To study the in vivo expression of dopamine D2 receptors in nonfunctioning pituitary adenoma and the predictive role of dopamine dopamine D2 receptors PET-MR imaging in the therapeutic effect of dopamine agonists（DA）.

Dopamine agonists are the first line therapy for prolactinoma,which are also effective in some cases of other subtypes of pituitary tumors. It had been showed that dopamine agonists inhibit prolactin secretion by binding to and activating dopamine D2 receptors. PET-MR combined MR images with PET function images is substantial to evaluate the expression of dopamine D2 receptors.The aim is to study the in vivo expression of dopamine D2 receptors in prolactinoma and the predictive role of dopamine D2 receptors PET-MR imaging in the therapeutic effect of dopamine agonists.

Inclusion Criteria:

1. Normal serum pituitary hormone levels or mild increase of serum prolactin.
2. Enhanced MRI shows a pituitary tumor and tumor diameter>1cm.
3. Aged between 18 and 65 years old, either sex.
4. Karnofsky performance status ≥ 70.
5. The patient has signed the informed consent.

Exclusion Criteria:

1. Patients concomitantly taking the psychotropic drugs.
2. Patients with parkinson disease and is taking dopaminergic agents.
3. Patients with pituitary adenoma who received Gamma knife treatment.
4. Pregnant or lactating women.
5. Patients with poor compliance, who cannot implement the program strictly.
6. History of allergic reactions attributed to compounds of similar chemical or biologic composition to cabergoline.
7. Patients with claustrophobia. -

The individual patient Data would not be shared to the third facility, but the sponsor hasn't decided whether to share the individual patient date to the other related studies hold by himself in the future.