Nonlinear Imaging with Dual Band Pulse Complexes

A method for measurement or imaging of a region of an object with waves where object material parameters for wave propagation are modified by the wave field strength, comprising the steps of:

• a) transmitting at least two pulse wave complexes in each of at least two transmit directions towards the region, each of said pulse complexes comprising
• a low frequency (LF) pulse with frequencies in an LF band transmitted from an LF aperture, and
• a high frequency (HF) pulse with frequencies in an HF band transmitted from an HF aperture, —wherein the pulse length of the transmitted HF pulse is less than half an oscillation period of the transmitted LF pulse;
• wherein the transmitted HF pulse propagates spatially so close to or within the transmitted LF pulse that the HF pulse observes a manipulation of the object material parameters by the co-propagating LF pulse for at least a part of a propagation depth of the HF pulse;
• and
• wherein at least the transmitted LF pulse varies for each transmitted pulse complex to produce different manipulations of the object, and for each transmit direction at least one LF pulse is non-zero and the transmitted LF pulse can also be zero;
• b) picking up HF receive signals from one or both of scattered and transmitted HF components from each transmitted pulse complex and for each transmit direction, using a HF receive beam former;
• c) combining said HF receive signals from given, different transmit directions to form synthetic HF receive signals with synthetic HF transmit beams for each image point within a set of image points;
• d) correcting said synthetic HF receive signals by at least one of
• i) delay corrections in a fast time with correction delays that approximately compensate for an average nonlinear propagation delay for the multiple scattered HF pulses that are found in the HF receive signal, and
• ii) speckle corrections in the fast time that approximately compensate for the LF pressure variations of the speckle of the multiple scattered HF pulses that are found in the HF receive signal,
• wherein one or both of said delay corrections and speckle corrections can be zero for at least one HF receive signal, to form corrected HF signals for said fast time interval;
• and
• e) combining said corrected HF signals from the at least two transmitted pulse complexes to form at least one noise suppressed HF signal with suppression of pulse reverberation noise.