Method for determining density distributions and atomic number distributions during radiographic examination methods

• US 7,158,611 B2
• Filed: 08/21/2002
• Issued: 01/02/2007
• Est. Priority Date: 09/03/2001
• Status: Expired due to Fees

• Current Assignee: Siemens Healthcare GMBH (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Stierstorfer, Karl, Heismann, Bjo
• Primary Examiner(s): Ho; Allen C.
• Application Number:
  US10/488,397
• Publication Number:
  US 20040223585A1
• Time in Patent Office: 1,595 Days
• Field of Search: 378/5, 378/16, 378/53, 378/57, 378/98.9, 378/98.11
• US Class Current: 378/98.9
• CPC Class Codes: A61B 6/4035 the source being combined with a filter or grating
• CPC Class Codes: A61B 6/4241 using energy resolving detectors, e.g. photon counting
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• CPC Class Codes: A61B 6/50 specially adapted for specific body parts; specially adapted for specific clinical applications
• CPC Class Codes: A61B 6/501 for diagnosis of the head, e.g. neuroimaging or craniography
• CPC Class Codes: A61B 6/502 for diagnosis of breast, i.e. mammography
• CPC Class Codes: A61B 6/505 for diagnosis of bone
• CPC Class Codes: A61B 6/508 for non-human patients
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: G01N 23/04 and forming images of the material

Abstract

The functional dependency of a first X-ray absorption value of density and atomic number is determined in the instance of a first X-ray spectrum, and at least the functional dependency of a second X-ray absorption value of density and atomic number is determined in the instance of a second X-ray spectrum. Based on a recording of a first distribution of X-ray absorption values of the object to be examined in the instance of a first X-ray spectrum, and on a recording of at least one second distribution of X-ray absorption values of the object to be examined in the instance of a second X-ray spectrum, the values for density and atomic number are determined by comparing the functional dependency of a first X-ray absorption value of the first distribution of X-ray absorption values with the functional dependency(ies) of the X-ray absorption values, which are assigned to the first X-ray absorption value, of the second and/or other distributions of X-ray absorption values.

Claims

1. A method for determining distributions of density and atomic number in an object to be examined, comprising:

recording a first distribution of X-ray absorption values of the object to be examined using a first X-ray spectrum;

recording at least a further distribution of X-ray absorption values of the object to be examined using a further X-ray spectrum;

selecting, from the recorded first distribution of X-ray absorption values, a first X-ray absorption value;

selecting from the recorded further distribution of X-ray absorption values, a further X-ray absorption value assigned to said first X-ray absorption value or selecting, from each of said recorded further distribution of X-ray absorption values, a further X-ray absorption value assigned to said first X-ray absorption value;

specifying a first function representing paired values of density and atomic number that correspond to said first X-ray absorption value selected from said recorded first distribution of X-ray absorption values;

specifying a further function representing paired values of density and atomic number that correspond to said further X-ray absorption value selected from said recorded further distribution of X-ray absorption values of specifying a further function representing paired values of density and atomic number for each X-ray absorption value assigned to said first X-ray absorption value in the recorded further distributions of X-ray absorption values; and

determining a value for the density and determining a value for the atomic number from a comparison of said first function representing paired values of density and atomic number that correspond to said first X-ray absorption value with one or more of said further functions representing paired values of density and atomic number that correspond to said respective further X-ray absorption values, and which are assigned to said first X-ray absorption value.

2. The method as claimed in claim 1, wherein a function representing paired values of density and atomic number that correspond to a respective X-ray absorption value selected from said recorded first or further distribution of X-ray absorption values is specified based on a reference measurement on a calibration sample.

3. The method as claimed in claim 2, wherein a function representing paired values of density and atomic number that correspond to a respective X-ray absorption value selected from said recorded first or further distribution of X-ray absorption values is specified based on a simulation utilizing a physical model.

4. The method as claimed in claim 2, wherein a transformation of the distributions of the X-ray absorption values into corresponding distributions of density and atomic number is carried out for each of the first X-ray absorption values and the further X-ray absorption values assigned to the respective the first X-ray absorption values based on the determination of a paired value for the density and the atomic number such that a paired value of the first function is chosen, which corresponds to a paired value of a further function.

5. The method as claimed in claim 2, wherein the first X-ray spectrum has a quantum energy that results in a higher fraction of X-ray absorption based on the photoelectric effect when using a further X-ray spectrum.

6. The method as claimed in claim 2, wherein at least one of at least one operating parameter of the X-ray tube and the detector characteristic is varied in order to vary an X-ray spectrum for recording the object to be examined.

7. The method as claimed in claim 2, wherein at least a subregion of the object to be examined is recorded with an increased X-ray dose.

8. The method as claimed in claim 1, wherein a function representing paired values of density and atomic number that correspond to a respective X-ray absorption value selected from said recorded first or further distribution of X-ray absorption values is specified based on a simulation utilizing a physical model.

9. The method as claimed in claim 1, wherein a transformation of the distributions of the X-ray absorption values into corresponding distributions of density and atomic number is carried out for each of the first X-ray absorption values and the further X-ray absorption values assigned to the respective first X-ray absorption value based on the determination of a paired value for the density and the atomic number such that a paired value of the first function is chosen, which corresponds to a paired value of a further function.

10. The method as claimed in claim 1, wherein the first X-ray spectrum has a quantum energy that results in a higher fraction of X-ray absorption based on the photoelectric effect when using a further X-ray spectrum.

11. The method as claimed in claim 1, wherein at least one of at least one operating parameter of the X-ray tube and the detector characteristic is varied in order to vary an X-ray spectrum for recording the object to be examined.

12. The method as claimed in claim 1, wherein at least a subregion of the object to be examined is recorded with an increased X-ray dose.

13. A computer-readable medium having code portions embodied thereon that, when read by a computer device, cause the computer device to perform the method of claim 1.

14. An X-ray apparatus for determining distributions of density and atomic number in an object to be examined, comprising:

an X-ray source adapted to emit X-radiation;

an X-ray detector adapted to detect the X-radiation emitted by the X-ray source and to convert the X-radiation into electrical signals for further processing; and

a signal processing device, adapted to process the electrical signals of the X-ray detector, wherein the signal processing device is adapted to determine distributions of density and atomic number in an object to be examined on the basis of a first and at least one further distribution of X-ray absorption values of the object to be examined recorded on the X-ray apparatus with different X-ray spectra such that, a value for the density and a value for the atomic number are determined for each absorption value of a first distribution of X-ray absorption values recorded with a first X-ray spectrum by

specifying a first function representing paired values of density and atomic number that correspond to an X-ray absorption value from said recorded first distribution of X-ray absorption values and specifying an at least second function representing paired values of density and atomic number that correspond to a further X-ray absorption value of the at least one further distribution of X-ray absorption values and that is further assigned to said absorption value of the first distribution of X-ray absorption values; and

by

comparing the first function with the at least second function to obtain a paired value for density and atomic number common to the first and the at least second function.

15. The X-ray apparatus as claimed in claim 14, wherein the X-ray source is adapted to emit a first X-ray spectrum in a first operating state and a second X-ray spectrum, different from the first operating state, in a second operating state.

16. The X-ray apparatus as claimed in claim 15, wherein the X-ray detector is adapted to convert spectral subregions of the X-radiation received from the X-ray source into mutually independent electrical signals.

17. The X-ray apparatus as claimed in claim 15, wherein a material is adapted to be introduced into the beam path of the X-radiation to record a first distribution of an X-ray absorption of the object to be examined, and no corresponding material is introduced into the beam path of the X-radiation to record a second distribution of an X-ray absorption of the object to be examined.

18. The X-ray apparatus as claimed in claim 14, wherein the X-ray detector is adapted to convert spectral subregions of the X-radiation received from the X-ray source into mutually independent electrical signals.

19. The X-ray apparatus as claimed in claim 18, wherein a material is adapted to be introduced into the beam path of the X-radiation to record a first distribution of an X-ray absorption of the object to be examined, and no corresponding material is introduced into the beam path of the X-radiation to record a second distribution of an X-ray absorption of the object to be examined.

20. The X-ray apparatus as claimed in claim 14, wherein a material is adapted to be introduced into the beam path of the X-radiation to record a first distribution of an X-ray absorption of the object to be examined, and no corresponding material is introduced into the beam path of the X-radiation to record a second distribution of an X-ray absorption of the object to be examined.

21. An X-ray apparatus for determining distributions of density and atomic number in an object to be examined, comprising:

means for emitting X-radiation;

means for detecting the emitted X-radiation and for converting the X-radiation into electrical signals for further processing; and

means for processing the electrical signals and for determining distributions of density and atomic number in an object to be examined, on the basis of a first and at least one further distribution of X-ray absorption values of the object to be examined, recorded on the X-ray apparatus with different X-ray spectra such that, a value for the density and a value for the atomic number are determined for each absorption value of a first distribution of X-ray absorption values recorded with a first X-ray spectrum by

specifying a first function representing paired values of density and atomic number that correspond to an X-ray absorption value from said recorded first distribution of X-ray absorption values and specifying an at least second function representing paired values of density and atomic number that correspond to a further X-ray absorption value of the at least one further distribution of X-ray absorption values and that is further assigned to said absorption value of the first distribution of X-ray absorption values; and

by

comparing the first function with the at least second function to obtain a paired value for density and atomic number common to the first and the at least second function.

22. The X-ray apparatus as claimed in claim 21, wherein the means for emitting is for emitting a first X-ray spectrum in a first operating state and a second X-ray spectrum, different from the first operating state, in a second operating state.

23. The X-ray apparatus as claimed in claim 21, wherein the means for detecting is for converting spectral subregions of the X-radiation into mutually independent electrical signals.

24. The X-ray apparatus as claimed in claim 21, wherein a material is adapted to be introduced into the beam path of the X-radiation to record a first distribution of an X-ray absorption of the object to be examined, and no corresponding material is introduced into the beam path of the X-radiation to record a second distribution of an X-ray absorption of the object to be examined.

25. The X-ray apparatus as claimed in claim 21, wherein the means for emitting includes an x-ray source.

26. The X-ray apparatus as claimed in claim 21, wherein the means for detecting includes an x-ray detector.

27. A method for determining distributions of density and atomic number in an object to be examined, comprising:

detecting emitted X-radiation;

converting the X-radiation into electrical signals; and

determining distributions of density and atomic number in an object to be examined on the basis of a first and at least one other distribution of X-ray absorption values of the object to be examined, recorded with different X-ray spectra such that, a value for the density and a value for the atomic number are determined for each absorption value of a first distribution of X-ray absorption values recorded with a first X-ray spectrum by

specifying a first function representing paired values of density and atomic number that correspond to an X-ray absorption value from said recorded first distribution of X-ray absorption values and specifying an at least second function representing paired values of density and atomic number that correspond to a further X-ray absorption value of the at least one further distribution of X-ray absorption values and that is further assigned to said absorption value of the first distribution of X-ray absorption values; and

by

comparing the first function with the at least second function to obtain a paired value for density and atomic number common to the first and the at least second function.

28. A computer-readable medium having code portions embodied thereon that, when read by a computer device, cause the computer device to perform the method of claim 27.

29. A computer-readable medium having code portions embodied thereon that, when read by a computer device, cause the computer device to determine the distributions of density and atomic number in an object to be examined, on the basis of a first and at least one other image data record recorded for different distributions of X-ray absorption values in the object to be examined using at least a first and at least one other X-ray spectrum such that, a value for the density and a value for the atomic number are determined for each absorption value of a first distribution of X-ray absorption values by

specifying a first function representing paired values of density and atomic number that correspond to an X-ray absorption value from said recorded first distribution of X-ray absorption values and specifying a further function representing paired values of density and atomic number that correspond to a further X-ray absorption value of the at least one further distribution of X-ray absorption values and that is further assigned to said absorption value of the first distribution of X-ray absorption values;

and by

comparing the first function with the further function to obtain a paired value for density and atomic number common to the first and the further function;

whereby a further function may be specified for each absorption value assigned to said absorption value of the first distribution of X-ray absorption values in each further distribution of X-ray absorption values of the object to be examined, and the corresponding density and atomic number be determined as the paired value for density and atomic number common to the first function and the further function or functions.