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At least 379 records · Page 21Linked to original sources
PubMed1999

The PEP transducer: a new way of measuring respiratory rate in the non-intubated patient.

OBJECTIVES: To explore the use of a pyroelectric polymer (PEP) film as a transducer for a simple respiratory rate monitor and to evaluate the transducer in a laboratory situation. METHODS: Laboratory evaluation of a new pyroelectric transducer for measurement of respiratory rate. RESULTS: The amplified output from the pyroelectric film produced an excellent respiratory trace when used on a normal spontaneously breathing subject. The transducer is cheap, robust, and reliable. CONCLUSIONS: PEP films have the potential to be used as cheap and effective transducers in respiratory rate monitors for non-intubated patients. In the laboratory, they have many desirable characteristics which should now be evaluated in a clinical setting.

Evaluation Studies as Topic↗
PubMed1979

Comparability and reproducibility of apex cardiogram recorded with six different transducer systems.

A comparison was made in 7 dogs of the results obtained by 6 different apex cardiographic transducers applied before, during, and after controlled infusion of angiotensin and isoprenaline. The electrocardiogram, internal phonocardiogram, aortic and left ventricular pressure using a Telco micromanometer, and apex cardiogram were recorded simultaneously on magnetic tape and paper. Digital computer techniques were used to derive various measurements. The comparison of the 6 transducer systems was made expecially with respect to measurements derived from the normalised derivative, calculated using total as well as developed pressure or displacement. Measurements derived from left ventricular pressure were very reproducible. Differences in results of 'contractility' indices varied between 0.5 and 1.9 per cent. Indices from the apex cardiogram using 6 different transducer systems showed variations up to 20 per cent, with mean values varying between 3.2 and 8.1 per cent. There was a systematic deviation for one transducer system, which was responsible for a significant part of the observed variability. It may be concluded that in order to assure maximal reproducibility, technical characteristics of the apex cardiograph transducer should be taken into account and an optimal recording technique should be used.

Angiotensins↗
PubMed1978

A miniature transducer for recording intestinal motility in unrestrained chronic rats.

An extraluminal strain gage force transducer has been developed for recording gastrointestinal motility in small animals such as rats. Two commercial strain gages are bonded and wires attached to form half a Wheatstone bridge. The device is placed between silicone sheeting and prepared for implantation. As many as six implanted transducers can record simultaneously contractions and tone variations of circular or longitudinal gastrointestinal muscles. The transducers have been implanted in more than 20 rats, with some units lasting up to 4 mo. Furthermore, good relationships exist between intraluminal pressure waves registered by a small intraluminal balloon and gut contractions registered by the transducer. The transducers are a useful and accurate tool for rodent gut motility studies.

Animals↗
PubMed1979

A technique for measuring frequency response of pressure, volume, and flow transducers.

A device and methodology is presented for testing the frequency response of pressure, volume, or flow transducers. Also reported are responses of selected transducers of all three types over the range of 2--120 Hz. Several pressure transducers tested had good frequency response when connected to the test system with a minimum of interconnecting fittings; others did not. Use of additional connectors degraded the response as did the addition of air-filled catheters. The frequency response of the pneumotachometers tested were influenced largely by the response characteristics of the associated pressure transducer and interconnecting fittings. These results emphasize the need to test the response characteristics of any transducer with specific connectors and fittings that are to be used to make the actual measurements of pressure, volume, or flow.

Mathematics↗
PubMed1990

Transducer characterization from pressure amplitude distribution measurements using a Kalman filter as parameter estimation algorithm.

The amplitude and frequency contents of a received ultrasound pulse depends on the spatial pressure amplitude distribution of the sound field, as produced by the transducer in the medium, and on the position and orientation of the reflecting surface in this field. Often, the geometry of the reflecting surface and the acoustical properties of the medium are known or can be estimated. Then it is practical to determine the transducer parameters in order to calculate the distortion of a reflected ultrasound pulse. Apart from geometrical parameters such as size and mechanical focusing, the surface velocity amplitude distribution (SVAD) of a transducer is of major importance. For some transducer configurations this SVAD may be described with a limited number of parameters. This paper presents a method, based on a Kalman filter algorithm, to assess the transducer parameters by measurement of the spatial sound field pressure amplitude distribution in various planes for different emission frequencies. Comparison of the measured pressure amplitudes with those calculated using the estimated values of the parameters shows that this method yields reliable results.

Acoustics↗
PubMed1992

Simulation of B-scan images from two-dimensional transducer arrays: Part II--Comparisons between linear and two-dimensional phased arrays.

Two-dimensional (2-D) arrays have been proposed as a solution to the degradation in medical ultrasound image quality occurring as a result of asymmetric focusing properties of linear phased array transducers. The 2-D phased transducer array is also capable of electronically steering the symmetrically focused ultrasound beam throughout a three-dimensional volume. In a companion paper the potential of 2-D transducer arrays for medical imaging has been investigated using simulated B-scan images. In this paper, the advantages of 2-D over linear transducer arrays is demonstrated by simulating images of spherical cysts embedded in a large scattering volume. The large elevation beamwidth in the nearfield of a 5 MHz linear phased transducer array results in a severe reduction in the image contrast measured between a 4 mm diameter cyst and the surrounding scattering media. By employing a 2-D array with symmetric focusing, the contrast between the cyst and surrounding scatterers is significantly improved. The use of additional elements in the elevation direction of a linear array is also investigated. In this case the additional elements are included only to focus, but not to steer the ultrasound beam. Using the contrast characteristics of a 4 mm diameter cyst, it is shown that relatively few elevation elements are required to significantly improve the nearfield imaging capability of the linear array.

Artifacts↗
PubMed1995

Phase aberration correction in two dimensions using a deformable array transducer.

Phase aberrations due to tissue inhomogeneities degrade medical ultrasound images by disrupting the ultrasound beam focus. Currently, phase correction algorithms are implemented by adjusting the electronic phase delays uses to steer and focus the ultrasound beam. This means that a two-dimensional array is necessary to completely correct two-dimensional aberrations in tissue. However, two-dimensional arrays are a complex option due to their large number of elements and poor sensitivity. Instead of using a full two-dimensional array, a new technique is proposed, similar to one used in adaptive optics, which used a deformable transducer of significantly fewer channels for two-dimensional phase correction. Phase correction in azimuth is achieved by altering the electronic phase delay of the element. However, phase correction in elevation is achieved by tilting the element in elevation with a piezoelectric actuator. Comparison of simulations of the new phase correction transducer versus the conventional phase correction technique have shown that a deformable 1 x N or 2 x N transducer can approach the image quality of a 4 x N two-dimensional array or greater. A prototype 1 x 32 array with eight low frequency piezoelectric actuators has been constructed such that every four ultrasonic transducer elements in azimuth are mounted on one independently controlled actuator. This prototype transducer was used to test the ability of a deformable array to produce real time phased array scans and to simulate on-line phase correction by tilting the elements in the elevation direction.

Algorithms↗
PubMed1997

Multiple-transducer scheme for scanning tomographic acoustic microscopy using transverse waves.

We propose a new type of multiple-transducer scheme with functions of multiple-angle and multiple-frequency tomography for scanning tomographic acoustic microscopy (STAM) using transverse waves. We review the data acquisition system and mode conversion of the acoustic waves for STAM and the multiple-angle and multiple-frequency tomography. Our multiple-transducer scheme has three insonification angles and three resonance frequencies in order to operate, in the transverse wave mode, multiple-angle and multiple frequency tomography for STAM. In order to evaluate the performance of our transducer scheme, we have simulated tomographic reconstruction with a back-and-forth propagation algorithm. Simulation results show that our multiple-transducer scheme is capable of obtaining good resolution with transverse wave mode and multiple-frequency tomography. We also show that our multiple-transducer scheme is an efficient rotation tool for a number of projections.

Microscopy↗
PubMedDate not supplied

Laboratory evaluation of pressure transducer domes containing a diaphragm.

Pressure transducers are being used with increasing frequency in patient care. The recent availability of sterile transducer domes containing a diaphragm provides a means for reducing the risk of bacteremia when using these devices. The present studies measured the effect of diaphragm domes on the accuracy of pressure measurement. The sensitivity and frequency responses of 5 pressure transducers utilizing diaphragm and nondiaphragm domes were compared. The results indicate that the type of dome utilized and the method of dome application can significantly modify pressure transducer performance. The data are useful in providing optimal accuracy and reliability of pressure measurments when using a diaphragm dome, pressure transducer combination.

Blood Pressure Determination↗
PubMed1998

The design of a vibration transducer to monitor the integrity of dental implants.

Bone-anchored titanium implants are being used increasingly to provide support for prostheses replacing missing teeth in edentulous and partially dentate patients. A technique is required to monitor bone formation at the implant-tissue interface during healing, and also to check whether there has been bone loss from around the top of the implant. One possible method is to screw a beam into the implanted fixture and to measure the first flexural resonance frequency of the resulting system. This resonance frequency is affected by both the exposed length of fixture and the stiffness of the interface between the implant and the bone. This paper describes the design of a beam-like transducer for clinical trials of the technique. The sensitivity of the transducer resonance frequency to the changes of interest is dependent on the thickness and length of the beam element. However, the choice of these dimensions is constrained by the need to avoid closely spaced resonances. The performance of different transducer shapes and the influence of the thickness and length of the beam element in the transducer has been studied. The results have been used to finalize a transducer design for the clinical trials.

Biomechanical Phenomena↗
PubMed1976

Pressure transducers as a source of bacteremia after open heart surgery. Report of an outbreak and guidelines for prevention.

During four weeks in 1974, eight (26 percent) of 31 intensive care unit patients who had undergone open-heart surgery developed symptomatic Pseudomonas cepacia bacteremia in the intensive care unit one to three days after the open-heart surgery. An investigation demonstrated that operating room pressure transducers were being contaminated during cleaning with a detergent that contained P cepacia at the rate of 10(4) organisms per milliliter and that the organisms were transmitted to patients after open-heart surgery as a result of one to three days of contact with transducer-monitoring lines used in the operating room and brought to the intensive care unit with the patient. Pressure-transducer contamination, a frequently unappreciated but preventable cause of nosocomial bacteremia, can be minimized by sterilizing transducers between use on different patients by paying strict attention to aseptic technique when setting up, calibrating, and using monitoring systems; and by changing transducers, tubing, and monitoring fluid for each monitored patient at regular intervals.

Antisepsis↗
PubMed1990

[A transducer for the measurement of torque transmitted to abutment teeth of removable partial dentures].

A transducer for the measurement of torque transmitted to abutment teeth of removable partial dentures was newly developed. The transducer was composed of a right cylinder (12.0 mm x 3.5 mmø) made of phosphor bronze as the torsion bar, to the surface of which two strain gauges (KFC-2-D2-11, KYOWA) are adhered symmetrically about the axis of the bar. Torque transmitted to the transducer was detected and evaluated as tensile strain and compressive strain on the torsion bar surface by means of strain gauges. The transducer was small enough to be easily applied to removable partial dentures for the measurement of torque transmitted to crowns of abutment teeth, and showed satisfactory precision (The instrumental error in measurement was within 3%). In the present study, the newly developed transducer was revealed to be useful for the measurement of torque transmitted to crowns of abutment teeth by removable partial dentures.

Dental Abutments↗
PubMed1981

Sonographic transducer performance cannot be evaluated with clinical images.

A wide variety of in vitro tests, some too sophisticated to perform in a clinical setting, is available to provide information on the performance of sonographic transducers. However, it is a common belief among many clinicians that clinically generated in vivo images are a necessary and sufficient test of sonographic image quality. In order to examine the sensitivity and reliability of quality judgments made from clinical images, some transducers that failed elaborate in vitro tests were used to create clinical scans. In a discrimination test between clinical images created by normal and abnormal transducers, a panel of experienced sonographers was unable to consistently identify scans made by transducers with major flaws in the beam uniformity when the defect occurred only in the near field. The study confirms that rigorous in vitro tests provide unique information on transducer performance and can reveal performance flaws that are overlooked in routine clinical images.

Humans↗
PubMedDate not supplied

A compliance-independent pressure transducer for biomedical device-tissue interfaces.

The measurement of the interface pressure between a biomedical device and part of the human body is useful to improve the performance and safety of such devices during design. Testing of a selection of existing interface pressure transducers has demonstrated that many are dependent on device and tissue compliance. Such a transducer is useful only in an application where it has been calibrated for specific device-tissue compliance combinations. To overcome this limitation, the authors developed an interface pressure transducer whose output signal is not affected by changes in interface compliance. This enables the transducer to quantitatively measure pressure in many applications without the need to calibrate it for varying compliance conditions. Surgical retraction and surgical tourniquets were selected as demonstration applications for the developed transducer, because they represent a wide spectrum of device and tissue characteristics and properties, and are in common use.

Animals↗
PubMed1988

[A study of the cardiotocograms recorded by a separated 1MHz ultrasound transducer].

Fetal heart rate records were obtained in 12 antepartum and 13 intrapartum cases, with an ultrasonic Doppler transducer with five separated crystals and a conventional transducer. The loss of the FHR record due to increased noise in 30 minutes before delivery ranged from 1.1 to 23.2% (6.4 +/- 6.5%) in the separate type transducer, and it was 0.6 to 29.9% (10.5 +/- 7.6%) in the conventional one. During the 5 minutes before delivery, it was 3.3 to 58.0% (20.2 +/- 18.5%) in the separate type, and 3.3 to 70.0% (31.6 +/- 19.5%) in the conventional one. Clearer FHR records were obtained with the use of the separate type than the conventional one (p less than 0.05). Noise was mostly recorded in the 5 minutes before delivery. In the NST, the loss of the FHR record due to maternal posture change decreased when the new transducer (p less than 0.05) was used. The loss was 0 to 56.7% (14.9 +/- 18.2%) with the new type, and 2.0 to 100% (42.9 +/- 36.4%) with the conventional one for the maternal posture which showed the worst record. By using the separate type transducer, maternal posture need not to be limited in the NST, and the somatic and mental discomfort is less than when the conventional one is used.

Female↗
PubMed1983

Transducers for ultrasonic limb plethysmography.

Shifts in blood content of tissues cause dimension changes which can be measured with an ultrasonic dimension gauge. We have previously described the construction of a limb plethysmograph which uses this principle. Although other workers have described the construction of ultrasonic dimension gauge transducers intended for use inside animals, these transducers are not ideal for plethysmographic application. In this report we describe the design, construction, and performance characteristics of transducers suitable for limb plethysmography. Good signal quality is obtained with minimum care in transducer placement. These transducers incorporate a rugged external housing which provides for simple attachment to the calf by use of double-sided adhesive collars.

Humans↗
PubMed1981

[Comparative trial of a new epidural transducer for intracranial pressure monitoring (author's translation)].

The measurement of intracranial pressure using a new epidural pressure transducer has been compared with the classical method of measuring intraventricular pressure. Comparative measures in vitro have been carried out with acid of an enclosure in which the hydrostatic pressure can be varied. Four positions of the epidural transducer with the respect to the dura mater have been studied; of these, only one, coplanarity between the epidural transducer and the dura, gives an excellent correlation between values of epidural pressure and hydrostatic pressure. Twenty-nine prolonged recordings have been carried out in vivo. Fifteen of these have given comparable recordings for E.D.P. and I.V.P. In the other fourteen cases the recordings were considered non comparable, either because of a significant difference between the average values of E.D.P. and P.I.V. or because the two curves were not parallel. It is considered that these differences are due to the problems of correctly positioning the epidural pressure transducer and hence an inability to achieve the condition of coplanarity. These problems should be resolved by a modification of the method of positioning the epidural pressure transducer. The use of this type of materiel is of interest for the monitoring of the I.C.P. of neurosurgical patients, as the epidural pressure follows the variations of I.C.P. and indicates pressures waves when they exist.

Epidural Space↗
PubMed1994

Comparison of three types of ultrasound transducers in evaluating the amniotic fluid index.

The purpose of this study was to determine whether there was good correlation between amniotic fluid index measurements obtained with different types of ultrasound transducer. Women undergoing obstetric ultrasonography for multiple indications between 26 and 40 weeks' gestation had the four-quadrant amniotic fluid index measured with three ultrasound transducers: 3.5-MHz linear, 3.5-MHz sector and 3.5-MHz convex. Pearson product-moment correlation and linear regression analysis were utilized to compare the amniotic fluid index values. Sixty-five women participated in the study. A statistically significant correlation was noted between the three ultrasound transducers evaluated (P < .001). Placental location did not appear to affect the results. Amniotic fluid index values obtained with the sector or convex transducers were as reliable as those obtained with the "gold standard" linear transducer and may be interpreted in the same manner.

Adolescent↗