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1.
J Acoust Soc Am ; 154(6): R11-R12, 2023 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-38038611

RESUMO

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.


Assuntos
Acústica , Ultrassonografia
2.
Clin Linguist Phon ; 37(2): 196-222, 2023 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-35254181

RESUMO

Ultrasound biofeedback therapy (UBT), which incorporates real-time imaging of tongue articulation, has demonstrated generally positive speech remediation outcomes for individuals with residual speech sound disorder (RSSD). However, UBT requires high attentional demands and may therefore benefit from a simplified display of articulation targets that are easily interpretable and can be compared to real-time articulation. Identifying such targets requires automatic quantification and analysis of movement features relevant to accurate speech production. Our image-analysis program TonguePART automatically quantifies tongue movement as tongue part displacement trajectories from midsagittal ultrasound videos of the tongue, with real-time capability. The present study uses such displacement trajectories to compare accurate and misarticulated American-English rhotic /ɑr/ productions from 40 children, with degree of accuracy determined by auditory perceptual ratings. To identify relevant features of accurate articulation, support vector machine (SVM) classifiers were trained and evaluated on several candidate data representations. Classification accuracy was up to 85%, indicating that quantification of tongue part displacement trajectories captured tongue articulation characteristics that distinguish accurate from misarticulated production of /ɑr/. Regression models for perceptual ratings were also compared. The simplest data representation that retained high predictive ability, demonstrated by high classification accuracy and strong correlation between observed and predicted ratings, was displacements at the midpoint of /r/ relative to /ɑ/ for the tongue dorsum and blade. This indicates that movements of the dorsum and blade are especially relevant to accurate production of /r/, suggesting that a predictive parameter and biofeedback target based on this data representation may be usable for simplified UBT.


Assuntos
Transtornos da Articulação , Transtorno Fonológico , Criança , Humanos , Transtorno Fonológico/diagnóstico por imagem , Transtorno Fonológico/terapia , Fala , Ultrassonografia/métodos , Língua/diagnóstico por imagem , Biorretroalimentação Psicológica/métodos , Fonética
3.
J Acoust Soc Am ; 150(6): 4128, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34972294

RESUMO

Quantitative elasticity estimation in medical and industrial applications may benefit from advancements in reconstruction of shear wave speed with enhanced resolution. Here, shear wave speed is reconstructed from pulse-echo ultrasound imaging of elastic waves induced by high-frequency (>400 Hz), time-harmonic mechanical excitation. Particle displacement in shear wavefields is mapped from measured interframe phase differences with compensation for timing of multiple scan lines, then processed by spatial Fourier analysis to estimate the predominant wave speed and analyzed by algebraic wavefield inversion to reconstruct wave speed maps. Reconstructions of shear wave speed from simulated wavefields illustrate the accuracy and spatial resolution available with both methods, as functions of signal-to-noise ratio and sizes of windows used for Fourier analysis or wavefield smoothing. The methods are applied to shear wavefields with frequencies up to six times the Nyquist rate, thus extending the frequency range measurable by a given imaging system. Wave speed measurements in tissue-mimicking phantoms are compared with supersonic shear imaging and mechanical tensile testing, demonstrating feasibility of the wavefield measurement and wave speed reconstruction methods employed.


Assuntos
Técnicas de Imagem por Elasticidade , Elasticidade , Técnicas de Imagem por Elasticidade/métodos , Imagens de Fantasmas , Razão Sinal-Ruído , Som
4.
J Acoust Soc Am ; 147(6): EL478, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32611173

RESUMO

A numerical model for three-dimensional echo decorrelation imaging, a pulse-echo ultrasound method applicable to thermal ablation monitoring, is presented. Beam patterns for steered transmit and receive array apertures are combined with a three-dimensional numerical tissue model to yield beamformed scan lines in a pyramidal configuration, volumetric B-mode images, and spatial maps of normalized decorrelation between sequential image volumes. Simulated three-dimensional echo decorrelation images of random media are analyzed as estimators of local tissue reflectivity decoherence, mimicking thermal ablation effects. The estimation error is analyzed as a function of correlation window size, scan line density, and ensemble averaging of decorrelation maps.


Assuntos
Hipertermia Induzida , Imageamento Tridimensional , Imagens de Fantasmas , Ultrassonografia
5.
J Acoust Soc Am ; 144(6): 3563, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30599638

RESUMO

A method is developed for compensating absolute pressure measurements made by a calibrated passive cavitation detector (PCD) to estimate the average acoustic power radiated from a region of interest (ROI) defined to encompass all cavitating bubbles. A diffraction correction factor for conversion of PCD-measured pressures to cavitation-radiated acoustic power per unit area or volume is derived as a simple analytic expression, accounting for position- and frequency-dependent PCD sensitivity. This approach can be applied to measurements made by any PCD without precise knowledge of the number, spatial, or temporal distribution of cavitating bubbles. The diffraction correction factor is validated in simulation for a wide range of ROI dimensions and frequencies. The correction factor is also applied to emission measurements obtained during in vitro ultrasound-enhanced sonophoresis experiments, allowing comparison of stable cavitation levels between therapeutic configurations with different source center frequencies. Results incorporating sonication at both 0.41 and 2.0 MHz indicate that increases in skin permeability correlate strongly with the acoustic power of subharmonic emissions radiated per unit skin area.


Assuntos
Microbolhas , Sonicação/métodos , Modelos Teóricos , Espalhamento de Radiação , Sonicação/normas
6.
J Acoust Soc Am ; 138(5): EL469-73, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26627816

RESUMO

A recent method for calibrating single-element, focused passive cavitation detectors (PCD) compares bistatic scattering measurements by the PCD and a reference hydrophone. Here, effects of scatterer properties and PCD size on frequency-dependent receive calibration accuracy are investigated. Simulated scattering from silica and polystyrene spheres was compared for small hydrophone and spherically focused PCD receivers to assess the achievable calibration accuracy as a function of frequency, scatterer size, and PCD size. Good agreement between measurements was found when the scatterer diameter was sufficiently smaller than the focal beamwidth of the PCD; this relationship was dependent on the scatterer material. For conditions that result in significant disagreement between measurements, the numerical methods described here can be used to correct experimental calibrations.


Assuntos
Processamento de Sinais Assistido por Computador , Transdutores , Ultrassom/instrumentação , Algoritmos , Calibragem , Desenho de Equipamento , Microesferas , Imagens de Fantasmas , Poliestirenos , Dióxido de Silício , Som
7.
J Acoust Soc Am ; 138(3): EL193-8, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26428812

RESUMO

Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here.


Assuntos
Acústica/instrumentação , Processamento de Sinais Assistido por Computador , Som , Transdutores de Pressão/normas , Calibragem , Desenho de Equipamento , Modelos Teóricos , Movimento (Física) , Análise Numérica Assistida por Computador , Pressão , Espectrografia do Som , Fatores de Tempo
8.
Phys Med Biol ; 68(2)2023 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-36595327

RESUMO

Objective.Mapping of dose delivery in proton beam therapy can potentially be performed by analyzing thermoacoustic emissions measured by ultrasound arrays. Here, a method is derived and demonstrated for spatial mapping of thermoacoustic sources using numerical time reversal, simulating re-transmission of measured emissions into the medium.Approach.Spatial distributions of thermoacoustic emission sources are shown to be approximated by the analytic-signal form of the time-reversed acoustic field, evaluated at the time of the initial proton pulse. Given calibration of the array sensitivity and knowledge of tissue properties, this approach approximately reconstructs the acoustic source amplitude, equal to the product of the time derivative of the radiation dose rate, mass density, and Grüneisen parameter. This approach was implemented using two models for acoustic fields of the array elements, one modeling elements as line sources and the other as rectangular radiators. Thermoacoustic source reconstructions employed previously reported measurements of emissions from proton energy deposition in tissue-mimicking phantoms. For a phantom incorporating a bone layer, reconstructions accounted for the higher sound speed in bone. Dependence of reconstruction quality on array aperture size and signal-to-noise ratio was consistent with previous acoustic simulation studies.Main results.Thermoacoustic source distributions were successfully reconstructed from acoustic emissions measured by a linear ultrasound array. Spatial resolution of reconstructions was significantly improved in the azimuthal (array) direction by incorporation of array element diffraction. Source localization agreed well with Monte Carlo simulations of energy deposition, and was improved by incorporating effects of inhomogeneous sound speed.Significance.The presented numerical time reversal approach reconstructs thermoacoustic sources from proton beam radiation, based on straightforward processing of acoustic emissions measured by ultrasound arrays. This approach may be useful for ranging and dosimetry of clinical proton beams, if acoustic emissions of sufficient amplitude and bandwidth can be generated by therapeutic proton sources.


Assuntos
Terapia com Prótons , Prótons , Terapia com Prótons/métodos , Acústica , Som , Radiação Ionizante , Imagens de Fantasmas , Método de Monte Carlo
9.
Am J Speech Lang Pathol ; 32(3): 1252-1274, 2023 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-36961960

RESUMO

PURPOSE: Ultrasound biofeedback therapy (UBT) is a relatively new type of technology-assisted speech-language therapy and has shown promise in remediating speech sound disorders. However, there is a current lack of understanding of the barriers and benefits that may influence the usage behavior and clinical decision making for the implementation of UBT from a clinician perspective. In this qualitative study, we explore the perspectives of speech-language pathologists (SLPs) who have used ultrasound biofeedback in programs of speech sound therapy using the unified theory of acceptance and use of technology (UTAUT) model. METHOD: Seven SLPs who had clinical experience treating speech sound disorders with UBT participated. Semistructured in-depth interviews were conducted and video-recorded. Two coders coded and categorized the transcribed data, with consensus established with a third coder. Using thematic analysis, the data were exploratorily grouped into themes along components of the UTAUT model. RESULTS: The highest number of codes was sorted into the "effort expectancy" theme, followed by "performance expectancy," "social influence," and "facilitating conditions" themes of the UTAUT model. Clinicians identified multiple perceived barriers and benefits to the use of ultrasound technology. The top identified barrier was limited accessibility, and the top benefit was the ability to visualize a client's articulatory response to cues on a display. CONCLUSIONS: Clinicians prioritized "effort expectancy" and "performance expectancy" when reflecting on the use of ultrasound biofeedback for speech sound disorders. Clinicians spoke favorably about using UBT for speech sound disorder treatment but acknowledged institutional barriers and limitations at organizational and social levels.


Assuntos
Transtornos da Comunicação , Transtorno Fonológico , Patologia da Fala e Linguagem , Humanos , Transtorno Fonológico/terapia , Biorretroalimentação Psicológica , Ultrassonografia , Fonoterapia , Fala
10.
J Acoust Soc Am ; 132(1): 544-53, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-22779500

RESUMO

Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set.


Assuntos
Fígado/fisiologia , Ultrassom/métodos , Animais , Masculino , Imagens de Fantasmas , Coelhos , Espalhamento de Radiação , Espectrografia do Som , Transdutores de Pressão
11.
Ultrasound Med Biol ; 47(8): 2360-2376, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34023187

RESUMO

Bulk ultrasound ablation is a thermal therapy approach in which tissue is heated by unfocused or weakly focused sonication (average intensities on the order of 100 W/cm2) to achieve coagulative necrosis within a few minutes exposure time. Assessing the role of bubble activity, including acoustic cavitation and tissue vaporization, in bulk ultrasound ablation may help in making bulk ultrasound ablation safer and more effective for clinical applications. Here, two series of ex vivo ablation trials were conducted to investigate the role of bubble activity and tissue vaporization in bulk ultrasound ablation. Fresh bovine liver tissue was ablated with unfocused, continuous-wave ultrasound using ultrasound image-ablate arrays sonicating at 31 W/cm2 (0.9 MPa amplitude) for either 20 min at a frequency of 3.1 MHz or 10 min at 4.8 MHz. Tissue specimens were maintained at a static overpressure of either 0.52 or 1.2 MPa to suppress bubble activity and tissue vaporization or at atmospheric pressure for control groups. A passive cavitation detector was used to record subharmonic (1.55 or 2.4 MHz), broadband (1.2-1.5 MHz) and low-frequency (5-20 kHz) acoustic emissions. Treated tissue was stained with 2% triphenyl tetrazolium chloride to evaluate thermal lesion dimensions. Subharmonic emissions were significantly reduced in overpressure groups compared with control groups. Correlations observed between acoustic emissions and lesion dimensions were significant and positive for the 3.1-MHz series, but significant and negative for the 4.8-MHz series. The results indicate that for bulk ultrasound ablation, where both acoustic cavitation and tissue vaporization are possible, bubble activity can enhance ablation in the absence of tissue vaporization, but can reduce thermal lesion dimensions in the presence of vaporization.


Assuntos
Ablação por Ultrassom Focalizado de Alta Intensidade , Pressão , Sonicação , Volatilização , Acústica , Animais , Bovinos
12.
J Acoust Soc Am ; 128(3): EL99-104, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20815433

RESUMO

A model is presented for pulse-echo imaging of three-dimensional, linear, weakly-scattering continuum media by ultrasound array transducers. The model accounts for the diffracted fields of focused array subapertures in both transmit and receive modes, multiple transmit and receive focal zones, frequency-dependent attenuation, and aberration caused by mismatched medium and beamformer sound speeds. For a given medium reflectivity function, computation of a B-scan requires evaluation of a depth-dependent transmit/receive beam product, followed by two one-dimensional convolutions and a one-dimensional summation. Numerical results obtained using analytic expressions for transmit and receive beams agree favorably with measured B-scan images and speckle statistics.


Assuntos
Interpretação de Imagem Assistida por Computador , Modelos Estatísticos , Ultrassonografia Doppler de Pulso , Simulação por Computador , Imageamento Tridimensional , Modelos Lineares , Análise Numérica Assistida por Computador , Imagens de Fantasmas , Transdutores de Pressão , Ultrassonografia Doppler de Pulso/instrumentação
13.
J Acoust Soc Am ; 126(6): 3071-83, 2009 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-20000921

RESUMO

A method is presented for passive imaging of cavitational acoustic emissions using an ultrasound array, with potential application in real-time monitoring of ultrasound ablation. To create such images, microbubble emissions were passively sensed by an imaging array and dynamically focused at multiple depths. In this paper, an analytic expression for a passive image is obtained by solving the Rayleigh-Sommerfield integral, under the Fresnel approximation, and passive images were simulated. A 192-element array was used to create passive images, in real time, from 520-kHz ultrasound scattered by a 1-mm steel wire. Azimuthal positions of this target were accurately estimated from the passive images. Next, stable and inertial cavitation was passively imaged in saline solution sonicated at 520 kHz. Bubble clusters formed in the saline samples were consistently located on both passive images and B-scans. Passive images were also created using broadband emissions from bovine liver sonicated at 2.2 MHz. Agreement was found between the images and source beam shape, indicating an ability to map therapeutic ultrasound beams in situ. The relation between these broadband emissions, sonication amplitude, and exposure conditions are discussed.


Assuntos
Processamento de Imagem Assistida por Computador/métodos , Ultrassonografia/métodos , Acústica , Algoritmos , Animais , Calibragem , Bovinos , Simulação por Computador , Instalação Elétrica , Processamento de Imagem Assistida por Computador/instrumentação , Fígado/diagnóstico por imagem , Microbolhas , Modelos Teóricos , Cloreto de Sódio , Aço , Ultrassonografia/instrumentação
14.
Phys Med Biol ; 64(16): 165015, 2019 08 21.
Artigo em Inglês | MEDLINE | ID: mdl-31189149

RESUMO

Ultrasound-enhanced recombinant tissue plasminogen activator (rt-PA) thrombolysis is under development as an adjuvant to ischemic stroke therapy. The goal of this study was to design a pulsed ultrasound (US) exposure scheme that reduced intracranial constructive interference and tissue heating, and maintained thrombolytic efficacy relative to continuous wave (CW) insonation. Three 220 kHz US schemes were evaluated, two pulsed insonation schemes (15 cycles, 68 µs pulse duration, 33% or 62.5% duty cycle) and an intermittent CW insonation scheme (50 s active, 30 s quiescent) over a 30-min treatment period. An in silico study using a finite-difference model of transcranial US propagation was performed to estimate the intracranial acoustic field and temperature rise in the skull for each insonation scheme. In vitro measurements with flow were performed to assess thrombolysis using time-lapse microscopy. Intracranial constructive interference was not reduced with pulsed US using a pulse length of 15 cycles compared to intermittent CW US. The 33.3% duty cycle pulsed US scheme reduced heating in the temporal bone as much as 60% relative to the intermittent CW scheme. All insonation schemes promoted sustained stable cavitation in vitro and augmented thrombolysis compared to rt-PA alone (p  < 0.05). Ultraharmonic (UH) and harmonic cumulative energy over a 30 min treatment period was significantly higher (p  < 0.05) for the intermittent CW US scheme compared to either pulsed US scheme. Despite the difference in cavitation emissions, no difference was observed in the clot lysis between the three US schemes. These findings demonstrate that a 33.3% duty cycle pulsed US scheme with a 15-cycle burst can reduce bone heating and achieve equivalent thrombolytic efficacy as an intermittent CW scheme.


Assuntos
Fibrinolíticos/farmacologia , Proteínas Recombinantes/farmacologia , Terapia Trombolítica/métodos , Ativador de Plasminogênio Tecidual/farmacologia , Terapia por Ultrassom , Isquemia Encefálica/complicações , Fibrinolíticos/uso terapêutico , Humanos , Proteínas Recombinantes/uso terapêutico , Acidente Vascular Cerebral/complicações , Acidente Vascular Cerebral/terapia , Ativador de Plasminogênio Tecidual/uso terapêutico
15.
PLoS One ; 14(12): e0226001, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31805129

RESUMO

The utility of echo decorrelation imaging feedback for real-time control of in vivo ultrasound thermal ablation was assessed in rabbit liver with VX2 tumor. High-intensity focused ultrasound (HIFU) and unfocused (bulk) ablation were performed using 5 MHz linear image-ablate arrays. Treatments comprised up to nine lower-power sonications, followed by up to nine higher-power sonications, ceasing when the average cumulative echo decorrelation within a control region of interest exceeded a predefined threshold (- 2.3, log10-scaled echo decorrelation per millisecond, corresponding to 90% specificity for tumor ablation prediction in previous in vivo experiments). This threshold was exceeded in all cases for both HIFU (N = 12) and bulk (N = 8) ablation. Controlled HIFU trials achieved a significantly higher average ablation rate compared to comparable ablation trials without image-based control, reported previously. Both controlled HIFU and bulk ablation trials required significantly less treatment time than these previous uncontrolled trials. Prediction of local liver and VX2 tumor ablation using echo decorrelation was tested using receiver operator characteristic curve analysis, showing prediction capability statistically equivalent to uncontrolled trials. Compared to uncontrolled trials, controlled trials resulted in smaller thermal ablation regions and higher contrast between echo decorrelation in treated vs. untreated regions. These results indicate that control using echo decorrelation imaging may reduce treatment duration and increase treatment reliability for in vivo thermal ablation.


Assuntos
Ablação por Ultrassom Focalizado de Alta Intensidade/métodos , Neoplasias Hepáticas/diagnóstico por imagem , Neoplasias Hepáticas/cirurgia , Cirurgia Assistida por Computador/métodos , Animais , Estudos de Viabilidade , Neoplasias Hepáticas/patologia , Coelhos , Reprodutibilidade dos Testes , Ultrassonografia
16.
Perspect ASHA Spec Interest Groups ; 4(6): 1644-1652, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32524032

RESUMO

PURPOSE: Because it shows the movement of different parts of the tongue in real time, ultrasound biofeedback therapy is a promising technology for speech research and remediation. One limitation is the difficulty of interpreting real-time ultrasound images of tongue motion. Our image processing system, TonguePART, tracks the tongue surface and allows for the acquisition of quantitative tongue part trajectories. METHOD: TonguePART automatically identifies the tongue contour based on ultrasound image brightness and tracks motion of the tongue root, dorsum, and blade in real time. We present tongue part trajectory data from 2 children with residual sound errors on /r/ and 2 children with typical speech, focusing on /r/ (International Phonetic Alphabet ɹ) in the phonetic context /ɑr/. We compared the tongue trajectories to magnetic resonance images of sustained vowel /ɑ/ and /r/. RESULTS: Measured trajectories show larger overall displacement and greater differentiation of tongue part movements for children with typical speech during the production of /ɑr/, compared to children with residual speech sound disorders. CONCLUSION: TonguePART is a fast, reliable method of tracking articulatory movement of tongue parts for syllables such as /ɑr/. It is extensible to other sounds and phonetic contexts. By tracking tongue parts, clinical researchers can investigate lingual coordination. TonguePART is suitable for real-time data collection and biofeedback. Ultrasound biofeedback therapy users may make more progress using simplified biofeedback of tongue movement.

17.
Ultrasound Med Biol ; 34(9): 1421-33, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18378380

RESUMO

Ultrasound has been shown previously to act synergistically with a thrombolytic agent, such as recombinant tissue plasminogen activator (rt-PA) to accelerate thrombolysis. In this in vitro study, a commercial contrast agent, Definity, was used to promote and sustain the nucleation of cavitation during pulsed ultrasound exposure at 120 kHz. Ultraharmonic signals, broadband emissions and harmonics of the fundamental were measured acoustically by using a focused hydrophone as a passive cavitation detector and used to quantify the level of cavitation activity. Human whole blood clots suspended in human plasma were exposed to a combination of rt-PA, Definity and ultrasound at a range of ultrasound peak-to-peak pressure amplitudes, which were selected to expose clots to various degrees of cavitation activity. Thrombolytic efficacy was determined by measuring clot mass loss before and after the treatment and correlated with the degree of cavitation activity. The penetration depth of rt-PA and plasminogen was also evaluated in the presence of cavitating microbubbles using a dual-antibody fluorescence imaging technique. The largest mass loss (26.2%) was observed for clots treated with 120-kHz ultrasound (0.32-MPa peak-to-peak pressure amplitude), rt-PA and stable cavitation nucleated by Definity. A significant correlation was observed between mass loss and ultraharmonic signals (r = 0.85, p < 0.0001, n = 24). The largest mean penetration depth of rt-PA (222 microm) and plasminogen (241 microm) was observed in the presence of stable cavitation activity. Stable cavitation activity plays an important role in enhancement of thrombolysis and can be monitored to evaluate the efficacy of thrombolytic treatment.


Assuntos
Meios de Contraste/administração & dosagem , Fluorocarbonos/administração & dosagem , Terapia Trombolítica/métodos , Trombose/tratamento farmacológico , Terapia por Ultrassom/métodos , Terapia Combinada , Fibrinolíticos/administração & dosagem , Fibrinolíticos/uso terapêutico , Humanos , Microscopia de Fluorescência , Microesferas , Proteínas Recombinantes/uso terapêutico , Processamento de Sinais Assistido por Computador , Trombose/diagnóstico por imagem , Ativador de Plasminogênio Tecidual/administração & dosagem , Ativador de Plasminogênio Tecidual/uso terapêutico , Ultrassonografia
18.
Ultrasound Med Biol ; 34(9): 1434-48, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18420337

RESUMO

Acoustic emissions associated with cavitation and other bubble activity have previously been observed during ultrasound (US) ablation experiments. Because detectable bubble activity may be related to temperature, tissue state and sonication characteristics, these acoustic emissions are potentially useful for monitoring and control of US ablation. To investigate these relationships, US ablation experiments were performed with simultaneous measurements of acoustic emissions, tissue echogenicity and tissue temperature on fresh bovine liver. Ex vivo tissue was exposed to 0.9-3.3-s bursts of unfocused, continuous-wave, 3.10-MHz US from a miniaturized 32-element array, which performed B-scan imaging with the same piezoelectric elements during brief quiescent periods. Exposures used pressure amplitudes of 0.8-1.4 MPa for exposure times of 6-20 min, sufficient to achieve significant thermal coagulation in all cases. Acoustic emissions received by a 1-MHz, unfocused passive cavitation detector, beamformed A-line signals acquired by the array, and tissue temperature detected by a needle thermocouple were sampled 0.3-1.1 times per second. Tissue echogenicity was quantified by the backscattered echo energy from a fixed region-of-interest within the treated zone. Acoustic emission levels were quantified from the spectra of signals measured by the passive cavitation detector, including subharmonic signal components at 1.55 MHz, broadband signal components within the band 0.3-1.1 MHz and low-frequency components within the band 10-30 kHz. Tissue ablation rates, defined as the thermally ablated volumes per unit time, were assessed by quantitative analysis of digitally imaged, macroscopic tissue sections. Correlation analysis was performed among the averaged and time-dependent acoustic emissions in each band considered, B-mode tissue echogenicity, tissue temperature and ablation rate. Ablation rate correlated significantly with broadband and low-frequency emissions, but was uncorrelated with subharmonic emissions. Subharmonic emissions were found to depend strongly on temperature in a nonlinear manner, with significant emissions occurring within different temperature ranges for each sonication amplitude. These results suggest potential roles for passive detection of acoustic emissions in guidance and control of bulk US ablation treatments.


Assuntos
Acústica , Fígado/diagnóstico por imagem , Terapia por Ultrassom/métodos , Animais , Bovinos , Meios de Contraste , Microbolhas , Processamento de Sinais Assistido por Computador , Temperatura , Ultrassonografia
19.
J Ultrasound Med ; 27(12): 1685-97, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-19022994

RESUMO

OBJECTIVE: The purpose of this study was to test ultrasound echo decorrelation imaging for mapping and characterization of tissue effects caused by radio frequency ablation (RFA). METHODS: Radio frequency ablation procedures (6-minute duration, 20-W power) were performed on fresh ex vivo bovine liver tissue (n = 9) with continuous acquisition of beam-formed ultrasound echo data from a 7-MHz linear array. Echo data were processed to form B-scan images, echo decorrelation images (related to rapid random changes in echo waveforms), and integrated backscatter images (related to local changes in received echo energy). Echo decorrelation and integrated backscatter values at the location of a low-noise thermocouple were assessed as functions of temperature. Echo decorrelation and integrated backscatter images were directly compared with ablated tissue cross sections and quantitatively evaluated as predictors of tissue ablation and overtreatment. RESULTS: Echo decorrelation maps corresponded with local tissue temperature and ablation effects. Consistent echo decorrelation increases were observed for temperatures above 75 degrees C, whereas integrated backscatter maps showed a nonmonotonic temperature dependence complicated by acoustic shadowing, with high variance at large temperature elevations. In receiver operating characteristic curve analysis of echo decorrelation and integrated backscatter maps as predictors of local tissue ablation, echo decorrelation performed well (area under the receiver operating characteristic curve [AUROC] = 0.855 for ablation and 0.913 for overtreatment), whereas integrated backscatter performed poorly (AUROC < 0.6). CONCLUSIONS: Echo decorrelation imaging can map tissue changes due to RFA in vitro, with local echo decorrelation corresponding strongly to local tissue temperature elevations and ablation effects. With further development and in vivo validation, echo decorrelation imaging is potentially useful for improved image guidance of clinical RFA procedures.


Assuntos
Ablação por Cateter/métodos , Hepatectomia/métodos , Interpretação de Imagem Assistida por Computador/métodos , Fígado/diagnóstico por imagem , Fígado/cirurgia , Cirurgia Assistida por Computador/métodos , Ultrassonografia de Intervenção/métodos , Animais , Bovinos , Feminino , Humanos , Técnicas In Vitro , Masculino , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Termografia/métodos
20.
Artigo em Inglês | MEDLINE | ID: mdl-29994657

RESUMO

Feasibility of controlling bulk ultrasound (US) thermal ablation using echo decorrelation imaging was investigated in ex vivo bovine liver. The first of two ablation and control procedures used a sequence of constant-intensity sonication cycles, ceased when the minimum echo decorrelation within a control region of interest (ROI) exceeded a predetermined threshold. The second procedure used a variable-intensity sonication sequence, with spatially averaged decorrelation as the stopping criterion. US exposures and echo decorrelation imaging were performed by a linear image-ablate array. Based on preliminary experiments, control ROIs and thresholds for the minimum-decorrelation and average-decorrelation criteria were specified. Controlled trials for the minimum-decorrelation and average-decorrelation criteria were compared with uncontrolled trials employing 9 or 18 cycles of matching sonication sequences. Lesion dimensions, treatment times, ablation rates, and areas under receiver operating characteristic curves were statistically compared. Successfully controlled trials using both criteria required significantly shorter treatment times than corresponding 18-cycle treatments, with better ablation prediction performance than uncontrolled 9-cycle and 18-cycle treatments. Either control approach resulted in greater ablation rate than corresponding 9-cycle or 18-cycle uncontrolled approaches. A post hoc analysis studied the effect of exchanging control criteria between the two series of controlled experiments. For either group, the average time needed to exceed the alternative decorrelation threshold approximately matched the average duration of successfully controlled experimental trials. These results indicate that either approach, using minimum-decorrelation or average-decorrelation criteria, is feasible for control of bulk US ablation. In addition, use of a variable-intensity sonication sequence for bulk US thermal ablation can result in larger ablated regions compared to constant-intensity sonication sequences.


Assuntos
Ablação por Ultrassom Focalizado de Alta Intensidade/métodos , Processamento de Imagem Assistida por Computador/métodos , Ultrassonografia/métodos , Algoritmos , Animais , Bovinos , Desenho de Equipamento , Retroalimentação , Fígado/diagnóstico por imagem , Fígado/cirurgia
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