A magnetic resonance imaging (MRI) phantom includes an outer container that includes a first portion comprising a first wall; a second portion opposingly disposed to the first portion and sealingly engaged to the first portion, the second portion including a second wall; and an internal volume bounded by the first wall and the second wall, the internal volume being hollow and configured to receive a fluid; and a sample holder disposed in the internal volume of the outer container, wherein the MRI phantom is configured to maintain a constant temperature of the internal volume. A process for acquiring an MRI image includes providing an MRI; disposing a sample member in the sample holder; disposing a fluid in the MRI phantom; disposing the MRI phantom in an MRI device; achieving thermal equilibrium in the MRI phantom at a selected temperature; and subjecting the MRI phantom to MRI imaging at the selected temperature to acquire the MRI image of the sample.