Loss of Echogenicity and Onset of Cavitation from Echogenic Liposomes: Pulse Repetition Frequency Independence

Abstract

Echogenic liposomes (ELIP) are being developed for the early detection and treatment of atherosclerotic lesions. An 80% loss of echogenicity of ELIP (Radhakrishnan et al. 2013) has been shown to be concomitant with the onset of stable and inertial cavitation. The ultrasound pressure amplitude at which this occurs is weakly dependent on pulse duration. Smith et al. (2007) have reported that the rapid fragmentation threshold of ELIP (based on changes in echogenicity) is dependent on the insonation pulse repetition frequency (PRF). The current study evaluates the relationship between loss of echogenicity and cavitation emissions from ELIP insonified by duplex Doppler pulses at four PRFs (1.25 kHz, 2.5 kHz, 5 kHz, and 8.33 kHz). Loss of echogenicity was evaluated on B-mode images of ELIP. Cavitation emissions from ELIP were recorded passively on a focused single-element transducer and a linear array. Emissions recorded by the linear array were beamformed and the spatial widths of stable and inertial cavitation emissions were compared to the calibrated azimuthal beamwidth of the Doppler pulse exceeding the stable and inertial cavitation thresholds. The inertial cavitation thresholds had a very weak dependence on PRF and stable cavitation thresholds were independent of PRF. The spatial widths of the cavitation emissions recorded by the passive cavitation imaging system agreed with the calibrated Doppler beamwidths. The results also show that 64%–79% loss of echogenicity can be used to classify the presence or absence of cavitation emissions with greater than 80% accuracy.

Scavenging dissolved oxygen via acoustic droplet vaporization

“…ADV was induced by a single-element 2 MHz focused transducer (H106, Sonic concepts, Bothell, WA, USA) as the droplets flowed through the EVA tubing. Based on a previous study [28] the EVA tubing was used because it had an inner diameter of 1 mm which was comparable to the −6 dB elevational beamwidth of the 2 MHz focused transducer (1.1 mm), thin walls (0.38 mm), and high acoustic transmission coefficient (94%) to ensure uniform insonation of the droplets. The 2 MHz focused transducer had an aperture diameter of 6.3 cm and a focal distance of 6.4 cm.…”

Micro/nano-bubble-assisted ultrasound to enhance the EPR effect and potential theranostic applications

“…Marmottant et al 75 presented a model that incorporates the effect of coating on the response of a microbubble to ultrasound. Based on the US-induced SC or IC, UCAs have wide applications in medical diagnosis and treatment such as contrast harmonic imaging and ultrasound-induced gene/drug delivery 76-78.…”

Quantitative Frequency-Domain Passive Cavitation Imaging

“…Passive cavitation imaging has been reported on multiple systems, including those produced by Zonare Medical Systems (Z.one Imaging System, Mountain View, CA, USA) [30], [33]–[35], [39], [40], [45], [49], [61], Ardent Sound (Iris 2 Ultrasound Imaging System, Mesa, AZ, USA) [31], [37], Terason (Terason 2000 Ultrasound System, Burlington, MA, USA) [32], Verasonics (V-1 and Vantage sytems, Bothell, WA, USA) [36], [38], [42], [47], [59], and Ultrasonix, now BK Ultrasound, (SonixDAQ, Richmond, BC, Canada) [52], [54]. Some of the systems, such as the Z.one, Vantage, and Sonix-DAQ provide direct access to pre-beamformed radio frequency or in-phase and quadrature signals so that the beamforming can be performed using the researchers’ algorithms.…”

“…Direct access to pre-beamformed signals provides researchers with more flexibility in beamforming, such as windowing, apodization, and nonlinear approaches. These systems have been used to beamform emissions induced by pulsed ultrasound at a variety of duty cycles [45]–[47], [49], [53], [61]. …”