Marker Registration Research Articles

Investigation of the clinical inter-observer bias in prostate fiducial marker image registration between CT and MR images

Background and purposeInter-modality image registration between computed tomography (CT) and magnetic resonance (MR) images is associated with systematic uncertainties and the magnitude of these uncertainties is not well documented. The purpose of this study was to investigate the potential uncertainty of gold fiducial marker (GFM) registration for localized prostate cancer and to estimate the inter-observer bias in a clinical setting.Methods Four experienced observers registered CT and MR images for 42 prostate cancer patients. Manual GFM identification was followed by a landmark-based registration. The absolute difference between observers in GFM identification and the displacement of the clinical target volume (CTV) was investigated. The CTV center of mass (CoM) vector displacements, DICE-index and Hausdorff distances for the observer registrations were compared against a clinical baseline registration. The time allocated for the manual registrations was compared.ResultsAbsolute difference in GFM identification between observers ranged from 0.0 to 3.0 mm. The maximum CTV CoM displacement from the clinical baseline was 3.1 mm. Displacements larger than or equal to 1 mm, 2 mm and 3 mm were 46%, 18% and 4%, respectively. No statistically significant difference was detected between observers in terms of CTV displacement. Median DICE-index and Hausdorff distance for the CTV, with their respective ranges were 0.94 [0.70–1.00] and 2.5 mm [0.7–8.7].ConclusionsRegistration of CT and MR images using GFMs for localized prostate cancer patients was subject to inter-observer bias on an individual patient level. A CTV displacement as large as 3 mm occurred for individual patients. These results show that GFM registration in a clinical setting is associated with uncertainties, which motivates the removal of inter-modality registrations in the radiotherapy workflow and a transition to an MRI-only workflow for localized prostate cancer.

A marker registration method to improve joint angles computed by constrained inverse kinematics.

Accurate computation of joint angles from optical marker data using inverse kinematics methods requires that the locations of markers on a model match the locations of experimental markers on participants. Marker registration is the process of positioning the model markers so that they match the locations of the experimental markers. Markers are typically registered using a graphical user interface (GUI), but this method is subjective and may introduce errors and uncertainty to the calculated joint angles and moments. In this investigation, we use OpenSim to isolate and quantify marker registration–based error from other sources of error by analyzing the gait of a bipedal humanoid robot for which segment geometry, mass properties, and joint angles are known. We then propose a marker registration method that is informed by the orientation of anatomical reference frames derived from surface-mounted optical markers as an alternative to user registration using a GUI. The proposed orientation registration method reduced the average root-mean-square error in both joint angles and joint moments by 67% compared to the user registration method, and eliminated variability among users. Our results show that a systematic method for marker registration that reduces subjective user input can make marker registration more accurate and repeatable.

Augmented reality-based robot teleoperation system using RGB-D imaging and attitude teaching device

Augmented reality (AR)-based programming using the demonstration method has been widely studied. However, studies on AR-based programming for remote robots are lacking because of the limitation of human–computer interaction. This paper proposes an AR-based robot teleoperation system and method using RGB-D imaging and an attitude teaching device. By sending the color and depth images of the remote robot environment to the local side, the operators can complete the teleoperation of the robot at the local side. First, the operators select key positions on the motion path of the robot endpoint from color images via a mouse, and the computer calculates the 3D coordinates of these key points in the robot base coordinate system to complete the position teaching process. In the robot attitude teaching process, the AR technology is used to superimpose the virtual robot model onto the color images of the robot teleoperation environment, so as to make the virtual robot endpoint to move along the teaching path. An operator can use the portable attitude teaching device designed in this study to control the robot movement parameters, such as the attitude and motion speed, during the movement of the virtual robot. After the position and attitude teaching processes, the robot movement trajectory can be generated. To make the base coordinate system of the virtual model consistent with that of the physical robot, we propose an online AR registration method, which does not require manually placing the AR registration marker. The proposed AR-based robot teleoperation system can quickly and easily complete robot teleoperation at the local side.

Development of Augmented Reality System for Productivity Enhancement in Offshore Plant Construction

As the scale of offshore plants has gradually increased, the amount of management points has significantly increased. Therefore, there are needs for innovative process control, quality management, and an installation support system to improve productivity and efficiency for timely construction. In this paper, we introduce a novel approach to deal with these issues using augmented reality (AR) technology. The core of successful AR implementation is up to scene matching through accurate pose (position and alignment) estimation using an AR camera. To achieve this, this paper first introduces an accurate marker registration technique that can be used in huge structures. In order to improve the precision of marker registration, we propose a method that utilizes the natural feature points and the marker corner points in the optimization step simultaneously. Subsequently, a method of precisely generating AR scenes by utilizing these registered markers is described. Finally, to validate the proposed method, the best practices and its effects are introduced. Based on the proposed AR system, construction workers are now able to quickly navigate to onboard destinations by themselves. In addition, they are able to intuitively install and inspect outfitting parts without paper drawings. Through field tests and surveys, we confirm that AR-based inspection has a significant time-saving effect compared to conventional drawing-based inspection.

Monitoring the three-dimensional distribution of endogenous species in the lungs by matrix-assisted laser desorption/ionization mass spectrometry imaging.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is routinely employed to monitor the distribution of compounds in tissue sections and generate two-dimensional (2D) images. Whilst informative the images do not represent the distribution of the analyte of interest through the entire organ. The generation of 3D images is an exciting field that can provide a deeper view of the analyte of interest throughout an entire organ. Serial sections of mouse and rat lung tissue were obtained at 120 μm depth intervals and imaged individually. Homogenate registration markers were incorporated in order to aid the final 3D image construction. Using freely available software packages, the images were stacked together to generate a 3D image that showed the distribution of endogenous species throughout the lungs. Preliminary tests were performed on 16 serial tissue sections of mouse lungs. A 3D model showing the distribution of phosphocholine at m/z 184.09 was constructed, which defined the external structure of the lungs and trachea. Later, a second experiment was performed using 24 serial tissue sections of the left lung of a rat. Two molecular markers, identified as [PC (32:1) + K]+ at m/z 770.51 and [PC (36:4) + K]+ at m/z 820.52, were used to generate 3D models of the parenchyma and airways, respectively. A straightforward method to generate 3D MALDI-MS images of selected molecules in lung tissue has been presented. Using freely available imaging software, the 3D distributions of molecules related to different anatomical features were determined.

Accuracy of Le Fort I osteotomy with combined computer-aided design/computer-aided manufacturing technology and mixed reality

The aim of this study was to verify the reproducibility and accuracy of preoperative planning in maxilla repositioning surgery performed with the use of computer-aided design/manufacturing technologies and mixed reality surgical navigation, using new registration markers and the HoloLens headset. Eighteen patients with a mean age of 26.0 years were included. Postoperative evaluations were conducted by comparing the preoperative virtual operation three-dimensional image (Tv) with the 1-month postoperative computed tomography image (T1). The three-dimensional surface analysis errors ranged from 79.9% to 97.1%, with an average error of 90.3%. In the point-based analysis, the errors at each point on the XYZ axes were calculated for Tv and T1 in all cases. The median signed value deviation of all calculated points on the XYZ axes was −0.03mm (range −2.93mm to 3.93mm). The median absolute value deviation of all calculated points on the XYZ axes was 0.38mm (range 0mm to 3.93mm). There were no statistically significant differences between any of the points on any of the axes. These values indicate that the method used was able to reproduce the maxilla position with high accuracy.

Creating CT- and MRI-guided urethra planning-risk-volumes for urethra-sparing prostate stereotactic body radiotherapy

Dose-escalation in prostate cancer SBRT improves PSA nadir and negative post-treatment biopsy rates, but increases genitourinary toxicity. The definition of the urethra PRV (uPRV) is not standardized. A Foley-catheter based uPRV incorporates catheter-induced anatomic variability that is not reproduced during daily treatment without catheter, whereas anatomic uncertainty during MRI-CT registration is inherent to the MRI-based uPRV. We thus examined the urethra as delineated on CT and MRI to identify an optimal urethral PRV. The urethra was contoured on CT with catheter (uCT) and T2 MRI without catheter (uMRI) in 25 men with prostate cancer. Men received three intraprostatic gold fiducial markers for localization, and rectal spacer to reduce rectal toxicity. MRI was first registered to the CT (reg1) using automated rigid registration of fiducial markers; u_MRI in this position was labelled uMRI_1. MRI was rigidly registered to the CT again (reg2); this time manually to the posterior prostate/anterior rectal wall interface (a clinically relevant region of interest in delineating a hydrogel spacer for radiation planning without taking into account fiducial markers). The uMRI volume created from this manual MRI-CT registration was labeled uMRI_2. Urethral PRVs were created by uniform, and anterior-posterior (A-P) only, expansions in 1 mm increments around uCT. The proportion of uMRI_1, and uMRI_2 covered by each successive uPRV was measured, as was the decrement in the volume PTV-uPRV. Mean and standard deviation uCT and uMRI volumes were 1.72±0.58 and 1.01±0.51 cc, respectively. Automated MRI-CT registration (reg1) with fiducial markers resulted, on average, in 0.2 mm translational separation of each fiducial marker on MRI to its intended fiducial marker target on CT. The translation and rotation matrix differences between reg1 and reg2 (manual) were: -1.1±2.47, -2.87±6.17 and 0.08±4.68 mm; and -0.16±8.29, 0.75±3.17 and 1.42±4.01 degrees. The smallest average urethra contour that would encompass uCT and uMRI_1 was 2.34±0.75 cc; that for uCT, uMRI_1 and uMRI_2 was 2.87±1.04 cc. The likelihood of urethra coverage and mean percent PTV-uPRV for a given uPRV are shown in the table. Uniform 3 mm uPRV encompassed 88% of uCT and uMRI_1, and 83% of uCT, uMRI_1 and uMRI_2, versus 82% and 75% with A-P only uPRV. Uniform and A-P 3 mm uPRVs are created at the expense of 7% and 4% of PTV, respectively. Three-quarters of potential urethra variability on CT and MRI are included in an A-P 3 mm PRV around a catheter. Additional uniform, or A-P, uPRV expansions for urethral protection must be weighed against clinically relevant declines in PTV-uPRV.Abstract 4128; TablePRV (mm)123456% of:uCT, uMRI_1 included in uniform PRV808588919395uCT, uMRI_1 included in A-P PRV768082848687uCT, uMRI_1 and uMRI_2 included in uniform PRV717883889193uCT, uMRI_1 and uMRI_2 included in A-P PRV677275788183PTV decrease by uniform PRV457101215PTV decrease by A-P PRV344567 Open table in a new tab

Prescribing joint co-ordinates during model preparation in OpenSim improves lower limb unplanned sidestepping kinematics

ObjectivesInvestigate how prescribing participant-specific joint co-ordinates during model preparation influences the measurement agreement of inverse kinematic (IK) derived unplanned sidestepping (UnSS) lower limb kinematics in OpenSim in comparison to an established direct kinematic (DK) model. DesignParallel forms repeatability. MethodsThe lower limb UnSS kinematics of 20 elite female athletes were calculated using: 1) an established DK model (criterion) and, 2) two IK models; one with (IKPC) and one without (IK0) participant-specific joint co-ordinates prescribed during the marker registration phase of model preparation in OpenSim. Time-varying kinematic analyses were performed using one dimensional (1D) statistical parametric mapping (α=0.05), where zero dimensional (0D) Root Mean Squared Error (RMSE) estimates were calculated and used as a surrogate effect size estimates. ResultsStatistical differences were observed between the IKPC and DK derived kinematics as well as the IK0 and DK derived kinematics. For the IKPC and DK models, mean kinematic differences over stance for the three dimensional (3D) hip joint, 3D knee joint and ankle flexion/extension (F/E) degrees of freedom (DoF) were 46±40% (RMSE=5±5°), 56±31% (RMSE=7±4°) and 3% (RMSE=2°) respectively. For the IK0 and DK models, mean kinematics differences over stance for the 3D hip joint, 3D knee joint and ankle F/E DoF were 70±53% (RMSE=14±11°), 46±48% (RMSE=8±7°) and 100% (RMSE=11°) respectively. ConclusionsPrescribing participant-specific joint co-ordinates during model preparation improves the agreement of IK derived lower limb UnSS kinematics in OpenSim with an established DK model, as well as previously published in-vivo knee kinematic estimates.

A novel extraoral registration method for a dynamic navigation system guiding zygomatic implant placement in patients with maxillectomy defects

Zygomatic implants (ZIs) are used for the oral rehabilitation of patients with maxillectomy defects as an alternative to extensive bone grafting surgeries. New technologies such as computer-assisted navigation systems can improve the accuracy and safety of ZI placement. The intraoral anchorage of fiducial markers necessary for navigation registration is not possible in the case of a severe maxillary defect and lack of residual bone. This technical note presents a novel extraoral registration method for a dynamic navigation system guiding ZI placement in patients with maxillectomy defects. Titanium microscrews were inserted in the mastoid process, supraorbital ridge, and posterior zygomatic arch as registration markers. The mean fiducial registration error (FRE) was 0.53 ± 0.20 and the deviations between the planned and placed ZIs were 1.56 ± 0.54 mm (entry point), 1.87 ± 0.63 mm (exit point), and 2.52 ± 0.84° (angulation). The study results indicate that the placement of fiducial markers at extraoral sites can be used as a registration technique to overcome anatomical limitations in patients after maxillectomy, with a clinically acceptable registration accuracy.

Comparison of positioning accuracy of different registration methods and dosimetric analysis of adaptive radiotherapy for breast cancer after breast conserving surgery.

BackgroundThis study explores the effect of different registration methods on the placement accuracy and dosimetric analysis of adaptive radiation therapy (ART) after breast conserving surgery for breast cancer, based on cone-beam computed tomography (CBCT).MethodsThirty breast cancer patients, who underwent breast conserving surgery, were divided into three groups, with 10 patients in each group: automatic grayscale registration (group A), automatic bony marker registration (group B), and automatic grayscale registration combined with manual bony marker registration (group C). Three registration methods were conducted before the first radiotherapy, and once a week under the guidance of CBCT. The dosimetric comparison was made with the original plan.ResultsThe X direction was significantly different between groups A and B (P=0.036). The X and Y direction were significantly different between groups A and C (P=0.001, P=0.019). The placement errors were significantly different between groups B and C in the X and Y directions (P<0.001, P=0.003). The ART plan was significantly better than the original plan, in terms of the Dmax, Dmean, D90, V90, V100, V95, HI and CI of planning target volume (PTV) (P<0.05). Furthermore, the ART plan was significantly better, in terms of the Dmean, V5, V10, V20 and V30 of the affected lung, the Dmean, V5, V10, V20 and V30 of the double lung, and the Dmean, V5, V10, V20 and V30 of the heart. Moreover, the Dmax, V5 and V10 of the contralateral breast were significantly lower than those in the original CT plan (P<0.05).ConclusionsFor the CBCT placement verification after breast conserving surgery, the accuracy and stability of automatic gray-scale registration combined with manual bone markers are better than those of the automatic gray-scale registration and automatic bone marker registration.

Fully Digital Workflow for Planning Static Guided Implant Surgery: A Prospective Accuracy Study.

The accuracy of static guided implant surgery (sGIS) using conventional planning workflow has been extensively examined; however, more information is required to justify the application of fully digital planning protocol. The purpose of this study was to investigate the clinical accuracy of sGIS with a fully digital planning workflow. Twenty-one partially edentulous patients were enrolled in this prospective study. Cone-beam computed tomography (CBCT) and intraoral scans were taken and superimposed by matching the dental surface images directly (surface registration protocol) or by matching fiducial markers on a stereolithographic (SLA) radiographic template fabricated from the digital data of the intraoral scan (fiducial marker registration protocol). Virtual implant treatment plans were then determined, and tooth-supported SLA surgical guides were fabricated according to the plans. Twenty-six implant surgeries were performed via the surgical guide by one surgeon. Pre- and post-operative CBCT images were superimposed, and the positional and angular deviations between placed and planned implants were measured with metrology software. A total of 43 fully guided implants were placed, in which 25 implants were planned with the surface registration protocol. Implants planned based on the surface registration protocol had a larger mean angular deviation than the fiducial marker registration protocol. No significant differences were found for any deviations of the examined variables. Within the limits of this study, we concluded that the clinical accuracy of the sGIS planned with a fully digital workflow was consistent with the conventional workflow for partially edentulous patients.

Application of an open position splint integrated with a reference frame and registration markers for mandibular navigation surgery

Navigation surgery plays an important role in modern craniomaxillofacial surgery, but it is difficult to apply navigation surgery to the mandible, due to its mobility. At present, headbands or headpins are widely used for fixation of the reference frame, and three strategies are generally used for the application of navigation surgery to the mandible. This article reports the application of a novel open position splint integrated with a reference frame and registration markers for mandibular navigation surgery as a fourth strategy. Using this custom-made integrated splint, a marker-based pair-point registration procedure was completed easily and non-invasively. Furthermore, the neurovascular canal tract could be easily identified, and the cyst, as well as the surrounding daughter cysts, could be removed with high accuracy. This strategy has potential for widespread clinical application in mandibular navigation surgery.

Precision study of stereotactic electroencephalograph electrode implantation under neuronavigation in children with refractory epilepsy

Objective To explore the accuracy of stereotactic electroencephalograph (SEEG) electrode implantation under neuronavigation in children with refractory epilepsy. Methods Twenty-one children with refractory epilepsy underwent SEEG electrode implantation for identification of epileptogenic zone at Neurosurgery Department of Shenzhen Children's Hospital from March 2016 to December 2017 and were retrospective enrolled into this study MR surface registration and CT registration with anatomic markers were used for the electrode implantation. The accuracy of electrode implantation was compared between the 2 registration methods. The correlation between the depth of electrode implantation (the distance from cortical entry point to target) and the error of target and the error of entry point was analyzed. Results A total of 139 electrodes were implanted in 21 patients. Among them, 56 electrodes were implanted by MR surface registration method, and 83 implanted electrodes were placed by CT anatomical marker registration method. The registration time, registration error, electrode entry error and target error of MR Surface registration group were (37±9) min, (2.3±0.5) mm, (2.7±0.7) mm and (3.1±0.5) mm; those in anatomical marker registration group were (10±4) min, (1.1±0.3) mm, (1.5±0.5) mm, (2.2±0.6) mm respectively. The differences were statistically significant (all P<0.05) in the comparison between the 2 groups. In 139 electrodes, the electrode implantation depth was (4.7±1.7) mm, the entry point error was (2.1±1.3) mm, and the target error was (2.8±1.2) mm. Correlation analysis showed that the depth of electrode implantation was positively correlated with the target error (r=0.57, P=0.034), and there was no correlation with the error of the entry point (r=0.27, P=0.121). None of the patients had complications such as bleeding and infection after electrode implantation. After epileptogenic zonectomy, all patients were followed up for 6 months and included 20 cases as Engel Ⅰ and 1 case as Engel Ⅱ. Conclusion In children with refractory epilepsy, the accuracy of SEEG electrode implantation under neuronavigation seems to be relatively high. Compared with MR surface registration method, the registration efficiency and the accuracy of electrode implantation can be improved by using CT anatomical marker registration. Key words: Epilepsy; Child; Error; Neuronavigation; Stereoelectroencephalography

Abstract No. 512 Augmented reality for transperineal prostate procedures with smart-glasses or smartphone needle planning and guidance

The grid template based guidance method in transperineal prostate procedure is associated with limited positioning resolution and lack of needle angulation options. To overcome the limitations, and to free the operator from the constraints of a grid, a novel augmented reality system was developed that uses smart see-through glasses, a smartphone, or a tablet for needle planning and guidance in transperineal prostate procedures. The custom IR AR system was developed to display the planned needle path on the smartphone and smart-glasses’ screens, in real-time, superimposed over the patient’s anatomy. A special designed image marker registration frame with fiducial markers embedded was attached to a phantom patient perineum, and was used to orient and track the pre-procedural volumetric image with the AR system. The displayed needle plan was always referenced to the patient and independent from the physical pose of the devices. The AR feature allows the operator to continuously compare the actual needle location with the plan as well as with the superimposed anatomy and target. Multiple devices can be used simultaneously and communicate via a local network. The AR app’s on-the-spot planning function allow defining needle path at the bedside. The system was evaluated using interventional prostate phantoms with iPhone and ODG R-7 glasses. The overlay accuracy was defined as the 2D angular difference between the actual needle inserted into the phantom and the derived virtual needle on the AR device. After free-hand insertion with AR assistance, the guidance accuracy was measured by the distance between the needle tip and the target in the post CT. The overlay accuracy was 0.58±0.43º and 1.62±1.52º in iPhone and R-7 respectively. The iPhone guidance accuracy was 1.9±0.97 mm (lateral) and 1.0±0.5 mm (in-direction), the R-7 guidance accuracy was 2.8±1.4 mm (lateral) and 2.3±1.5 mm (in-direction). A custom AR system using smart-glasses and smartphone can provide accurate needle guidance and see-through-the-skin display of anatomy, needle, and targets for transperineal prostate interventions. How such devices might assist or augment standard procedures remains to be defined.

Errors according to the number of registered markers used in navigation-assisted surgery of the mandible

BackgroundThe aim of this study was to evaluate the accuracy of navigation according to the number of markers in terms of target registration errors (TREs) at each anatomical location during the registration process of the navigation system for the mandible.MethodsThe TREs were measured in five different experiments, varying only in the number of registration reference markers, which ranged from three to seven. To measure the TREs according to the number of registration reference markers, two experimental navigation devices were used: 1) Cbyon navigation surgery equipment 2) Polaris optical tracker. Both experiments were conducted to obtain the TREs at the anatomical locations of the mandible according to the number of registration markers during the navigation process. Statistical analysis was performed using the SPSS 23.0 software.ResultsAt all anatomical locations, errors were 2 mm or less. Further, significant differences in the target errors measured by the Cbyon system were found according to the number of registration markers. Significant differences in the target errors measured by the Polaris optical tracker were found according to the registration markers at the posterior border only. In both groups, the target errors did not decrease as the number of registration markers increased.ConclusionsThis study demonstrates that an increase in the number of registration markers is not associated with a decrease in the TRE, and that a specific number of registration markers could reduce the TREs at each anatomical site. It is important to determine the minimum number of image registration markers at which the smallest TRE would be observed for different surgical sites.

Texture mapping based on photogrammetric reconstruction of the coded markers.

Texture mapping is one of the key procedures to generate photorealistic three-dimensional (3D) models. To avoid dependence on the features of the texture and the geometric model, coded markers are introduced as the control points to assist the texture mapping. Multiple texture images containing the markers are captured, and the 3D coordinates of the markers are reconstructed with photogrammetry; meanwhile, the parameters of the texture camera are optimized with the bundle adjustment strategy. Then the pose parameters of the texture mapping can be calculated with the assistance of the marker registration and the iterative closest point (ICP) algorithms. The validity of the proposed algorithm is demonstrated with an experiment on an ordinary object.

Front shape similarity measure for data-driven simulations of wildland fire spread based on state estimation: Application to the RxCADRE field-scale experiment

Data-driven wildfire spread modeling is emerging as a cornerstone for forecasting real-time fire behavior using thermal-infrared imaging data. One key challenge in data assimilation lies in the design of an adequate measure to represent the discrepancies between observed and simulated firelines (or “fronts”). A first approach consists in adopting a Lagrangian description of the flame front and in computing a Euclidean distance between simulated and observed fronts by pairing each observed marker with its closest neighbor along the simulated front. However, this front marker registration approach is difficult to generalize to complex front topology that can occur when fire propagation conditions are highly heterogeneous due to topography, biomass fuel and micrometeorology. To overcome this issue, we investigate in this paper an object-oriented approach derived from the Chan–Vese contour fitting functional used in image processing. The burning area is treated as a moving object that can undergo shape deformations and topological changes. We combine this non-Euclidean measure with a state estimation approach (a Luenberger observer) to perform simulations of the time-evolving fire front location driven by discrete observations of the fireline. We apply this object-oriented data assimilation method to the three-hectare RxCADRE S5 field-scale experiment. We demonstrate that this method provides more accurate forecast of fireline propagation than if either the fire spread model or the observations were taken separately. Results show that when the observation frequency becomes lower than 1/60 s−1, the forecast performance of data assimilation is improved compared to simply extrapolating observation data. This highlights the need of a physics-based forward model to forecast flame front propagation. We also demonstrate that the front shape similarity measure is suitable for both Eulerian and Lagrangian-type front-tracking solvers and thereby can provide a unified framework to track moving structures such as flame front position and topology in combustion problems.

Accuracy Assessment of Different Registration and Imaging Methods on Image-Guided Surgery of Lateral Skull Base

Background: The use of Image Guided Surgery (IGS) systems at lateral skull base surgery is controversial due to the limitation of the accuracy of the systems. The intraoperative accuracy of the IGS is dependent on deferent parameters, mainly the precision of the system, resolution of utilized imaging, rigidity of the reference frame/adaptor, registration method, calibration of the utilized instruments, and intraoperative movement of the reference markers. Objectives: In this study the researchers examined the target registration error of an electromagnetic IGS system on different important structures of lateral skull base through different approaches. This study compared two registration methods and two scanning systems. Methods: In 10 formaldehyde-fixed human cadaver heads, 69 target points were marked with titanium screws for determining target registration errors. The target points were facial nerve, lateral semi-circular canal, geniculate ganglion, superior semi-circular canal, internal auditory canal, and the foramen rotundum. Seven heads were scanned using a Cone Beam CT Scanner (CBCT) and three heads were scanned using a CT scanner. Three screws were implanted around the mastoidectomy cavity as Fiducial Markers (FM). Two different registration methods were applied, including point based registration using the FM versus surface registration. All samples were dissected via the middle cranial fossa approach, retrosigmoid approach, and transmastoid approaches. Results: The overall accuracy of the IGS-system was 1.2 mm and plusmn; 0.15 mm. Optimum accuracy was reached with CBCT-scan and the FM registration marker. Navigation using CT scans with the surface registration method, using CT scans with FM registration method, and using CBCT-scans with surface registration method had lower accuracy, respectively, yet their difference was not statistically significant (P > 0.5). The best accuracy was noted on the facial nerve in the mastoid approach (mean 0.8 mm). Conclusions: The feasibility of the use of an electromagnetic IGS system in lateral skull base, surgery using Cone Beam CT as well as conventional CT scanner with fiducial marker registration as well as surface registration were evaluated. The accuracy was best at the lateral region of the temporal bone and decreased on further medial targets, such as lower cranial nerve and trigeminal ganglion.

Marker Registration Technique for Handwritten Text Marker in Augmented Reality Applications

Marker registration is a fundamental process to estimate camera poses in marker-based Augmented Reality (AR) systems. We developed AR system that creates correspondence virtual objects on handwritten text markers. This paper presents a new method for registration that is robust for low-content text markers, variation of camera poses, and variation of handwritten styles. The proposed method uses Maximally Stable Extremal Regions (MSER) and polygon simplification for a feature point extraction. The experiment shows that we need to extract only five feature points per image which can provide the best registration results. An exhaustive search is used to find the best matching pattern of the feature points in two images. We also compared performance of the proposed method to some existing registration methods and found that the proposed method can provide better accuracy and time efficiency.

Reconstruction of a Deformed Tumor Based on Fiducial Marker Registration: A Computational Feasibility Study

Interstitial photodynamic therapy has shown promising results in the treatment of locally advanced head and neck cancer. In this therapy, systemic administration of a light-sensitive drug is followed by insertion of multiple laser fibers to illuminate the tumor and its margins. Image-based pretreatment planning is employed in order to deliver a sufficient light dose to the complex locally advanced head-and-neck cancer anatomy, in order to meet clinical requirements. Unfortunately, the tumor may deform between pretreatment imaging for the purpose of planning and intraoperative imaging when the plan is executed. Tumor deformation may result from the mechanical forces applied by the light fibers and variation of the patient’s posture. Pretreatment planning is frequently done with the assistance of computed tomography or magnetic resonance imaging in an outpatient suite, while treatment monitoring and control typically uses ultrasound imaging due to considerations of costs and availability in the operation room. This article presents a computational method designed to bridge the gap between the 2 imaging events by taking a tumor geometry, reconstructed during preplanning, and by following the displacement of fiducial markers, which are initially placed during the preplanning procedure. The deformed tumor shape is predicted by solving an inverse problem, seeking for the forces that would have resulted in the corresponding fiducial marker displacements. The computational method is studied on spheres of variable sizes and demonstrated on computed tomography reconstructed locally advanced head and neck cancer model. Results of this study demonstrate an average error of less than 1 mm in predicting the deformed tumor shape, where 1 mm is typically the order of uncertainty in distance measurements using magnetic resonance imaging or computed tomography imaging and high-quality ultrasound imaging. This study further demonstrates that the deformed shape can be calculated in a few seconds, making the proposed method clinically relevant.