A swept-scanning mode for estimation of blood velocity in the microvasculature

In contrast to previous systems in which an ultrasonic pulse was repeatedly directed to a discrete line of sight, a new method has been developed to c ontinuously scan over a region in order to rapidly assess blood velocities in superficial small blood vessels. Using this technique, which we call swe pt-scan, a high frequency transducer can rapidly translate across a region of interest, and sensitive maps of blood velocity in small blood vessels ca n be constructed. This system has been applied to flow mapping in the anter ior segment of the eye, which is clinically significant in cases of trauma and glaucoma. No previous imaging technique has been capable of estimating blood velocities within this region in a clinically useful manner. With thi s new technique, each 2-D scan of the eye can be obtained in an interval on the order of I second, and blood flow through the iris and ciliary body ca n be detected in vessels as small as 40 microns. A major implication of thi s new technique is that a wall filter can be applied continuously to the re turn from all regions, thus eliminating the transient response that occurs along each line of sight in traditional Doppler systems.