MRI gradients

I have a large pool of research images I generated and I think they're really interesting so I will start posting them.
This image shows segmentation of arteries from a Time of Flight-MRI. The arteries are about the brightest thing in the image and we used that to segment them. But the magnetic field of the MRI is not consistent so the other tissue in the back of the brain came out bright.
Arterial segmentation from Time of Flight MRI
To remove this we ran a median filter over the image and created a blurred image.
Median filtered image
We subtracted the blurry median filtered image from the original image which got rid of the intensity gradient. Then reran the segmentation and isolated the arteries without the background.
Segmented arteries after subtracting median filter blurred image
Then we could make quantitative measurements on the isolated arteries. I used this technique to extract the small arteries from a 7T time-of-flight MRI image of hypertensive subject in this paper http://www.biomedcentral.com/1471-2105/12/S10/S15. 

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