Microwave-based examination using hypothesis testing

• US 20060058606A1
• Filed: 09/15/2004
• Published: 03/16/2006
• Est. Priority Date: 09/15/2004
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Van Veen, Barry D., Davis, Shakti K., Hagness, Susan C.
• Granted Patent: US 8,050,740 B2
• Time in Patent Office: Days
• US Class Current: 600/407
• CPC Class Codes: A61B 2562/143 for coupling microwaves
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/0507 using microwaves or terahertz waves
• CPC Class Codes: A61B 6/502 for diagnosis of breast, i.e. mammography

Abstract

Microwave examination of individuals is carried out by transmitting microwave signals from multiple antenna locations into an individual and receiving the backscattered microwave signals at multiple antenna locations to provide received signals from the antennas. The received signals are processed to remove the skin interface reflection component of the signal and the corrected signal data are provided to a hypothesis testing process. In hypothesis testing for detecting tumors, image data are formed from the test statistic used to perform a binary hypothesis test at each voxel. The null hypothesis asserts that no tumor is present at a candidate voxel location. The voxel threshold is determined by specifying a false discovery rate to control the expected proportion of false positives in the image. When the test statistic value associated with a voxel is greater than the threshold, the null hypothesis is rejected and the test statistic is assigned to the voxel. For voxels where the test statistic falls below the threshold, the null hypothesis is accepted and the voxel value is set to zero. The resulting image indicates the locations or other characteristics of detected tumors.

Claims

1. A microwave system for examining an object comprising:

(a) an array of antennas for radiating and receiving microwaves;

(b) a microwave source connected to the array of antennas to provide microwave signals of a selected bandwidth to the antennas;

(c) a receiver connected to the antennas to detect the microwave signals received by the antennas and provide signal data corresponding thereto; and

(d) a computer connected to receive the signal data, the computer programmed to process the signal data to form a space-time vector of signal data from each antenna for a candidate location, to determine a test statistic for the candidate location as the ratio of the sample variances under the two hypotheses of scatterer or no scatterer at the candidate location, to compare the test statistic with a selected threshold and assign a null hypothesis value to the selected location if the test statistic is below the threshold and to assign the test statistic value to the candidate location if the statistic is above the threshold, and to repeat the process for a plurality of different candidate locations in the object to be examined to generate multi-dimensional output data.

2. The system of claim 1 including an output device connected to the computer to display the multi-dimensional output data as a function of candidate locations.

3. The system of claim 1 wherein the computer is further programmed to determine the test statistic t_l for time series data of length N for M channels as

$t_l=\left(\mathrm{NM}-1\right)$

 

⁢

x T ⁢

P l ⁢

x x T ⁢

P l ⊥

⁢

x

where x is the multichannel data, u(θ

_l) is the multichannel signal vector, and P_t=u(θ

_l)[u^T(θ

_l)u(θ

_l)]<sup>−

1</sup>u^T(θ

_l) and P_l¹⁹⁵ =I_NM−

P_l are orthogonal projection matrices.

4. The system of claim 3 wherein the null hypothesis value is zero.

5. The system of claim 1 wherein the microwave source provides pulses having pulse widths on the order of 100 picoseconds or less in duration.

6. The system of claim 1 wherein the microwave source is connected to the antennas to provide signals to one antenna at a time.

7. The system of claim 1 wherein the microwave source is connected to the antennas to provide signals to all of the antennas simultaneously.

8. The system of claim 1 wherein the threshold value provides a selected false detection rate by rejecting the null hypotheses.

9. The system of claim 1 further including signal processing circuitry that receives pulses from the microwave source and passes the pulses through a delay and a filter for each antenna before providing the delayed and filtered pulses to the antennas, the delays and filters selected to focus the radiated microwave energy from the array of antennas at a selected candidate location in the object.

10. The system of claim 1 wherein the computer is programmed to carry out clutter whitening on the corrected data.

11. The system of claim 1 wherein the computer programmed to estimate an artifact reflection component of the signal at each antenna as a filtered combination of the signals at all other antennas and to subtract the estimated artifact reflection component from the signal data to provide corrected signal data, with weights of the filters chosen to minimize the residual signal over that portion of the received data dominated by the reflection.

12. A method of carrying out microwave examination of an individual comprising:

(a) transmitting microwave signals from a plurality of antenna locations into an individual to be examined;

(b) receiving backscattered microwave signals at a plurality of antenna locations to provide received signals from the plurality of antenna locations;

(c) processing the received signals in a computer to form a space-time vector of signal data from each antenna for a candidate location, determining a test statistic for the candidate location as the ratio of the sample variances under the two hypotheses of scatterer or no scatterer at the candidate location, comparing the test statistic with a selected threshold and assigning a null hypothesis value to the candidate location if the test statistic is below the threshold and assigning the test statistic value to the candidate location if the statistic is above the threshold; and

(d) then scanning the process to a plurality of different candidate locations in the individual and repeating steps (a), (b) and (c) at each candidate location to generate multi-dimensional output data.

13. The method of claim 12 wherein the step of transmitting microwave signals comprises transmitting microwave pulses having pulse widths on the order of 100 picoseconds or less in duration.

14. The method of claim 12 wherein the step of transmitting microwave signals comprises transmitting microwave pulses having frequency content at 10 GHz or higher.

15. The method of claim 12 including transmitting the microwave signals from an array of antennas so as to focus the microwave power on a candidate location.

16. The method of claim 12 further including, before the step of processing the received signals, the step of:

carrying out an artifact response subtraction process on the received signals in the computer by estimating the interface reflection component of the signal at each antenna location as a combination of the received signals at the other antenna locations passed through filters to provide corrected signal data, the filters having weights chosen to minimize the received signal over that portion of the received signal dominated by the artifact response, and providing the corrected signal data to the beamformer process.

17. The method of claim 12 wherein microwave signals are provided to one antenna at a time and backscattered microwave signals are received from one antenna at a time for each of the antenna locations.

18. The method of claim 12 wherein microwave signals are transmitted from all of the antennas simultaneously and backscattered microwave signals are received from all of the antennas simultaneously.

19. The method of claim 12 wherein the step of transmitting the microwave signals is carried out simultaneously from all of the antenna locations by passing microwave pulses for each antenna at an antenna location through a delay and a filter for each antenna, the delays and filters selected to focus the radiated microwave energy from the antennas at a selected candidate location in the object.

20. The method of claim 12 wherein the computer is further programmed to determine the test statistic t_l for time series data of length N for M channels as

$t_l=\left(\mathrm{NM}-1\right)$

 

⁢

x T ⁢

P l ⁢

x x T ⁢

P l ⊥

⁢

x

where x is the multichannel data, u(θ

_l) is the multichannel signal vector and P_l=u(θ

_l)[u^T(θ

_l)u(θ

_l)]<sup>−

1</sup>u^T(θ

_l) and P_l^⊥

=I_NM−

P are orthogonal projection matrices.

21. The method of claim 12 wherein the null hypothesis value is zero.

22. The method of claim 12 further including the step of carrying out clutter whitening on the signal data.

23. A microwave system for examining an object comprising:

(a) an array of antennas for radiating and receiving microwaves;

(b) a microwave source connected to the array of antennas to provide microwave signals of a selected bandwidth to the antennas;

(c) a receiver connected to the antennas to detect the microwave signals received by the antennas and provide signal data corresponding thereto; and

(d) a computer connected to receive the signal data, the computer programmed to process the signal data to form a space-time vector of signal data from each antenna for a candidate location, to determine a generalized likelihood ratio test (GLRT) statistic for the candidate location as the ratio of the sample variances under the two hypotheses of a scatterer having a selected characteristic or no scatterer having the selected characteristics at the candidate location and to repeat the process for a plurality of different candidate locations in the object to be examined to generate multi-dimensional output data.

24. The system of claim 23 wherein the computer is programmed to compare the GLRT test statistic with a selected threshold and assign a null hypothesis value to the selected location if the test statistic is below the threshold and to assign the test statistic value to the candidate location if the statistic is above the threshold.

25. The system of claim 24 including an output device connected to the computer to display the multi-dimensional output data as a function of candidate locations.

26. The system of claim 23 wherein the computer is programmed to determine the GLRT test statistic t_l for time series data of length N for M channels as

$t_l=\left(\mathrm{NM}-1\right)$

 

⁢

x T ⁢

P l ⁢

x x T ⁢

P l ⊥

⁢

x

where x is the multichannel data, u(θ

_l) is the multichannel signal vector, and P_l=u(θ

_l)[u^T(θ

_l)u(θ

_l)]<sup>−

1</sup>u^T(θ

_l) and P_l^⊥

=I_NM−

P are orthogonal projection matrices.

27. The system of claim 23 wherein the microwave source provides pulses having pulse widths on the order of 100 picoseconds or less in duration.

28. The system of claim 23 wherein the microwave source is connected to the antennas to provide signals to one antenna at a time.

29. The system of claim 23 wherein the microwave source is connected to the antennas to provide signals to all of the antennas simultaneously.

30. The system of claim 23 wherein computer programmed to estimate an artifact reflection component of the signal at each antenna as a filtered combination of the signals at all other antennas and to subtract the estimated artifact reflection component from the signal data to provide corrected signal data, with weights of the filters chosen to minimize the residual signal over that portion of the received data dominated by the reflection.

31. The system of claim 23 wherein the computer is programmed to determine if there are more than one target scatterer locations and to carry out one or more iterations of the GLRT test using the scatterer locations determined in a prior iteration of the GLRT test.

32. The system of claim 23 wherein the computer is programmed to carry out clutter whitening on the corrected data.

33. A method of carrying out microwave examination of an individual comprising:

(a) transmitting microwave signals from a plurality of antenna locations into an individual to be examined;

(b) receiving backscattered microwave signals at a plurality of antenna locations to provide received signals from the plurality of antenna locations;

(c) processing the received signals in a computer to form a space-time vector of signal data from each antenna for a candidate location, determining a generalized likelihood ratio test (GLRT) statistic for the candidate location as the ratio of the sample variances under the two hypotheses of scatterer having a selected characteristic or no scatterer having the selected characteristic at the candidate location; and

(d) then scanning the process to a plurality of different candidate locations in the individual and repeating steps (a), (b) and (c) at each candidate location to generate multi-dimensional output data.

34. The method of claim 33 further comprising comparing the GLRT test statistic with a selected threshold and assigning a null hypothesis value to the candidate location if the test statistic is below the threshold and assigning the test statistic value to the candidate location if the statistic is above the threshold.

35. The method of claim 33 wherein the step of transmitting microwave signals comprises transmitting microwave pulses having pulse widths on the order of 100 picoseconds or less in duration.

36. The method of claim 33 wherein the step of transmitting microwave signals comprises transmitting microwave pulses having frequency content at 10 GHz or higher.

37. The method of claim 33 further including, before the step of processing the received signals, the step of:

carrying out an artifact response subtraction process on the received signals in the computer by estimating the interface reflection component of the signal at each antenna location as a combination of the received signals at the other antenna locations passed through filters to provide corrected signal data, the filters having weights chosen to minimize the received signal over that portion of the received signal dominated by the artifact response, and providing the corrected signal data to the beamformer process.

38. The method of claim 33 wherein the computer is programmed to determine the GLRT test statistic t_l for time series data of length N for M channels as

$t_l=\left(\mathrm{NM}-1\right)$

 

⁢

x T ⁢

P l ⁢

x x T ⁢

P l ⊥

⁢

x

where x is the multichannel data, u(θ

_l) is the multichannel signal vector and P_l=u(θ

_l)[u^T(θ

_l)u(θ

_l)]<sup>−

1</sup>u^T(σ

_l) and P_l^⊥

=I_NM−

P_l are orthogonal projection matrices.

39. The method of claim 33 wherein the null hypothesis value is zero.

40. The method of claim 33 further including the step of carrying out clutter whitening on the signal data.

41. The method of claim 33 wherein if more than one target scatterer location is found, steps (a)-(d) are carried out in one or more iterations using the scatterer locations determined in a prior iteration.