High-Temperature Superconducting (HTS) radiofrequency coils can improve sensitivity by more than an order of magnitude, but their propensity to warp the magnetic field as a result superconducting diamagnetism could cause image degradation. We report on the observation of these B0 artefacts. They are shown to be predominant at lower working temperatures of the HTS coil (60 K) and negligible at 80 K and can be avoided altogether by cooling the HTS coil in B0. We also propose a phenomenological model of these field perturbations. This work studies and solves an important issue in the integration of HTS coil in MRI.