Method and system for removing scatter and veiling glate and other artifacts in digital radiography

• US 4,841,555 A
• Filed: 08/03/1987
• Issued: 06/20/1989
• Est. Priority Date: 08/03/1987
• Status: Expired due to Term

• Current Assignee: University of Chicago The (University of Chicago)
• Original Assignee: University of Chicago
• Inventors: Kume, Yuichiro, Doi, Kunio
• Primary Examiner(s): Church, Craig E.
• Assistant Examiner(s): Freeman, John C.
• Application Number:
  US07/081,001
• Time in Patent Office: 687 Days
• Field of Search: 358/111, 378/62, 378/99, 378/146
• US Class Current: 378/98.4
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating

Abstract

A method and system for reconstructing image data obtained from plural sequential exposures of an object by a radiation source through a multiple slit beam scanning assembly, wherein frames of original image data in the form of plural pixels are obtained for each discrete scanning step/exposure and a minimum pixel value of at least one frame is determined. Based on this determined minimum value, a cutoff value is determined. The pixel values of each frame are compared with the cutoff value, and the image is reconstructed by summation of all the pixel image data above the cutoff value for each respective pixel. In order to improve spatial resolution, the slit width of the scanning assembly is selected be the narrower than the pixel size. Pixel image data produced by exposure from radiation passing through the same slit of the scanning assembly in consecutive scanning steps are then assigned to adjacent pixels in a direction perpendicular to the scanning beam of an enlarged pixel matrix. To achieve a balanced aspect ratio, pixel values for pixels in a direction parallel to the scanning beam are assigned by interpolation between pixel values assigned in the perpendicular direction.

Claims

1. A method for reconstructing an image obtained from plural sequential radiographic exposures of an object using a multiple slit beam scanning system including a radiation source for radiating the object, a multiple slit beam scanning assembly positioned between the source and the object, and means for performing plural successive image acquisition steps for acquiring successive frames of original image data, wherein the original image data of each successive frame is in the form of plural pixels and corresponds to radiation passing through the scanning assembly and the object at respective of successive image acquisition steps, comprising the following steps:

producing relative movement between the source and the scanning assembly;

performing plural successive image acquisitioin steps during production of said relative movement, wherein original image data are acquired for each pixel at each of said successive image acquisition steps during production of said relative movement;

determining for each pixel a minimum pixel value of original image data acquired during the successive image acquisition steps;

comparing the image data of each pixel acquired at each of the image acquisition steps with a respective comparison cutoff value which bears a predetermined relationship to the minimum value for each pixel determined in said determining step;

summing for each pixel only the values of original image data acquired during the plural image acquisition steps which exceed said cutoff value as determined in the comparing step; and

outputting a reconstructed image data based at least in part on the sums produced in said summing step.

2. The method according to claim 1, wherein said comparing step comprises:

selecting said comparison cutoff value, I_cutoff, as follows,

space="preserve" listing-type="equation">I.sub.cutoff =I.sub.min +k√

I.sub.min,

where I_min equals the minimum value of original image data acquired during said successive image acquisition steps, and k equals a predetermined positive fraction less than one.

3. The method according to claim 2, wherein k equals one-fourth.

4. The method according to claim 1, comprising:

selecting a slit beam width of said scanning assembly to be larger than a pixel size of the original image data acquired by said means for performing plural successive image acquisition steps, and producing said relative movement at a distance step smaller than the slit beam width so that beams from the scanning assembly overlap during consecutive image acquisition steps.

5. The method according to claim 1, comprising:

selecting a slit beam width of said scanning assembly to be narrower than a pixel size of said original image data acquired by said means for performing plural successive image acquisition steps at an image plane of said means for performing plural successive image acquisition steps.

6. The method according to claim 5, wherein the slit beam width is selected to be less than the pixel size, further comprising:

acquiring a series of image data derived from radiation passing through a common slit of said scanning assembly in consecutive image acquisition steps; and

forming an enlarged matrix by assigning said series of image data to adjacent respective series of pixels in the enlarged matrix in which the adjacent series of pixels are arranged in a direction perpendicular to the scanning beams.

7. The method according to claim 6, comprising:

balancing an image aspect ratio of the enlarged matrix by assigning pixel values using linear interpolation to selected pixels of the enlarged matrix in a direction parallel to the scanning beams.

8. A system for reconstructing an image obtained from plural sequential exposures of an object by a radiation source comprising:

multiple slit beam scanning means positioned between the source and the object for exposing said object with radiation emanating from said source and passing through said scanning means;

means for performing plural successive image acquisition steps in which successive frames of original image data each in the form of plural pixels are acquired at said plural successive image data acquisition steps during relative movement of said source and said scanning means;

means for determining for each pixel a minimum value (I_min) of image data acquired during the successive image data acquisition steps;

means for comparing the image data of each pixel acquired for each frame with a comparison cutoff value which bears a predetermined relationship to the minimum pixel value for that frame;

means for summing for each pixel all of the values of original image data which exceed said cutoff value for all of said frames of original image data; and

means for outputting a reconstructed image data based at least in part on the sums produced by said summing means.

9. The system according to claim 8, wherein said comparing means comprises:

means for producing a cutoff value, I_cutoff, as follows;

space="preserve" listing-type="equation">I.sub.cutoff =I.sub.min +k√

I.sub.min,

where k is a predetermined positive fraction less than one.

10. The system according to claim 9, wherein k equal one-fourth.

11. The system according to claim 8, comprising:

said scanning means having a slit beam width selected to be larger than a pixel size of the original image data acquired by said means for performing plural successive image acquisition steps; and

said relative movement producing means producing relative movements at a distance increment smaller than the slit beam width so that beams from the scanning means overlap during consecutive image acquisition steps.

12. The system according to claim 8, comprising:

said scanning means having a slit beam width selected to be narrower than a pixel size of said original image data acquired by said means for performing plural successive image acquisition steps at an image plane of said means for performing plural successive image acquisition steps.

13. The system according to claim 12, further comprising:

means for producing based on said original image data a series of image data derived from radiation passing through a common slit of the scanning means in successive image acquisition steps; and

means for forming an enlarged image data matrix by assigning said series of image data to a respective series of adjacent pixels in said enlarged matrix in which the respective series of adjacent pixels are arranged in a direction perpendicular to the scanning beams.

14. The method according to claim 13 comprising:

means for balancing an image aspect ratio of the enlarged matrix by assigning pixel values using interpolation to selected pixels of the enlarged matrix in a direction parallel to the scanning beams.

15. A method for reconstructing an image obtained from plural sequential radiographic exposures of an object using a multiple slit beam scanning assembly including a radiation source for radiating the object, a multiple slit beam scanning assembly positioned between the source and the object, means for producing relative movement between the source and the scanning assembly, and means for performing plural successive image acquisition steps in which original image data in the form of plural pixels are acquired at said successive image acquisition steps during relative movement of said source and said scanning assembly, said original image data corresponding to radiation passing through the scanning assembly and the object at each of said image acquisition steps comprising:

selecting a slit beam width of said scanning assembly to be narrower than a pixel size of said original image data acquired by said means for performing plural successive image acquisition steps at an image plane of said means for performing plural successive image acquisition steps;

producing relative movement between the source and the scanning assembly;

producing a series of image data derived from radiation passing through a common slit of the scanning assembly in consecutive image acquisition steps performed by said means for performing plural successive image acquisition steps during relative movement of said source and scanning assembly steps;

forming an enlarged pixel matrix by assigning said series of image data to respective series of adjacent pixels arranged in a direction perpendicular to the scanning beams of said scanning assembly in the enlarged pixel matrix; and

forming an image based at least in part on said series of image data assigned to said enlarged pixel matrix.

16. The method according to claim 15 further comprising:

balancing an image aspect of the enlarged pixel matrix by assigning pixel values using linear interpolation to pixels in the enlarged matrix arranged in a direction parallel to the scanning beams.

17. A system for reconstructing an image obtained from plural sequential exposures of an object by a radiation source, comprising:

multiple slit beam scanning means positioned between the source and the object for exposing the object with radiation emanating from said source and passing through said scanning means;

means for producing relative movement between the source and the scanning means;

means for performing plural successive image acquisition steps in which successive frames of original image data each in the form of a matrix of plural pixels are acquired at each of said plural image data acquisition steps upon relative movements of said source and said scanning means;

said scanning means having a slit beam width selected to be narrower than a pixel size of the pixel matrix at an image plane of said means for performing plural image acquisition steps;

means for producing based on said original image data a series of image data derived from radiation passing through a common slit of the scanning means in consecutive image acquisition steps;

means for forming an enlarged pixel matrix by assigning said series of image data to a respective series of adjacent pixels arranged in a direction perpendicular to the scanning beams of said scanning means in the enlarged pixel matrix; and

means for forming an image based at least in part on said series of image data assigned in said enlarged pixel matrix.

18. The system according to claim 17, comprising:

means for balancing an image aspect ratio of the enlarged matrix by assigning pixel values using interpolation to selected pixels of the enlarged matrix in a direction parallel to the scanning beams.