Background Bile duct cancer (cholangiocarcinoma) represents the second most common type of hepatobiliary cancer worldwide with an incidence of 0.35 to 2 per 100.000 annually. Currently, surgical resection is the only curative option. However, patients are not eligible for surgery if the tumor cannot be resected or the cancer has spread. For this group of patients, palliative chemotherapy is the most suited treatment option. To find out if a patient is suited for surgery, CT and MRI are performed. These imaging techniques, however, struggle to correctly identify small cancer spreads that are smaller than 1 cm. Therefore, cancer that has already spread can be found during surgery. In these cases, the tumor cannot be removed and the surgery therefore has not been of any benefit for the patient. These surgeries could be avoided by implementing a diagnostic tool with significantly higher accuracy than those currently used. Single center studies have shown that fibroblast activation protein inhibitor (FAPI) PET-CT is a very promising technique for determining metastases in tumors with prominent desmoplastic reactions, like cholangiocarcinoma. The investigators predict that implementation of preoperative FAPI PET-CT could prevent futile surgery for at least half of patients in whom intra-operative metastasized disease is found using the current work-up. Patient population Patients ≥18 years with potentially curable proximal cholangiocarcinoma (perihilar, intrahepatic and gall bladder cholangiocarcinoma) who are planned to undergo surgery based on imaging using CT thorax/abdomen and MRI of the upper abdomen. Exclusion criteria are previous abdominal surgery or chemotherapy, known pregnancy or lactation and indication for FDG PET-CT. Participation in this study Participation would mean to undergo FAPI PET-CT prior to the scheduled surgery. This will take up about half a day of the participant's time. Afterwards, participants receive questionnaires about quality of life and use of healthcare services over a period of six months in order for the researchers to be able to calculate the cost-effectiveness of additional FAPI PET-CT. Risks and benefits of participation Patients may benefit directly from \[18F\]F-FAPI PET-CT by allowing for more targeted treatment, possibly avoiding futile surgery and receiving chemotherapy or best clinical support instead, minimizing treatment delay. Avoiding futile surgery will also prevent patients from being exposed to the risks and discomfort associated with surgery: hospital stay, possibility of intraoperative or postoperative complications, postoperative pain and recovery, and mortality. Potential risks and burdens associated with this study are an extra hospital visit and a time burden of approximately half a day. Risks associated with administering FAPI are (re)bleed and infection. Both risks have a minimal probability of onset and can usually easily be treated. As \[18F\]F-FAPI is a sub-pharmacologically micro-dosed diagnostic tracer, the risk of allergic reactions is expected to be minimal and no tissue damage is expected. The burden associated with undergoing a PET-CT may be laying still for a certain time, and possible experience of claustrophobia. Possible metastases of the cancer will have to be confirmed when suspicious findings are seen on FAPI PET-CT. This could mean that participants will have to undergo additional testing such as imaging (CT or MRI) or biopsy. Undergoing FAPI PET-CT prior to surgery will result in a surgical delay when compared with the current clinical practice. The investigators do not expect this delay to influence the patient's prognosis. Follow-up will result in a time burden for patients to answer questionnaires on a two-weekly or monthly basis.