A 30-year-old woman complains of irregular copious painful menstruations, pain irradiates to the rectum. Anamnesis states 10-year-long infertility. On bimanual examination: uterus is of normal size; uterine appendages on the both sides are corded, with rectricted mobility, painful; there are dense nodular painful growths detected in the posterior fornix. A doctor suspects endometriosis. What method allows to verify this diagnosis?