CT and MR perfusion techniques to assess diffuse liver disease
Authors: Ronot M, Leporq B, Van Beers BE, Vilgrain V.
Journal: Abdom Radiol (NY). Published online 25 Nov 2019. https://doi.org/10.1007/s00261-019-02338-z
Perfusion imaging provides quantitative information about tissue microcirculation and relies on monitoring the variation of the injected contrast medium over time with the acquisition of signal intensity/time curves. Perfusion imaging in the liver permits the quantitative extraction of physiological perfusion parameters of liver microcirculation at levels far below the spatial resolution of conventional CT and MR imaging. It enables not only malignant liver tumours assessment but also the evaluation of chronic liver diseases. Liver perfusion imaging is challenging and demanding due to the dual blood supply of the liver, the fenestration of its sinusoidal capillaries and its movement during respiration.
In this comprehensive review article, the authors describe the pathophysiology of hepatic architecture and function changes in chronic liver diseases and the characteristics of liver CT and MR perfusion imaging for chronic liver disease assessment. In addition, they analyze difficulties of liver perfusion imaging and provide useful suggestions for reliable perfusion imaging analysis.
In a normal liver, portal perfusion varies over time depending on the splanchnic venous flow and respiratory movements. When portal perfusion decreases, arterial blood supply increases (1). In patients with chronic liver disease, chronic liver injuries lead to progressive deposition of extravascular fibrous tissue that causes capillarization of the sinusoids, intrahepatic vascular resistance increase and eventually portal venous perfusion decrease (2). This decrease is only partially compensated by an increase in arterial blood supply resulting in global liver perfusion decrease.
High spatial and temporal resolution and whole liver imaging are the most important requirements that should be fulfilled in order to perform reliable liver perfusion analysis with CT and MR (3).
The main advantages of CT perfusion imaging are low cost, high spatial and temporal resolution and accurate measurement of tracer concentrations. To obtain reliable CT perfusion imaging analysis, the quality of injection and the reduction of respiratory artefacts are of utmost importance. The authors suggest contrast agent injection (350mg of iodine/mL) at a rate of 4 mL/s and slow and superficial breathing.
The most common technique used for MR perfusion imaging is dynamic contrast-enhanced imaging (DCE imaging). In order to achieve high temporal resolution and to reduce motion sensitivity, partial k-space updating methods are used combined with partial Fourier and parallel imaging. To avoid signal enhancement saturation at high concentrations, low contrast agent concentrations (0.025 mmol/kg) and/or lower injection rates are recommended. The intravoxel incoherent motion (IVIM) model of diffusion-weighted MR imaging can also be used to calculate microperfusion without contrast injection.
Analysis of hepatic perfusion is performed with a semi-quantitative and a quantitative mathematical approach. The first is based on the analysis of the shape of the signal intensity/time curves and the latter on various pharmacokinetic models, that allow calculation of various parameters such as perfusion and extraction fraction.
Temporal noise caused by respiratory motion is the main difficulty of liver perfusion imaging. The use of coronal views, registration-based motion correction methods and motion insensitive pulse sequences such as golden-angle radial sparse parallel (GRASP) can help overcome this problem (4).
Perfusion imaging in the liver is usually performed with extracellular contrast agents, which enable discrimination of patients with various stages of liver fibrosis (5) since perfusion alteration is correlated with the severity of portal hypertension and the degree of liver dysfunction (6). Recently, hepatobiliary contrast agents have been introduced, allowing quantification of both liver perfusion and hepatocyte transport function (7). In chronic liver disease, liver signal intensity decrease is observed during the hepatobiliary phase, and pharmacokinetic rate constants decrease during dynamic MR (8). It has been shown that changes in the hepatocyte transfer rates are earlier markers of liver fibrosis than perfusion parameters (9). Finally, the IVIM model of diffusion MR is another technique that enables liver perfusion evaluation. In patients with liver cirrhosis, an ADC decrease is observed compared with controls due to changes in microperfusion (10).
Overall, the authors provide an important review and enhance the latest knowledge on perfusion imaging of the liver, highlighting its complementary role in assessing the severity of cirrhosis and portal hypertension. The authors also suggest that MR perfusion with the use of hepatobiliary contrast agents is very promising since it can help in recognition of earlier stages of chronic liver disease.
References
1. Itai Y, Matsui O (1997) Blood flow and liver imaging. Radiology 202 (2):306-314. https ://doi.org/10.1148/radio logy.202.2.9015047
2. Friedman SL (2003) Liver fibrosis – from bench to bedside. J Hepatol 38 Suppl 1:S38-53
3. Pandharipande PV, Krinsky GA, Rusinek H, Lee VS (2005) Perfusion imaging of the liver: current challenges and future goals. Radiology 234 (3):661-673. doi.org/10.1148/radio l.2343031362
4. Weiss J, Ruff C, Grosse U, Grozinger G, Horger M, Nikolaou K, Gatidis S (2019) Assessment of Hepatic Perfusion Using GRASP MRI: Bringing Liver MRI on a New Level. Invest Radiol. https ://doi.org/10.1097/rli.00000 00000 00058 6
5. Ronot M, Asselah T, Paradis V,Michoux N, Dorvillius M, Baron G, Marcellin P, Van Beers BE, Vilgrain V (2010) Liver fibrosis inchronic hepatitis C virus infection: differentiating minimal from intermediate fibrosis with perfusion CT. Radiology 256 (1):135- 142. https ://doi.org/10.1148/radio l.10091 295
6. Annet L, Materne R, Danse E, Jamart J, Horsmans Y, Van Beers BE (2003) Hepatic flow parameters measured with MR imagingand Doppler US: correlations with degree of cirrhosis and portal hypertension. Radiology 229 (2):409-414. https ://doi.org/10.1148/radio l.22920 21128
7. Van Beers BE, Garteiser P, Leporq B, Rautou PE, Valla D (2017) Quantitative Imaging in Diffuse Liver Diseases. Semin Liver Dis 37 (3):243-258. doi.org/10.1055/s-0037-16036 51
8. Lagadec M, Doblas S, Giraudeau C, Ronot M, Lambert SA, FasseuM, Paradis V, Moreau R, Pastor CM, Vilgrain V, Daire JL, Van Beers BE (2015) Advanced fibrosis: Correlation betweenpharmacokinetic parameters at dynamic gadoxetate-enhanced MR imaging and hepatocyte organic anion transporter expression in rat liver. Radiology 274 (2):379-386.https ://doi.org/10.1148/radio l.14140 313
9. Leporq B, Daire JL, Pastor CM, Deltenre P, Sempoux C, Schmidt S, Van Beers BE (2018) Quantification of hepatic perfusion and hepatocyte function with dynamic gadoxetic acid enhanced MRI in patients with chronic liver disease. ClinSci (Lond) 132 (7):813-824. https ://doi.org/10.1042/cs201 71131
10. Yoon JH, Lee JM, Baek JH, Shin CI, Kiefer B, Han JK, Choi BI (2014) Evaluation of hepatic fibrosis using intravoxel incoherent motion in diffusion-weighted liver MRI. J Comput Assist Tomogr38 (1):110-116. https ://doi.org/10.1097/rct.0b013e3182a589be
Dr. Ekaterini Xinou, PhD, is a consultant radiologist at the Computed Tomography Department of ‘Theagenion’ Cancer Hospital in Thessaloniki, Greece. She is an active ESGAR member since 2005, attending regularly annual meetings and workshops. Her main interest is in abdominal and oncologic radiology, and also in swallowing disorders. She completed her thesis at the Aristotle University of Thessaloniki regarding swallowing disorders encountered during videofluoroscopy in head and neck cancer patients after chemoradiotherapy.
Comments may be sent to katxinou@otenet.gr