Rotary encoding for intravascular ultrasonic imaging systems

Images produced with an intravascular ultrasound system (IVUS) can be disto rted because of uncertainty in the instantaneous angular position of a rota ting ultrasonic transducer. A rotary encoder placed in proximity to the tra nsducer is required to detect the problem; however, size constraints make a conventional electromechanical or optomechanical encoder difficult to impl ement. Measurements that test the feasibility of a software-derived encoder , based of the rate of decorrelation of ultrasonic RF lines with angle, are reported. Provided that the instantaneous angular velocity of the transduc er can be measured, adjustments can be made to the pulse rate of the transd ucer, which would eliminate the image distortion.