Major scientific contributions

This work contributes a system which has undergone informal usability testing in the context o f real domain experts doing real work, but it also presents the results of laboratory-based experimental evaluations which illustrate general behavioural principles. Some o f the informal design issues, which user observations have suggested, are now supported by formal experimental evaluations. Moreover, the selection of experimental evaluations has been tempered by design experience, so there is some assurance that subjective and objective assessments apply to design in a meaningful way. Together, these approaches make a decisive statement that using the prototype discussed in this thesis can result in improved computer-assisted microsurgery.

The major contributions o f the author’s work are:

• Human-centred design: The author contributes an ergonomic interface design which, by creating physical and behavioural aspect models o f conventional ENT surgery, is based on the surgeon’s mental model during the microsurgical procedure,

• Application to EN T surgery: The author contributes the design, implementation and usability testing o f a stereo video camera system which captures stereo pairs o f images from a surgical microscope and displays them in an autostereoscopic 3D display,

• Mechanical coupler design: The author contributes a coupling component design which can align two disparate camera views onto the display plane of

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a 3D display (stereoscopic or autostereoscopic), and can be optimised for various focal settings,

• Training and teaching at remote locations: The author contributes the design and implementation of a dedicated optical fibre network for CAESAR surgery in three operating theatres and a computer laboratory, as well as real time stereo imaging at a remote seminar room,

• Research methodology: The author contributes a thesis which provides a case study for an interdisciplinary approach to the design and evaluation o f new human-computer interfaces.

From a task analysis o f conventional microsurgical operations, it was realised that there are strict limitations as to which direction the microscope can be physically expanded. Even though microelectronics technology can offer these days inexpensive, state-of-art optical and video components, there are always additional human factors that need to be considered when altering the original design o f the instrument. The physical aspect model o f microscope-affected tasks derived from the first design cycle suggested that a “sideways” or “away from the surgeon” (z-axis, see Figure 5.10) addition o f new modules could damage the instrument’s counterbalance and overall movement, particularly tilt. As a result, an “upwards” (parallel to the eyepiece) module design was chosen.

The broader vision o f this research is eventually to replace the microscope binoculars with a more natural viewing medium and limit the instrument’s use to a video magnifying “torch”. In this way, surgeons would be completely relieved from the burden o f immersive interfaces. This has been delivered through the development o f the stereo video camera system shown in Figure 6.17. The main characteristics o f the design are the parallel-camera viewing geometry and open-architecture which ensures that the system can be used for different microscope brands. This openness is extended further, as modifications in the design o f the mechanical coupler enable users to adjust the system to various FOV and DOF settings, therefore optimising the appearance o f 3D content on the autostereoscopic 3D display.

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The success o f a CAS system depends on its ability to process and display accurately high levels of interaction in real time. This becomes more difficult when stereoscopic viewing is required, as in the case o f microsurgery. Up to date supergraphics computers, with digital video frame grabbers and graphics pipelines, can provide sufficient computing power for real time implementation o f CAS applications. However, such computers are bulky and need to be stored in air-conditioned rooms. The optical fibre network, described in Chapter 8 o f this thesis, offers an end-to-end digital audiovisual communications platform for CAS surgery in any o f three operating theatres and the hospital’s imaging laboratory, all located far away from the computer mainframe room. Furthermore, it allows real time stereo multicasting o f the surgical procedure in a seminar room, also located far away from the supergraphics computer. The network is implemented with fibre redundancies, thus providing the infrastructure for future tele- robotic surgical applications.

The research methodology o f this case study is statistically correct. Statistical analysis methods need to be carefully chosen during product evaluation. As part of the research work included some quantitative and qualitative analysis o f usability and effectiveness testing, the appropriate statistical analysis techniques were selected. A paired t-test analysis was chosen for the quantitative analysis o f the interface’s accuracy and precision. The need for a parametric test arose from two main reasons. First, the nature o f the experiment (task execution by an operator who uses two different viewing media in succession) was such that suggested a matched comparison^^. Secondly, sample homogeneity (86% o f participants being ENT surgeons) and a quick inspection o f results from a single operator suggested that experimental data form a Gaussian distribution. For the qualitative analysis o f the interface’s effectiveness, a Kruskall- Wallis non-parametric test was selected. The choice o f this analysis technique was because the author needed to test viewing comfort and depth appreciation over a large set o f stereo camera disparities.

I f the au th o r h ad ch o sen free-view ing m easurem ents as a th ird m atch ed group data, a n alternative m eth o d o f estim ating statistical erro r w ould be repeated-m easures A N O V A . H ow ever, the “golden standard” value w as the actual p o sition o f the selected p o in t as it w as m easured w ith a great deal o f h aptic feedback.

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