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].