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E1939. CT Body Perfusion Tutorial: Whole-Liver Imaging in Normal, Cirrhotic, and Post-Transplant Livers
Authors
  1. Ankur Pandey; University of Maryland Medical Center
  2. Barton Lane; University of Maryland Medical Center
Background
Hepatic perfusion is unique due to the dual blood flow to liver, with 70-75% portal venous perfusion and 25-30% arterial perfusion. Hepatic perfusion can be evaluated using various imaging modalities, each with its own challenges. Scintigraphy offers low resolution and is limited in left hepatic lobe; US has limited reproducibility for the volumetric flow assessment along with limitations related to regional hepatic evaluation; MRI can be challenging due to motion and in patients with claustrophobia, however it probably holds promising future. CT perfusion needs further reduction of radiation dose and there is the need to address questions regarding reproducibility of results. However, CT offers the advantage of rapid assessment with easy availability.

Educational Goals / Teaching Points
The goals of this exhibit are: (1) To understand the physiology behind and physics of whole-liver CT perfusion imaging, (2) To become familiar with measured liver perfusion parameters, and (3) To recognize normal liver perfusion values, and alterations that occur with cirrhosis as well as post-liver transplantation.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
This exhibit will familiarize the audience with: - • Physiology of normal liver perfusion o Dual vascular inflow o Interplay between the dual blood supply (e.g. hepatic arterial buffer response) • Requirements for acquiring perfusion data o Multiple time-point multiphase CT o High IV contrast injection rate o Motion correction across phases • Measuring liver perfusion with CT o Parameters (ROI) to measure: ? Hepatic arterial inflow (aorta/hepatic artery) ? Portal venous inflow (portal vein) ? Liver enhancement (liver parenchyma) ? Spleen enhancement (surrogate for arterial enhancement) o Calculation methods: ? 2-slope model ? Dual input – dual compartment model ? Dual input – single compartment model • Perfusion parameters and what they mean o Mean blood flow (MBF) o Mean blood volume (MBV) o Mean transit time (MTT) o Portal venous perfusion (PVP) o Arterial liver perfusion (ALP) o Hepatic perfusion index (HPI) • Liver perfusion in normal and altered states o Normal liver o Cirrhosis o Post transplantation

Conclusion
CT perfusion has significant potential for assessment of hepatic perfusion, but it needs standardization of minimum acquisition requirements, further radiation dose reduction, and establishment of the reproducibility of results. Applications of CT Liver Perfusion include early detection and severity assessment of cirrhosis, tumor detection and classification for hepatic masses (metastases, HCC, cholangiocarcinoma and benign lesions), treatment evaluation after therapy, and post-liver transplant evaluation.