Contrast agent harmonic imaging has become a very important tool for studying blood perfusion. Due to the extensive amount of angiogenesis that occurs around malignant tumors, the use of ultrasound contrast agents has the potential to improve cancer diagnosis and to direct therapies. However, existing transducers are limited in their ability to form images from contrast agent harmonics because they lack sufficient bandwidth. This is especially true if both second and sub-harmonics are to be used to construct an image. In the Phase I program TRS Technologies, Blatek, Inc., J&W Medical, LLC, and Thomas Jefferson University Hospital demonstrated a solution to this problem by constructing a very broad band transducer using single crystal ferroelectric. This material (PbCMgi/sNb^CVPbTiOs - PMN-PT) has a very high electromechanical coupling coefficient (kss > 90%) so that ultrasound transducers constructed from it have an inherently broad bandwidth. In the Phase I program a single element, focused transducer was constructed from a crystal/epoxy 1-3 composite. The transducer had a bandwidth of 130% with excellent receive sensitivity at 9 and 2.25 MHz, the second and subharmonics, respectively, of the 4.5 MHz transmit frequency. Feasibility for contrast agent detection was demonstrated by using the transducer to measure the strength of 2nd harmonic signals generated by Sonazoid microbubbles in water. For the Phase II program, TRS proposes to build on these results by constructing a broad band single crystal linear array and using it for contrast agent enhanced imaging VX2 liver tumors in rabbits.
