The accuracy of Cobb angle measurement on CT scan projection radiograph images

Introduction: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that can affect young children. It requires frequent exposure to X-rays to monitor the deformity, which can lead to the development of radiation-induced cancer later in life. The aim of this study is to test the accuracy of using scan projection radiography (SPR) in computed tomography (CT) scans for AIS assessment. This scanning mode delivers low radiation compared with conventional radiography. Method: A bespoke phantom with a 14° scoliotic spine was scanned in CT SPR mode using 18 imaging acquisitions. These images were visually evaluated against set criteria to determine their suitability for Cobb angle measurements Those deemed of insufficient quality were excluded from the study (n = 8, excluded). Cobb angle measurements were then performed on the remaining images (n = 10, included) by 13 observers. Results: On average, the difference between the measured Cobb angle and the known angle was −2.75° (SD 1.46°). The agreement between the observers was good (p = 0.861, 95% CI 0.70–0.95) and comparable to similar studies on other imaging modalities which are used for Cobb angle estimation. Conclusion: CT SPR images can be used for AIS assessment with the 5° margin of error that is clinically acceptable. Implications for practice: The outcome is promising for patients and health providers because it provides an opportunity to reduce patient dose, achieve clinically acceptable Cobb angle measurements whilst using existing (CT) technology that is available in most hospital.