In order for the images produced by the future MRI to be free of distortions or artifacts, the magnetic field generated by the Iseult magnet must be homogeneous to 0.5 PPM (parts per million) around the patient's brain. To meet this challenging specification, it was necessary to provision means of "shimming" the field, i.e. of correcting all the small defects that would inevitably arise from the manufacturing process. 5904 pieces of shim (small iron platelets) were screwed onto rails and installed inside the magnet tunnel. This first configuration was tested on Thursday, July 9, 2020 by mapping its effect on the magnetic field of Iseult at 3 T. The results are very encouraging as this first shimming iteration allowed to increase the homogeneity of the field in the useful zone from 138.8 to 3.2 PPM (value extrapolated to 11.72 T from magnetic measurements at 3 T).
In its most common version, muon imaging is intrinsically a 2D technique: the resulting density map is indeed integrated along the observation direction. However, a 3D map can be obtained by combining several projections, like for medical imaging. But in the muon case, the number of projections is dramatically reduced because of the required acquisition time. A 3D algorithm has been recently developed using the Irfu TomoMu setup, within a collaboration between Florence University and Irfu. The 3D structure of the test object has been reconstructed from only 3 points of view, thanks to the high precision of the instrument. This technique will soon be extended to more applications, from reactor dismantling to civil engineering or mining exploration.