Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal.
Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant.
Couture
Olivier
O
Laboratoire Ondes et Acoustique, ESPCI, 10 rue Vauquelin, 75005 Paris, France. olicou@gmail.com
Aubry
Jean-François
JF
Montaldo
Gabriel
G
Tanter
Mickael
M
Fink
Mathias
M