Regularization method for scatter-glare correction in fluoroscopic images

Fluoroscopic images are degraded by scattering of x rays from within the pa tient and by veiling glare in the image intensifier. Both of these degradat ions are well described by a response function applied to either the scatte r-free or primary intensity. The response function is variable, with depend ence on such factors as patient thickness and imaging geometry. We describe an automated regularization technique for obtaining response function para meters with a minimal loss of signal. This method requires a high-transmiss ion structured reference object to be interposed between the x-ray source a nd the subject. We estimate the parameters by minimizing residual correlati ons between the reference object and the computed subject density after a s catter-glare correction. We use simulated images to evaluate our method for both ideal and clinically realistic conditions. We find that the residual root-mean-square (rms) error ideally decreases with an increasing number of independent pixels (N) as (1/N)(1/2). In simulated 256 x 256 angiograms me an normalized rms errors were reduced from 40% to 11% in noise-free images, and from 41% to 17% in noisy images, with a similar improvement in densito metric vessel cross-section measurements. These results demonstrate the val idity of the method for simulated images and characterize its expected perf ormance on clinical images. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)00709-9].