For a retrospective study, the researchers wanted to assess the image quality of low-radiation-dose computed tomography (LD-CT) of the thoracolumbar spine while assessing pedicle diameter with model-based iterative reconstruction (MBIR).  Although MBIR can significantly lower radiation dose, its utility in planning spine surgery is questionable. Within two years, the researchers identified patients (mean age, 70.5 ± 13.3 years) who had both standard-radiation-dose CT (SD-CT) with hybrid iterative reconstruction and LD-CT with MBIR of the thoracolumbar spine. The two experiments were compared in terms of radiation dose, perceived picture sharpness, signal-to-noise ratio, and contrast-to-noise ratio. Inner pedicle diameters were also assessed on SD-CT (DSD) and LD-CT (DLD) and compared statistically. For each CT group, the researchers used 24 CT and 84 pedicles. The radiation dose of LD-CT was 1.21±0.42 mGy, or one-sixth the dose of SD-CT, according to the volume CT dose index. In a prior study, the effective dose of LD-CT was 0.58  ± 0.31 mSv, which was equivalent to or less than that of a one-time lumbar X-ray. Subjective image sharpness for the contour of vertebrae and trabecular structure was significantly lower with LD-CT, although signal-to-noise ratio and contrast-to-noise ratio were much higher. DLD intra-rater reliability (intra-RR) and inter-rater reliability (inter-RR) were both 0.985 and 0.892, which were comparable to DSD. When examined inside the same pedicle, DLD was consistently 0.30 mm smaller than DSD, independent of pedicle diameter. The radiation dose using LD-CT with MBIR was similar to a single lumbar X-ray, and the pictures were excellent for determining pedicle diameter. If the association between DSD and DLD was well understood, LD-CT can be used instead of SD-CT when planning spine surgery.