Resting-state functional magnetic resonance imaging in hepatic encephalopathy: current status and perspectives

Association Between MRI-Assessed Patterns of Connectome Gradient and Gene-Expression Profiles in Two Independent Patient Cohorts With Hepatitis B Virus-Related Cirrhosis

BACKGROUND

Patients with hepatitis B virus-related cirrhosis (HBV-RC) exhibit progressive neurologic dysfunction from primary sensorimotor to high-order cognition, as their disease advances. However, the exact neurobiologic mechanisms and the potential association with gene-expression profiles are not fully understood.

PURPOSE

To explore the hierarchical disorganization in the large-scale functional connectomes in HBV-RC patients and to investigate its potential underlying molecular basis.

STUDY TYPE

Prospective.

POPULATION

Fifty HBV-RC patients and 40 controls (Cohort 1) and 30 HBV-RC patients and 38 controls (Cohort 2).

FIELD STRENGTH/SEQUENCE

Gradient-echo echo-planar and fast field echo sequences at 3.0 T (Cohort 1) and 1.5 T (Cohort 2).

ASSESSMENT

Data were processed with Dpabi and the BrainSpace package. Gradient scores were evaluated from global to voxel level. Cognitive measurement and patients grouping were based on psychometric hepatic encephalopathy scores. The whole-brain microarray-based gene-expression data were obtained from the AIBS website.

STATISTICAL TESTS

One-way ANOVA, chi-square test, two-sample t-test, Kruskal-Wallis test, Spearman's correlation coefficient (r), the gaussian random field correction, false discovery rate (FDR) correction and the Bonferroni correction. Significance level: P < 0.05.

RESULTS

HBV-RC patients exhibited a robust and replicable connectome gradient dysfunction, which was significantly associated with the gene-expression profiles in both cohorts (r = 0.52 and r = 0.56, respectively). The most correlated genes were enriched in γ-aminobutyric acid (GABA) and GABA-related receptor genes (FDR q value <0.05). Moreover, the connectome gradient dysfunction at network level observed in HBV-RC patients correlated with their poor cognitive performance (Cohort 2: visual network, r = -0.56; subcortical network, r = 0.66; frontoparietal network, r = 0.51).

DATA CONCLUSION

HBV-RC patients had hierarchical disorganization in the large-scale functional connectomes, which may underly their cognitive impairment. In addition, we showed the potential molecular mechanism of the connectome gradient dysfunction, which suggested the importance of GABA and GABA-related receptor genes.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Functional MRI for Acute Covert Consciousness: Emerging Data and Implementation Case Series

Although research studies have begun to demonstrate relationships between disorders of consciousness and brain network biomarkers, there are limited data on the practical aspects of obtaining such network biomarkers to potentially guide care. As the state of knowledge continues to evolve, guidelines from professional societies such as the American and European Academies of Neurology and many experts have advocated that the risk-benefit ratio for the assessment of network biomarkers has begun to favor their application toward potentially detecting covert consciousness. Given the lack of detailed operationalization guidance and the context of the ethical implications, herein we offer a roadmap based on local institutional experience with the implementation of functional MRI in the neonatal, pediatric, and adult intensive care units of our local government-supported health system. We provide a case-based demonstrative approach intended to review the current literature and to assist with the initiation of such services at other facilities.

Identifying Mild Hepatic Encephalopathy Based on Multi-Layer Modular Algorithm and Machine Learning

Hepatic encephalopathy (HE) is a neurocognitive dysfunction based on metabolic disorders caused by severe liver disease, which has a high one-year mortality. Mild hepatic encephalopathy (MHE) has a high risk of converting to overt HE, and thus the accurate identification of MHE from cirrhosis with no HE (noHE) is of great significance in reducing mortality. Previously, most studies focused on studying abnormality in the static brain networks of MHE to find biomarkers. In this study, we aimed to use multi-layer modular algorithm to study abnormality in dynamic graph properties of brain network in MHE patients and construct a machine learning model to identify individual MHE from noHE. Here, a time length of 500-second resting-state functional MRI data were collected from 41 healthy subjects, 32 noHE patients and 30 MHE patients. Multi-layer modular algorithm was performed on dynamic brain functional connectivity graph. The connection-stability score was used to characterize the loyalty in each brain network module. Nodal flexibility, cohesion and disjointness were calculated to describe how the node changes the network affiliation across time. Results show that significant differences between MHE and noHE were found merely in nodal disjointness in higher cognitive network modules (ventral attention, fronto-parietal, default mode networks) and these abnormalities were associated with the decline in patients’ attention and visual memory function evaluated by Digit Symbol Test. Finally, feature extraction from node disjointness with the support vector machine classifier showed an accuracy of 88.71% in discrimination of MHE from noHE, which was verified by different window sizes, modular partition parameters and machine learning parameters. All these results show that abnormal nodal disjointness in higher cognitive networks during brain network evolution can be seemed as a biomarker for identification of MHE, which help us understand the disease mechanism of MHE at a fine scale.

Delirium

Delirium, a syndrome characterized by an acute change in attention, awareness and cognition, is caused by a medical condition that cannot be better explained by a pre-existing neurocognitive disorder. Multiple predisposing factors (for example, pre-existing cognitive impairment) and precipitating factors (for example, urinary tract infection) for delirium have been described, with most patients having both types. Because multiple factors are implicated in the aetiology of delirium, there are likely several neurobiological processes that contribute to delirium pathogenesis, including neuroinflammation, brain vascular dysfunction, altered brain metabolism, neurotransmitter imbalance and impaired neuronal network connectivity. The Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) is the most commonly used diagnostic system upon which a reference standard diagnosis is made, although many other delirium screening tools have been developed given the impracticality of using the DSM-5 in many settings. Pharmacological treatments for delirium (such as antipsychotic drugs) are not effective, reflecting substantial gaps in our understanding of its pathophysiology. Currently, the best management strategies are multidomain interventions that focus on treating precipitating conditions, medication review, managing distress, mitigating complications and maintaining engagement to environmental issues. The effective implementation of delirium detection, treatment and prevention strategies remains a major challenge for health-care organizations globally.

Disturbance of thalamic metabolism and its association with regional neural dysfunction and cognitive impairment in minimal hepatic encephalopathy

PURPOSE

To conduct the first investigation on thalamic metabolic alterations in minimal hepatic encephalopathy (MHE) and elucidate their association with intrinsic neural activity change and cognitive dysfunction.

METHODS

Thirty-eight cirrhotic patients [18 with MHE, 20 without MHE (NHE)] and 21 healthy controls (HC) were included, all of whom underwent ¹H-magnetic resonance spectroscopy, resting-state functional magnetic resonance imaging (fMRI), as well as cognitive assessment based on the Psychometric Hepatic Encephalopathy Score (PHES). Metabolite ratios in the thalamus were measured, including N-acetyl aspartate (NAA)/creatine (Cr), glutamate plus glutamine (Glx)/Cr, choline (Cho)/Cr, and myo-inositol (mI)/Cr. Intrinsic neural activity was evaluated based on frequency-specific amplitude of low-frequency fluctuations (ALFF) using fMRI signals.

RESULTS

MHE patients showed an increase in Glx/Cr and a decrease in Cho/Cr and mI/Cr, compared with HC. These changes were aggravated from NHE to MHE. Cho/Cr and mI/Cr were positively correlated with regional ALFF derived from the frequency-specific band (0.01-0.027 Hz) and PHES. Receiver operating characteristic curve analysis showed that Cho/Cr and mI/Cr measurements exhibited moderate discrimination ability between NHE and MHE.

CONCLUSION

Our findings provide evidence that MHE is associated with disturbed metabolism in the thalamus, which may contribute to the altered neural activity and underlie the mechanisms of cognitive impairments. MRS measurements in the thalamus could serve as the potential biomarker for diagnosing MHE among cirrhotic patients.

Chemotherapy-induced brain changes in breast cancer survivors: evaluation with multimodality magnetic resonance imaging

Chemotherapy related cognitive impairments are common in breast cancer patients undergoing chemotherapy. These cognitive dysfunctions are mainly attributable to chemotherapy related brain structural and functional alterations. Multimodality magnetic resonance imaging (MRI) can reveal brain gray matter volume loss, white matter microstructural disruption, reduced gray matter density, impaired cerebral blood flow and brain structural and functional connection networks at both local and global levels. This review outlines the potential applications of multimodality MR imaging techniques in chemotherapy induced cognitive deficit in breast cancer survivors and provides future research perspective in this field.

Donepezil's Effects on Brain Functions of Patients With Alzheimer Disease: A Regional Homogeneity Study Based on Resting-State Functional Magnetic Resonance Imaging

PURPOSE

Donepezil is known to increase cholinergic synaptic transmission in Alzheimer disease (AD), although how it affects cortical brain activity and how it consequently affects brain functions need further clarification. To investigate the therapeutic mechanism of donepezil underlying its effect on brain function, regional homogeneity (ReHo) technology was used in this study.

PATIENTS AND METHODS

This study included 11 mild-to-moderate AD patients who completed 24 weeks of donepezil treatment and 11 matched healthy controls. All participants finished neuropsychological assessment and resting-state functional magnetic resonance imaging scanning to compare whole-brain ReHo before and after donepezil treatment.

RESULTS

Significantly decreased Alzheimer's Disease Assessment Scale-Cognitive Subscale scores (P = 0.010) and increased Mini-Mental State Examination scores (P = 0.043) were observed in the AD patients. In addition, in the right gyrus rectus (P = 0.021), right precentral gyrus (P = 0.026), and left superior temporal gyrus (P = 0.043) of the AD patients, decreased ReHo was exhibited.

CONCLUSION

Donepezil-mediated improvement of cognitive function in AD patients is linked to spontaneous brain activities of the right gyrus rectus, right precentral gyrus, and left superior temporal gyrus, which could be used as potential biomarkers for monitoring the therapeutic effect of donepezil.

The short-term effect of liver transplantation on the low-frequency fluctuation of brain activity in cirrhotic patients with and without overt hepatic encephalopathy

Previous neuropsychological studies have demonstrated that liver transplantation (LT) is an effective method for improving the cognitive function of cirrhotic patients. However, the neural basis underlying the effects of LT is still unclear. Neuroimaging studies investigating changes in brain structures or functional networks mainly focus on patients without overt hepatic encephalopathy (HE). In this study, we recruited patients with and without overt HE and studied alterations in resting-state brain activity by quantizing the amplitude of low-frequency fluctuation (ALFF) before and 1 month after LT to study the short-term effect of LT in each group. Neuropsychological analyses indicated significant improvement of cognitive function in both groups. ALFF analysis showed that the brain activity in regions regulating motor function, vision, attention, and working memory were restored in both groups, reflecting the neuroplasticity of the brain. However, some persistent impairments and new-onset impairments in other regions related to these cognitive functions were observed in each group. Between-group comparison showed that although cognitive performance improved in both groups, the specific neural basis of LT in each group was different. The significant correlations of altered brain activity in regions showing LT and group effect with altered performance in neuropsychological and biochemical tests suggest a possible neuroimaging marker for the monitoring of short-term recovery of HE and the difference in individual recovery of cognitive performance. The findings in the present study help us further understand the neural effect of LT in patients with and without overt HE.

Multimodal MR imaging in hepatic encephalopathy: state of the art

Hepatic encephalopathy (HE) is a neurological or neuropsychological complication due to liver failure or portosystemic shunting. The clinical manifestation is highly variable, which can exhibit mild cognitive or motor impairment initially, or gradually progress to a coma, even death, without treatment. Neuroimaging plays a critical role in uncovering the neural mechanism of HE. In particular, multimodality MR imaging is able to assess both structural and functional derangements of the brain with HE in focal or neural network perspectives. In recent years, there has been rapid development in novel MR technologies and applications to investigate the pathophysiological mechanism of HE. Therefore, it is necessary to update the latest MR findings regarding HE by use of multimodality MRI to refine and deepen our understanding of the neural traits in HE. Herein, this review highlights the latest MR imaging findings in HE to refresh our understanding of MRI application in HE.

Abnormalities of voxel-based whole-brain functional connectivity patterns predict the progression of hepatic encephalopathy

Resting state functional magnetic resonance imaging (fMRI) is an important tool for understanding the functional reorganization of the brain in cirrhotic patients. Previous studies revealed that functional integration failure were observed in the whole brain. However, the whole-brain functional connectivity analysis methods used in these studies have the limitation that the result relied on a priori definition of network nodes. Moreover, the utility of resting state functional connectivity in the diagnosis and prediction of hepatic encephalopathy (HE) is not well examined. In this study, we recruited 87 subjects consisting of patients without HE, with HE, and healthy controls. We employed a voxel-based, unbiased functional connectivity analysis and the functional connectivity density (FCD) metric to precisely study abnormalities in the intrinsic functional connectivity patterns of cirrhotic patients. FCD analyses showed that hub regions in the brain were less topologically important in cirrhotic patients, whereas non-hub regions became topologically important in the disease state. This trend was more apparent with the progression of cirrhosis severity. Most FCD abnormalities were associated with deficits in psychomotor function, executive control, or visual-spatial abilities (p < 0.05, AlphaSim corrected). FCD alterations in the left inferior parietal lobe and the right hippocampal gyrus/parahippocampal gyrus were significantly correlated with cognitive ability and blood ammonia level (p < 0.05, AlphaSim corrected). A pattern classification analysis indicated that whole-brain FCD differences distinguished cirrhotic patients from healthy controls and predicted disease severity with high accuracies. These findings suggest that voxel-based FCD analysis may be clinically important for the diagnosis and prediction of HE.

Advancing the Neurophysiological Understanding of Delirium

Delirium is a common problem associated with substantial morbidity and increased mortality. However, the brain dysfunction that leads some individuals to develop delirium in response to stressors is unclear. In this article, we briefly review the neurophysiologic literature characterizing the changes in brain function that occur in delirium, and in other cognitive disorders such as Alzheimer's disease. Based on this literature, we propose a conceptual model for delirium. We propose that delirium results from a breakdown of brain function in individuals with impairments in brain connectivity and brain plasticity exposed to a stressor. The validity of this conceptual model can be tested using Transcranial Magnetic Stimulation in combination with Electroencephalography, and, if accurate, could lead to the development of biomarkers for delirium risk in individual patients. This model could also be used to guide interventions to decrease the risk of cerebral dysfunction in patients preoperatively, and facilitate recovery in patients during or after an episode of delirium.

The brain following transjugular intrahepatic portosystemic shunt: the perspective from neuroimaging

Hepatic encephalopathy (HE) is a common complication after implantation of a transjugular intrahepatic portosystemic shunt (TIPS). Neuroimaging offers a variety of techniques for non-invasive evaluation of alterations in metabolism, as well as structural and functional changes of the brain in patients after TIPS implantation. In this article, we review the epidemiology and pathophysiology of post-TIPS HE. The potential of neuroimaging including positron emission tomography and multimodality magnetic resonance imaging to investigate the pathophysiology of post-TIPS HE is presented. We also give a perspective on the role of neuroimaging in this field.

Role of local and distant functional connectivity density in the development of minimal hepatic encephalopathy

The progression of functional connectivity (FC) patterns from non-hepatic encephalopathy (non-HE) to minimal HE (MHE) is not well known. This resting-state functional magnetic resonance imaging (rs-fMRI) study investigated the evolution of intrinsic FC patterns from non-HE to MHE. A total of 103 cirrhotic patients (MHE, n = 34 and non-HE, n = 69) and 103 healthy controls underwent rs-fMRI scanning. Maps of distant and local FC density (dFCD and lFCD, respectively) were compared among MHE, non-HE, and healthy control groups. Decreased lFCD in anterior cingulate cortex, pre- and postcentral gyri, cuneus, lingual gyrus, and putamen was observed in both MHE and non-HE patients relative to controls. There was no difference in lFCD between MHE and non-HE groups. The latter showed decreased dFCD in inferior parietal lobule, cuneus, and medial frontal cortex relative to controls; however, MHE patients showed decreased dFCD in frontal and parietal cortices as well as increased dFCD in thalamus and caudate head relative to control and non-HE groups. Abnormal FCD values in some regions correlated with MHE patients’ neuropsychological performance. In conclusion, lFCD and dFCD were perturbed in MHE. Impaired dFCD in regions within the cortico-striato-thalamic circuit may be more closely associated with the development of MHE.

PET and MR imaging of neuroinflammation in hepatic encephalopathy

Neurological or psychiatric abnormalities associated with hepatic encephalopathy (HE) range from subclinical findings to coma. HE is commonly accompanied with the accumulation of toxic substances in bloodstream. The toxicity effect of hyperammonemia on astrocyte, such as the alteration in neurotransmission, oxidative stress, astrocyte swelling, is considered as an important factor in the pathogenesis of HE. Besides, neuroinflammation has captured more attention in the process of HE, but the mechanism of neuroinflammation leading to HE remains unclear. Molecular imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) targeting activated microglia and/ or other mediators appear to be promising noninvasive approaches to assess HE. This review focuses on novel imaging and therapy strategies of neuroinflammation in HE.

Default mode network functional connectivity: a promising biomarker for diagnosing minimal hepatic encephalopathy: CONSORT-compliant article

To investigate the contribution of brain default mode network (DMN) in the early diagnosis of the minimal hepatic encephalopathy (MHE), the mildest form of HE from cirrhotic patients by using resting-state functional magnetic resonance imaging (rs-fMRI). This study was approved by the local ethical committee, and a written informed consent was obtained from each participant. A total of 103 cirrhotic patients (34 MHE, 69 non-HE) and 103 matched healthy controls underwent rs-fMRI scanning. The DMN correlation map was acquired by using unbiased seed-based functional connectivity analysis and compared among MHE patients, non-HE patients, and healthy controls with analysis of variance tests. Pearson correlation analysis was performed between the abnormal DMN connectivity and neuropsychological performances. Receiver operator characteristic (ROC) analysis was used to evaluate the contribution of DMN connectivity strength in the differential diagnosis between MHE and non-HE. Compared with the healthy controls, MHE and non-HE patients showed decreased DMN connectivity in medial prefrontal cortex (MPFC), left superior frontal gyrus (SFG), left temporal lobe, and bilateral middle temporal gyri (MTG). The MHE patients showed even more decreased connectivity in MPFC, left SFG, and right MTG when compared with non-HE patients. Pearson correlation analyses revealed that the decreased connectivity strength of some DMN regions correlated with patients' neuropsychological tests scores. Connectivity strength of the MPFC, right MTG, and left SFG could differentiate MHE from non-HE, of which the MPFC had the highest effectiveness (sensitivity = 81.5%, specificity = 70.4%). Cirrhotic patients had gradually reduced DMN functional connectivity from non-HE patients to MHE patients. DMN function, especially the MPFC, might be a useful imaging marker for differentiating MHE from cirrhotic patients.