Time of flight estimation method using beamforming for acoustic tomography

An acoustic tomography method to improve the time of flight estimation, the method being performed with a tomography set up which comprises transmitters and receivers located around a volume to be scanned, said method comprising the steps of:

• sequentially triggering a set of N transmitters so as to generate a sequence of N acoustic waves which are passed completely through a volume being scanned;
• receiving each of said acoustic waves after transmission through said volume with a set of M receivers, which are called received signals;
• delaying by varying delays the N different said received signals that each receiver receives from the N different transmitters, and adding them together to form a new received signal, which is called transmit-beamformed signal for one of the M receivers, such that the transmit-beamformed signal is focused onto a focal point located at said one receiver, wherein said varying delays used to generate said transmit-beamformed signal from a transmitter to a receiver are computed as:
• (i) selecting a set of close by transmitters around said transmitter, which is called seti transmitters
• (ii) passing a reference signal from the seti transmitters completely through a reference medium which does not reflect the reference signal, to the receiver;
• (iii) computing the delays that need to be applied on said received signals at receiver from said seti transmitters based on difference between the time of flights of reference received signals at said receiver from said seti transmitters, and
• (iv) repeating both aforementioned steps, the selecting step and the computing step, for all N times M pairs of N transmitters and M receivers;
• delaying by varying delays the M different said transmit-beamformed signals for each receiver and adding them together at each receiver to form a new signal, which is called transmit-receive-beamformed signal for one of the N transmitters, such that the transmit-receive-beamformed signal is focused onto a focal point located at said one transmitter, wherein said varying delays used to generate transmit-receive-beamformed signal from a transmitter to a receiver is computed as:
• (i) selecting a set of close by receivers around said receiver, which are called seti receivers;
• (ii) passing reference signal from transmitted completely through a reference medium which does not reflect the reference signal, to the setj receivers;
• (iii) computing the delays that need to be applied on said transmit-beamformed signals for setj receivers from said transmitter based on the difference between the time of flights of reference signals from said transmitter to setj receivers;
• and
• (iv) repeating both aforementioned steps, the selecting step and the computing step, for all N times M pairs of N transmitters and M receivers;
• calculating the time of flight by determining the time difference between the transmit-receive-beamformed signal and a reference signal.