The intensity of the APT signal depends on the pH and protein content within the tissue. The later the bleeding stage is, the lower the APT value is. The ectopic endometrium repeatedly bleeds in the ovary. The blood components deposited in the cyst fluid decomposition, so the APT value of the cyst fluid is reduced. The metabolic level of tumor tissue is increased, and more protein is synthesized. Therefore, the protein content of ovarian cystadenoma and cystadenocarcinoma fluid is higher, so the APT value is increased.