High resolution blood flow mapping in the anterior segment of the eye

A new high frequency ultrasound system has been developed to visualize and measure blood flow parameters in the superficial microvasculature with a resolution of 40 μm. A recently reported method, which we call swept-scan or swept Doppler, has been developed to rapidly acquire 2-D frames data for blood velocity estimation using sweeping scans of a single element focused transducer. Using this new method combined with the M-mode technique, experiments were performed to quantify blood flow in the highly vascular, anterior segment of the eye. Scans of radial vessels in the rabbit iris indicate that blood flow can be mapped in arterioles down to 40 μm in diameter with velocities as low as 0.5 mm/sec. Furthermore, preliminary estimates of the effect of vasoactive drugs show that blood flow changes due to application of topical atropine can be measured in the 200 μm rabbit major arterial circle with both M-mode and swept-scan techniques. In particular, the M-mode technique was sufficiently sensitive to detect changes in peak systolic and diastolic blood flow, and these velocity measurements were consistent with those obtained from the swept-scan.