Biomedical subjects

Mingxi Wan

Publications and source records attributed to Mingxi Wan.

At least 19 recordsLinked to original sources

PubMed2006

High-speed observation of cavitation bubble cloud structures in the focal region of a 1.2 MHz high-intensity focused ultrasound transducer.

Cavitation bubble clouds in the focal region of HIFU play important roles in therapeutic applications of HIFU. Temporal evolution and spatial distribution of cavitation bubble clouds generated in the focal region of a 1.2 MHz single element concave HIFU transducer in water are investigated by high-speed photography. It is found that during the initial 600 micro s insonation cavitation bubble clouds organize to the "screw-like structure" or "cap-like structure". The screw-like structure is characterized by a nearly fixed tip at the geometrical focus of the HIFU transducer, and the cap-like structure is marked by a dent formed in the direction of ultrasound transmission. After 600 micro s, another two structures are recorded - "streamer structure" and "cluster structure". The streamer structure is also featured by a nearly fixed bottom position at the focus, while the cluster structure is distinguished by agglomerations of bubbles around the focus.

Journal Article↗

PubMed2006

The effect of tonal changes on voice onset time in Mandarin esophageal speech.

SUMMARY: The present study investigated the effect of tonal changes on voice onset time (VOT) between normal laryngeal (NL) and superior esophageal (SE) speakers of Mandarin Chinese. VOT values were measured from the syllables /pha/, /tha/, and /kha/ produced at four tone levels by eight NL and seven SE speakers who were native speakers of Mandarin. Results indicated that Mandarin tones were associated with significantly different VOT values for NL speakers, in which high-falling tone was associated with significantly shorter VOT values than mid-rising tone and falling-rising tone. Regarding speaker group, SE speakers showed significantly shorter VOT values than NL speakers across all tone levels. This may be related to their use of pharyngoesophageal (PE) segment as another sound source. SE speakers appear to take a shorter time to start PE segment vibration compared to NL speakers using the vocal folds for vibration.

Aged↗

PubMed2006

Design and experiment of 256-element ultrasound phased array for noninvasive focused ultrasound surgery.

A 256-element phased array high intensity focused ultrasound system has been designed and constructed in our laboratory. The 256-element spherical-section ultrasound phased array made from piezocomposite material operates at 1.1 MHz with 11-cm radius of curvature, 14-cm outer diameter, and 3.4-cm diameter central hole for mounting diagnostic ultrasound imaging probe. First, the explicit sound field calculation approach for the spherical-section phased array and the genetic optimal algorithm are briefly introduced as the optimal focus pattern control methods. Then, the design guidelines of 256-element spherical-section focused ultrasound phased array and 256-channel driver system are given. The results of single on and off axial focus, multiple on and off axial foci, half sub-array focus pattern provide further evidence for the 3D focus steering and sub-array mode for avoiding obstacles in focused ultrasound surgery. The multi-foci pattern can enlarge the treatment volume to 22 times larger than that of a single focus in one sonication. Finally, in vitro and transparent tissue-mimicking phantom experiment results confirm the ability of 256-element spherical-section phased array system to induce thermal lesions for noninvasive ultrasound surgery.

Equipment Design↗

PubMed2006

Differential ultrasonic imaging for the characterization of lesions induced by high intensity focused ultrasound.

High intensity focused ultrasound (HIFU) is an effective technique for noninvasive local creating coagulative necrotic lesions in deep target volumes without damage to the overlaying or surrounding tissues. It is very important to detect and evaluate lesions generated by HIFU during treatment procedures. This study describes the development of several differential ultrasonic imaging techniques to characterize lesions based on estimation of relative changes in tissue properties derived from backscattered RF data. A single, spherical HIFU transducer was used to produce lesions in soft tissues. The RF signals were recorded as outputs from a modified diagnostic ultrasound system. After some preprocessing, the integrated backscatter values, which can be used as an indicator of the microstructure and backscattering property of tissues, were calculated before and after HIFU treatment. The differential integrated backscatter values were subsequently used to form images revealing the lesion areas. The differential attenuation imaging with the same RF data was also performed, which has been proposed by a few researchers. The results of the differential integrated backscatter imaging were compared with that of the differential attenuation imaging and the former method offers some advantages over the latter method. The two methods above are both based on spectrum analysis and would spend much computational time. Therefore, some simple digital differential imaging methods, including absolute difference (AD), sum absolute differences (SAD), and sum squared differences (SSD) algorithms, were also proposed to detect HIFU-induced lesions. However, these methods cannot provide the information of the degree of tissue damage. Experiments in vitro bovine muscle and liver validated the method of differential integrated backscatter imaging for the characterization of HIFU-induced lesions. And the AD, SAD, and SSD algorithms can be implemented in real-time during HIFU therapy to visualize the lesions.

Image Enhancement↗

PubMed2006

Optimal design and experimental investigation of surfactant encapsulated microbubbles.

The diagnostic capabilities of ultrasound imaging can be improved with contrast-specific nonlinear imaging modalities such as harmonic and subharmonic imaging. The nonlinear response of an encapsulated microbubble in an acoustic field is strongly influenced by the shell viscoelastic properties that are determined by the shell composition and thickness. In this paper, the subharmonic performance of a surfactant encapsulated microbubble was optimized by choosing the appropriate composition of shell material with the aid of theoretical model. To study the effects of viscoelastic properties of microbubble shell materials on the nonlinear scattered response of microbubbles, a theoretical model-modified Herring equation for the oscillation of encapsulated microbubbles in the ultrasound field was employed. Based on this model, a computer aided design system was developed to optimize and analyze the acoustic properties, particularly subharmonic responses, of microbubbles under different shell parameters. Furthermore, surfactant encapsulated microbubbles with different viscoelastic properties were prepared by changing the shell composition. Their shell viscoelastic behavior was measured indirectly as dilational modulus of monolayer film formed with surfactant molecular. Moreover, in vitro quantitative acoustic properties measurements of these microbubbles were carried out to evaluate their subharmonic performance. Both of the theoretical simulation and acoustic measurement showed that the surfactant encapsulated microbubbles with good subharmonic properties could be designed and prepared by adjusting the shell material composition with the guide of the computer aided design system.

Capsules↗

PubMed2006

The inception of cavitation bubble clouds induced by high-intensity focused ultrasound.

In many therapeutic applications of high-intensity focused ultrasound (HIFU) the appearance of cavitation bubbles is unavoidable, whereas the dynamics of the bubbles induced by HIFU have not been clarified. The objective of the present work is to observe the inception process of cavitation bubble clouds generated by HIFU transducer in water using high-speed photography. Sequential images captured within 600 micros after the onset of ultrasound transmission show the dynamics of cavitation bubbles' generation, growth, deformation, expansion and collapse in the focal region. However, when the observation time is narrowed to the initial 145 micros, both the still and streak images reveal that the cavitation bubbles astonishingly stay stable in the focal region for at least 60 micros. The results imply that through adjusting the HIFU exposure time while other physical parameters are appropriately chosen, it might be possible to control the generation of stable cavitation bubbles locally in the focal region.

Dose-Response Relationship, Radiation↗

PubMed2006

Spatial-temporal dynamics of cavitation bubble clouds in 1.2 MHz focused ultrasound field.

Cavitation bubbles have been recognized as being essential to many applications of ultrasound. Temporal evolution and spatial distribution of cavitation bubble clouds induced by a focused ultrasound transducer of 1.2 MHz center frequency are investigated by high-speed photography. It is revealed that at a total acoustic power of 72 W the cavitation bubble cloud first emerges in the focal region where cavitation bubbles are observed to generate, grow, merge and collapse during the initial 600 micros. The bubble cloud then grows upward to the post-focal region, and finally becomes visible in the pre-focal region. The structure of the final bubble cloud is characterized by regional distribution of cavitation bubbles in the ultrasound field. The cavitation bubble cloud structure remains stable when the acoustic power is increased from 25 W to 107 W, but it changes to a more violent form when the acoustic power is further increased to 175 W.

Acoustics↗

PubMed2006

The effect of three-dimensional glottal geometry on intraglottal quasi-steady flow distributions and their relationship with phonation.

Vocal fold geometry plays an important role in human phonation. The intraglottal quasi-steady pressure and velocity distributions depend upon the shape, size, and diameter of the glottis. This study reports the effects of the variation of glottal shapes on intraglottal pressures and velocities using a Plexiglas model with a glottis having nine symmetric glottal angles (uniform, as well as convergent and divergent 5 degrees, 10 degrees, 20 degrees and 40 degrees), while the minimal glottal diameter was held constant at 0.06 cm. The empirical data were supported by penalty finite element computational results. The results suggest that larger convergent glottal angles correspond to increased pressures and decreased velocities in the glottis upstream of the minimum glottal location, with a reversal of this pattern at the minimal glottal diameter location. The pressure dip near the glottal entrance for divergent glottal angles was greatest for the 10 degrees divergence angle condition, and was sequentially less for 5 degrees, 20 degrees, and 40 degrees. Flow resistance was greater for a convergent angle than a divergent angle of the same value, and least for the 10 degrees divergent condition. Pressure recovery in the glottis suggested that the optimal glottal diffuser angle was near 10 degrees. Results suggest that the glottal geometry has a critical relationship with phonation (especially for vocal efficiency), and therefore important significance to understanding artistic voice and clinical voice management.

Glottis↗

PubMed2006

Enhancement of electrolarynx speech based on auditory masking.

Electrolarynx (EL) speech provides a valuable means of verbal communication for the laryngectomees. Yet EL speech tends to be less intelligible speech due to the presence of background noise. This paper addresses the issue of EL speech enhancement. The proposed approach takes into account the frequency-domain masking properties of the human auditory system for a subtractive-type enhancement process. Subtractive-type algorithms can efficiently reduce the radiated noise of EL speech but not to reduce the additive noise from the environment due to the use of fixed subtraction parameters. Considering the particular characteristics of EL speech, a new computationally efficient algorithm based on the perceptual weighting technique is developed to adapt the subtraction parameters. This leads to a significant reduction of the unnatural structure of the residual noise. Acoustic and perceptual experiments confirm that the enhanced EL speech is more pleasant to human listeners and the proposed algorithm results in improved performance over classical subtractive-type algorithms.

Algorithms↗

PubMed2006

Numerical study of the effects of inferior and superior vocal fold surface angles on vocal fold pressure distributions.

Vocal fold geometry plays an important role in human phonation. A wide range of inferior and superior vocal fold surface angles has been shown to be present during phonation [Nanayakkara, Master's thesis, Bowling Green State University, Bowling Green, OH (2005)]. This study explored how these angles affect pressure distributions on the vocal folds, and thus how they may affect phonation. The computational code FLUENT was used to obtain pressure distributions for laminar, incompressible flow. Eighteen inferior vocal fold surface angles and nineteen superior vocal fold surface angles were selected for three specific glottal angles, uniform 0 degrees, convergent 10 degrees, and divergent 10 degrees. Minimal glottal diameter (0.01 cm), transglottal pressure (8 cm H2O), and glottal entrance radius (0.15 cm) were held constant, and the glottal exit radius was constant for each glottal angle. Results suggest that the vocal fold surface pressures are independent of the inferior and superior vocal fold surface angles realistic for human phonation. These results suggest that, in contrast to the important effects of glottal entrance and exit radii, minimal diameter, and angle on intraglottal pressures, the inferior and superior vocal fold surface angles (excluding possible interactive effects with the false vocal folds) do not have an influence on the intraglottal pressures.

Binomial Distribution↗

PubMed2006

Application of spectral subtraction method on enhancement of electrolarynx speech.

Although electrolarynx (EL) serves as an important method of phonation for the laryngectomees, the resulting speech is of poor intelligibility due to the presence of a steady background noise caused by the instrument, even worse in the case of additive noise. This paper investigates the problem of EL speech enhancement by taking into account the frequency-domain masking properties of the human auditory system. One approach is incorporating an auditory masking threshold (AMT) for parametric adaptation in a subtractive-type enhancement process. The other is the supplementary AMT (SAMT) algorithm, which applies a cross-correlation spectral subtraction (CCSS) approach as a post-processing scheme to enhancing EL speech dealt with the AMT method. The performance of these two algorithms was evaluated as compared to the power spectral subtraction (PSS) algorithm. The best performance of EL speech enhancement was associated with the SAMT algorithm, followed by the AMT algorithm and the PSS algorithm. Acoustic and perceptual analyses indicated that the AMT and SAMT algorithms achieved the better performances of noise reduction and the enhanced EL speech was more pleasant to human listeners as compared to the PSS algorithm.

Adult↗

PubMed2006

Tonal perceptions in normal laryngeal, esophageal, and electrolaryngeal speech of Mandarin.

The present study attempted to investigate if alaryngeal speakers of Mandarin Chinese could differentially produce the four tone levels of Mandarin: high-level, mid-rising, falling-rising and high-falling, as perceived by native listeners. Syllables /ma/ and /ba/ produced at four different tone levels by 8 normal laryngeal (NL), 7 standard esophageal (SE), and 8 electrolaryngeal (EL) speakers of Mandarin were perceived by 8 naïve listeners. Results from the listening experiments showed a higher percent correct identification of tone for NL speech than SE and EL speech. Perceptual data showed different patterns of tone confusion associated with the three types of speech. SE and EL speakers were not able to produce the four tone levels as accurately as were NL speakers. NL speakers achieved a near-perfect level of accuracy in signaling tonal contrasts. SE speakers produced the falling-rising and high-falling tones more accurately than high-level and mid-rising tones, but tonal confusions existed between mid-rising tone and falling-rising tone, and between high-level tone and high-falling tone. In EL phonation, high-level tone was produced more accurately than the other tones which were often misidentified as a high-level tone.

Aged↗

PubMed2005

Wavelet-based estimation of EEG coherence during Chinese Stroop task.

Wavelet-based estimation of instantaneous EEG coherence was applied to investigate the synchronization of different brain regions whilst 10 subjects performing Stroop task presented in Chinese. In contrast to coherence based on Fourier transform, wavelet-based coherence, which does not depend on the stationarity of signals, applies an adaptive window to the frequency of the signal and has a more accurate time-frequency resolution. In the present study, a greater negativity for the incongruent situation than congruent situation appeared from 350 to 600 ms post-stimulus onset over frontal, central, and parietal regions, and significantly higher EEG coherences for the incongruent situation than congruent situation were observed over frontal, parietal, and frontoparietal regions from 100 to 400 ms at beta1 (13-18Hz) frequency band, which was found to be sensitive in the discrimination between congruent and incongruent situations. The findings in the present study may indicate that functional synchronization as indexed by EEG coherence at beta1 frequency band is enhanced at the earlier stage while processing the conflicting information from the incongruent stimulus, and that beta1 frequency band is close related to interactions of brain areas in the selected attention task.

Adult↗

PubMed2005

Parameter measurement of the cylindrically curved thin layer using low-frequency circumferential Lamb waves.

The characteristic parameters of a cylindrically curved thin layer include its elastic constants, thickness and curved radius. A layer is considered thin if the echoes from the front and back surfaces of the layer cannot be separated in the time domain, and/or that the wave arrivals corresponding to longitudinal and shear wave part cannot be identified in the time or space domain. This paper describes a low-frequency circumferential Lamb wave method to characterize those parameters of a cylindrically curved thin layer. The technique is based on the measurement of circumferential Lamb wave phase velocity and the unknown parameter is estimated through minimizing the mean square error obtained by comparing theoretical and experimental phase velocities. The sensitivity and accuracy of the proposed technique to different parameters are analyzed. Using the present technique, a cylindrically curved thin layer with thickness down to ten percent of the longitudinal wavelength can be successfully measured with an average relative error less than two-percent in our experiment.

Journal Article↗

PubMed2005

A comparison of HIFU-induced lesion size measurement based on gross histological examination and image of bovine thigh in vitro.

The aim of this study was to investigate the agreement in HIFU-induced lesion sizes between measurements based on gross histological examination and those from images. Experiments were conducted in an experimental arrangement with a three-way multiscan ultrasonic inspection system and imaging was done by B-mode ultrasound (US). Bovine thigh muscle with and without fascia lata was treated with an in situ spatially averaged focal intensity ranging between 750 W cm(-2) and 1565 W cm(-2) and sonication-time was variable from 8 to 20s. Assessment of the two measurement methods showed a rather weak correlation in the samples without fascia lata. For clarity and convenience in the discussion, sample muscles with and without fascia lata were labeled F and M, respectively. It was difficult to measure the lesion size from ultrasonographic images of F samples, so there was disagreement in the samples with fascia lata. This investigation showed that the presence of fascia lata in bovine thigh muscle has the likely effect of affecting the ultrasound image and makes it difficult to distinguish coagulated tissue from surrounding healthy tissue. There was no significant correlation between ultrasonography and the gross histological findings in M samples. Data supported that at for an in situ spatially averaged focal intensity ranging between 750 W cm(-2) and 1565 W cm(-2) and relatively shorter exposures (sonication-time variable from 1 to 8s) higher correlation between image and gross histology measurement was found in excised bovine muscle specimens.

Animals↗

PubMed2005

Focused beam control for ultrasound surgery with spherical-section phased array: sound field calculation and genetic optimization algorithm.

This study aims at a sound field calculation for the spherical-section phased array and an optimization algorithm for the focus patterns of phased array ultrasound surgery. An efficient field calculation formula represented as an explicit expression is derived by the strategies of projection and binomial expansion. An optimization algorithm based on genetic algorithm is constructed by the suitable fitness function and the selection strategies. The simulation results of 256-element spherical-section phased array show the capability of controlling focus accurately and effectively with the combined method made up of the explicit expression method and the genetic optimization algorithm. The simulation results of single focus, multiple foci, on-axial focus, and off-axial focus further convince the feasibility of three-dimensional (3-D) focus steering with excellent acoustic performances. A single focus with the focus dimension of 1.25 mm x 1.25 mm x 7 mm and with the intensity of 6080 W/cm2 is formed. The multiple-focus pattern can enlarge the treatment volume 22 times larger than that of single focus with a sonication. In addition, a comparison between the explicit expression approach and the point source approach testifies to the applicability of the explicit expression approach. The experiment and simulation results of 16-element array actually confirm the feasibility of the combined method.

Algorithms↗

PubMed2005

Acoustic characteristics of Mandarin esophageal speech.

The present study attempted to investigate the acoustic characteristics of Mandarin laryngeal and esophageal speech. Eight normal laryngeal and seven esophageal speakers participated in the acoustic experiments. Results from acoustic analyses of syllables /ma/and /ba/ indicated that, F0, intensity, and signal-to-noise ratio of laryngeal speech were significantly higher than those of esophageal speech. However, opposite results were found for vowel duration, jitter, and shimmer. Mean F0, intensity, and word per minute in reading were greater but number of pauses was smaller in laryngeal speech than those in esophageal speech. Similar patterns of F0 contours and vowel duration as a function of tone were found between laryngeal and esophageal speakers. Long-time spectra analysis indicated that higher first and second formant frequencies were associated with esophageal speech than that with normal laryngeal speech.

Aged↗

PubMed2004

A fast snake model based on non-linear diffusion for medical image segmentation.

In this paper, the traditional snake model and gradient vector flow (GVF) snake model are studied, which are believed to be quite slow due to the need to compute inverse matrix. Actually, the GVF in the latter snake model is formed by a biased linear diffusion procedure, and there would be oscillations around the edge of the object. Based on GVF generated through non-linear diffusion, we present a fast GVF (FGVF) snake model which is much faster than the traditional snake model and GVF snake model, and would cause no degradation of stability and flexibility, meanwhile, it could reduce the oscillations around the edges. The segmentation results using FGVF and error analysis on simulated images are presented. Finally, the demonstration of FGVF applied to Computed Tomography and Magnetic Resonance images are shown, the segmentation results are satisfactory visually with much less computation time in comparison with former snakes.

Algorithms↗