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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 90 out of 330
| Title |
Digital computer analysis of M-scan echocardiograms. |
| Author |
Pai AL, Cahill NS, Dubroff RJ, Fozzard HA, Brooks HL. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1976 |
| Abstract |
In the past few years, echocardiography has emerged as a useful noninvasive clinical tool in cardiac diagnosis. Conventional methods for analyzing echocardiographic data involve time consuming and tedious manual techniques for measuring various distances and computing cardiac parameters of interest. This paper describes a useful method for automating the analysis of M scan echocardiograms both for routine clinical work as well as for special research oriented ultrasonic cardiac studies. Using a GRAF/PEN digitizer interfaced to a PDP-11 minicomputer system, relevant points of the ventricular and mitral valve interfaces, R-R intervals, and time and distance calibration points are entered from hard copies of M scan echocardiograms. The computer then determines all the parameters of interest such as left ventricular (LV) diameters, LV volumes, LV mass, ejection fraction, stroke volume, cardiac output, septal and posterior wall dynamics, as well as such mitral valve (MV) parameters as opening/closing velocities, excursions, and areas subtended by both MV leaflets. The data and results are stored on disc or tape and a report of the results is immediately available from a printer for incorporation into the patient's record file. |
| Title |
Digital filter models for media having linear with frequency loss characteristics. |
| Author |
Kuc R. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1981 |
| Abstract |
Linear with frequency acoustic loss characteristics have been observed for soft biological tissue when probed with diagnostic ultrasound and for Plexiglas when used for underwater applications. Two digital filter models are described that exhibit this linear characteristic. The first filter model, designed using a frequency sampling technique, produces a symmetric unit sample response and a linear with frequency phase characteristic. Several features of this linear phase model, however, are found to be incompatible with the physical mechanisms producing the loss. Upon resolving these incompatibilities, a second filter model is obtained which has a minimum phase transfer function. Experimental verification, using Plexiglas as an acoustic propagation medium, demonstrates the superiority of the minimum phase model for describing the physical mechanisms which produce a linear with frequency loss characteristic. |
| Title |
Digital processing to enhance features of ultrasound images. |
| Author |
Waag RC, Lee PPK, Gramiak R. |
| Journal |
Proc IEEE Comput Soc Conf |
| Volume |
|
| Year |
1978 |
| Abstract |
Digital processing of pulse echo ultrasound data has been utilized to study signal and image characteristics. Data was acquired by a dual processor, disk-based minicomputer system that permitted interactive processing and display. Fluctuating RF echoes obtained with a stationary beam from cardiac structures have been analyzed using Fourier techniques to show temporal changes during the cardiac cycle and to reveal variations in echo frequency content from disease. Processing has also been carried out on matrices representing cross-sectional images that were produced by beam scanning. Small differences in signal amplitude have been emphasized by amplitude mapping based on histogram analysis of original images. Fourier domain filtering has been used to enhance spatial characteristics of ultrasonic images including tissue texture, reflector spacing, and structure boundaries. Ultrasound has been developed into an important tool in medical diagnosis, primarily because of its unique capability to image soft tissues without exposure to ionizing radiation or the use of exogenous contrast agents (1,2). Recent advances in instrumentation have included gray scale presentation from analog scan conversion systems which have improved the visualization of detail within organs (3). The availability of this tissue detail prompts us to attempt to extend the diagnostic capabilities of ultrasound through the use of backscattered spectrum, amplitude distribution, and spatial frequency for emphasis and better evaluation of tissue detail. |
| Title |
Digital radiofrequency echocardiography in the detection of myocardial contrast following intravenous administration of Albunex. |
| Author |
Monaghan MJ, Metcalfe JM, Odunlami S, Waaler A, Jewitt DE. |
| Journal |
Eur Heart J |
| Volume |
|
| Year |
1993 |
| Abstract |
Conventional contrast echo techniques have proved inadequate for the detection of myocardial perfusion using intravenously injected echo contrast agents because of the limitations and relative.insensitivity of standard echocardiographic equipment. In order to avoid these problems, we have obtained pure digital radiofrequency ultrasound data from the left ventricle and myocardium during i.v. contrast myocardial perfusion echo studies. In 30 patients, following coronary arteriography, i.v. injections of the echo contrast agent Albunex (sonicated human serum albumin) in two doses of 0.08 and 0.22 ml.kg-1 were administered during digital radiofrequency echocardiography sampling of data from the myocardium and left ventricular cavity. Analysis of mean integrated backscatter (MIB, a measure of the total ultrasound energy) was performed before, during and after Albunex injection. The data were also analysed for a shift in frequency spectrum which could be caused by resonance of the Albunex contrast microspheres in the heart, a phenomenon which has been previously demonstrated in vitro. Digital radiofrequency ultrasound data were successfully obtained and analysed in 23 patients. In 31 segments where reasonable resting perfusion was expected, there was a significant increase in MIB from 0.644 to 1.245, P < 0.001 and time intensity curves could be constructed showing wash-in and wash-out of contrast from the myocardium. In 10 segments supplied by significantly diseased vessels, MIB intensity increased from 1.044 to 1.874, P = 0.054. In myocardial segments supplied by non-diseased vessels, microsphere resonance also caused a drop in mean frequency of 140 KHz, P < 0.001, and permitted similar temporal analysis of myocardial perfusion. |
| Title |
Digital reconstruction and display of compound scan ultrasound images. |
| Author |
Robinson DE. |
| Journal |
IEEE Trans Sonics Ultrason |
| Volume |
|
| Year |
1984 |
| Abstract |
Ultrasonic image reconstruction can be divided into three areas: scan conversion, pixel value assignment (in compound scan imaging), and image display. In scan conversion, the method of allocation of image values in pixels not intersected by scan lines has a dramatic effect on the image quality. Use of an appropriate interpolation scheme can greatly improve image quality and at the same time reduce the required line density and hence increase the frame rate. Peak-detected, averaged, and minimum-detected pixel value assignment lead to dramatically different appearances of the resulting compound scan image. The three methods have different effects on the resolution and on differential diagnosis in clinical conditions. In the display of images formed by the three methods, different postprocessing is required to yield comparable images. This is achieved by an adaptive method based on the required histogram. Results are presented for the reconstruction, assignment, and postprocessing techniques of experimental target studies and clinical data obtained with the U.I. Octoson. The effect of these processes on the appearance of clinical images and application of the techniques to produce image enhancement and differential diagnosis are demonstrated using clinical images of the abdomen. |
| Title |
Diminishing exposure to doppler ultrasound the sonographer's role. |
| Author |
Taylor KJ, Kremkau FW. |
| Journal |
J Diagn Med Sonogr |
| Volume |
|
| Year |
1988 |
| Abstract |
Diagnostic ultrasound has an unblemished record for safety. The induction of pulsed Doppler may involve higher intensities exceeding 1 W/cm2 (SPTA). These intensities must cause concern for fetal exposure, and the FDA has introduced strict guidelines to limit such exposure. Presented here are practical ways in which sonography can minimize exposure. These include the use of Doppler only when clinically indicated or part of an approved research protocol, knowledge of the imitted intensity, and how to attenuate this to prudent levels. It is desirable to use sensitive equipment and increase the TGC before increasing power. Such prudent use will allow ultrasound to be used in these new applications without hazard. |
| Title |
Direct and indirect effect of ultrasound on bone marrow cell suspensions. |
| Author |
Hrazdira I. |
| Journal |
Folia Biol (Praha) |
| Volume |
|
| Year |
1965 |
| Abstract |
The direct and indirect effect of ultrasound (frequency 800 kc, intensity 0.8 and 1.5 W/cm2) on rat bone marrow cells suspended in saline and in aline containing 5% (10%) Subtosan (3.5% polyvinylpyrrolidone) was studied. The number of surviving cells, the pH change and the amount of free HNO2 formed as a result of exposure to ultrasound were determined in every experimental sample. The experiments conclusively demonstrated the indirect effect of ultrasound on suspended bone marrow cells and showed that it increased with the time of exposure of the suspension solutions. A connection between this effect and physicochemical changes in the suspension medium was also demonstrated. The presence of a small amount of a colloidal substance limited the formation of chemically active substances and the indirect effect of ultrasound on the suspended bone marrow cells. |
| Title |
Direct computation of ultrasound phased-array driving signals from a specified temperature distribution for hyperthermia. |
| Author |
McGough RJ, Ebbini ES, Cain CA. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1992 |
| Abstract |
This paper presents a new method which obtains ultrasound hyperthermia applicator phased-array element driving signals from a desired temperature distribution. The approach combines a technique which computes array element driving signals from focal point locations and intensities with a new technique which calculates focal point locations and power deposition values from temperature requirements. Temperature specifications appear here as upper and lower bounds within the tumor volume, and a focal point placement algorithm chooses focal patterns capable of achieving the temperature range objective. The linear algebraic structure of the method allows rapid calculation of both the phased-array driving signals and an approximate temperature field response. Computer simulations verify the method with a spherical section array (SSA) for a variety of temperature specifications and blood perfusion values. This scheme, which applies to any phased-array geometry, completes an essential step in both treatment planning and feedback for hyperthermia with ultrasound phased-array applicators. |
| Title |
Direct evidence of cavitation in vivo from diagnostic ultrasound. |
| Author |
Holland CK, Deng CX, Apfel RE, Alderman JL, Fernandez LA, Taylor KJW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1996 |
| Abstract |
Recent increases in the pressure output of diagnostic ultrasound scanners have led.to an interest in establishing thresholds for bioeffects in many organs including.the lungs of mammals. Damage may be mediated by inertial cavitation, yet there.have been no such direct observations in vivo. To explore the hypothesis of.cavitation-based bioeffects from diagnostic ultrasound, research has been.performed on the thresholds of damage in rat lungs exposed to 4.0-MHz pulsed.Doppler and color Doppler ultrasound. A 30-MHz active cavitation detection.scheme complementing these studies provides the first direct evidence of.cavitation in vivo from diagnostic ultrasound pulses. |
| Title |
Direct in vivo visualization of intravascular destruction of microbubbles by ultrasound and its local effects on tissue. |
| Author |
Skyba DM, Price RJ, Linka AZ, Skalak TC, Kaul TC. |
| Journal |
Circulation |
| Volume |
|
| Year |
1998 |
| Abstract |
BACKGROUND: Our aim was to observe ultrasound-induced intravascular microbubble destruction in vivo and to characterize any resultant bioeffects. METHODS AND RESULTS: Intravital microscopy was used to visualize the spinotrapezius muscle in 15 rats during ultrasound delivery. Microbubble destruction during ultrasound exposure caused rupture of < or = 7-microm microvessels (mostly capillaries) and the production of nonviable cells in adjacent tissue. The number of microvessels ruptured and cells damaged correlated linearly (P<0.001) with the amount of ultrasound energy delivered. CONCLUSIONS: Microbubbles can be destroyed by ultrasound, resulting in a bioeffect that could be used for local drug delivery, angiogenesis, and vascular remodeling, or for tumor destruction.
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