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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 137 out of 330
| Title |
High frequency ultrasound imaging with optical arrays. |
| Author |
Hamilton JD, O'Donnell M. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
1998 |
| Abstract |
Dynamically focused and steered high frequency ultrasound imaging systems require arrays with fine element spacing, wide bandwidths, and large apertures. However, these characteristics are difficult to achieve at frequencies greater than 30 MHz using conventional array construction methods. Optical schemes offer a solution. Focused laser beams incident on a suitable surface can generate and detect acoustic radiation. Precisely controlling the position and size of the beams defines points of transmission and detection, making it possible for pulse-echo image formation by synthetic aperture methods. An optical detection array was built, relying on a conventional piezoelectric transducer as an ultrasound source. The detection system, with near optimal resolution over a wide depth of field, demonstrates the potential for high frequency array implementation using optical techniques. A possible application is in pathology, where 2-D or 3-D fine resolution pulse-echo imaging can be performed in situ without the need for biopsies. |
| Title |
High frequency ultrasound scanning of the arterial wall. |
| Author |
Foster FS, Ryan LK, Lockwood GR. |
| Journal |
J Roelandt |
| Volume |
|
| Year |
1993 |
| Abstract |
No abstract available. |
| Title |
High frequency ultrasound tissue characterization and acoustic microscopy of intracellular changes. |
| Author |
Brand S, Weiss EC, Lemor RM, Kolios MC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
The objective of this work is to investigate changes in the acoustic properties of cells when exposed to chemotherapy for monitoring treatment response. High frequency ultrasound spectroscopy (10-60 MHz) and scanning acoustic microscopy (0.9 GHz) were performed on HeLa cells (Ackermann et al. 1954, Masters 2002) that were exposed to the chemotherapeutic agent cisplatin. Ultrasonic radio-frequency data were acquired from pellets containing HeLa cells after exposure to cisplatin to induce apoptosis. Scanning acoustic and laser fluorescence microscopy images were recorded from single HeLa cells exposed to the same drug. Data acquisition in both cases was performed at several time points throughout the chemotherapeutic treatment for up to 27 h. In the high frequency ultrasound investigation, normalized power spectra were calculated within a region-of-interest. A 20 MHz transducer (f-number 2.35) and a 40 MHz transducer (f-number 3) were used for the data collection in the high frequency ultrasound experiments. The backscatter coefficients, integrated backscatter coefficients, mid-band fit and spectral slope were computed as a function of treatment time to monitor acoustical property changes during apoptosis. Acoustic attenuation was measured using the spectral substitution technique at all time points. Spectral parameter changes were detected after 12 h of exposure and coincided with the initiation of cell damage as assessed by optical microscopy. Integrated backscatter coefficients increased by over 100% between 0 h and 24 h of treatment, with small changes in the associated attenuation ( approximately 0.1 dB/[MHz cm]). Acoustic microscopy was performed at 0.9 GHz frequency. The cell structure was imaged using staining in laser fluorescence microscopy. All cells showed excellent correspondence between the locations of apoptotic nuclear condensation observed in optical imaging and changes in attenuation contrast in acoustic microscopy images. The time after drug exposure at which such changes occurred in the optical images were coincident with the time of changes detected in the acoustic microscopy images and the high frequency ultrasound experiments. |
| Title |
High intensity focused ultrasound for the treatment of benign prostatic hyperplasia: early United States clinical experience. |
| Author |
Bihrle R, Foster RS, Sanghvi NT, Donohue JP, Hood PJ. |
| Journal |
J Urol |
| Volume |
|
| Year |
1994 |
| Abstract |
High intensity focused ultrasound via a transrectal approach was used to treat 15 patients with symptomatic benign prostatic hyperplasia. The first 10 of these 15 patients underwent continuous temperature monitoring of the periprostatic region throughout the treatment. Patients undergoing transperineal thermocouple placement for the purpose of thermometry were treated while under general or spinal anesthesia, whereas 4 of the 5 remaining patients were successfully treated using intravenous sedation alone. Of the 10 patients 9 did not demonstrate a significant temperature elevation. One patient with a small prostatic anteroposterior diameter had a transient elevation of 17C. No patient experienced a complication related to periprostatic heating. Followup was available at 90 days in all patients. At 90 days the symptom scores decreased from a pretreatment value (American Urological Association questions 1 to 7) of 31.2 (range 22 to 38) to 15.8 (range 8 to 31). Peak flow rate increased by a mean of 4.7 ml per second from 9.3 ml per second before treatment to 14.0 ml per second at 90 days. The most frequent complication was that of transient urinary retention in 11 of 15 patients (73.3%) and hematospermia in 7 (46.7%). No adverse reactions persisted at 90 days. This study represents an initial attempt using high intensity focused ultrasound to treat symptomatic benign prostatic hyperplasia. Overall, the safety and effectiveness of high intensity focused ultrasound demonstrated in this pilot study are encouraging. |
| Title |
High intensity focused ultrasound treatment of human BPH. |
| Author |
Foster RS, Bihrle R, Sanghvi NT, Donohue JP, Fry FJ. |
| Journal |
J Urol |
| Volume |
|
| Year |
1994 |
| Abstract |
No abstract available. |
| Title |
High intensity focused ultrasound: physical principles and devices. |
| Author |
Haar GT, Coussios C. |
| Journal |
Int J Hyperthermia |
| Volume |
|
| Year |
2007 |
| Abstract |
High intensity focused ultrasound (HIFU) is gaining rapid clinical acceptance as a treatment modality enabling non-invasive tissue heating and ablation for numerous applications. HIFU treatments are usually carried out in a single session, often as a day case procedure, with the patient either fully conscious, lightly sedated or under light general anaesthesia. A major advantage of HIFU over other thermal ablation techniques is that there is no necessity for the transcutaneous insertion of probes into the target tissue. The high powered focused beams employed are generated from sources placed either outside the body (for treatment of tumours of the liver, kidney, breast, uterus, pancreas and bone) or in the rectum (for treatment of the prostate), and are designed to enable rapid heating of a target tissue volume, while leaving tissue in the ultrasound propagation path relatively unaffected. Given the wide-ranging applicability of HIFU, numerous extra-corporeal, transrectal and interstitial devices have been designed to optimise application-specific treatment delivery. Their principle of operation is described here, alongside an overview of the physical mechanisms governing HIFU propagation and HIFU-induced heating. Present methods of characterising HIFU fields and of quantifying HIFU exposure and its associated effects are also addressed. |
| Title |
High power transcranial beam steering for ultrasonic brain therapy. |
| Author |
Pernot M, Aubry JF, Tanter M, Thomas JL, Fink M. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
2003 |
| Abstract |
A sparse phased array is specially designed for non-invasive ultrasound transskull brain therapy. The array is made of 200 single elements corresponding to a new generation of high power transducers developed in collaboration with Imasonic (Besancon, France). Each element has a surface of 0.5 cm2 and works at 0.9 MHz central frequency with a maximum 20 W cm(-2) intensity on the transducer surface. In order to optimize the steering capabilities of the array, several transducer distributions on a spherical surface are simulated: hexagonal, annular and quasi-random distributions. Using a quasi-random distribution significantly reduces the grating lobes. Furthermore, the simulations show the capability of the quasi-random array to electronically move the focal spot in the vicinity of the geometrical focus (up to +/- 15 mm). Based on the simulation study, the array is constructed and tested. The skull aberrations are corrected by using a time reversal mirror with amplitude correction achieved thanks to an implantable hydrophone, and a sharp focus is obtained through a human skull. Several lesions are induced in fresh liver and brain samples through human skulls, demonstrating the accuracy and the steering capabilities of the system. |
| Title |
High resolution image reconstruction in ultrasound computer tomography using deconvolution. |
| Author |
Stotzka R, Ruiter NV, Muller TO, Liu R, Gemmeke H. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
2005 |
| Abstract |
Ultrasound computer tomography is an imaging method capable of producing volume images with high spatial resolution. The imaged object is enclosed by a cylindrical array of transducers. While one transducer emits a spherical wavefront (pulse), all other transducers are recording the radiofrequency (RF) a-scans simultaneously. Then another transducer acts as the emitter and so on. In this paper we describe the image reconstruction method and an enhanced algorithm for the a-scan preprocessing. The image reconstruction is based on a 'full aperture sum-and-delay' algorithm evaluating the reflected and scattered signals in the a-scans. The a-scans are modelled as the tissue response of the imaged object convoluted with the shape of the ultrasound pulse, which is determined by the transfer function of the transducers and the excitation. Spiking deconvolution and blind deconvolution with different parameters are used to build inverse filters of the ultrasound pulse. Applying the inverse filters to the a-scans results in sharper signals which are used for image reconstruction. Smallest scatterers of 0.1 mm size corresponding to one fifth of the used ultrasound wavelength are visible in the reconstructed images. Compared to conventional b-scans the resulting images show an approximately tenfold better resolution. |
| Title |
High spatial resolution ultrasonic mesurement techniques for characterization of static and moving tissues. |
| Author |
Johnson SA, Greenleaf JF, Rajagopalan B, Bahn RC, Baxter B, Christensen D. |
| Journal |
Proc Second Int Symp Ultrason Tissue Character |
| Volume |
|
| Year |
1977 |
| Abstract |
Clinical and pathology-based arguments are presented for the need for higher resolution ultrasound images. The theoretical foundation and experimental characteristics of a high resolution sampled aperture reflection technique termed synthetic focus imaging are given. It is shown by theory and simulation that such synthetic focus images may be corrected for attenuation and refraction effects and thereby approach one-half wavelength resolution. The similarity between synthetic focus and seismic migration techniques is discussed. An example of a high resolution, seismic processed (i.e., migrated) image obtained from real data at medical ultrasound frequencies is shown. Synthetic focus imaging theory is extended to moving coordinate systems and the effect of Doppler shift effects on echo pulse shape is discussed. A generalized wide aperture Doppler imaging theory is presented which suggests further improvements in signal-to-noise ratio, spatial resolution and flow velocity over narrow aperture systems is possible. A new computed tomographic flow measurement and reconstruction based on transmission measurements is presented. This technique permits imaging the three flow velocity components and temperature of homogenous fluids in a three-dimensional domain. |
| Title |
High-contrast RF correlation imaging of defects in food package seals. |
| Author |
Tian Q, Ozguler A, Morris SA, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1999 |
| Abstract |
Previous research work to detect channel defect in package seals using pulse-echo ultrasound inspired the Backscattered Amplitude Integral (BAI) imaging and RF sample (RFS) imaging techniques. The two former image formation techniques, as well as the newly proposed technique, are evaluated from the same acquired pulse-echo RF data set. All images are formed with a 17.3-MHz 6.35-mm-diameter focused ultrasound transducer (f/2, 173-μm-6 dB pulse-echo lateral beamwidth at the focus, λ-86 μm) scanned over a rectangular grid, keeping the package material in the focal region. All techniques are evaluated with the same set of laboratory-made channel defects: plastic and aluminum foil trilaminate film with 6-, 10-, 15-, 38- and 50-μm-diameter channels filled with water or air. The new RF correlation image technique is formed from the correlation coefficient of each RF echo signal relative to a reference signal that does not pass through a channel defect. Prior to processing, the acquired RF echo signals are first windowed to match within the sample the range where the two materials are bonded, that is, the range where channel defects occur. The statistical study on the laboratory-made channel defects shows that RF correlation technique has the highest detection rate relative to BAI-mode and RFS-mode image for 15-, 10- and 6-μm channel defects. It also is the most effective at smoothing the background, leading to the greatest CNR enhancement. |
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