The gold standard for detecting the patency of the fallopian tubes is to perform a tubal iodography, which involves injecting a contrast medium from the uterine cavity into the fallopian tubes. The contrast agent emits a certain bright light under the X-ray and can be seen in the fallopian tubes and the pelvic cavity. If the fallopian tube is open, after reaching the tubal lumen, it will free into the pelvic cavity. If the fallopian tube is not open, it will be blocked in one part of the tube. As soon as you see this part become thicker and larger, and there is contrast agent retained there, it means that the tube is not open. All of this can be seen through x-rays, so this is the gold standard for checking whether the fallopian tubes are open or closed.