A method for improving the contrast-to-noise ratio (CNR) while maintaining the -6 dB axial resolution of ultrasonic Bmode\r\nimages is proposed. The technique proposed is known as eREC-FC, which enhances a recently developed REC-FC\r\ntechnique. REC-FC is a combination of the coded excitation technique known as resolution enhancement compression (REC)\r\nand the speckle-reduction technique frequency compounding (FC). In REC-FC, image CNR is improved but at the expense of a\r\nreduction in axial resolution. However, by compounding various REC-FC images made from various subband widths, the tradeoff\r\nbetween axial resolution and CNR enhancement can be extended. Further improvements in CNR can be obtained by applying\r\npostprocessing despeckling filters to the eREC-FC B-mode images. The despeckling filters evaluated were the following: median,\r\nLee, homogeneous mask area, geometric, and speckle-reducing anisotropic diffusion (SRAD). Simulations and experimental\r\nmeasurements were conducted with a single-element transducer (f /2.66) having a center frequency of 2.25MHz and a -3 dB\r\nbandwidth of 50%. In simulations and experiments, the eREC-FC technique resulted in the same axial resolution that would be\r\ntypically observed with conventional excitation with a pulse. Moreover, increases in CNR of 348% were obtained in experiments\r\nwhen comparing eREC-FC with a Lee filter to conventional pulsing methods.
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