Simulation of diagnostic ultrasound image pulse sequences in cavitation bioeffects research
Oscilloscope traces showing the image pulse sequences for diagnostic ultrasound (a) and for a damped transducer (b). The pulse peak amplitudes, both compressional and rarefactional, are captured, but the pulse shapes are not resolved at this time scale. The lower trace produced by amplitude modulation of a fixed beam by a Gaussian envelope adequately simulates the diagnostic image pulse sequence produced as the beam scans by the hydrophone element.
Oscilloscope traces of the pulse wave forms (a) for the diagnostic ultrasound and (b) for the damped transducer with the laboratory exposure system. The two pulses are approximately equal in terms of peak rarefactional pressure amplitude and pulse duration.
Oscilloscope trace showing the pulse for the air-backed transducer with the laboratory exposure system. This transducer has a somewhat longer duration due to the “ringing” of the transducer element, but was able to generate substantially higher pressure amplitudes than the other transducers (Fig. 2).
An illustration of the laboratory exposure system. The view of the water bath is vertically downward, showing the rat positioned on a mounting board on its left side and with its right kidney imaged by diagnostic ultrasound (DUS). The DUS image was used to locate the kidney and aim the scan plane at the middle of the kidney (indicated by the appearance of a darker, low echo region in the center). The laboratory (LAB) transducer, driven by the associated electronic instruments, was translated horizontally into place for exposure of the kidney, which was controlled manually by a switch (SW). This aiming scheme was helpful to avoid the bowel gas in the intestines and the spine, which block the ultrasound transmission (note the acoustical shadows distal to these features).
A comparison of results for the diagnostic ultrasound (DUS, circles) and damped laboratory transducer (LAB, squares) exposures. The glomerular capillary hemorrhage was determined for the entire sections for the DUS, but only for the entry beam area for the LAB system. The guideline upper limit for DUS would correspond to about on this plot, which precluded use of the DUS system at higher exposure RPAs (e.g., from the LAB system).
Results for glomerular capillary hemorrhage induced by the DUS scan, compared to fixed beam exposure at one, three, or five spots, all at a peak RPA of . These were scored as the percentage of glomerular hemorrhage over the entire histological sections. Statistical values are given for the multipoint exposure relative to the DUS exposure. The multiposition exposures provide a better approximation of the scanned exposure bioeffects determined over the entire sections.
Results for glomerular capillary hemorrhage in the beam entry area for different pulse sequence envelopes using the damped laboratory transducer at a peak RPA of . Statistical values are for comparisons of the two groups indicated. The square envelopes, which gave bursts of pulses at intervals, produced an apparently increasing effect with increasing numbers of pulses, but this increase was not statistically significant. A long Gaussian envelope, which simulates a slow image frame rate, eliminated the bioeffect seen for a Gaussian envelope, which confirmed a previous observation of the mitigation of this bioeffect for slow frame rate Doppler DUS. This mitigation strategy for the bioeffect was also confirmed using two similar but reversed ramp envelops: The ramp-up envelope gave no significant effect, while a large effect was seen for the ramp-down envelope.
Beam and timing parameters for the three ultrasound exposure sources used in this research. The diagnostic ultrasound (DUS) probe and damped transducer were operated at , while the air-backed transducer was operated at . The beamwidth (BW) for the DUS probe was the thickness of the scan plane, but the diameter of the cylindrical beams for the other transducers. The image pulse sequence (IPS) duration (Dur) was the full width at half maximum of the RPAs fitted with a Gaussian function to simulate the DUS IPS.
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