The correlation between cerebral glucose metabolism and benzodiazepine receptor density in the acute vegetative state

Evaluation of consciousness rehabilitation via neuroimaging methods

Accurate evaluation of patients with disorders of consciousness (DoC) is crucial for personalized treatment. However, misdiagnosis remains a serious issue. Neuroimaging methods could observe the conscious activity in patients who have no evidence of consciousness in behavior, and provide objective and quantitative indexes to assist doctors in their diagnosis. In the review, we discussed the current research based on the evaluation of consciousness rehabilitation after DoC using EEG, fMRI, PET, and fNIRS, as well as the advantages and limitations of each method. Nowadays single-modal neuroimaging can no longer meet the researchers` demand. Considering both spatial and temporal resolution, recent studies have attempted to focus on the multi-modal method which can enhance the capability of neuroimaging methods in the evaluation of DoC. As neuroimaging devices become wireless, integrated, and portable, multi-modal neuroimaging methods will drive new advancements in brain science research.

Mapping the Unconscious Brain: Insights From Advanced Neuroimaging

SUMMARY

Recent advances in neuroimaging have been a preeminent factor in the scientific effort to unravel mechanisms of conscious awareness and the pathophysiology of disorders of consciousness. In the first part of this review, we selectively discuss operational models of consciousness, the biophysical signal that is measured using different imaging modalities, and knowledge on disorders of consciousness that has been gleaned with each neuroimaging modality. Techniques considered include diffusion-weighted imaging, diffusion tensor imaging, different types of nuclear medicine imaging, functional MRI, magnetoencephalography, and the combined transcranial magnetic stimulation-electroencephalography approach. In the second part of this article, we provide an overview of how advanced neuroimaging can be leveraged to support neurological prognostication, the use of machine learning to process high-dimensional imaging data, potential applications in clinical practice, and future directions.

Organ Transplantation in Iran; Current State and Challenges with a View on Ethical Consideration

Organ transplantation is a new issue in medical science. It is an important achievement and a sign of the progression and ability of medical centers around the world. Governments, populations, the medical community and people involved in culture, art, and media all have a decisive role in the culture of organ donation, which is the only way to guarantee that the healthy organs of a brain-dead person can continue to work and save the lives of people in need of organ transplantation. The brain death phenomenon and its possible application in organ transplantation, while offering new hope for the salvation of a number of patients, has led to many ethical, cultural, and legal issues. Ethical issues in organ transplantation are very complicated due to many social factors such as religion, culture, and traditions of the affected communities. The ethical and legal points of removing organs from the body of a living or cadaveric source, the definition of brain death, the moral and legal conditions of the donor and the recipient, and the financial relationship between them and many others, are all critical issues in organ transplantation. While there may be no available explicit solution to these issues, they should be rigorously considered by the experts. Efforts to systematically eliminate barriers and solve problems in organ transplantation, can not only reduce the costs of maintaining brain-dead patients and encourage patients that need organ transplantation but can also prevent immoral and illegal activities. In this paper, we have reviewed the most important and current challenges in organ transplantation with a view to the ethical considerations, and we have suggested some strategies to extend it in Iran.

Early prognostication markers in cardiac arrest patients treated with hypothermia

BACKGROUND AND PURPOSE

Established prognostication markers, such as clinical findings, electroencephalography (EEG) and biochemical markers, used by clinicians to predict neurological outcome after cardiac arrest (CA) are altered under therapeutic hypothermia (TH) conditions and their validity remains uncertain.

METHODS

MEDLINE and Embase were searched for evidence on the current standards for neurological outcome prediction for out-of-hospital CA patients treated with TH and the validity of a wide range of prognostication markers. Relevant studies that suggested one or several established biomarkers and multimodal approaches for prognostication are included and reviewed.

RESULTS

Whilst the prognostic accuracy of various tests after TH has been questioned, pupillary light reflexes and somatosensory evoked potentials are still strongly associated with negative outcome for early prognostication. Increasingly, EEG background activity has also been identified as a valid predictor for outcome after 72 h after CA and a preferred prognostic method in clinical settings. Neuroimaging techniques, such as magnetic resonance imaging and computed tomography, can identify functional and structural brain injury but are not readily available at the patient's bedside because of limited availability and high costs.

CONCLUSIONS

A multimodal algorithm composed of neurological examination, EEG-based quantitative testing and somatosensory evoked potentials, in conjunction with newer magnetic resonance imaging sequences, if available, holds promise for accurate prognostication in CA patients treated with TH. In order to avoid premature withdrawal of care, prognostication should be performed more than 72 h after CA.

GABAA receptor deficits predict recovery in patients with disorders of consciousness: A preliminary multimodal [(11) C]Flumazenil PET and fMRI study

OBJECTIVES

Disorders of consciousness (DoC)-that is, unresponsive wakefulness syndrome/vegetative state and minimally conscious state-are debilitating conditions for which no reliable markers of consciousness recovery have yet been identified. Evidence points to the GABAergic system being altered in DoC, making it a potential target as such a marker.

EXPERIMENTAL DESIGN

In our preliminary study, we used [(11) C]Flumazenil positron emission tomography to establish global GABAA receptor binding potential values and the local-to-global (LTG) ratio of these for specific regions. These values were then compared between DoC patients and healthy controls. In addition, they were correlated with behavioral improvements for the patients between the time of scanning and 3 months later. Functional magnetic resonance imaging resting-state functional connectivity was also calculated and the same comparisons made.

PRINCIPAL OBSERVATIONS

lobal GABAA receptor binding was reduced in DoC, as was the LTG ratio in specifically the supragenual anterior cingulate. Both of these measures correlated with behavioral improvement after 3 months. In contrast to these measures of GABAA receptor binding, functional connectivity did not correlate with behavioral improvement.

CONCLUSIONS

Our preliminary findings point toward GABAA receptor binding being a marker of consciousness recovery in DoC.

Resting brain activity in disorders of consciousness: a systematic review and meta-analysis

OBJECTIVE

To quantitatively synthesize results from neuroimaging studies that evaluated patterns of resting functional activity in patients with disorders of consciousness (DOC).

METHODS

We performed a systematic review and coordinate-based meta-analysis of studies published up to May 2014. Studies were included if they compared resting-state functional neuroimaging data acquired in patients with DOC (coma, minimally conscious state, emergence from minimally conscious state, or vegetative state) with a group of healthy controls. Coordinate-based meta-analysis was performed in studies that included voxel-based comparisons at the whole-brain level and if analysis was accomplished with data-driven approaches.

RESULTS

A total of 36 studies (687 patients, 637 healthy controls) were included in the systematic review. Reported DOC were vegetative state (43.2%), coma (23.4%), minimally conscious state (22.8%), and emergence from minimally conscious state (1.6%); the most common etiologies of DOC were traumatic brain injury (37.7%) and anoxic brain injury (36.9%). Functional neuroimaging was accomplished using fMRI (16 studies), PET (15 studies), SPECT (4 studies), and both PET and SPECT in one study. Meta-analysis in 13 studies (272 patients, 259 healthy controls) revealed consistently reduced activity in patients with DOC in bilateral medial dorsal nucleus of the thalamus, left cingulate, posterior cingulate, precuneus, and middle frontal and medial temporal gyri.

CONCLUSIONS

In patients with DOC evaluated in the resting state, functional neuroimaging indicates markedly reduced activity within midline cortical and subcortical sites, anatomical structures that have been linked to the default-mode network. Studies are needed to determine the relation between activation (and coherence) within these structures and the emergence of conscious awareness.

PET in coma and in vegetative state

Advances in resuscitation and critical care management have resulted in the survival of many patients despite severe brain damage. These patients may remain in coma or in vegetative state. The probability of recovery of conscious function is dependent on the extent of structural brain damage, which is difficult to assess by clinical, laboratory or functional tests. Positron emission tomography (PET) of 18F-fluordeoxyglucose (FDG) can be used to investigate metabolic and functional impairment of the brain. In acute vegetative state (AVS, duration <1 month), overall glucose utilization was significantly reduced in comparison with age-matched controls. In a few cases with locked-in syndrome, cortical metabolism was in the normal range. 11C-Flumazenil (FMZ) measures the density of benzodiazepine receptors (BZRs) and thereby furnishes an estimate of neuronal integrity. PET with this tracer demonstrated a considerable reduction in BZRs in cortical areas, but indicated that the cerebellum was spared from neuronal loss. The comparison of FDG- and FMZ-PET findings in AVS demonstrates that alterations of cerebral glucose consumption do not represent mere functional inactivation, but also irreversible structural damage. In some cases with minimally conscious state, auditory stimuli with emotional valence induced more brain activation (investigated by H215O-PET) than meaningless noise; such studies can be used to detect residual cortical function. To improve prognostication of chances for recovery, a combination of functional activation studies and assessment of the extent of neuronal damage might be the optimal procedure and should be tested in larger cohorts of patients with comatose states of different severity.

Focal neuronal damage in patients with neuropsychological impairment after diffuse traumatic brain injury: evaluation using ¹¹C-flumazenil positron emission tomography with statistical image analysis

This study was conducted to identify the regional neuronal damage occurring in patients with neuropsychological impairment following diffuse traumatic brain injury (TBI) compared with normal control subjects. In addition, measures of the neuropsychological tests were correlated with regional ¹¹C-flumazenil (FMZ) binding potential (BP) reductions to clarify the relationship between cognitive impairment and regional neuronal damage. We performed ¹¹C-flumazenil positron emission tomography (FMZ-PET) studies using three-dimensional stereotactic surface projection (3D-SSP) statistical image analysis in eight diffuse axonal injury (DAI) patients (mean age 29.1 ± 11.1 years, range 19-46 years). All patients underwent assessment with the Wechsler Adult Intellectual Scale-Third Edition (WAIS-III) to evaluate general intelligence. Twenty healthy control subjects (mean age 24.4 ± 2.8 years, range 22-30 years) were also studied to obtain a normal database for 3D-SSP. Group comparisons showed significant regional low FMZ uptake in the bilateral medial frontal gyri, the anterior cingulate gyri, and the thalamus. Individual analysis also showed decreased FMZ uptake in these regions; however, the distribution and extent of low FMZ uptake were different in each individual patient. Full-scale IQ (FIQ) and performance IQ (PIQ) negatively correlated with the degree of FMZ BP reduction (BZR index) in the right thalamus. FIQ, verbal IQ (VIQ), and PIQ also negatively correlated with the BZR index in the left medial frontal gyrus. DAI uniformly induced neuronal damage in the medial frontal cortex and the thalamus, which may be related to underlying cognitive impairments in diffuse TBI patients. Future studies to confirm a common area of focal neuronal damage and a direct correlation with neuropsychological testing may validate the use of FMZ-PET for the functional diagnosis of neuropsychological impairments after TBI.

Functional imaging of vegetative state applying single photon emission tomography and positron emission tomography

Nuclear medicine techniques, such as single photon emission tomography (SPECT) and positron emission tomography (PET) have been applied in patients in a vegetative state to investigate brain function in a non-invasive manner. Parameters investigated include glucose metabolism, perfusion at rest, variations of regional perfusion after stimulation, and benzodiazepine receptor density. Compared to controls, patients in a vegetative state show a substantial reduction of glucose metabolism and perfusion. While patients post-anoxia exhibit a rather homogenous cortical reduction of glucose metabolism, patients after head trauma often show severe cortical and sub-cortical reductions at the site of primary trauma. To distinguish reduced glucose metabolism due to neuronal inactivation from neuronal loss, flumazenil-PET, an indicator of benzodiazepine receptor density, could add valuable information on the extent of brain damage. Activation studies focus on the evaluation of residual brain network, looking for processing in secondary projection fields. So far the predictive strength concerning possible recovery for the individual patient is limited, and PET and SPECT are not routine procedures in the assessment of patients in a vegetative state.

Brain function in coma, vegetative state, and related disorders

We review the nosological criteria and functional neuroanatomical basis for brain death, coma, vegetative state, minimally conscious state, and the locked-in state. Functional neuroimaging is providing new insights into cerebral activity in patients with severe brain damage. Measurements of cerebral metabolism and brain activations in response to sensory stimuli with PET, fMRI, and electrophysiological methods can provide information on the presence, degree, and location of any residual brain function. However, use of these techniques in people with severe brain damage is methodologically complex and needs careful quantitative analysis and interpretation. In addition, ethical frameworks to guide research in these patients must be further developed. At present, clinical examinations identify nosological distinctions needed for accurate diagnosis and prognosis. Neuroimaging techniques remain important tools for clinical research that will extend our understanding of the underlying mechanisms of these disorders.