Single Tone Bursts Research Articles

Evaluation of the properties of daughter bubbles generated by inertial cavitation of preformed microbubbles

Inertial cavitation (IC) of the preformed microbubbles is being investigated for ultrasound imaging and therapeutic applications. However, microbubbles rupture during IC, creating smaller daughter bubbles (DBs), which may cause undesired bioeffects in the target region. Thus, it is important to determine the properties of DBs to achieve controllable cavitation activity for applications. In this study, we theoretically calculated the dissolution dynamics of sulfur hexafluoride bubbles. Then, we applied a 1-MHz single tone burst with different peak negative pressures (PNPs) and pulse lengths (PLs), and multiple 5-MHz tone bursts with fixed acoustic conditions to elicit IC of the preformed SonoVue microbubbles and scattering of DBs, respectively. After the IC and scattering signals were received by a 7.5-MHz transducer, time- and frequency-domain analysis was performed to obtain the IC dose and scattering intensity curve. The theoretical dissolution curves and measured scattering intensity curves were combined to determine the effect of the incident pulse parameters on the lifetime, mean radius and distribution range of DBs. Increased PNP reduced the lifetime and mean size of the DBs population and narrowed the size distribution. The proportion of small DBs (less than resonance size) increased from 36.83% to 85.98% with an increase in the PNP from 0.6 to 1.6 MPa. Moreover, increased PL caused a shift of the DB population to the smaller bubbles with shorter lifetime and narrower distribution. The proportion of small bubbles increased from 25.74% to 95.08% as the PL was increased from 5 to 100 µs. Finally, increased IC dose caused a smaller mean size, shorter lifetime and narrower distribution in the DB population. These results provide new insight into the relationship between the incident acoustic parameters and the properties of DBs, and a feasible strategy for achieving controllable cavitation activity in applications.

Shear wave elastography with combined high spatial and temporal frequency excitations

Shear wave elastography is a method for quantitatively measuring the mechanical properties of soft tissues. Shear wave attenuation is high in soft tissues and increases with frequency. In a recent work, high resolution and accuracy can be reached at higher temporal frequencies. To combat the high shear wave attenuation and to obtain higher accuracy and lower variability, we propose to combine acoustic radiation force excitations that have multiple push beams and high temporal frequencies. Multiple push beams were generated with multiple focused beams and multiple intersecting unfocused beams. Measurements made with tonebursts of ultrasound with length 200 μs repeated at 500 and 1000 Hz were compared against a single toneburst. Measurements were made in commercial homogeneous and heterogeneous phantoms. Wave velocity images were reconstructed from the acquired data. The accuracy and variance were evaluated in the homogeneous phantoms. The contrast and accuracy were evaluated in the heterogeneous phantoms. In both types of phantoms, the magnitude at selected frequencies will be compared among the different excitations. The frequency bandwidth for each excitation will be compared. This work highlights that the combination of multiple push beams and excitations with high temporal frequencies can be combined for improved imaging in shear wave elastography.

Study on the measurement speed and signal to noise ratio of multi tone burst wave for high speed non-contact acoustic inspection method

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method which uses the conventional single tone burst wave, since only one frequency was used for one sound wave emission, the length of measurement time had become a problem. Therefore, the multi-tone burst wave was devised for high speed improvement. However, measurement time and signal to noise (S/N) ratio change with the parameters in which a multi-tone burst wave is contained at the time of one sound wave emission, such as the number of frequency, the arranging method, pulse length, and the average number of times. Therefore, the experiment using the concrete test object having the styrofoam which imitated the cavity defect was conducted and a multi-tone burst wave was used, it was investigated how the measurement time and the S/N ratio of this method would change. From the experimental result, it became clear that the improvement in the measurement speed of several or more times was realizable maintaining a comparable S/N ratio as compared with the conventional single tone burst wave.

High speed non-contact acoustic inspection method using multi tone burst wave

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method using a single tone burst wave, the length of the measurement time of a two-dimensional scan was a practical problem. This is because only one frequency was used for one sound wave emission so that a high signal to noise (S/N) ratio could be obtained with the laser Doppler vibrometer (LDV) of a weak laser power (e.g., He-Ne 1mW). However, two or more frequency can be used at the time of one sound wave emission (multi tone burst wave) by taking into consideration the difference of the propagation velocity of a sound wave and laser light. That is, it becomes possible to perform high-speed measurement as compared with the conventional method, using effectively the time & frequency gate for raising a S/N ratio by terminating measurement before the reflective sound wave reaches a laser head from the measurement surface. The experiment using a concrete test object was carried out and the validity of this multi tone burst wave as high-speed measurement was confirmed from the experimental result.

Nonlinear multi-frequency generation for underwater application

This study examines the feasibility of designing a multi-frequency acoustic surveying tool based on the saturation effect. The transmitter is driven by a high-power single tone-burst: nonlinear propagation creates the beams at harmonic frequencies. A simple pseudo one-dimensional model is used to estimate the expected on-axis harmonic levels generated with a rectangular aperture. First measurements are reported and compared with the estimations.

Underwater speed of sound and ranging measurements using the sliding discrete Fourier transform.

It is often desirable to extract parametric information from a signal in order to determine its properties with high accuracy. Such parameters might be the time delay, the amplitude, the frequency, and/or the phase. These parameters are usually highly correlated with the material through which the signal has passed or from which it has been reflected. Time delay estimation is a fundamental step in source localization or beamforming applications, and has attracted considerable research attention over the past few decades in many fields. In this paper, we propose a novel time delay estimation approach based on the sliding discrete Fourier transform (DFT). The analysis window is slid sample by sample over the received single frequency tone burst signal with the DFT evaluated successively. The optimal peak spectrum and its corresponding phase are used to estimate the time delay of the signal. We use the corresponding time as the first estimate, which is improved based on the related phase. Simulated examples are given with synthetic signals. An underwater application for speed of sound measurements using this approach compared to those obtained by a commercial device is then demonstrated. Finally, the proposed method is shown to outperform standard correlator‐based approaches.

Embedded System for Real-Time Digital Processing of Medical Ultrasound Doppler Signals

Ultrasound (US) Doppler systems are routinely used for the diagnosis of cardiovascular diseases. Depending on the application, either single tone bursts or more complex waveforms are periodically transmitted throughout a piezoelectric transducer towards the region of interest. Extraction of Doppler information from echoes backscattered from moving blood cells typically involves coherent demodulation and matched filtering of the received signal, followed by a suitable processing module. In this paper, we present an embedded Doppler US system which has been designed as open research platform, programmable according to a variety of strategies in both transmission and reception. By suitably sharing the processing tasks between a state-of-the-art FGPA and a DSP, the system can be used in several medical US applications. As reference examples, the detection of microemboli in cerebral circulation and the measurement of wall _distension_ in carotid arteries are finally presented.

Age-related differences in discrimination of an interval separating onsets of successive tone bursts as a function of interval duration

The study measured listener sensitivity to increments in the inter-onset interval (IOI) separating pairs of successive 20-ms 4000-Hz tone pulses. A silent interval between the tone pulses was adjusted across conditions to create reference tonal IOI values of 25-600 ms. For each condition, a duration DL for increments of the tonal IOI was measured in listeners comprised of young normal-hearing adults and two groups of older adults with and without high-frequency hearing loss. Discrimination performance of all listeners was poorest for the shorter reference IOIs, and improved to stable levels for longer reference intervals exceeding about 200 ms. Temporal sensitivity of the young listeners was significantly better than that of the elderly listeners in each condition, with the largest age-related differences observed for the shortest reference interval. Age-related differences were also observed for duration DLs measured using single 4000-Hz tone bursts set to three reference durations in the range 50-200 ms. The tone DLs of all listeners were smaller than the corresponding tone-pair IOI DLs, particularly for the shorter reference stimulus durations. There were no significant performance differences observed between the older listeners with and without hearing loss for either discrimination task.

Environmental Enrichment Increases Paired-Pulse Depression in Rat Auditory Cortex

Temporal features are important for the identification of natural sounds. Earlier studies have shown that cortical processing of temporal information can be altered by long-term experience with modulated sounds. In a previous study, we observed that environmental enrichment dramatically increased the response of cortical neurons to single tone and noise burst stimuli in both awake and anesthetized rats. Here, we evaluate how enrichment influences temporal information processing in the auditory cortex. We recorded responses to repeated tones and noise bursts in awake rats using epidural evoked potentials and in anesthetized rats using microelectrodes. Enrichment increased the response of cortical neurons to stimuli presented at slow rates and decreased the response to stimuli presented at fast rates relative to controls. Our observation that enrichment substantially increased response strength and forward masking is consistent with earlier reports that long-term potentiation of cortical synapses is associated with increased paired-pulse depression. Enrichment also increased response synchronization at slow rates and decreased synchronization at fast rates. Paired-pulse depression increased within days of environmental enrichment and was restored to normal levels after return to standard housing conditions. These results are relevant to several clinical disorders characterized by abnormal gating of sensory information, including autism, schizophrenia, and dyslexia.

On the acoustic vaporization of micrometer-sized droplets

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 micros tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 microm, independent of droplet diameter which ranged from 5 to 27 microm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet's imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.

Comparison of ABR Stimuli for the Early Detection of Ototoxicity: Conventional Clicks Compared with High Frequency Clicks and Single Frequency Tonebursts

Effective objective testing methodology is needed for early detection of the effects of ototoxicity on hearing in patients. The requirements for such testing include responses that are: 1) reliable across test sessions; 2) sensitive to ototoxic change ( > 8 kHz), and 3) recordable in a time-efficient manner. Auditory brainstem responses (ABR) appear well suited to this task however, conventional clicks stimulate primarily mid-frequencies (1-4 kHz) and high frequency tonebursts require too much time. We hypothesized that delivery of a band of high frequencies (a high frequency "click"), would elicit reliable and useful ABRs. In the current study, flat and sloped HF (high frequency) clicks with a bandwidth of 8-14 kHz were used. The purpose was to compare brainstem responses elicited by tonebursts, two HF clicks and conventional clicks. The results show that the reliability of responses to the HF clicks were comparable to the tonebursts and further, both HF clicks produced responses slightly larger than tonebursts.

Optical observations of single droplets during acoustic vaporization

It has been shown previously that Acoustic Droplet Vaporization (ADV) causes bubbles to form from small droplets. This paper shows that prior to vaporization the droplets undergo translatory (dipole) oscillations when exposed to tone bursts. A high speed video system was used to monitor droplets in a flow tube when single-element focused transducers (3.5 and 10 MHz) were used for ADV on individual droplets. Single sinusoidal tone burst (<3.3 μs) were sufficient for ADV of droplets with 5 to 25 micrometer diameter. Dipole oscillations of 1.3 μm independent of diameter were found. Variations in the droplet diameter of up to 15% were observed during the onset of acoustic irradiation. The pressure threshold for ADV decreased with increasing droplet diameter. The onset of vaporization was seen either as a localized event within or homogeneously throughout the imaged droplet (possibly due to the temporal resolution of the imaging system). Localized nucleation was solely observed along the direction of dipole motion of the droplet, which is the same as the direction of the propagating acoustic wave. Typically, sites on ‘‘north and/or south poles’’ were observed. [Research supported by PHS Grant No. R01HL54201 and US Army Grant No. DAMD17-00-1-0344.]

Acoustic vaporization of single droplets

It has been observed in the past that droplets in emulsions can be vaporized into gas bubbles by the application of acoustic tone bursts. This paper will show the vaporization of single albumin stabilized droplets as they are exposed to single acoustic tone bursts. An optical microscope was used to monitor single droplets in a flow tube (200 μm diameter). The flow tube was mounted in a small water tank with degassed and heated water (37<th>°C). A single-element focused transducer with a center frequency of 10 MHz was aimed at the intersect of the tube and the optical beam. A highly dilute droplet emulsion was injected into the flow tube and a special syringe setup was used to move the fluid column in the flow tube back and forth to position individual droplets in the volume of interest. A single sinusoidal tone burst (33 cycles at 10 MHz) was sufficient to transition single droplets in the range from 5 to 15 μm diameter. The formation of the corresponding gas bubbles was monitored and measured in the range of 30 to 90 μm. [Work supported by PHS Grant No. R01HL54201 and US Army Grant No. DAMD17-00-1-0344.]

Multiple combination-sensitive neurons in the auditory cortex of the mustached bat

The mustached bat, Pteronotus parnellii, emits biosonar pulses consisting of four constant-frequency (CF1–4) and four frequency-modulated (FM1–4) components. The FM–FM area of its auditory cortex consists of three subdivisions, containing either FM1–FM2, FM1–FM3 or FM1–FM4 combination-sensitive neurons. The FM–FM area also contains ‘multiple combination-sensitive’ neurons: FM1–FM2,3, FM1–FM3,4, FM1–FM2,4, and FM1–FM2,3,4 neurons. All FM–FM neurons are tuned to a time delay (echo delay) of FMn (n=2–4) from FM1. In the present study, we made the following four major findings. (1) Multiple combination-sensitive neurons show the strongest response to a combination of more than two signal elements. (2) Multiple combination-sensitive neurons are located in about 100 μm wide bands at the boundaries between two adjacent subdivisions of the FM–FM area. (3) Iso-best-delay contour lines across the three single combination-sensitive subdivisions are not interrupted by multiple combination-sensitive bands. (4) Each subdivision of the FM–FM area has frequency-vs.-frequency coordinates in terms of best FM1 and best FMn frequencies for facilitation, although such coordinates were not obtained with single tone bursts.

Suppression of tone burst evoked otoacoustic emissions in relation to frequency separation

Tone burst evoked otoacoustic emissions (TBEOAEs) were measured for two tone bursts presented separately and as a two-tone burst complex to examine the linearity of TBEOAE generators for different frequency separations of the stimuli. The stimuli were: (a) tone bursts of 5-ms duration and center frequencies of 1, 1.5, 2 and 3 kHz; (b) complex stimuli with the 1-kHz tone burst combined digitally with each of the other specified tone bursts. Signals were delivered at 70 dB SPL using a non-linear processing method and at 60 dB SPL using a linear method to 21 ears of normally hearing adults. Spectra of TBEOAEs obtained with single-tone bursts were superimposed (composite) and compared to those of the two-tone burst complex. A close correspondence between the composite and complex spectra was present in all ears. However, the components on the higher-frequency slope of the 1-kHz spectral peak were reduced in the complex spectra obtained with a frequency separation of 0.5 kHz when compared to the corresponding composite spectra. The reduction was greater at a stimulus level of 70 dB SPL than with 60 dB SPL. The effect was smaller for a frequency separation of 1 kHz, and almost absent for the tone burst separation of 2 kHz. Thus, suppression leads to weak non-linear frequency superposition for higher-level, closely spaced stimuli.

Perceived continuity and pitch perception.

Three experiments investigated the importance of perceived stimulus continuity for the perception of the fundamental frequency (F0) of an unresolved complex tone. The F0 of the complex was 250 Hz and the harmonics were bandpass filtered between 5500 and 7500 Hz. In the first experiment, F0 discrimination was measured for single-burst tones with durations of 20, 40, and 80 ms, and for stimuli containing two 20- or 40-ms tone bursts separated by an 8- or 16-ms gap. For the single-burst conditions, there was a large decrease in threshold as the duration was increased from 20 to 40 ms. However, performance in the gapped conditions was much worse than that for the single-burst condition with the same cumulative duration (e.g., two 20-ms bursts separated by 8 ms produced higher thresholds than one 40-ms burst). Adding a bandpass noise (with the same spectral envelope as the tone) in the gap between the two tone bursts improved performance to the level of the single-burst condition. When the noise was added, the two discrete tone bursts were perceived as one single tone burst interrupted by the noise, and this seemed to facilitate discrimination. In a second experiment, the effects on pitch of an envelope delay (phase shift) of 0.75 periods between two tone bursts separated by an 8-ms gap were investigated. If the gap was silent, the pitch of the pair was unaffected by the phase shift. However, if the gap contained the bandpass noise, the phase shift between the bursts did produce a significant downward shift in the pitch of the pair. Finally, the third experiment showed that presenting a noise before a single 20-ms burst may improve discrimination performance in some listeners, but not sufficiently to account for the results of the first experiment purely in terms of an improvement in the discriminability of the second tone burst in the pair. The experiments suggest that a level decrease between two tone bursts may disrupt or reset a long integration mechanism, decreasing performance. When there is no level decrease between the bursts, the auditory system may assume that the two bursts belong to the same single tone and analyze them together in order to derive F0.

Reliability of auditory brainstem responses from sequenced high-frequency (> or = 8 kHz) tonebursts.

An auditory brainstem response method is described for evoking responses to 4 high-frequency (8, 10, 12 and 14 kHz) tonebursts in the same amount of time normally required to obtain responses to single tonebursts. Reliability of responses to high-frequency toneburst stimuli presented in the conventional manner (one at a time) has been previously documented. In the present study, high-frequency tonebursts were presented to 20 normal-hearing subjects singly and in a 4-stimulus sequence. The reliability of resulting responses did not differ significantly between single- and multiple-stimulus test conditions. It is concluded that this sequenced-stimulus concept could be developed for use in serial monitoring of individuals receiving ototoxic agents as well as being broadly applicable to clinical situations in which patients cannot or will not respond voluntarily.

Peripheral analysis of frequency in human ears revealed by tone burst evoked otoacoustic emissions

Otoacoustic emissions were evoked in the same ears with single tone bursts at 1, 2 and 3 kHz and with a complex stimulus consisting of a digital addition of the three tone bursts. Stimuli were presented at 75, 59 and 37 dB SPL to 28 ears of human subjects with normal hearing. The purpose was to determine if comparisons of responses to the complex stimulus with a posthoc addition of responses from single tone bursts could delineate features of cochlear frequency analysis of short-duration signals. For processing of the data, the results from the individual tone bursts were combined offline to form a composite response. This was then compared with the response obtained with the complex stimulus. Results revealed close correspondence between the spectra of the complex and composite responses in all ears despite interindividual differences in response morphology. Correlations between the complex and composite waveforms exceeded 80% for all stimulus levels. Subtractions of the two spectra revealed that the majority of the differences occurred at frequencies on the high-frequency slopes of the 1- and 2-kHz spectral peaks. This was due to a reduction in energy for the responses obtained with the complex stimulus. There was little variation between the two response types in the peak frequencies of their spectra, in the energy at frequencies on the lower frequency sides of the spectral peaks at 1 and 2 kHz, or in the spectral components at 3 kHz. Results reveal characteristics of the analysis of frequency in the preneural stages of cochlear processing.

Delay lines and amplitude selectivity are created in subthalamic auditory nuclei: the brachium of the inferior colliculus of the mustached bat.

1. The biosonar pulse of the mustached bat, Pteronotus parnellii parnellii, consists of four harmonics of a constant-frequency component (CF1-4) followed by a frequency-modulated component (FM1-4). FM-FM combination-sensitive neurons in the auditory cortex and the medical geniculate body (MGB) show facilitative responses to certain combinations of FM components in a pulse-echo pair. They are tuned to particular delays of echo FMn (EFMn) (n = 2, 3, or 4) from pulse FM1 (PFM1). The neural mechanisms for creating their response properties involve delay lines, coincidence detection, and multiplication. Coincidence detection and multiplication take place in the MGB. It is not yet known where and how delay lines are created. The first aim of the present studies is to examine whether delay lines are created by subthalamic nuclei. FM-FM neurons are tuned to not only echo delays but also echo amplitudes. Therefore, the second aim of the present studies is to examine the extent to which amplitude selectivity is created by subthalamic nuclei. Responses of single nerve fibers to acoustic stimuli were recorded from the brachium of the inferior colliculus (BIC) using tungsten wire microelectrodes, and their response latencies and best amplitudes were measured. 2. All BIC fibers responded strongly to single tone bursts. No FM-FM combination-sensitive neurons were found in the BIC. The best frequencies of BIC fibers were predominantly within the frequency ranges of four harmonics of the species-specific biosonar pulse. 3. The response latencies of BIC fibers tuned to FM1 were more diverse (3.5-15.0 ms) than those of BIC fibers tuned to FMn (3.8-6.5 ms). This difference in latency distribution was independent of stimulus amplitude. These data are consistent with the theory that delay lines utilized by FM-FM neurons are created by neurons tuned to the "FM1 frequency," and indicate that the delay lines are mostly, if not all, created in a subthalamic nucleus or nuclei. 4. The best amplitudes of BIC fibers tuned to FM1 or CF1 were 63.2 +/- 4.5 (SE) dB SPL, and those of BIC fibers tuned to FMn or CFn were 48.2 +/- 10.7 dB SPL. The distribution of the best amplitudes of BIC fibers were very similar to those of FM-FM and CF/CF neurons in the MGB. These data indicate that the amplitude selectivity of thalamic FM-FM and CF/CF neurons is mainly a product of a subthalamic nucleus or nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Parametric modeling of the temporal dynamics of neuronal responses using connectionist architectures

1. We describe an exploratory approach to the parametric modeling of dynamical (time-varying) neurophysiological data. The models use stimulus data from a window of time to predict the neuronal firing rate at the end of that window. The most successful models were feedforward three-layered networks of input, hidden, and output "nodes" connected by weights that were adjusted during a training phase by the backpropagation algorithm. The memory in these models was represented by delay lines of varying length propagating activation between the layers. Connectionist models with no memory (1 sequential node per layer) as well as zero-memory nonlinear nonconnectionist models were also tested. 2. Models were tested with recordings of neuronal activity from the auditory thalamic nucleus ovoidalis of urethane-anesthetized zebra finches (Taeniopygia guttata). All cells reported here showed phasic/tonic responses. Extensive modeling of one neuron (cell 1) defined a "canonical" architecture, which was most successful in modeling this cell. The canonical model had a zero-memory input layer, a hidden layer with 29 bins representing 185.6 ms, and a single output node whose value as a function of sequential bin position represented the output of the neuron as a function of time. The canonical model achieved convergence on the entire data set for cell 1, including responses to single tone bursts and zebra finch songs. The "frequency" weights of the canonical model matched well excitatory and inhibitory frequencies for cell 1 as determined by the cell's frequency tuning curve. The "memory" weights of the canonical model were dominated by excitation over the first 25 ms followed by inhibition. 3. When trained with only the dynamical responses to tone bursts, the canonical model also accurately predicted the responses to song (average R2 = 0.823). Thus for this neuron the responses to single tone bursts were sufficient to predict most of the responses to six different songs, each presented at three different amplitudes, although a Monte Carlo procedure indicated the residual variance was not just due to noise (P < 0.001). 4. The model's ability to predict the responses to song was further explored by altering the tone burst (training) data. For cell 1, the responses to songs were most strongly related to the phasic/tonic details of the temporal responses to tone bursts. Changes in the characteristic frequency, frequency tuning curves, and rate/intensity function of the neuron had less effect. These experiments would be difficult or impossible to conduct electrophysiologically.(ABSTRACT TRUNCATED AT 400 WORDS)