Recently, it has been demonstrated that through the use of contrast agents and multi-frequency transducer technology, high resolution and high signal to noise ultrasound images can be obtained which illustrate microvascular structure in unprecedented detail for an ultrasound modality. The enabling technology is ultrasound transducers which are fabricated with elements which can excite microbubble contrast agents near resonance and detect their broadband harmonics at a much higher bandwidth (several times the fundamental frequency). The resulting images contain very little background from tissue scattering and thus provide high contrast, and can have a resolution on the order of 130 microns with an appropriate high frequency receiving element. Because microbubbles are strictly an intravascular agent, this approach enables visualization of microvascular morphology with unique clarity, providing insight into angiogenesis associated with tumor development.