PROJECT SUMMARY The use of noninvasive ultrasound for quantitative tissue characterization has been an exciting research prospect for several decades now. Herein the challenge is to find hidden patterns in the ultrasound data to reveal more information about tissue function and pathology that cannot be seen in the more conventional ultrasound images. Bypassing some of the limitations associated with traditional tissue characterization approaches, a new modality has emerged for the ultrasound classification of acoustic scatterers like cancer cells. Termed H-scan ultrasound (where the ‘H’ stands for Hermite or hue), this innovative real-time imaging technique reveals the local frequency dependence of different-sized scatterer aggregates found in soft tissue. Our preliminary preclinical findings using in vivo H-scan ultrasound have indicated that this new imaging technique is useful for detecting apoptotic activity and an early response to chemotherapy. Here changes in H-scan ultrasound image intensity were shown to have a strong correlation to local cancer cell nuclear size. Guided by knowledge gained from these previous studies, the purpose of the current research project is to develop a next-generation in vivo H-scan ultrasound imaging system and tumor characterization method. Our first goal is to implement a multifrequency H-scan ultrasound imaging functionality on programmable scanner equipped with a wideband capacitive micromachined ultrasonic transducer (CMUT). This new ultrasound imaging technology will be tested and optimized using a series of phantom materials embedded with scatterers of known size. Next, we will quantify success of H-scan ultrasound imaging for monitoring an early response to chemotherapy using a preclinical model of breast cancer that recapitulates human disease. We will then compare H-scan ultrasound findings to physical measurements of cancer cell size and results obtained by competing imaging technologies. Lastly, we will conduct the first human study of multifrequency H-scan ultrasound imaging of breast cancer and evaluate the potential for helping with disease management.