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Biomedical subjects

S B Barnett

Publications and source records attributed to S B Barnett.

At least 37 records · Page 2Linked to original sources
PubMed1993

Heating of guinea-pig fetal brain during exposure to pulsed ultrasound.

Ultrasound-induced temperature elevations in fresh and formalin-fixed fetal guinea-pig brains were measured during in vitro insonation, with a stationary beam in a tank containing water at 38 degrees C. The pulsing regimen used 6.25 microseconds pulses, repeated at a frequency of 4 kHz emitted from a focussed transducer operating with a centre frequency of 3.2 MHz. The greatest temperature rise in brain tissue occurred close to bone and correlated with both gestational age and progression in bone development. After a 2 min insonation with a spatial peak temporal average intensity (ISPTA) of 2.9 W/cm2, a mean temperature elevation of 5.2 degrees C was recorded in fetuses of 60 days gestation (dg). The same exposure produced an increase of 2.6 degrees C in the centre of whole brains of 60 dg fetuses when the bony cranium was removed. As most of the heating occurs within 40 s, these findings have implications for the safety of pulsed Doppler examinations where dwell-time may be an important factor.

Animals↗
PubMed1990

Effects of pulsed ultrasound and temperature on the development of rat embryos in culture.

Rat embryos in culture were exposed to pulsed ultrasound at SPTA intensity of 1.2 W/cm2 for 5, 15, and 30 min on day 9.5 of development. The whole embryo culture system allowed precise temperature control for directly examining the effects of ultrasound on the developing neural plate. After exposure, embryos were maintained in culture for a further 48 hr. No major morphological abnormalities were observed but a reduction in somite number occurred in the group insonated for 30 min, which was equivalent to a 2 hr delay in embryonic development. Similar delay in growth and "blistering" in the prosencephalon region of some embryos were observed after insonation for 15 min at 40.0 degrees C, an elevation of 1.5 degrees C over the temperature used for controls. Exposure to ultrasound for 15 min at 40 degrees C caused significant reduction in the growth of the head compared with that of control embryos. Heat shock genes for hsps 71/73 and 88 kD were induced after insonation for 30 min at 38.5 degrees C. Insonation did not cause any temperature changes in the culture medium. However, when the temperature of the culture medium was increased during insonation, defective development occurred. The results of these in vitro experiments suggest that ultrasound if resulting in significant hyperthermia could affect the development during early organogenesis of the neural plate and in particular they suggest that the embryo is at greater risk of damage during hyperthermic conditions. These results should provoke discussion of the concept that ultrasound in the febrile patient may present an increased embryonic risk which should be considered when deliberating on the use of diagnostic ultrasound procedures in the pregnant patient.

Animals↗
PubMed1990

Identification of mechanisms responsible for fetal weight reduction in mice following ultrasound exposure.

This study challenges existing interpretations of the effects of ultrasound on fetal development. The results demonstrated that a lower mean fetal weight in mice observed after intrauterine exposure to 2 MHz ultrasound resulted from maternal distress, and was not simply a direct effect of ultrasound interaction with the fetuses. At day 8 of gestation continuous wave ultrasound was applied to different regions of the maternal abdomen at spatial average intensities between 0.5 and 5.5 W cm-2 for 3 min. Insonating the uterus directly resulted in resorptions, abortions and gross developmental abnormalities, with rare instances of fetal weight reduction which were apparently associated with maternal distended bladder syndrome (DBS). When the ultrasound beam deliberately avoided the uterus, by a dorsal approach centred on the vertebral column, mean fetal weight at day 18 was significantly lower in all mothers showing DBS. Fetuses of insonated mothers not affected by DBS were not significantly different from the sham-insonated group whether the uterus was directly exposed or not. The fetal weight reduction endpoint was therefore found to be more closely correlated with maternal damage (DBS) than with ultrasound intensity.

Abdomen↗
PubMed1990

Novel approach to evaluate the interaction of pulsed ultrasound with embryonic development.

An in vitro whole-embryo culture system was used which allowed ultrasound to interact directly with rat embryos, at 9.5 days of gestation, under conditions of controlled temperature. Neural plate damage, expressed during a critical period of forebrain development, was evaluated 48 h post-insonation. Ultrasound-induced effects were thus identified in the absence of significant temperature changes or complications from the influence of maternal physiology. Exposures to 3.2 microseconds pulses of 3.14 MHz ultrasound at a PRF of 2 kHz and 1.2 W cm-2 intensity (ISPTA) for durations of 5, 15 or 30 min produced no major morphological abnormalities at a temperature of 38.5 degrees C. Embryonic response to stress was evidenced by changes in protein synthesis, and delayed development was indicated by a reduction in somite number. These effects were enhanced when the insonation temperature was elevated by 1.5 degrees C.

Animals↗
PubMed1988

Increased sister chromatid exchanges in Chinese hamster ovary cells exposed to high intensity pulsed ultrasound.

This study comprised two repeat experiments in which Chinese hamster ovary (CHO) cells were exposed to nominal peak intensity Im = 2500 W/cm2, 2.5 MHz, pulsed ultrasound. Cells contained in a 0.53 cm diameter chamber in 0.48 cm thick Plexiglas were exposed to 10 microseconds pulses at 200 Hz prf in 9 sites for 3 min per site for a total duration of 27 min. The -3 dB focal beamwidth was 0.115 cm at an axial distance of 4.8 cm. Analysis of the pooled data from each series of experiments showed a statistically significant increase in the mean frequency of sister chromatid exchanges (SCE) in exposed compared to control cells. The results show a high degree of variability in the controls and insonated samples, which suggests that large numbers of insonations may be required in studies with SCE to reduce the high probability of missing an effect. The results of this series of experiments provide the first confirmation of an increase in SCEs following exposure to pulsed ultrasound.

Animals↗
PubMed1987

Sister chromatid exchange frequency in human lymphocytes after long duration exposure to pulsed ultrasound.

The aim of this study is to determine whether sister chromatid exchange (SCE) frequency increases in human lymphocytes that are exposed to pulsed ultrasound conditions within the range typically employed in ultrasound Doppler measurements of fetal blood flow. Whole blood diluted with culture medium was exposed in vitro to 3.1 MHz pulsed ultrasound at spatial peak pulse average (SPPA) intensities from 15 to 135 W/cm2. Insonation for 5 min did not significantly alter the base level frequency of SCEs compared to that observed in sham-insonated controls. To avoid missing an effect, due to differing sensitivities of the division stages within the mitotic cycle, insonation was also applied for 24 hr to include one complete cell division cycle. No change in SCE was observed after this extended insonation at SPPA intensity of 33 W/cm2.

Cell Cycle↗
PubMed1987

Sister chromatid exchanges in laboratory cultured cells after repeated exposures to pulsed ultrasound.

In this in vitro study, suspensions of DON cells (lung diploid cell line from the Chinese hamster) were exposed to ultrasound regimes using pulse lengths similar to those used in ultrasonic Doppler measurements of fetal blood flow. The base level frequency of sister chromatid exchanges (SCE) was not significantly altered following exposure to a range of spatial peak temporal average intensities from 0.1 to 4.0 W/cm2. Repeating the exposure on three further occasions during the 20 generations following the initial insonation also had no effect. When DON cells were incubated in the presence of Mitomycin C (MCC), a positive dose-related increase in SCE frequency was observed, indicating the sensitivity of these cells to in vitro SCE induction. Coincidental exposure to ultrasound and Mitomycin C did not increase the SCE level above that obtained with MCC alone, and it was concluded that there was no evidence of a synergistic association.

Analysis of Variance↗
PubMed1984

Temporal peak intensity as a critical parameter in ultrasound dosimetry.

The in vitro effect of microsecond pulses of ultrasound is studied in mammalian cells using two different biologic endpoints. The frequency of sister chromatid exchanges (SCE) is unchanged in Chinese hamster ovarian cells insonated with a stationary transducer for 1-30 minutes at an SPTA intensity of 0.1 W/cm2. Raising the temporal average intensity to 2 W/cm2 by increasing the pulse repetition frequency alone still has no effect, whereas a change in temporal peak intensity produces an increase in SCE after insonation for only 1 minute. From experiments involving aggregation of platelets in suspension around acoustically active hydrophobic pores, pulse duration is found to be a more effective factor than the pulse repetition frequency. Results of the two studies show the biologic response to be strongly dependent on temporal peak intensity and pulse duration, but weakly dependent on duration of exposure. The temporal average intensity as a singular dosage specification is considered to be a poor indicator of potential nonthermal bioeffects associated with microsecond pulses.

Animals↗
PubMed1983

Ultrasound exposure in diagnostic echography.

The output characteristics and spatial distribution of pulses were studied in static and real time B-mode imaging, and M-mode procedures to assess the ultrasound exposure occurring over the total examination area and at a single point tissue target during a diagnostic examination.

Biophysical Phenomena↗
PubMed1983

Is pulsed ultrasound mutagenic?

The possibility that microsecond pulses of 3 MHz ultrasound may interact at the cellular level, with genetic consequences, was investigated using two different endpoints. The Ames mammalian microsome test was employed to assess mutagenicity and viability in Salmonella typhimurium bacteria, while the sister chromatid exchange frequency provided an indicator of ultrasound induced effects at the chromosome level in Chinese hamster ovary cells.

Animals↗
PubMed1982

Ultrasonic exposure in static and real time echography.

Measurement of ultrasonic output from static and real time devices has shown both types of equipment to emit approximately the same amount of energy per pulse and the same peak instantaneous intensity. The major differences in exposure were related to the amount of energy used to produce an image, the total amount of energy used to perform an examination, and the amount of energy passing through a single point in tissue. the highest single point exposure occurred during static M-mode examinations when an energy exposure of 120 mJ per minute was measured. By comparison a real time B-mode examination resulted in a single point exposure of 0.018 mJ/echogram or 27 mJ/min. The single point exposure per echogram in a static examination was 0.12 mJ for a simple scan and 1.15 mJ for a compound scan with contact equipment, and 0.01 and 0.08 mJ for simple and compound scans using water path equipment.

Ultrasonics↗
PubMed1982

An investigation of the mutagenic potential of pulsed ultrasound.

The possible mutagenic effect of microsecond pulses of ultrasound was investigated using 3 MHz ultrasound at diagnostic dosages, and also under conditions of increased pulse repetition frequency and acoustic power output. The first part of the study involved 5 strains of Salmonella typhimurium bacteria in which mutagenicity and viability were assessed using the Ames test, while functional competence was evaluated from microscopic observations of motility. No changes were observed in survival, in the incidence of mutants, or in microbial motility following irradiation with ultrasound intensities of 4.5 W/cm2 at temperatures ranging from 37 degrees to 43 degrees C. In the second part of this study, the frequency of sister chromatid exchange (SCE) in Chinese hamster ovary (CHO) cells, treated with similar ultrasound dosages, remained unaltered when cells were irradiated at temperatures up to 41 degrees C. At 43 degrees C and above, cell division was arrested by hyperthermia, an effect unrelated to ultrasound.

Animals↗
PubMed1980

The influence of ultrasound and temperature on the cochlear microphonic response following a round window irradiation.

Impairment of cochlear function was investigated following ultrasonic irradiation of the vestibule and the cochlea through the round window in cats and guinea pigs. Selective destruction of the vestibular balance mechanism with negligible impairment of cochlear microphonic response was achieved, provided that the ultrasound beam was directed away from the cochlea and towards the ampulla of the superior semicircular canal. Directing ultrasound into the cochlea produced a depression in C.M. which was greatest in the higher frequency responsive area corresponding to the region of the first two cochlear turns. The degree of cochlear microphonic depression increased as the duration of irradiation was extended. The occurrence of a significant temperature increase accompanying the application of ultrasound implicated the involvement of a thermal mechanism in addition to the mechanical disruptive effect of ultrasound.

Animals↗
PubMed1977

Round window ultrasonic treatment of Meniere disease.

The neurosensory structures within the vestibular labyrinth of the inner ear are selectively irradiated with ultrasonic energy to alleviate the vertiginous symptoms of Meniere disease. However, correct application and coupling of the ultrasonic transducer to the inner ear is essential for maximum transmission of energy into the vestibule. The importance of assessing the results of long-term postoperative treatment is demonstrated by a change in the success rate that decreased by approximately 10% when the results obtained within the first 12 months of treatment were compared with those after four years. In this investigation, 32 patients were treated by the round window approach between 1970 and 1972, and after four years it was found that 72% of these were successful in relieving the giddiness symptoms.

Evaluation Studies as Topic↗