The Usability Evaluation of Web-Based 3D Medical Image Visualization Sittapong Settapat1, Tiranee Achalakul2, and Michiko Ohkura3 1
Graduate School of Engineering, Shibaura Institute of Technology, Tokyo, Japan 2 Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand 3 Faculty of Engineering, Shibaura Institute of Technology, Tokyo, Japan
[email protected],
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Abstract. 3D visualization in virtual space simultaneously provides depth information with 2D information visualization ability. Since, web-based e-learning system has become popular alternative framework for improving learning performance and increasing convenience and flexibility to learners. Integrating a 3D medical image visualization into e-learning system aims to accomplish the needs of biomedical engineering education where learners can navigate, browsing, and interact with 3D models of reconstructed medical images. In this paper, we present the usability evaluation results of our web-based 3D medical image visualization comparing with conventional 2D visualization for web-based learning. The experimental results show that 3D visualization method improves learners’ education performance with tasks involving 2D information. Keywords: web3d, 3D visualization, e-learning, distance learning, biomedical engineering education, medical image visualization.
1 Introduction Since rapid growth of internet environment, web-based e-learning system allows learners, instructors, and facilitators to meet in geographically dispersed places using modern learning pedagogies, methods and facilities [1-5]. Unlike conventional programs in face-to-face teaching and learning, e-learning systems enable anywhere and anytime educations to encourage students to learn either by themselves or from facilitators. However, the available presentation and visualization tools and services mostly are limited in 2D visualization methods including characters, images, animations, and movies. Besides that, immersive virtual environment provides scene simulations and multimedia communication presented in 3D space help influencing learners’ behavior and motivation to increase learner satisfaction and efficiency [6-10]. 3D virtual environment enrich the learning environment and learning material to be more interactive and perceptive. The integration of 3D virtual environment and webbased e-learning system is not only improves learners’ performance and behavior, but this integrated system also provide a convenience and flexibility to learners. A. Marcus (Ed.): Design, User Experience, and Usability, Pt II, HCII 2011, LNCS 6770, pp. 507–516, 2011. © Springer-Verlag Berlin Heidelberg 2011
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Meanwhile, in the field of education, information visualization and user interface design affect the effectiveness of learning [6-7]; there are few reports on the effectiveness of the visualization methods for engineering educations such as biomedical engineering education. The biomedical engineering requires the principle understanding in both medical and engineering fields. The understandings in biology and anatomy are basically required, when the medical images are normally used as learning materials. The results of medical imaging are often given a set of 2D cross-section images, there are several applications that can render these set of image in 3D. However, to visualize these medical images in 3D over the Web require real time 3D reconstruction and visualization services [11]. In general, these services contain high calculation complexity [12]. Putting these services into practical, high computational performance but low cost framework is addressed to promote the web-based 3D medical image visualization service. Since our research concentrates on a web-based collaborative virtual environment for distance learning [13, 14], we designed and implemented high performance but low cost framework that allows us to reconstruct medical images and to visualize 3D reconstructed models over the Web in real time. Our system implementation was motivated based on a working hypothesis that a 3D visualization method should provide advantages for improving usability more than a 2D visualization method. However in the field of human computer interaction, there are few reports on the usability evaluation of 3D visualization methods for medical images over the Web. Then to validate our hypothesis, we evaluate the usability of our implemented web-based 3D visualization tools and services.
2 Related Research E-learning systems provide the opportunity to learn in both synchronous and asynchronous learning environments [5]. However, to enhance the learning performance, the selection of a certain combination of available e-learning facilities and tools based on instructional models and strategies has major consequences on learner behaviors and performance [2-4]. A collaborative virtual space is an approach for computer-generated scenes and multimedia communication. The generated scenes, which include scene appearance, interaction, navigation, and browsing, affect user feelings and emotions that in turn influence learning behavior and performance [8]. In virtual classrooms, learners interact with classmates and facilitators through avatars that enhance satisfaction and enjoyment [4]. For education, learning usability and effectiveness are as important as learning satisfaction and enjoyment. Enrichment of information visualization for distance learning with better collaboration through web-based e-learning integration improves the learning performance [4, 9]. Moreover, virtual space also offers the ability to spatially present virtual scenes and in 3D interaction [15, 16]. However, the usage of virtual space and 3D visualization is not widespread in engineering education. To promote 3D visualization in biomedical engineering education, we address the integration of 3D visualization and web-based e-learning system. Integrating 3D visualization into web system as a web service, XML based standard
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file format are recommended. In this paper, we propose the Web3D standard which is the application of XML and VRML technologies Web3D called X3D can deliver interactive 3D objects and 3D worlds across the Internet or CVE. The definition of X3D complies with that defined by the Web3D consortium. Web-based 3D visualization using Web3D standardized visualization tools and a file format increased the maintainability and the flexibility of the system implementation [17]. Web3D allows authors to simply create 3D contents [18]. The created contents can be visualized by any web browser with identical expected visualization using Web3D players. Moreover, Web3D technology allows authors to add more specific interaction for any specific purposes by adding some script and interactive virtual objects. Using this visualization framework, the implemented system becomes a flexible and maintainable scheme that is compatible with web technology.
3 Implemented Application The reconstructed model from medical images could be visualized over the web using X3D player [19, 20]. However, the X3D player is limited in interaction and operation [21]. Browsing through a reconstructed model normally requires constant page remodeling and reloading, even though we sufficiently minimized the generated model’s size to enable loading over web browsers in a reasonable time, so to prevent such an unnecessary model reloading are required. In this paper, we propose our model browsing approach using 2D image navigation. The set of low resolution images is used for the 2D navigation with smaller image resolution.
(a)
(b)
Fig. 1. The sample of two visualization methods; (a) Proposed method, (b) 2D slide show
Our 2D navigator shown in Fig. 1a allows users to navigate the model in the 2D mode. The navigator shows the 2D images in three shared planes: X, Y, and Z. In each plane, users can select the position that they want to see, and the image in each plane will be simultaneously changed to the selected coordinates. The model’s 2D navigator will not trigger a reload of the model, but the 3D model will reload when
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users submit the selected position and plane. With this result, users can still seamlessly navigate in 3D through the 2D navigator without unnecessary model reloading. In our system, the medical images can be visualized using a conventional 2D slide show that shown in Fig. 1b.
4 Experimental Research In this research, we visualized 2D images using two visualization methods; 2D image slide show, and Web3D visualization with 2D navigator. We used a mouse and keyboard for model operation and visualized them via a normal PC display size 36.5 cm. x 23 cm. with screen resolutions 1280 x 960 pixels. The sample of visualization methods are shown in Fig. 1. The motivation behind the system implementation for engineering education was based on working hypothesis that “3D visualization method should provide an advantage for biomedical engineering education with tasks involving 2D information, and students can perform studies using 3D visualization methods effectively.” In order to verify the validity of the hypothesis, we perform an experiment to evaluate our proposed method for biomedical engineering education in anatomy. System usability is defined in ISO 9241 draft standard as the “extend to which a product can be used with effectiveness, efficiency and satisfaction in a specified context of used” [22]. The experiment is intended to compare the level of knowledge obtained through the use of two different visualization systems. Specified tasks are designed to evaluate. After finished the tasks, all subjects need to answer the questionnaire to verify which visualization system is satisfied in anatomy subject for webbased biomedical engineering education. To carry out the experiment, the three specified tasks were designed to evaluate the level of knowledge obtained through the use of the system. − In the first task, we introduced subjects to the structures of the human brain through the 2D model with labels, and then subjects have to determine approximate areas of the following structures on the real MR images: Cerebrum, Corpus collosum, Ventricles, Cerebellum, Brain Stem, Frontal Lobe, Left eye, Right Ear and Optic nerve. − In the second task, subjects have to determine layer positions of the selected MR images on the human head model. − In the third task, subjects have to determine the name of the structures from the selected human brain areas shown in selected MR image. The design of these three specified tasks covers the knowledge obtaining from MR image which are “To understand and recognize the human brain structures from image of cross-section model to MR images and vice versa,” and “To understand and recognize the approximate real positions on the human head from MR images”. To evaluate the system efficiency, spending time of task completion were recorded to compare between two visualization methods. Our two visualization methods, a conventional 2D image slide show method and a proposed 3D visualization method, were performed. Finally, we designed the questionnaire to evaluate the system satisfaction. The Likert 5-scale questionnaires, with the highest score being 5, on seven items
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shown in Table 1 were used. We group the all items into 3 topics. Items Q1, Q2 are asked to evaluate the information visualization difficulty and satisfaction, items Q3, Q4 are asked to evaluate the usability and operation difficulty, and Q5, Q6 and Q7 are asked to evaluate the overall system satisfaction. Table 1. The Likert 5-scale questionnaires on 7 items
Item
Question
Item
Question
Q1
It is easy to see the information.
Q5
You are familiar with this system.
Q2
It is easy to understand the information.
Q6
It is user friendly
Q3
The model is easy to control.
Q7
You are satisfied with this system
Q4
The navigator is easy to use.
4.1 Experimental Procedure Twelve subjects participated in this experiment, ten graduate students (five males and five females) and two lecturers with MDs (one male and one female). All subjects are Thai nationality. Six of the subjects had experience in interpreting MR images. The other subjects had taken a basic anatomy course. Eleven of twelve subjects used computers daily. Seven of twelve subject used computers daily for educational purposes and the remainder used them several times a week. Six of twelve had experienced virtual space, typically for 3D games and movies; the remainder had never experienced virtual space. Subjects self-reported their familiarity with computers and Internet. Each subject performed the experiment individually. First, we showed each visualization methods to subjects and train subjects how to use them, and subjects try to use them. All subjects performed the tasks using the same environment. We checked the correctness score that each subject can obtain, and we also recorded the times from start to finish for each visualization method. After the tasks were finished, all subjects answered questionnaires.
5 Experimental Results For each trail, the collected dependent variables were: time, correctness scores and user ratings of satisfaction and difficulty. Paired samples t-tests were used to find significant contrasts when visualization method effects were discovered. We performed ANOVA to analyze the effect of both gender and the subject’s experience in virtual space factors. We chose a significance level of p
