K. Mcgee et S. Shalev, REDUCTION OF INTERPOLATION ARTIFACTS INTRODUCED BY MOVING HISTOGRAM EQUALIZATION (MHE) IN DIGITAL ONLINE PORTAL IMAGES, Physics in medicine and biology, 38(5), 1993, pp. 601-614
Digital on-line portal imaging provides almost real time images of pat
ients undergoing radiation treatments, and is used to verify treatment
field size and shape, and to achieve greater set-up and treatment acc
uracy. A major problem with this new modality is the lack of contrast
of anatomical structures due to the relatively small differences in at
tenuation coefficients of bone and soft tissue. and the large amount o
f scatter at megavoltage photon energies. One solution to this problem
is to process the images using adaptive contrast enhancement techniqu
es, one example of which is known as moving histogram equalization (MH
E). A disadvantage of MHE is that artifacts often appear in the enhanc
ed image, especially in regions of relative uniformity. A technique ha
s been developed to remove these artifacts while retaining the high co
ntrast of the enhanced image using matched Fourier domain filtering te
chniques. The artifact reduction factor is found to be about 0.6 for a
variety of on-line portal images.