PURPOSE: CT is considered the gold standard to assess bone morphology, whereas MRI is the imaging modality of choice to assess soft tissue. To reduce the ionising radiation exposure of the patient from CT, new MRI technologies have been developed to obtain images of bone. Two promising methods include MRI-based synthetic CT (sCT) and T1-weighted isotropic MRI. METHODS: A prospective study including twenty-four adult patients receiving lumbar or sacral spine stabilisation surgery was performed. For each patient, two scans were acquired: a 3D dual echo T1-weighted gradient image, from which a sCT was reconstructed, and a 3D isotropic T1-weighted MRI sequence. Three observers assessed the sCT images for adequate visualisation of relevant vertebral anatomies and confidence using sCT in preoperative planning compared to the isotropic MRI based on a series of statements scored using a Likert-scale. Summary statistics and intraclass correlation coefficients were calculated. RESULTS: All observers agreed that the sCT provided adequate visualization (94% of cases). Compared to the isotropic MRI, the sCT provided added value (89% of cases) and improved confidence (92% of cases) for the preoperative planning stage. No unexpected poor intraclass correlations were identified. The observers diagnosed patients with spondylolysis, scoliosis, arthrosis, spina bifida occulta, various Castellvi classifications, or without pathology. CONCLUSIONS: sCT adequately visualised vertebral structures relevant for surgical spine planning with good confidence and added value for sCT compared to 3D T1-weighted isotropic MRI is shown. sCT could be a valuable method to reduce the radiation exposure associated with CT.