Diagnostic levels of ultrasound may disrupt myelination
Mark H Ellisman, Darryl Erik Palmer, Michael P André
Experimental Neurology 1987, 98, 78-92 · 10.1016/0014-4886(87)90073-2
Abstract
Neonatal rats 3 to 5 days of age were exposed to the ultrasound beam from a medical ultrasound imaging system. Dorsal nerve roots were examined by electron microscopy. Comparison between exposed and sham-exposed controls revealed disruption of the nodes of Ranvier attributable to ultrasound. Morphologic changes ranged from vacuole formation in the paranodal region to frank demyelination and were still evident after 24 h of recovery. Rats of this age are at a stage of myelination similar to that of a human fetus 4 to 5 months. The ultrasound intensities used in this study are consistent with those used for human imaging (SPTA 0.135 mW/cm2, SATA 0.045 mW/cm2, SPTP 8.7 W/cm2, SPPA 1.9 W/cm2), but the relevance of these findings to clinical ultrasound will require further study.
Abstract via europepmc.
Exposures
Exposure 1: Diagnostic ultrasound beam directed at the dorsal surface of neonatal rat pups (spinal roots examined)
Target: lumbar spinal cord — “dorsal and ventral lumbar spinal roots”
Device: other named manufacturer · ADR · ADR model 2130 real-time linear array scanner ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 3,500 | ✓?⚑ |
| Pulse duration (ms) | not reported | |
| Pulse repetition frequency (Hz) | 42 | ✓✓✓ |
| Duty cycle (%) | not reported | |
| Sonication duration (s) | 1,800 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 1.9 | ✓✓✓⚑ |
| Free-field Ispta (W/cm²) | 0.000135 | ✓✓✓ |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Rat pups were mounted dorsal-surface-toward a diagnostic linear-array scanner at 8.5 cm (just beyond the focal length) in a 37C water tank and exposed for 30 min. The linear array pulsed four elements simultaneously (10x11 mm transmitting surface), with one element added and one dropped before each sequential pulse so that several pulses contributed to the exposure at each point; pulse repetition frequency for any given set of four elements was 42 Hz. Some animals were fixed immediately after exposure, others after a 24 h recovery period.
Flags from extraction
exposures[0].fundamental_frequency_khz— The transducer is described as a 'nominal 3.5-MHz transducer', but later the paper states that the measured center frequency of the pulse waveform was found to be 2.4 MHz; the nominal value is recorded here, with the measured value noted as a discrepancy.sham_type— Control animals were 'bound and placed in the tank for 30 min but not exposed'; the exact mechanism (transducer present but powered off vs. absent) is not fully described, so classification as inactive_transducer is inferred.exposures[0].free_field.isppa_w_cm2— SPPA and SPTP were calculated from hydrophone measurements made 'at the position of the rat in our exposure tank' (i.e. in water, not through animal tissue), so classified as free_field; SPTA/SATA were separately reported by the manufacturer as measured in water.