The effect of added fat on the accuracy of Cobb angle measurements in CT SPR images: A phantom study.

INTRODUCTION: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that mostly affects females aged between 10 and 17 years old. Cobb's method is the gold standard for assessing AIS. Being overweight is a common characteristic in AIS patients; therefore, the aim of this study is to investigate the effect fat mass has on the accuracy of Cobb angle measurements in 10-year-old female AIS patients. METHODS: A purpose-built phantom representing an AIS patient was scanned after adding several thicknesses of lard fat (0,2,4 and 8 cm). The phantom was scanned in an antero-posterior position using the scout mode of the CT scanner. 18 observers performed Cobb angle measurements on the images. RESULTS: The average Cobb angle at 0 cm of fat was 10.83° (SD = 3.06), at 2 cm it was 10.90° (SD = 3.16), at 4 cm it was 10.64° (SD = 3.06) and at 8 cm it was 10.88° (SD = 3.02). No significant difference was observed between the measurements at these thicknesses. CONCLUSION: Cobb angle measurements are not affected by the presence of fat. IMPLICATIONS FOR PRACTICE: When assessing overweight AIS patients, it not necessary to manipulate the acquisition parameters, which could lead to increased patient dose, in order to get more accurate Cobb angle measurement.

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

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.

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.

Scoliosis imaging: An analysis of radiation risk in the CT scan projection radiograph and a comparison with projection radiography and EOS.

INTRODUCTION: Scoliosis is defined as a deformity of the spine with lateral curvature in the coronal plane. It requires regular X-ray imaging to monitor the progress of the disorder, therefore scoliotic patients are frequently exposed to radiation. It is important to lower the risk from these exposures for young patients. The aim of this work is to compare organ dose (OD) values resulting from Scan Projection Radiograph (SPR) mode in CT against projection radiography and EOS® imaging system when assessing scoliosis. METHODS: A dosimetry phantom was used to represent a 10-year old child. Thermoluminescent dosimetry detectors were used for measuring OD. The phantom was imaged with CT in SPR mode using 27 imaging parameters; projection radiography and EOS machines using local scoliosis imaging procedures. Imaging was performed in anteroposterior, posteroanterior and lateral positions. RESULTS: 17 protocols delivered significantly lower radiation dose than projection radiography (p < 0.05). OD values from the CT SPR imaging protocols and projection radiography were statistically significant higher than the results from EOS. No statistically significant differences in OD were observed between 10 imaging protocols and those from projection radiography and EOS imaging protocols (p > 0.05). CONCLUSION: EOS has the lowest dose. Where this technology is not available we suggest there is a potential for OD reduction in scoliosis imaging using CT SPR compared to projection radiography. Further work is required to investigate image quality in relation to the measurement of Cobb angle with CT SPR.