Exploiting Partial Structural Symmetry for Patient-Specific Image Augmentation in Trauma Interventions

Abstract

In unilateral pelvic fracture reductions, surgeons attempt to reconstruct the bone fragments such that bilateral symmetry in the bony anatomy is restored. We propose to exploit this "structurally symmetric" nature of the pelvic bone, and provide intra-operative image augmentation to assist the surgeon in repairing dislocated fragments. The main challenge is to automatically estimate the desired plane of symmetry within the patient's pre-operative CT. We propose to estimate this plane using a non-linear optimization strategy, by minimizing Tukey's biweight robust estimator, relying on the partial symmetry of the anatomy. Moreover, a regularization term is designed to enforce the similarity of bone density histograms on both sides of this plane, relying on the biological fact that, even if injured, the dislocated bone segments remain within the body. The experimental results demonstrate the performance of the proposed method in estimating this "plane of partial symmetry" using CT images of both healthy and injured anatomy. Examples of unilateral pelvic fractures are used to show how intra-operative X-ray images could be augmented with the forward-projections of the mirrored anatomy, acting as objective road-map for fracture reduction procedures.

Development and application of the average pelvic shape in virtual pelvic fracture reconstruction

“…Deviation analyses were conducted to compare these reductions with ones that were performed by using the reflected intact hemipelves as templates, since these were established to be effective reconstructions. [15][16][17] Table 6 shows a summary of the quantitative results. The average RMS was close in deviation analysis 1 and 2,…”

“…This technique maintains patient-specificity, yields satisfactory results and can reduce the wait-times for patients. [15][16][17] However, for bilateral pelvic fractures, where both sides of the pelvis are damaged, there is no viable model to serve as a template for the virtual reconstruction procedure. 18 Virtual pelvis reconstruction is becoming more popular in the surgical planning process, as it is expected to reduce operation times and provide more accurate reductions, which ultimately decreases the risk for the patients.…”

Exploring Partial Intrinsic and Extrinsic Symmetry in 3D Medical Imaging

“…The symmetry outliers are the results of i) unilateral dislocations and fractures, and ii) imperfect symmetry in the original anatomy. Normalized Cross-Correlation (NCC) is a commonly used intensitybased measure which is greatly sensitive to noise and outliers [51]. Therefore, it is crucial to employ a symmetry detection mechanism that is robust to the outlier regions.…”