An Ultrasonic Imaging Speckle Supression and Contrast Enhancement Technique by Means of Frequency Compounding and Coded Excitation

A method for improving the contrast resolution of B-mode images is proposed by combining the speckle reduction technique of frequency compounding (FC), and the coded excitation and pulse compression technique called resolution enhancement compression (REC). FC suppresses speckle but at the expense of a reduction in axial resolution. Using REC the axial resolution and bandwidth of the imaging system was doubled. Therefore, by combining REC with FC (RECFC), the trade-off between axial resolution and contrast enhancement was extended significantly. Simulations and experimental measurements were conducted with a singleelement transducer (f/2.66) having a center frequency of 2.25 MHz and a -3-dB bandwidth of 50%. Simulations and measurements of hyperechoic (+6dB) tissue-mimicking targets were imaged. Two FC cases were evaluated: full-, and half-width of the true impulse response bandwidth. The image quality metrics used to compare REC-FC to conventional pulsing (CP) and CP-FC were: contrast-tonoise ratio (CNR), speckle signal-to-noise ratio and histogram percent overlap. Increases in CNR of 121%, and 230% were obtained in experiments when comparing REC-FC for the full-, and half-width cases to CP. Improved lesion detectability was observed by using RECFC. Coded excitation; pulse compression; contrast; frequency compounding; frequency diversity; speckle