The placenta is a challenging MRI target. Acquisition schemes developed for other organs, with implicit assumptions about motion, tissue composition and perfusion, should be vetted for applicability to the placenta. We have developed an ex vivo placental perfusion chamber with integrated MRI receive coil for high SNR and imaging acceleration to validate in vivo acquisitions in a controlled environment. Here we examine the effect of flowing spins on MRF relaxometry. We offer evidence that T1 is sensitive to overall fluid volume, while T2 is additionally sensitive spin inflow. Our placental perfusion system appears promising for validating in vivo quantitative MRI.