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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 316 out of 330
| Title |
Ultrasound phased array hyperthermia applicator. |
| Author |
Benkeser PJ, Ocheltree KB, Frizzell LA, Cain CA. |
| Journal |
Proc Seventh Annu Conf IEEE Eng Med Biol Soc |
| Volume |
|
| Year |
1985 |
| Abstract |
Ultrasonic linear phased array transducers for hyperthermia provide the advantage of electronic steering of the sound beam rather than mechanical movement of the transducer assembly. The use of an ultrasonic tapered phased array transducer, consisting of a linear phased array employing elements with a tapered thickness is examined. The focal region of this transducer is steered in two dimensions by controlling the phases of the driving signals on each element, and in the third dimension by controlling the driving frequency. The design of the transducer is discussed and comparisons of theoretical and experimental field intensity profiles are presented for the tapered phased array and linear array transducers. |
| Title |
Ultrasound phased arrays for hyperthermia treatment. |
| Author |
Frizzell LA, Benkeser PJ, Ocheltree KB, Cain CA. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1985 |
| Abstract |
Ultrasonic hyperthermia systems currently use fixed or mechanically scanned transducers for controlling the energy deposition in the tumor. Alternatively, phased arrays can electronically generate and move a focal region within the treatment field without moving the transducer assembly. Two approaches are examined which employ specially designed linear phased arrays: (1) a stack of linear phased arrays and (2) a tapered linear phased array. The focal region is steered in two dimensions by controlling the phases on each element, and in the third dimension by (1) shifting from one group of linear arrays to another or by (2) shifting frequency, respectively. A practical design of these arrays consists of approximately 64 elements with a center-to-center spacing between 0.5 and 0.8 wavelengths. Theoretical and experimental results are presented for the two array designs. |
| Title |
Ultrasound phased arrays for prostate treatment. |
| Author |
Tan JS, Frizzell LA, Sanghvi N, Wu SJ, Seip R, Kouzmanoff JT. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2001 |
| Abstract |
The effect of array geometry on the steering performance of ultrasound phased arrays is examined theoretically, in order to maximize array performance under the given anatomical constraints. This paper evaluates the performance of arrays with spherical and cylindrical geometry, determined by using computer simulations of the pressure fields produced at various extremes of steering. The spherical segment arrays were truncated for insertion into the rectum, and contained either annular or linear elements. The cylindrical arrays were either flat or had a variable curvature applied along their length. Fields were computed by dividing the array elements into many point sources. The effectiveness of an array configuration when steered to a particular focal location was assessed by defining a parameter, G, as the ratio of the intensity at the desired focus to the maximum intensity of any unwanted lobes. The performance of truncated spherical arrays with annular elements was evaluated for focal steering along the array axis (in depth, in the z direction). When steered 15 mm toward the source, these truncated spherical annular arrays exhibited excellent performance, with G>5.7 for arrays containing more than 10 elements. Similarly, the spherical arrays with linear elements performed well when steered along the array axis to the same degree, with G>7 (for element widths up to 3 lambda), though many more array elements were required. However, when these arrays were steered 15 mm laterally, along the length of the prostate (the y direction), the value for G fell below 1 for element widths greater than about 1.6 lambda. It was found that the cylindrical arrays performed much better for y-direction steering (G>4, for 60 mm arrays with an element width of 1.75 lambda), but their performance was poorer when steered in the z direction (G approximately 4 for an element width of 1.5 lambda). In order to find a compromise between these extremes, a curved cylindrical array was examined, which was a cylindrical array with additional curvature along its length. These curved cylindrical arrays yielded performance between that of spherical linear arrays and cylindrical arrays, with better steering along the y direction than the spherical arrays and better z-direction steering than the cylindrical arrays. |
| Title |
Ultrasound phased arrays for prostate treatment. |
| Author |
Tan JS, Frizzell LA, Sanghvi NT, Seip R, Wu JS, Kouzmanoff JT. |
| Journal |
Proc IEEE Ultrason Symp |
| Volume |
|
| Year |
2000 |
| Abstract |
The effect of array geometry on the steering performance of ultrasound phased arrays is examined theoretically, in order to maximize array performance under the given anatomical constraints. This paper evaluates the performance of arrays with spherical and cylindrical geometry, determined by using computer simulations of the pressure fields produced at various extremes of steering. The spherical segment arrays were truncated for insertion into the rectum, and contained either annular or linear elements. The cylindrical arrays were either flat or had a variable curvature applied along their length. Fields were computed by dividing the array elements into many point sources. The effectiveness of an array configuration when steered to a particular focal location was assessed by defining a parameter, G, as the ratio of the intensity at the desired focus to the maximum intensity of any unwanted lobes. The performance of truncated spherical arrays with annular elements was evaluated for focal steering along the array axis ~in depth, in the z direction!. When steered 15 mm toward the source, these truncated spherical annular arrays exhibited excellent performance, with G.5.7 for arrays containing more than 10 elements. Similarly, the spherical arrays with linear elements performed well when steered along the array axis to the same degree, with G.7 ~for element widths up to 3 l!, though many more array elements were required. However, when these arrays were steered 15 mm laterally, along the length of the prostate ~the y direction!, the value for G fell below 1 for element widths greater than about 1.6 l. It was found that the cylindrical arrays performed much better for y-direction steering ~G.4, for 60 mm arrays with an element width of 1.75 l!, but their performance was poorer when steered in the z direction ~G>4 for an element width of 1.5 l!. In order to find a compromise between these extremes, a curved cylindrical array was examined, which was a cylindrical array with additional curvature along its length. These curved cylindrical arrays yielded performance between that of spherical linear arrays and cylindrical arrays, with better steering along the y direction than the spherical arrays and better z-direction steering than the cylindrical arrays. © 2001 Acoustical Society of America. |
| Title |
Ultrasound properties of liver with and without particulate contrast agents. |
| Author |
Tuthill TA, Baggs RB, Violante MR, Parker KJ. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
Basic acoustic parameters are examined in rabbit liver with and without a solid contrast agent used for tumor detection. In normal liver, backscatter, attenuation, and sound speed are found to decrease with increasing water content. The addition of micron-sized particles made from iodipamide ethyl ester (IDE) can increase backscatter and attenuation depending on size and concentration. A discrepancy of the increased backscatter from theoretical predictions based on random scatterers is attributed to the particle's biodistribution in the liver. |
| Title |
Ultrasound properties of lung tissue and their measurements. |
| Author |
Pedersen PC, Ozcan HS. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
In-vitro measurements have been carried out for the group velocity and the attenuation, in dB/cm, in cow lung tissue. The velocity and the attenuation were measured both as a function of air content, from 32 to 68%, and as a function of frequency, from 10 to 800 KHz. The group velocity was determined from measurement of the phase difference between the transmitted and incident acoustic signal while the attenuation was measured from the insertion loss with correction for the water-lung interface transmission losses. The measured group velocities indicate only a small degree of dispersion, but a strong dependence on air content. The attenuation is very high and exhibits strong frequency dependence, but weak air content dependence. |
| Title |
Ultrasound pulse propagation in dispersive media. |
| Author |
Leeman S. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1980 |
| Abstract |
Human tissues show dispersive ultrasound absorption, and it is important to understand how ultrasound pulses in the diagnostic frequency range, 1-10 MHz, propagate in such media. An uncomplicated wave-equation model for human soft.tissues is postulated, and its dispersion law for absorption is demonstrated to be compatible with existing experimental findings. Propagative solutions for the simple one-dimensional, homogeneous case (no scattering) are derived. It is shown that the transmitted pulse consists of an undistorted, damped replica of the incident pulse, plus a depth-dependent, time-extended 'rumble', both of which travel at a fixed, finite velocity through the medium. The constancy of this (signal) velocity reconciles the predicted velocity dispersion with the observed weakness of such an effect in many tissues, and some consequences for the measurement of both velocity and absorption are indicated. |
| Title |
Ultrasound reflection-mode computerized tomography for in-vivo imaging of small organs. |
| Author |
Ermert H, Rohrlein G. |
| Journal |
Proc IEEE Ultrasonic Symposium |
| Volume |
|
| Year |
1986 |
| Abstract |
No Abstract Available. |
| Title |
Ultrasound safety: What are the issues? |
| Author |
Merritt CRB. |
| Journal |
Radiology |
| Volume |
|
| Year |
1989 |
| Abstract |
No abstract available, editorial. |
| Title |
Ultrasound scatterer size estimation technique based on a 3D acoustic impedance map from histologic sections. |
| Author |
Mamou J, Oelze ML, Zachary JF, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2003 |
| Abstract |
Identifying the scatterers and obtaining accurate estimates of ultrasonic scatterer sizes are beneficial adjuncts to characterize (diagnose) disease from ultrasonic backscatterer measurements. A new scatterer size estimation technique has been developed that is based on a 3D acoustic impedance map. Ultrasonic scatterer estimation techniques rely extensively on form factor functions to obtain estimates, and 3D impedance maps can be used to derive independently form factors. The 3D acoustic impedance map is derived from a 3D histological data set of tissue, and is independent of ultrasonically acquired data. A rat fibroadenoma and a mouse 4T1 mouse mammary tumor (MMT) were fixed (10% neutral-buffered formalin), embedded in paraffin, serially sectioned at 10 /spl mu/m and 5 /spl mu/m respectively, and stained with H&E for histologic evaluation. Each section was digitally photographed through the light microscope. Tissue structures in each section were assigned distinct acoustic impedance values. The images from serial sections were aligned to yield two 3D impedance data set. A Gaussian form factor was used to estimate scatterer size and acoustic concentration. The scatterer size estimates were compared to previous values that were obtained from ultrasonic backscatterer measurements (also using a Gaussian form factor). For both 3D impedance maps, the relative difference between the size estimates were below 10%. The optimization scheme was also conducted on two simulated medium and led to relative errors below 1% for the scatterer size. This approach demonstrates that the use of 3D impedance maps has significant potential for improving parametric imaging by evaluating form factor functions. |
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