Convection triggers MRI amplitude and phase signal changes during proton beam irradiation of liquid water phantoms

In-beam MRI has recently proven capable of visualising proton beams in liquid-filled
phantoms based on beam-induced local MR signal amplitude loss. This holds promise for on-
line beam range verification and dosimetric as well as geometric quality assurance for hybrid
MRI-proton therapy systems currently under development. The purpose of this study was
firstly to determine whether, in addition to MR signal amplitude loss, the MRI phase signal is
affected by the proton beam and secondly, to test whether these changes in MRI signals are
triggered by beam-induced convection.