Advanced x-ray imaging spectrometer

• US 5,757,005 A
• Filed: 11/08/1996
• Issued: 05/26/1998
• Est. Priority Date: 10/04/1996
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Callas, John L., Soli, George A.
• Primary Examiner(s): Wong, Don
• Application Number:
  US08/745,572
• Time in Patent Office: 564 Days
• Field of Search: 250/363.06, 378/2
• US Class Current: 250/363.06
• CPC Class Codes: G01T 1/2928 using solid state detectors
• CPC Class Codes: G01T 1/295 using coded aperture devices, e.g. Fresnel zone plates handling of radiation of particles, e.g. using diaphragms, collimators, diffraction G21K1/00

Abstract

An x-ray spectrometer that also provides images of an x-ray source. Coded aperture imaging techniques are used to provide high resolution images. Imaging position-sensitive x-ray sensors with good energy resolution are utilized to provide excellent spectroscopic performance. The system produces high resolution spectral images of the x-ray source which can be viewed in any one of a number of specific energy bands.

Claims

1. A system for detecting high energy photons comprising:

a coded aperture disposed to receive said photons from a source, wherein said photons passing through the coded aperture generates a predetermined spatial pattern;

a detector array disposed to receive the photons passing through the coded aperture, the detector array having a plurality of individual detectors, each receiving one pixel of said spatial pattern, said detectors producing an output signal indicating the number of said photons received as well as the energy of each photon, wherein said detectors in said array each comprise deeply depleted high purity silicon detectors; and

a processor receiving said output signal from each detector and performing a reconstruction operation on said signals to reconstruct the spatial position of each photon that it had prior to passing through the coded aperture, whereby an image of the source is produced.

2. The system of claim 1 wherein said processor also includes means for generating a spectrogram for each pixel comprising the number of photons received in each of a plurality of ranges of energy for each pixel.

3. The system of claim 1 wherein said coded aperture is a uniformly redundant array.

4. The system of claim 1 wherein said coded aperture is composed of gold.

5. The system of claim 1 further comprising a means for displaying separate spectral images of the source, each one comprising one of said images created solely by the photons received in a single energy band.

6. The system of claim 1 wherein said detectors further comprise on-pixel low noise preamps.

7. A system for detecting high energy photons comprising:

a coded aperture disposed to receive said photons from a source, wherein said photons passing through the coded aperture generates a predetermined spatial pattern;

a detector array disposed to receive the photons passing through the coded aperture, the detector array having a plurality of individual detectors, each receiving one pixel of said spatial pattern, said detectors producing an output signal indicating the number of said photons received as well as the energy of each photon wherein said detectors in said array each comprise deeply depleted high purity silicon detectors;

a processor receiving said output signal from each detector and performing a reconstruction operation on said signals to reconstruct the spatial position of each photon that it had prior to passing through the coded aperture, whereby an image of the source is produced; and

a signal correction unit for normalizing the detector outputs.

8. The system of claim 7 wherein the correction unit calculates a corrected signal S_j,k, using the equation:

space="preserve" listing-type="equation">S.sub.j,k =(N.sub.j,k -B.sub.j,k)/A.sub.j,k,

where j is the number of the pixel, k is the energy bin of the photons detected at the pixel, S_j,k is the corrected signal, N_j,k is the uncorrected signal, B_j,k is the background signal determined by calibration, and A_j,k is the effective area of each detector pixel, determined by calibration.

9. The system of claim 8 wherein said reconstruction operation performed by the processor is accomplished by a deconvolution process.

10. The system of claim 9 wherein the deconvolution process performed by the processor is performed by solving the set of equations:

space="preserve" listing-type="equation">D.sub.i,j θ

.sub.i,j =S.sub.j,k

where θ

_i,k is the photon fluence at image pixel i in energy bin k of the spectral image, and D_i,j is a forward response matrix.

11. The system of claim 10 wherein the deconvolution process is performed with the constraint that θ

_i,j is greater than or equal to zero.

12. A method of generating spectral images of an x-ray source, comprising:

passing x-rays from a source through a coded aperture;

receiving said x-rays in a detector having an individual detector for each pixel;

measuring the number of photons of said received x-rays reaching each detector;

measuring the energy of said photons of x-rays reaching each detector;

reconstructing the information regarding the number of photons and their energy levels to create an image of the source of x-rays; and

calculating a correction signal S_j,k using the equation;

space="preserve" listing-type="equation">S.sub.j,k =(N.sub.j,k -B.sub.j,k)/A.sub.j,k,

where j is the number of the pixel, k is the energy bin of the photons detected at the pixel, N_j,k is the uncorrected signal, S_j,k is the corrected signal, B_j,k is the background signal determined by calibration, and A_j,k is the effective area of each detector pixel, determined by calibration.

13. The method of claim 12 comprising the step of displaying separate spectral images of the x-ray source, each one comprising one of said images created solely by the photons received in a single energy band.

14. The method of claim 12 further comprising displaying the number of counts in each of several energy ranges for an individual pixel detector.

15. The method of claim 12 wherein said reconstruction step is performed by a deconvolution process.

16. The method of claim 15 wherein the deconvolution process is performed by solving the set of equations:

space="preserve" listing-type="equation">D.sub.i,j θ

.sub.i,j =S.sub.j,k

where θ

_i,k is the photon fluence at image pixel i in energy bin k of the spectral image, and D_i,j is a forward response matrix.

17. The method of claim 16 wherein the deconvolution process is performed with the constraint that θ

_i,j is greater than or equal to zero.