualized. However, depiction of internal structures in large pathologic ovarian lesions was markedly limited because of the shallow scanning range of the high-frequency transducer. CONCLUSION: LAIPS with a high-frequency real-time miniature transducer might be a useful diagnostic modality to evaluate the normal physiologic textures of the ovary, as well as those with PCOS.

Adult↗

PubMed1994

Identification of coronary artery stenoses and poststenotic blood flow patterns using a miniature high-frequency epicardial transducer.

BACKGROUND: Intraoperative epicardial coronary Doppler ultrasound has the potential to provide anatomic and functional information. This technique has been hindered by the large size of standard transducers, but a miniature transducer is available that may fulfill the potential of coronary ultrasound. METHODS AND RESULTS: Twenty consecutive patients who were undergoing coronary artery bypass grafting were studied and compared with 9 control patients with normal coronary arteries who were undergoing routine mitral valve surgery. A miniature 6.5-MHz transducer was used to image coronary arteries and measure coronary blood flow velocities. Seventeen proximal left anterior descending and 3 right coronary artery stenoses were studied. As defined by coronary angiography (1 to 34 days before surgery), there were 13 severe stenoses (> 70%), 4 moderate stenoses (40% to 70%), 2 minor stenoses (< 40%), and 1 subtotal occlusion. Stenoses were readily identified by ultrasound. Color flow mapping demonstrated laminar flow in normal arteries and nonlaminar flow across moderate and severe stenoses. In the control patients with unobstructed arteries, peak and mean diastolic velocities were 35 +/- 2.1 and 26 +/- 1.9 cm/s with peak and mean systolic velocities of 16 +/- 1.4 and 11 +/- 0.8 cm/s, respectively. Prestenotic flow velocities were not significantly different from normal control values, but a wide range of poststenotic flow disturbances were detected. Analysis of the 20 study patients did not reveal significant differences in poststenotic compared with prestenotic flow. A subgroup analysis of 12 patients with severe left anterior descending coronary artery stenoses was performed, and reversed poststenotic systolic flow was seen in 9. Prestenotic peak and mean systolic velocities were 16.5 +/- 1.7 and 11.9 +/- 1.1 cm/s, respectively, and were significantly altered downstream of the stenoses at -22.7 +/- 17.2 and -15.9 +/- 10.9 cm/s (P < .05 and P < .01, respectively). Reversed systolic flow was seen only distal to severe left anterior descending coronary artery stenoses and did not correlate with retrograde collateral filling as determined by preoperative coronary angiography. Moderate stenoses appeared to increase both systolic and diastolic components of poststenotic flow. CONCLUSIONS: Epicardial Doppler ultrasound with a miniature transducer identifies coronary stenoses and associated blood flow disturbances. Compared with moderate lesions, severe stenoses demonstrated different poststenotic flow patterns. Intraoperative use of this technique may determine the hemodynamic significance of coronary stenoses.

Adult↗

PubMed2005

Field computation for two-dimensional array transducers with limited diffraction array beams.

A method is developed for calculating fields produced with a two-dimensional (2D) array transducer. This method decomposes an arbitrary 2D aperture weighting function into a set of limited diffraction array beams. Using the analytical expressions of limited diffraction beams, arbitrary continuous wave (cw) or pulse wave (pw) fields of 2D arrays can be obtained with a simple superposition of these beams. In addition, this method can be simplified and applied to a 1D array transducer of a finite or infinite elevation height. For beams produced with axially symmetric aperture weighting functions, this method can be reduced to the Fourier-Bessel method studied previously where an annular array transducer can be used. The advantage of the method is that it is accurate and computationally efficient, especially in regions that are not far from the surface of the transducer (near field), where it is important for medical imaging. Both computer simulations and a synthetic array experiment are carried out to verify the method. Results (Bessel beam, focused Gaussian beam, X wave and asymmetric array beams) show that the method is accurate as compared to that using the Rayleigh-Sommerfeld diffraction formula and agrees well with the experiment.

Algorithms↗

PubMed1992

Simulation of B-scan images from two-dimensional transducer arrays: Part I--Methods and quantitative contrast measurements.

Recently, theoretical investigations of the beamforming capability of two-dimensional (2-D) transducer arrays have characterized the array parameters required to steer a symmetrically focused ultrasound beam up to 45 degrees off-axis. These investigations have also shown that the number of elements in a steered 2-D array can be dramatically reduced by using a sparse set of elements, randomly distributed throughout the aperture of the transducer. The penalty paid for the use of a sparse array is the development of a "pedestal" sidelobe in the beam profile, the amplitude of which increases as the number of elements in the array decreases. In this paper the potential of 2-D arrays for medical imaging is assessed by simulating B-scan images of spherical lesions, both cystic and scattering, embedded in a large random scattering volume. Similar contrast characteristics over a range of cyst sizes are demonstrated for a dense 2-D array and a sparse array with 1/8th the number of elements, both operating at 5 MHz. A 32nd order sparse array is shown to perform at a reduced level, producing unacceptable artifactual echoes within images of cysts. The 8th order sparse array pattern has been fabricated on a fixed-focus poly(vinylidene difluoride) transducer using photolithographic techniques. Experimental images from this transducer are used to verify some of the theoretical predictions made in this paper. Comparisons between simulated B-scan images from linear and 2-D phased arrays are presented in a companion paper.

Artifacts↗

PubMed1978

Failure of disposable domes to prevent septicemia acquired from contaminated pressure transducers.

Between January and June 1976, eight cases of primary bacteremia due to Enterobacter cloacae occurred in patients after open-heart surgery in a hospital in Connecticut. Epidemiologic studies implicated radial arterial catheters as the route of acquistion of E cloacae, and bacteriologic studies confirmed arterial pressure transducers as the sources of bacteria. Prospective studies indicated that the disposable domes from the pressure transducers did not prevent the spread of bacteria from contaminated transducers to the arterial catheters. This is the first report of transducer-acquired bacteremic infections occurring with the use of disposable domes. Although disposable domes may decrease the chances of cross-contamination of circuits for monitoring pressure, they do not, as previously thought, eliminate the risk of bacteremia from this source.

Blood Pressure↗

PubMed1993

Sonographically guided laparoscopy and mediastinoscopy using miniature catheter-based transducers.

Miniature ultrasound transducers (12.5 MHz) housed in 9 Fr catheters were passed through a laparoscope or mediastinoscope to image a variety of normal and abnormal structures within the peritoneal cavity and mediastinum in 20 patients. These transducers made it possible to visualize the gallbladder and bile ducts and evaluate for the presence of stones, to detect masses and provide guidance for their aspiration or biopsy, and to image the internal structures of the ovary and fallopian tube. In addition, these miniature transducers were used to locate such normal vital structures as blood vessels, thereby allowing the surgeon to decide on the best approach for dissection during mediastinoscopy. During conventional surgery, the surgeon or gynecologist can palpate an area of abnormality not directly visualized. However, during laparoscopy and mediastinoscopy direct palpation is not possible. Therefore, it is important to find another method to determine what structures lie beneath the visualized surface. These miniature ultrasound transducers appear to offer a means for making such determinations.

Adult↗

PubMed1999

Effects of transducer frequency and output power on the ultrasonographic contrast produced by Optison using fundamental and harmonic imaging techniques.

This in vivo study demonstrated the effects of transducer frequency and output power on the sonographic contrast produced by Optison during continuous ultrasonographic imaging in both fundamental and harmonic modes. During fundamental imaging, Optison produced greater contrast intensity while imaging at higher transducer frequencies. However, in the harmonic mode, lower imaging frequencies caused Optison to produce more intense myocardial enhancement. Regardless of imaging mode, increases in transducer output power caused decreases in both contrast intensity and contrast duration produced by Optison. Proper selection of transducer frequency and output power will help optimize the quality and duration of contrast produced by Optison during continuous ultrasonographic imaging.

Albumins↗

PubMed1983

[The use of a heat flux transducer for measuring non-evaporative heat exchange in man].

Ten healthy males, 20-45 years of age, were subjected to measure the non-evaporative heat exchange by using thermal flux transducers at different ambient temperatures, atmospheric pressures, air velosities and body postures. Fifteen thermal flux transducers were mounted on each subject at the same points as Winslow's method (1936) proposed for calculating mean skin temperature. Non-evaporative heat exchange (Q) was computed from 15 heat flux measurements using the same weighting formula of Winslow. Evaporative heat loss (E) was estimated from body weight changes measured on a Potter bed scale. Metabolic heat production (M) was estimated indirectly from the oxygen consumption and carbon dioxide production. Mean body temperature was estimated from mean skin temperature calculated from 15 points and the esophageal temperature. In a wide variation of environmental conditions the summation of body heat storage during the experiment equaled that of the heat that reduced E and Q from M. However, the transducer seemed to overestimate the non-evaporative heat exchange of the body at high ambient temperatures where sweat rate was very high. The above results suggest that thermal flux transducer is a reliable tool in estimating non-evaporative heat exchange under a wide variation of environmental and physical conditions when used with great caution.

Adult↗

PubMed2000

The effect of the "floating mass transducer" in the middle ear on hearing sensitivity.

OBJECTIVE: The Vibrant soundbridge is a semi-implantable hearing device; the transducer is implanted, coupled directly to the incus. The influence of the implant surgery and the presence of the transducer on hearing sensitivity was studied in six implanted subjects. STUDY DESIGN: Longitudinal case reports. SETTING: Tertiary referral center. Subjects. The subjects had bilateral sensorineural hearing loss with an average hearing loss of 40 to 70 dB HL. RESULTS: In five of the six subjects, no long-term effect of the surgery or the presence of the transducer on hearing thresholds was found. In the remaining subject, a deterioration in hearing thresholds was found of 20 dB, with a high and low frequency component. In the 2-kHz region, hearing sensitivity was not deteriorated. In addition, chronic negative middle ear pressure occurred after surgery. CONCLUSION: Hearing thresholds did not change significantly in five of the six patients after placement of the "floating mass transducer." It was speculated that the high frequency component of the hearing deterioration in the remaining patient was caused by cochlear damage caused by the surgery and that the low frequency component was caused by the chronic aeration problems indirectly related to the surgery.

Audiometry, Pure-Tone↗

PubMed2000

[Analysis of impulse response of rectangular ultrasound transducer].

A new expression for calculating the impulse response of rectangular pistonlike transducers, proper to any points of acoustic field, is presented. The radiated field of ultrasound transducer can be analyzed using impulse response method, avoiding paraxial and farfield approximation. The velocity potential at an observation point is expressed as the convolution of the excitation velocity and the impulse response. A time-amplitude shift method for the far field impulse response of small aperture transducers is presented. The radiated field of rectangular transducers is calculated through the new method and the previous method and excellent agreement is observed.

Algorithms↗

PubMed2001

Force transducer design: a new approach combining nonlinear finite element analysis and robust design.

Designing a strain gage based force transducer is considered more of an art than an engineering process. Only general guidelines are available, and many trial and error iterations are needed to optimize the geometry and minimize the errors caused by nonlinear behavior of the structure. A new method, based on nonlinear finite element analysis and robust design principles, is proposed. A matrix of experiments considers relevant geometric and loading parameters. The behavior of the structure under different combinations of these parameters is determined by calculating the strain at different locations (suitable for strain gage installation) using finite element models. The nonlinear behavior of the transducer is identified by comparing the results of the nonlinear finite element analysis with those obtained using a linear finite element analysis. A signal-to-noise ratio is defined to quantify the nonlinearities and how the considered parameters affect them. An analysis of variance is employed to determine their relative influence. Based on the results of the statistical analysis, it is possible to identify the best value for each geometric parameter that would reduce, if not eliminate the nonlinearities. Once these optimal geometric parameters are chosen, a prototype can be built, instrumented with strain gages, and tested, to validate the obtained design. To illustrate this new proposed methodology, and appreciate its advantages over current practice of designing a force transducer, an example of the step-by-step procedure is illustrated considering a thin-wall cylindrical transducer.

Equipment Design↗

PubMed1976

A calibration system for catheter transducer pressure measurement.

A patient-isolated calibration system is described for use with catheter transducer physiological pressure measuring apparatus. A subatmospheric calibration pressure is applied to the rear of the transducer diaphragm, the latter isolating the patient hydraulic circuit from the calibration system. The calibration system need not therefore be sterile and remains assembled to the transducer table. Risk of air embolus in the patient and of over-pressurising the transducer during calibration are minimised. Simplification of the hydraulic circuit reduces the chance of air entrapment, improving frequency response and reproducability of results and preparation time is greatly reduced. The system is easy to make and has proved simple, rugged and reliable in use.

Catheterization↗