Abstract: Catheter-based ultrasonic intravascular imaging is a very effective method in medical diagnosis and therapy.Because the number of the connection between the array and the control unit is limited,cla-ssic beamforming technique can not get a satisfied result.The synthetic aperture technique can be applied to solve this problem.This scheme used here is based on the synthetic aperture focusing technique with reconstruction done by an optimal filter.The optimal filtering reconstruction exhibits finer resolution as well as reduced sidelobes.