Positron emission tomography imaging for the assessment of mild traumatic brain injury and chronic traumatic encephalopathy:recent advances in radiotracers

A chronic phase following repetitive mild traumatic brain injury can present as chronic traumatic encephalopathy in some cases,which requires a neuropathological examination to make a definitive diagnosis.Positron emission tomography(PET)is a molecular imaging modality that has high sensitivity for detecting even very small molecular changes,and can be used to quantitatively measure a range of molecular biological processes in the brain using different radioactive tracers.Functional changes have also been reported in patients with different forms of traumatic brain injury,especially mild traumatic brain injury and subsequent chronic traumatic encephalopathy.Thus,PET provides a novel approach for the further evaluation of mild traumatic brain injury at molecular levels.In this review,we discuss the recent advances in PET imaging with different radiotracers,including radioligands for PET imaging of glucose metabolism,tau,amyloid-beta,γ-aminobutyric acid type A receptors,and neuroinflammation,in the identification of altered neurological function.These novel radiolabeled ligands are likely to have widespread clinical application,and may be helpful for the treatment of mild traumatic brain injury.Moreover,PET functional imaging with different ligands can be used in the future to perform largescale and sequential studies exploring the time-dependent changes that occur in mild traumatic brain injury.

Survivors of COVID-19 exhibit altered amplitudes of low frequency fluctuation in the brain: a resting-state functional magnetic resonance imaging study at 1-year follow-up

Although some short-term follow-up studies have found that individuals recovering from coronavirus disease 2019(COVID-19)exhibit anxiety,depression,and altered brain microstructure,their long-term physical problems,neuropsychiatric sequelae,and changes in brain function remain unknown.This observational cohort study collected 1-year follow-up data from 22 patients who had been hospitalized with COVID-19(8 males and 11 females,aged 54.2±8.7 years).Fatigue and myalgia were persistent symptoms at the 1-year follow-up.The resting state functional magnetic resonance imaging revealed that compared with 29 healthy controls(7 males and 18 females,aged 50.5±11.6 years),COVID-19 survivors had greatly increased amplitude of low-frequency fluctuation(ALFF)values in the left precentral gyrus,middle frontal gyrus,inferior frontal gyrus of operculum,inferior frontal gyrus of triangle,insula,hippocampus,parahippocampal gyrus,fusiform gyrus,postcentral gyrus,inferior parietal angular gyrus,supramarginal gyrus,angular gyrus,thalamus,middle temporal gyrus,inferior temporal gyrus,caudate,and putamen.ALFF values in the left caudate of the COVID-19 survivors were positively correlated with their Athens Insomnia Scale scores,and those in the left precentral gyrus were positively correlated with neutrophil count during hospitalization.The long-term follow-up results suggest that the ALFF in brain regions related to mood and sleep regulation were altered in COVID-19 survivors.This can help us understand the neurobiological mechanisms of COVID-19-related neuropsychiatric sequelae.This study was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University(approval No.2020 S004)on March 19,2020.

Morphometric changes in the cortex following acute mild traumatic brain injury

Morphometric changes in cortical thickness(CT),cortical surface area(CSA),and cortical volume(CV) can reflect pathological changes after acute mild traumatic brain injury(m TBI).Most previous studies focused on changes in CT,CSA,and CV in subacute or chronic m TBI,and few studies have examined changes in CT,CSA,and CV in acute m TBI.Furthermore,acute m TBI patients typically show transient cognitive impairment,and few studies have reported on the relationship between cerebral morphological changes and cognitive function in patients with m TBI.This prospective cohort study included 30 patients with acute m TBI(15 males,15 females,mean age 33.7 years) and 27 matched healthy controls(12 males,15 females,mean age 37.7 years) who were recruited from the Second Xiangya Hospital of Central South University between September and December 2019.High-resolution T1-weighted images were acquired within 7 days after the onset of m TBI.The results of analyses using Free Surfer software revealed significantly increased CSA and CV in the right lateral occipital gyrus of acutestage m TBI patients compared with healthy controls,but no significant changes in CT.The acute-stage m TBI patients also showed reduced executive function and processing speed indicated by a lower score in the Digital Symbol Substitution Test,and reduced cognitive ability indicated by a longer time to complete the Trail Making Test-B.Both increased CSA and CV in the right lateral occipital gyrus were negatively correlated with performance in the Trail Making Test part A.These findings suggest that cognitive deficits and cortical alterations in CSA and CV can be detected in the acute stage of m TBI,and that increased CSA and CV in the right lateral occipital gyrus may be a compensatory mechanism for cognitive dysfunction in acute-stage m TBI patients.This study was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University,China(approval No.086) on February 9,2019.