Anomalous Quantization Error Lobes in Phased Array Images

Abstract

Time quantization errors result from the discrete time increment delay lines used to steer and focus phased array ultrasonic imaging systems. These quantized time delays, required for the phasing of the individual elements within the transducer aperture, create a phase grating which can produce anomalous quantization error lobes within the field of view of the imaging system [1,2]. The manifestation of these lobes can be seen in computer simulations of the azimuthal impulse response and in scans made of point reflectors as an increased sidelobe amplitude which can limit the dynamic range of the imaging system.

A simulation program predicting the position and amplitude of these anomalous lobes has been developed to study the effects of transmitted pulse length and shape on the amplitude of these lobes. Three temporal integration processing techniques for decreasing the anomalous lobe amplitudes are discussed. These involve changing the phase error grating from frame to frame thereby varying the amplitude and position of these lobes. The processors also have the ability to reduce the speckle contrast and therefore the potential to further improve the quality and usefulness of medical images.