Title :
Improved range resolution and side lobe level of ultrasound echoes using nonlinear frequency-modulated excitation signal and modified compressing filter
Author :
Dantas, Tarcisio M. ; Costa-Felix, Rodrigo P B ; Machado, João C.
Author_Institution :
Telecommun. Eng. Dept., Fed. Fluminense Univ., Niteroi, Brazil
Abstract :
Linear frequency modulated (LFM) pulses are used as excitation for ultrasonic imaging systems. Temporal sidelobes, due to echo compression, are generated and impart a degradation of the range resolution. This work proposes a compensated frequency-modulated (CFM) excitation signal that improves the range resolution of compressed pulses, keeping low the sidelobe levels. An experimental pulse-eco system setup was used employing a 2.25 MHz transducer (-3 dB relative bandwidth of 45%) excited with a CFM signal, with a duration of 20 μs, immersed in a water tank containing a flat aluminum reflector. The spectrum magnitude of the CFM signal was determined as the nth power of the pseudo-inverted pulse-echo system transfer function magnitude. Its phase was calculated from the group delay determined from the CFM power spectrum. The echoes were compressed with a modified Wiener filter and the best range resolution of 0.47 mm, measured in -30 dB level, was achieved. This result is superior to the latest best published result, which is 42% larger than the one from this present work.
Keywords :
Wiener filters; biomedical transducers; biomedical ultrasonics; medical signal processing; pulse compression; signal resolution; ultrasonic transducers; CFM power spectrum; CFM signal; compensated frequency-modulated excitation signal; compressed pulses; flat aluminum reflector; frequency 2.25 MHz; group delay; modified Wiener filter; modified compressing filter; nonlinear frequency-modulated excitation signal; pseudoinverted pulse-echo system transfer function magnitude; pulse-eco system setup; range resolution; side lobe level; spectrum magnitude; time 20 mus; transducer; ultrasonic imaging systems; ultrasound echoes; water tank; Frequency modulation; Image coding; Image resolution; Signal resolution; Ultrasonic imaging; Wiener filters; Modulated excitation signal; Pulse compression; Range resolution;
Conference_Titel :
Ultrasonics Symposium (IUS), 2011 IEEE International
Conference_Location :
Orlando, FL
Print_ISBN :
978-1-4577-1253-1
DOI :
10.1109/ULTSYM.2011.0356