The Role of Gadoxetate (Eovist) Enhanced CT in Evaluating Cholangiocarcinoma

The purpose of this project is to evaluate the role of gadoxetate (Eovist) enhanced dual-energy CT in better evaluating perihilar cholangiocarcinoma, by exploiting the combination of the physiologic behavior of gadoxetate in liver tissue combined with the advantageous mass attenuation coefficient of Gadolinium achievable through dual energy technique. This combination of unique CT imaging sensitivity, high resolution and differential enhancement potentially allows improved visualization and detection of tumor relative to enhancing surrounding hepatic parenchyma and ductal anatomy in the hepatobiliary phase, due to the biliary excretion of the agent.

Cholangiocarcinoma is a hepatic adenocarcinoma that arises from the bile duct epithelium and is the second most prevalent liver cancer after hepatocellular carcinoma. The hilar intrahepatic variety of cholangiocarcinoma can present as an infiltrative, exophytic, or polypoid lesion. Most extra-hepatic cholangiocarcinomas are infiltrative, causing a focal stricture of the bile duct and result in proximal biliary ductal dilatation.

While magnetic resonance (MR) cholangiography is diagnostic in the majority of patients with malignant hilar strictures, evaluation is limited by spatial resolution and in some patients, the inability to have an MRI scan. Standard Multi Detector CT (MDCT) using iodinated contrast agents, on the other hand, is limited in evaluation of cholangiocarcinomas, due to the lack of consistent enhancement of the tumor with iodinated contrast.

Single-source, Dual-Energy (SSDE) Spectral MDCT utilizes a single fast switching x-ray beam source to acquire near simultaneous data sets at two different photon energies during a single acquisition. Data is acquired at 80 kilovolt peak (kVp) and 140 kVp with image reconstruction achievable as a selectable monochromatic presentation over a range of 40 - 140 kiloelectron volt (keV), typically 70-78 keV for diagnostic image presentation. At lower tube voltage, the frequency of photoelectric interactions increases exponentially and is strongly dependent on the atomic number. Therefore, for substances with higher atomic number, such as iodine and gadolinium the increased frequency of photoelectric and k-edge interactions at low tube voltage substantially increases CT attenuation, thus improving contrast. Gadolinium is further unique with k-edge attenuation at approximately 53 keV, within the available monochromatic reconstruction range, thus allowing for significant greater detectability. Additional material decomposition technique allows for unique material presentation and analysis such as gadolinium/ water pair analysis with high spatial resolution.

Dual-Energy technology is limited by the types of contrast agents currently available, all based on Iodine. Gadoxetate (Eovist) is a relatively new Gadolinium based MRI contrast agent that is capable of producing not only standard appearing MRI images in the hepatic arterial and portal venous phases, but also provides an opportunity to better visualize the bile ducts and liver parenchyma as it is excreted by the liver into the biliary system during the hepatobiliary phase.

This pilot project aims to address a long-term pitfall in the imaging of cholangiocarcinomas, by providing higher resolution delineation of these often infiltrative tumors on single-source, Dual-Energy Spectral MDCT, capitalizing on improved spatial resolution achievable with MDCT compared to MRI and at the same time producing a non-invasive CT cholangiogram to aid in accurate diagnosis and treatment planning of cholangiocarcinoma, particularly, the hilar variety.