|
|
|
BRL Abstracts Database |
|
Your search for ultrasound produced 3296 results. Page 217 out of 330
| Title |
Reduction of signal decorrelation from mechanical compression of tissues by temporal stretching: Applications to elastography. |
| Author |
Alam KS, Ophir J. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1997 |
| Abstract |
Elastography is based on the estimation of strain due to tissue compression. Strain is computed from the estimates of time delays between gated precompression and postcompression echo signals. Time delay estimates are obtained from the location of the peak of the crosscorrelation function between gated precompression and postcompression signals. It is of paramount importance to accurately estimate the time delays for good quality elastograms. A main source of time delay estimation (TDE) error in elasticity imaging is the decorrelation of the echo signal as a result of tissue compression (decorrelation noise). The effect of decorrelation on the mean of the cross-correlation function and the correlation coefficient has been investigated. The expected value of the cross-correlation function between the precompression and postcompression signals was shown to be a filtered version of the autocorrelation function of the precompression signal. In this article, the effect of temporal stretching of the postcompression echo signal on the cross-correlation function will be investigated along the same line. The applied compression is assumed to be uniform; the decorrelations introduced by the lateral and elevational tissue movements are ignored. The theory predicts that if the postcompression echo signals are stretched before the TDE step, then for small strains, the cross-correlation function very closely resembles the autocorrelation function. For larger strains, correlation is improved if temporal stretching is applied. The theory is corroborated by results from simulation and homogeneous phantom experiments. Thus, the decorrelation noise in elastograms can be reduced by temporal stretching of the postcompression signal. |
| Title |
Reduction of the grating lobes of annular arrays used in focused ultrasound surgery. |
| Author |
Dupenloup F, Chapelon JY, Cathignil DJ, Sapozhnikov OA. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
1996 |
| Abstract |
An annular array with variable focus, used in focused ultrasound surgery, generates grating lobes responsible for undesirable lesions. It is known that the amplitude and the location of the lobes depend on both the geometry and the frequency of the transducer. A new procedure based on the use of a wide-band CW signal, i.e., a signal phase modulated by a pseudorandom code, is proposed to reduce the amplitude of these lobes. The theoretical study enables us to determine the location and the amplitude of these lobes and to simulate the effect of the transmitted signal bandwidth. In particular, a simple analytical relation gives the intensity ratio between the grating lobes and the main lobe. This equation shows that this ratio is inversely proportional to the number of rings and to the bandwidth of the transmitted signal. A system was developed and tested with two transducer arrays of 35- and 150-mm diameter, respectively. The simulations and experiments demonstrate the validity of the theoretical study and the efficacy of the proposed procedure. In conclusion, it is possible to reduce the grating lobes without geometric modification of the array by increasing the bandwidth of the transmitted signal. |
| Title |
Reference points method for in vivo measurement of mean ultrasound velocity. |
| Author |
Ohtsuki S. |
| Journal |
Proc JSUM |
| Volume |
|
| Year |
1984 |
| Abstract |
Ultrasound velocity in human body gives us useful information for a diagnosis. An in vivo measurement method of ultrasound velocity was proposed here. It is based on the measurement of the range between two reference points in the direction of linear scanning and the measurement of traveling time of ultrasound from the A-mode image of the points. Then, this method was named as reference points method. The extension of this method and the example of mean velocity measurement in the gall bladder are presented here. |
| Title |
Reflected ultrasound in the detection and localization of pleural effusion. |
| Author |
Joyner CR, Herman RJ, Reid JM. |
| Journal |
JAMA |
| Volume |
|
| Year |
1967 |
| Abstract |
No abstract available. |
| Title |
Reflection imaging of nonlinearity parameter distribution. |
| Author |
Akiyama I, Koide T, Kumakura Y. |
| Journal |
Jpn J Appl Phys |
| Volume |
|
| Year |
1991 |
| Abstract |
This paper describes two imaging methods based on harmonic generation due to propagation of finite amplitude ultrasound waves. One is a method using the magnitude of the second order harmonic and the other is a method using phase difference between the fundamental and the second harmonic waves. To verify the efficacy of these methods experiments are made using a phantom based on agar-gel and bovine tissues. The images correspond to the distribution of the nonlinearity parameter, confirming that the techniques are effective for investigating the distribution of this parameter of the medium. |
| Title |
Refocusing dual-mode ultrasound arrays in the presence of strongly scattering obstacles. |
| Author |
Yao H Ebbini E. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2004 |
| Abstract |
This paper provides a first experimental verification of the use of image-based feedback for refocusing the therapeutic beam in the presence of strongly scattering objects. This capability may be critical in the use of dual mode ultrasound array (DMUA) systems for noninvasive targeting of liver tumors and noninvasive cardiac ablation. In both cases, the target is partially obstructed by the rib cage, which limits the access and distorts the geometrically-focused high-intensity focused ultrasound (HIFU) therapeutic beam. The optimization procedure is based on the use of single-transmit focus (STF) imaging, in which a single transmit imaging beam employing delays derived from phasing for the therapeutic beam is used. We present experimental results of a DMUA refocusing algorithm that selects the control points from the target(s) and the ribs visible in the STF image. In addition, STF images before and after refocusing provide similar feedback by consistently showing increased echogenicity of the target region while the echogenicity of the ribs is not increased (often reduced). |
| Title |
Regularized estimation of contrast agent attenuation to improve the imaging of microbubbles in small animal studies. |
| Author |
Mulé S, De Cesare A, Lucidarme O, Frouin F, Herment A. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
Quantitative analysis of tissue perfusion using contrast-enhanced ultrasound is still limited by shadowing, which is caused by inadequate compensation for microbubble contrast agent attenuation. Many previous methods have been developed for attenuation correction in soft tissues. However, no method has been proposed to correct for microbubble attenuation in vivo. In this article, a model to estimate microbubble attenuation is presented, using the time-intensity variation in a highly echogenic distal area without contrast uptake. This model is based on the assumption that a linear relationship holds between local microbubble attenuation and local backscatter. The model was applied to 12 murine renal perfusion studies. Parametric images of microbubble attenuation were generated, corresponding to dynamic contrast agent-specific sequences without shadowing. Contrast uptake kinetics consistent with the physiology were retrieved in all perfused areas. This method therefore proved to be of potential interest in the quantification of tissue perfusion in small animal studies.
|
| Title |
Relation of acoustic characteristics of human gastic juice to its composition for some stomach diseases. |
| Author |
Klemin VA, Karev ID, Sarvazyan AP, Timokhina LM, Ruchkin VV, Mayorov EA. |
| Journal |
Studia Biophys |
| Volume |
|
| Year |
1981 |
| Abstract |
Acoustic properties of human gastric juice in some stomach diseases were measured by means of resonator method. Contributions of constituent components of gastric juice to its acoustic characteristics were estimated. It was shown that the value of absorption of ultrasound is determined by the concentration of proteins, the velocity of ultrasound is determined by concentrations of Na(+) ions, polypeptides and proteins and depends on the type of pathology. The temperature and frequency dependences of ultrasound velocity and absorption are less sensitive to the pathological changes in gastric juice composition. |
| Title |
Relationship between acoustic nonlinearity and the bound and the unbound states of water. |
| Author |
Sehgal CM, Porter B, Greenleaf JF. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1985 |
| Abstract |
This paper discusses a method for measuring isentropic and isothermal components of B/A. Measurements of these parameters of excised human tissues indicate fatty tissues to be highly non-linear to sound propagation. The isentropic and isothermal components of B/A of aqueous solutions of alcohol go through a minimum at 10% volume fraction as the concentration of alcohol is increased. On the contrary, sound speed shows a maximum at 20% concentration. These changes in acoustic parameter with alcohol concentration are qualitatively explained in terms of the variations in the free and the bound states of water due to the addition of alcohols. Finally, we discuss the possibility of imaging weighted nonlinear parameter of excised breast by measuring the difference frequency generated by transmitting two frequencies of ultrasound. |
| Title |
Relationship between cavitation threshold and dissolved air in ultrasound in the Mhz range. |
| Author |
Naito T,Ohdaira E,Masuzawa N,Ide M. |
| Journal |
Jpn J Appl Phys |
| Volume |
|
| Year |
1998 |
| Abstract |
Bioeffects caused by high power ultrasound in medicine must be understood. A significant cause of bioeffects is cavitation. This paper reports on the relationship between cavitation threshold and the amount of dissolved air for ultrasound in the MHz range used mainly in medicine. The cavitation threshold varies according to the amount of dissolved air in water and the frequency of ultrasound. |
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
|
|
|
|
