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PubMed1998

Ultrasound transducers.

Sonography is facing a new technological revolution. Recent advances in ultrasound technology are increasing spatial, contrast and vascular resolution. Transducers play an important role in achieving these improvements; their technology is widely reviewed in this paper. Physics and technology relate to image quality and its clinical potentials. Large annular arrays made the progression of imaging quality; they are still a very good choice for scanning superficial structures. New broadband linear arrays approach their quality and allow to visualize the flow within very small vessels; they permit new harmonic imaging that reduces image noise and clutter caused by the body wall. New advances include digital beamformers that work at their best when coupled with broadband technology. New multi-layer and multi-array scanheads improve the signal-to-noise ratio and increase the transmitted energy. New transducers and imaging algorithms allow real-time acquisition of large fields of view and even of three-dimensional volumes. Further refinement of two-dimensional matrix transducers will produce high-definition volumetric images. Evolution in transducers technology permits to interrogate the vessels with higher Doppler frequencies extending the anatomical perception and opening new fields of investigation.

Acoustics↗
PubMed1992

[Monitoring of intracranial pressure with intraparenchymal fiberoptic transducer. Technical aspects and clinical reliability].

A fiberoptic intracranial pressure transducer (Camino) was assessed prospectively in 100 patients. In all, 122 sensors were inserted intraparenchymally at the bedside, without the help of a neurosurgeon. Before the procedure, patients were given 2 to 4 mg of phenoperidine. The scalp was opened over a few millimeters in the frontal paramedian area. A burr holc was made with a 2 mm bit. The dura mater was opened and a hollow screw inserted in the diploë. When the zero of the transducer had been obtained, a 5 cm length was inserted within the screw. The transducer was then about 5 mm deep within cerebral parenchyma. The procedure took an average of about 15 min. An intracerebral haematoma around the transducer occurred five times. One had to be drained surgically. There were no infectious complications. The daily baseline drift was about 0.3 mmHg. The system seemed to be reliable: there was close agreement between the intracranial pressure (ICP), neurological status and CT scan findings. In trauma cases, there was also good correlation between mean ICP and the basal cistern obliteration score, finally, ICP became equivalent to mean arterial blood pressure in all brain dead patients. It is concluded that this system may be used in all cases where ICP requires to be monitored, even when the lateral ventricles are no longer visible, or when craniotomy has been performed. This will most probably result in a more extended use of ICP monitoring in neurosurgical intensive care.

Adolescent↗
PubMed1990

The anatomical location of the transesophageal echocardiographic transducer during a short-axis view of the left ventricle.

This study was performed to clarify the location of a transesophageal echocardiographic (TEE) transducer when obtaining the short-axis view of the left ventricle (S-LV). The depth of the probe tip from the incisors when obtaining a S-LV, the relationship to the diaphragm, and the location of the cardia of the stomach using a gastroscope attached to the TEE probe were measured in 24 patients undergoing coronary artery bypass grafting. The location of the transducer relative to the cardia and diaphragm was determined. The study demonstrated that when obtaining a S-LV, the transducer was in the stomach in 72.7%, at the cardia in 13.6%, and in the esophagus in 13.6% of the patients. The predominantly intragastric position of the transducer suggests that gastric diseases should be included as contraindications to TEE. When the probe was advanced about 40 cm from the incisors, some resistance was often encountered by the TEE operator at about the level of the diaphragm. Careful manipulation is mandatory to avoid tissue damage by the probe. Visualization of the S-LV can be disturbed by gas in the stomach. This is a specific problem in anesthetized patients because gas is often pushed into the stomach at the time of induction.

Adult↗
PubMed1997

Toroidal geometry: novel three-dimensional intracardiac imaging with a phased-array transducer.

Recent advances in small, linear-array transducers have opened new avenues for three-dimensional image acquisition from an intracardiac approach. The purpose of this study was to introduce a novel method of image acquisition using toroidal geometry, explore its fidelity of reproduction of three-dimensional cardiac anatomy, and determine whether a whole-heart scan is achievable. Acquisition was accomplished through 360-degree incremental rotation of a rigid endoscope with a side-mounted ultrasound transducer. The procedure was first tested with the use of a gelatin model to define far-field slice resolution with 1.8-degree rotational increments. Comparison of three-dimensional scans of cardiac specimens with corresponding photographs confirmed that toroidal geometry can provide a high-quality display of structures from all sides. We conclude that whole-heart three-dimensional scanning from within the cardiac chambers is possible with toroidal geometry. The quality of depicted anatomy depends on transducer location within the heart, distance from the transducer, density of slices, and image resolution. The potential of intracardiac three-dimensional ultrasound imaging includes detailed spatial evaluation of cardiac morphology, determination of appropriate placement of investigative or therapeutic devices (catheters, closure devices, etc.), and assessment of cardiac function.

Animals↗
PubMed1998

Construction and testing of ultrasound broadband transducers for blood flow sensing.

Ultrasound pulsed transducers are very important for blood flow measurement and imaging. Ultrasound pulsed transducers are broadband transducers which require relatively heavy external damping to achieve a good axial resolution and an adequately wide bandwidth. In this work, using a simple RLC circuit model, broadband transducers were constructed and tested. The results are quite applicable for pulsed Doppler blood flow measurements.

Equipment Design↗
PubMed2001

Feasibility of continuous transthoracic cardiac imaging using a novel ultrasound transducer.

BACKGROUND: The feasibility of hands-free transthoracic continuous ultrasonic cardiac imaging has not been demonstrated previously. We developed a 2.5-MHZ spherical transducer mounted in an external housing to permit steering in 360 degrees (CONTISON). The external housing was attached to the chest wall using an adhesive patch. METHODS AND RESULTS: The transducer was placed in the third or fourth interspace at the left sternal border to permit imaging of the left ventricle (LV) in its short axis and attached to the chest wall. The transducer then was attached to an ultrasound machine. Ten normal subjects and 20 patients with previous myocardial infarction were studied. The following maneuvers were performed at the beginning of the study: (1) The patient was rotated from the supine position (0 degrees ) in 20 degrees increments to the left lateral decubitus position (90 degrees ). The echocardiogram was displayed continuously and was recorded on videotape (parasternal short-axis view) at 0 degrees, 20 degrees, 40 degrees, 60 degrees, 80 degrees, and 90 degrees. (2) The patient was returned to the supine position and an echocardiogram was obtained. The patient was then seated up 20 degrees, 40 degrees, 60 degrees, 80 degrees, and 90 degrees by using the controls on the bed. (3) The patient then was returned to the supine position and the echocardiogram was displayed continuously on the monitor. The echocardiogram was recorded every 15 minutes for a period of 4 hours. All segments of the LV were visualized in the supine position and during lateral rotation (0 degrees -90 degrees ). Thus, body position did not affect the image. All segments of the LV were visualized during sitting up (0 degrees -90 degrees ), and all segments were visualized during the 4 hours of imaging. The patients were able to move around without distortion of the image. CONCLUSION: The CONTISON transducer permitted continuous imaging of LV wall motion. Body position did not affect interpretation of wall motion. This device has potential applicability in monitoring LV function in the intensive care setting.

Adult↗
PubMed1994

[Significance of intravascular ultrasound in arteriosclerotic calcified intima plaques: in vitro comparison of 20 and 12.5 MHz transducers].

The aim of this in vitro study was to analyze the diagnostic performance of intravascular ultrasound (IVUS) in vessel wall calcifications and to compare the accuracy of mechanical 12.5 and 20 MHz transducers. Fourty-three sections of 10 vessels with signs of arteriosclerotic disease on pathologic examination were examined. Slices 500 microns thick were obtained and examined radiographically at 9 fold magnification. In each section, identical segments were defined, amounting to a total of 344 segments. The IVUS sections were analyzed by 3 experienced readers. For statistical evaluation ROC analysis was performed using magnification radiography as a reference. An area under the curve (AUC) of 0.79 was obtained for the 12.5 transducer and of 0.83 for the 20 MHz transducer. Additionally, sensitivity, specificity, and accuracy were determined. Sensitivity depended on the morphology, size, and density of the calcified lesions. We therefore conclude that the sensitivity of intravascular ultrasound concerning calcified arteriosclerotic plaques is limited and that there is no significant (p < 0.01) difference between mechanical 20 and 12.5 MHz transducers in examining iliac arteries.

Angiography↗
PubMed2002

Continuous recording of pulmonary artery diastolic pressure and cardiac output using a novel ultrasound transducer.

BACKGROUND: The feasibility of hands-free transthoracic continuous determination of pulmonary artery (PA) diastolic pressure (PAD) and cardiac output (CO) by Doppler ultrasound has not been previously demonstrated. We developed a 2.5-MHz spherical transducer mounted in an external housing to permit steering in 360 degrees (Contison). The external housing was attached to the chest wall using an adhesive patch. METHODS AND RESULTS: Fifty patients in the coronary care department who had PA catheters had Doppler ultrasound studies. The 2.5-MHz spherical transducer was placed at the left sternal border to permit imaging of the pulmonic valve and was attached to a commercial ultrasound machine. The PA was imaged and its diameter measured. The pulmonary flow velocity signal was recorded and the time velocity integral obtained. The CO was calculated as: CO = time velocity integral of the PA systolic flow velocity signal x pi diameter(2) divided by 4 x heart rate. The pulmonary regurgitation signal was then recorded and the end-diastolic velocity of the regurgitant signal was measured. Right atrial pressure was assessed from the jugular venous pressure or from the size and pulsatility of the inferior vena cava. The PADP was calculated as: PADP = 4 end-diastolic velocity of the regurgitant signal(2) + right atrial pressure. The CO, PADP, and pulmonary wedge pressure were recorded from the PA catheter immediately after the ultrasound studies. Serial data were obtained every half hour or 1 hour up to a maximum of 5 hours. Adequate Doppler signals were obtained in 43 patients. RESULTS: There was a good correlation between the PADP by Doppler versus PA catheter (r = 0.90, standard error of the estimate = 3.3 mm Hg); PADP by Doppler versus PA wedge pressure (r = 0.88, standard error of the estimate = 3.7 mm Hg); and CO by Doppler versus PA catheter (r = 0.92, standard error of the estimate = 0.7 L/min). CONCLUSION: The 2.5-MHz spherical transducer permitted accurate assessment of CO and PAD. This transducer could be of potential value in monitoring patients in the intensive care setting.

Adult↗
PubMed2006

Bone-conducted auditory brainstem-evoked responses and skull vibratory velocity measurement in rats at frequencies of 0.5-30 kHz with a new giant magnetostrictive bone conduction transducer.

CONCLUSIONS: A new giant magnetostrictive bone conduction transducer (GMT) measuring 8 mm (length) by 2 mm (diameter) is capable of outputting sounds over a wider range of frequencies than conventional electromagnetic transducers (EMTs). The GMT can vibrate the rat skull about 3-100 times faster than the EMT, especially above 2 kHz. OBJECTIVES: Since the GMT can generate high sound quality and output sounds above 10 kHz, we investigated the width of the frequency response of the GMT and evaluated its mechanical performance. MATERIALS AND METHODS: We chose Wistar rats to estimate the GMT performance by measuring the bone-conducted ABR and the skull vibratory velocity because their hearing frequency range extends from 0.15 kHz to 67 kHz. We also measured the bone-conducted auditory brainstem responses (ABRs) and the skull vibratory velocity of rats with the EMT. Skull vibratory velocity was measured with a laser Doppler vibrometer (LDV). RESULTS: The skull vibratory velocity at the ABR threshold obtained with each transducer was within the -35 to -50 dB range (0 dB re 1 mm/s). When 1 Vpp was applied to each transducer, the GMT had a higher velocity at frequencies of 2-30 kHz, and the EMT at frequencies of 0.5-1 kHz.

Animals↗
PubMedDate not supplied

ICP measurement control: laboratory test of 7 types of intracranial pressure transducers.

Intracranial pressure (ICP) monitoring has become an important parameter in the assessment of comatose patients, with raised intracranial pressure. The transducers in use have to fulfill the criteria of measurement accuracy, practicability and cost-effectiveness. However, these requirements are not always met in clinical practice. The need for ongoing quality control through independent laboratories remains. We have developed a laboratory set-up for the evaluation of intracranial pressure probes. Seven different types of currently used transducers have been tested for measurement accuracy. Under in vitro conditions 3 parameters were assessed: measurement accuracy, a 24 h drift and 10 day drifts. Tests for measurement accuracy were performed at increasing pressure levels of up to 80 mmHg. They were repeated 10 times per probe. This test allowed the simultaneous assessment of 5 different ICP probes. Drift was evaluated for 24 h and 10 days, at 6 pressure levels between 0 and 50 mmHg. Seven different types of ICP probes were tested (HanniSet, Camino, Codman, Spiegelberg, Medex, Epidyn and Gaeltec). Measurement accuracy was best with HanniSet probes. The maximum errors with this transducer were 3 mmHg. Camino and Codman showed similar results. Spiegelberg had slightly larger deviations. With Epidyn and Gaeltec the highest error were noted, up to 10 mmHg in the high pressure range. The 24 h drift was lowest with HanniSet (0.2 mmHg) and Camino (0.8 mmHg). The largest drifts were seen with Medex, Spiegelberg and Gaeltec (1.8 mmHg). Ten day drift was lowest with HanniSet (0.1 mmHg/day) and Codman (0.2 mmHg/day). The highest long-term drifts were found with Epidyn and Gaeltec (1.5 mmHg/day). Drift did not exhibit a linear pattern. After an initial rise in drift during the first 24-72 h, it decreased slowly during the next 7 days. Most ICP probes revealed measurement inaccuracy and drift. These results emphasize the necessity for ongoing evaluations of ICP probes. Therefore, tests for quality assurance are essential to establish a consistent standard of proficiency of ICP transducers.

Intracranial Pressure↗
PubMed1989

A transducer for recording fetal movements and sounds based on an inductive principle.

Recording fetal breathing movements requires a transducer with a large dynamic range. The compliance of the transducer should be matched to the compliance of the maternal abdominal wall in order to pass the very weak acoustic signal caused by heart sounds and fetal breathing movements on to the transducer. The output signal is stored on the hard disc of a 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 synchronisation of data and image. Substantial digital filtering is necessary to discriminate between actual breathing movements and other fetal activities. It is shown that by optimal adjustment of the transducer's compliance to that of the maternal abdominal wall individual breathing movements can indeed be measured.

Female↗
PubMed1993

A transducer for detecting foetal breathing movements using PVDF film.

Foetal breathing movement (FBM) in utero has come to play an important role in foetal diagnosis. FBM may be monitored using real time ultrasound imaging of the foetus in utero. Foetal breathing activities can also be detected by monitoring maternal abdominal wall movement in the frequency range of 0.5-2.5 Hz. This paper presents a transducer which detects FBM non-invasively by monitoring maternal abdominal wall movements. Foetal heart sounds can also be monitored. The transducer presented uses piezo-electric film as the transducing medium. Results from preliminary clinical trials of prototype transducers on 10 patients are discussed.

Female↗
PubMed1987

Oocyte retrieval under the guidance of a vaginal transducer: evaluation of patient acceptance.

Follicle puncture under the guidance of ultrasound has now been used for some years. The most important advantage of the ultrasound-guided technique compared with the laparoscopic technique is that the former can be performed under local anaesthesia. However, both the trans-vesical and the perurethral ultrasound-guided puncturing routes may be quite painful for the patient. For that reason we have developed a trans-vaginal follicle puncture technique using a vaginal transducer. The aim of this study was to evaluate the patients' experience of pain with this new technique. Scanning of follicles was performed using a specially designed vaginal transducer that makes the patients having a full bladder unnecessary. Local anaesthesia was applied as a paracervical block. Follicles were then punctured through the vagina with a needle inserted through a needle guide attached to the transducer. Fifty-one patients answered a questionnaire about their experience of the puncture procedure. Only 10% of the patients found the puncture painful. Ninety-eight per cent of the patients felt no anxiety about going through the procedure again. We therefore conclude that trans-vaginal oocyte pick-up using a vaginal transducer is very well accepted by most women.

Anesthesia, Local↗
PubMed1990

Administering audiometric speech tests via bone conduction: a comparison of transducers.

This study compared the intelligibility of speech delivered via three transducers: a TDH-39 earphone, a Pracitronic KH 70 bone vibrator, and a Radioear B-72 bone vibrator. CID W-1 spondees were presented to normal-hearing listeners via each transducer over a range of intensity levels. Functions relating the percentage of spondees correctly identified to stimulus level were similar for the three transducers, and notably, their slopes were comparable. This suggests that it is appropriate to use the W-1 word lists to determine speech reception thresholds (SRTs) with the KH 70 and B-72 bone vibrators, even though these word lists were originally developed for testing by air conduction. Our subjects also identified NU-6 monosyllabic words equally well for each transducer when the words were delivered at 40 dB above SRT. This result suggests that it is also valid to deliver the NU 6 speech test via the two types of bone vibrators.

Adolescent↗
PubMed1996

A clinical study of parenchymal and subdural miniature strain-gauge transducers for monitoring intracranial pressure.

OBJECTIVE: Previous studies have shown that a new strain-gauge MicroSensor (Codman/Johnson & Johnson Professional, Inc., Randolph, MA) for measuring intracranial pressure (ICP) performs well in the intraventricular space. We hoped to evaluate the MicroSensor in the subdural space and the brain parenchyma, because ICP is often measured in these compartments when the ventricles are difficult to cannulate. METHODS: Fifteen patients had simultaneous recordings of ICP from an externally transduced fluid-filled subdural catheter, a MicroSensor placed within the subdural catheter, and a nearby MicroSensor placed intraparenchymally in the right frontal lobe. RESULTS: The total number of valid simultaneous recordings of ICP was 95,946. A highly significant correlation was found between the tissue MicroSensor ICP (TMICP) and the subdural MicroSensor ICP (SMICP) (n = 95,946; r = 0.89; P < 0.00005), the TMICP and the fluid-transduced subdural catheter ICP (r = 0.86, P < 0.00005), and the fluid-transduced subdural catheter ICP and SMICP (r = 0.88, P < 0.00005). The mean simultaneous difference between the TMICP and the SMICP was 0.1 +/- 3.8 mm Hg with no obvious bias. The fluid-transduced subdural catheter ICP was 2.8 +/- 3.9 mm Hg lower than the TMICP and 2.7 +/- 3.9 mm Hg lower than the SMICP (P < 0.0005). The mean zero drifts of the tissue and subdural MicroSensors were 0.312 and 0.475 mm Hg/d, respectively. The tissue MicroSensor recordings showed the best quality wave form with the least damping. CONCLUSION: The strain-gauge MicroSensor is highly accurate and stable in the tissue and subdural spaces.

Brain↗
PubMed2005

The effects of mass loading the ossicles with a floating mass transducer on middle ear transfer function.

HYPOTHESIS: The aim of this study was to measure the mass loading effect of an active middle-ear implant (the Vibrant Soundbridge) in cadaver temporal bones. BACKGROUND: Implantable middle ear hearing devices such as Vibrant Soundbridge have been used as an alternative to conventional hearing aids for the rehabilitation of sensorineural hearing loss. Other than the obvious disadvantage of requiring implantation middle ear surgery, it also applies a direct weight on the ossicular chain which, in turn, may have an impact on residual hearing. Previous studies have shown that applying a mass directly on the ossicular chain has a damping effect on its response to sound. However, little has been done to investigate the magnitude and the frequency characteristics of the mass loading effect in devices such as the Vibrant Soundbridge. METHODS: Five fresh cadaver temporal bones were used. The stapes displacement was measured using laser Doppler vibrometry before and after the placement of a Vibrant Soundbridge floating mass transducer. The effects of mass and attachment site were compared with the unloaded response. Measurements were obtained at frequencies between 0.1 and 10 kHz and at acoustic input levels of 100 dB sound pressure level. Each temporal bone acted as its own control. RESULTS: Placement of the floating mass transducer caused a reduction of the stapes displacement. There were variations between the bones. The change of the stapes displacement varied from 0 dB to 28 dB. The effect was more prominent at frequencies above 1,000 Hz. Placing the floating mass transducer close to the incudostapedial joint reduced the mass loading effect. CONCLUSION: The floating mass transducer produces a measurable reduction of the stapes displacement in the temporal bone model. The effect is more prominent at high frequencies.

Acoustic Stimulation↗
PubMed1990

A comparison of response characteristics of airflow and pressure transducers commonly used in rhinomanometry.

Although the ranges in which pneumotachographs evidence linear output to static flows are documented in the literature, measures of output reliability or the stability of calibration functions resulting from the input of dynamic nonsinusoidal flows (such as those which occur during nasal breathing) have not been investigated. Furthermore, it is not known whether the type of requisite pressure transducer used in conjunction with the pneumotachograph influences the pneumotachograph's linearity, output reliability, or dynamic response. To provide information on these points, we determined the dynamic and static responsiveness of three pneumotachographs commonly used in rhinomanometry, in combination with three requisite pressure transducers. In general, a) output reliability depended on the pneumotachograph/pressure transducer combination and was not readily predictable from the reliabilities of the individual components, b) heating increased pneumotachograph reliability, and c) differences in accuracy existed among transducer combinations at high, but not low, flow frequencies. In addition, results from the calibration syringe study (in which the pneumotachograph is calibrated with dynamic non-sinusoidal flows) suggested that: a) a single calibration factor, as supplied by most pneumotachograph manufacturers, is inadequate for accurately measuring the full range of flows produced in sniffing and breathing tasks; b) the measurement of complex waveforms, even when the dominate frequencies of such waveforms are low, requires pneumotachographs that accurately respond to relatively high frequencies; and c) the use of dynamic nonsinusoidal flows (as opposed to static flows) to calibrate pneumotachographs results in a calibration function with higher reliability.

Calibration↗
PubMed1993

Accelerometer type cardiac transducer for detection of low-level heart sounds.

New applications in phonocardiography require transducers with high sensitivity, low noise, and extended frequency range. This paper compares several different cardiac transducers and describes the development of a low-mass, accelerometer type cardiac transducer which fulfills these objectives. The accelerometer weighs approximately 5 g and has a theoretical sensitivity of 125 mV/g in the frequency range 200-800 Hz. The basic design allows for easy modification of sensitivity and resonant frequency. This transducer has been effective in detecting sounds associated with turbulent blood flow in partially occluded coronary arteries.

Adult↗