<qa>  What is the second session of neuroimaging?After stabilisation of the stimulation parameters at least for more than 1 month, the second session of neuroimaging will occur T1 with the RestoreSensor SureScan MRI neurostimulator in MRI mode. Minimal one month later 2 months after implantation of definitive SCS system the patient will undergo the last session of neuroimaging T2 with the stimulator in MRI mode. During that period prior to the MR-session, a new protocol will occur with paresthesia free high density SCS. The MRI protocol will occur after stabilisation of the stimulation parameters at least for more than 1 month. During the whole period, patients will fill in a VAS diary back and leg pain separately and at time of neuroimaging T1 and T2 a Likert-scale in order to evaluate the satisfaction grade of the patient. Additionally, patients will also wear during the whole period an Actiwatch, measuring sleep patterns and filling in questionnaires at B, T1 and T2 Pittsburgh Sleep Quality Index PSQI and Holland Sleep Disorders Questionnaire HSDQ. 