Opto-Acoustic Interrogation and Ultrasound Imaging of Acoustically Sensitive Microcapsules

A novel drug reservoir termed an Acoustically Sensitive Microcapsule (ASM) was designed and sensitized using ultrasound contrast agents (UCAs) for the long-term goal of facilitating localized treatment of breast cancer. In this thesis, two objectives were met. First, an opto-acoustic interrogation system coupled with a microfluidic device was developed for visualizing the role of UCAs within ASMs in the drug-release process. The displacement of UCAs under continuous wave ultrasound (fc = 2.25 MHz, for 4 s) was 3.5 µm and pulsed wave (fc = 2.25 MHz, for 30 s) was 333 µm. It was concluded that by altering the acoustic pressure, center frequency, pulse repetition frequency, and duty cycle of the ultrasound, the UCAs could be manipulated. Second, ultrasound-imaging signatures were extracted from ASMs to help in differentiation of ASMs from surrounding tissue. During harmonic imaging with diagnostic ultrasound, ASMs generated second and third harmonic components that were 7 dB and 3 dB greater than the tissue- mimicking media. Sub-harmonic imaging offered 4 dB spectral amplitude increases for ASMs at sub-harmonic peaks. Phase Inversion and Signal Subtraction imaging techniques effectively suppressed the tissue echoes by 80% and improved the ASM to tissue contrast ratio. B-Mode and Power Doppler showed only marginal contrast. In conclusion, these imaging schemes could help successfully differentiate ASMs from surrounding tissue during an in vivo drug delivery process