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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 5 out of 330
| Title |
A comparison of displacement and pressure waveforms of a nonlinear ultrasonic field. |
| Author |
Bacon DR. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1984 |
| Abstract |
No abstract available. |
| Title |
A comparison of doppler ultrasound waveform indices in the umbilical artery. I. Indices derived from the maximum velocity waveform. |
| Author |
Thompson RS, Trudinger BJ, Cook CM. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
Various Doppler waveform indices have been used for assessment of the fetal circulation. Comparisons were made to show what relations exist between the indices, and to identify any differences or difficulties which might arise from using one as opposed to another in clinical practice. Both normal pregnancy and cases of fetal growth failure were studied. Indices were obtained from the maximum velocity envelope of the umbilical artery waveform using a curve fitting technique. The values were very reproducible for all indices. The FHR, which varied over the entire normal range, did not significantly affect the values of any index. The downstream impedance indices calculated included the AB ratio, pulsatility index (PI) and Pourcelot ratio. These all gave very closely correlated results for normals but discrepancies occurred in the at risk group, where values were elevated. This could be attributed to differences in the underlying distributions. The indices suggested for cardiac contractility were not as closely related to each other, and moreover the differences between them showed no clear pattern. None of the indices varied independently of the others. The rising slope, which is by definition related to the PI, was more highly correlated with the downstream indices than the relative flow rate index. |
| Title |
A comparison of doppler ultrasound waveform indices in the umbilical artery. II. Indices derived from the mean velocity and first moment waveforms. |
| Author |
Thompson RS, Trudinger BJ, Cook CM. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
Umbilical artery Doppler recordings in both normal pregnancy and cases of fetal growth failure were processed by computer. Representative waveforms for the maximum velocity, mean velocity and first moment were obtained after ensemble averaging and correction for thump filtering. The same set of indices, which included the AB ratio, pulsatility index, rising slope and relative flow rate index, were calculated for each of the waveforms. The results were compared to identify differences which might arise in clinical practice if a waveform other than the usual (maximum velocity) was used. The ratio of the mean to the maximum velocity, which gives an indication of the velocity profile, was shown to be very error prone. The reproducibility of the mean velocity and first moment indices was inferior to that of the maximum velocity indices. The results from the different waveforms were highly correlated for normals for most indices. However, in the growth retarded group there was a tendency for the mean velocity and first moment indices to classify as normal studies classified as abnormal by the maximum velocity index. The values of indices derived from the first moment waveform were generally larger than the maximum and mean velocity values. For the relative flow rate index, where results were often different to the general trend, the values were more nearly equal. .. |
| Title |
A comparison of finite aperture phase sensitive and phase insensitive detection in the near field of inhomogeneous material. |
| Author |
Busse LJ, Miller JG. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1981 |
| Abstract |
An analysis is presented of the responses of finite sized phase sensitive and phase insensitive ultrasound receivers when each is used to detect spatially non-uniform pressure distributions. The computationally efficient angular spectrum propagation technique is used to model the detection properties of phase sensitive and phase insensitive receiver apertures. Comparisons are based upon amplitude estimates of the ultrasonic field produced by random and non-random source distributions. This study concludes by examining the focusing properties of phase sensitive and phase insensitive array systems. Calculated point spread functions are used to evaluate focal plane properties of each system in the presence of phase variations resulting, for example, from inhomogeneities exhibited by the medium. Results suggest that phase insensitive processing may lead to substantial reduction in the speckle present in conventional ultrasonic imaging systems. The potential application of phase insensitive receivers to ultrasonic nondestructive testing materials and tissue characterization, and imaging is discussed. |
| Title |
A comparison of grey-scale ultrasound with other methods for the detection of liver metastases from breast carcinoma. |
| Author |
Smith IE, Taylor KJW, McCready VR, Powles TJ, Bondy PK. |
| Journal |
Clin Oncol |
| Volume |
|
| Year |
1976 |
| Abstract |
The accurate and early detection of liver metastases in patients with breast cancer is important in planning appropriate treatment. In this study a technique of grey-scale ultrasonography is described, and compared with isotope liver scanning, serum liver function tests, and clinical examination in detecting metastatic liver disease in 70 female patients with breast carcinoma, either at the time of initial presentation or after primary therapy. Fifteen of these patients had established liver metastases (21%). Grey-scale ultrasonography correctly detected 14 of the 15 patients (93%), serum alkaline phosphatase correctly detected 13 patients (87%) and clinical examination correctly detected 5 patients (33%). Isotope liver scanning was done on only 9 of the 15 patients and correctly detected 7 of the 9 (78%). The false positive rate for each group was as follows: grey-scale ultrasonography wrongly detected 3 out of 55 patients (5%), serum alkaline phosphatase wrongly detected 4 out of 55 (7%), and clinical examination wrongly detect 1 out of 55 (2%). Isotope liver scanning was done on 35 of the 55 patients without liver involvement and wrongly detected 8 out of these 35 patients (23%). These results suggest that the technique of grey-scale ultrasonography described here is as accurate as other investigations in the detection of liver metastases from breast cancer and has a lower false positive rate than isotope liver scans. This, combined with the fact that grey-scale ultrasound is safe, non-invasive and painless suggests that the technique might in the future have wider use; it is emphasized at present, however, that the apparatus was specially built, is rather sophisticated, and skilled and experienced interpretation was required for these results. |
| Title |
A comparison of hemolytic and sonochemical activity of ultrasonic cavitation in a rotating tube. |
| Author |
Miller DL, Thomas RM. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1993 |
| Abstract |
Biological effects of in vitro ultrasonic exposure may result from mechanical and from sonochemical mechanisms related to ultrasonic cavitation. Mechanical cell lysis by 1.61 MHz ultrasonic cavitation was assessed in a rotating tube exposure system by hemolysis measurements. Free radical generation was assessed by the terephthalic acid dosimeter, calibrated by gamma-ray dosage. Sonochemical production was assessed by measuring residual hydrogen peroxide using the sensitive isoluminol method. Exposure conditions were similar for all tests, except longer durations were needed for the free radical and hydrogen peroxide tests. The sonochemical mechanisms were relatively more important for increasing intensity, and increasing temperature. Increasing rotation speed or bubbling with argon before exposure enhanced all cavitation activity. Stopping the rotation reduced all cavitation activity. Burst-mode ultrasound (10.5 microseconds bursts, 1:1 or 1:3 duty cycle) reduced cavitation activity, but gave relatively greater sonochemical activity under some conditions. These results indicate that the mechanical and sonochemical mechanisms can be separately favored to some extent by varying exposure conditions. The observed trends.should be helpful for selecting exposure conditions favorable for studying bioeffects of the sonochemical mechanism. |
| Title |
A comparison of matched signals used in three different phase-aberration correction algorithms. |
| Author |
Li Y, Gill R. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1998 |
| Abstract |
The Nearest-Neighbor Cross-Correlation (NNCC), Translating Apertures (TA), and Near-Field Signal Redundancy (NFSR) algorithms have a common feature: they all calculate cross-correlation functions between signals that are assumed to be highly correlated (matched signals), and then derive the aberration profile from the peak positions of these cross-correlation functions. One of the major differences between them is the way matched signals are collected. In this paper, a sub-signal analysis of matched signals is performed to demonstrate the different sub-signal components in matched signals collected with these three algorithms. The sub-signal components of matched signals influence the similarity between them and they have significant impact on the performance of an algorithm. The similarity between matched signals collected with these three algorithms is experimentally compared by calculating the cross-correlation coefficient between matched signals. Signals are collected from a phantom with a modified ATL Ultramark(R) 8 ultrasound scanner. It shows that the degree of similarity between matched signals in these algorithms is in the following order (from more to less similar): NFSR, TA, and NNCC. It also shows that, when phase aberrations exist, the cross-correlation coefficients between matched signals in the NNCC and TA algorithms decrease more dramatically than those in the NFSR algorithm. |
| Title |
A comparison of material classification techniques for ultrasound inverse imaging. |
| Author |
Zhang X, Broschat SL, Flynn PJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2002 |
| Abstract |
The conjugate gradient method with edge preserving regularization (CGEP) is applied to the ultrasound inverse scattering problem for the early detection of breast tumors. To accelerate image reconstruction, several different pattern classification schemes are introduced into the CGEP algorithm. These classification techniques are compared for a full-sized, two-dimensional breast model. One of these techniques uses two parameters, the sound speed and attenuation, simultaneously to perform classification based on a Bayesian classifier and is called bivariate material classification (BMC). The other two techniques, presented in earlier work, are univariate material classification (UMC) and neural network (NN) classification. BMC is an extension of UMC, the latter using attenuation alone to perform classification, and NN classification uses a neural network. Both noiseless and noisy cases are considered. For the noiseless case, numerical simulations show that the CGEP?BMC method requires 40% fewer iterations than the CGEP method, and the CGEP?NN method requires 55% fewer. The CGEP?BMC and CGEP?NN methods yield more accurate reconstructions than the CGEP method. A quantitative comparison of the CGEP?BMC, CGEP?NN, and GN?UMC methods shows that the CGEP?BMC and CGEP?NN methods are more robust to noise than the GN?UMC method, while all three are similar in computational complexity. |
| Title |
A comparison of methods for estimating attenuation using backscattered ultrasound. |
| Author |
Johnston PH, Thomas LJ Jr. Miller JG. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1982 |
| Abstract |
No abstract available. |
| Title |
A comparison of the AIUM/NEMA, IEC and FDA (1980) definitions of various acoustic output parameters for ultrasonic transducers. |
| Author |
Livett AJ, Preston RC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
Comparison is made between the values obtained for the acoustic output from different types of medical ultrasonic equipment when determined according to the definitions given in different documents. In particular, the American Insititute of Ultrasound in Medicine with the National Electrical Manufacturers Association Safety Standard for Diagnostic Ultrasound Equipment, the U.S. Food and Drug Administration Diagnostic Ultrasound Reporting Guide (1980) and the proposed International Electrotechnical Commission standard are compared for pulse-echo and Doppler equipment. Differences of up to 40% in the spatial-average temporal-average and spatial-peak pulse-average intensities are shown to be a result of the different definitions of beam area and pulse duration. |
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