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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 213 out of 330
| Title |
Quantitative vascularity of breast masses by Doppler imaging: regional variations and diagnostic implications. |
| Author |
Sehgal CM, Arger PH, Rowling SE, Conant EF, Reynolds C, Patton JA. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
2000 |
| Abstract |
Seventy-four biopsy proven breast masses were imaged by color and power Doppler imaging to evaluate vascular pattern of malignant and benign breast masses. The images were analyzed for vascularity. The measurements were made over the entire mass as well as regionally at its core, at its periphery, and in the tissue surrounding it. The surgical specimens were analyzed for microvessel density. The diagnostic performance of Doppler sonographic vascularity indices was evaluated by receiver operating characteristic analysis. The malignant masses were 14 to 54% more vascular than the benign masses. Both types of masses were more vascular by ultrasonography than the tissue surrounding them. Whereas benign masses were 2.2 times more vascular than the surrounding tissue, the malignant masses were 5.0 times more vascular. In a subset of patients the regional vascularity at the core, periphery, and surrounding tissue by Doppler imaging exhibited a strong correlation (R2 > 0.9) with the corresponding histologic microvessel density measurements. Although the malignant masses exhibited a strong gradient in vascularity, core> periphery > surrounding tissue, the benign masses had relatively uniform distribution of vascularity. The area under the receiver operating characteristic curve (Az) for the Doppler indices range from 0.56 +/- 0.07 to 0.56 +/- 0.07. A nonlinear analysis including age-specific values of Doppler indices improved the diagnostic performance to Az = 0.85 +/- 0.06. In conclusion, quantitative Doppler imaging when used in combination with a nonlinear rule-based approach has the potential for differentiating between malignant and benign masses. |
| Title |
Question of risk still hovers over routine prenatal use of ultrasound. |
| Author |
Bolsen B. |
| Journal |
JAMA |
| Volume |
|
| Year |
1982 |
| Abstract |
No abstract available |
| Title |
Quo vadis elasticity imaging? |
| Author |
Konofagou EE. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2004 |
| Abstract |
In the past decade, an important field that has emerged as complementary to ultrasonic imaging is that of elasticity imaging. The term encompasses a variety of techniques that can depict a mechanical response or property of tissues. In ultrasound, its premise is built on two important facts: (a) that significant differences between mechanical properties of several tissue components exist and (b) that the information contained in the coherent scattering, or speckle, is sufficient to depict these differences following an external or internal mechanical stimulus. Parameters, such as velocity of vibration, displacement, strain, strain rate, velocity of wave propagation and elastic modulus, have all been demonstrated feasible in their estimation and have resulted in the accurate depiction of stiffer tissue masses, such as tumors, high-intensity focused ultrasound (HIFU) lesions and atherosclerotic plaques. More recently, through the development of ultrafast algorithms tailored to suitable hardware as well as the familiarity of the physician with the sensitivity of the methods used, one elasticity imaging technique in particular, elastography, has been shown applicable in a typical clinical ultrasound setting. In other words, elastograms can currently be obtained at quasi real-time (approximately at a frame rate of 8 frames/s) and with the use of a hand-held transducer (as opposed to the previously used frame-suspended setup) during and simultaneously with an ultrasound exam of, e.g., the breast or the prostate. The higher frame rate available with certain clinical ultrasound scanners has also resulted in the successful application of elasticity imaging techniques on the myocardium and monitoring its deformation over several cardiac cycles for the detection of ischemic regions. As a result, elasticity imaging with its ever increasing number of applications and demonstrated applicability in a typical, clinical ultrasound setting promises to make an important contribution to the ultrasound practice as we know it. |
| Title |
Rabbit and pig lung damage comparison from exposure to continuous wave 30-kHz ultrasound. |
| Author |
O'Brien WD Jr, Zachary JF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1996 |
| Abstract |
Previous comparative studies of ultrasound-induced pulmonary hemorrhage in mice and rabbits suggested that sensitivity to damage was species dependent.(O'Brien and Zachary 1994b). In order to understand better these differences in species more analogous to the human, 74 pigs and 75 rabbits were each exposed for 10 min at 1 of 6 acoustic pressure levels (0, 145, 290, 340 [rabbits only], 460.and 490 [pigs only] kPa) at an ultrasonic frequency of CW 30 kHz. Eighteen mice were used as positive controls (10-min duration at 145 kPa). Because pig lung has numerous physiological and anatomical similarities to human lung, it was selected as the appropriate animal model for these studies. Pig lung data were compared to rabbit lung data; rabbit lung data have already been compared with mouse lung data (O'Brien and Zachary 1994a). Comparative analyses and extrapolation of these experimental data are intended to provide a better scientific basis for understanding the potential biological effects of ultrasound on human lungs since such studies will probably never be conducted with humans. Under the same exposure conditions and lung assessment criteria, mouse lung was determined to be more sensitive to ultrasound-induced damage than that of the rabbit by a factor of 3.9, the rabbit lung was more sensitive to ultrasound-induced.damage than that of the pig by a factor of 3.7, and the mouse lung was more sensitive to ultrasound-induced damage than that of the pig by a factor of 14.4. |
| Title |
Radial reflection diffraction tomography. |
| Author |
Lehman SK, Norton SJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2004 |
| Abstract |
A wave-based tomographic imaging algorithm based upon a single rotating radially outward oriented transducer is developed. At successive angular locations at a fixed radius, the transducer launches a primary field and collects the backscattered field in a "pitch/catch" operation. The hardware configuration, operating mode, and data collection method are identical to that of most medical intravascular ultrasound (IVUS) systems. IVUS systems form images of the medium surrounding the probe based upon ultrasonic B scans, using a straight-ray model of sound propagation. The goal of this research is to develop a wave-based imaging algorithm using diffraction tomography techniques. Given the hardware configuration and the imaging method, this system is referred to as "radial reflection diffraction tomography." Two hardware configurations are considered: a multimonostatic mode using a single transducer as described above, and a multistatic mode consisting of a single transmitter and an aperture formed by multiple receivers. In this latter case, the entire source/receiver aperture rotates about the fixed radius. Practically, such a probe is mounted at the end of a catheter or snaking tube that can be inserted into a part or medium with the goal of forming images of the plane perpendicular to the axis of rotation. An analytic expression for the multimonostatic inverse is derived, but ultimately the new Hilbert space inverse wave (HSIW) algorithm is used to construct images using both operating modes. Applications include improved IVUS imaging, bore hole tomography, and nondestructive evaluation (NDE) of parts with existing access holes. |
| Title |
Radiated power characteristics of diagnostic ultrasound transducers. |
| Author |
Szabo TL, Seavey GA. |
| Journal |
Hewlett-Packard Journal |
| Volume |
|
| Year |
1983 |
| Abstract |
No abstract available. |
| Title |
Radiation force measurements at a water-air interface. |
| Author |
Sakai S. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
2003 |
| Abstract |
Many scientific advances led to the discovery of ultrasound. Its history is rooted in the study of sound with Sir Isaac Newton first proposing his theory that sound is a wave in 1687 [Newton, 1687]. In 1877, Lord Rayleigh discussed what is known today as modern acoustics [Rayleigh, 1945]. In 1880, the Curie brothers discovered the piezoelectric effect [Curie and Curie, 1880] which led Paul Langevin to develop one of the first uses of underwater ultrasound
at a frequency of about 150 kHz [Hunt, 1982]. The development of ultrasound and echo detection advanced and in the 1920s, Boyle and his colleagues were the first to observe ultrasound-induced gas bubbles forming in liquid, which today is known as cavitation [Boyle and Lehmann, 1926], [Boyle, 1927], [Boyle and Taylor, 1929]. In 1932, the use of ultrasound to therapeutically heat tissues was suggested [Freundlich et al., 1932]. Ten years later, in 1942, the idea to burn focal tissues deep in the body was proposed as a noninvasive neurosurgery
technique [Lynn et al., 1942], [Lynn and Putman, 1944]. In the 1950s and 1960s, the use of diagnostic ultrasound equipment for clinical applications started [O’Brien, 1998]. |
| Title |
Radiation force on a spherical object in the field of a focused cylindrical transducer. |
| Author |
Chen X, Apfel RE. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1997 |
| Abstract |
An exact solution of the radiation force on a spherical object, when positioned on the acoustic axis of a cylindrical transducer, is provided. The solution is valid for any type of sphere of any size. The radiation force function allows the calibration of high-frequency focused ultrasound fields from radiation force measurements and expands the utility of the elastic sphere radiometer developed by Dunn et al. [Acustica 38, 58?61 (1977)]. Numeral results reveal an oscillatory behavior of the radiation force function for small spheres near the transducer surface and this behavior may present an opportunity for particle sorting based on the mechanical properties of the particle and other types of manipulation. |
| Title |
Radiation force. |
| Author |
Kossoff G. |
| Journal |
Proc Interact Ultrasound Biol Tissues Workshop - Seattle |
| Volume |
|
| Year |
1971. |
| Abstract |
No abstract available. |
| Title |
Radiation pressure and acoustic streaming. |
| Author |
Duck FA ( Duck FA , Baker AC , Starritt HC eds.). |
| Journal |
Book Chapter |
| Volume |
|
| Year |
1998 |
| Abstract |
This chapter deals with two linked but separate phenomena, radiation force and acoustic streaming, both of which have some practical importance in medical applications of ultrasound. We will start with qualitative descriptions of these phenomena, before giving an outline of their theoretical basis, then discuss some reports in the literature of their appearance in a medical context, and speculate about the difficulties still remaining.
When a solid object is placed in a progressive ultrasound wave it experiences a small force which is directed along the beam in a direction of propagation. This is called radiation force. If the solid target is larger than the beam, this force is proportional to the total acoustic power. As a result, radiation force has been used as the basis of well established methods for measuring acoustic power. When an ultrasound wave propagates in a fluid (liquid or gas),the fluid within the beam flows away from the transducer in the direction of propagation. This is called acoustic streaming. ( In some older texts it is referred to as 'quartz wind'.)
These two phenomena both exist because of the inherent non linearity of acoustic wave propagation in real media. While the magnitude of the force on the target, or of the streaming velocity , also depend on a number of other factors (absorption and reflection coefficient , geometry of the beam and target/container and so on) streaming and radiation force would not exist if pressure and density were linearly related (Beyer 1997).
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