JNM: PET/MR reveals long-term brain changes after brain trauma

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Simultaneous MRI + PET of a brain.
Image source: Siemens Healthcare

PET fused with MRI can help researchers better understand the long-term functional and structural changes that take place after traumatic brain injury (TBI), according to study results in the November issue of the Journal of Nuclear Medicine (JNM).

TBI has a high incidence of long-term neurologic and neuropsychiatric morbidity. "The results provide new insights into the progressive nature of the brain changes occurring following TBI, demonstrating that changes in brain structure and function after TBI are dynamic and continue to progress and evolve for months," said Viviane Bouilleret, MD, PhD, from the department of neurophysiology and epilepsy at the Universite Paris-Sud in Paris.

The model used in the study was lateral fluid percussion injury in rats. The metabolic and structural changes in rat brains were assessed after TBI using serial 18F-FDG PET and 3D MRI in vivo. The researchers acquired PET and MR images at one week and at one, three and six months after injury.

Many of the brain regions that showed early hypometabolism on 18F-FDG PET images later showed progressive atrophy on serial MRI scans, particularly the cortex and hippocampi. The functional changes occurred earlier and decreased or resolved by six months after fluid percussion injury, while the structural were delayed in onset and continued to progress for at least six months after fluid percussion injury, according to Bouilleret and colleagues.

The structural and functional changes were dynamic, appearing to consolidate between three and six months after fluid percussion injury, which can have implications for understanding the mechanisms underlying the long-term neurological and psychiatric consequences of TBI.

The finding that the cerebral hypometabolism predates the progressive cerebral atrophy suggests that it may play a mechanistic role in the subsequent neurodegeneration affecting these brain regions. Importantly, these findings indicated the potential of an extended time window for application of neuroprotective strategies that may mitigate secondary neurodegenerative processes after fluid percussion injury, noted the authors.

This study also has provided a practical paradigm for testing the biological effectiveness of potential therapies prior to embarking on expensive and lengthy clinical trials, the authors said.

"The approach would also be applicable to the study of other neurological diseases, such as stroke, dementia, multiple sclerosis brain infections and epilepsy, which are associated with long-term progressive degenerative changes in the brain," Bouilleret said.