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.

Inclusion Criteria:

1. Subjects will be adult (age 19 or older) with suspected cholangiocarcinoma of the
liver.

2. Subject must be able to provide a written informed consent.

3. Subject will be scheduled for gadoxetate contrast enhanced MRI scan of the liver
(obtained as part of usual clinical practice).

Exclusion Criteria:

1. Standard MRI safety screening criteria will be employed, and subject will be excluded
if any contraindications to undergo MRI are met.

2. Subjects with metallic biliary stents or multiple peripancreatic surgical clips on
abdominal MDCT will be excluded.

3. Subjects on hemodialysis or with glomerular filtration rate (GFR) less than 30 will
be excluded.

4. Subjects will not be excluded on the basis of gender, race, ethnicity, or religion.

5. Subject may not be pregnant or lactating.