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

Alrehily, F; Hogg, P; Twiste, M; Johansen, S; Tootell, AK

Abstract

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.

Method: 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 15olateral 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 degrees.

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.

Citation

Alrehily, F., Hogg, P., Twiste, M., Johansen, S., & Tootell, A. (2020). Development and validation of a bespoke phantom to test accuracy of Cobb angle measurements. Radiography, 26(2), e78-e87. https://doi.org/10.1016/j.radi.2019.11.002

• Journal Article Type: Article
• Acceptance Date: Nov 10, 2019
• Online Publication Date: Nov 25, 2019
• Publication Date: May 1, 2020
• Deposit Date: Nov 13, 2019
• Publicly Available Date: Nov 25, 2020
• Journal: Radiography
• Print ISSN: 1078-8174
• Electronic ISSN: 1532-2831
• Publisher: Elsevier
• Volume: 26
• Issue: 2
• Pages: e78-e87
• DOI: https://doi.org/10.1016/j.radi.2019.11.002
• Publisher URL: https://doi.org/10.1016/j.radi.2019.11.002
• Related Public URLs: https://www.radiographyonline.com/