The patients underwent 2 DSE studies: 1 with and 1 without a contrast agent. The order of the 2 tests was randomized, and they were performed at least 4 h apart within a period of 24 h. Cardiovascular medications were not withheld before the tests, as is routinely accepted. The ultrasound systems used for acquisition of images were a Hewlett Packard Sonos 5500 (Andover, Massachusetts), an Acuson Sequoia (Mountain View, California), or an Advanced Technology Laboratories (Bothel, Washington) system. To control for sonographer variability in image acquisition, the same sonographer performed both noncontrast and contrast agent DSE studies for a particular subject. Harmonic imaging was used for both studies.