Replacing cutting guides with an augmented reality-based navigation system: A feasibility study in the maxillofacial region.

PURPOSE: The work presents outcomes of simulated maxillofacial skeleton osteotomies supported with cutting guides or one of two AR-based intraoperative navigation systems. MATERIAL AND METHODS: The series of osteotomies supported with a cutting guide, simple AR (sAR) or navigated AR (nAR) module were carried out on 15 (five per each method) skull models according to the virtual surgical plan (VSP). Each method was used to support 40 osteotomies involving the upper jaw and 40 involving the orbital region (16 osteotomies on each model). Postoperative computed tomography scans were fused with the VSP to analyse angular deviations from the planned cutting trajectory (°) and the deviations of labelled control points (mm). RESULTS: Guides provided the highest accuracy, with a mean osteotomy angular deviation of 3.73 ± 2.94° and a mean control point deviation of 1.30 ± 0.73 mm. Mean angular deviations for the sAR- and nAR-assisted osteotomies were 5.93 ± 5.12° and 6.75 ± 5.33°, and mean control point deviations amounted to 1.86 ± 0.88 mm and 1.97 ± 0.70 mm.

"Image to patient" equal-resolution surface registration supported by a surface scanner: analysis of algorithm efficiency for computer-aided surgery.

PURPOSE: The "image to patient" registration procedure is crucial for the accuracy of surgical instrument tracking relative to the medical image while computer-aided surgery. The main aim of this work was to create an equal-resolution surface registration algorithm (ERSR) and analyze its efficiency. METHODS: The ERSR algorithm provides two datasets with equal, high resolution and approximately corresponding points. The registered sets are obtained by projection of a user-designed rectangle(s)-shaped uniform clouds of points on DICOM and surface scanner datasets. The tests of the algorithm were performed on a phantom with titanium microscrews. We analyzed the influence of DICOM resolution on the effect of the ERSR algorithm and compared the ERSR to standard paired-points landmark transform registration. The methods of analysis were Target Registration Error, distance maps, and their histogram evaluation. RESULTS: The mean TRE in case of ERSR equaled 0.8 ± 0.3 mm (resolution A), 0.8 ± 0.5 mm (resolution B), and 1.0 ± 0.7 mm (resolution C). The mean values were at least 0.4 mm lower than in the case of landmark transform registration. The distance maps between the model achieved from the scanner and the CT-based model were analyzed by histogram. The frequency of the first bin in a histogram of the distance map for ERSR was about 0.6 for all three resolutions of DICOM dataset and three times higher than in the case of landmark transform registration. The results were statistically analyzed using the Wilcoxon signed-rank test (alpha = 0.05). CONCLUSION: The tests proved a statistically significant higher efficiency of equal resolution surface registration related to the landmark transform algorithm. It was proven that the lower resolution of the CT DICOM dataset did not degrade the efficiency of the ERSR algorithm. We observed a significantly lower response to decreased resolution than in the case of paired-points landmark transform registration.

Analysis of muscle activity during rowing stroke phases.

PURPOSE: Rowing engages large muscle groups and electromyography (EMG) analysis is used to assess athletes' condition and refine sports technique. The aim of the experiment was to evaluate the muscle activation level during different phases of the rowing cycle on an ergometer. METHODS: In a study involving one professional and five amateurs, the mean EMG amplitudes from the quadriceps, gastrocnemius, biceps and triceps brachii were analyzed during different phases of rowing. A comparison was made between the degree of muscle engagement during the exercise between the professional and inexperienced individuals as well as among the different individuals during recordings obtained at different rowing speeds. The correlation coefficient between the values recorded using a strain gauge and the EMG amplitude recorded from the surface of the biceps and triceps brachii muscles was evaluated. RESULTS: The muscle activation pattern during rowing has a predictable character. A difference in the muscle activation pattern during rowing between the professionals and amateurs was observed. The EMG signal is correlated with the force recorded by the resistive strain gauge only in the experienced rower at stroke rates 20 and 25 [1/min]. CONCLUSIONS: Electromyographic analysis can be useful for assessing the correctness of rowing techniques. The activation pattern of muscles during rowing has a predictable nature. The force generated by the participants increases with an increase in rowing frequency.

Quantitative evaluation f stereoscopic augmented reality visualization using an optical see-through head-mounted display.

PURPOSE: The authors of the current study aimed to propose a calibration method for accurate augmented reality visualisation using an optical see-through head-mounted display, and to qualitatively evaluate visualisation accuracy for the application in computer assisted surgery. METHODS: An adaptation of stereo single-point active alignment method was proposed as the calibration procedure together with verification. Three tests were performed: display of points in 3D space, on the plane and on the surface of a skull phantom on inexperience users (5 participants) and experienced users (17 participants). RESULTS: The highest accuracy of visualization was obtained for skull phantom visualisation for an inexperienced user (3.00 mm, std 0.75 mm), while the lowest accuracy was obtained in a 3D visualisation test for an inexperienced user (22.95 mm, std 18.04 mm). The largest error was related to the depth component and amounted to 18.49 mm, std 18.10 mm for an inexperienced user. CONCLUSIONS: It is possible to achieve relatively high visualisation accuracy (less than 5 mm for visualisation in space) for selected users but providing it for the group of inexperienced users seems to remain a major challenge. The accuracy of point indication can be substantially and statistically significantly increased by visualising objects on surfaces. The proposed methods and obtained results can serve as a basis for further implementation of augmented reality visualisation on an optical see-through head-mounted display in applications requiring high-quality augmented reality guidance of manual tasks.

Biodegradable Fiducial Markers for Bimodal Near-Infrared Fluorescence- and X-ray-Based Imaging.

This study aimed to evaluate, for the first time, implantable, biodegradable fiducial markers (FMs), which were designed for bimodal, near-infrared fluorescence-based (NIRF) and X-ray-based imaging. The developed FMs had poly(l-lactide-co-caprolactone)-based core-shell structures made of radiopaque (core) and fluorescent (shell) composites with a poly(l-lactide-co-caprolactone) matrix. The approved for human use contrast agents were utilized as fillers. Indocyanine green was applied to the shell material, whereas in the core materials, iohexol and barium sulfate were compared. Moreover, the possibility of tailoring the stability of the properties of the core materials by the addition of hydroxyapatite (HAp) was examined. The performed in situ (porcine tissue) and in vivo experiment (rat model) confirmed that the developed FMs possessed pronounced contrasting properties in NIRF and X-ray imaging. The presence of HAp improved the radiopacity of FMs at the initial state. It was also proved that, in iohexol-containing FMs, the presence of HAp slightly decreased the stability of contrasting properties, while in BaSO4-containing ones, changes were less pronounced. A comprehensive material analysis explaining the differences in the stability of the contrasting properties was also presented. The tissue response around the FMs with composite cores was comparable to that of the FMs with a pristine polymeric core. The developed composite FMs did not cause serious adverse effects on the surrounding tissues even when irradiated in vivo. The developed FMs ensured good visibility for NIRF image-supported tumor surgery and the following X-ray image-guided radiotherapy. Moreover, this study replenishes a scanty report regarding similar biodegradable composite materials with a high potential for application.

Augmented reality visualization for aiding biopsy procedure according to computed tomography based virtual plan.

PURPOSE: The purpose of this study was to develop and verify an intraoperative module for supporting navigated biopsy procedures using optical see-through head-mounted display (HMD). METHODS: Biopsy procedure including entry and endpoints of needle insertion was planned preoperatively having regard to the resection region segmentation and safety margin definition. Biopsy procedures were performed by two users using an intraoperative optical navigation module on a specially prepared brain phantom. Two visualization techniques were compared: an accurate augmented reality one, where a virtual plan is superimposed onto surgical field by using optical see-through HMD together with personalized calibration method and visualization on the external display. RESULTS: Averaged errors from 24 trials using external display were 2.04 ± 0.83 mm for the first user and 2.69 ± 1.11 mm for the second one, while applying HMD 2.50 ± 0.93 mm (the first user) and 2.17 ± 0.82 mm (the second user), respectively. CONCLUSIONS: Proper usage of HMD visualization preceded by the personalized calibration allows the user to perform navigated biopsy procedure with comparable accuracy to its equivalent with the external display. Additionally, augmented reality visualization improves ergonomics and enables focusing on the surgical field without losing a direct line of sight with the field of view as it happens for external displays. However, ensuring high accuracy of augmented reality visualization still requires proper calibration and some user experience, which is challenging.

Supporting fibula free flap harvest with augmented reality: A proof-of-concept study.

OBJECTIVE: To analyze a novel navigation system utilizing augmented reality (AR) as a supporting method for fibula free flap (FFF) harvest and fabrication. METHODS: A total of 126 simulated osteotomies supported with a cutting guide or one of two AR-based intraoperative navigation modules-simple AR (sAR) or navigated AR (nAR)-were carried out on 18 identical models of the fibula (42 osteotomies per method). After fusing postoperative computed tomography scans of the operated fibulas with the virtual surgical plan based on preoperative images, the objective outcomes-angular deviations from the planned osteotomy trajectory (o ) and deviations of control points marked on the trajectory (mm)-were determined. RESULTS: All analyzed methods provided similar accuracy of assisted osteotomies. The only significant difference referred to angular deviation in the sagittal plane, which was smaller after the cutting guide-assisted procedures than after the application of sAR and nAR (4.1 ± 2.29 vs. 5.08 ± 3.64 degrees, P = 0.031 and 4.1 ± 2.29 vs. 4.97 ± 2.91, P = 0.002, respectively). Mean deviation of control points after the cutting guide-assisted procedures was 2.76 ± 1.06 mm, as compared with 2.67 ± 1.09 mm for sAR and 2.95 ± 1.11 mm for nAR. CONCLUSION: Our study demonstrated that both novel AR-based methods provided similar accuracy of assisted harvesting and contouring of the FFF as the cutting guides. This fact, as well as the acceptability of the concept by clinicians, justify their further development and evaluation in preclinical settings. LEVEL OF EVIDENCE: NA Laryngoscope, 130:1173-1179, 2020.

Supporting mandibular resection with intraoperative navigation utilizing augmented reality technology - A proof of concept study.

OBJECTIVE: The aim of this study was to compare the accuracy of simulated mandibular osteotomies performed with cutting guides and two different intraoperative navigation systems based on simple (sAR) and navigated (nAR) augmented reality technology. MATERIAL AND METHODS: A total of 126 osteotomies were performed on 21 identical mandible models according to a prespecified virtual surgery plan. The data from postoperative computed tomography (CT) images were fused with preoperative CT scans to objectively compare the outcomes, i.e. angular deviations from the osteotomy trajectory (°) and displacement of two control points (mm). RESULTS: Osteotomies performed with cutting guides turned out to be the most accurate, with mean angular deviation of 4.94 ± 4.62° and mean control point displacement of 1.65 ± 0.88 mm. Mandibular osteotomies assisted with sAR and nAR were less accurate in terms of mean angular deviations (5.34 ± 3.67° and 7.14 ± 5.19°, respectively) and control point displacements (1.79 ± 0.94 mm and 2.41 ± 1.34 mm, respectively). CONCLUSION: Our findings imply that in future, AR-based intraoperative navigation systems may find application in everyday clinical practice. Although AR technology still requires some improvements, it can already be used for presentation of digital navigation data, enhancing surgeon's awareness and hand-eye coordination during mandibular resection and reconstruction procedures.

Navigation-guided fibula free flap for mandibular reconstruction: A proof of concept study.

OBJECTIVE: To analyze a novel technique of supporting fibula free flap harvest and fabrication with intraoperative navigation technology. MATERIALS AND METHODS: In the first phase of the study, navigation accuracy achieved with two registration methods, namely, point-pair and hybrid technique utilizing point-pair with surface matching, were evaluated in the form of the fiducial (FRE) and target registration error (TRE). Next, a series of 42 simulated navigated fibular osteotomies were conducted on specially manufactured lower leg phantom. Postoperative results were analyzed in the form of the angular and position deviations between the virtually planned and the obtained osteotomies. RESULTS: Mean FRE values obtained with point-pair and hybrid registration methods were 1.82 ± 0.96 mm and 1.41 ± 0.44 mm, respectively. Mean TRE value in the fibula region was 2.00 ± 0.67 mm for the first method and 1.51 ± 0.72 mm for the second. For all performed surgeries, the total mean angular deviation between the planned and actual osteotomy trajectory equaled 3.66° ± 3.60°. The total mean position disparity of osteotomy control points was 1.85 ± 0.99 mm. CONCLUSIONS: Navigation-guided free fibula flap harvest and fabrication, due to encouraging study results and its superiority over currently popular cutting guides in many clinical aspects, may become a routine operative procedure for the reconstruction of complex mandibular defects. The presented method is especially well suited for plastic and maxillofacial surgery.

Image-guided bone resection as a prospective alternative to cutting templates­A preliminary study.

OBJECTIVE: To evaluate the accuracy of craniomaxillofacial resections performed with an image-guided surgical sagittal saw. MATERIAL AND METHODS: Twenty-four craniomaxillofacial resections were performed using an image-guided sagittal saw. Surgical outcomes were compared with a preoperative virtual plan in terms of the resected bone volume, control point position and osteotomy trajectory angle. Each measurement was performed twice by two independent observers. RESULTS: The best convergence between the planned and actual bone resection was observed for the orbital region (6.33 ± 4.04%). The smallest mean difference between the preoperative and postoperative control point positions (2.00 ± 0.66 mm) and the lowest mean angular deviation between the virtual and actual osteotomy (5.49 ± 3.17 degrees) were documented for the maxillary region. When all the performed procedures were analyzed together, mean difference between the planned and actual bone resection volumes was 9.48 ± 4.91%, mean difference between the preoperative and postoperative control point positions amounted to 2.59 ± 1.41 mm, and mean angular deviation between the planned and actual osteotomy trajectory equaled 8.21 ± 5.69 degrees. CONCLUSION: The results of this study are encouraging but not fully satisfactory. If further improved, the hereby presented navigation technique may become a valuable supporting method for craniomaxillofacial resections.

Improving surgical precision--application of navigation system in orthopedic surgery.

Navigation systems track objects with precision expressed as root mean square equalling even up to 0.15 mm. Application of navigation system combined with imaging technique makes surgical operations less invasive, which results in the reduced risk of infection, smaller scar and a shorter time of rehabilitation. Imaging techniques allow surgeon to create individual virtual models for virtual surgery planning. Navigation system tracks the positions of surgical tools in relation to the patient's coordinate systems. Medical imaging enables low-invasive surgery, whereas the position of surgical instruments is monitored on screen. The paper presents a newly developed computer-aided surgical system consisting of ultrasonographic probe and tracking system to measure bone geometry, design surgical scenario virtually and follow it intraoperatively. The system assists surgeon to correct bone deformities. The paper presents the results of several accuracy tests, which demonstrate good repeatability and accuracy.