Context :

Aims : We present mid-infrared observations and photometry of the circumstellar disks around PDS 66 and CRBR 2422.8-3423 , obtained with VISIR/VLT in the N band and for the latter also in the Q band .
Our aim is to resolve the inner regions of these protoplanetary disks , which carry potential signatures of intermediate or later stages of disk evolution and ongoing planet formation .

Methods : We determined the radial brightness profiles of our target objects and the corresponding PSF reference that were observed before and after our target objects .
Background standard deviations , the standard errors , and the seeing variations during the observations were considered .
Adopting a simple radiative transfer model based on parameters taken from previous studies , we derived constraints on the inner-disk hole radius of the dust disk .

Results : Neither of the circumstellar disks around our science targets are spatially resolved in our observations .
However , we are able to constrain the inner-disk hole radius to < 15.0 ^ { +0.5 } _ { -0.5 } AU and < 10.5 ^ { +0.5 } _ { -1.0 } AU for PDS 66 and CRBR 2422.8-3423 , respectively .
The photometry we performed yields N-band flux densities of 599 \pm 8 mJy for PDS 66 and 130 \pm 14 mJy for CRBR 2422.8-3423 , as well as a Q-band flux density of 858 \pm 109 mJy for CRBR 2422.8-3423 .

Conclusions :