Preliminary comparative results on axial resolution using both coded excitation and conventional pulses in ultrasound A-mode scan

This paper presents a comparative study of axial resolution of ultrasound system with waves generated by coded excitation pulse and conventional pulses both interacting with computational phantoms producing A-line and B-mode images. The mathematical phantoms were generated as two impulse reflectors positioned at 10 mm (first reflector) and at 10.9 mm (second reflector). The second reflector was moved towards the first reflector in 0.1 mm steps. Reflectors were in the farfield of a 5 MHz transducer and waves are travelling in water. The transducer was excited with conventional short pulse (CP) and with coded excitation pulse (CEP). CEP was achieved with chirps with 18 μs duration. The combinations of transducer excitation (CP and CEP) with conventional and matched (MF) and mismatched filters (MMF) were tested and our results have shown that the system resolution was around 0.5 mm and that the combination CEP+MMF presented worse resolution and speckle effects when compared to other combinations probably due to the broadening of the mainlobe caused by this kind of operation.