Current medical visualization systems provide comprehensive functionality for interactive image processing, collaboration, and partially also for stereoscopy in high quality. However, their usage is either bound to special imaging workstations and, thus, to specific locations or as described in Section 3.3 to remote visualization applications that require special deployments. None of them conjointly support all of the above described and desired visualization aspects with minimum user involvement (Section 1.1). This leads to following hypothesis:
A high performing remote visualization system, specialized for stereoscopy and ease of use, can provide access to real-time interactive, stereoscopic, and collaborative medical volume visualization.
This hypothesis can be sub-divided in the following four research requirements, each highlighting a specific aspect that needs to be considered for such a system:
1. Minimum user knowledge and involvement during setup and usage of interactive remote visualization in real-time.
1.4 Rationale and Objectives
2. Support of multiple participants at different locations with different stereoscopic systems simultaneously.
3. Generic support of any existing and future visualization application.
4. Automatic quality adjustment during the runtime to optimize the balance between perfor-mance and quality on a given network condition.
Many applications, including modern Hospital Information Systems (HISs) and recent related work systems, are of pure web-based nature, which results in a wide availability of web browsers and people being familiar with it. Thus, an equally simple provision of highly interactive and stereoscopic volume visualization via pure web browsers would be beneficial. The following main question arose:
Can we evoke a solution that fulfills all requirements by only using a pure standard web browser at the client side?
As described in Section 3.3.3, none of the related work systems can be used simultaneously with multiple stereoscopic setups nor do the pure web-based systems provide an optimized performance for the real-time usage on different network conditions. Thus, the focus of this work lies on fulfilling all requirements, but especially on requirement 2 and requirement 4. It is expected that such a system is used by not more than four simultaneously collaborating remote groups (e.g.
classrooms) as discussed in Section 8.2.
A proof of concept conduction is a suitable method to test the feasibility of using web browsers without added software to remotely access stereoscopic volume visualization in real-time and collaboration. A proof of concept is "taking an idea and investigating to see if the idea has merit" [44, Ch. 2.2.1]. Thus, the basic idea of this thesis was the development of a prototype application that implements the approach introduced in Chapter 1 and its usage in a real practical scenario. The overall methodology is illustrated in Figure 2.1 by referencing the corresponding methodology and result sections.
The first task was to identify existing approaches that allow to answer the given problem of distributing visualization by only requiring a pure web-browser. This was done via a literature analysis and resulted in a state-of-the-art description of related work and enabling techniques, which is described in Section 2.1.
Several of these techniques were potentially usable for the development of a prototype system. It was therefore necessary to evaluate these techniques in order to find the most promising technique for an efficient data transfer. This evaluation was done by developing, testing, discussing, and grading several simple rapid prototype applications based on the requirements, which is described in Section 2.2.
This evaluation resulted in a single technique selection, which was then used to develop a more sophisticated prototype that implements the whole approach as described in the introduction (see Section 1.4). This system was then used for an inter-continentally shared medical anatomy class and further scenarios, which resulted in observations that led to further prototype improvements.
The optimized prototype was tested in detail to compare it with other visualization transfer methods and related work (see Section 2.3).
2.1 Literature analysis
The literature analysis was done on two levels: (1.) Finding literature about projects with the same topic and(2.) finding methods and techniques that enable such a system.
In order to get a quick overview about the topic in the beginning, the databases Pubmed [45] and Google Scholar [46] were searched. Pubmed is ideal to find publications in the field of medicine and medical informatics. Google Scholar in contrast has indexed a much broader scope of scientific and other publications (e.g. patents) and, thus, is a good addition to Pubmed. Google Scholar resulted in a very fast acquisition of popular literature ranked by search algorithms, but also in a
2.1 Literature analysis
Analysis of literature and existing techniques (Section 2.1)
State of the art technique overview (Chapter 3) Evaluation of enabling techniques
via rapid prototypes (Section 2.2)
Grading and technique selection (Chapter 4) Development of a prototype
(Section 2.3)
Prototype:
CoWebViz (Chapter 5)
Show feasibility via practical usage in classroom
(Section 2.3.2.2)
Observations (Chapter 6)
Measure performance and compare to related
work (Section 2.3.2.3) Performance comparison
(Chapter 7)
Verification against requirements (Chapter 8)
Figure 2.1. Flow diagram of the overall methodology (white boxes) and subsequent results (gray rounded boxes), each linked to the corresponding sections and chapters.
very large amount of publications that were off-topic. Among others, following search terms where used on both databases: "shared collaborative visualization", "shared medical visualization",
"stereoscopic classroom", "state of the art visualization", "web visualization education", and
"web-based remote visualization". In case of Pubmed, it was also tested to find literature via the MeSH terms "Education" and "Depth Perception" [47], which, however, only resulted in medical articles that were not relevant for the very technical problem of this thesis.
A systematic literature analysis was done afterwards to get a profound state of the art description of current systems, which is illustrated by a flow diagram in Figure 2.2. Pubmed was used again to find the usage of the desired systems in the medical discipline. IEEE Xplore digital library (IEEE DL) [48] and ACM digital library (ACM DL) [49] were used to find related work in technical disciplines. The search term that was used on each database was "remote AND visualization AND (browser OR web based)", which was adapted to each specific database search
Identified articles through search
Articles removed because of topical mis-match (n=146)
Screening of full-text articles (n=437)
Removed articles (n=400)
• Off-topic, e.g. not web-based nor interactive (n=193)
• Information visualization with HTML 5 (n=53) and applets (n=49)
• Interactive local 3D visualization with HTML 5 (n=11) and applets (n=85)
Figure 2.2. Flow chart of the literature analysis.
engine. The search was conducted in December 2011 without constraining the publication date.
However, due to the search term, the first publications were not older than the early 1990’s. The search was updated in February 2013 by constraining the publication date to the years 2011 to 2013. The process resulted in 583 publications after duplicate removal. These publications were screened on the basis of their title and abstract, which led to the removal of 146 publications.
The resulting 437 articles were screened and categorized based on their full text. Categories are 1) "off-topic", 2) "information visualization"1, 3) "interactive local 3D visualization", 4) "pre-rendered visualization" (such was often used for web-based medical education), and5)"interactive remote 3D visualization". Categories 2, 3, and 5 were further sub-divided into a) "utilizing
1Information visualization is a field of research about the visual representation of "non-spatial abstract data" [50], which is frequently used on web-browsers.