Brain Imaging and Hepatic Encephalopathy

Abstract

KEY WORDSHepatic encephalopathy; Brain imaging; Magnetic resonance imaging; Magnetic resonance spectroscopy, Computed tomography, Single photon emission computed tomography; Positron emission tomography. 2 SYNOPSISNovel imaging techniques are allowing hepatologists to investigate the structural and functional neuropathology of hepatic encephalopathy (HE) in greater detail but only limited techniques are applicable to the clinic. Computed tomography and magnetic resonance imaging (MRI) can rule out other diagnoses and in the case of MRI, give certain key diagnostic features in widely available sequences. While increased brain water content is a hallmark of HE, the localisation of low-grade cerebral edema, the extent of regional swelling or atrophy and the different functional characteristics of affected brain regions continue to be debated. More specialised volumetric, diffusion-tensor, magnetization transfer, functional magnetic resonance imaging and magnetic resonance spectroscopy, in conjunction with positron emission tomography continue to enrich the investigative findings in HE. Nevertheless an internationally accepted diagnostic framework that includes an objective imaging test to replace or augment psychometry remains elusive. Quantitative MRI is likely to be the best candidate to become such a test and the utility of MR and nuclear medical techniques to the clinic and results from recent research are described in this article.3

Brain edema: a valid endpoint for measuring hepatic encephalopathy?

“…To date several methods have been used to measure brain edema (i.e. brain water content) either directly or indirectly: 1) Direct/absolute value of the amount of water in the brain can be measured through; i) dry/wet weight technique (Marmarou et al 1978), ii) specific gravity method (Marmarou et al 1978;Hayazaki et al 1995) and iii) brain water mapping using magnetic resonance imaging (MRI) (Shah et al 2003(Shah et al , 2008Neeb et al 2006;Dam et al 2015); 2) Indirect/relative information regarding the content of water in the brain can be calculated using several advanced MRI techniques; i) magnetization transfer (MT), ii) diffusion weighted or tensor imaging (DWI or DTI) and iii) fast fluidattenuated inversion recovery (FLAIR) ( Table 1) (Häussinger et al 1994;Córdoba et al 2001;Spahr et al 2002;McPhail et al 2012;Braissant et al 2013;Cudalbu 2013). The dry/wet weight and specific gravity methods are performed ex-vivo, using dissected tissue from sacrificed animals.…”

Brain edema in acute liver failure and chronic liver disease: Similarities and differences

“…However, with more advanced, highly sensitive MRI T 2 -weighted sequences (ex. diffusion-weighted imaging (DWI) and magnetization transfer ration (MTR)), there is increasing evidence that brain edema is present in CLD patients (Córdoba et al, 2001, Häussinger, 2006, Kale et al, 2006, McPhail et al, 2012, Rovira et al, 2002, Shah et al, 2008and Sugimoto et al, 2008. MRI provides a good contrast between soft tissues, based on their water content.…”

“…MRI provides a good contrast between soft tissues, based on their water content. It can assess water diffusion and differentiate between free water and macromolecule-bound water (McPhail et al, 2012). However, the high-operating cost of these sensitive imaging techniques limits their utilisation in clinical practice as a diagnostic device and therefore remains a research tool.…”

1H and 31P magnetic resonance spectroscopy in a rat model of chronic hepatic encephalopathy: in vivo longitudinal measurements of brain energy metabolism

“…High magnetic fields enable the detection of additional brain metabolites and thus the pathogenic mechanisms involved in HE can be more accurately assessed. High field proton ( 1 H) MRS, characterized by its excellent spectral resolution, provides information about amino acid disturbances, alterations in neurotransmitters, oxidative stress, osmoregulation, myelination/ cell proliferation and disturbances in cerebral energy metabolism (McPhail et al 2012;Cudalbu 2013). Phosphorus ( 31 P) MRS is very useful for the study of in vivo energy metabolism by providing information on the energy status of phosphate compounds and phospholipid metabolism.…”