Major Depressive Disorder (MDD) is a debilitating psychiatric disorder characterized by feelings of low self-worth, loss of interest and suicidal thoughts. An estimated 350 million people are affected worldwide, 15% being adolescents. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive intervention that modulates cortical excitability by inducing electric currents in neurons by administering pulsating magnetic fields to the scalp. Studies have shown the left dorsolateral prefrontal cortex (DLPFC) to be implicated in positive effects on emotion, and glutamate/Glx levels to be decreased in MDD patients. In adults, rTMS has been shown to significantly improve mood, decrease Hamilton Depression Scores and increase glutamate, glutamine and choline levels in the DLPFC. We hypothesize an increase in DLPFC glutamate levels following treatment.