Nonlinear imaging using orthogonal transmit and receive codes

摘要

A method and an apparatus for imaging the nonlinear components of an ultrasound signal returned from ultrasound scatterers in tissue or contrast agents in blood. The method employs a code-modulated wavelet for transmission combined with correlation filtering on reception. Transmit codes (38) are used to modulate the phases of wavelets for successive transmit firings focused at the same transmit focal position. For example, for a first transmit firing a first transmit code (38) is used to modulate (24') a base wavelet to form a first coded wavelet and for a second transmit firing a second transmit code is used to modulate the same base wavelet to form a second coded wavelet. On reception, the receive signals resulting from the first and second transmit firings are decoded by correlating (46) the receive signals with first and second receive codes (42) respectively. The transmit and receive codes satisfy the orthogonality condition that the sum of the correlation of the first transmit code with the first receive code and the correlation of the second transmit code with the second receive code equals zero. The combined transmission and reception operations will exactly cancel the linear echo component of the signal, leaving the nonlinear components for imaging.