Most gravitational lens systems consist of two or four observable images .
The absence of detectable odd images allows us to place a lower limit on the power-law slope of the inner mass profile of lensing galaxies .
Using a sample of six two-image radio-loud lens systems and assuming a singular power-law surface density ( \Sigma \propto r ^ { - \beta } ) for the inner several kpc of the mass distribution , we find that there is less than a 10 % probability that the data are consistent with profile slopes \beta < 0.80 .
Furthermore , individual mass modeling yields \beta > 0.85 for B0739+366 and \beta > 0.91 for B1030+074 .
Modeling central black holes as additional point masses changes the constraints in these systems to \beta > 0.84 and \beta > 0.83 , respectively .
The inner mass profiles of lensing galaxies are therefore not much shallower than isothermal .