TIME OF FLIGHT ESTIMATION METHOD USING BEAMFORMING FOR ACOUSTIC TOMOGRAPHY

• US 20100010351A1
• Filed: 07/14/2009
• Published: 01/14/2010
• Est. Priority Date: 07/14/2008
• Status: Active Grant

• Current Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Original Assignee: Ecole Polytechnique Federal de Lausanne
• Inventors: Hormati, Ali, Roy, Oliver, Vetterli, Martin, Jovanovic, Ivana
• Granted Patent: US 8,574,158 B2
• Time in Patent Office: Days
• US Class Current: 600/447
• CPC Class Codes: A61B 8/15 Transmission-tomography
• CPC Class Codes: G01N 29/0672 by acoustic tomography medical tomography A61B8/13
• CPC Class Codes: G01S 15/8913 using separate transducers for transmission and reception

Abstract

It is disclosed an acoustic tomography method to improve the time of flight estimation, said method comprising the steps of: sequentially triggering a set of N transmitters so as to generate a sequence of N acoustic waves 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 that receiver; 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 we call transmit-receive-beamformed signal.

Claims

1. An acoustic tomography method to improve the time of flight estimation, said method comprising the steps of:

sequentially triggering a set of N transmitters so as to generate a sequence of N acoustic waves 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 that receiver;

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.

2. The method of claim 1, where said volume is a known medium, such as water, and the received signals through said known medium are called reference signals.

3. The method of claims 1, comprising a step of weighting said N different received signals and said M different transmit-beamformed signals before the addition.

4. The method of claim 1, wherein said varying delays used to generate said transmit-beamformed signal from a transmitter to a receiver are computed as:

selecting a set of close by transmitters around said transmitter, which is called set_i transmitters;

computing the delays that need to be applied on said received signals at receiver from said set_i transmitters based on difference between the time of flights of reference received signals at said receiver from said set_i transmitters; and

repeating both aforementioned steps, the selecting step and the computing step, for all N times M pairs of N transmitters and M receivers.

5. The method of any of the claim 1, wherein said varying delays used to generate transmit-receive-beamformed signal from a transmitter to a receiver is computed as:

selecting a set of close by receivers around said receiver, which are called set_j receivers;

computing the delays that need to be applied on said transmit-beamformed signals for set_j receivers from said transmitter based on the difference between the time of flights of reference signals from said transmitter to set_j receivers; and

repeating both aforementioned steps, the selecting step and the computing step, for all N times M pairs of N transmitters and M receivers.

6. The method of claim 4, where the transmit-beamformed signal from said transmitter to said receiver is generated by applying said varying delays to received signals from set_i transmitters to receiver and adding them together.

7. The method of claim 5, where the transmit-receive-beamformed signal from said transmitter to said receiver is generated by applying said varying delays to transmit-beamformed signals from transmitter to set_j receivers and adding them together.

8. The method of claim 4, wherein the difference between the time of flights are computed as the difference in the position of the first significant peak in said reference signals, or the difference between any other marker point in the reference signals.

9. The method of claim 4, wherein the difference between the time of flights is found by using position of the peak of the cross-correlation between said reference signals.

10. The method of claim 1, comprising a background detector for classifying as background portions of said volume through which acoustic waves pass at the same speed as through a reference medium.

11. A method to compute the time of flight from a transmitter to a receiver by computing the difference of the time of flights between the transmit-receive-beamformed signal from said transmitter to a receiver and the reference signal from said transmitter to said receiver by any of the methods in any of the claim 8;

and adding that to the time of flight computed based on the physical distance between the transmitter and receiver and the known sound speed of said known medium.