Laboratory evaluation of the Maltese cross processor: Speckle reduction for circular transducers
An online signal-processing technique to reduce speckle noise in ultrasound images is described. In the imaging system, a focused piston transducer is divided into 32 sectors. In the receive mode, parallel signal processing arranges the sectors into eight Maltese crosses. The RF signals of the perpendicular arms of each cross are multiplied in a phase-sensitive process. The orthogonal receive-mode multiplication is designed to reduce side lobes resulting from the sector shapes while maintaining lateral resolution through the use of the full aperture diameter. The signals from the crosses are then combined via postdetection summation. The Maltese crosses show decorrelated signals equivalent to three independent samples of the speckle noise, which decreases noise contrast by a factor of 1.6 with no measurable loss of spatial resolution. Logarithmic compression is included to retain the conventional signal dynamic range. Parallel signal processing maintains the normal image line rate. Images of tissue-mimicking phantoms including speckle targets show improved detectability of simulated lesions.
