|
|
|
BRL Abstracts Database |
|
Your search for ultrasound produced 3296 results. Page 60 out of 330
| Title |
Cavitation induced by asymmetric, distorted pulses of ultrasound: A biological test. |
| Author |
Ayme EJ, Carstensen EL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1989 |
| Abstract |
Prediction of the response of gaseous microbubbles to ultrasonic waves is complicated by the finite-amplitude distortion associated with large amplitude acoustic fields. Typical finite-amplitude pulses in medical applications consist of a sharp positive spike followed by a smaller, slowly varying negative pressure. In previous theoretical studies it was found that: (a) the peak-positive pressure is a very poor index of bubble response; (b) the peak-negative pressure typically underestimates the bubble response; (c) a better predictor of bubble response is the pressure amplitude of the fundamental in a Fourier series expansion of the distorted pulse. It is reported here that the killing of Drosophila larvae exposed to pulsed, symmetric, sinusoidal fields and to pulsed, asymmetric, distorted fields is consistent with these predictions. |
| Title |
Cavitation nucleation agents for nonthermal ultrasound therapy. |
| Author |
Miller DL, Kripfgans OD, Fowlkes JB, Carson PL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2000 |
| Abstract |
The use of a nucleation-promoting agent can greatly enhance therapeutically useful nonthermal bioeffects. A blank agent (saline), Optison ultrasound contrast agent, a stabilized perfluoropentane droplet suspension (SDS), and retained air space were compared as nucleation agents in whole blood. Fresh canine whole blood with added agent was exposed in 1.3-ml disposable pipette bulbs to lithotripter shock waves (2-Hz rate; +24.4, -5.2 MPa peak pressure amplitudes). Cavitation activity was assessed by measuring hemolysis. The droplet suspension performed nearly as well as retained air when added at a concentration sufficient to provide a roughly equal volume of gas after vaporization. Optison also yielded nucleation, but a concentration of 10%-20% was needed for large enhancement of hemolysis comparable to 5% SDS. Exposure at room temperature, which was less than the 29 degrees C boiling point of perfluoropentane, eliminated the enhancement of the hemolysis effect relative to the blank. Application of 100-kPa excess pressure during exposure reduced but did not eliminate the nucleation ability of Optison, SDS, or retained air. However, this small pressure (relative to the peak positive pressure of the shock waves) eliminated the hemolysis induced with the blank agent. The stabilized perfluoropentane droplet suspension appears to be a good nucleation agent for nonthermal ultrasound therapy applications. |
| Title |
Cavitation threshold measurements for.microsecond length pulses of ultrasound. |
| Author |
Fowlkes JB, Crum LA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1988 |
| Abstract |
The acoustic cavitation threshold of an aqueous solution has been.measured at megahertz frequencies as a function of pulse width and.pulse repetition frequency for various combinations of these.quantities. The fluid tested was a 0.1M KOH-H3BO3 buffer solution.with pH 10.9, which contained luminol, was saturated with argon,.and filtered to 25 mu. The presence of cavitation was detected by a.photomultiplier tube that required the emission of visible light that.was both larger in magnitude and longer in duration than a preset.criterion. It was observed that the cavitation threshold of water under.pulse conditions decreases both when the pulse width is fixed and the.pulse repetition frequency is increased, and when the pulse repetition.frequency is fixed and the pulse width is increased. Acoustic.cavitation thresholds measured in aqueous solutions are significantly.less than those acoustic pressures associated with instruments that are.currently in widespread use in medicine. |
| Title |
Cavitation threshold of microbubbles in gel tunnels by focused ultrasound. |
| Author |
Sassaroli E, Hynynen K. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2007 |
| Abstract |
The investigation of inertial cavitation in micro-tunnels has significant implications for the development of therapeutic applications of ultrasound such as ultrasound-mediated drug and gene delivery. The threshold for inertial cavitation was investigated using a passive cavitation detector with a center frequency of 1 MHz. Micro-tunnels of various diameters (90 to 800 μm) embedded in gel were fabricated and injected with a solution of Optison™ contrast agent of concentrations 1.2% and 0.2% diluted in water. An ultrasound pulse of duration 500 ms and center frequency 1.736 MHz was used to insonate the microbubbles. The acoustic pressure was increased at 1-s intervals until broadband noise emission was detected. The pressure threshold at which broadband noise emission was observed was found to be dependent on the diameter of the micro-tunnels, with an average increase of 1.2 to 1.5 between the smallest and the largest tunnels, depending on the microbubble concentration. The evaluation of inertial cavitation in gel tunnels rather than tubes provides a novel opportunity to investigate microbubble collapse in a situation that simulates in vivo blood vessels better than tubes with solid walls do. |
| Title |
Cavitation-generated free radicals during shock wave exposure: Investigations with cell-free solutions and suspended cells. |
| Author |
Suhr D, Brummer F, Hulser DF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
Extracorporeally generated shock waves as used in lithotripsy of urinary and biliary stones exhibit side effects in vivo. Furthermore, these shock waves destroy eukaryotic cells during in vitro treatment in suspension. A possible cause of these damaging effects might be cavitation, the growth and collapse of bubbles in liquids exposed to tensile stresses. During the collapse, temperature inside these cavitation bubbles rises up to several thousand K, leading to the formation of free radicals. We demonstrated the occurrence of cavitation-generated free radicals by direct reaction with fluorescent dyes in solution after shock wave treatment and investigated the resulting cell killing by variation of the cellular antioxidative defense status. We present evidence for the generation of intracellular free radicals during shock wave treatment of suspended cells. |
| Title |
Cavitational bio-effects of 1.5 MHz. |
| Author |
Graham E, Hedges M, Leeman S, Vaughan P. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1980 |
| Abstract |
The effects of continuous wave ultrasound on three different classes of biosystems have been investigated at a frequency of 1.5 MHz. The criteria for cavitation are given, and these are applied to experimentally observed growth retardation of plant roots, cell death and DNA degradation in bacteria and pyknosis of human lymphocytes. An attempt is being made to find common physical mechanisms for all these biological responses, and cavitation processes in particular are examined here. A description is given of the techniques used to monitor the presence of cavitation, and indirect evidence, drawn from pulsed field and elevated pressure experiments, is presented to show that other-non-linear processes are also operative. |
| Title |
Cavitational mechanisms in ultrasound-accelerated thrombolysis at 1 Mhz. |
| Author |
Everbach EC,Francis CW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
Inertial cavitation is hypothesized to be a mechanism by which ultrasound (US) accelerates the dissolution of human blood clots when the clot is exposed to a thrombolytic agent such as tissue plasminogen activator (t-PA). To test this hypothesis, radiolabeled fibrin clots were exposed or sham-exposed in vitro to 1 MHz c.w. US in a rotating sample holder immersed in a water-filled tank at 37 degrees C. Percent clot dissolution after 60 min of US exposure was assessed by removing the samples, centrifuging, and measuring the radioactivity of the supernatant fluid relative to the pelletized material. To suppress acoustic cavitation, the exposure tank was contained within a hyperbaric chamber capable of pneumatic pressurization to 10 atmospheres (gauge). Various combinations of static pressure (0, 2, 5, and 7.5 atm gauge), US (0 or 4 W/cm2 SATA), and t-PA (0 or 10 µg/mL) were employed, showing statistically significant reductions in thrombolytic activity as static pressure increased. To gain further insight, an active cavitation detection scheme was employed in which 1-µs duration tonebursts of 20-MHz US (< 1 kPa peak negative pressure, 1 Hz PRF) were used to interrogate clots subjected to US and static pressure. Results of this cavitation detection scheme showed that scattering from within the clot and broadband acoustic emissions that were both present during insonification were significantly reduced with application of static pressure. However, only about half of the acceleration of thrombolysis due to US could be removed by static pressure, suggesting the possibility of other mechanisms in addition to inertial cavitation. |
| Title |
Cell death thresholds in Elodea for 0.45-10 MHz ultrasound compared to gas-body resonance theory. |
| Author |
Miller DL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1979 |
| Abstract |
Leaves of the aquatic plant Elodea were sonicated continuously for 100 sec at ten frequencies in the range 0.45-10 MHz. Cell death thresholds were determined for three cell populations in the leaves for each frequency. The intensity thresholds were strongly dependent on frequency, and the minimum threshold for each population generally occurred near the expected resonance frequency of the gas bodies associated with each population. The thresholds were as low as 75 mW/cm2 at 0.65 MHz and 180 mW/cm2 at 5 MHz. |
| Title |
Cell disruption by ultrasound. |
| Author |
Hughes DE, Nyborg WL. |
| Journal |
Science |
| Volume |
|
| Year |
1962 |
| Abstract |
Streaming and other activity around sonically induced bubbles is a cause of damage to living cells. |
| Title |
Cell lysis due to ultrasound gel in fine needle aspirates; an important new artefact in cytology. |
| Author |
Molyneux AJ, Coghill SB. |
| Journal |
Cytopathology |
| Volume |
|
| Year |
1994 |
| Abstract |
An important new artefact in cytopathology is described. The initial observation of the artefact followed contamination of a breast fine needle aspiration (FNA) sample by ultrasound gel which was used to localize the lesion. The changes proved reproducible ex vivo. The changes varied depending on the conditions and degree of contamination, and ranged from cell swelling to leakage of nuclear chromatin and cell lysis. This artefact is discussed in the context of other major sources of cytology artefact. Pathologists and radiologists should beware of the detrimental effects of ultrasound gel on cytology specimens. |
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
|
|
|
|
