Small Lesion Detection with Resolution Enhancement Compression: a Method of Coded Excitation/pulse Compression by Paul Mitchell Linden

A novel coded excitation method, resolution enhancement compression (REC), increases the axial resolution and the echo signal-to-noise ratio (eSNR) for an ultrasonic imaging system. The REC technique was examined for its ability to improve lesion detectability. In addition to lesion detectability, the REC technique was examined in the context of being peak voltage limited or peak pressure limited. The REC technique was used to double the –3-dB fractional pulse-echo bandwidth of an ultrasonic source in both simulations and experiments. The increase in usable bandwidth increased lesion detectability compared to conventional pulsing (CP) techniques and coded excitation using a linear chirp (LC). Lesion detectibility was quantified through lesion signal-to-noise ratio (lSNR), which is a metric that quantifies the ability of an isolated observer to detect a focal lesion against a background. In simulations, a higher lSNR value was observed using the pressure limited REC technique for lesions ranging in size from 1 mm to 8 mm in diameter. In addition, the eSNR was increased by almost 15 dB. Simulations also demonstrated that the voltage limited and the pressure limited form of REC outperformed the LC with respect to lSNR. To validate simulation results, a hydrogel cone phantom was constructed to provide lesions of different diameters with +6-dB contrast. A transducer was scanned perpendicular to the major axis of the cone at different levels to provide lesions of 3, 5, and 8 mm in diameter. The lSNR was estimated for lesions of different sizes and using the three excitation techniques, i.e., CP, LC, and REC. In experiments the lSNR was observed to be higher using the REC technique than the other pulsing techniques. The lSNR scores for REC were higher by 15%, 45%, and 40% for the 3, 5, and 8-mm as compared to the other two excitation iii techniques. The eSNR was increased by 5.7 dB. Therefore, according to the lSNR metric, the improvement in spatial resolution from the REC technique resulted in improved detectability of small lesions. iv Acknowledgments