Robust initialisation for single-plane 3D CT to 2D fluoroscopy image registration

Evaluating similarity measure for multimodal 3D to 2D registration

The 3D to 2D registration technique in spine surgery is vital to aid surgeons in avoiding the wrong site surgery by estimating the vertebral pose. The vertebral poses are estimated by generating the spatial correspondence relationship between pre-operative MR with intra-operative x-ray images, then evaluated using a similarity measure. Different similarity measures are used in 3D to 2D registration techniques to assess the spatial correspondence between the pre-operative and intra-operative images. However, to evaluate the registration performance of the similarity measures, the proposed framework employs three different similarity measures: Binary Image Matching, Dice Coefficients, and Normalized Cross-correlation technique to compare the images based on pixel positions. The registration accuracy of the proposed similarity measures is compared based on the mean Target Registration Error, mean Iteration Times, and success rate. In the absence of simulated test images, the experiment is conducted on the simulated AP and Lateral test images. The experiment conducted on the simulated test images shows that all three similarity measures work well for the feature based 3D to 2D registration in that BIM gives better results. The experiment also indicates high registration accuracy when the initial displacements are varied up to ±20 mm and ±100of the translational and rotational parameters, respectively, for three similarity measures.

Analysis of Kneeling by Medical Imaging Shows the Femur Moves Back to the Posterior Rim of the Tibial Plateau, Prompting Review of the Concave-Convex Rule

BACKGROUND

Physical therapists assess joint movement by observation and palpation. New imaging technologies that enable vision of bones and joints during functional activities can be used to analyze joint kinematics and review traditional assumptions.

PURPOSE

The purpose was to measure relations between flexion, rotation, and translation at the knee and to validate these visually.

DESIGN

This was a prospective, observational study.

METHODS

Twenty-five healthy participants aged >45 years (13 males) knelt from upright kneeling to full flexion with the foot free. Fluoroscopy recorded movement at 30 frames per second of x-ray. A computed tomography scan provided 3-dimensional data, which were registered to the fluoroscopy frames to provide a moving model. Motion in 6 degrees of freedom was analyzed for coupling of movements.

RESULTS

Mean (standard deviation) flexion reached by participants was 142 (6)° in kneeling. Posterior femoral translation was coupled to flexion (r = 0.96). From 90° to 150° flexion, the femur translated posteriorly by 36 (3) mm to finish 23 (3) mm posterior to the center of the tibia at 150° flexion. From 90° to 150° flexion, the femur externally rotated from 8 (6)° to 16 (5)°. Flexion was coupled to rotation (r = 0.47). Abduction was <3° and lateral translation was <3 mm. Visually, the femur appeared to translate posteriorly until the femoral condyles rested on the posterior rim of the tibial plateau with concurrent external rotation so that the popliteal fossa aligned with the posterior margin of the medial tibial plateau.

LIMITATIONS

A limitation of the study is that knee flexion can include squat and lunge as well as kneeling.

CONCLUSION

Deep flexion requires femoral posterior translation and external rotation. These findings invite review of the concave-convex rule as it might apply to manual therapy of the knee.