Method and apparatus for physiologic facsimile imaging of biologic targets without multipath contamination using remote microwave interrogation

• US 4,271,389 A
• Filed: 06/04/1979
• Issued: 06/02/1981
• Est. Priority Date: 05/22/1979
• Status: Expired due to Term

• Current Assignee: The United States Of America As Represented By The Secretary Of The Army
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Larsen, Lawrence E., Jacobi, John H.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US06/045,442
• Time in Patent Office: 729 Days
• Field of Search: 324/58, 324/5 A, 324/58 A, 324/57 SS, 73/602, 73/619, 73/620, 128/653, 128/660
• US Class Current: 324/639
• 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 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01N 24/008 by using resonance effects in zero field, e.g. in microwave, submillimetric region by measuring absorption of microwaves by the material G01N22/00
• CPC Class Codes: G01R 27/04 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies

Abstract

A physiologic facsimile image of a biological target without multipath comination is obtained by first producing, for each one of a plurality of sample locations which are spaced so as to define a two-dimensional array, a time delay spectrum wherein the frequency of each spectral ordinate represents the instantaneous differential propagation delay between a first microwave signal which has been propagated through the target and a second microwave signal which initially corresponds to the first microwave signal, and which has been propagated through means having a predetermined propagation delay, and measuring the amplitude of the spectral ordinate corresponding to the direct ray path of propagation through the target, so as to obtain a set of data. The set of data is then digitized and converted from time domain to frequency domain. The transformed data is then processed by sorting the data into column order; magnifying data derived from the sorting step so as to enhance and preserve the resolution of the image; mapping data derived from the magnifying step into further data using a predetermined mapping function so as to enhance the contrast between selected portions of the image; and obtaining a set of control signals which are used to actuate a display device to generate the facsimile image by filtering data derived from the mapping step using a band pass function which rejects spatial frequencies below a predetermined first frequency and/or rejects spatial frequencies above a predetermined second frequency so as to minimize, respectively, the effects of variations in the thickness of the target and/or spurious frequencies resulting from the magnifying step.

Claims

1. A microwave imaging method of producing a physiologic facsimile image of a biological target on an image display device in which multipath contamination is minimized, comprising the steps of:

(a) for each one of a plurality of sample locations which are spaced so as to define a two-dimensional array, producing a time delay spectrum wherein the frequency of each spectral ordinate represents the instantaneous differential propagation delay between a first microwave signal which has been propagated through the target and a second microwave signal, initially corresponding to said first microwave signal, which has been propagated through means having a predetermined propagation delay, and measuring the amplitude of the spectral ordinate corresponding to the direct ray path of propagation through the target, so as to obtain a set of data;

(b) processing said set of data to obtain a corresponding set of control signals for the display device; and

(c) producing a two-dimensional image array on the display device using said set of control signals, and thereby obtaining the facsimile image.

2. The microwave imaging method of claim 1 wherein said first and second microwave signals are derived from a constant amplitude swept signal in which the frequency varies linearly from a first frequency to a second frequency in a predetermined time period.

3. The microwave imaging method of claim 2 wherein said first frequency is approximately 3143 MHz and said second frequency is approximately 3763 MHz and said predetermined time period is approximately 15 msec in duration.

4. The microwave imaging method of claim 2 wherein said time delay spectrum is produced by multiplying said first and second microwave signals in a mixer and said amplitude measuring comprises digitizing the output of a filter connected to the output of said mixer, and measuring the amplitude of the spectral line having the largest amplitude.

5. The microwave imaging method of claim 2 wherein said first microwave signal is propagated using a remote interrogation system comprising a liquid medium having a high relative dielectric constant and in which the target is immersed, and a pair of selectively positionable microwave antenna probes immersed in said liquid medium in spaced relationship to the target and such that the target is coupled thereto by said liquid medium;

said time delay spectrum is produced by multiplying said first and second microwave signals in a mixer; and

said amplitude measuring comprises digitizing the output of a filter connected to the output of said mixer, and measuring the amplitude of the spectral line having a frequency corresponding to a predetermined reference frequency determined by the highest amplitude of a time delay spectrum produced by mixing a further microwave signal, initially corresponding to said first microwave signal, and which has been transmitted between said antenna probes in the absence of the target, with said second microwave signal.

6. The microwave imaging method of claim 1 further comprising the step of contrast stretching or high pass filtering the facsimile image so as to facilitate photographic reproduction of the displayed image.

7. The microwave imaging method of claim 3 wherein the center-to-center distance between sample location in both azimuth and elevation is less than or equal to approximately 1.5 mm.

8. The microwave imaging method of claim 1 wherein the sample locations are scanned in a raster pattern sequence without flyback at the end of each line.

9. The microwave imaging method of claim 1 wherein said set of data is in digital form and said processing step comprises the steps of:

(a) transforming said set of data from time domain to frequency domain;

(b) sorting said transformed set of data into column order;

(c) magnifying data derived from said sorting step so as to enhance and preserve the resolution of the image;

(d) mapping data derived from said magnifying step into further data using a predetermined mapping function so as to enhance the contrast between selected portions of the image; and

(e) obtaining said set of control signals by filtering data derived from said mapping step using a band pass function which rejects spatial frequencies below a predetermined first frequency and/or rejects spatial frequencies above a predetermined second frequency so as to minimize, respectively, the effects of variations in the thickness of the target and/or spurious frequencies resulting from said magnifying of step (c).

10. The microwave imaging method of claim 9 wherein said magnifying step (c) comprises the steps of interpolating data derived from said sorting step (b) with a cubic spline function.

11. The microwave imaging method of claim 9 wherein said mapping function of step (d) is determined by analyzing a histogram of data derived from said magnifying step (c) to select a mapping function which distributes data derived from said magnifying step and corresponding to the target or selected anatomical features thereof over the entire dynamic range of pixel values for the display device, and which excludes other data derived from said magnifying step.

12. The microwave imaging method of claim 9 wherein said mapping function is a ramp function.

13. The microwave imaging method of claim 9 wherein said mapping function is a two-piece hinged function.

14. The microwave imaging method of claim 9 wherein said predetermined first frequency is determined by computing the psd function of data derived from said mapping step and determining the spatial frequency below which approximately 20% of the power is contained in the data from which said psd function is computed.

15. The microwave imaging method of claim 9 wherein said predetermined second frequency is determined by the folding frequency as established by the sampling increment at the time of data collection.

16. The microwave imaging method of claim 14 or 15 wherein said psd function is normalized for unity effective bandwidth.

17. The microwave imaging method of claim 9 wherein said filtering comprises the steps of two-dimensional Fourier transforming data derived from said mapping step, multiplying data derived from said Fourier transforming by said band pass function, and inverse Fourier transforming data derived from said multiplying step.

18. The microwave imaging method of claim 9 wherein said band pass function is radially symmetric.

19. The microwave imaging method of claim 2 wherein said first microwave signal is propagated using a remote interrogation system comprising a liquid medium having a high relative dielectric constant and in which the target is immersed, and a pair of selectively positionable microwave antenna probes immersed in said liquid medium in spaced relationship to the target and such that the target is coupled thereto by said liquid medium;

said time delay spectrum is produced by multiplying said first and second mircowave signals in a mixer; and

said amplitude measuring comprises digitizing the output of a filter connected to the output of said mixer, and measuring the amplitude of the spectral line having a frequency corresponding to a predetermined reference frequency determined by measuring the amplitude of a time delay spectrum produced by mixing a further microwave signal, initially corresponding to said first microwave signal, and which has been transmitted between said antenna probes in the absence of the target, with said second microwave signal at each one of a plurality of frequencies within a predetermined range wherein the plurality of facsimile images so produced encompass the frequency at which the amplitude of the time delay spectrum is highest as well as adjacent frequencies among which the direct ray path is collectively represented.