Design of a virtual data shelf to effectively explore a large database of 3D medical surface models in VR.

PURPOSE: Medical researchers deal with a large amount of patient data to improve future treatment decisions and come up with new hypotheses. To facilitate working with a large database containing many patients and parameters, we propose a virtual data shelf, displaying the 3D anatomical surface models in an immersive VR environment. METHODS: Thereby, different functionalities such as sorting, filtering and finding similar cases are included. To provide an appropriate layout and arrangement of 3D models that optimally supports working with the database, three layouts (flat, curved and spherical) and two distances are evaluated. A broad audience study with 61 participants was conducted to compare the different layouts based on their ease of interaction, to get an overview and to explore single cases. Medical experts additionally evaluated medical use cases. RESULTS: The study revealed that the flat layout with small distance is significantly faster in providing an overview. Applying the virtual data shelf to the medical use case intracranial aneurysms, qualitative expert feedback with two neuroradiologists and two neurosurgeons was gathered. Most of the surgeons preferred the curved and spherical layouts. CONCLUSION: Our tool combines benefits of two data management metaphors, resulting in an efficient way to work with a large database of 3D models in VR. The evaluation gives insight into benefits of layouts as well as possible use cases in medical research.

A two-step risk assessment method for radiofrequency ablations of spine metastases.

BACKGROUND: Spine metastases (MTS) can be treated via Radiofrequency Ablation (RFA) electrodes. To bring these electrodes into vertebral MTS, pathways have to be created. This can be done via transpedicular hammering or drilling. However, this is challenging due to spatial constraints, and because MTS can alter bone density considerably. METHOD: In this work a two-step method is presented that intends to offer cognitive and physical assistance. Step 1 comprises two visualization methods that depict safety margins between and in risk structures. For Step 2, the correlation between Hounsfield Units (HUs) and drilling forces was analyzed to support manual and robot-assisted RFAs. RESULTS: In-depth descriptions of two clinical cases and detailed feedback from the local clinic of neuroradiology are used to present the capabilities of the proposed method. Furthermore, a stiffness criterion is presented to predict drilling force changes from the local distribution and homogeneity of HUs with an inaccuracy of less than 1 mm. CONCLUSIONS: The combination of visualization and drilling force prediction shows potential to support manual and robot-assisted spine RFAs. However, limitations have to be addressed in the future. For example, it has to be carefully evaluated to which extent the proposed method can speed up the planning process and increase intervention safety.

Does the DSA reconstruction kernel affect hemodynamic predictions in intracranial aneurysms? An analysis of geometry and blood flow variations.

BACKGROUND: Computational fluid dynamics (CFD) blood flow predictions in intracranial aneurysms promise great potential to reveal patient-specific flow structures. Since the workflow from image acquisition to the final result includes various processing steps, quantifications of the individual introduced potential error sources are required. METHODS: Three-dimensional (3D) reconstruction of the acquired imaging data as input to 3D model generation was evaluated. Six different reconstruction modes for 3D digital subtraction angiography (DSA) acquisitions were applied to eight patient-specific aneurysms. Segmentations were extracted to compare the 3D luminal surfaces. Time-dependent CFD simulations were carried out in all 48 configurations to assess the velocity and wall shear stress (WSS) variability due to the choice of reconstruction kernel. RESULTS: All kernels yielded good segmentation agreement in the parent artery; deviations of the luminal surface were present at the aneurysm neck (up to 34.18%) and in distal or perforating arteries. Observations included pseudostenoses as well as noisy surfaces, depending on the selected reconstruction kernel. Consequently, the hemodynamic predictions show a mean SD of 11.09% for the aneurysm neck inflow rate, 5.07% for the centerline-based velocity magnitude, and 17.83%/9.53% for the mean/max aneurysmal WSS, respectively. In particular, vessel sections distal to the aneurysms yielded stronger variations of the CFD values. CONCLUSIONS: The choice of reconstruction kernel for DSA data influences the segmentation result, especially for small arteries. Therefore, if precise morphology measurements or blood flow descriptions are desired, a specific reconstruction setting is required. Furthermore, research groups should be encouraged to denominate the kernel types used in future hemodynamic studies.

Fluid-Structure Simulations of a Ruptured Intracranial Aneurysm: Constant versus Patient-Specific Wall Thickness.

Computational Fluid Dynamics is intensively used to deepen the understanding of aneurysm growth and rupture in order to support physicians during therapy planning. However, numerous studies considering only the hemodynamics within the vessel lumen found no satisfactory criteria for rupture risk assessment. To improve available simulation models, the rigid vessel wall assumption has been discarded in this work and patient-specific wall thickness is considered within the simulation. For this purpose, a ruptured intracranial aneurysm was prepared ex vivo, followed by the acquisition of local wall thickness using µCT. The segmented inner and outer vessel surfaces served as solid domain for the fluid-structure interaction (FSI) simulation. To compare wall stress distributions within the aneurysm wall and at the rupture site, FSI computations are repeated in a virtual model using a constant wall thickness approach. Although the wall stresses obtained by the two approaches-when averaged over the complete aneurysm sac-are in very good agreement, strong differences occur in their distribution. Accounting for the real wall thickness distribution, the rupture site exhibits much higher stress values compared to the configuration with constant wall thickness. The study reveals the importance of geometry reconstruction and accurate description of wall thickness in FSI simulations.

A cytoarchitecture-driven myelin model reveals area-specific signatures in human primary and secondary areas using ultra-high resolution in-vivo brain MRI.

This work presents a novel approach for modelling laminar myelin patterns in the human cortex in brain MR images on the basis of known cytoarchitecture. For the first time, it is possible to estimate intracortical contrast visible in quantitative ultra-high resolution MR images in specific primary and secondary cytoarchitectonic areas. The presented technique reveals different area-specific signatures which may help to study the spatial distribution of cortical T1 values and the distribution of cortical myelin in general. It may lead to a new discussion on the concordance of cyto- and myeloarchitectonic boundaries, given the absence of such concordance atlases. The modelled myelin patterns are quantitatively compared with data from human ultra-high resolution in-vivo 7T brain MR images (9 subjects). In the validation, the results are compared to one post-mortem brain sample and its ex-vivo MRI and histological data. Details of the analysis pipeline are provided. In the context of the increasing interest in advanced methods in brain segmentation and cortical architectural studies, the presented model helps to bridge the gap between the microanatomy revealed by classical histology and the macroanatomy visible in MRI.

Impact of model-based risk analysis for liver surgery planning.

PURPOSE: A model-based risk analysis for oncologic liver surgery was described in previous work (Preim et al. in Proceedings of international symposium on computer assisted radiology and surgery (CARS), Elsevier, Amsterdam, pp. 353­358, 2002; Hansen et al. Int I Comput Assist Radiol Surg 4(5):469­474, 2009). In this paper, we present an evaluation of this method. METHODS: To prove whether and how the risk analysis facilitates the process of liver surgery planning, an explorative user study with 10 liver experts was conducted. The purpose was to compare and analyze their decision-making. RESULTS: The results of the study show that model-based risk analysis enhances the awareness of surgical risk in the planning stage. Participants preferred smaller resection volumes and agreed more on the safety margins' width in case the risk analysis was available. In addition, time to complete the planning task and confidence of participants were not increased when using the risk analysis. CONCLUSION: This work shows that the applied model-based risk analysis may influence important planning decisions in liver surgery. It lays a basis for further clinical evaluations and points out important fields for future research.

Automatic generation of anatomic characteristics from cerebral aneurysm surface models.

PURPOSE: Computer-aided research on cerebral aneurysms often depends on a polygonal mesh representation of the vessel lumen. To support a differentiated, anatomy-aware analysis, it is necessary to derive anatomic descriptors from the surface model. We present an approach on automatic decomposition of the adjacent vessels into near- and far-vessel regions and computation of the axial plane. We also exemplarily present two applications of the geometric descriptors: automatic computation of a unique vessel order and automatic viewpoint selection. METHODS: Approximation methods are employed to analyze vessel cross-sections and the vessel area profile along the centerline. The resulting transition zones between near- and far- vessel regions are used as input for an optimization process to compute the axial plane. The unique vessel order is defined via projection into the plane space of the axial plane. The viewing direction for the automatic viewpoint selection is derived from the normal vector of the axial plane. RESULTS: The approach was successfully applied to representative data sets exhibiting a broad variability with respect to the configuration of their adjacent vessels. A robustness analysis showed that the automatic decomposition is stable against noise. A survey with 4 medical experts showed a broad agreement with the automatically defined transition zones. CONCLUSION: Due to the general nature of the underlying algorithms, this approach is applicable to most of the likely aneurysm configurations in the cerebral vasculature. Additional geometric information obtained during automatic decomposition can support correction in case the automatic approach fails. The resulting descriptors can be used for various applications in the field of visualization, exploration and analysis of cerebral aneurysms.

Automatic Detection and Visualization of Qualitative Hemodynamic Characteristics in Cerebral Aneurysms.

Cerebral aneurysms are a pathological vessel dilatation that bear a high risk of rupture. For the understanding and evaluation of the risk of rupture, the analysis of hemodynamic information plays an important role. Besides quantitative hemodynamic information, also qualitative flow characteristics, e.g., the inflow jet and impingement zone are correlated with the risk of rupture. However, the assessment of these two characteristics is currently based on an interactive visual investigation of the flow field, obtained by computational fluid dynamics (CFD) or blood flow measurements. We present an automatic and robust detection as well as an expressive visualization of these characteristics. The detection can be used to support a comparison, e.g., of simulation results reflecting different treatment options. Our approach utilizes local streamline properties to formalize the inflow jet and impingement zone. We extract a characteristic seeding curve on the ostium, on which an inflow jet boundary contour is constructed. Based on this boundary contour we identify the impingement zone. Furthermore, we present several visualization techniques to depict both characteristics expressively. Thereby, we consider accuracy and robustness of the extracted characteristics, minimal visual clutter and occlusions. An evaluation with six domain experts confirms that our approach detects both hemodynamic characteristics reasonably.

A survey of medical image registration on graphics hardware.

The rapidly increasing performance of graphics processors, improving programming support and excellent performance-price ratio make graphics processing units (GPUs) a good option for a variety of computationally intensive tasks. Within this survey, we give an overview of GPU accelerated image registration. We address both, GPU experienced readers with an interest in accelerated image registration, as well as registration experts who are interested in using GPUs. We survey programming models and interfaces and analyze different approaches to programming on the GPU. We furthermore discuss the inherent advantages and challenges of current hardware architectures, which leads to a description of the details of the important building blocks for successful implementations.

[Virtual endoscopy of the nose and paranasal sinuses in real-time. Surgical planning system "Sinus endoscopy" (SPS-SE)]. / Virtuelle Echtzeit-Endoskopie der Nase und Nasennebenhöhlen. Surgical-Planning-System "Sinus Endoscopy" (SPS-SE).

PROBLEM: The aim of this study was the development and clinical evaluation of a new method for virtual endoscopy of the nose and paranasal sinuses. MATERIAL AND METHODS: The surgical planning system "sinus endoscopy" (SPS-SE) was completely newly developed. The surfaces of the CT images are represented with direct volume rendering (raycasting) which allows a sufficiently high image repetition frequency with the movement of the virtual endoscopy and material effects for a natural appearance were added. Detail accuracy of the virtual illustrations was examined with the help of a picture-statistic comparison between optical and the virtual endoscopy. The evaluation of the system by the patients and physicians was made with a validated questionnaire. RESULTS: The deviations from defined landmarks of virtual in comparison to optical endoscopy are between 1.4 mm and 11.1 mm. Manoeuvering the virtual endoscope was found to be better than with the optical endoscope but the important parameters for visualization were similar. The accuracy of volume rendering, the high variability of scaling of the anatomical borders and orientation were judged to be negative factors. Altogether there was a balanced opinion from the ENT surgeons but without exception patients judged the system positively. DISCUSSION: This investigation proved the efficiency of SPS-SE for three-dimensional real time reconstruction of high-resolution CT data of the nose and paranasal sinuses. However, some modifications are necessary before introduction into routine use.

Generalizing the evaluation of medical image processing tools by use of Gabor patterns.

OBJECTIVE: Tools for medical image processing are usually evaluated by observers with radiological experience and with complex tasks. For easing evaluation of filtering and enhancement tools, the observer's task can be generalized. METHODS: By describing aspects of the MCS method (Mammographic Contrast Sensitivity) we illustrate issues of selecting a metric for assessing visual performance, the observer's task and the image material to be used, aiming at a generalization of the design of studies for the evaluation of medical image processing tools. Concerning the metric, we distinguish acuity from contrast sensitivity. With respect to the observer's task, we distinguish tasks of discrimination from those at a higher level of recognition. Finally, we show the advantage of using medical images for evaluating image processing tools by comparing the results for measurements on homogeneous background and mammographic images. RESULTS: The perceptual level of the observer's task and the complexity of the used image material influences the outcome of observer studies, particularly also from crowding effects. The design of a study should minimize the impact of the observer's experience on the outcome. This can be achieved by using non-anatomical, standardized perceptual targets like Gabor patterns, used in the context of medical images. CONCLUSIONS: Understanding the concepts of perception helps designing observer studies that are as complex as required, but at the same time as simple and general as possible. Performing an observer study may be simplified by a study design which does not require radiological experience of the observers, if the study aims at the evaluation of tools that shall support basic perception tasks, such as e.g. contrast enhancement.

[Three-dimensional visualization for preoperative planning and evaluation in head and neck surgery]. / Dreidimensionale Bildprozessierung in der HNO-Onkologie zur präoperativen Planung und Evaluierung.

There are a lot of diagnostic possibilities for the preoperative planning in head and neck surgery. So far, no study was performed to evaluate if there is an advantage of three-dimensional visualization compared to conventional computed tomography yet. Additionally, there are no specifications for such a visualization prior surgery in head and neck surgery. This work describes different possibilities for segmentation and three-dimensional visualization for preoperative planning in head and neck surgery and tumor volumetry compared to conventional computed tomography. We describe new techniques and specifications for three-dimensional visualization.

[Three-dimensional visualization of CT of the neck for surgical planning]. / Dreidimensionale Darstellung von CT-Datensätzen des Halses für die chirurgische Planung: Eine Machbarkeitsstudie.

BACKGROUND: Surgical planning in ENT profits from computer assisted preoperative visualization and planning. The informative capability is to be improved by three-dimensional illustrating of the preoperative available data. The possibility of a 3-D-visualization of lymph nodes stands in the center of the interest. METHODS: 16 CT data sets with a tumor-classification of T1N1 or higher were included. Altogether 720 pseudo-3-D-illustrations were provided with an average of 9.3 objects. Current algorithms were used for the segmentation and visualization and the results were divided in three classes. RESULTS: The average time requirement for visualization and segmenting amounted to 122 minutes, the minimum value is at 61 minutes per data set. Automatic segmenting succeeded only with structures with clear grey tone differences to the environment. In all other cases an additional manual interaction had to take place. CONCLUSIONS: 3-D-Visualising of CT of the neck represents a new quality in preoperative planning. A clear trend at increasing detail loyalty and information efficiency showed up in the groups of B and C. It is possible to make from these pictures a quantitative statement on surgery relevant infiltration. Likewise conceivable are the postoperative quality control or planning and process control of a postoperative radio-chemotherapy. The automatic algorithms can be estimated as reliable. Application is still far from a clinically efficient use. With the rising efficiency of the computing systems, the improved software and the imaging systems the problems mentioned are, however, solvable.

[Acceptance of computer-assisted surgery planning in visceral (abdominal) surgery]. / Akzeptanz einer computergestützten Operationsplanung in der Viszeralchirurgie - Ergebnisse einer bundesweiten Befragung -

The acceptance of computer assisted surgical planning was studied by polling 500 German surgeons. 500 questionnaires were sent, from which 105 have been returned, from which 102 could be analysed. The questionnaire consisted of 14 questions relating to the current practice of surgery planning as well as to desired improvements. In general, the computer assisted surgical planning was assessed as a promising tool in the future. 82 % of the surgeons expected a benefit by computer assisted surgical planning. Better assessment of resectability, better training of residents and more safety of surgical procedures were mentioned in the majority. Computer assisted surgical planning should focus on 3D visualization of spatial relations between lesions and vascular structures, on facilities for the preoperative trial of resection strategies and on the documentation of the planned procedure. The current version of a research prototype (Surgery-Planner) is presented which is dealing with these goals.