Four models, standard diffusion approximation (SDA), single Monte Carlo (SMC), delta-P1, and isotropic similarity (ISM), are developed and evaluated as forward calculation tools in the estimation of tissue optical properties. The inverse calculation uses the ratio of the fluences and phase difference at two locations close to an intensity modulated isotropic source to recover the reduced scattering coefficient µ′s and the absorption coefficient µa. Diffusion theory allows recovery of optical properties (OPs) within 5% for media with µ′s/µa>10. The performance of the delta-P1 model is similar to SDA, with limited enhanced accuracy. The collimation approximation may limit the use of the delta-P1 model for spherical geometry, and/or the fluence may not be accurately calculated by this model. The SMC model is the best, recovering OPs within 10% regardless of the albedo. However, the necessary restriction of the searched OPs space is inconvenient. The performance of ISM is similar to that of diffusion theory for media with µ′s/µa>10, and better for 1<µ′s/µa<10, i.e., determines absorption within 5% and reduced scattering within 20%. In practice, satisfactory estimates (within 5 to 10%) can be achieved using SDA to recover µ′s and ISM to recover µa for media with µ′s/µa>5.