Radiography | 2019
Development and validation of a bespoke phantom to test accuracy of Cobb angle measurements.
Abstract
INTRODUCTION\nAdolescent 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.\n\n\nMETHODS\nPoly-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.\n\n\nRESULTS\nThe HU of the PoP vertebrae was 628 (SD\xa0=\xa056), human vertebrae was 598 (SD\xa0=\xa079) and sheep vertebra was 605 (SD\xa0=\xa083). The SNR values of the two phantoms correlated strongly (r\xa0=\xa00.93 (p\xa0=\xa00.00)). The measured scoliosis angle was 14°.\n\n\nCONCLUSION\nThe 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.\n\n\nIMPLICATIONS FOR PRACTICE\nA phantom to investigate new x-ray imaging techniques and technology in the assessment of scoliosis and to optimise currently used protocols.