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At least 109 records · Page 6Linked to original sources
PubMed1995

Frequency requirements for zeroing transducers in hemodynamic monitoring.

BACKGROUND: Accurate hemodynamic monitoring information can be obtained only if the transducer/amplifier system is used correctly. One major component of correct use is zeroing the transducer to provide a relative reference point on which to measure hemodynamic pressures. However, nursing requirements for frequency of zeroing are inconsistent. In addition, the concepts of leveling and zeroing are frequently confused. OBJECTIVE: To determine whether transducers drift from zero (+/- 2 mm Hg), and if they do not drift from zero, how long they hold a zero value. METHODS: The study, conducted in four midwestern hospitals, was carried out in two parts: an initial 10-day bench test of 50 transducers and an evaluation of 388 transducers attached to patients for 1 to 5 days. Transducers were monitored over time after being consistently leveled. RESULTS: Bench testing indicated that 100% of transducers did not drift +/- 2 mm Hg from zero during the study period. In the clinical study, only 1.3% of transducers drifted from zero. Five transducers drifted +/- 2 mm Hg from zero, with a range of -5 to 3 mm Hg. CONCLUSIONS: We conclude that transducers used for hemodynamic monitoring require zeroing only on initial setup and disconnection from the amplifier.

Calibration↗
PubMed1984

Structure of the Trg protein: Homologies with and differences from other sensory transducers of Escherichia coli.

Transducer proteins are central to chemotaxis in Escherichia coli. Three transducer genes comprise a homologous gene family, while a fourth gene, trg, is more distantly related. We have determined the nucleotide sequence of trg. The deduced sequence of the Trg protein has features in common with other transducers as well as regions of significant divergence. The protein sequence suggests the same transmembrane structure postulated for other transducers: an extra cytoplasmic NH2-terminal domain connected by a membrane-spanning region to an intracellular COOH-terminal domain. The COOH-terminal domain of Trg exhibits substantial sequence identity with the corresponding domains of the other transducers, particularly near the sites of covalent modification. Trg appears to have the same five methyl-accepting sites identified in the Tsr protein. Two of those sites are glutamines that are deamidated to yield methyl-accepting glutamates, while the remainder are synthesized as glutamates. Conservation in number but not in position of modified glutamines in Trg compared to the other transducers is consistent with the notion that uncharged glutamines at a specific number of modification sites serve to balance the signaling state of newly synthesized transducers. The NH2-terminal domain of Trg exhibits no significant homology with other transducers, implying that trg may be a fusion of the common COOH-terminal transducer sequence with an unrelated NH2-terminal sequence. The location of specific mutations within trg provides support for the suggestion that ligand-binding sites are in the NH2-terminal domains.

Amino Acid Sequence↗
PubMed2005

Transduced bovine articular chondrocytes affect the metabolism of cocultured nucleus pulposus cells in vitro: implications for chondrocyte transplantation into the intervertebral disc.

STUDY DESIGN: Biologic study on the effects of coculture of bovine articular chondrocytes transduced ex vivo with genes expressing bone morphogenetic proteins (BMPs) on nucleus pulposus (NP) cells. OBJECTIVE: To evaluate the effects of bovine articular chondrocytes transduced with adenoviruses expressing various BMPs on proteoglycan and collagen production, and cellular proliferation of NP cells in vitro. SUMMARY OF BACKGROUND DATA: Matrix synthesis by intervertebral disc cells is promoted by exposing the cells to growth factors or delivering genes that permit sustained expression of growth factors. We propose a novel therapeutic approach involving delivery of autologous chondrocytes, transduced ex vivo with bioactive proteins, to provide both the cells and proteins required to stimulate disc healing. METHODS: Adult bovine articular chondrocytes were transduced with adenoviruses (Ads) expressing either BMP-2, 4, 5, 7, 10, or 13 and plated as monolayers. Bovine NP cells encapsulated in alginate beads were cocultured, floating in the medium. Proteoglycan and collagen accumulation, and NP cell proliferation were measured after 6 days of coculture. As a positive control, beads were cocultured with articular chondrocytes in the presence of rhBMP-7. RESULTS: NP cells cocultered with articular chondrocytes transduced with BMPs-2, 4, 7, and 10 accumulated significantly (P < 0.05) more proteoglycan than when cocultured with chondrocytes transduced with AdGFP (control) [AdBMP-2: 23.6%; AdBMP-4: 27.0%; AdBMP-7: 129.1%; AdBMP-10: 102.1% increases respectively]. Collagen accumulation was significantly (P < 0.05) increased by NP cells cocultured with articular chondrocytes transduced with BMPs-2, 4, 5, and 7. [AdBMP-2: 104.6%; AdBMP-4: 40.6%; AdBMP-5: 58.6%; AdBMP-7: 55.5% increases respectively]. NP cells proliferated when cocultured with articular chondrocytes transduced with AdBMP-2 and -7. CONCLUSIONS: Bovine NP cells are stimulated to produce proteoglycans and collagen when exposed to chondrocytes transduced with genes for various BMPs. If applied to the treatment of disc degeneration, this strategy could provide the disc with not only metabolically active chondrocytes but also promote matrix replenishment by stimulating native NP cells.

Animals↗
PubMed2002

Distinct roles of adenovirus vector-transduced dendritic cells, myoblasts, and endothelial cells in mediating an immune response against a transgene product.

Adenovirus-mediated gene delivery via the intramuscular route efficiently promotes an immune response against the transgene product. In this study, a recombinant adenovirus vector encoding beta-galactosidase (Ad beta Gal) was used to transduce dendritic cells (DC), which are antigen-presenting cells, as well as myoblasts and endothelial cells (EC), neither of which present antigens. C57BL/6 mice received a single intramuscular injection of Ad beta Gal-transduced DC, EC, or myoblasts and were then monitored for anti-beta-galactosidase (anti-beta-Gal) antibody production, induction of gamma interferon-secreting CD8(+) T cells, and protection against melanoma tumor cells expressing beta-Gal. While all transduced cell types were able to elicit an antibody response against the transgene product, the specific isotypes were distinct, with exclusive production of immunoglobulin G2a (IgG2a) antibodies following injection of transduced DC and EC versus equivalent IgG1 and IgG2a responses in mice inoculated with transduced myoblasts. Transduced DC induced a strong ex vivo CD8(+) T-cell response at a level of 50% of the specific response obtained with the Ad beta Gal control. In contrast, this response was 6- to 10-fold-lower in animals injected with transduced myoblasts and EC. Accordingly, only animals injected with transduced DC were protected against a beta-Gal tumor challenge. Thus, in order to induce a strong and protective immune response to an adenovirus-encoded transgene product, it is necessary to transduce cells of dendritic lineage. Importantly, it will be advantageous to block the transduction of DC for adenovirus-based gene therapy strategies.

Adenovirus Infections, Human↗
PubMed2005

Dendritic cells transduced with tumor-associated antigen gene elicit potent therapeutic antitumor immunity: comparison with immunodominant peptide-pulsed DCs.

Several studies have shown that vaccine therapy using dendritic cells (DCs) pulsed with specific tumor antigen peptides can effectively induce antitumor immunity. Peptide-pulsed DC therapy is reported to be effective against melanoma, while it is still not sufficient to show the antitumor therapeutic effect against epithelial solid tumors such as gastrointestinal malignancies. Recently, it has been reported that vaccine therapy using DCs transduced with a surrogate tumor antigen gene can elicit a potent therapeutic antitumor immunity. In this study, we investigated the efficacy of vaccine therapy using DCs transduced with the natural tumor antigen in comparison with peptide-pulsed DCs. DCs derived from murine bone marrow were adenovirally transduced with murine endogenous tumor antigen gp70 gene, which is expressed in CT26 cells, or DCs were pulsed with the immunodominant peptide AH-1 derived from gp70. We compared these two cancer vaccines in terms of induction of antigen-specific cytotoxic T lymphocyte (CTL) responses, CD4+ T cell response against tumor cells, migratory capacity of DCs and therapeutic immunity in vivo. The cytotoxic activity of splenocytes against CT26 and Meth-A pulsed with AH-1 in mice immunized with gp70 gene-transduced DCs was higher than that with AH-1-pulsed DCs. CD4+ T cells induced from mice immunized with gp70 gene-transduced DCs produced higher levels of IFN-gamma by stimulation with CT26 than those from mice immunized with AH-1-pulsed DCs (p < 0.0001), and it was suggested that DCs transduced with tumor-associated antigen (TAA) gene induced tumor-specific CD4+ T cells, and those CD4+ T cells played a critical role in the priming phase of the CD8+ T cell response for the induction of CD8+ CTL. Furthermore, DCs adenovirally transduced with TAA gene showed an enhancement of expression of CC chemokine receptor 7 and improved the migratory capacity to draining lymph nodes. In subcutaneous models, the vaccination using gp70 gene-transduced DCs provided a remarkably higher therapeutic efficacy than that using AH-1-pulsed DCs. These results suggested that vaccine therapy using DCs adenovirally transduced with TAA gene can elicit potent antitumor immunity, and may be useful for clinical application.

Adenocarcinoma↗
PubMed2004

Transplantation of transduced retinal pigment epithelium in rats.

PURPOSE: To examine the effects of transplanting retinal pigment epithelial (RPE) cells transduced with neurotrophic factor genes into the subretinal space of rats. METHODS: RPE cells were transduced with plasmids carrying the cDNAs of Axokine (ciliary neurotrophic factor [CNTF]; Sumitomo Pharmaceuticals Co., Ltd., Tokyo, Japan), brain derived-neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF) genes. These RPE cells were transplanted into the subretinal space of rats, and the localization was examined. The expression of enhanced green fluorescent protein (eGFP)-BDNF-transduced RPE in the subretinal space was examined by real-time polymerase chain reaction (PCR) after the transplanted cells were collected by cell sorting. The expression of major histocompatibility complex (MHC) class I and -II after gene transduction was examined by real-time PCR. The ratio of CD4(+) and CD8(+) T cells and antibody production against transplanted cells were analyzed by flow cytometry. RESULTS: The transplant sites were not significantly different among the neurotrophic factors tested. The RPE cells expressed the BDNF gene in the subretinal region at approximately the same level as that in vitro. RPE cells transduced with Axokine stimulated MHC-I expression, and the cell transplantation changed the ratio of CD4(+) and CD8(+) T cells. A significant production of antibody against the Axokine-transduced RPE cells was also observed after Axokine-transduced RPE transplantation. CONCLUSIONS: RPE cells transduced with neurotrophic factors express the factors after transplantation into the subretinal space. RPE transduced with Axokine or bFGF, in contrast to RPE transduced with BDNF, stimulate an immunologic reaction of the host.

Animals↗
PubMed1998

Mechanisms for ganciclovir resistance in gastrointestinal tumor cells transduced with a retroviral vector containing the herpes simplex virus thymidine kinase gene.

Transfer of the herpes simplex thymidine kinase (HSV-TK) gene into tumor cells confers sensitivity to the cells to the viral drug ganciclovir (GCV). Although the efficacy of the HSV-TK/GCV approach is well studied, the mechanisms for the resistance of HSV-TK-transduced tumor cells to GCV are poorly understood. Here, we examined the mechanisms for GCV resistance in HSV-TK-transduced gastrointestinal (GI) cell lines. Our results show that GCV sensitivities vary in vitro and in vivo among the different HSV-TK-transduced GI tumor cell lines. GCV-resistant colonies were isolated from several different HSV-TK-transduced GI tumor cell lines after 14 days of GCV treatment. Characterization of GCV-resistant colonies demonstrated that the HSV-TK gene was either partially or completely deleted from the resistant HSV-TK-transduced cells. In the HT-29 RM and MIAPACA-2 RM cells, a 220-bp deletion of the gene was found, whereas in the HT-29 R1-R5-resistant cells, the whole TK gene was found to be absent. Immunocytochemical studies using a polyclonal antibody to the TK protein demonstrated that the HSV-TK protein was absent in the GCV-resistant, HSV-TK-transduced cells. Transfection of the resistant cells with an adenoviral vector containing a HSV-TK gene restored sensitivity to GCV. The presence of GCV-resistant cells was only demonstrable in GI tumor cell lines that also demonstrated a poor bystander effect. Our results suggest that GCV resistance found in tumor cells transduced with a retroviral HSV-TK gene is due to the lack of a functional TK protein in the tumor cells rather than any intrinsic resistance of the cells to GCV. In tumor cells with a good bystander effect, the small percentage of TK-transduced cells that do not express the TK protein are probably killed by the bystander effect because GCV-resistant tumor cells were not found in these cell lines. GCV-resistant tumor cells were found only in tumor cell lines with a poor bystander effect, by which, presumably, the transduced tumor cells lacking a functional TK gene were not killed by the bystander killing effect.

Antiviral Agents↗
PubMed1990

Transducer manometry and the effect of body position on anal canal pressures.

Anal canal manometry is performed conventionally with balloons, sleeves, perfused or nonperfused open-tipped catheters, or with multiport probes. The authors constructed a new manometer with four transducers embedded in a probe (15 mm outside diameter) and oriented radially, 90 degrees apart. The transducer probe was validated in 27 healthy volunteers by comparing its performance to that of a standard four-port perfused manometer and then used to measure anal canal and rectal pressures in body positions more physiologic (standing, sitting) than that usually employed (left lateral) for such measurements. Both devices measured similar anal canal resting pressure in the left lateral position (mid canal, 58 +/- 3 mm Hg perfused vs. 62 +/- 4 mm Hg transducer; P greater than 0.05). The transducer probe, however, recorded higher squeeze pressures (mid canal, 100 +/- 6 mm Hg perfused vs. 143 +/- 14 mm Hg transducer; P less than 0.05). The transducer probe detected higher intrarectal and resting anal canal pressures when subjects were standing or sitting, compared with the left lateral position (rectum, 3 +/- 1 mm Hg left lateral; 17 +/- 2 mm Hg standing; 20 +/- 1 mm Hg sitting; P less than 0.05; mid anal canal, 57 +/- 3 mm Hg left lateral; 86 +/- 4 mm Hg standing; 81 +/- 5 mm Hg sitting, P less than 0.05). The rise in resting anal canal pressure was uniform circumferentially. Neither anal canal length nor squeeze pressure changed with change in position. The authors concluded that 1) transducer manometry recorded similar resting but higher squeeze pressures compared with perfused manometry; 2) transducer manometry recorded the same radial variation in anal canal resting and squeeze pressures as that recorded by the perfused manometer; and 3) standing and sitting caused a four-fold rise in intrarectal pressure, which was associated with a concomitant rise in resting anal canal pressure.

Adult↗
PubMed1991

Recording and processing of fetal movements and sounds obtained with the Inpho inductive transducer.

A recently developed transducer based on an inductive principle allows recording of fetal displacement signals on the maternal abdominal wall. The transducer is a relatively passive device, in contrast to commonly applied ultrasound transducers. This permits long-term observation of fetal movements and sounds. The bandwidth of the system is DC-200 Hz (+/- 3 dB), and signal-to-noise ratios of more than 96 dB have been measured in a laboratory setup, whereas in the practical situation a signal-to-noise ratio of 78 dB has been established. The transducer has been applied to study fetal respiratory sinus arrhythmia, which means that fetal breathing movements have to be extracted from the transducer's output. This proved possible by digital filtering of the displacement signal as detected by the transducer. The transducer has also been applied in a study where the signal-to-noise ratio of fetal heart sounds as a function of location of the fetus and position of the transducer on the maternal abdominal wall has been studied. It proved possible to adequately record fetal heart sounds for measurement of fetal heart rate. Also uterine activity could be recorded using the sensor's DC output.

Female↗
PubMed1998

[A micromanipulator for intraoperative vibratory hearing assessment with an implantable hearing aid transducer].

First concepts of implantable hearing aids to be coupled to the ossicular chain are available for patients with combined or sensorineural hearing loss (SNHL). To ensure that hearing can be improved intraoperative coupling of a test transducer to the ossicular chain is mandatory for allowing surgical anatomy to be checked and vibratory hearing tests to be performed. To achieve this, the test transducer has to be held and positioned securely in situ for some minutes, avoiding risks for middle or inner ear structures. This is not possible using conventional surgical instruments. Thus, a micromanipulator to hold the test transducer during intraoperative hearing tests was developed. This surgical device allows the surgeon safe, risk-free, and controlled coupling of the test transducer to the ossicular chain with one axial and three rotational degrees of freedom. With the aid of a conventional ear retractor (2x2 prongs), the manipulator is fixed at the patient's ear. In conjunction with a piezoelectric test transducer, the manipulator was used in nine patients during local anesthesia. The test transducer is part of an electronic hearing implant (Tübingen implant) specifically designed for SNHL that may be coupled to a middle ear ossicle or the perilymph of the cochlea. The micromanipulator was easy to handle. It allowed accurate positioning of the test transducer in the ear and the desired coupling of the transducer's probe tip to the ossicular chain during auditory tests. According to the principles of integrated safety, the intraoperative risk of ossicular or inner ear injuries caused, for instance, by the patient's head movement is minimized. The design of the manipulator system is universal, also allowing its use for other electronic hearing implants or minimal invasive surgery after minor modifications.

Ear Ossicles↗
PubMed1982

Hall effect transducer for apexcardiography and sphygmography.

Recording of mechanograms (Recording of mechanical activity of internal organs and vessels, often non-invasively eg. apex cardiogram) can be performed by applying different kinds of mechano-electric transducers. In this paper the idea and construction of a new transducer with Hall-generator are presented. This transducer is self-adjusting in the range of its linear characteristics, and exerts practically constant touching pressure independent of the configuration of the patients thorax. This facilitates the measuring process and allows for calibration of the obtained records. The sensitivity of the transducer is 250 mV/mm, frequency bandwidth 0-45 Hz and it has a linearity of +/- 1.5% in the range of displacements +/- 1.5 mm. The transducer also generates the signal of the first derivative of the investigated vibrations. Assessment of the transducer was carried out in a cardiology clinic on 27 patients with a normal heart and with different kind and degree of heart damage. The mechanograms obtained from different transducers for each patient were compared in respect of the essential time intervals and morphological elements. The comparison shows a good detecting capability, correctness and reproducibility of the data obtained by means of the Hall-effect transducer. Some recordings of mechanograms (apexcardiograms and different kinds of pulse) from patients with normal heart, valvular aortic stenosis and atrial heart defect are shown and discussed in the paper.

Heart Diseases↗
PubMed1987

Two-dimensional echocardiographic imaging: in vitro comparison of conventional and dynamically focused annular array transducers.

Quantitative two-dimensional echocardiography has been adversely affected by a tendency for underestimation of cross-sectional areas of cardiac chambers, a difficulty that might be ameliorated by recent advances in imaging technology. To determine if this were so, we measured echocardiographic cross-sectional areas of 25 formalin-fixed animal left ventricular (LV) sections in vitro using conventional 13 mm and 15 mm diameter fixed-focused single element transducers, and a 15 mm diameter dynamically focused annular array transducer at 3 different distances between myocardial slice and transducer (2 cm, 6 cm and 10 cm) and compared the 2-dimensional echocardiographic areas to the corresponding anatomic cross-sectional areas of the same hearts. LV total and cavity area were measured by computer assisted planimetry of videotaped echo images, performed blinded to the transducer used, and photographed anatomic slices; LV myocardial area was derived by subtraction. Comparison of two-dimensional echocardiographic total, myocardial, and cavity areas with corresponding anatomic measurements showed excellent correlation for each transducer at all depths (r = 0.97 to 0.98 for total area; r = 0.98 to 0.99 for cavity area; r = 0.93 to 0.97 for myocardial area). For total and myocardial cross-sectional areas, the slope of the relation between echographic and anatomic areas did not differ significantly from unity, but for LV cavity area this was achieved only by the dynamically focused transducer. In contrast, the conventional 13 mm transducer significantly underestimated larger LV cavity areas in both the near and middle fields (slopes = 0.90 and 0.91, respectively) and the 15 mm transducer yielded slopes from 0.86 to 0.91 in all fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Echocardiography↗
PubMed2004

A comparison of a mechanical sector and a linear array transducer for ultrasound-guided transvaginal oocyte retrieval (OPU) in the cow.

A comparison was made between a linear array and a mechanical multiple angle sector (MAP) transducer for ultrasound-guided transvaginal oocyte retrieval (ovum pick-up, OPU) in the cow. The ovaries of five dairy cows were punctured, in a twice-weekly OPU program lasting for 4 weeks, using two different 5.0-MHz transducers equipped with an identical disposable needle-guidance system. Both ovaries were visualized using each transducer before puncture and the number of follicles with a diameter of less than 5 mm (small) and with a diameter equal to or greater than 5 mm (large) was recorded. Subsequently, one ovary of the pair was punctured guided by the MAP, while the other was punctured using the linear array transducer. During the next puncture session on a given animal, the two systems were switched and used on the alternate ovary in a crossover design. Parameters assessed for each system were: the total number of follicles visualized in each diameter class, and the total number of retrieved oocytes per cow. A significant difference was found for the ability to visualize smaller follicles in favor of the MAP transducer, with an average visualization of 71.6 +/- 30.3 small follicles per cow during the 4-week trial period, compared to 59.8 +/- 25.7 for the linear array transducer (t-test for paired samples, P = 0.007). No differences were found in the visualization of large follicles. A numerically greater number of oocytes were retrieved using the MAP transducer, compared to the linear array, (averages of 14.2 +/- 7.2 versus 7.4 +/- 6.1, respectively), although these differences were not statistically significant. In conclusion, both systems can be effectively used for oocyte retrieval in the cow, however, the MAP transducer demonstrated superior visualization of small follicles.

Animals↗
PubMed2003

Nonlinear characterization with burst excitation of 1-3 piezocomposite transducers.

Ultrasonic transducers made with 1-3 connectivity piezocomposites are frequently used in Medical applications and nondestructive testing. When the transducer is used for special applications as, for instance air-coupled transmission, it is necessary to compensate for the high difference of acoustic impedance between transducer and medium using high amplitude pulses to generate high acoustic signal. Thus, the nonlinear behavior of the transducer must be taken into account in similar application conditions. The newly developed method, which performs the nonlinear characterization with burst signal excitation near the thickness resonance frequency, is based on the measure of the current as well as the vibration velocity of the piezocomposite transducer. The current of the stationary response is measured before the end of the burst signal excitation. Burst excitation enables us to measure the nonlinear characterization without producing overheating in the transducers. The amplitude level dependence of mechanical losses tandelta(m) and the stiffness increases |Deltac/c(0)| have been studied, as well as the velocity dependence of a point of the transducer, measured with a laser vibrometer. In this method, the power level applied to the transducers can be higher than other nonlinear measurement methods, providing measurements of high accuracy.

Equipment Design↗
PubMed2003

Efficacy of linear and convex transducers for ultrasound-guided transvaginal follicle aspiration.

A new device was developed to hold linear transducers for transvaginal follicle aspiration. Efficacy of follicle aspiration was compared using a linear 6 MHz and a convex 5 MHz transducer. Fifty-five cows were submitted to follicle aspiration at random days of the estrous cycle. Aspirations were conducted with linear (n=28) and convex (n=38) transducers with 18 G needles at a negative pressure corresponding to 13 ml H(2)O/min. A greater number of follicles were aspirated using convex than to linear probe (12.4 versus 7.8, respectively, P<0.05). Mean number of oocytes and recovery rates were similar for convex (5.4 and 48.6%) and linear (4.6 and 59.3%) transducers. Limited space between the linear transducer and needle guide restricted access to some portions of the ovary, reducing the number of follicles aspirated using a linear transducer. The newly developed adaptor allowed greater stability, holding the ovaries firmly against the linear transducer. This diminished mobility permitted a similar number of oocytes to be recovered with both transducers. In conclusion, this new adaptor provided a low cost alternative for routine follicle aspiration and oocyte recovery in cattle.

Animals↗
PubMed2000

Human studies of a piezoelectric transducer and a microphone for a totally implantable electronic hearing device.

OBJECTIVE: For the surgical treatment of patients with moderate and severe sensorineural hearing loss, the authors have developed a totally implantable hearing device, the totally integrated cochlea amplifier (TICA). To evaluate the effectiveness of transducer and microphone of this device, three separate human studies were conducted. STUDY DESIGN: The first study using transducer prototypes involved self experiments in investigators with normal hearing. The second study used the transducer prototypes in patients with hearing loss, and the third study involved the temporary implantation of the final transducer prototype and microphone in patients undergoing otologic surgery. PATIENTS: In routine middle ear surgery, transducer prototypes were coupled to the ossicular chain of 28 patients. In addition to the transducer, in 5 patients the microphone was placed beneath the skin of the auditory canal, allowing the skin to cover the microphone membrane completely. RESULTS: The piezoelectric transducer reached an equivalent sound pressure level of 145 dB SPL < or =10 kHz. The dynamics for music reached 32 dB, which was identical with the results of the preoperative investigations using high-fidelity headsets (33 dB). The low nonlinear distortions of <0.1% and the frequency range of 10 kHz are reflected in the positive evaluation of the sound quality by 84% of the patients involved. When phonetically balanced speech material and music were presented under free field conditions at a sound level of 65 dB SPL, understanding of the phonetically balanced speech material was 100%. Most patients judged the presentations of music as clear and undistorted with all broadband components. CONCLUSIONS: Data in humans on the performance of the two main components of the TICA implant, the transducer and the microphone, are reported.

Amplifiers, Electronic↗
PubMed2000

A theoretical study of cylindrical ultrasound transducers for intracavitary hyperthermia.

PURPOSE: The purpose of this paper was to examine the heating patterns and penetration depth when a cylindrical ultrasound transducer is employed for intracavitary hyperthermia treatments. METHODS AND MATERIALS: The present study employs a simulation program based on a simplified power deposition model for infinitely long cylindrical ultrasound transducers. The ultrasound power in the tissue is assumed to be exponentially attenuated according to the penetration depth of the ultrasound beam, and a uniform attenuation for the entire treatment region is also assumed. The distribution of specific absorption rate (SAR) ratio (the ratio of SAR for a point within the tissue to that for a specific point on the cavity surface) is used to determine the heating pattern for a set of given parameters. The parameters considered are the ultrasound attenuation in the tissue, the cavity size, and the transducer eccentricity. RESULTS: Simulation results show that the ultrasound attenuation in the tissue, the cavity size, and the transducer eccentricity are the most influential parameters for the distribution of SAR ratio. A low frequency transducer located in a large cavity can produce a much better penetration. The cavity size is the major parameter affecting the penetration depth for a small cavity size, such as interstitial hyperthermia. The heating pattern can also be dramatically changed by the transducer eccentricity and radiating sector. In addition, for a finite length of cylindrical transducer, lower SAR ratio appears in the regions near the applicator's edges. CONCLUSION: The distribution of SAR ratio indicates the relationship between the treatable region and the parameters if an appropriate threshold of SAR ratio is taken. The findings of the present study comprehend whether or not a tumor is treatable, as well as select the optimal driving frequency, the appropriate cavity size, and the eccentricity of a cylindrical transducer for a specific treatment.

Algorithms↗
PubMed1987

Infection potential of nondisposable pressure transducers prepared prior to use.

This study was designed to examine whether pressure transducer systems prepared hours or days before actual use represent an infection potential. Twenty-one nondisposable transducers assembled with sterile plastic disposable domes and extension tubing were utilized. The systems were prefilled with heparinized flush solution (2 U sodium heparin per ml normal saline). Flush solution samples were cultured from the distal end of the equipment immediately after set-up (time 0) and 24, 48, and 72 h after set-up in all 21 transducers. In 11 of 21 transducers, cultures were also taken at 168 h (1 wk) and 336 h (2 wk) after set-up. Out of the total 106 cultures, only two showed growth, both of which proved to be external skin or mouth contaminants. Binomial distribution testing indicated that if a .05 probability level was used, the chance was 1.3% that one or more transducers in 100 could become contaminated by 72 h. Using the same statistical analyses for the 66 cultures involving the 11 transducers cultured for 2 wk, the chance of contamination in 100 cultures is 2.7% at 2 wk. We conclude from these data that nondisposable transducer systems, when preassembled using standard aseptic precautions and sterile disposable plastics, show no evidence of significant contamination when allowed to stand in readiness after assembly but not connected to a patient. We feel it is safe to preassemble transducers for at least a 72-h period before use. Longer intervals from set-up to use may also be justified.

Equipment Contamination↗