The inverse Monte Carlo (IMC) reconstruction algorithm achieved compensation for two degrading collimator effects in SPECT (single-photon-emission computed tomography) imaging: position dependence and radial/tangential asymmetry in reconstructed resolution. With filtered backprojection using a ramp filter, full width at half maximum (FWHM, radial and tangential, respectively) for a line source on axis with a high-sensitivity collimator were 19.3 mm and 16.4 mm. At 12 cm off axis, FWHM were 14.8 mm and 8.2 mm, respectively. With IMC after 35 iterations, FWHM on axis were 8.4 mm and 7.7 mm and off axis were 6.0 mm and 7.4 mm, respectively. Thus, for the simple imaging task of line sources with no background activity using simulated projection data, IMC provides compensation for the collimator effects in addition to providing higher resolution.<>