Traumatic brain injury (TBI) is the leading cause of disability in children and young adults. Children with moderate to severe TBI are typically at risk of poor functional outcome in terms of neurocognitive impairment and behavior problems. Neurocognitive impairments include deficits in attention and working memory, learning and memory, and executive functioning, whereas behavior problems include anxiety, depression and aggression. Neuroimaging techniques based on multi-modal magnetic resonance image (MRI) can detect the structural and functional brain abnormalities objectively and sensitively. Recent evidence indicates that even after mild TBI, children with risk factors for intracranial pathology are at risk of poor neurocognitive and behavioral outcome.Meanwhile, recently, the concept of "gut-brain axis" has been proposed and hint gut microbiota could shape the brain. Some studies have emphasized that human gut microbiota plays an important role in the pathogenesis and development of TBI. However, how the gut affects the brain in patients with TBI is unclear. Thus, combining analysis of neuroimaging and "gut-brain axis" will provide more information for finding the risk factors and imaging diagnostic markers of brain impairment in TBI. It will also helpful for explaining the underlying mechanisms of brain impairment in TBI, providing an objective basis for clinical diagnosis and prediction of the prognosis.

Inclusion Criteria:

• age 6-14 years at time of recruitment.
• hospital admission with a clinical diagnosis of TBI for inclusion in the TBI group
• GCS = 15-13.
• loss of consciousness duration≤30 min.
• post-traumatic amnesia duration ≤1 h.

Exclusion Criteria:

• previous TBI.
• visual or auditory disorder interfering with neurocognitive testing.
• current neurological condition affecting the central nervous system with known effects on neurocognitive functioning, other than TBI.

All of the patients of mTBI group are in-patients and out-patients in the nephrology department from three research centers. The subjects of control group are recruited from community.