Ultrasound speckle reduction using coded excitation, frequency compounding,and postprocessing despeckling filters

A technique for improvement of ultrasonic B-mode imaging that uses codedexcitation, pulse compression, and frequency compounding was developed. A codedexcitation and pulse compression technique known as resolution enhancementcompression (REC) was used to enhance the bandwidth of an imaging system by afactor of two. This bandwidth was subdivided into smaller subbands through thespeckle-reducing technique known as frequency compounding (REC-FC). Frequencycompounded images were generated using various subband widths and then averagedto reduce speckle and to improve contrast while preserving spatial resolution,known as enhanced REC-FC (eREC-FC). In this study, further improvements incontrast and reduction in speckle were obtained by applying post-processingdespeckling filters. The following post-processing despeckling filters wereexplored and analyzed in regard to contrast improvement, speckle reduction, andimage feature preservation: median, Lee, homogeneous mask area, geometric, andspeckle reducing anisotropic diffusion (SRAD). To quantify the performance ofeach filter, contrast-to-noise ratio was used. Data from thirty simulatedphantoms and experimental data from a tissue-mimicking phantom were generatedand filtered. Results demonstrated that post-processing despeckling filterscoupled with the eREC-FC technique could improve the image by up to 563%, interms of the contrast-to-noise ratio, when compared to conventional ultrasonicimaging.