Maximum PA area (AMAX) and minimum PA area (AMIN) were measured at rest (AMAX REST and AMIN REST) and stress (AMAX STRESS and AMIN STRESS) on ds-MRI images by manual planimetry using Osirix for Mac v5.8 (Pixmeo, Bernex, Switzerland). Example images are shown in Fig. 1 . The change in AMAX (ΔAMAX) and AMIN (ΔAMIN) between rest and stress were calculated as (AMAX or MIN STRESS – AMAX or MIN REST). RAC at rest (RACREST) and RAC during stress (RACSTRESS) were calculated as RAC = (AMAX – AMIN)/AMIN, using PA measurements recorded under appropriate conditions, as in earlier publications. The change in RAC between rest and stress (ΔRAC) was calculated as (RACSTRESS – RACREST).
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Representative MRI images of the main pulmonary artery (MPA) acquired at rest (a, b) and at stress (c, d) in PH patient 1. The intima of the MPA was manually contoured at all time points using Osirix for Mac v5.8 (Pixmeo, Bernex, Switzerland) allowing measurement of the minimum PA area (AMIN (a, c)) and maximum PA area (AMAX (b, d)). These data were used to calculate RACREST, RACSTRESS, and ΔRAC, which were 12%, 9%, and −3% for this patient, respectively.