Application of chemical shift imaging for measurement of NAA in head injured patients

Abstract

Neurochemical damage following brain injury can be assessed non-invasively by measurement of N-Acetyl-Aspartate (NAA) using Proton Magnetic Resonance Spectroscopy (1HMRS). This report documents results of applying Chemical Shift Imaging (CSI) post-processing for measuring NAA in traumatically injured brain. Following stabilization, severely head-injured patients (GCS 8 or less) were transported to the MRI suite. Semi-quantitative measurement of NAA, crearine (Cr/PCr) and choline (Cho) were obtained from single voxels (8 cm3) and CSI for acquisition of smaller voxels (2 cm3) throughout areas of the brain. Studies were completed with no complication. In focal injury, SVS positioned at the site of lesion demonstrated reduced NAA, compared to contralateral hemisphere. In diffuse injury, CSI demonstrated uniform reduction of NAA throughout the brain. NAA/Cho showed normal levels within 24 hours of injury averaging 2.4 and decreased over the next 10 days reaching a plateau of 0.75. At 30 days, NAA showed no recovery in poor outcome patients. In patients with good outcome, NAA initially low recovered near baseline levels. CSI provides a comprehensive neurochemical assessment of neuronal damage. NAA decreases and remains low in patients with poor outcome. NAA recovers in patients with favorable outcome, suggesting marginal metabolic impairment and possible re-synthesis of the NAA pool.