How to operate a liver tumor you cannot see

SEEG4D: a tool for 4D visualization of stereoelectroencephalography data

Epilepsy is a prevalent and serious neurological condition which impacts millions of people worldwide. Stereoelectroencephalography (sEEG) is used in cases of drug resistant epilepsy to aid in surgical resection planning due to its high spatial resolution and ability to visualize seizure onset zones. For accurate localization of the seizure focus, sEEG studies combine pre-implantation magnetic resonance imaging, post-implant computed tomography to visualize electrodes, and temporally recorded sEEG electrophysiological data. Many tools exist to assist in merging multimodal spatial information; however, few allow for an integrated spatiotemporal view of the electrical activity. In the current work, we present SEEG4D, an automated tool to merge spatial and temporal data into a complete, four-dimensional virtual reality (VR) object with temporal electrophysiology that enables the simultaneous viewing of anatomy and seizure activity for seizure localization and presurgical planning. We developed an automated, containerized pipeline to segment tissues and electrode contacts. Contacts are aligned with electrical activity and then animated based on relative power. SEEG4D generates models which can be loaded into VR platforms for viewing and planning with the surgical team. Automated contact segmentation locations are within 1 mm of trained raters and models generated show signal propagation along electrodes. Critically, spatial-temporal information communicated through our models in a VR space have potential to enhance sEEG pre-surgical planning.

Beyond the visible: preliminary evaluation of the first wearable augmented reality assistance system for pancreatic surgery

PURPOSE

The retroperitoneal nature of the pancreas, marked by minimal intraoperative organ shifts and deformations, makes augmented reality (AR)-based systems highly promising for pancreatic surgery. This study presents preliminary data from a prospective study aiming to develop the first wearable AR assistance system, ARAS, for pancreatic surgery and evaluating its usability, accuracy, and effectiveness in enhancing the perioperative outcomes of patients.

METHODS

We developed ARAS as a two-phase system for a wearable AR device to aid surgeons in planning and operation. This system was used to visualize and register patient-specific 3D anatomical models during the surgery. The location and precision of the registered 3D anatomy were evaluated by assessing the arterial pulse and employing Doppler and duplex ultrasonography. The usability, accuracy, and effectiveness of ARAS were assessed using a five-point Likert scale questionnaire.

RESULTS

Perioperative outcomes of five patients underwent various pancreatic resections with ARAS are presented. Surgeons rated ARAS as excellent for preoperative planning. All structures were accurately identified without any noteworthy errors. Only tumor identification decreased after the preparation phase, especially in patients who underwent pancreaticoduodenectomy because of the extensive mobilization of peripancreatic structures. No perioperative complications related to ARAS were observed.

CONCLUSIONS

ARAS shows promise in enhancing surgical precision during pancreatic procedures. Its efficacy in preoperative planning and intraoperative vascular identification positions it as a valuable tool for pancreatic surgery and a potential educational resource for future surgical residents.

Comparing a virtual reality head-mounted display to on-screen three-dimensional visualization and two-dimensional computed tomography data for training in decision making in hepatic surgery: a randomized controlled study

OBJECTIVE

Evaluation of the benefits of a virtual reality (VR) environment with a head-mounted display (HMD) for decision-making in liver surgery.

BACKGROUND

Training in liver surgery involves appraising radiologic images and considering the patient's clinical information. Accurate assessment of 2D-tomography images is complex and requires considerable experience, and often the images are divorced from the clinical information. We present a comprehensive and interactive tool for visualizing operation planning data in a VR environment using a head-mounted-display and compare it to 3D visualization and 2D-tomography.

METHODS

Ninety medical students were randomized into three groups (1:1:1 ratio). All participants analyzed three liver surgery patient cases with increasing difficulty. The cases were analyzed using 2D-tomography data (group "2D"), a 3D visualization on a 2D display (group "3D") or within a VR environment (group "VR"). The VR environment was displayed using the "Oculus Rift ™" HMD technology. Participants answered 11 questions on anatomy, tumor involvement and surgical decision-making and 18 evaluative questions (Likert scale).

RESULTS

Sum of correct answers were significantly higher in the 3D (7.1 ± 1.4, p < 0.001) and VR (7.1 ± 1.4, p < 0.001) groups than the 2D group (5.4 ± 1.4) while there was no difference between 3D and VR (p = 0.987). Times to answer in the 3D (6:44 ± 02:22 min, p < 0.001) and VR (6:24 ± 02:43 min, p < 0.001) groups were significantly faster than the 2D group (09:13 ± 03:10 min) while there was no difference between 3D and VR (p = 0.419). The VR environment was evaluated as most useful for identification of anatomic anomalies, risk and target structures and for the transfer of anatomical and pathological information to the intraoperative situation in the questionnaire.

CONCLUSIONS

A VR environment with 3D visualization using a HMD is useful as a surgical training tool to accurately and quickly determine liver anatomy and tumor involvement in surgery.

IMHOTEP: cross-professional evaluation of a three-dimensional virtual reality system for interactive surgical operation planning, tumor board discussion and immersive training for complex liver surgery in a head-mounted display

BACKGROUND

Virtual reality (VR) with head-mounted displays (HMD) may improve medical training and patient care by improving display and integration of different types of information. The aim of this study was to evaluate among different healthcare professions the potential of an interactive and immersive VR environment for liver surgery that integrates all relevant patient data from different sources needed for planning and training of procedures.

METHODS

3D-models of the liver, other abdominal organs, vessels, and tumors of a sample patient with multiple hepatic masses were created. 3D-models, clinical patient data, and other imaging data were visualized in a dedicated VR environment with an HMD (IMHOTEP). Users could interact with the data using head movements and a computer mouse. Structures of interest could be selected and viewed individually or grouped. IMHOTEP was evaluated in the context of preoperative planning and training of liver surgery and for the potential of broader surgical application. A standardized questionnaire was voluntarily answered by four groups (students, nurses, resident and attending surgeons).

RESULTS

In the evaluation by 158 participants (57 medical students, 35 resident surgeons, 13 attending surgeons and 53 nurses), 89.9% found the VR system agreeable to work with. Participants generally agreed that complex cases in particular could be assessed better (94.3%) and faster (84.8%) with VR than with traditional 2D display methods. The highest potential was seen in student training (87.3%), resident training (84.6%), and clinical routine use (80.3%). Least potential was seen in nursing training (54.8%).

CONCLUSIONS

The present study demonstrates that using VR with HMD to integrate all available patient data for the preoperative planning of hepatic resections is a viable concept. VR with HMD promises great potential to improve medical training and operation planning and thereby to achieve improvement in patient care.

[Navigated liver surgery : Current state and importance in the future]

The preoperative computer-assisted resection planning is the basis for every navigation. Thanks to modern algorithms, the prerequisites have been created to carry out a virtual resection planning and a risk analysis. Thus, individual segment resections can be precisely planned in any conceivable combination. The transfer of planning information and resection suggestions to the operating theater is still problematic. The so-called stereotactic liver navigation supports the exact intraoperative implementation of the planned resection strategy and provides the surgeon with real-time three-dimensional information on resection margins and critical structures during the resection. This is made possible by a surgical navigation system that measures the position of surgical instruments and then presents them together with the preoperative surgical planning data. Although surgical navigation systems have been indispensable in neurosurgery and spinal surgery for many years, these procedures have not yet become established as standard in liver surgery. This is mainly due to the technical challenge of navigating a moving organ. As the liver is constantly moving and deforming during surgery due to respiration and surgical manipulation, the surgical navigation system must be able to measure these alterations in order to adapt the preoperative navigation data to the current situation. Despite these advances, further developments are required until navigated liver resection enters clinical routine; however, it is already clear that laparoscopic liver surgery and robotic surgery will benefit most from navigation technology.

Virtual and Augmented Reality in Oncologic Liver Surgery

Virtual reality (VR) and augmented reality (AR) in complex surgery are evolving technologies enabling improved preoperative planning and intraoperative navigation. The basis of these technologies is a computer-based generation of a patient-specific 3-dimensional model from Digital Imaging and Communications in Medicine (DICOM) data. This article provides a state-of-the- art overview on the clinical use of this technology with a specific focus on hepatic surgery. Although VR and AR are still in an evolving stage with only some clinical application today, these technologies have the potential to become a key factor in improving preoperative and intraoperative decision making.

Augmented Reality Guidance for the Resection of Missing Colorectal Liver Metastases: An Initial Experience

BACKGROUND

Modern chemotherapy achieves the shrinking of colorectal cancer liver metastases (CRLM) to such extent that they may disappear from radiological imaging. Disappearing CRLM rarely represents a complete pathological remission and have an important risk of recurrence. Augmented reality (AR) consists in the fusion of real-time patient images with a computer-generated 3D virtual patient model created from pre-operative medical imaging. The aim of this prospective pilot study is to investigate the potential of AR navigation as a tool to help locate and surgically resect missing CRLM.

METHODS

A 3D virtual anatomical model was created from thoracoabdominal CT-scans using customary software (VR RENDER(®), IRCAD). The virtual model was superimposed to the operative field using an Exoscope (VITOM(®), Karl Storz, Tüttlingen, Germany). Virtual and real images were manually registered in real-time using a video mixer, based on external anatomical landmarks with an estimated accuracy of 5 mm. This modality was tested in three patients, with four missing CRLM that had sizes from 12 to 24 mm, undergoing laparotomy after receiving pre-operative oxaliplatin-based chemotherapy.

RESULTS

AR display and fine registration was performed within 6 min. AR helped detect all four missing CRLM, and guided their resection. In all cases the planned security margin of 1 cm was clear and resections were confirmed to be R0 by pathology. There was no postoperative major morbidity or mortality. No local recurrence occurred in the follow-up period of 6-22 months.

CONCLUSIONS

This initial experience suggests that AR may be a helpful navigation tool for the resection of missing CRLM.

Augmented Reality Guidance for the Resection of Missing Colorectal Liver Metastases: An Initial Experience

BACKGROUND

Modern chemotherapy achieves the shrinking of colorectal cancer liver metastases (CRLM) to such extent that they may disappear from radiological imaging. Disappearing CRLM rarely represents a complete pathological remission and have an important risk of recurrence. Augmented reality (AR) consists in the fusion of real-time patient images with a computer-generated 3D virtual patient model created from pre-operative medical imaging. The aim of this prospective pilot study is to investigate the potential of AR navigation as a tool to help locate and surgically resect missing CRLM.

METHODS

A 3D virtual anatomical model was created from thoracoabdominal CT-scans using customary software (VR RENDER(®), IRCAD). The virtual model was superimposed to the operative field using an Exoscope (VITOM(®), Karl Storz, Tüttlingen, Germany). Virtual and real images were manually registered in real-time using a video mixer, based on external anatomical landmarks with an estimated accuracy of 5 mm. This modality was tested in three patients, with four missing CRLM that had sizes from 12 to 24 mm, undergoing laparotomy after receiving pre-operative oxaliplatin-based chemotherapy.

RESULTS

AR display and fine registration was performed within 6 min. AR helped detect all four missing CRLM, and guided their resection. In all cases the planned security margin of 1 cm was clear and resections were confirmed to be R0 by pathology. There was no postoperative major morbidity or mortality. No local recurrence occurred in the follow-up period of 6-22 months.

CONCLUSIONS

This initial experience suggests that AR may be a helpful navigation tool for the resection of missing CRLM.

Current and future challenges in the surgical treatment of hepatocellular carcinoma: a review

Challenges in the treatment of hepatocellular carcinoma Hepatocellular carcinoma (HCC) represents one of the most frequent types of cancer worldwide. Surgery, although only a part of the armamentarium against HCC, represents the cornerstone in the management of this aggressive disease. This article will review the current and future challenges in the surgical management of HCC, with a special emphasis on the following areas: (1) the evolution of staging of the disease and the importance of the biological nature and behavior of HCC, (2) the effort to increase resectability, (3) technical innovations and the role of image-guided surgery, and, finally, (4) the role of liver transplantation in the continuum of care for these patients. Although by no means an exhaustive list, the issues mentioned above represent some of the most promising prospects for significant progress in the management of HCC.

The Surgeon's Contribution to Image-Guided Oncology

Background

Advances in surgical and in imaging technology permit the performance of complex tumour resections in a safe and oncologically correct manner. To date, this has mainly implicated refined preoperative imaging methods, such as three-dimensional computer-assisted planning (3D-CASP). With the advent of modern hybrid operating rooms, intraoperative imaging has spread and various techniques of intraoperative image guidance have been developed.

Methods

We review recent advances in intraoperative image guidance. We also delineate the role of intraoperative imaging techniques such as intraoperative ultrasound and computed tomography for real-time image guidance in laparoscopic liver surgery.

Results

Our review shows that advances in intraoperative imaging accompany the increasing use of laparoscopic approaches in visceral surgery. For the liver surgeon working laparoscopically, the loss of tactile sensation and the complex three-dimensional anatomy of the human liver make 3D-imaging techniques and intraoperative image guidance indispensable. We describe the role of 3D-CASP in preoperative surgical planning in liver surgery.

Conclusion

An innovative imaging strategy for identifying liver segments during laparoscopic liver surgery by applying a fluorescent imaging method is proposed.

Liver remnant hypertrophy induction--how often do we really use it in the time of computer assisted surgery?

PURPOSE

To evaluate the significance of the hypertrophy concept in patients requiring extended liver resections for colorectal metastasis in the time of computer assisted surgery.

METHODS

Retrospective analysis of patient collective undergoing major liver surgery. 2D CT, 3D CAS with Fraunhofer MeVis Sofware. Portal vein embolisation (PVE) with the Amplazer Plug, portal vein ligation (PVL) as 1. Stage operative procedure.

RESULTS

2D CT data identified 29 patients out of 319 (2002-2009) to be at risk for liver failure after resection. After 3D CAS analysis and virtual operation planning, only 7/29 were at true risk and were submitted to portal vein occlusion (PVO). Another 5 patients were submitted to the hypertrophy concept for intraoperative finding of insufficient parenchyma quality. In total, 12 patients underwent PVO (6 PVE/6 PVL). 9/12 patients went to stage 2 and were successfully operated. There was no difference in future remnant liver volume (FRLV) gain or waiting time to step 2 between the groups, though survival was better in the PVE group.

CONCLUSION

PVO is an effective approach if the patient's future remnant liver (FRL) is too small on 2D CT volumetry. 3D CAS has great impact on the analysis of FRL capacity and in augmenting resectability - in our experience only patients with insufficient FRLV on the virtual resection plan have to take the risk of PVO to maintain the chance of liver resection.

Navigation systems in liver surgery: the new challenge for surgical research

Abstract The authors describe the theoretical basis and development of simulation systems that led to the birth of "navigation in liver surgery." Navigation is a new technological application in the surgical field that has already been successfully used in neurosurgery and orthopedic surgery. A precondition to navigate a liver resection is the availability of a map. There are three main methods to acquire images and build a three-dimensional map. Efforts to make navigation "feasible" have been made, but some limits are still affecting the method. Lack of millimetric accuracy, deformation of the liver parenchyma during resection, and breathing movements are some of the most important criticisms of this method, which, however, is still in its infancy. Not only experimental applications but also current and future foreseeable applications of such a technology are overviewed. Goals of this technology should be to reduce the intraoperative stress on surgeons, to shorten resection time, and even indirectly to enlarge resectability of patients. Further developments of this new technology applied to liver surgery could lead in the near future to safer and more precise resections, reducing the risk of postoperative liver failure, even in the presence of large anatomical alterations or, even more frequently in this surgical field, anatomical variants.

Auditory support for resection guidance in navigated liver surgery

BACKGROUND

An alternative mode of interaction with navigation systems for open liver surgery was requested. Surgeons who use such systems are impeded by having to constantly switch between viewing the navigation system screen and the patient during an operation.

METHODS

To this end, an auditory display system for open liver surgery is introduced with support for guiding the tracked instrument towards and remaining on a predefined resection line. To evaluate the method, a clinically orientated user study with 12 surgeons was conducted.

RESULTS

It is shown in qualitative results from the user study that the proposed auditory display is recognized as a useful addition to the current visual mode of interaction. It was revealed in a statistical analysis that participants spent less time looking on the screen (10% vs. 96%). Accuracy for resection guidance was significantly improved when using auditory display as an additional information channel (0.6 vs. 1.4 mm); however, the overall time for the resection task was shorter without auditory display (47 vs. 24 s).

CONCLUSIONS

By reducing dependence on the visual modality during resection guidance, the auditory display is well suited to become integrated in navigation systems for liver surgery.

Surgical options for initially unresectable colorectal liver metastases

Although the frontiers of liver resection for colorectal liver metastases have broadened in recent decades, approximately 75% of these patients present with unresectable metastases at the time of their diagnosis. In the past, these patients underwent only palliative treatment, without the chance of a cure. In the previous two decades, several therapeutic strategies have been developed that render resectable those metastases that were initially unresectable, thus offering the chance of long-term survival and even a cure to these patients. The oncosurgical modalities that are available include liver resection following portal vein ligation/embolization, “two-stage” liver resection, one-stage ultrasonically guided liver resection, hepatectomy following conversion chemotherapy, and liver resection combined with thermal ablation. Moreover, in recent years, certain authors have recommended the revisiting of the concept of liver transplantation in highly selected patients with unresectable colorectal liver metastases and favorable prognostic factors. By employing such therapies, the number of patients with colorectal liver metastases who undergo a potentially curative treatment could increase to 40%. The safety profile of these approaches is acceptable (morbidity rates as high as 45%, mortality rates of less than 5%). Furthermore, the 5-year survival rates (approximately 30%) are significantly increased over those that were achieved with palliative treatment.

Ultrasound internal tattooing

PURPOSE

The ability of remotely tagging tissues in a controlled and three-dimensional manner during preoperative imaging could greatly help surgeons to identify targets for resection. The authors' objective is to selectively and noninvasively deposit markers under image guidance for such internal tattooing.

METHODS

This study describes the production of new ultrasound-inducible droplets carrying large payloads of fluorescent markers and the in vivo proof of concept of their remote and controlled deposition via focused ultrasound. The droplets are monodispersed multiple emulsions produced in a microfluidic system, consisting of aqueous fluorescein in perfluorocarbon in water. Their conversion (either by vaporization or cavitation) is performed remotely using a clinical ultrasonic imaging probe.

RESULTS

When submitted to 5 MHz imaging pulses, the droplets vaporize in vitro at 1.4 MPa peak-negative pressure and eject their content. After several seconds, a brightly fluorescent spot (0.5 mm diameter) is observed at the focus of the transducer. Experiments in the chorioallantoique membrane of chicken eggs and chicken embryo demonstrate that the spot is stable and is easily seen by naked eye.

CONCLUSIONS

These ultrasound-inducible multiple emulsions could be used to deliver large amounts of contrast agents, chemotherapy, and genetic materials in vivo using a conventional ultrasound scanner.

A portable image overlay projection device for computer-aided open liver surgery

Image overlay projection is a form of augmented reality that allows surgeons to view underlying anatomical structures directly on the patient surface. It improves intuitiveness of computer-aided surgery by removing the need for sight diversion between the patient and a display screen and has been reported to assist in 3-D understanding of anatomical structures and the identification of target and critical structures. Challenges in the development of image overlay technologies for surgery remain in the projection setup. Calibration, patient registration, view direction, and projection obstruction remain unsolved limitations to image overlay techniques. In this paper, we propose a novel, portable, and handheld-navigated image overlay device based on miniature laser projection technology that allows images of 3-D patient-specific models to be projected directly onto the organ surface intraoperatively without the need for intrusive hardware around the surgical site. The device can be integrated into a navigation system, thereby exploiting existing patient registration and model generation solutions. The position of the device is tracked by the navigation system's position sensor and used to project geometrically correct images from any position within the workspace of the navigation system. The projector was calibrated using modified camera calibration techniques and images for projection are rendered using a virtual camera defined by the projectors extrinsic parameters. Verification of the device's projection accuracy concluded a mean projection error of 1.3 mm. Visibility testing of the projection performed on pig liver tissue found the device suitable for the display of anatomical structures on the organ surface. The feasibility of use within the surgical workflow was assessed during open liver surgery. We show that the device could be quickly and unobtrusively deployed within the sterile environment.

Surgical treatment of hepatic metastases from colorectal cancer

Colorectal carcinoma is one of the most frequent cancers in Western societies with an incidence of around 700 per million people. About half of the patients develop metastases from the primary tumor and liver is the primary metastatic site. Improved survival rates after hepatectomy for metastatic colorectal cancer have been reported in the last few years and these may be the result of a variety of factors, such as advances in systemic chemotherapy, radiographic imaging techniques that permit more accurate determination of the extent and location of the metastatic burden, local ablation methods, and in surgical techniques of hepatic resection. These have led to a more aggressive approach towards liver metastatic disease, resulting in longer survival. The goal of this paper is to review the role of various forms of surgery in the treatment of hepatic metastases from colorectal cancer.

Novel 3-D laparoscopic magnetic ultrasound image guidance for lesion targeting

OBJECTIVES

Accurate laparoscopic liver lesion targeting for biopsy or ablation depends on the ability to merge laparoscopic and ultrasound images with proprioceptive instrument positioning, a skill that can be acquired only through extensive experience. The aim of this study was to determine whether using magnetic positional tracking to provide three-dimensional, real-time guidance improves accuracy during laparoscopic needle placement.

METHODS

Magnetic sensors were embedded into a needle and laparoscopic ultrasound transducer. These sensors interrupted the magnetic fields produced by an electromagnetic field generator, allowing for real-time, 3-D guidance on a stereoscopic monitor. Targets measuring 5 mm were embedded 3-5 cm deep in agar and placed inside a laparoscopic trainer box. Two novices (a college student and an intern) and two experts (hepatopancreatobiliary surgeons) targeted the lesions out of the ultrasound plane using either traditional or 3-D guidance.

RESULTS

Each subject targeted 22 lesions, 11 with traditional and 11 with the novel guidance (n= 88). Hit rates of 32% (14/44) and 100% (44/44) were observed with the traditional approach and the 3-D magnetic guidance approach, respectively. The novices were essentially unable to hit the targets using the traditional approach, but did not miss using the novel system. The hit rate of experts improved from 59% (13/22) to 100% (22/22) (P < 0.0001).

CONCLUSIONS

The novel magnetic 3-D laparoscopic ultrasound guidance results in perfect targeting of 5-mm lesions, even by surgical novices.

A navigation system for open liver surgery: design, workflow and first clinical applications

BACKGROUND

The surgical treatment of liver tumours relies on precise localization of the lesions and detailed knowledge of the patient-specific vascular and biliary anatomy. Detailed three-dimensional (3D) anatomical information facilitates complete tumour removal while preserving a sufficient amount of functional liver tissue.

METHODS

We present an easy to use, clinically applicable navigation system for efficient visualization and tool guidance during liver surgery. Accurate instrument guidance within 3D planning models was achieved with a fast registration procedure, assuming a locally rigid and temporarily static scenario. After deformations occurring during the procedure, efficient means for registration updates are provided. Special focus was given to workflow integration and the minimization of overhead time. The navigation system was validated with nine clinical cases.

RESULTS

Navigated surgical interventions were performed with a median time overhead of 16.5 min. The navigation technology had a median accuracy of 6.3 mm, improving anatomical orientation and the detection of structures at risk.

CONCLUSIONS

Successful application of the navigation technology to open liver surgery was achieved by minimizing the procedural complexity and optimizing integration within the existing surgical environment. The assumption of locally rigid patient registration was validated, and clinical evaluation shows clear benefits for the surgeon.

The focus of Langenbeck's Archives of Surgery in the 21st century

BACKGROUND

The Langenbeck's Archives of Surgery has been serving as a publication platform for clinical and scientific progress in the field of surgery for 150 years. In order to maintain this long-standing tradition throughout the coming decades, it will be mandatory to face the challenges posed by increasing specialization of surgical subdisciplines, modern technologies, and interdisciplinary treatment options.

DISCUSSION

Continued efforts need to be directed at minimizing surgical trauma, not at least with respect to current demographic development. Adoption of progressive technologies from the fields of biophysics, mechatronics, and biomedical imaging solutions will likely gain a major impact on the further development of surgical operation techniques. Expanding insight from genomic and molecular medicine will facilitate personalized, interdisciplinary treatment concepts for malignant disease, in which surgical resection techniques will need to be integrated. The introduction of novel diagnostic and treatment concepts will mandate solid evaluation of their clinical effectiveness and safety, which can only be achieved by randomized, controlled trials in the field of surgery.

CONCLUSION

Extracting study ideas from the contributions by clinicians and basic scientists, and promoting the conduction of clinical trials will therefore range among the most important tasks for the Langenbeck's Archives of Surgery in the 21st century.

Illustrative visualization of 3D planning models for augmented reality in liver surgery

PURPOSE

Augmented reality (AR) obtains increasing acceptance in the operating room. However, a meaningful augmentation of the surgical view with a 3D visualization of planning data which allows reliable comparisons of distances and spatial relations is still an open request.

METHODS

We introduce methods for intraoperative visualization of 3D planning models which extend illustrative rendering and AR techniques. We aim to reduce visual complexity of 3D planning models and accentuate spatial relations between relevant objects. The main contribution of our work is an advanced silhouette algorithm for 3D planning models (distance-encoding silhouettes) combined with procedural textures (distance-encoding surfaces). In addition, we present a method for illustrative visualization of resection surfaces.

RESULTS

The developed algorithms have been embedded into a clinical prototype that has been evaluated in the operating room. To verify the expressiveness of our illustration methods, we performed a user study under controlled conditions. The study revealed a clear advantage in distance assessment with the proposed illustrative approach in comparison to classical rendering techniques.

CONCLUSION

The presented illustration methods are beneficial for distance assessment in surgical AR. To increase the safety of interventions with the proposed approach, the reduction of inaccuracies in tracking and registration is a subject of our current research.