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.

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.

Physical analysis of normally-off ALD Al_(2)O_(3)/GaN MOSFET with different substrates using self-terminating thermal oxidation-assisted wet etching technique

Based on the self-terminating thermal oxidation-assisted wet etching technique,two kinds of enhancement mode Al_(2)O_(3)/GaN MOSFETs(metal-oxide-semiconductor field-effect transistors)separately with sapphire substrate and Si sub-strate are prepared.It is found that the performance of sapphire substrate device is better than that of silicon substrate.Comparing these two devices,the maximum drain current of sapphire substrate device(401 mA/mm)is 1.76 times that of silicon substrate device(228 mA/mm),and the field-effect mobility(μ_(FEmax))of sapphire substrate device(176 cm^(2)/V·s)is 1.83 times that of silicon substrate device(96 cm^(2)/V·s).The conductive resistance of silicon substrate device is 21.2Ω-mm,while that of sapphire substrate device is only 15.2Ω·mm,which is 61%that of silicon substrate device.The significant difference in performance between sapphire substrate and Si substrate is related to the differences in interface and border trap near Al_(2)O_(3)/GaN interface.Experimental studies show that(i)interface/border trap density in the sapphire substrate device is one order of magnitude lower than in the Si substrate device,(ii)Both the border traps in Al_(2)O_(3) dielectric near Al_(2)O_(3)/GaN and the interface traps in Al_(2)O_(3)/GaN interface have a significantly effect on device channel mobility,and(iii)the properties of gallium nitride materials on different substrates are different due to wet etching.The research results in this work provide a reference for further optimizing the performances of silicon substrate devices.