A novel imaging method of coded THI using multi chirp signals

In medical ultrasound imaging, tissue harmonic imaging (THI), coded excitation and a combination of both (coded THI) have been investigated by many researchers. In THI, a spectral overlap occurs between fundamental and harmonic components, and it makes axial resolution worse. Especially, the spectral overlap in coded THI causes a specific artifact which is caused by inappropriate cross-correlation between fundamental component of echo signal and the matched filter for harmonic. To avoid the spectral overlap, the pulse inversion (PI) method, which excites two phase-inverted pulses, has been used. However, the PI is sensitive to tissue motion. In coded excitation especially chirp, a longer coded signal enables a higher signal-to-noise ratio (SNR) imaging However, there is temporal overlap between a transmitted signal and echo signal from near region when the longer coded signal is used. The objective of this study is to realize high SNR and high axial resolution imaging by removing the time and the spectral overlaps existing in the coded THI.