For a study, the researchers examined the differences between pedicle diameter measurements obtained using magnetic resonance imaging (MRI) and the ones obtained using computed tomography (CT). Cross-sectional research was conducted. Between April 2009 and October 2019, 21 AIS Lenke type 1 patients (19 females and 2 males, mean age at surgery: 15.4 years) had a posterior spinal fusion. Pedicle diameters on CT and MRI differ. 2 spine surgeons measured the inner and outer diameters of the right and left pedicles from T1 to L3 separately for statistical comparisons. Inner and outer diameter CT-MRI readings were -3.7 mm and 4.7 mm for inner diameter and -4.6 mm and 5.3 mm for outer diameter, respectively. The chance of a 2 mm variation in measurement was less than 5% for both modalities in terms of inter-examiner error. A 1 mm difference had a likelihood of less than 5%, while a 3 mm or more difference had a probability of 2.1% for the inner diameter and 2.9% for the outer diameter. Pedicle laterality was not substantially linked with measurement discrepancies, although low body weight was. At the time, MRI did not have the accuracy needed to determine pedicle size in AIS patients. The accuracy of pedicle size estimation by MRI might have soon increased because of advances in image processing technologies.