Abstract-A technique for improvement of ultrasonic B-mode imaging that uses coded excitation, pulse compression, and frequency compounding was developed. A coded excitation and pulse compression technique known as resolution enhancement compression (REC) was used to enhance the bandwidth of an imaging system by a factor of two. This bandwidth was subdivided into smaller subbands through the speckle-reducing technique known as frequency compounding (REC-FC). Frequency compounded images were generated using various subband widths and then averaged to reduce speckle and to improve contrast while preserving spatial resolution, known as enhanced REC-FC (eREC-FC). In this study, further improvements in contrast and reduction in speckle were obtained by applying post-processing despeckling filters. The following post-processing despeckling filters were explored and analyzed in regard to contrast improvement, speckle reduction, and image feature preservation: median, Lee, homogeneous mask area, geometric, and speckle reducing anisotropic diffusion (SRAD). To quantify the performance of each filter, contrast-to-noise ratio was used. Data from thirty simulated phantoms and experimental data from a tissue-mimicking phantom were generated and filtered. Results demonstrated that post-processing despeckling filters coupled with the eREC-FC technique could improve the image by up to 563%, in terms of the contrast-to-noise ratio, when compared to conventional ultrasonic imaging.

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