**Core Concept**
Cholangiocarcinoma is a malignancy arising from the bile ducts, with key diagnostic and staging tools based on imaging and clinical evaluation. Accurate staging is essential for determining treatment and prognosis, and it relies on validated imaging modalities.

**Why the Correct Answer is Right**
Staging of cholangiocarcinoma is **not** done by PET CT. While PET CT may show metabolic activity, it is not the standard for staging this tumor. The **current gold standard** is **CECT (Contrast-Enhanced Computed Tomography)** or **MRCP (Magnetic Resonance Cholangiopancreatography)**, which evaluates biliary tree involvement and local spread. PET CT is primarily used in select cases for detecting metastases, especially in advanced or suspected recurrent disease, but **not as primary staging**. Therefore, stating that staging is done by PET CT is **false**.

**Why Each Wrong Option is Incorrect**
Option A: MRCP is a non-invasive, highly sensitive imaging modality for visualizing biliary anatomy and detecting obstructive lesions. It is **correctly used** in initial evaluation of cholangiocarcinoma.
Option C: CECT is widely used for staging due to its ability to assess tumor size, local invasion, and lymph node involvement. It is a **standard tool** in clinical practice.
Option D: Choledochal cysts are associated with increased risk of biliary tract malignancies, including cholangiocarcinoma, due to chronic inflammation and altered bile flow. This is a **well-established risk factor**.

**Clinical Pearl / High-Yield Fact**
In cholangiocarcinoma, **MRCP is preferred over CECT** for initial evaluation due to superior visualization of biliary anatomy. PET CT is **not** used for primary staging and should be avoided in this context.

✓ Correct Answer: B. Staging is done by PET CT