|
|
|
BRL Abstracts Database |
|
Your search for ultrasound produced 3296 results. Page 129 out of 330
| Title |
Frequency dependence of kidney injury induced by contrast-aided diagnostic ultrasound in rats. |
| Author |
Miller DL, Dou C, Wiggins RC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
This study was performed to examine the frequency dependence of glomerular capillary hemorrhage (GCH) induced by contrast-aided diagnostic ultrasound (DUS) in rats. Diagnostic ultrasound scanners were used for exposure at 3.2, 5.0 and 7.4 MHz, and previously published data at 1.5 and 2.5 MHz was also included. A laboratory exposure system was used to simulate DUS exposure at 1.0, 1.5, 2.25, 3.5, 5.0 and 7.5 MHz, with higher peak rarefactional pressure amplitudes (PRPAs) than were available from our DUS systems. The right kidneys of rats mounted in a water bath were exposed to intermittent image pulse sequences at 1 s intervals during infusion of diluted ultrasound contrast agent. The percentage of GCH was zero for low PRPAs, and then rapidly increased with increasing PRPAs above an apparent threshold, pt. The values of pt were approximately proportional to the ultrasound frequency, f, such that pt /f was approximately 0.5 MPa/MHz for DUS and 0.6 MPa/MHz for laboratory system exposures. The increasing thresholds with increasing frequency limited the GCH effect for contrast-aided DUS, and no GCH was seen for DUS at 5.0 or 7.4 MHz for the highest available PRPAs. |
| Title |
Frequency dependence of ultrasound attenuation and backscatter in breast tissue. |
| Author |
D'Astous FT, Foster FS. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
Attenuation and backscatter of ultrasound in human breast tissues were measured over the frequency range relevant to breast imaging (3-7 MHz). The first step in the measurement process consisted of generating an ultrasound attenuation image of a macroscopic slice of excised breast tissue. This image depicted the various tissue constituents in the samples so that a region of homogeneous tissue could be selected for further investigation. Ultrasound signals used in the computation of the frequency dependent attenuation and backscatter coefficients were then collected from several points within this region of interest. The measured attenuation and backscatter were averaged over all the points in the region of interest and plotted as functions of frequency which ranged from 3 to 7 MHz. The results showed that the attenuation coefficient of homogeneous regions of infiltrating duct carcinoma was higher than that of fat but somewhat less than that of fibrous and parenchymal tissues. On the other hand the backscattering coefficient of ductal carcinoma samples was similar to that of fat but much lower than the backscatter coefficient of parenchymal tissue. The discriminability of the different breast tissue types under these measures, as well as the relevance of the results to clinical imaging are discussed. |
| Title |
Frequency dependent attenuation of malignant breast tumors studied by the fast Fourier transform technique. |
| Author |
Kelly-Fry E, Sanghvi NT, Fry FJ. |
| Journal |
Proc Second Int Symp Ultrason Tissue Character |
| Volume |
|
| Year |
1977 |
| Abstract |
The work discussed comprises one aspect of an experimental design concerned with the use of multi-discipline examination methods to provide detailed information on the interaction of normal and malignant breast tissues with a high frequency sound field. The complete experimental design included X-ray and needle biopsy examination of the breast of a patient prior to mastectomy, followed by: X-ray examination of the excised breast; ultrasound visualization and FFT studies of the formalin-fixed, excised breast specimen; X-ray examination of 0.5 cm thick, whole breast sections of the tissue; and finally, sectioning and histological staining of the primary malignant tumor region and other tissue areas of interest. Emphasis is given to a study of attenuation of the sound beam as a function of frequency for specific tissue paths (i.e., from skin to back surface of the excised breast), which included (1) the malignant tumor, (2) the nipple and (3) the areola. For the tissue path which included the malignant tumor, the FFT studies indicate that the attenuation for the full range of frequencies studied (1.1 to 4.4 Mhz) was greater than that of any other area of the breast. A significant result of the investigations reported in this paper is the determination that the analytical technique is feasible and can yield data on malignant and normal regions of breast tissue which correlate with the ultrasound visualization imaging information and with the tissue structure as revealed by histological examination. |
| Title |
Frequency domain techniques for ultrasound breast imaging. |
| Author |
Kelly-Fry E, Jackson VP, Sanghvi NT. |
| Journal |
Proc Twenty-Fourth Nat Conf Breast Cancer |
| Volume |
|
| Year |
1990 |
| Abstract |
The primary purpose of this study is to determine whether certain ultrasound frequency ranges and frequency bands will yield distinct differences in ultrasound pulse-echo image characteristic of benign and malignant breast masses as a result of back scattering changes. It is well established that the ultrasound back scattering strength is dependant on the backscattering particle size, particle distribution and structure and is a function of interrogating frequency of the beam. |
| Title |
Frequency independent ultrasound contrast-detail analysis. |
| Author |
Smith SW, Lopez H., Bodine WJ Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
An ultrasound contrast-detail phantom has been developed to evaluate the image quality of diagnostic ultrasound imaging systems. The phantom includes eight conical targets whose B-mode images show disk lesions such that the object contrast of each lesion relative to background is independent of the imaging device or transducer frequency/spectrum. By maintaining conditions for Rayleigh scattering and Rayleigh speckle statistics in the phantom gel, the object contrast of each lesion depends only on the scatterer concentration in the lesion relative to the scatterer concentration in the background. Experimental data confirmed this frequency independence. Results of contrast-detail performance of an ultrasound imaging system are shown, and a standard technique for error analysis of contrast-detail data is described. |
| Title |
Frequency relationships for ultrasonic activation of free microbubbles, encapsulated microbubbles, and gas-filled micropores. |
| Author |
Miller DL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1998 |
| Abstract |
The ultrasonic activation of free microbubbles, encapsulated microbubbles, and gas-filled micropores was explored using available linear theory. Encapsulated microbubbles, used in contrast agents for diagnostic ultrasound, have relatively high resonance frequencies and damping. At 2 MHz the resonance radii are 1.75 µm for free microbubbles, 4.0 µm for encapsulated microbubbles, and 1.84 µm for gas-filled micropores. Higher-pressure amplitudes are needed to elicit equivalent subharmonic, fundamental, or second-harmonic responses from the encapsulated microbubbles, and this behavior increases for higher frequencies. If an encapsulated microbubble becomes destabilized during exposure, the resulting liberated microbubble would be about twice the linear resonance size, which would be likely to produce subharmonic signals. Scattered signals used for medical imaging purposes may be indicative of bioeffects potential: The second harmonic signal is proportional to local shear stress for a microbubble on a boundary, and a strong subharmonic signal may imply destabilization and nucleation of free-microbubble cavitation activity. The potential for bioeffects from contrast agent gas bodies decreases rapidly with increasing frequency. This information should be valuable for understanding of the etiology of bioeffects related to contrast agents and for developing exposure indices and risk management strategies for their use in diagnostic ultrasound |
| Title |
Frequency spectrum shifts of ultrasound echoes as a functio of depth in a female breast |
| Author |
Kelly Fry E, Morris ST, Sanghvi NT, Madsen EL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1987 |
| Abstract |
Knowledge of the changes in waveform characteristics as an ultrasound wave penetrates multiple layers of soft tissues within a breast can be important for both detection and diagnosis of breast pathologies by ultrasound mammography techniques. Using a spectrum analyzer system in combination with an automatic, bi-plane scanning, B-mode breast imaging unit, techniques were developed for recording the center frequency and bandwidth characteristics of signals received from the subcutaneous fat, mid-breast, retromammary, and pectoralis muscle regions of the breast of a post-menopausal subject. The same techniques were applied to a breast phantom that has internal architectural features and acoustic parameters (density, speed, attenuation coefficient) that are comparable to those of a normal breast. A single focus, 7.5-MHz transducer was used for most of the recorded data. Lower frequency transducers were also used. Spectral analysis data accompanied by relevant breast and phantom images will be presented. |
| Title |
Frequency-dependent angle scattering of ultrasound by liver. |
| Author |
Waag RC, Lee PP, Persson HW, Schenk EA, Gramiak R. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1982 |
| Abstract |
Ultrasonic scattering by one specimen of normal pig liver and two specimens of abnormal human liver has been measured as a function of angle and frequency at each angular position of transmit and receive transducers which were rotated in equal and opposite directions about the axis of a cylindrically shaped tissue sample. Mean data values were determined by averaging points at like frequencies and angular positions in scans made at intervals along the axis of the specimen. Sections of the specimens were obtained throughout its length and stained to emphasize structures containing collagen and connective tissue shown by acoustic microscopy to produce sound speed variations which are known to cause scattering. Using the stained sections as diffraction screens, calculations of scattering were carried out via Fourier transforms on a scale comparable to that.in the acoustic studies for comparison with the acoustic data. In all specimens studied, mean acoustic scattering exhibited a general decrease in level with increasing scattering angle. The rate of decrease in acoustic scattering with angle agreed qualitatively with the calculations of average angular falloff of scattering by the stained sections. Lower rates of decrease were observed in tissues with more closely spaced collagen containing structures. Although the data derived from the few substantially different specimens studied is not intended to be representative of all liver, the results show a qualitative correspondence between acoustic scattering and visual appearance which depends on tissue components and their arrangement. |
| Title |
Frequency-dependent angular scattering of ultrasound by tissue-mimicking materials and excised tissue. |
| Author |
Davros WJ, Zagzebski JA, Madsen EL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1986 |
| Abstract |
An apparatus and method of experimentation for measuring frequency-dependent angle scattering from in vitro tissue samples and tissue-like scattering media have been developed. Distinguishing features of this method are that data collection is rapid, data reduction is simple, and results, given in the form of the differential scattering cross section per unit volume, are accurate and absolute. Reported are the results of tests to determine the overall accuracy of the method. Also, results of the differential scattering cross section per unit volume from female human breast tissue are presented. |
| Title |
Frequency-dependent attenuation effects in pulsed Doppler ultrasound: experimental results. |
| Author |
Holland SK, Orphanoudakis SC, Jaffe CC. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1984 |
| Abstract |
The quantitative capability of pulsed Doppler ultrasound in clinical practice is limited by the effects of frequency-dependent attenuation of ultrasound in tissue, as well as several other spectral-broadening mechanisms which distort the Doppler spectrum of an ultrasonic echo. In this communication, we present results of in vitro experiments which demonstrate the magnitude of the errors expected in clinical measurements of blood flow parameters when frequency-dependent attenuation of ultrasound in biological tissue is ignored. It is shown that errors as large as 15 percent may occur in Doppler measurements of blood flow velocity through 7 cm of intervening tissue. A comparison is also made between experimental results and a theoretical model which includes the effects of scattering and attenuation. |
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
|
|
|
|
