Fill in a logic image: possible in IDL ?

[jsilva(at)ci.uc.pt]

Hello
I have a grayscale image (512 x 512 x 1 byte from medical TAC).
I applied a threshold to have a logic mask and tried to do a fill in that mask
in order to remove some background. Most of languages have a fill command, like
FILL in draw programs that FILLs the image starting in X,Y (user defined)
coordenations.
I search throw IDL commands and I never found any FILL command (or identical
command). 
As most of languages (eg MATLAB and many others) have a FILL (BWFILL in MATLAB,
as morphologic operation), did I miss the FILL in IDL or there isn’t any FILL in
IDL?
I tried to use POLYFILL but my mask is very irregular, not being possible to
apply a POLYFILL in a predefined region.
Any commend on this subject is welcome…

level=100
mask= (image LE level) ; TAC of lungs (from TAC) with many irregularities
; FILL to “fill” mask starting (eg) in 1,1 pixel coordination

jsilva @ ci.uc.pt