ALS surrogate markers. MRS.

Magnetic resonance spectroscopy (MRS) allows the quantitative assessment of neuronal integrity in vivo based on the resonance intensity of N-acetylaspartate (NAA). A simple approach to quantitation that is commonly used is to quantify the resonance intensity of NAA with respect to creatine (Cr). In patients with ALS, NAA/Cr density is decreased in areas of the brain that contribute significantly to the corticospinal tract. Since MRS is non-invasive, it can be easily used to monitor the evolution of regional changes in NAA/Cr over time. The changes in NAA/Cr over a period of months are small, however, and challenge the precision of the method.