Ultrafast 2-dimensional image monitoring and array-based passive cavitation detection for ultrasound contrast agent destruction in a variably sized region.

OBJECTIVES: A combined approach was proposed, based on programmable ultrasound equipment, to simultaneously monitor surviving microbubbles and detect cavitation activity during microbubble destruction in a variably sized region for use in ultrasound contrast agent (UCA)-enhanced therapeutic ultrasound applications. METHODS: A variably sized focal region wherein the acoustic pressure was above the UCA fragmentation threshold was synthesized at frequencies of 3, 4, 5, and 6 MHz with a linear broadband imaging probe. The UCAs' temporal and spatial distribution during the microbubbles' destruction was monitored in a 2-dimensional imaging plane at 5 MHz and a frame rate of 400 Hz, and simultaneously, broadband noise emissions during the microbubbles' fragmentation were extracted by using the backscattered signals produced by the focused release bursts (ie, destruction pulses) themselves. Afterward, the temporal evolution of broadband noise emission, the surviving microbubbles in a region of interest (ROI), and the destruction area in a static UCA suspension were computed. Then the inertial cavitation dose, destruction rate of microbubbles in the ROI, and area of the destruction region were determined. RESULTS: It was found that an increasing pulse length and a decreasing transmit aperture and excitation frequency were correlated with an increased inertial cavitation dose, microbubble destruction rate, and destruction area. Furthermore, it was obvious that the microbubble destruction rate was significantly correlated with the inertial cavitation dose (P < .05). In addition, the intensity decrease in the ROI was significantly correlated with the destruction area (P < .05). CONCLUSIONS: By the proposed strategy, microbubbles could be destroyed in a variably sized region, and destruction efficiency as well as the corresponding inertial cavitation dose could be regulated by manipulating the transmission parameters.

Minimizing the thermal losses from perfusion during focused ultrasound exposures with flowing microbubbles.

This paper demonstrated the use of flowing microbubbles (MBs) to minimize thermal losses from perfusion during focused ultrasound exposures due to acoustic cavitation. Temperature and cavitation were simultaneously investigated as MBs flowing through a wall-less flow phantom with varying flow velocities (2-55 cm/s) and concentrations (0%-0.1%) when exposed at different acoustic power levels (5-120 W). The peak temperature at the end of ultrasonic exposures in the flow and in the outer of the vessel as well as the cavitation were higher than those pure controls measured at the same exposure parameters and flow velocities but without MBs. All the peak temperatures initially increased with increasing flow velocities of MBs, followed by a decrease of the peak temperatures with increasing flow velocities when the velocity was higher than the inflection velocity. Meanwhile, cavitation showed a trend of increases with increasing flow velocity. The inflection velocity and cavitation increased with increasing acoustic power and MBs concentration. Thermal lesion appeared around the vessel as MBs flow through the vessel, at which lesion was not observed originally without MBs. These results suggested that this may provide an effective way to minimize thermal losses from perfusion during focused ultrasound exposures.

Flow quantification with nakagami parametric imaging for suppressing contrast microbubbles attenuation.

Flow quantification with contrast-enhanced ultrasound is still limited by the effects of contrast microbubble attenuation. Nakagami parametric imaging (NPI) based on the m parameter, which is related to the statistical property of echo envelope, is implemented to suppress contrast attenuation. Flow velocity (FV) and volumetric flow rate (VFR) are estimated through the least square fitting of burst depletion kinetic model to time m parameter curves (TMCs). A non-recirculating flow phantom is imaged as contrast microbubbles are infused at 10, 15, 20, 25, and 30 mL/min. Contrast microbubbles with two different concentrations are used to generate variations of contrast microbubble attenuation. The results suggest that 4 × 4 mm(2) is the optimal size of a sliding window of NPI for flow quantification under current experiment condition. At a lower microbubble concentration, the FV calculated from TMCs correlates strongly with actual FV in both unattenuated (R(2) = 0.97; p < 0.01) and attenuated regions (R(2) = 0.92; p < 0.01) within phantom. And there is a strong correlation (R(2) = 0.98; p < 0.01; slope = 0.96; intercept = 0.68) between VFR calculated from TMCs and actual VFR within the whole phantom. Similar results are obtained at higher microbubble concentrations. Compared with conventional ultrasound imaging that is intensity dependent, NPI achieves better performance on flow quantification in the presence of contrast microbubble attenuation.

Measuring body-cover vibration of vocal folds based on high frame rate ultrasonic imaging and high-speed video.

Vibration of vocal folds is a body-cover layered vibration pattern due to the two-layer tissue structures of vocal folds. A method based on a synchronal imaging system is proposed in order to image and measure the body-cover vibration pattern of vocal folds. This imaging system contains two parts: high-frame-rate ultrasonic imaging part and high-speed video part, which can synchronously image the vibration of the body and cover layers a thigh speed. Then, image analysis methods are applied to measure the body-cover vibration of vocal folds from both recorded image sequences. We analyze characteristics of body-layer vibration based on the measurements from designed experiments. Moreover, these results meet simulations of a body-cover model.