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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 328 out of 330
| Title |
Vibro-acoustography: An imaging modality based on ultrasound-stimulated acoustic emission. |
| Author |
Fatemi M, Greenleaf JF. |
| Journal |
Proc Natl Acad Sci USA |
| Volume |
|
| Year |
1999 |
| Abstract |
We describe theoretical principles of an imaging modality that uses the acoustic response of an object to a highly localized dynamic radiation force of an ultrasound field. In this method, named ultrasound-stimulated vibro-acoustography (USVA), ultrasound is used to exert a low-frequency (in kHz range) force on the object. In response, a portion of the object vibrates sinusoidally in a pattern determined by its viscoelastic properties. The acoustic emission field resulting from object vibration is detected and used to form an image that represents both the ultrasonic and low-frequency (kHz range) mechanical characteristics of the object. We report the relation between the emitted acoustic field and the incident ultrasonic pressure field in terms of object parameters. Also, we present the point-spread function of the imaging system. The experimental images in this report have a resolution of about 700 &mgr;m, high contrast, and high signal-to-noise ratio. USVA is sensitive enough to detect object motions on the order of nanometers. Possible applications include medical imaging and material evaluation. |
| Title |
Viscoelasticity imaging using ultrasound: parameters and error analysis. |
| Author |
Sridhar M, Liu J, Insana MF. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
2007 |
| Abstract |
Techniques are being developed to image viscoelastic features of soft tissues from time-varying strain. A compress-hold-release stress stimulus commonly used in creep-recovery measurements is applied to samples to form images of elastic strain and strain retardance times. While the intended application is diagnostic breast imaging, results in gelatin hydrogels are presented to demonstrate the techniques. The spatiotemporal behaviour of gelatin is described by linear viscoelastic theory formulated for polymeric solids. Measured creep responses of polymers are frequently modelled as sums of exponentials whose time constants describe the delay or retardation of the full strain response. We found the spectrum of retardation times τ to be continuous and bimodal, where the amplitude at each τ represents the relative number of molecular bonds with a given strength and conformation. Such spectra indicate that the molecular weight of the polymer fibres between bonding points is large. Imaging parameters are found by summarizing these complex spectral distributions at each location in the medium with a second-order Voigt rheological model. This simplification reduces the dimensionality of the data for selecting imaging parameters while preserving essential information on how the creeping deformation describes fluid flow and collagen matrix restructuring in the medium. The focus of this paper is on imaging parameter estimation from ultrasonic echo data, and how jitter from hand-held force applicators used for clinical applications propagate through the imaging chain to generate image noise. |
| Title |
Visualisation of abdominal masses using ultrasound. |
| Author |
Kossoff G. |
| Journal |
Proc IREE Aust |
| Volume |
|
| Year |
1964 |
| Abstract |
An ultrasonic echoscope for the visualisation of the pregnant uterus is described. Pertinent properties of ultrasonic waves are discussed and the employed method of visualisation is outlined. The acoustic, electronic, and mechanical design of the echoscope is discussed and some of the clinical results are presented. |
| Title |
Visualisation of HIFU lesions using elastography of the human prostate in vivo: preliminary results. |
| Author |
Souchon R, Rouvière O, Gelet A, Detti V, Srinivasan S, Ophir J, Chapelon JY. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2003 |
| Abstract |
An imaging system was developed for prostate elastography in vivo using a transrectal ultrasound (US) probe to guide high-intensity focused US (HIFU) therapy of prostate cancer. Uniform compression was applied using a balloon, while a sector image was acquired. Strain was calculated from the gradient of the displacements obtained from the ultrasonic signal using the cross-correlation technique. Elastograms were acquired on a total of 31 patients undergoing HIFU therapy for localised prostate cancer. For two patients, only part of the prostate was treated and posttherapy magnetic resonance imaging (MRI) confirmed the size and position of the HIFU lesions seen in the elastograms as low strain areas, with a strain contrast ratio between 1.6 and 3.2. The whole prostate was treated for the next 29 patients. After treatment, the whole prostate appeared to be stiff in the elastograms and a 40% to 60% (mean 50%) decrease in average strain was observed when compared to strains measured before HIFU application. Tumours identified by biopsies and sonograms could occasionally be seen in the preoperative elastograms. Decorrelation effects occurred mainly because of low sonographic signal-to-noise ratio (SNR) and of out-of-plane motion induced by respiration. |
| Title |
Visualisation systems. |
| Author |
Kossoff G. |
| Journal |
Proc Interact Ultrasound Biol Tissues Workshop - Seattle |
| Volume |
|
| Year |
1971 |
| Abstract |
No abstract available. |
| Title |
Visualization of cardiac dynamics with real time B-mode ultrasonic scanner. |
| Author |
Eggleton RC, Feigenbaum H, Johnston KW, Weyman AE, Dillon JC, Chang S. |
| Journal |
Proc First Ultrasound Med Conf - Seattle |
| Volume |
|
| Year |
1974 |
| Abstract |
Discusses the choice of operating conditions for any sector scanner including frame rate, pulse repetition rate, line density, scan angle and maximum depth of examination. The choice of PRF imposes an upper limit to the transit time available for the acoustic pulse, thus limiting the maximum depth of examination. The line density is likewise fixed when the scan angle, frame rate and PRF are chosen. |
| Title |
Visualization of the intensity field of a high intensity focused ultrasound (HIFU) source in situ |
| Author |
Nguyen T, Do M, Oelze ML |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2015 |
| Abstract |
High intensity focused ultrasound (HIFU) can provide a means of noninvasive ablation of tissues such as tumors. However, currently the gold standard for monitoring HIFU is MRI temperature mapping. Because of the expense, lack of portability and slow update of temperature maps from MRI, ultrasonic solutions to monitoring of HIFU remain an important clinical goal. Real-time visualization of the field distribution of the HIFU source during treatment would allow the localization of the intersection of the beam with the tissue. Real-time visualization of the beam in the context of the tissue is important for proper placement of therapy especially during tissue motion. To visualize the HIFU field in a tissue, a reconstruction technique was employed using a Fourier-domain f-k migration approach with a linear array system co-aligned with the HIFU source. The reconstruction technique used the scattered signal from the medium to reconstruct the intensity field pattern of the HIFU field in situ and superimpose the intensity field image on a B-mode of the scattering medium. A 6-MHz single-element transducer (f/3) was used as the HIFU source and aligned perpendicular to the field of a linear array (L14-5) operated by a SonixRP system equipped with a Sonix-DAQ. The array had 128 elements and a measured center frequency of 6.5 MHz. The 6-MHz HIFU source was pulse excited and the fields scattered from a sample, i.e., a homogeneous tissue-mimicking phantom or a chicken breast, were received by each element of the linear array. Beam forming based on Fourier-domain f-k migration techniques were applied to the channel data to reconstruct the intensity field pattern from the HIFU source. For comparison, a wire target was placed in the field and the intensity field pattern was reconstructed by moving the wire throughout the focal region. The intensity field pattern reconstructed from the sample was compared to the field characteristics of the 6-MHz source characterized by the wire techn- que. The intensity field pattern was then superimposed on a registered B-mode image of the sample acquired using conventional B-mode imaging with the linear array and the SonixRP to provide context to the therapy beam placement. The beam width estimates at the HIFU focus using the in situ reconstruction technique and the wire technique were 1.7 mm and 1.5 mm, respectively. The depth of field estimates for the in situ reconstruction technique and the wire technique were 20.1 mm and 19.0 mm, respectively. Therefore, the novel reconstruction technique was able to accurately visualize the field of a focused source in the context of the interrogated medium. The visualization technique would allow real-time adjustment of the HIFU beam location in tissues during therapy. |
| Title |
Vitreous dispersion by ultrasound. |
| Author |
Coleman DJ, Lizzi F, Weininger R, Burt WJ. |
| Journal |
Ann Ophthalmol |
| Volume |
|
| Year |
1970 |
| Abstract |
Vitreous dispersion during ultrasonic irradiation was studied by means of radiation pressure measurements, Schlieren photography, piezoelectric sensors, calorimetric sensors, and x-ray photographs. The results of the reported investigations indicate that ultrasonic energy can disperse intravitreal substances and may provide an important means of hastening the resorption of vitreous hemorrhages. |
| Title |
Volume measurement variability in three-dimensional high-frequency ultrasound images of murine liver metastases. |
| Author |
Wirtzfeld LA, Graham KC, Groom AC, Macdonald IC, Chambers AF, Fenster A, Lacefield JC. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
2006 |
| Abstract |
The identification and quantification of tumour volume measurement variability is imperative for proper study design of longitudinal non-invasive imaging of pre-clinical mouse models of cancer. Measurement variability will dictate the minimum detectable volume change, which in turn influences the scheduling of imaging sessions and the interpretation of observed changes in tumour volume. In this paper, variability is quantified for tumour volume measurements from 3D high-frequency ultrasound images of murine liver metastases. Experimental B16F1 liver metastases were analysed in different size ranges including less than 1 mm3, 1-4 mm3, 4-8 mm3 and 8-70 mm3. The intra- and inter-observer repeatability was high over a large range of tumour volumes, but the coefficients of variation (COV) varied over the volume ranges. The minimum and maximum intra-observer COV were 4% and 14% for the 1-4 mm3 and <1 mm3 tumours, respectively. For tumour volumes measured by segmenting parallel planes, the maximum inter-slice distance that maintained acceptable measurement variability increased from 100 to 600 microm as tumour volume increased. Comparison of free breathing versus ventilated animals demonstrated that respiratory motion did not significantly change the measured volume. These results enable design of more efficient imaging studies by using the measured variability to estimate the time required to observe a significant change in tumour volume. |
| Title |
Volumetric arterial flow quantification using echo contrast. An in vitro comparison of three ultrasonic intensity methods: Radio frequency, video and doppler |
| Author |
Schwarz KQ, Bezante GP, Chen X, Mottley JG, Schlief R. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1993 |
| Abstract |
The two hypotheses presented in this paper are: (1) absolute and relative volumetric flow rates in vessels can be measured by echo contrast time-intensity curves; and (2) echo contrast time-intensity curves generated by different ultrasound backscatter intensity techniques have equivalent capability for flow measurements. A nonpulsatile flow system was built for quantitative ultrasound backscatter measurements from bolus echo contrast injections using two different volumes of mixing. A total of 49 echo contrast bolus injections were made at various flow rates (0.44–2.59 L/min). Ultrasound backscatter time-intensity curves were generated by ultrasound radio frequency, video and Doppler techniques. The rate of backscattered ultrasound intensity washout for each technique (WASHOUT RATE), and relative change in WASHOUT RATE (∂WASHOUT RATE) were compared to the volumetric flow rate (FLOW) and changes in flow rate (∂FLOW), respectively. The relationship between WASHOUT RATE, FLOW and the volume of contrast mixing was studied. A linear relationship was demonstrated between WASHOUT RATE and ∂WASHOUT RATE and the corresponding FLOW and ∂FLOW by all three methods (r > 0.90 for all comparisons). The WASHOUT RATE was found to depend on the FLOW and the volume of contrast mixing, but the ∂WASHOUT RATE was equal to the ∂FLOW and independent of the volume of mixing. Time-intensity curves can be generated from different ultrasound backscatter intensity techniques and the WASHOUT RATE correlates well with FLOW. ∂FLOW can be determined directly from the corresponding ∂WASHOUT RATE. Doppler ultrasound, because of its natural association with the assessment of flow in chambers and vessels, is uniquely suited to assessment of arterial volumetric blood flow in vivo. |
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