Method of imaging the atomic number of a sample
First Claim
1. A method of obtaining an atomic number image of an unknown material, said method comprising the steps of:
- scanning a plurality of calibration materials with a computerized axial tomographic scanner (CAT) at a first energy, said plurality of calibration materials having a plurality of different known atomic numbers, Zi, and densities, ρ
i ;
scanning said plurality of calibration materials with a CAT at a second energy;
determining from attenuation coefficients from reconstructed images of said plurality of calibration materials at said first and second energies two energy-dependent coefficients, a and b, at said first and second energies according to the following equation
space="preserve" listing-type="equation">μ
.sub.i =aZ.sup.m.sub.i ρ
.sub.i +bρ
.sub.iwhereμ
i ;
attenuation coefficient for the ith calibration materiala;
energy-dependent coefficientZi ;
atomic number for the ith calibration materialm;
constant in the range of 3.0-4.0ρ
i ;
electron density for the ith calibration materialb;
energy-dependent coefficient; and
scanning said unknown material with a CAT at said first energy;
scanning said unknown material with a CAT at said second energy; and
using said two determined energy coefficients and attenuation coefficients from reconstructed images for said unknown material at said first and second energies to determine an atomic number image of said unknown material.
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Abstract
A method of obtaining an atomic number image of an unknown material. A plurality of calibration materials which have a plurality of different known atomic numbers and densities are scanned with a CAT at first and second energies to determine the attenuation coefficients for the plurality of calibration materials at these energies. The energy-dependent coefficients at the first and second energies are determined from the attenuation coefficients for the plurality of calibration materials at the first and second energies according to a predetermined relation. The unknown material is scanned with a CAT at the first and second energies to determine the attenuation coefficients at a plurality of points in a cross section of the unknown material at these energies. The determined energy-dependent coefficients and the determined attenuation coefficients for the unknown material at the first and second energies are used to determine an atomic number image for the unknown material.
367 Citations
24 Claims
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1. A method of obtaining an atomic number image of an unknown material, said method comprising the steps of:
- scanning a plurality of calibration materials with a computerized axial tomographic scanner (CAT) at a first energy, said plurality of calibration materials having a plurality of different known atomic numbers, Zi, and densities, ρ
i ;
scanning said plurality of calibration materials with a CAT at a second energy;
determining from attenuation coefficients from reconstructed images of said plurality of calibration materials at said first and second energies two energy-dependent coefficients, a and b, at said first and second energies according to the following equation
space="preserve" listing-type="equation">μ
.sub.i =aZ.sup.m.sub.i ρ
.sub.i +bρ
.sub.iwhere μ
i ;
attenuation coefficient for the ith calibration materiala;
energy-dependent coefficientZi ;
atomic number for the ith calibration materialm;
constant in the range of 3.0-4.0ρ
i ;
electron density for the ith calibration materialb;
energy-dependent coefficient; and
scanning said unknown material with a CAT at said first energy;
scanning said unknown material with a CAT at said second energy; and
using said two determined energy coefficients and attenuation coefficients from reconstructed images for said unknown material at said first and second energies to determine an atomic number image of said unknown material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
- scanning a plurality of calibration materials with a computerized axial tomographic scanner (CAT) at a first energy, said plurality of calibration materials having a plurality of different known atomic numbers, Zi, and densities, ρ
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12. A method of obtaining a density image of an unknown material that is corrected for the effects of atomic composition of said unknown material, said method comprising the steps of:
- scanning a plurality of calibration materials with a computerized axial tomographic scanner (CAT) at a first energy, said plurality of calibration materials having a plurality of different known atomic numbers, Zi, and densities, ρ
i ;
scanning said plurality of calibration materials with a CAT at a second energy;
determining from attenuation coefficients from reconstructed images of said plurality of calibration materials at said first and second energies two energy-dependent coefficients, a and b, at said first and second energies according to the following equation
space="preserve" listing-type="equation">μ
.sub.i =aZ.sup.m.sub.i ρ
.sub.i +bρ
.sub.iwhere μ
i ;
attenuation coefficient for the ith calibration materiala;
energy-dependent coefficientZi ;
atomic number for the ith calibration materialm;
constant in the range of 3.0-4.0ρ
i ;
electron density of the ith calibration materialb;
energy-dependent coefficient; and
scanning said unknown material with a CAT at said first energy;
scanning said unknown material with a CAT at said second energy; and
using said two determined energy coefficients and attenuation coefficients from reconstructed images for said unknown material at said first and second energies to determine a density image of said unknown material. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
- scanning a plurality of calibration materials with a computerized axial tomographic scanner (CAT) at a first energy, said plurality of calibration materials having a plurality of different known atomic numbers, Zi, and densities, ρ
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23. A method of obtaining an atomic number image of an unknown material, comprising:
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scanning a plurality of calibration materials having known different atomic numbers, Zi, and densities, ρ
i, and said unknown material at a first energy with a computerized axial tomograph (CAT) scanner,scanning said plurality of calibration materials and said unknown material at a second energy with said CAT scanner, calculating two energy-dependent coefficients from attenuation coefficients of said calibration materials obtained from reconstructed images of said calibration materials at said first and second energies, and calculating an effective atomic number image for said unknown material from attenuation coefficients for said unknown material obtained from reconstructed images of said unknown material and said energy-dependent coefficients at said first and second energies.
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24. A method of obtaining a density image of an unknown material, comprising;
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scanning a plurality of calibration materials having known different atomic numbers, Zi, and densities, ρ
i, and said unknown material at a first energy with a computerized axial tomograph (CAT) scanner,scanning said plurality of calibration materials and said unknown material at a second energy with said CAT scanner, calculating two energy-dependent coefficients from attenuation coefficients of said calibration materials obtained from reconstructed images of said calibration materials at said first and second energies, and calculating a density image for said unknown material from attenuation coefficients for said unknown material obtained from reconstructed images of said unknown material and said energy-dependent coefficients at said first and second energies.
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Specification