|
|
|
BRL Abstracts Database |
|
Your search for ultrasound produced 3296 results. Page 21 out of 330
| Title |
A test for the effects of low-temporal-average-intensity pulsed ultrasound on the rat fetus. |
| Author |
Child SZ, Carstensen EL, Davis H. |
| Journal |
Exp Cell Biol |
| Volume |
|
| Year |
1984 |
| Abstract |
In 1978, Pizzarello and co-workers reported that exposure of rat fetuses to diagnostic levels of ultrasound caused marked reduction in fetal weight. Replicates of these experiments have been conducted and, in addition, exposures at 10 times the peak and average intensity were used. No effect on fetal weight, numbers of living fetuses or resorptions could be attributed to ultrasound at either exposure level. |
| Title |
A test of I(2)T as a dose parameter for fetal weight reduction from exposure to ultrasound. |
| Author |
Child SZ, Hoffman D, Strassner D, Carstensen EL, Gates AH, Cox C, Miller MW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1989 |
| Abstract |
It has been suggested that fetal weight reduction by ultrasound exposure is linearly related to the dose parameter I(2)T, where I is the intensity and t the exposure time. A direct test of the oncept was conducted using CF-1 mice. No effect on fetal weight was found at values of the dose parameter large enough to produce measurable heating in the fetal and maternal tissues. |
| Title |
A test of the hypothesis that diagnostic ultrasound disrupts myelination in neonatal rats. |
| Author |
del Cerro M, Child SZ, Raeman CH, Carstensen EL, Miller MW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1994 |
| Abstract |
Neonatal rats were exposed or sham exposed for 30 min to pulsed ultrasound.[2.25 MHz carrier frequency, 1 microsecond pulse length, 50 Hz pulse repetition.frequency (PRF), 50 W/cm2 Imax, 2 mW/cm2 ITA], euthanised and prepared for electron microscopic analysis of the nodes of Ranvier of the dorsal and ventral.roots of the spinal cord. There was also a cage control. All materials were.processed and scored blindly, evaluating whether perinodal myelin was normal. Rats from all regimens had areas of disrupted myelination. There was no statistically significant difference among the regimens for absence of myelination. The results did not confirm an earlier report that diagnostic ultrasound disrupts myelination in neonatal rats. |
| Title |
A theoretical assessment of the relative performance of spherical phased arrays for ultrasound surgery. |
| Author |
Gavrilov LR, Hand JW. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
2000 |
| Abstract |
Computer modeling of spherical-section phased arrays for ultrasound surgery (tissue ablation) is described. The influence on performance of the number of circular elements (68 to 1024), their diameter (2.5 to 10 mm), frequency (1 to 2 MHz), and degree of sparseness in the array is investigated for elements distributed randomly or in square, annular, and hexagonal patterns on a spherical shell (radius of curvature, 120 mm). Criteria for evaluating the quality of the intensity distributions obtained when focusing the arrays both on and away from their center of curvature, and in both single focus and simultaneous multiple foci modes, are proposed. Of the arrays studied, the most favorable performance, for both modes, is predicted for 256 5-mm diameter, randomly distributed elements. For the single focus mode, this performed better than regular arrays of 255 to 1024 elements and, for the case of nine simultaneous foci produced on a coplanar 3x3 grid with 4-mm spacing, better than square, hexagonal, or annular distributed arrays with a comparable number of elements. Randomization improved performance by suppressing grating lobes significantly. For single focus mode, a several-fold decrease in the number of elements could be made without degrading the quality of the intensity distribution. |
| Title |
A theoretical comparison of attenuation measurement techniques from backscattered ultrasound echoes. |
| Author |
Labyed Y, Bigelow TA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2011 |
| Abstract |
Accurate characterization of tissue pathologies using ultrasonic attenuation is strongly dependent on the accuracy of the algorithm that is used to obtain the attenuation coefficient estimates. In this paper, computer simulations were used to compare the accuracy and the precision of the three methods that are commonly used to estimate the local ultrasonic attenuation within a region of interest (ROI) in tissue; namely, the spectral log difference method, the spectral difference method, and the hybrid method. The effects of the inhomgeneities within the ROI on the accuracy of the three algorithms were studied, and the optimal ROI size (the number of independent echoes laterally and the number of pulse lengths axially) was quantified for each method. The three algorithms were tested for when the ROI was homogeneous, the ROI had variations in scatterer number density, and the ROI had variations in effective scatterer size. The results showed that when the ROI was homogeneous, the spectral difference method had the highest accuracy and precision followed by the spectral log difference method and the hybrid method, respectively. Also, when the scatterer number density varied, the spectral difference method completely failed, while the log difference method and hybrid method still gave good results. Lastly, when the scatterer size varied, all of the methods failed. |
| Title |
A theoretical comparison of energy sources--microwave, ultrasound and laser--for interstitial thermal therapy. |
| Author |
Skinner MG, Iizuka MN, Kolios MC, Sherar MD. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
A number of heating sources are available for minimally invasive thermal therapy of tumours. The purpose of this work was to compare, theoretically, the heating characteristics of interstitial microwave, laser and ultrasound sources in three tissue sites: breast, brain and liver. Using a numerical method, the heating patterns, temperature profiles and expected volumes of thermal damage were calculated during standard treatment times with the condition that tissue temperatures were not permitted to rise above 100 degrees C (to ensure tissue vaporization did not occur). Ideal spherical and cylindrical applicators (200 microm and 800 microm radii respectively) were modelled for each energy source to demonstrate the relative importance of geometry and energy attenuation in determining heating and thermal damage profiles. The theoretical model included the effects of the collapse of perfusion due to heating. Heating patterns were less dependent on the energy source when small spherical applicators were modelled than for larger cylindrical applicators due to the very rapid geometrical decrease in energy with distance for the spherical applicators. For larger cylindrical applicators, the energy source was of greater importance. In this case, the energy source with the lowest attenuation coefficient was predicted to produce the largest volume of thermally coagulated tissue, in each tissue site. |
| Title |
A theoretical framework for performance characterization of elastography: The strain filter. |
| Author |
Varghese T, Ophir J. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1997 |
| Abstract |
This paper presents a theoretical framework for the performance characterization in strain estimation which includes the effect of signal decorrelation, quantization errors due to the finite temporal sampling rate, and electronic noise. An upper bound on the performance of the strain estimator in elastography is obtained from a strain filter constructed using these limits. The strain filter is a term used to describe the nonlinear filtering process in the strain domain (due to the ultrasound system and signal processing parameters) that allows the elastographic depiction of a limited range of strains from the compressed tissue. The strain filter predicts the elastogram quality by specifying the elastographic signal-to-noise ratio (SNRe), sensitivity, and the strain dynamic range at a given resolution. The dynamic range is limited by decorrelation errors for large tissue strain values, and electronic noise for low strain values. Tradeoffs between different techniques used to enhance elastogram image quality may also be analyzed using the strain filter. |
| Title |
A theoretical study of acoustic cavitation produced by "positive-only" and "negative-only" pressure waves in relation to in vivo studies. |
| Author |
Church CC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2003 |
| Abstract |
This study investigated the responses of gas bubbles in water, "viscous water" or "lung surfactant" exposed to "positive-only" or "negative-only" pressure pulses. The computational results obtained were compared to the in vivo experimental findings of Bailey et al. (1996), for the thresholds for, and extents of, biological damage endpoints in Drosophila larvae and mouse lungs exposed to similar pressure pulses. It is shown that, if cavitation were the mechanism responsible for these biologic effects, the two pulse types would be expected to produce very different thresholds and amounts of damage unless: 1. the bubbles involved were larger than the linear resonance radius, or 2. the cavitational activity were located within a fraction of a wavelength of an air-tissue interface. A noncavitational, acoustic force mechanism for the effects also is considered. Finally, it is suggested that the mechanical index may require modification when the focus of the acoustic field lies near an air-tissue interface.
|
| Title |
A theoretical study of nonlinear effects with focused ultrasound in tissues: an "acoustic bragg peak". |
| Author |
Swindell W. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
This is a theoretical study of the absorbed power density that arises when a focused.ultrasound beam is absorbed in a tissue-like medium. The specific application is.selective tissue heating for cancer hyperthermia. Results are expressed in terms of an.enhancement ratio which describes the fractional gain in absorbed power density.when nonlinear effects are taken into account relative to the absorbed power density.that results when only linear effects are considered. Starting from a standard.configuration in which the transducer has a (Gaussian) diameter of 0.12 m, a radius.of curvature of 0.16 m and an operating frequency of 1 MHz a numerical sensitivity.analysis is performed in which transducer and tissue parameters are varied one at a.time. Enhancement ratios are invariably greater than unity, often being in the range of.1.5-2 for regions near the focus of the beam. The prediction is that nonlinear effects.will probably be useful in selectively increasing the temperature rise in the focal.region of a focused applicator. |
| Title |
A theoretical study of the scattering of ultrasound from blood. |
| Author |
Angelsen BA. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1980 |
| Abstract |
A theoretical treatment of the scattering of ultrasound from blood is given, assuming that blood behaves essentially as a continuum. The scattering then arises from fluctuations in the mass density and compressibility of the blood, which is caused by a fluctuation in the red cell concentration. An expression for the received signal in ultrasonic blood velocity measurements is given. The stochastic properties of the signal are discussed with reference to the information content about the velocity field of the blood. Since the signal is Gaussian, all available information is contained in the power spectrum, which is a blurred approximation to the velocity distribution in the region of observation. |
Page 1
| 2
| 3
| 4
| 5
| 6
| 7
| 8
| 9
| 10
| 11
| 12
| 13
| 14
| 15
| 16
| 17
| 18
| 19
| 20
| 21
| 22
| 23
| 24
| 25
| 26
| 27
| 28
| 29
| 30
| 31
| 32
| 33
| 34
| 35
| 36
| 37
| 38
| 39
| 40
| 41
| 42
| 43
| 44
| 45
| 46
| 47
| 48
| 49
| 50
| 51
| 52
| 53
| 54
| 55
| 56
| 57
| 58
| 59
| 60
| 61
| 62
| 63
| 64
| 65
| 66
| 67
| 68
| 69
| 70
| 71
| 72
| 73
| 74
| 75
| 76
| 77
| 78
| 79
| 80
| 81
| 82
| 83
| 84
| 85
| 86
| 87
| 88
| 89
| 90
| 91
| 92
| 93
| 94
| 95
| 96
| 97
| 98
| 99
| 100
| 101
| 102
| 103
| 104
| 105
| 106
| 107
| 108
| 109
| 110
| 111
| 112
| 113
| 114
| 115
| 116
| 117
| 118
| 119
| 120
| 121
| 122
| 123
| 124
| 125
| 126
| 127
| 128
| 129
| 130
| 131
| 132
| 133
| 134
| 135
| 136
| 137
| 138
| 139
| 140
| 141
| 142
| 143
| 144
| 145
| 146
| 147
| 148
| 149
| 150
| 151
| 152
| 153
| 154
| 155
| 156
| 157
| 158
| 159
| 160
| 161
| 162
| 163
| 164
| 165
| 166
| 167
| 168
| 169
| 170
| 171
| 172
| 173
| 174
| 175
| 176
| 177
| 178
| 179
| 180
| 181
| 182
| 183
| 184
| 185
| 186
| 187
| 188
| 189
| 190
| 191
| 192
| 193
| 194
| 195
| 196
| 197
| 198
| 199
| 200
| 201
| 202
| 203
| 204
| 205
| 206
| 207
| 208
| 209
| 210
| 211
| 212
| 213
| 214
| 215
| 216
| 217
| 218
| 219
| 220
| 221
| 222
| 223
| 224
| 225
| 226
| 227
| 228
| 229
| 230
| 231
| 232
| 233
| 234
| 235
| 236
| 237
| 238
| 239
| 240
| 241
| 242
| 243
| 244
| 245
| 246
| 247
| 248
| 249
| 250
| 251
| 252
| 253
| 254
| 255
| 256
| 257
| 258
| 259
| 260
| 261
| 262
| 263
| 264
| 265
| 266
| 267
| 268
| 269
| 270
| 271
| 272
| 273
| 274
| 275
| 276
| 277
| 278
| 279
| 280
| 281
| 282
| 283
| 284
| 285
| 286
| 287
| 288
| 289
| 290
| 291
| 292
| 293
| 294
| 295
| 296
| 297
| 298
| 299
| 300
| 301
| 302
| 303
| 304
| 305
| 306
| 307
| 308
| 309
| 310
| 311
| 312
| 313
| 314
| 315
| 316
| 317
| 318
| 319
| 320
| 321
| 322
| 323
| 324
| 325
| 326
| 327
| 328
| 329
| 330
|
|
|
|
