Spot-size effect reduction

• US 7,418,078 B2
• Filed: 05/06/2005
• Issued: 08/26/2008
• Est. Priority Date: 05/06/2005
• Status: Expired due to Fees

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Inventors: Bani-Hashemi, Ali, Blanz, Wolf-Ekkehard
• Primary Examiner(s): KAO, CHIH CHENG G
• Application Number:
  US11/123,749
• Publication Number:
  US 20060251212A1
• Time in Patent Office: 1,208 Days
• Field of Search: 378/4, 378/16, 378/19, 378/62, 378/901, 378/65, 378/98.3, 382/131, 382/260
• US Class Current: 378/62
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4085 Cone-beams
• CPC Class Codes: A61B 6/4233 using matrix detectors
• CPC Class Codes: A61B 6/583 using calibration phantoms

Abstract

A radiographic imaging device includes an X-ray source having a finite focal spot characterized by a determined intensity distribution. The X-ray source emits a beam of X-ray radiation toward an object. A detector assembly receives at least part of the X-ray radiation after it passes through the object. The detector assembly produces a signal in response to the received radiation. An image processor constructs an image from the signal generated by the detector assembly using the determined intensity distribution of the X-ray source. By inverse filtering the aggregated detector image from the detector assembly, the effects of the finite focal spot size of the X-ray source are mitigated, improving the quality of the resulting image.

Claims

1. A radiographic imaging device, comprising:

an X-ray source for emitting a beam of X-ray radiation toward an object, the X-ray source having a finite focal spot characterized by an X-ray intensity distribution;

a detector assembly for receiving at least part of the X-ray radiation after the X-ray radiation passes through the object and producing a signal in response thereto; and

an image processor configured to construct an image from the signal generated by the detector,

wherein the image processor constructs the image by;

scaling the intensity distribution for a first object layer;

scaling the intensity distribution for a second object layer;

aggregating the first and second scaled intensity distributions; and

applying a filter to the aggregated scaled intensity distributions.

2. The radiographic imaging device as claimed in claim 1, wherein the application of the filter is a convolution of the aggregated scaled intensity distributions and an inverse filter derived from the X-ray intensity distribution.

3. The radiographic imaging device as claimed in claim 1, wherein the application of the filter comprises:

multiplication of a Fourier transform of the aggregated scaled intensity distributions with an inverse of a Fourier transform of an inverse filter derived from the X-ray intensity distribution; and

computation of a transform of the product of the multiplication from the Fourier domain to an image domain.

4. The radiographic imaging device as claimed in claim 1, wherein the object comprises a plurality of layers, and the image is constructed by filtering utilizing a scaled point spread function (PSF) determined for a specified object layer of the plurality of layers, the image being for at least one of a video presentation, a maximum sharpness projection of the object, and reconstruction of a voxel associated with the specified object layer.

5. The radiographic imaging device as claimed in claim 1, further comprising an apparatus for determining the X-ray intensity distribution of the X-ray source, including:

a scintillation screen placed within the beam of the X-ray radiation, the beam of X-ray radiation causing the scintillation screen to emit light having an intensity distribution corresponding to the intensity distribution of the finite focal spot;

an imaging device for detecting the light emitted by the scintillation screen and producing an image signal in response thereto, the image signal containing the intensity distribution; and

a digitizer for converting the image signal into a computer-readable matrix of pixel information,

wherein the scintillation screen is positioned substantially adjacent to the object.

6. The radiographic imaging device as claimed in claim 5, wherein the apparatus further comprises a mirror for directing light from the scintillation screen to the imaging device.

7. The radiographic imaging device as claimed in claim 6, wherein the mirror is positioned at an angle of forty-five degrees (45°

) with respect to the imaging device and the scintillation screen.

8. The radiographic imaging device as claimed in claim 6, wherein the imaging device comprises a camera.

9. A method for mitigating the effect of finite focal spot size in a radiographic imaging device, the radiographic imaging device having an X-ray source having a finite focal spot for emitting X-ray radiation toward an object so that at least part of the X-ray radiation passes through the object, comprising:

determining an intensity distribution for the X-ray source;

receiving at least part of a beam of X-ray radiation emitted by the X-ray source after the beam of X-ray radiation passes through the object and producing a signal in response thereto;

constructing an image from the signal generated by the detector by;

scaling the intensity distribution for a first object layer;

scaling the intensity distribution for a second object layer;

aggregating the first and second scaled intensity distributions; and

filtering the aggregated scaled intensity distributions, and

displaying the image on a display console.

10. The method as claimed in claim 9, wherein the filtering comprises:

computing a convolution of the aggregated scaled intensity distributions and an inverse filter derived from the X-ray intensity distribution.

11. The method as claimed in claim 9, wherein the filtering comprises:

multiplying a Fourier transform of the aggregated scaled intensity distributions and an inverse of a Fourier transform of an inverse filter derived from the X-ray intensity distribution; and

computing a transform of the product of the multiplication from the Fourier domain to an image domain.

12. The method as claimed in claim 9, wherein the object comprises a plurality of layers, and the image is constructed by filtering utilizing a scaled point spread function (PSF) determined for a specified object layer of the plurality of layers, the image being for at least one of a video presentation, a maximum sharpness projection of the object, and reconstruction of a voxel associated with the specified object layer.

13. The method as claimed in claim 9, wherein determining the intensity distribution for the X-ray source comprises:

passing the beam of X-ray radiation through a scintillation screen, the beam of X-ray radiation causing the scintillation screen to emit light having an intensity distribution corresponding to the intensity distribution of the finite focal spot;

detecting the light emitted by the scintillation screen and producing an image signal in response thereto, the image signal containing the intensity distribution; and

converting the image signal into a computer-readable matrix of pixel information, wherein the scintillation screen is positioned substantially adjacent to the object.

14. The radiographic imaging device as claimed in claim 13, further comprising directing light from the scintillation screen to the imaging device so that the imaging device is not within the beam of X-ray radiation.

15. The method as claimed in claim 14, wherein the step of directing the light comprises reflecting the light with a mirror positioned at an angle of forty-five degrees (45°

) with respect to the imaging device and the scintillation screen.

16. The method as claimed in claim 14, wherein the imaging device comprises a camera.