|
|
|
BRL Abstracts Database |
|
Your search for ultrasound produced 3296 results. Page 329 out of 330
| Title |
Volumetric blood flow via time-domain correlation: Experimental verification. |
| Author |
Embree PM, O'Brien WD Jr. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1990 |
| Abstract |
A novel ultrasonic volumetric flow measurement method using time-domain correlation of consecutive pairs of echoes has been developed. An ultrasonic data acquisition system determined the time shift between a pair of range gated echoes by searching for the time shift with the maximum correlation between the RF sampled waveforms. Experiments with a 5-MHz transducer indicate that the standard deviation of the estimate of steady fluid velocity through 6-mm-diameter tubes is less than 10% of the mean. Experimentally, Sephadex (G-50; 20-80 μm dia.) particles in water and fresh porcine blood have been used as ultrasound scattering fluids. Two-dimensional (2-D) flow velocity can be estimated by slowly sweeping the ultrasonic beam across the blood vessel phantom. Volumetric flow through the vessel is estimated by integrating the 2-D flow velocity field and then is compared to hydrodynamic flow measurements to assess the overall experimental accuracy of the time-domain method. Flow rates from 50-500 ml/min have been estimated with an accuracy better than 10% under the idealized characteristics used in this study, which include straight circular thin-walled tubes, laminar axially-symmetric steady flow, and no intervening tissues. |
| Title |
Volumetric measurement of pulsatile flow via ultrasound time-domain correlation. |
| Author |
Hein IA, O'Brien WD Jr. |
| Journal |
J Cardiovasc Technol |
| Volume |
|
| Year |
1989 |
| Abstract |
Previous research has shown that the application of ultrasound time-domain correlation (UTDC) can be used to measure accurately and precisely volumetric flow under continuous flow conditions without previous knowledge of the vessel size, flow velocity profile, or transducer measurement angle. This paper presents the results of applying the UTDC technique to estimate volumetric flow under pulsatile flow conditions and shows that pulsatile flow can be measured with similar accuracy as continuous flow. |
| Title |
Volumetric ultrasound system for left ventricle motion imaging. |
| Author |
Canals R, Lamarque G, Chatain P. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1999 |
| Abstract |
An external ultrasound oscillating probe has been developed for the purpose of visualizing dynamically the left cardiac ventricle three-dimensional (3D) movements and deformations. The fundamental principle of this probe is to maintain in continuous oscillation a classical one-dimensional (1D) transducer array around its axis at a maximum oscillation rate of 3 degrees per millisecond. A global medical system, including hardware elements and a software package, has been designed for this application. A motorization set and electronic boards enable this new oscillating probe to be used with any recent echograph equipped with a cardiac module and an external triggering cineloop. Moreover, in order to obtain 3D/4D left ventricle movements from a set of 2D recorded images, a rendering method based on the 2D discrete Fourier transform is applied. Promising preliminary results have been obtained on some patients, and a clinical study on a great number of subjects (both healthy and heart complaint people) was carried out. |
| Title |
Waveguides in medical ultrasonics. |
| Author |
Nicholson NC, McDicken WN. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1988 |
| Abstract |
Propagation of ultrasound in a number of thin solid elastic waveguides is described from the Pochhammer theory. The waveguides discussed have radii equal to the radii of stylets of the most frequently used biopsy needles. The groups velocities of the modes and the form of the particle amplitudes of the lowest longitudinal and flexural modes in each of the styles at a frequency of 3.5 MHz are presented. |
| Title |
Wide frequency range miniature hydrophone for the measurement of pulse ultrasonic field. |
| Author |
Ide M, Ohdaira E. |
| Journal |
Jpn J Appl Phys |
| Volume |
|
| Year |
1981 |
| Abstract |
Ultrasonic diagnostic equipment utilizing the pulse reflection method is widely used in the field of medicine. For evaluation of the equipment and for studies on bioeffects of ultrasound, it is necessary to know the sound field generated by the equipment. This paper reports on wide frequency range miniature hydrophones for the measurements of pulse ultrasonic fields of several MHz range. Construction of the developed hydrophones, experimental data on their performance, and measured results of sound fields obtained by the hydrophones are presented. |
| Title |
Wide-band piezoelectric polymer acoustic sources. |
| Author |
Lewin PA, Schafer ME. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1988 |
| Abstract |
The design of a wide-band acoustic source made of piezoelectric polymer (PVDF) material is described. The source was developed for the characterization and absolute calibration of ultrasonic hydrophone probes. Construction details are described and performance characteristics of the wide-band PVDF transmitter, including its transmitting voltage response and directivity patterns, are compared with theoretical predictions in the frequency range up to 40 MHz. The Krimholtz-Leedom-Mattaei (KLM) model was used to examine the influence of the PVDF polymer film thickness, the backing acoustic impedance, the cable length, and the electrical source resistance on overall transmit transfer characteristics. A comparison is made with traditional piezoelectric ceramic acoustic sources, and it is shown that piezopolymer transmitters exhibit some improved properties and are well suited for certain ultrasound dosimetry applications. In particular, the polymer sources have been found useful in measurements based on swept-frequency excitation. Those measurements allow characterization of transmitters and receivers to be performed as a virtually continuous function of frequency. |
| Title |
Wideband quantitative ultrasonic imaging by time-domain diffraction tomography. |
| Author |
Mast TD. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1999 |
| Abstract |
A quantitative ultrasonic imaging method employing time-domain scattering data is presented. This method provides tomographic images of medium properties such as the sound speed contrast; these images are equivalent to multiple-frequency filtered-backpropagation reconstructions using all frequencies within the bandwidth of the incident pulse employed. However, image synthesis is performed directly in the time domain using coherent combination of far-field scattered pressure waveforms, delayed and summed to numerically focus on the unknown medium. The time-domain method is more efficient than multiple-frequency diffraction tomography methods, and can, in some cases, be more efficient than single-frequency diffraction tomography. Example reconstructions, obtained using synthetic data for two-and three-dimensional scattering of wideband pulses, show that the time-domain reconstruction method provides image quality superior to single-frequency reconstructions for objects of size and contrast relative to medical imaging problems such as ultrasonic mammography. The present method is closely related to existing synthetic-aperture imaging methods such as those employed in clinical ultrasound scanners. Thus, the new method can be extended to incorporate available image-enhancement techniques such as time-gain compensation to correct for medium absorption and aberration correction methods to reduce error associated with weak scattering approximations. |
| Title |
WOLD decomposition of the backscatter echo in ultrasound images of soft tissue organs. |
| Author |
Cohen FS, Georgiou G, Halpern EJ. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1997 |
| Abstract |
This paper deals with a method of detecting and estimating the scatterer spacing between the regularly spaced resolvable coherent scatterers in tissue. Scatterer spacing has been successfully used in classifying tissue structure, in differentiating between normal and cirrhotic liver, and in detecting diffuse liver disease. This paper presents a WOLD decomposition of the radio frequency (RF) field into its diffused and coherent components from which maximum likelihood estimates (MLE) or minimum mean square error (MMSE) estimates of the scattering spacing are easily computed. The MLE are efficient and for relatively long record are unbiased. They result in accurate estimates in low signal-to-noise (SNR) ratios. Unfortunately, they require nonlinear minimization and knowledge of the probability density associated with the RF backscatter echo. The MMSE estimates, on the other hand, are computationally simple, yield unique closed form solutions, do not require a-priori knowledge of the probability distribution function of the backscatter echo, and result in accurate estimates in low SNR ratios. This paper also presents an unbiased decision rule to detect whether or not an RF echo exhibits any specular scattering relative to the wavelength of the interrogating ultrasonic pulse. The approach has been tried on simulations as well as on in-vivo scans of liver data, and appears to perform well. |
| Title |
X-ray inactivation of cultured mammalian cells:.enhancement by ultrasound. |
| Author |
Todd P, Schroy CB. |
| Journal |
Radiology |
| Volume |
|
| Year |
1974 |
| Abstract |
Ultrasound (0.14 W/cm2, 920 kHz) was found to decrease the dose of 50-kVp x rays required to prevent 99% of cultured M3-1 Chinese hamster cells from forming colonies by a factor of 1.3 when delivered during the first 10 minutes after irradiation. Ultrasound alone had no detectable effect. Postirradiation heating for 10 minutes at the maximum temperature tolerated by the cells (42 C) had no detectable effect on radiation dose-survival curves. |
| Title |
X-ray linear attenuation coefficients in the mammographic range for ultrasonic breast phantom materials. |
| Author |
Burke TM, Madsen EL, Zagzebski JA. |
| Journal |
Radiology |
| Volume |
|
| Year |
1982 |
| Abstract |
X-ray linear attenuation coefficients for simulated fat and glandular parenchyma used.in ultrasound breast phantoms were measured at 15.2, 20.3, 30.0, 40.0, and 60.0.keV and values compared with published figures calculated from the experimentally determined elemental composition of excised breast parenchyma. Agreement was excellent. These ultrasonic tissue-mimicking (TM) materials can be used in radiographic or ultrasound phantoms for testing imaging instruments as well as for training personnel. |
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
|
|
|
|
