The overall goal of this proposal is to create a system and conduct the required studies to propel ultrasound contrast imaging into breast cancer management. Ultrasound contrast agents, which are shell-encapsulated microbubbles, are used to increase the acoustic backscatter from blood providing the opportunity for ultrasound molecular imaging and the detection of angiogenic tumor vasculature. Imaging modes, including phase-inversion and subharmonic modes, exploit nonlinear oscillation of these agents; however, these modes are most effective for a range of transmission frequencies below 6 MHz. When contrast imaging has been attempted with higher transmitted frequencies, poor depth of penetration, limited signal to noise ratio, and poor tissue/contrast echo separation have resulted. High resolution clinical systems operating near 15 MHz are becoming more available and are particularly important for cancer imaging, however, they lack sensitive harmonic imaging modes for contrast agent detection. We propose a new strategy to greatly increase the effective bandwidth utilizing arrays with separated center frequencies arranged confocally and show that with this wide bandwidth a contrast agent-to-tissue ratio above 20 dB can be created with a single ultrasound pulse. The resulting new imaging mode shows similar resolution, higher frame rate, higher signal to noise ratio, and greatly reduced attenuation compared to transmission at a higher frequency, and superior resolution compared to transmission and reception at a lower frequency. The proposed method can reduce the effective sample volume size more than tenfold compared with current systems, decrease sensitivity to tissue motion by eliminating multi-pulse strategies, and allow new wideband signal processing methods to be developed. This high resolution system could have a substantial advantage in the diagnosis of small tumors, where the increased vascular density is limited to a region on the order of several millimeters