Disruption of contrast agents for monitoring blood flow

Abstract

An experimental system is being developed for controlling the flow of ultrasound contrast agent to create abrupt changes in contrast levels in tissues. Such changes can be used to monitor blood flow through bolus passage and to identify specific feeder vessels. Focused ultrasound (2.25 MHz) has been used to interrupt flow of the contrast agent MRX-115 (ImaRx Pharmaceuticals, Tucson AZ) in a tube (2. I mm id., average velocity of 9.45 cm/s) and in vivo using short bursts 20 cycles in duration with a pulse repetition frequency (PRF) of 0.75-6.0 kHz. Peak rarefactional pressures (PRP) for effective disruption of contrast agent were only 0.6-1.2 MPa. This corresponds to mechanical indices (MI) of 0.4-0.8 and intensity values which are well within the recommended limits for diagnostic ultrasound. Up to 90% of contrast agent signal was eliminated and positive boluses were produced by turning the field off and on. Similar results were achieved with in vivo in a rabbit model. Therefore the potential exists to use common diagnostic ultrasound to produce contrast disruption suitable for short bolus production without arterial catheterization.