Magnetic resonance spectroscopy of traumatic brain injury and concussion

Imaging modalities such as CT and magnetic resonance imaging (MRI) are powerful tools to detect and assess focal injury such as hemorrhagic lesions and edema and brain swelling in severe injury. However, acute and chronic injury at a cellular level is sometimes difficult to discern from normal features by anatomical imaging. Magnetic resonance spectroscopy (MRS) offers a unique non-invasive approach to assess injury at microscopic levels by quantifying cellular metabolites. Most clinical MRI systems are equipped with this option and MRS is thus a widely available modality. For the brain in particular, MRS has been a powerful research tool and has also been proven to provide additional clinically relevant information for several disease families such as brain tumors, metabolic disorders, and systemic diseases. The most widely-available MRS method, proton (H-1; hydrogen) spectroscopy, is FDA approved for general use and can be ordered by clinicians for patient studies if indicated. The findings obtained with MRS in concussion and more severe head trauma are heterogeneous, reflecting the different time after injury, degree of injury and different physiologic and pathologic response of the brain to injury in individuals. The most important findings are that elevated lactate (and lipids) in apparently normal tissue observed 2-5 days after injury are indicators of severe global hypoxic injury and poor outcome. Also, N-acetylaspartate (NAA), a marker for "healthy" neurons and axons, is generally reduced in traumatic brain injury signaling neuronal and axonal loss/damage. The extent of NAA reduction after injury is an objective and quantitative surrogate marker for the severity of injury and is useful for outcome prediction.