Development and validation of a bespoke phantom to test accuracy of Cobb angle measurements

F. Alrehily*, P. Hogg, M. Twiste, S. Johansen, A. Tootell

*Corresponding author for this work

Research output: Contribution to journalArticle (journal)peer-review

4 Citations (Scopus)


Introduction: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that causes the spine to bend laterally. Patients with AIS undergo frequent X-ray examinations to monitor the progression of the disorder by through the measurement of the Cobb angle. Frequent exposure of adolescents poses the risk of radiation-induced cancer. The aim of this research was to design and build a bespoke phantom representing a 10-year-old child with AIS to allow optimisation of imaging protocols for AIS assessment through the accuracy of Cobb angle measurements. Methods: Poly-methyl methacrylate (PMMA) and plaster of Paris (PoP) were used to represent human soft tissue and bone tissue, respectively, to construct a phantom exhibiting a 15° lateral curve of the spine. The phantom was validated by comparing the Hounsfield unit (HU) of its vertebrae with that of human and sheep. Additionally, comparisons of signal-to-noise ratio (SNR) to those from a commercially available phantom. An assessment of the accuracy of the radiographic assessment of the Cobb angle measurement was performed. Results: The HU of the PoP vertebrae was 628 (SD = 56), human vertebrae was 598 (SD = 79) and sheep vertebra was 605 (SD = 83). The SNR values of the two phantoms correlated strongly (r = 0.93 (p = 0.00)). The measured scoliosis angle was 14°. Conclusion: The phantom has physical characteristics (in terms of spinal deformity) and radiological characteristics (in terms of HU and SNR values) of the spine of a 10-year-old child with AIS. This phantom has utility for the optimisation of x-ray imaging techniques in 10 year old children. Implications for practice: A phantom to investigate new x-ray imaging techniques and technology in the assessment of scoliosis and to optimise currently used protocols.

Original languageEnglish
Pages (from-to)e78-e87
Number of pages10
Issue number2
Early online date25 Nov 2019
Publication statusPublished - 31 May 2020


  • Adolescent idiopathic scoliosis
  • Cobb angle
  • Dose optimisation
  • Phantom


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