The 3D rib cage deformities in AIS and their relationship to the spinal deformity are still unelucidated.Ī total of 200 AIS and 71 controls underwent low-dose biplanar x-rays and had their spine and rib cage reconstructed in 3-dimensional (D). Subjects with AIS present with rib cage deformity that can affect respiratory functions. To analyze patterns of 3D rib cage deformity in subjects with adolescent idiopathic scoliosis (AIS) and their relationship with the spinal deformity. This was a multicentric cross-sectional descriptive study. This VSPI is defined as the percentage of rib cage volume occupied by the penetration of the spine and reflects the functional space available for the lungs: the higher the VSPI, the more likely it is for the scoliotic deformity to produce respiratory impairment. 2 Another parameter, first described by Dubousset et al 23 for the assessment of the rib cage in subjects with neuromuscular diseases with severe thoracic lordoscoliosis, known as the volumetric spinal penetration index (VSPI), was later adapted for use in subjects with AIS. This gibbosity, often regarded as the fourth-dimension of scoliotic deformity, was shown to be directly related to the Cobb angle 22 and was found to be the second most frequently cited factor leading patients to seek surgical treatment due to its esthetically unpleasant nature. 18 This 3D deformity directly influences the chest wall through the costo-vertebral joints and leads to rib cage asymmetry, which in turn produces a gibbus, or rib hump. A new uncertainty-based formulation of the TRE also appeared as a good alternative to the unknown true TRE, that has been replaced in previous works by an alternative TRE not fully reflecting the gold standard accuracy.
Results showed that considering possible noise anisotropy and including corrupted 3D fiducials in the optimization resulted in improved accuracy of the gold standard. The gold standard transformations were derived from a novel method modeling the uncertainty in extracted 2D and 3D fiducials.
MISSHAPEN RIBS REGISTRATION
We proposed a new gold standard dataset for validation of CT-to-X-ray registration of the hip joint. In contrast, the uncertainty-based uTRE was statistically closer to the true TRE. However, a formulation of the TRE commonly found in these gold standard datasets was found to significantly miscalculate the true TRE computed in synthetic experiments with known ground truths. Reported results were comparable to previous published works of gold standard datasets. The proposed MPPC method was statistically more accurate compared to validation methods for 2D-3D registration that did not optimize the 3D fiducial positions or wrongly assumed the isotropy of the noise.
The accuracy of the transformations obtained with the MPPC was assessed in both synthetic and real experiments using different formulations of the target registration error (TRE), including a novel formulation of the TRE (uTRE) derived from the uncertainty analysis of the MPPC. We devised the multiple projective points criterion (MPPC) that jointly optimizes the transformations and the noisy 3D fiducial locations for all views. These were assumed to be corrupted by Gaussian noise, without any restrictions of isotropy. The ground truth transformations were estimated based on corresponding pairs of extracted 2D and 3D fiducial locations. The gold standard dataset included a 3D CT scan of a female hip phantom and nineteen 2D fluoroscopic images acquired at different views and voltages. As the ground truth computed with fiducial markers is affected by localization errors in the image datasets, we proposed a new methodology based on uncertainty propagation to estimate the accuracy of a gold standard dataset. Given the large use of 2D-3D registration in biomechanics, we introduced the first gold standard validation dataset for Computed Tomography (CT)-to-X-ray registration of the hip joint, based on fluoroscopic images with large rotation angles. Publicly available datasets with standardized evaluation methodology are necessary for validation and comparison of 2D-3D registration techniques. Estimation of the accuracy of 2D-3D registration is paramount for a correct evaluation of its outcome in both research and clinical studies.
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