Future Generation Computer Systems 21 (2005) 1167–1176
Bringing combined interaction to a problem solving environment for vascular reconstruction E.V. Zudilova ∗ , P.M.A. Sloot Section Computational Science, Faculty of Science, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands Available online 12 May 2004
Abstract The paper addresses the problem of how to make a human–computer interaction user-friendlier within a problem solving environment (PSE). Pre-operative planning of a vascular reconstruction procedure is a case study for this research. The Virtual Radiology Explorer (VRE) presented in the paper has being deployed for the virtual reality (VR) and desktop projection modalities. Both projection modalities have been compared in respect to the interaction capabilities provided to the potential users of the VRE. The heuristic usability evaluation of the VRE as well as the first results of user profiling show that the combination of VR and desktop within the same interaction–visualisation medium could help to satisfy the wider range of the VRE users. A Personal Space Station (PSS) is a possible solution for the implementation of this concept. © 2004 Elsevier B.V. All rights reserved. Keywords: Vascular reconstruction; PSE; Projection modality; User profiling
1. Introduction The goal of a problem solving environment (PSE) is to provide end-users with a set of hardware and software resources for building a specific framework to solve a target class of problems. Ideally this framework has to be built in such a way that a user can exploit modern technologies without specialised knowledge of underlying hardware and software [15]. In reality the situation is far from ideal. It is supposed that a user knows how to use simulation and visuali∗ Corresponding author. Tel.: +31 20 525 7542; fax: +31 20 525 7419. E-mail addresses:
[email protected] (E.V. Zudilova),
[email protected] (P.M.A. Sloot).
0167-739X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.future.2004.04.004
sation programs (libraries, modules, software components, etc.) and that he or she is able to characterise a problem to be solved using a specific definition language. Most of developers do not take into account the fact that end-users of a PSE are scientists, who focus mostly on their specific research areas, and they are not always experienced computer users, and as a result they need intuitive interaction capabilities and feedback adapted to their skills and knowledge. PSEs’ developers use today more and more often modern advanced projection equipment for deploying an interaction–visualisation medium. However, the choice of this equipment is still mostly task-related or even spontaneous. Therefore, a Human–Computer Interaction (HCI) provided by a PSE is usually far from intuitive. Existing projection modalities have not been
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investigated yet in respect to usability factors. Meanwhile, the selection of an appropriate projection modality in accordance with user’s tasks, preferences and personal features could be used as a basis for building a motivated PSE. The PSE introduced in this paper is a framework for rapid prototyping and development of an exploration environment that permits a user to explore interactively the visualised results of a simulation and manipulate simulation parameters in near real-time. Pre-operative planning of a vascular reconstruction procedure is a test case for making experiments. The rest of the paper is organised as follows. Section 2 provides the introduction to the procedure of the vascular disorders diagnosis and treatment planning. Section 3 presents the main design concept of a PSE for vascular reconstruction: its functionality, architecture and interaction capabilities. Two different approaches of deploying interaction–visualisation medium within a PSE are investigated. Virtual reality (VR) and desktop are compared in respect to the interaction capabilities provided. Section 4 classifies the end-users of the VRE and presents the first results of user profiling conducted recently. Users’ attitudes towards existing projection modalities are discussed. In Section 5 the notion of the Personal Space Station is introduced as a possible solution to combine VR and desktop within the same environment. Finally, in Section 6 conclusions and plans for future research are presented.
2. Vascular disorders diagnosis and treatment Vascular diseases affect arteries and veins. Vascular disorders in general fall into two categories: aneurisms and stenosis. An aneurysmal disease is a balloon-like swelling in the artery. Stenosis is a narrowing or blockage of the artery. The purpose of the vascular reconstruction is to redirect and increase blood flow or repair a weakened or aneurysmal artery if necessary. In the Netherlands the process of making a diagnosis starts when a patient comes to the First Health Care. A specialist has to confirm that a patient is really suffering from a vascular disorder. On this early stage information to be processed by a specialist can vary from a history told by a patient to a complete data set of scans made earlier.
The next step is consultancy, which is usually conducted by a vascular surgeon. The consultation includes diagnosis and identification of contra-indications with the corresponding explanations for minimisation of risk factors in future (e.g., stop smoking or low cholesterol level) [6]. The physical examination can be also conducted. It includes measurements of blood pressure and pulse rhythm, as well as special tests, e.g., the ‘walk test’ [8]. If a vascular surgeon is an experienced practitioner, this examination will be enough to make a diagnosis and to plan the further treatment for a typical case, even including a surgical intervention if necessary. As for non-typical cases, the further testing will be required, which assumes the collaborative work of radiologists and surgeons to make the correct diagnosis and plan a proper treatment. Several imaging techniques can be used to determine the location of the obstruction or narrowing of the artery. One of them is the echo-doppler (duplex) examination. It permits to picture the vein to determine the location of a vascular disorder. The echo-doppler examination utilises an ultrasound probe to visualise the vein structure either through the chest wall or by placing a probe through the mouth into the oesophagus. If the echo-doppler examination does not help in better understanding of a patient’s conditions, computed tomography (CT), magnetic resonance imaging (MRI) or magnetic resonance angiography (MRA) can be used for the further examination [14]. 3D data acquired by CT or MRI is always converted into a set of 2D slices that can be displayed and evaluated from various perspectives and at different levels. MRA is a technique for imaging blood vessels that contain flowing blood. It is very popular among cardiovascular specialists because of its ability to non-invasively visualise a vascular disease. The choice of the imaging technique is determined by the structure or anomaly that needs to be observed, given that some techniques are better suited for certain cases than others. Although the data acquired by imaging techniques is always presented in 2D, both radiologists and surgeons can easily process it. However, the diagnosis and the best treatment are not always obvious even for medical experts due to the complexity of a vascular disease and other diseases that a patient may have. The verification of the operation plan for a non-typical case is one of the most complicated tasks in the vascular surgery. Different treatments for vascular diseases exist today.
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They include adding shunts and bypasses in the case of aneurysms and applying thrombolysis techniques, balloon angioplasty, bypasses and stent placement for a stenosis [16]. A PSE, in which real-time situations are simulated and several treatments can be tested, is very helpful in this respect and provides useful clues for surgeons. It can also assist medical students and novice surgeons in understanding the complexity of a treatment.
3. A problem solving environment for vascular reconstruction 3.1. Design concept The Virtual Radiology Explorer (VRE) is a PSE that puts a user at the centre of an experimental cycle simulated by a computer and let him or her apply an expertise to find better solutions for treatment of a vascular disorder [3,17]. The aim of the VRE is to provide an enduser with an intuitive virtual simulated environment to
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visualise and explore patient’s vascular condition. The criterion of the success of a treatment is the normalisation of a blood flow in the affected area. The procedure of adding a bypass is of the most interest to us as it can be used both for the treatment of aneurysms and stenosis. The input for conducting an experiment is scanned data of a patient stored in a database, which also contains an archive of interesting cases and vascular images. The core component of the VRE is a simulator [2], which simulates the parameters of a patient’s blood flow (velocity, pressure and shear stress). A user monitors the simulation process and controls the blood flow parameters. The results of a blood flow simulation are provided before and after a simulated bypass procedure. A user has a possibility to change the geometry and position of a bypass to check whether a blood flow is normalised or not. Both the geometry of an artery and the simulated blood flow parameters are visualised. In Fig. 1 the current architecture of the PSE for vascular reconstruction is shown, where the starting point is a scanner and the front-end to the VRE is available
Fig. 1. VRE—a PSE for vascular reconstruction.
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both via the Distributed Real-time Interactive Virtual Environment (DRIVE) system [1,19] and a desktop workstation. Two versions of the VRE have been developed to have a possibility to access the VRE from both VR and desktop projection modalities. ‘Immersive VRE’ (I-VRE) is available from the DRIVE and CAVE and ‘Desktop VRE’ (D-VRE) from a common PC. The immersive version of the VRE provides a multimodal interface, which combines natural input modes of context sensitive interaction by voice, hand gestures and direct manipulation of virtual 3D objects [17]. We called the interaction mode provided by I-VRE the ‘Virtual Operating Theatre’ [2], because a user ‘plays a role’ of a physician applying a treatment of a vascular disease on a simulated patient. As for the desktop version, the interaction capabilities here are similar to those supported by a typical PC/PDA application. Both the interaction and visualisation are restricted due to the projected representation of 3D data in a 2D space and oriented more to the individual work of a user. So we called this interaction mode the ‘Personal Desktop Assistant’. The research presented in the paper is focused on comparison of the concepts of the Virtual Operating Theatre and the Personal Desktop Assistant supported by the VRE. I-VRE and D-VRE are compared in respect to interaction and visualisation capabilities provided, given the condition of ‘equal complexity’, which means that both versions have a similar set of functionality [4]. Like it was already mentioned the VRE is aimed to assist in pre-surgical planning of abdominal vascular bypasses. That is why both versions of the VRE provide 3D visualisation of medical scans, simulation and visualisation of a possible treatment solution. The 3D reconstructions of scanned data can be explored and measured in both I- and D-VRE. The architecture of the VRE is as it is shown in Fig. 1. Many components are aimed to solve different computational tasks, i.e. segmentation of medical scans, data conversion to the format supported by the visualisation compounds of the VRE (VTK [21]), generation of the Lattice Boltzmann grid [9], volume rendering of the 3D visualisation of the patient’s data, isosurface extraction to explore the region of interest (a piece of an artery or a vein), glyphs and streamlines generation for presenting the results of blood flow sim-
ulation. All these tasks demand additional computational resources. To solve this problem we are working currently on the concept of a Grid-based PSE described in Ref. [15]. Most of the compounds of the VRE are noninteractive due to their complexity. A user can only run, pause or stop their execution. As for the interaction capabilities within the VRE, the user can only explore data (e.g., by means of a clipping engine), conduct measurements or edit grid interactively. These three functional elements have been investigated in respect to different projection modalities. The results of this comparison can be found in Section 3.2. 3.2. Interaction capabilities: I-VRE and D-VRE Grid editing within the VRE provides a possibility to edit the initial geometry of an artery: to remove insignificant elements or restore the fragments lost during the segmentation. Grid editing also permits a user to create a bypass and place it on an artery. A bypass is a graft rerouting a blood flow around blockages. Usually it is a piece of vein taken from elsewhere in the body or an implant made from an organic material. Let us compare a procedure of adding a bypass in VR and desktop projection modalities. In the I-VRE users are capable to manipulate 3D objects directly. They deal with 3D representations of an artery and a bypass. For building a bypass within the I-VRE a spline primitive is used (Fig. 2b). Then the procedure of adding a bypass in VR comes down to re-scaling of a spline and its correct positioning on an artery. These manipulations can be conducted by means of a wand (6 degrees of freedom: position and orientation). To manipulate successfully in a 3D virtual world a user should possess special motor skills of navigation and manipulation in VR. Sometimes it is not trivial and depends on the level of the implementation of a VR system. As for the interaction in the D-VRE, a user does not need additional motor skills. The biggest problem arises from the fact that within a desktop application we cannot manipulate 3D objects directly, we always deal with 2D projected representations of these objects [12]. 3D representation of objects does not have a big sense for a desktop virtual environment. In most desktop applications it is used just as a passive viewer. Thus to add a bypass within the D-VRE a user has to deal with
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Fig. 2. I-VRE: (a) data exploration (volume rendering); (b) grid editing (geometry and bypass) [17].
several projections of an artery and specific dialogue elements. A clipping engine is an interactive component of the VRE, which helps to explore data. It permits to build clipping planes of different orientations in a 3D space. Having made a section of a 3D object by means of a clipping plane, a user can look inside an artery. By moving a clipping plane he or she can see the original data obtained from a scanner slice by slice. In the case of the I-VRE a user can change orientation of a clipping plane using a wand. He or she can navigate in a virtual world, look inside an artery and even walk through. In the desktop version additional interface capabilities have been applied: a user can select a slice (or set of slices) of interest by means of a
menu or a slider. A unique identification number helps to find out the concrete slice. Measurements are crucial for making a diagnosis. Clinical decision-making relies on evaluation of the vessels in terms of a degree of narrowing for stenosis and dilatation (increase over normal arterial diameter) for aneurysm. The selection of a correct bypass (its shape, length, diameter) also depends on sizes and geometry of an artery. The interactive measurement component of the I-VRE [3] provides the possibility to measure quantitatively a distance, angle, diameter and some other parameters characterising a 3D object in a virtual world. For conducting a measurement, a user has to position a corresponding number of active markers on an
Fig. 3. D-VRE: (a) data exploration (iso-surface rendering), selection of the region of interest; (b) adding a bypass, measurements.
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object (see Fig. 3b). Markers are building blocks of distance, angle and linestrip measurements. The number of necessary active markers depends on a measurement to be done. For measuring a distance, a user has to add two markers, if it is angle three, for conducting linestrip or tracing measurements at least two [3]. The procedure of adding a marker is similar to the procedure of grid editing. If within VR a user can add a marker by means of a direct manipulation (using the position and orientation of a wand), switching to a desktop projection modality leads to a necessity of deploying extra menus and sliders to simplify the work of a user in a projected 3D world. Figs. 2 and 3 contain several screen shots illustrating the I-VRE and the D-VRE in use.
4. User attitudes towards different projection modalities 4.1. User groups The end-users of the VRE are people who use it as a tool for conducting experiments. Like it is shown in Fig. 4, it is expected that the VRE will be used as a tool for the interactive decision support by
vascular surgeons and radiologists (both diagnosis and interventional), as well as by radiology and vascular technicians. Usually technicians are people from scientific or radiography background. They conduct patients’ testing for diagnosis of arterial and venous diseases. Technicians may use diagnosis and planning systems to prepare scan images for radiologists and surgeons so, that the assessment of these images can be performed then as fast as possible. In some cases, technicians and radiologists perform the first assessment of images together [7]. Another possibility is to use the VRE for training of medical students and novice physicians. The training process is guided and controlled by a lecturer, who is a confident user of the VRE. Potential users of the VRE differentiate by their background, skills, preferences, motivation, cognitive features and stress factors [18]. As a result, their expectations about the interaction within the VRE also vary. User comfort is very important for the success of any software application, even at a stage of an early prototype. That is why we focus our today’s efforts mostly on the improvement of the interaction and visualisation capabilities within the VRE. Although, now the largest user group of the VRE is software developers
Fig. 4. Users’ classification.
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and system administrators (since the VRE is still under the development), the main focus in investigating user attitudes towards different projection modalities is on the end-user groups. Most of our end-users are inexperienced computer users and they expect that a PSE will provide a HCI similar to the interaction that they expect or are familiar with. 4.2. The first results of user profiling A HCI in a PSE depends to a great extent on the projection equipment chosen for the deployment of an interaction–visualisation medium. Today’s existing solutions differentiate by information and visual design, provided forms of navigation, locomotion, selection and manipulation. After the heuristic usability evaluation [10] of the VRE, it was decided to investigate the real-life demands of end-users. Vascular surgeons and interventional radiologists from five different hospitals were interviewed to get an overview of the work processes surrounding the tasks of diagnosis and treatment planning for vascular disorders. After these interviews, observation sessions were carried out at six hospitals to gain detailed understanding of the tasks and the context in which these tasks were performed [6,7]. The heuristic evaluation of the VRE coupled with the results of the interviews and observations permits us to summarise several generic recommendations to help
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PSEs’ developers in making a choice which projection modality could be better and when (see Table 1). Even though 3D visualisation is now available in most hospitals, it was found that existing systems are not always in use. Currently, no intervention is carried out only by evaluation of 3D visualisations. It is related, first of all, to the bad resolution of 3D stereoscopic images in comparison to 2D high-resolution scans. The concept of the Virtual Operating Theatre cannot satisfy all end-users of the VRE, as well as the concept of the Personal Desktop Assistant. Both interviews and observations indicate that many surgeons and interventional radiologists would prefer to use desktop applications for accomplishing every day tasks. As for large immersive virtual environments, they would be more preferable for collaborative work and training. The advantage of a large immersive virtual environment [5] is that it provides possibilities for collaborative work, which is crucial if we talk about medical applications. During observation sessions it has been found that medical people spend significant part of their time in collaboration. It concerns both making a diagnosis and planning a treatment. However, the number of people involved in a work discussion as usual does not exceed a group of five people. The exception is a weekly medical conference, in which all staff of a medical department participates. The VRE could be also used for the interactive training both in lecture or tutorial mode [18]. If it is a ‘lecture
Table 1 Several criterions to choose in between VR and Desktop (more information can be found in Refs. [6,7]) VR 1 2
Desktop
A sense of presence is important for accomplishing a task Stereoscopic visualisation and ‘sense of immersion’ add significantly to the task understanding or performance The 3D stereoscopic representation is vital Insight view into a complex structure is more important than performance
1 2
5
Perception and field regard are important
5
6
Collaborative work of a relatively big group of people (4–10) is necessary to support For training in ‘lecture mode’ End-users are interested in new technologies and willing to spend extra time for training There is enough space to place equipment Enough budget is available
6
3 4
7 8 9 10
3 4
7 8 9 10
Users need to switch tasks quickly Stereoscopic visualisation and immersion do not add significantly to the task understanding or performance Image resolution is crucial Performance is vital. No extra time can be spend for running the specialised equipment or conducting complicated manipulations Perception and field regard do not add significantly to the understanding of a task Quick, informal collaboration needs to be provided for a relatively small group of people (2–4) For training in ‘tutorial mode’ End-users are less inclined to learn using new equipment and technology Space limits A budget is limited
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mode’, a lecturer, responsible for all training components, including theoretical, demonstrational and practical parts of a course, guides a class. In this case the concept of the Virtual Operating Theatre is a good solution accepted under the condition that the number of students in a group is optimal. A ‘tutorial mode’ is oriented mostly to self-studies of students. In this respect the individual desktop environment is more preferable. A desktop application cannot be treated as an instant solution to usability problems experienced while working with an immersive VR application [7], and vice versa. Success will depend on the usability of a desktop or VR version. However, the better understanding of the interaction capabilities provided by a desktop application by most of users makes it a viable alternative to immersive VR. Another factor has to be taken into account is a ‘simulator sickness’. A simulator sickness [18] is a kind of motion sickness except that it occurs in a simulated environment without actual physical motion. The simulator sickness occurs in conjunction with the virtual reality exposure. Users having simulator sickness cannot work in VR. According to Ref. [13] almost a quarter of computer users suffers from simulator sickness. So approximately the same proportion of the VRE users will be unable to exploit I-VRE. For this type of users desktop remains the only possible solution. Fig. 5. A Personal Space Station-experimental setup.
5. A personal space station as a combined interaction–visualisation medium A Personal Space Station (PSS) allows users to interact directly with a virtual world. A PSS consists of a mirror in which a stereoscopic image is reflected [11]. A user reaches under a mirror to interact with the virtual objects directly with hands or by using taskspecific input devices. Fig. 5 shows the experimental setup of a PSS built at the University of Amsterdam. The main advantage of a PSS is that it combines both elements of VR and desktop projection modalities and it is possible to switch in between if necessary. This relatively new concept for the implementation of an interaction–visualisation environment may help to satisfy the wider range of the VRE users. By definition a PSS is an individual environment, but there is a pos-
sibility to build a shared environment where users can manipulate the same virtual objects working on different PSSs. More information about the PSS concept can be found in Ref. [20]. The idea to combine VR and desktop projection modalities within the same interaction–visualisation medium sounds very attractive. In this case different types of users will be able to work within the same environment having a minimal feeling of discomfort. But building such combined medium is not an easy task. The interaction in VR and desktop projection modalities differentiates in respect to navigation, locomotion, manipulation and measurement capabilities [4]. Now both the I-VRE and D-VRE can be run on a PSS. To switch in between two of these versions a user
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has to reboot a system, which is very uncomfortable, especially if it is necessary to combine the capabilities of both. In our future research we are going to focus on the development of a mechanism permitting a user to switch between VR and desktop during the exploitation of the VRE. To switch in between the Virtual Operating Theatre and the Personal Desktop Assistant, the interactive elements of the VRE have to support input and output modalities of both VR and desktop at the same time.
6. Discussions and future work In this paper a PSE for simulated vascular reconstruction has been introduced. The work is still in progress and one of the crucial issues to focus on is the improvement of interaction capabilities within it. The heuristic usability evaluation conducted recently and the first results of user profiling indicate that the HCI aspects depend to a great extent on a projection modality chosen for deploying an interaction–visualisation medium. As the end-users of the VRE are physicians who are usually not very familiar with modern computer technologies, it is very important to make the process of their interaction within a PSE as much comfortable as possible. Two concepts—the Virtual Operating Theatre and the Individual Desktop Assistant—have been presented. It has been shown that both VR and desktop solution are viable alternatives for the VRE users. That’s why we decided to combine virtual and desktop interaction capabilities within one medium. A PSS may help to bring this idea to life. Its main advantage is that it permits to switch from one to another projection modality if necessary. To permit a user to switch in between VR and desktop, a combined version of the I-VRE and DVRE will be built. It will permit to combine the interaction–visualisation capabilities of VR and desktop version of the VRE. The next step of the research will be to compare navigation, locomotion, manipulation and measurement capabilities in VR and desktop projection modalities in respect to users’ satisfaction, performance and mistake inflicting. It is planned to use the VRE running on a PSS as a case study for this research.
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Acknowledgments The authors would like to thank Dr. Robert Belleman, Denis Shamonin, Roman Shulakov, Hans Ragas and Daniela Gavidia (Section Computational Science, University of Amsterdam) for their contribution to the development of the VRE. We also would like to acknowledge Dutch hospitals, especially the Twente Medical Spectrum, Leiden University Medical Centre and the Rotterdam Medical Centre for their participation in user profiling, as well as Henriette Cramer and Dr. Vanessa Evers (Social Science Informatics Department, University of Amsterdam) for their meaningful contribution to this research. The experimental setup of a PSS has been funded partially by the EU CrossGrid Project IST-2001-32243 and the Token 2000 project “Distributed Interactive Medical Exploratory for 3D Medical Images”.
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Elena Zudilova is a Post-Doctoral Researcher at the Department of the Section Computational Science at the University of Amsterdam and holds secondary appointment as a Senior Researcher at the Corning Scientific Center in St. Petersburg, Russia. She received the MS degree in technical cybernetics in 1993 and PhD in computer science in 1998 from the St. Petersburg State Technical University. She received a special award for R&D from the Welles-Johnson Foundation of Maryland in 1996. Her current research interests are in the area of human–computer interaction and scientific visualisation for biomedical systems. Peter Sloot received the Master’s degree in chemical physics and theoretical physics at the University of Amsterdam in 1983. He then received an appointment as a Research Fellow at the Dutch Cancer Institute. In 1988 he received a PhD from the Department of Mathematics and Computer Science after which he was appointed as a Research Associate in the department. In 1991 he became Assistant Professor and in 1993 an Associate Professor in parallel and scientific computing in the department. In 1997 he became a Professor in computational physics. He has written and managed a large number of externally funded projects (funded by FOM, STW, Biophysics, Esprit a.o.). In 1997 he founded the Section Computational Science. He has co-authored more than 100 papers on various topics in (parallel) scientific computing and simulation. He has served on the organising committees of a large number of national and international conferences on scientific (distributed) computing. His current research interest is in the modelling and implementation of dynamic complex systems for massive parallel computers.
