Optimization of Cranio-Orbital Remodeling: Application of a Mathematical Model.

Cranio-orbital remodeling aims to correct the dysmorphic skull associated with craniosynostosis. Traditionally, the skull is reconstructed into a shape that is subjectively normal according to the surgeon's perception. We present a novel technique using a mathematical algorithm to define the optimal location for bony osteotomies and to objectively reshape the fronto-orbital bar into an ideal normal skull contour. Using pre-operative computed tomography images, the abnormal skull contour at the frontal-orbital region was obtained for infants planned to undergo cranio-orbital remodeling. The ideal skull shape was derived from an age- and sex-matched normative skull library. For each patient, the mathematical technique of dynamic programming (DP) was applied to compare the abnormal and ideal skull shapes. The DP algorithm identifies the optimal location of osteotomy sites and calculates the objective difference in surface area remaining between the normative and dysmorphic skull shape for each solution applied. By selecting the optimal solution with minimal objective difference, the surgeon is guided to reproducibly recreate the normal skull contour with defined osteotomies. The DP algorithm was applied in 13 cases of cranio-orbital remodeling. Five female and 8 male infants with a mean age of 11 months were treated for craniosynostosis classified as metopic (n = 7), unicoronal (n = 4), or bicoronal (n = 2). The mean OR time was 190.2  min (SD 33.6), mean estimated blood loss 244  cc (SD 147.6), and 10 infants required blood transfusions. Compared with a historical crania-orbital remodeling group treated without application of the algorithm, there was no significant difference in OR time, estimated blood loss, or transfusion rate. This novel technique enables the craniofacial surgeon to objectively reshape the fronto-orbital bar and reproducibly reconstruct a skull shape resembling that of normal infants.

Generation of normative pediatric skull models for use in cranial vault remodeling procedures.

PURPOSE: While the goal of craniofacial reconstruction surgery is to restore the cranial head shape as much towards normal as possible, for the individual patient, there is, in fact, no normal three-dimensional (3D) model to act as a guide. In this project, we generated a library of normative pediatric skulls from which a guiding template could be fabricated for a more standardized, objective and precise correction of craniosynostosis. METHODS: Computed tomography data from 103 normal subjects aged 8-12 months were compiled and a 3D computational model of the skull was generated for each subject. The models were mathematically registered to a baseline model for each month of age within this range and then averaged, resulting in a single 3D point cloud. An external cranial surface was subsequently passed through the point cloud and its shape and size customized to fit the head circumference of individual patients. RESULTS: The resultant fabricated skull models provide a novel and applicable tool for a detailed, quantitative comparison between the normative and patient skulls for preoperative planning and practice for a variety of craniofacial procedures including vault remodeling. Additionally, it was possible to extract the suprafrontal orbit anatomy from the normative model and fabricate a bandeau template to guide intraoperative reshaping. CONCLUSIONS: Normative head shapes for pediatric patients have wide application for craniofacial surgery including planning, practice, standarized operative repair, and standardized measurement and reporting of outcomes.

Application of CAD/CAM prefabricated age-matched templates in cranio-orbital remodeling in craniosynostosis.

Infants with craniosynostosis involving the metopic and coronal sutures require cranio-orbital reshaping to correct craniofacial dysmorphologic feature and to improve facial balance. Currently, surgical techniques to create a balanced fronto-orbital region are based on the surgeon's subjective approach and artistic vision in creating a normal shape to the forehead. To date, the use of age-matched templates and computer-assisted design/computer-assisted manufacturing techniques in optimizing the outcomes of surgical intervention in this area have not been explored. The aim of this article was to describe the process of template generation and application based on age-matched controls using computer-assisted design/computer-assisted manufacturing technology and to present this application in 2 cases.

Analytical method to measure three-dimensional strain patterns in the left ventricle from single slice displacement data.

BACKGROUND: Displacement encoded Cardiovascular MR (CMR) can provide high spatial resolution measurements of three-dimensional (3D) Lagrangian displacement. Spatial gradients of the Lagrangian displacement field are used to measure regional myocardial strain. In general, adjacent parallel slices are needed in order to calculate the spatial gradient in the through-slice direction. This necessitates the acquisition of additional data and prolongs the scan time. The goal of this study is to define an analytic solution that supports the reconstruction of the out-of-plane components of the Lagrangian strain tensor in addition to the in-plane components from a single-slice displacement CMR dataset with high spatio-temporal resolution. The technique assumes incompressibility of the myocardium as a physical constraint. RESULTS: The feasibility of the method is demonstrated in a healthy human subject and the results are compared to those of other studies. The proposed method was validated with simulated data and strain estimates from experimentally measured DENSE data, which were compared to the strain calculation from a conventional two-slice acquisition. CONCLUSION: This analytical method reduces the need to acquire data from adjacent slices when calculating regional Lagrangian strains and can effectively reduce the long scan time by a factor of two.

Development of a patient-specific surgical simulator for pediatric laparoscopic procedures.

The purpose of this study is to develop and evaluate a pediatric patient-specific surgical simulator for the planning, practice, and validation of laparoscopic surgical procedures prior to intervention, initially focusing on the choledochal cyst resection and reconstruction scenario. The simulator is comprised of software elements including a deformable body physics engine, virtual surgical tools, and abdominal organs. Hardware components such as haptics-enabled hand controllers and a representative endoscopic tool have also been integrated. The prototype is able to perform a number of surgical tasks and further development work is under way to simulate the complete procedure with acceptable fidelity and accuracy.

Surgical outcomes in craniosynostosis reconstruction: the use of prefabricated templates in cranial vault remodelling.

Cranio-orbital reshaping for anterior cranial-vault deformities associated with craniosynostosis traditionally relies on the surgeon's subjective estimate of the shape and appearance of a normal forehead. Computer-aided design/computer-aided manufacture (CAD/CAM) bandeau templates to guide reconstruction were introduced in our centre to eliminate this subjectivity and to effect more reproducible surgical results. The aim of this study was to compare two groups of patients (template, n = 14 vs. no template, n = 23) to measure surgical outcomes. The virtual, computational version of the template was used as an outcome assessment tool. It was used to calculate an intervening area under the curve (AUC) between the normative template and the patient's reconstructed supra-orbital bar on a representative computed tomography (CT) axial section. A comprehensive chart review was conducted of patients in both groups to examine the preoperative and postoperative variables. Based on the analysis performed on the immediate postoperative CT scans, in the template group - as compared to the control, no-template group - the use of the bandeau template led to a greater reduction in AUC (74% vs. 56%, p = 0.016), indicating a better conformity between the reconstructed supra-orbital bar and the ideal, normal bandeau shape. The duration of operation was significantly reduced with the use of the template (212 vs. 258 min, p < 0.001). The application of prefabricated templates in cranio-orbital reshaping is highly useful for accurate preoperative planning; reproducible and efficient intra-operative correction of dysmorphology; and objective surgical outcomes assessment.

Construction of the global lagrangian strain field in the myocardium using DENSE MRI data.

The main aim of this study is to generate global strain maps within the myocardial wall. Transmural strain calculations are performed using DENSE MRI data, acquired in a long-axis plane for canine subjects over the complete cardiac cycle. Continuum mechanics formulations were applied to all segments of the myocardium and later analyzed from anatomical and physiological perspectives. Characteristic parameters of the myocardial wall - namely global strain distributions - were quantified by means of numerical analyses of DENSE MR data. Our study demonstrated the initiation of myocardial strain as well as heterogeneous contraction patterns across the ventricle wall. There were measurable wall shear strains throughout the cardiac cycle, with the maximum strain within the long-axis plane concentrated in the septal wall at the start of systole and later becoming more pronounced in the lateral wall in the diastolic period. The methods described will lead to a better understanding of the complex myocardial contraction from these space- and time-resolved data on wall motion.

Progress towards patient-specific computational flow modeling of the left heart via combination of magnetic resonance imaging with computational fluid dynamics.

A combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) methodology has been developed to simulate blood flow in a subject-specific left heart. The research continues from earlier experience in modeling the human left ventricle using time-varying anatomical MR scans. Breathing artifacts are reduced by means of a MR navigator echo sequence with feedback to the subject, allowing a near constant breath-hold diaphragm position. An improved interactive segmentation technique for the long- and short-axis anatomical slices is used. The computational domain is extended to include the proximal left atrium and ascending aorta as well as the left ventricle, and the mitral and aortic valve orifices are approximately represented. The CFD results show remarkable correspondence with the MR velocity data acquired for comparison purposes, as well as with previously published in vivo experiments (velocity and pressure). Coherent vortex formation is observed below the mitral valve, with a larger anterior vortex dominating the late-diastolic phases. Some quantitative discrepancies exist between the CFD and MRI flow velocities, owing to the limitations of the MR dataset in the valve region, heart rate differences in the anatomical and velocity acquisitions, and to certain phenomena that were not simulated. The CFD results compare well with measured ranges in literature.