Imaging Techniques for Partial Grafting

Multidetector Computed Tomography, Computed Tomography Angiography, and Computed Tomography Cholangiography

Hepatic CTA is comparable to conventional angiography for evaluation of arterial anatomy and can be performed on a 16-, 64-, 128- or higher detector row MDCT scanner. The optimal protocol includes a noncontrast sequence and postcontrast sequences in the arterial, portal venous, and venous phases. The noncontrast sequence can be acquired with 5-mm collimation thickness, arterial phase with 0.5- to 1.25-mm slice collimation at peak arterial enhancement, and portal venous and venous phases with 1- to 2.5-mm collimation. Three-dimensional (3-D) hepatic arteriograms, portal venograms, and hepatic venograms can then be rendered with any one of several types of commercially available software.

CT cholangiography can be performed using intravenously administered biliary contrast agents such as iodipamide meglumine (Cholografin), which can result in excellent depiction of the bile ducts. This is usually performed 15 minutes after the administration of the biliary contrast agent. The source images are then reconstructed and easily visualized by 3-D rendering.

Magnetic Resonance Imaging

MRI provides accurate evaluation of the liver parenchyma and detection of focal lesions and can be performed on a 1.5- or 3-T magnetic resonance (MR) magnet with a torso phased-array coil. Breath-hold axial T1-weighted in-phase and opposed-phase gradient-echo and T2-weighted images are acquired to assess for diffuse liver disease, particularly steatosis, and to rule out focal lesions that would render the allograft unacceptable for transplantation.

Magnetic Resonance Angiography

MRA can be performed on the same 1.5- or 3-T MR magnet. Intravenous gadolinium contrast is administered, and a 3-D gradient-echo sequence is usually acquired with generation of subtraction arteriograms and venograms. MRA provides accurate assessment of the hepatic vasculature despite poorer definition of smaller vessels because of larger slice thicknesses and increased motion degradation from longer acquisition times. The performance of MRA has been demonstrated to be comparable to CTA for evaluation of hepatic vascular anatomy in living donors.

Magnetic Resonance Cholangiopancreatography

MRCP can also be performed on the same 1.5- or 3-T MR magnet, and images can be obtained without contrast using breath-hold, heavily T2-weighted, half-Fourier rapid acquisition with relaxation enhancement sequence, usually in either the axial/coronal planes with contiguous thin sections (3 to 5 mm) or rotating (coronal and off-coronal) slabs of variable thickness (3, 5, 7, and 10 cm). The vertical axis of the common hepatic duct is used as the center of rotation in coronal/off-coronal thick slabs. Alternatively, contrast-enhanced MR cholangiography using hepatobiliary-specific agents such as gadoxetate disodium (Eovist) or gadobenate dimeglumine (MultiHance) can be performed for higher resolution images using a 3-D gradient-echo sequence. This also leads to better image quality because of shorter acquisition times and better patient cooperation.