2D-3D Registration of CT Vertebra Volume to Fluoroscopy Projection: A Calibration Model Assessment

Abstract

This study extends a previous research concerning intervertebral motion registration by means of 2D dynamic fluoroscopy to obtain a more comprehensive 3D description of vertebral kinematics. The problem of estimating the 3D rigid pose of a CT volume of a vertebra from its 2D X-ray fluoroscopy projection is addressed. 2D-3D registration is obtained maximising a measure of similarity between Digitally Reconstructed Radiographs (obtained from the CT volume) and real fluoroscopic projection. X-ray energy correction was performed. To assess the method a calibration model was realised a sheep dry vertebra was rigidly fixed to a frame of reference including metallic markers. Accurate measurement of 3D orientation was obtained via single-camera calibration of the markers and held as true 3D vertebra position; then, vertebra 3D pose was estimated and results compared. Error analysis revealed accuracy of the order of 0.1 degree for the rotation angles of about 1 mm for displacements parallel to the fluoroscopic plane, and of order of 10 mm for the orthogonal displacement.

Hierarchical model-based tracking of cervical vertebrae from dynamic biplane radiographs

“…Any contribution due to soft tissue and random noise is assumed negligible here. This approach also does not account for possible differences between kVp settings of the CT and the fluoroscopy system [13]. Although still an approximation, the resulting MDRRs have a more realistic signature in adjacent regions than the SDRRs (Fig.…”

A continuous description of intervertebral motion by means of spline interpolation of kinematic data extracted by videofluoroscopy

“…The analysis was confined to planar motion in the sagittal plane and was based on the assumption of negligible coupled motion, which can hold for flexion-extension movements (Bifulco et al, 2002(Bifulco et al, , 2010Hwang et al, 2008;Van Mameren et al, 1992). For each vertebra the hypothesis of rigidity was also held (Frankel and Burstein, 1974).…”

Hough transform‐based approach for estimating 3D rotation angles of vertebrae from biplanar radiographs using GPU‐acceleration

“…Currently, X‐ray is the most commonly used imaging modality for diagnosing scoliosis because it has the advantages of low costs, acceptable irradiation dose, and flexibility of being able to image the whole spine in different poses (standing, flexion, extension, bending, or torsion). In scoliotic clinics obtaining the full spinal radiographs is a standard imaging procedure for the diagnosis and follow‐up of the progression of scoliosis (Dewi et al, ). Measured in the posteroanterior (PA) radiographs the Cobb angle is the most widely used index, which has been adopted by the Scoliosis Research Society as the standard method for quantification of scoliotic deformities (Vrtovec et al, ).…”

“…Measured in the posteroanterior (PA) radiographs the Cobb angle is the most widely used index, which has been adopted by the Scoliosis Research Society as the standard method for quantification of scoliotic deformities (Vrtovec et al, ). Some computer‐aided methods were developed to automate the Cobb angle measurement (Zhang et al, ; Anitha and Prabhu, ). One of the main drawbacks of using the Cobb angle for assessing and monitoring scoliosis is that it is measured in two‐dimensional (2D) radiographs and therefore cannot be used to fully differentiate the 3D deformity, especially for the deformity in the transverse plane (e.g., the vertebral axial rotation).…”

“…However, there is considerable operator variability in these methods. Zhang et al () developed a computer‐aided system to improve the reliability by automating landmark identification. Besides the operator reliability problems in these methods, after surgery, the use of pedicle screws obscures some of the landmarks necessary to locate pedicles for rotation estimation.…”