Method for analyzing and representing x-ray projection images and x-ray examination unit

• US 7,469,034 B2
• Filed: 04/21/2006
• Issued: 12/23/2008
• Est. Priority Date: 04/27/2005
• Status: Expired due to Fees

• Current Assignee: Siemens Healthcare GMBH (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Bernhardt, Philipp, Kolarjk, Martin, Koch, Friedrich, Schramm, Helmuth, Rührnschopf, Ernst Peter
• Primary Examiner(s): Glick; Edward J
• Assistant Examiner(s): Midkiff; Anastasia
• Application Number:
  US11/409,419
• Publication Number:
  US 20060245538A1
• Time in Patent Office: 977 Days
• Field of Search: 378 4- 20, 378/51, 378/62, 378/65, 378/207, 378/901, 378/41, 378/42, 378 44- 56, 378/91, 378156-159, 378/204, 378/210, 382/132, 382/190, 382/192, 382/195, 382/274, 250/362, 250/363.01, 250/363.07, 250/363.09, 250/370.01, 25037006-37009, 250/371
• US Class Current: 378/62
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating

Abstract

The invention relates to a method and an x-ray examination unit for analyzing and representing x-ray projection images with an x-ray examination unit, where the function relation b_U=ƒ_U⁻¹(J^˜/J₀) is established between the attenuation value and a material-equivalent value as a function of the energy spectrum used, and for the purposes of projection representation, the magnitude of the material-equivalent value b_U of a specific material is represented as an image value.

Claims

1. A method of analyzing and displaying x-ray projection images using an x-ray examination unit, comprising the steps of:

radiographing an object using x-rays originating from a radiation source and a focus of the radiation source;

measuring the x-rays penetrating the object by a detector field having a plurality of detector elements, the detector field arranged opposite the focus and after the object relative to an x-radiation direction;

determining x-ray attenuation values from local x-ray intensity values captured by the detector field and from initial x-ray intensity values, the initial x-ray intensity values related to the x-rays before penetrating the object;

generating and displaying a projection image of the object based upon the determined x-ray attenuation values; and

determining a functional relationship between the x-ray attenuation values and a material-equivalent coefficient variable relative to an energy spectrum of the x-rays, wherein the material-equivalent coefficient variable is assigned a value characteristic for one specific material and displayed as an image value when displaying the projection image,

wherein the functional relationship is determined according to the formula

2. The method according to claim 1, wherein the object is a patient.

3. The method according to claim 1, wherein the material-equivalent coefficient variable represents water and is assigned with the value characteristic for water.

4. The method according to claim 1, wherein the material-equivalent coefficient variable represents tissue and is assigned with the value characteristic for tissue.

5. The Method according to claim 1, wherein the material-equivalent coefficient variable is a thickness of a material having a homogenous density.

6. The method according to claim 1, wherein the material-equivalent coefficient variable is a density of a material having a homogenous thickness.

7. The method according to claim 1, wherein the image value is a gray value of the projection image.

8. The method according to claim 1, wherein the image value is a color value of the projection image.

9. The method according to claim 1, wherein the functional relationship between the x-ray attenuation values and the material-equivalent coefficient variable is determined based on an empirical measurement.

10. The method according to claim 9, wherein an approximation formula for the functional relationship is determined from the empirically measured functional relationship.

11. The method according to claim 9, wherein the empirically measured functional relationship is stored in a lookup table.

12. The method according to claim 1, wherein the material-equivalent coefficient variable is calculated including a scattered radiation correction.

13. An x-ray examination device for generating two-dimensional projection images of a radiographed object, comprising:

a radiation source having a focus for radiographing an object;

a detector field arranged opposite the focus and after the object relative to an x-radiation direction and having a plurality of detector elements for detecting x-rays penetrating the object;

a display unit; and

a processing unit for determining x-ray attenuation values J^˜

/J₀ from local x-ray intensity values J^˜

captured by the detector field and from initial x-ray intensity values J₀, the initial x-ray intensity values related to the x-rays before penetrating the object and for generating a projection image of the object based upon the determined x-ray attenuation values, wherein the processing unit comprises a calculation unit for determining a functional relationship b_U=ƒ

_U<sup>−

1</sup>(J^˜

/J₀) between the x-ray attenuation values and a material-equivalent coefficient variable b_U relative to an energy spectrum of the x-rays,

the material-equivalent coefficient variable is assigned a value characteristic for one specific material, and

the projection image is displayed on the display unit including the value characteristic for the one specific material,

wherein the functional relationship is determined according to the formula

14. The x-ray examination device according to claim 13, wherein the calculation unit includes a computer program, a circuit or an ASIC.