“…Oxygen alters the T 1 -weighted signal intensity of the pulmonary blood circulation ( 14 , 230 , 231 ), permitting indirect imaging of the lungs. During tidal breathing, a series of T 1 -weighted images are acquired using a conventional MRI scanner during both normoxic and pure oxygen conditions ( 232 , 233 ), with output data represented as T 1 maps or quantified as relative enhancement ratio or oxygen transfer function (OTF) ( Figure 4 ) ( 235 ). Using these metrics, individuals with CF and COPD were found to exhibit a heterogeneous reduction in T 1 relaxation time compared to healthy individuals ( 233 , 236 , 237 ).…”