Fourier spectrum method to remove grid line artifacts without changing the diagnostic quality in X-ray images
AssigneeGeneral Electric Company
InventorsBirsen Yazici, Wen-Tai Lin, Jerome Johnson Tiemann
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Abstract
A method for removing “grid line artifacts” from x-ray images without changing the diagnostic quality of the x-ray image is presented. The method utilizes the Fourier spectrum of the image to detect the grid line frequencies and employs spectral domain filtering to remove the grid line spectral components. The diagnostic information is preserved by modifying the grid line spectral components to be indistinguishable from local variations in image intensity values, and edge density of the x-ray image.
Claims24
A method of removing grid line artifacts from an x-ray image collected by a detector having an anti-scatter grid, said x-ray image having edgy regions, and high intensity regions, said method comprising the steps of:
- generating a gradient image and an intensity image from said x-ray image wherein the gradient image comprises said edgy regions and non-edgy regions and wherein the intensity image comprising said high intensity regions and low intensity regions;
- replacing said edgy regions with non edgy regions using said gradient image;
- replacing said high intensity regions with low intensity regions using said intensity image;
- converting said x-ray image to the Fourier transform domain;
- and
- eliminating grid line artifacts caused by said anti-scatter grid to form a modified x-ray image;
- converting said modified x-ray image to the inverse-Fourier transform domain to restore said modified x-ray image to a human readable format;
- and
- restoring in said modified x-ray image each of said respective edgy regions and each of said respective high intensity regions.
A method for removing grid lines artifacts from an x-ray image collected by a detector having an anti-scatter grid, said x-ray image having a plurality of pixels said method comprising:
- convolving said x-ray image with a gradient operator;
- computing a histogram of the convolved x-ray image;
- determining a threshold value “Y” from said histogram;
- identifying in said x-ray image a first range of said plurality of pixels having a gradient greater than said threshold value “T” and a second range of said plurality of pixels having a gradient less than said threshold value “T” wherein said first range comprises edgy regions and said second range comprises non-edgy regions;
- generating a gradient image comprising at least said edgy regions and said non-edgy regions;
- dividing said gradient image into a pre-determined number of gradient windows comprising edgy windows and non-edgy windows wherein said each of said edgy windows comprises at least one edgy regions and wherein each of said non-edgy windows comprises at least one non-edgy region;
- analyzing each of said gradient windows in said gradient image to replace at least one respective edgy region in each of said edgy windows with a respective nearest non-edgy region;
- computing an intensity histogram from said x-ray image;
- determining a threshold value “I” from said intensity histogram;
- identifying high intensity regions and low intensity regions in said x-ray image wherein said high intensity regions comprise a predetermined percentage of said plurality of pixels having an intensity greater than the threshold value “I” and wherein said low intensity regions comprise a predetermined percentage of said plurality of pixels having an intensity lower than the threshold value “I”;
- generating an intensity quantized image comprising at least said high intensity regions and said low intensity regions;
- dividing the intensity quantized image into a predetermined number of intensity windows comprising high intensity windows and low intensity windows wherein each of said high intensity windows comprises at least one high intensity region and wherein each of said low intensity windows comprises at least one low intensity region;
- analyzing each of said intensity windows in said intensity quantized image to replace at least one respective high intensity window in each of said high intensity windows with a nearest low intensity window;
- perforning a Fourier transform on said x-ray image;
- removing said grid line artifacts caused by said anti-scatter grid to form a modified x-ray image;
- removing ringing artifacts from said modified x-ray image;
- performing an inverse-Fourier transform on said modified x-ray image to restore said modified x-ray image to a human readable format;
- restoring in said modified x-ray image each of said respective edgy regions removed from said edgy windows;
- and
- restoring in said modified x-ray image each of said respective high intensity regions removed from said high intensity windows.
Dependencies are inferred from the claim text.