New ultrasonic radiation reduces cerebral emboli during extracorporeal circulation

Trapping of embolic particles in a vessel phantom by cavitation-enhanced acoustic streaming

Cavitation clouds generated by short, high-amplitude, focused ultrasound pulses were previously observed to attract, trap, and erode thrombus fragments in a vessel phantom. This phenomenon may offer a noninvasive method to capture and eliminate embolic fragments flowing through the bloodstream during a cardiovascular intervention. In this article, the mechanism of embolus trapping was explored by particle image velocimetry (PIV). PIV was used to examine the fluid streaming patterns generated by ultrasound in a vessel phantom with and without crossflow of blood-mimicking fluid. Cavitation enhanced streaming, which generated fluid vortices adjacent to the focus. The focal streaming velocity, uf, was as high as 120 cm/s, while mean crossflow velocities, uc, were imposed up to 14 cm/s. When a solid particle 3-4 mm diameter was introduced into crossflow, it was trapped near the focus. Increasing uf promoted particle trapping while increasing uc promoted particle escape. The maximum crossflow Reynolds number at which particles could be trapped, Rec, was approximately linear with focal streaming number, Ref, i.e. Rec = 0.25Ref + 67.44 (R(2) = 0.76) corresponding to dimensional velocities uc = 0.084uf + 3.122 for 20 < uf < 120 cm/s. The fluidic pressure map was estimated from PIV and indicated a negative pressure gradient towards the focus, trapping the embolus near this location.

Ultrasound destruction of air microemboli as a novel approach to brain protection in cardiac surgery

OBJECTIVE

Evaluation of a novel approach to eliminate air microemboli from extracorporeal circulation via ultrasonic destruction.

DESIGN

In vitro proof-of-concept study.

SETTING

Research laboratory.

PARTICIPANTS

None.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

An extracorporeal circulation device was filled with human blood circulating at 3 L/min. Air bubbles were injected into the system. For bubble destruction, the blood in the tubing system was repeatedly insonated for 3 minutes using a therapeutic 60-kHz device, with variation of intensity and duty cycle settings, ranging from 0.2 W/cm² to 1.0 W/cm² and from duty cycle 60% to continuous wave (CW). Number and diameter of air microemboli were counted upstream and downstream of the ultrasound device by a 2-channel microemboli Doppler detector. For safety assessment, circulating blood was insonated continuously for 2 hours at 0.8 W/cm² CW and compared with circulation without insonation; and standard blood parameters were analyzed. Without treatment, 1,313 to 1,580 emboli were detected upstream, diameter ranging between 10 and 130 μm. Ultrasound treatment eliminated up to 87% of all detected bubbles in cw application (p<0.01) and showed comparable effects at intensities from 0.4 W/cm² to 1.0 W/cm² cw. Bubbles sized>15 μm almost were eliminated completely (p<0.001). Pulsed wave application rendered inferior results (p>0.05). No relevant changes of blood parameters were observed compared with control circulation.

CONCLUSIONS

Ultrasound destruction of air emboli is a very efficient method to reduce number and size of emboli. Within the limits of safety assessment, the authors could not detect relevant side effects on standard blood parameters.

Non-invasive embolus trap using histotripsy-an acoustic parameter study

Free-flowing particles in a blood vessel were observed to be attracted, trapped and eroded by a histotripsy bubble cloud. This phenomenon may be used to develop a non-invasive embolus trap (NET) to prevent embolization. This study investigates the effect of acoustic parameters on the trapping ability of the NET generated by a focused 1.063 MHz transducer. The maximum trapping velocity, defined by the maximum mean fluid velocity at which a 3-4 mm particle trapped in a 6 mm diameter vessel phantom, increased linearly with peak negative pressure (P-) and increased as the square root of pulse length and pulse repetition frequency (PRF). At 19.9 MPa P-, 1000 Hz PRF and 10 cycle pulse length, a 3 mm clot-mimicking particle could remain trapped under a background velocity of 9.7 cm/s. Clot fragments treated by NET resulted in debris particles <75 μm. These results will guide the appropriate selection of NET parameters.