Acoustic Threshold Research Articles

Acoustic Measurements of Nucleus Size Distribution at the Cavitation Threshold

An understanding of the acoustic cavitation threshold is essential for minimizing cavitation bio-effects in diagnostic ultrasound and for controlling cavitation-mediated tissue ablation in focused ultrasound procedures. The homogeneous cavitation threshold is an intrinsic material property of recognized importance to biomedical ultrasound as well as a variety of other applications requiring cavitation control. However, measurements of the acoustic cavitation threshold in water differ from those predicted by classic nucleation theories. This persistent discrepancy is explained by combining recently developed methods for acoustically nucleating single bubbles at threshold with numerical modeling to obtain a nucleus size distribution consistent with first-principles estimates for ion-stabilized nuclei. We identify acoustic cavitation at threshold as a reproducible subtype of heterogeneous cavitation with a characteristic nucleus size distribution. Knowledge of the nucleus size distribution could inspire new approaches to achieving cavitation control in water, tissue and a variety of other media.

Acoustic cavitation of encapsulated microbubble and its mechanical effect in soft tissue

Ultrasound-induced cavitation in the viscoelastic biological tissues has attracted considerable attention due to its mechanical bio-effects, such as cell sonoporation, hemolysis, vascular disruption and tissue erosion. Cavitation can exert strong mechanical stresses on the surrounding tissues during the rapid bubble growth and collapse. The occurrence of cavitation needs the ultrasound exposure exceeding a certain acoustic pressure threshold, and the cavitation threshold is very high in most tissues, probably causing undesirable side-effects. Introducing artificial cavitation nuclei, e.g., microbubbles and nanodroplets stabilized with a shell such as albumin, lipids or polymers, into the targeted region can effectively reduce the cavitation threshold and significantly enhance the cavitation effects. However, neither the cavitation dynamics of an encapsulated microbubble nor the cavitation-induced stress field around the bubble in a soft tissue is quite clear. In this study, a comprehensive numerical model is developed to describe the dynamics of a lipid-shelled microbubble <i>in vivo</i> and quantify the cavitation-induced mechanical stress in the tissue. Considering the nonlinear changes of both shell viscosity and elasticity, a Gilmore model that has been considered as the most developed and realistic cavitation model is coupled with the Zener viscoelastic model for precisely describing tissue viscoelastic behavior with both creep recovery and stress relaxation of tissue. The developed model has an advantage of accurately describing the bubble behaviors in different biological tissues at high ultrasound intensities, especially for the bubble collapse. Furthermore, the spatiotemporal evolution of mechanical stress in the surrounding tissue generated by the cavitation bubble is investigated. Finally, the effects of encapsulated shell, elasticity modulus and viscosity of tissue as well as ultrasound amplitude are examined. The results show that the viscoelasticity of encapsulated shell and tissue both inhibit the bubble oscillations, and the tissue viscoelasticity has a larger inhibition effect. During the bubble oscillation, the compressive (negative) stress is generated in the tissue with the bubble growing and it continuously increases until it reaches a maximum value at a maximum radius, while the tensile (positive) stress is generated at the stage of bubble collapse and initial stage of bubble rebound due to the restoration of deformed tissue. The stress magnitude is greatest near the bubble wall and decreases rapidly with depth extending into the surrounding tissue. By contrast, the tensile stress decreases at a higher rate than the compressive stress. The encapsulated bubble presents a smaller stress in the tissue, but the decrease of the stress can be ignored at large acoustic pressures. Moreover, the stress decreases with the increase of tissue elasticity modulus, whereas it first increases and then decreases with tissue viscosity increasing, showing a maximum at 15 mPa·s. The increasing of the ultrasound amplitude enhances the bubble oscillations and consequently increases the stress in the tissue. This study is helpful in understanding the bubble dynamics and cavitation-induced mechanical stress of an encapsulated microbubble in soft tissue, which is essential for a safe and precise ultrasound therapy.

Numerical investigation of acoustic vaporization threshold of microdroplets

A numerical model is presented for the acoustic vaporization threshold of a dodecafluoropentane (or perfluoropentane) microdroplet. The model is based on the Rayleigh-Plesset equation and is improved by properly treating the supercritical state that occurs when a bubble collapses rapidly and by employing the van der Waals equation of state to consider the supercritical state. The present computations demonstrate that the microdroplet vaporization behavior depends intricately on bubble compressibility, liquid inertia and phase-change heat transfer under acoustic excitation conditions. We present acoustic pressure-frequency diagrams for bubble growth regimes and the ADV threshold conditions. The effects of acoustic parameters, fluid properties and the droplet radius on the ADV threshold are investigated.

Do Impedance Changes Correlate With a Delayed Hearing Loss After Hybrid L24 Implantation?

Preservation of residual hearing is one of the main goals in present cochlear implantation surgery. Especially for this purpose, smaller and softer electrode carriers were developed that are to be inserted through the round window membrane to minimize trauma. By using these electrodes and insertion technique, residual hearing can be preserved in a large number of patients. Unfortunately, some of these patients with initially preserved residual hearing after cochlear implantation lose it later on. The reason for this is unknown but it is speculated about a correlation with an increase in impedance, since increased impedance values are linked to intracochlear inflammation and tissue reaction. Our hypothesis for this study design was that an increase in impedance predicts changes in residual hearing under clinical conditions. Data of all adult patients (N = 122) receiving a Hybrid-L24 cochlear implant at our center between 2005 and early 2015 were retrospectively evaluated. Impedance values in Common Ground mode as measured during clinical routine and referring audiological test data (audiometric thresholds under headphones) were collected. Changes between consecutive measurements were calculated for impedance values and hearing thresholds for each patient. Correlations between changes in impedances and acoustic hearing thresholds were calculated. Average values were compared as well as patients with largest impedance changes within the observation period were evaluated separately. Group mean values of impedances were between 5 and 7 kΩ and stable over time with higher values on basal electrode contacts compared with apical contacts. Average hearing thresholds at the time of initial fitting were between 40 to 50 dB (250 Hz) and 90 dB (1 kHz) with a loss of about 10 dB compared with preoperative values. Correlation between impedance changes and threshold changes was found, but too inconsistently to imply a true relationship. When evaluating the 20 patients with the largest impedance changes during the observation period (all >1 kΩ from one appointment to the next one), some patients were found where hearing loss is timely connected and highly correlated with an unusual impedance change. But large impedance changes were also observed without affecting hearing thresholds and hearing loss was found without impedance change. Changes in impedance as measured during clinical routine cannot be taken as an indicator for a late acoustic hearing loss.

Effects of different electrodes used in bone-guided extracochlear implants on electrical stimulation of auditory nerves in guinea pigs.

Objective:Conventional cochlear implants provide patients who are deaf with hearing via electrical intracochlear stimulations. Stimulation electrodes are inserted into the cochlea through a cochleostomy or round window membrane (RWM) approach. However, these methods might induce cochlear ossificans and loss of residual hearing by damaging inner ear structures. To avoid an invasive electrode insertion, we developed a novel bone-guided extracochlear implant that stimulated the auditory nerves between the cochlear bones and the RWM to prevent cochlea damage. Power consumption plays an important role in wireless implantable electronic devices. Therefore, we aimed to investigate the effects of different electrodes on the stimulating threshold currents of the auditory nerve and the power consumption of bone-guided extracochlear implants using a commercial stimulator.Materials and Methods:Inert aurum (Au) electrodes were compared with biocompatible platinum (Pt) and iridium oxide (IrOx) electrodes in practical implantable applications. IrOx electrodes were used for their high-charge storage capacity, low impedance, and biocompatibility. The electrodes were fabricated via sputtering and were experimentally characterized with cyclic voltammetry and then examined using in vivo tests.Results:Based on electrical auditory brainstem responses, IrOx electrodes yielded lower acoustic nerve-stimulating threshold currents (132 μA) compared with Au electrodes (204 μA). IrOx electrodes also had a lower acoustic nerve stimulating threshold current (132 μA) compared with Pt electrodes (168 μA).Conclusion:As expected, IrOx electrodes were beneficial in the development of multielectrode bone-guided extracochlear implants, with the lowest acoustic nerve-stimulating threshold and current consumptions compared with Au and Pt electrodes.

The role of electroneural versus electrophonic stimulation on psychoacoustic electric-acoustic masking in cochlear implant users with residual hearing

Cochlear implant (CI) candidates with residual low-frequency hearing are nowadays often implanted with CI electrode arrays that allow preserving their acoustic hearing in the implanted ear. These subjects receiving combined electric-acoustic stimulation (EAS) show enhanced speech perception scores when compared to traditional CI users without acoustic component. However, these benefits are limited by interaction effects such as masking between electric and acoustic stimulation.This study evaluates ipsilateral electric-acoustic masking in a psychophysical experiment conducted in 5 EAS subjects. The elevation of acoustic pure tone thresholds through simultaneous presentation of electric pulse trains and vice versa is measured for different acoustic frequencies and different settings of the electric stimuli. Electric-acoustic interaction could originate either from electroneural stimulation of auditory nerve fibers or from electrophonic stimulation of hair cells. The two fundamental goals of this study are to investigate the effects of stimulation rate and phase duration of the electric stimulus on electric-acoustic masking and to investigate the origin of electric-acoustic masking by assessing the contributions of electroneural versus electrophonic stimulation.The amount of electric-acoustic masking in the present study was independent of pulse rate and phase duration of the electric stimuli. Moreover, the results demonstrate that electric-acoustic masking depends on the spatial distance between the locations of electric or acoustic excitation in the cochlea, but not on the spectral content of the electric stimulus. We thereby conclude that psychoacoustic electric-acoustic masking in EAS users is dominated by electroneural-acoustic interaction, whereas the contribution of electrophonic stimulation is negligible.

Interaction Between Electric and Acoustic Stimulation Influences Speech Perception in Ipsilateral EAS Users.

Objectives:The aim of this study was to determine electric-acoustic masking in cochlear implant users with ipsilateral residual hearing and different electrode insertion depths and to investigate the influence on speech reception. The effects of different fitting strategies—meet, overlap, and a newly developed masking adjusted fitting (UNMASKfit)—on speech reception are compared. If electric-acoustic masking has a detrimental effect on speech reception, the individualized UNMASKfit map might be able to reduce masking and thereby enhance speech reception.Design:Fifteen experienced MED-EL Flex electrode recipients with ipsilateral residual hearing participated in a crosssover design study using three fitting strategies for 4 weeks each. The following strategies were compared: (1) a meet fitting, dividing the frequency range between electric and acoustic stimulation, (2) an overlap fitting, delivering part of the frequency range both acoustically and electrically, and (3) the UNMASKfit, reducing the electric stimulation according to the individual electric-on-acoustic masking strength. A psychoacoustic masking procedure was used to measure the changes in acoustic thresholds due to the presence of electric maskers. Speech reception was measured in noise with the Oldenburg Matrix Sentence test.Results:Behavioral thresholds of acoustic probe tones were significantly elevated in the presence of electric maskers. A maximum of masking was observed when the difference in location between the electric and acoustic stimulation was around one octave in place frequency. Speech reception scores and strength of masking showed a dependency on residual hearing, and speech reception was significantly reduced in the overlap fitting strategy. Electric- acoustic stimulation significantly improved speech reception over electric stimulation alone, with a tendency toward a larger benefit with the UNMASKfit map. In addition, masking was significantly inversely correlated to the speech reception performance difference between the overlap and the meet fitting.Conclusions:(1) This study confirmed the interaction between ipsilateral electric and acoustic stimulation in a psychoacoustic masking experiment. (2) The overlap fitting yielded poorer speech reception performance in stationary noise especially in subjects with strong masking. (3) The newly developed UNMASKfit strategy yielded similar speech reception thresholds with an enhanced acoustic benefit, while at the same time reducing the electric stimulation. This could be beneficial in the long-term if applied as a standard fitting, as hair cells are exposed to less possibly adverse electric stimulation. In this study, the UNMASKfit allowed the participants a better use of their natural hearing even after 1 month of adaptation. It might be feasible to transfer these results to the clinic, by fitting patients with the UNMASKfit upon their first fitting appointment, so that longer adaptation times can further improve speech reception.

Differences in hearing levels between siblings with hearing loss caused by GJB2 mutations

ObjectiveHearing loss caused by GJB2 mutations is inherited in an autosomal recessive manner (DFNB1); thus siblings of an affected child have a 25% chance of also being affected. Hearing loss among subsequent siblings carrying the same GJB2 mutation is a concern for parents and a frequent topic of enquiry during genetic counseling. Evidence exists for genotype-phenotype correlations of GJB2 mutations; however, no analysis of differences in hearing among siblings, in whom the common genetic background may decrease variation, has been reported. The purpose of the present study was to investigate hearing differences between siblings with identical GJB2 mutations. MethodsWe examined the hearing levels of 12 pairs of siblings; each pair had the same pathogenic GJB2 mutations. Differences in hearing acuity between sibling pairs detected by auditory evaluation. ResultsNo significant correlation was detected between the average hearing levels of first and second affected siblings. Average differences in acoustic threshold >30 dB were observed between four pairs of siblings, whereas the remaining eight pairs had average threshold values within 20 dB of one another. ConclusionOur results indicate that auditory acuity would be expected to approximate that found in the first child in approximately 70% of subsequent children with GJB2-mediated hearing loss, whereas 30% of subsequent siblings would have average differences of >30 dB.

Preventing presbycusis in mice with enhanced medial olivocochlear feedback

"Growing old" is the most common cause of hearing loss. Age-related hearing loss (ARHL) (presbycusis) first affects the ability to understand speech in background noise, even when auditory thresholds in quiet are normal. It has been suggested that cochlear denervation ("synaptopathy") is an early contributor to age-related auditory decline. In the present work, we characterized age-related cochlear synaptic degeneration and hair cell loss in mice with enhanced α9α10 cholinergic nicotinic receptors gating kinetics ("gain of function" nAChRs). These mediate inhibitory olivocochlear feedback through the activation of associated calcium-gated potassium channels. Cochlear function was assessed via distortion product otoacoustic emissions and auditory brainstem responses. Cochlear structure was characterized in immunolabeled organ of Corti whole mounts using confocal microscopy to quantify hair cells, auditory neurons, presynaptic ribbons, and postsynaptic glutamate receptors. Aged wild-type mice had elevated acoustic thresholds and synaptic loss. Afferent synapses were lost from inner hair cells throughout the aged cochlea, together with some loss of outer hair cells. In contrast, cochlear structure and function were preserved in aged mice with gain-of-function nAChRs that provide enhanced olivocochlear inhibition, suggesting that efferent feedback is important for long-term maintenance of inner ear function. Our work provides evidence that olivocochlear-mediated resistance to presbycusis-ARHL occurs via the α9α10 nAChR complexes on outer hair cells. Thus, enhancement of the medial olivocochlear system could be a viable strategy to prevent age-related hearing loss.

Manipulation of Nanodroplets via a Nonuniform Focused Acoustic Vortex

Techniques for the manipulation of nanodroplets are central to many miniaturized systems in chemical and biological research and applications. In this study, we demonstrate that the dispersed nanodroplets composed of perfluorocarbon can be manipulated to form a micron-sized elliptical aggregation via a nonuniform focused acoustic vortex, and the aggregation location can be further flexibly regulated. In addition, it is unveiled theoretically and experimentally that the fundamental mechanism for the elliptical aggregation is the nonuniform distribution of the pressure, which makes the acoustic radiation forces acting on the dispersed nanodroplets converge at a certain point. Moreover, the required acoustic droplet vaporization threshold for the nanodroplets is significantly lowered, while the generated microbubbles remain similar in size after aggregation. The findings of this study provide an alternative field of opportunities for targeted drug delivery and imaging using nanodroplet emulsions.

Underwater noise pollution in China’s Yangtze River critically endangers Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis)

Underwater sound plays an important role in some critical life functions of many aquatic animals. Underwater noise pollution has received relatively more attention in ocean systems. However, little attention has been paid to freshwater systems, such as the Yangtze River which is the habitat of critically endangered Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis). In 2012, the underwater noise levels in 25 sites along the middle and lower sections of the Yangtze River were measured. The root mean square sound pressure level (SPL) and unweighted sound exposure level (SEL) at each site ranged between 105 ± 2.4 (median ± quartile deviation) and 150 ± 5.5 dB. Obvious spatial and temporal variations in the SPL were detected among the 25 sites. The SPL and SEL in the middle section of the Yangtze River were smaller (approximately 15 dB) and fluctuated more compared to those in the lower section. The power spectrum in the mainstem was site specific. However, all the spectra levels were higher than the audiogram of Yangtze finless porpoises. Majority of the sites had an averaged cumulative unweighted SEL (72%) and cumulative weighted SEL (68%) that surpassed the underwater acoustic thresholds for onset of hearing temporal threshold shifts for finless porpoise. Porpoise bio-sonars were detected in 89% of sonar monitoring sites indicating that noise pollution in the Yangtze River greatly threatened porpoise survival. In 8% of the sites, the averaged cumulative weighted SEL exceeded that of underwater acoustic thresholds causing non-recoverable permanent threshold shifts of finless porpoises auditory system whereas it was less than 1 dB below the underwater acoustic thresholds in other 8% of the sites. These sites urgently needed noise mitigation and management strategies. These results will facilitate the evaluation of the impacts of anthropogenic noise pollution on local finless porpoises and give further guidelines on its effective conservation.

Acoustic reflex decay and acoustic reflex latency threshold test findings in patients with cerebellopontine angle tumors: Correlation with tumor type, size, and extent

Context: This was a comparative prospective study. Aims: (1) To characterize acoustic reflex decay (ARD) and acoustic reflex latency threshold (ARLT) profiles in cerebellopontine angle (CPA) tumors. (2) To correlate ARD and ARLT test results with the type, size, and extent of tumors. Study Design: Comparative prospective study. Setting: Primary versus Tertiary referral center. Subjects: The clinical group comprised 98 patients with CPA tumor and the control group comprised 100 normal hearing subjects. Subjects and Methods: ARD and ARLT were estimated at 500 Hz and 1000 Hz both ipsilaterally and contralaterally for both the groups. Statistical Analysis Used: Statistical analysis for clinical group versus control group was carried out using analysis of covariance for age and gender covariates. For discrete clinical groups, analysis of variance followed by post hoc (Turkey) test was used. An independent sample t-test was used for the statistical analysis of tumor ear versus nontumor ear. Results: Test results indicated that the proportion of ears with abnormal reflex decay (0%–25%) was less compared to those with normal findings (75%–100%) in the patient group reflecting the poor efficacy of ARD to identify the presence of CPA tumors. Statistical analysis for ARLT was possible mainly for nontumor ear stimulation and it did not give any clear indications regarding the presence of brain stem compression. Conclusions: In the present study, an estimation of ARD and ARLT did not appear to be useful indices for CPA tumor identification.

Audiological profile of patients with SARS-Co-V-2 PCR-positive cases

COVID-19 is a new pandemic caused by a novel coronavirus, SARS-CoV-2. COVID-19 has spread throughout China and received worldwide attention. On 11 February 2020, World Health Organization (WHO) officially declared COVID-19. The clinical symptoms of COVID-19 patients may vary, more often include symptoms affected by upper and lower respiratory tract damage. In ENT practice it is used to mention rhinitis, sore throat, anosmia/hyposmia. The effect of COVID-19 is an interesting issue in audiology. There were 78 patients who were confirmed positive for COVID-19 PCR-positive cases and 30 normal non-infected subjects in our study. The patients were divided into two groups according to severity their clinical symptoms from asymptomatic COVID-19 PCR-positive cases to severe form. All patients underwent audiological evaluation included tympanometry, acoustic threshold and transient evoked otoacoustic emission (TEOAE). Although hearing sensitivity was normal among some participants, it was statistically proved that TEOAEs could pick up subtle deterioration in the outer hair cells functions and impact on the cochlear.

Auditory Brainstem Changes in Timing may Underlie Hyperacusis in a Salicylate-induced Acute Rat Model

Hyperacusis, an exaggerated, sometimes painful perception of loudness even for soft sounds, is a poorly understood distressing condition. While the involvement of modified gain of central auditory neurons and the influence of nonauditory brain regions are well-documented, the issue of where in the auditory system these abnormalities arise remains open, particularly when hyperacusis comes without sensorineural hearing loss. Here we used acute intraperitoneal administration of sodium salicylate (150 mg/kg) in rats, enough to produce > 10-dB decrease in acoustic startle threshold with mild hearing loss at low frequencies (<10 kHz). Anesthesia, necessary for middle-ear-reflex (MEMR) threshold measurements, abolished the olivocochlear efferent reflex but not the MEMR acting on frequencies < 10 kHz, and its mean threshold increased from 55 dB SPL in controls to 80 dB SPL in salicylate-treated animals 60–90 minutes after injection, with an about 3-dB increase in acoustic energy reaching the cochlea. The mean latencies of auditory brainstem-evoked responses (ABR) conspicuously decreased after salicylate, by 0.25 millisecond at 6 kHz at every level, a frequency-dependent effect absent above 12 kHz. A generic model of loudness based upon cross-frequency coincidence detection predicts that with such timing changes, a transient sound may seem as loud at <40 dB SPL as it does in controls at >60 dB SPL. Candidate circuits able to act at the same time on the startle reflex, the MEMR and ABRs may be serotoninergic, as salicylate is known to increase brain serotonin and 5-HT neurons participate in MEMR and ABR circuits.

Pupil-associated states modulate excitability but not stimulus selectivity in primary auditory cortex.

Recent research in mice indicates that luminance-independent fluctuations in pupil size predict variability in spontaneous and evoked activity of single neurons in auditory and visual cortex. These findings suggest that pupil is an indicator of large-scale changes in arousal state that affect sensory processing. However, it is not known whether pupil-related state also influences the selectivity of auditory neurons. We recorded pupil size and single-unit spiking activity in the primary auditory cortex (A1) of nonanesthetized male and female ferrets during presentation of natural vocalizations and tone stimuli that allow measurement of frequency and level tuning. Neurons showed a systematic increase in both spontaneous and sound-evoked activity when pupil was large, as well as desynchronization and a decrease in trial-to-trial variability. Relationships between pupil size and firing rate were nonmonotonic in some cells. In most neurons, several measurements of tuning, including acoustic threshold, spectral bandwidth, and best frequency, remained stable across large changes in pupil size. Across the population, however, there was a small but significant decrease in acoustic threshold when pupil was dilated. In some recordings, we observed rapid, saccade-like eye movements during sustained pupil constriction, which may indicate sleep. Including the presence of this state as a separate variable in a regression model of neural variability accounted for some, but not all, of the variability and nonmonotonicity associated with changes in pupil size.NEW & NOTEWORTHY Cortical neurons vary in their response to repeated stimuli, and some portion of the variability is due to fluctuations in network state. By simultaneously recording pupil and single-neuron activity in auditory cortex of ferrets, we provide new evidence that network state affects the excitability of auditory neurons, but not sensory selectivity. In addition, we report the occurrence of possible sleep states, adding to evidence that pupil provides an index of both sleep and physiological arousal.

Novel acoustic coupling bath using magnetite nanoparticles for MR-guided transcranial focused ultrasound surgery.

Acoustic coupling baths, nominally composed of degassed water, play important roles during transcranial focused ultrasound surgery. However, this large water bolus also degrades the quality of intraoperative magnetic resonance (MR) guidance imaging. In this study, we test the feasibility of using dilute, aqueous magnetite nanoparticle suspensions to suppress these image degradations while preserving acoustic compatibility. We examine the effects of these suspensions on metrics of image quality and acoustic compatibility for two types of transcranial focused ultrasound insonation regimes: low-duty cycle histotripsy procedures and high-duty cycle thermal ablation procedures. Magnetic resonance guidance imaging was used to monitor thermal ablations of in vitro gel targets using a coupling bath composed of various concentrations of aqueous, suspended, magnetite nanoparticles in a clinical transcranial transducer under stationary and flowing conditions. Thermal deposition was monitored using MR thermometry simultaneous to insonation. Then, using normal degassed water as a coupling bath, various concentrations of aqueous, suspended, magnetite nanoparticles were placed at the center of this same transducer and insonated using high-duty cycle pulsing parameters. Passive cavitation detectors recorded cavitation emissions, which were then used to estimate the relative number of cavitation events per insonation (cavitation duty cycle) and thecavitation dose estimates of each nanoparticle concentration. Finally, the nanoparticle mixtures were exposed to low-duty cycle, histotripsy pulses. Passive cavitation detectors monitored cavitation emissions, which were used to estimate cavitation threshold pressures. The nanoparticles reduced the MR signal of the coupling bath by 90% in T2- and T2*-weighted images and also removed almost all imaging artifacts caused by coupling bath motion. The coupling baths caused <5% changes in peak temperature change achieved during sonication, as observed via MR thermometry. At low duty cycleinsonations, the nanoparticles decreased the cavitation threshold pressure by about 15±7% in a manner uncorrelated with nanoparticle concentration. At high duty cycleinsonations, the 0.5 cavitation duty cycle acoustic power threshold varied linearly with nanoparticle concentration. Dilute aqueous magnetite nanoparticle suspensions effectively reduced MR imaging artifacts caused by the acoustic coupling bath. They also attenuated acoustic power deposition by <5%. For low duty cycle insonation regimes, the nanoparticles decreased the cavitation threshold by 15±7%. However, for high-duty cycle regimes, the nanoparticles decreased the threshold for cavitation in proportion to nanoparticle concentration.

Evaluating project-related noise impacts on sleep in environmental assessments: A proposal to apply decibel adjustments to nighttime noise events based on their time of occurrence over the sleep period time

Health Canada is updating its Guidance for evaluating noise in environmental assessments. Current advice on sleep is drawn from the World Health Organization (WHO) which advises that average noise within the bedroom not exceed 30 dBA, and noise events not exceed 45 dB LAmax on more than 10–15 occasions. Both limits increase by 15 dB outdoors assuming partially opened windows. The WHO’s recommended outdoor nighttime annual average of 40 dBA is also used. Two situations commonly arise: (1) the outdoor annual average sound level is exceeded at baseline; or (2) the number of events during sleep exceeds 15, but are just below threshold. Under these situations, the estimated prevalence of high noise annoyance is applied to protect sleep because it includes a 10 dB nighttime penalty. However, this may not account for the variation in the acoustic threshold that has been observed throughout the sleep period. This paper presents two proposals: (1) apply a decibel adjustment to noise events occurring during periods where thresholds are known to be lower (i.e., the first hour and final 3 h) and/or (2) derive a rating level for estimating annoyance using an alternative nighttime adjustment that splits the night into distinct time periods.

Pupil-associated states modulate excitability but not stimulus selectivity in primary auditory cortex

Recent research indicates that luminance-independent fluctuations in pupil size predict variability in spontaneous and evoked activity of single neurons in auditory and visual cortex. These findings suggest that pupil is an indicator of large-scale changes in arousal state that affect sensory processing. It is not known whether pupil-related state also influences the selectivity of auditory neurons. We recorded pupil size and single-unit spiking activity in the primary auditory cortex (A1) of ferrets during presentation of vocalizations and tone stimuli. Neurons showed a systematic increase in both spontaneous and sound-evoked activity when pupil was large, as well as a decrease in trial-to-trial variability. Relationships between pupil size and firing rate were non-monotonic in some cells. In most neurons, several measurements of tuning, including acoustic threshold, spectral bandwidth, and best frequency, remained stable across large changes in pupil size. Across the population, however, there was a small but significant decrease in acoustic threshold when pupil was dilated. In some recordings, we observed rapid, saccade-like eye movements during sustained pupil constriction, which may indicate episodes of rapid eye movement sleep. Including the presence of this state as a separate variable in a regression model of neural variability accounted for some, but not all, of the variability associated with changes in pupil size.Recent research indicates that luminance-independent fluctuations in pupil size predict variability in spontaneous and evoked activity of single neurons in auditory and visual cortex. These findings suggest that pupil is an indicator of large-scale changes in arousal state that affect sensory processing. It is not known whether pupil-related state also influences the selectivity of auditory neurons. We recorded pupil size and single-unit spiking activity in the primary auditory cortex (A1) of ferrets during presentation of vocalizations and tone stimuli. Neurons showed a systematic increase in both spontaneous and sound-evoked activity when pupil was large, as well as a decrease in trial-to-trial variability. Relationships between pupil size and firing rate were non-monotonic in some cells. In most neurons, several measurements of tuning, including acoustic threshold, spectral bandwidth, and best frequency, remained stable across large changes in pupil size. Across the population, however, there was a sma...

Horses for courses (or something much smaller!): The design, development and acoustic testing of sub-micron cavitation nucleation agents for biomedical applications

Lipid and protein-shelled microbubbles have been the mainstay of cavitation nucleation strategies for therapeutic applications for several decades. However, a growing number of therapeutic ultrasound applications require nuclei that (i) are significantly smaller in size, in order to overcome a particular biological barrier such as the leaky vasculature of tumours or the stratum corneum; (ii) offer greatly increased cavitation persistence, both during a single extended ultrasound pulse and in terms of extended circulation following intravenous administration; and (iii) have better resilience to sudden ambient pressure changes in order to enable direct injection without nuclei destruction into tissue targets via a needle and syringe. We will review a range of novel cavitation agents currently under development, including sub-micron gas-stabilizing solid particles and nanodroplets, and provide an overview of their known characteristics in terms of acoustic emissions, activation and cavitation thresholds, cavitation persistence, and circulation. Where possible, the relevant performance of these cavitation nucleation agents will be compared to microbubbles for applications ranging from drug delivery to nucleated tissue fractionation.

Acoustic droplet vaporization threshold of perfluorocarbon droplets as a function of frequency: Effects of droplet cores and size

Phase shift liquid perfluorocarbon (PFC) droplets vaporizable by ultrasound can be used for many therapeutic and diagnostic applications. The ultrasound activation pressure required for the phase change of these droplets into echogenic microbubbles is termed acoustic droplet vaporization (ADV) threshold. We have studied the ADV and IC (inertial cavitation) thresholds in a tubeless setup using an acoustic means varying frequency of the excitation, the droplet core and their average size. The ADV threshold was found to increase with the increasing frequency for the lowest boiling point liquid, perfluoropentane (PFP), for both large and small average size droplets. For higher boiling point liquids, perfluorohexane (PFH) and perfluorooctyle bromide (PFOB), this study did not detect vaporization for small size droplets at the excitation levels (maximum 4 MPa peak negative) studied here. The large PFOB droplets experienced ADV only at the highest excitation frequency 15 MHz. For large PFH droplets, ADV threshold decreases with frequency that could possibly be due to the superharmonic focusing being a significant effect at larger sizes and the higher excitation pressures. ADV thresholds at all the frequencies studied here occurred at lower rarefactional pressures than IC thresholds indicating that phase transition precedes inertial cavitation.