We previously developed a flow cytometer system that incorporates the action of ultrasound to characterize shell properties of ultrasound contrast agents (UCA’s). The most recent manifestation involves a flow cytometer modified with a custom square quartz flow cell in place of the standard nozzle and fluid jet. Acoustic coupling to the carrier sheath fluid and UCA samples occurs through a PZT bonded to one side of the flow cell. The PZT-driven UCA oscillations were processed and fitted to the Marmottant UCA model. Shell properties for UCAs (including Definity, Optison, SonoVue, and even homemade bubbles) were determined. A major limitation of the previous work involved a lack of knowledge of the actual acoustic pressure incident on the UCA. The focus of this talk will be on optimization of the pressure inside the flow cell using finite element methods, and the comparison with additional measurements of unpublished data from targeted UCA’s. [Work funded in part by the Life Sciences Discovery Fund #3292512.]