Iron accumulation in the brain is an indicator of cognitive involvement in Parkinson disease (PD), a new neuroimaging study suggests. A team led by Rimona Weil at University College London, UK, performed quantitative susceptibility mapping (QSM) — an MRI technique that can measure the iron content of brain tissue — in 100 patients with early-stage to mid-stage PD and 37 age-matched controls. The researchers found that brain iron levels were elevated in the prefrontal cortex and putamen in patients with PD compared with controls. Within the PD group, the QSM signal in the parietal and prefrontal cortices correlated with the degree of cognitive impairment, as measured by the Montreal Cognitive Assessment. The results indicate that QSM can be used to track cognitive change in PD and could aid patient stratification and monitoring in clinical trials.