test and track the user's responses. ... In order to test the knowledge of spatial relations, we have ... identify the cross-section by specifying a slice location.
Testing Spatial Understanding of Anatomy Parvati DevI, Charles Friedman2, Bonnie Dafoe3 and Ramon FelcianoI
IStanford University School of Medicine, Stanford, California 2University of North Carolina, Chapel Hill, North Carolina 3Temple University, Philadelphia, Pennsylvania ABSTRACT A system was designed to test the medical student's ability to recognize and locate anatomical cross-sections. The computer was used to prepare the data, present the test and track the user's responses. The nature of the test was such that it could be prepared, presented and used much more easily on the computer than on paper. The system was used successfully by anatomists and medical students.
INTRODUCTION Introductory gross anatomy for medical students is taught through cadaver dissection, identification of structures and learning the relative position of structures. Later, as students encounter cross-sectional imaging in radiology, the importance of understanding spatial relationships is understood, and frequently has to be relearned. We are interested in testing how much knowledge of spatial relationships is developed by medical students as compared to professional anatomists.
SYSTEM Data preparation and tests were carried out on Macintosh Ilci computers with 8 bit color video display. A Barneyscan high-resolution slide digitizer was used to digitize the color slides into 24-bit images which were then reduced in size to fit the screen and converted to 8-bit images, each with its own, optimized color table. The software to administer the tests was developed by us in SuperCard. Additional routines were developed in Pascal and other development systems. Software to process the digitized color images included SuperCard and PhotoShop. Data processing will be done using Excel. DATA PREPARATION The test data consists of color slides of cross-sections of a cadaver thorax and pelvis from Peterson [2]. Selected images were processed so as to separate recognizable, large anatomic structures. For example, in the thorax, structures could include: each lung, each scapula, ribs, the arch of the aorta, the oesophagus, the muscles of the back and the pectoral muscles. Each such object was labeled and the coordinates of the enclosing rectangle were recorded. The object could be made invisible or visible on command. One or more of the objects could be displayed against a generic, fatty background (figure 1). It was felt by the authors that this background looked less distracting than an uniform white or colored background. The original cross-sectional image was also retained.
Existing methods of computer testing rely on textual or multiple-choice answers. Some methods have been developed to test the process of building a hypothesis [1]. In order to test the knowledge of spatial relations, we have developed some new methods of presenting anatomical information. These presentations depend on the computer either for test data preparation or for test presentation, and they take advantage of the opportunities presented by computer paint programs and by hypermedia programs.
HYPOTHESIS Our hypothesis was that an experienced anatomist identifies a cross-sectional image of the body by identifying the individual structures and by localizing the cross-section within the body. Therefore, we hypothesized that the ability to localize the cross-section correctly in the body is a measure of the viewer's anatomical expertise.We further hypothesized that an experienced anatomist would be able to identify the cross-section after viewing only a few of the structures in the cross-section. In our initial test, we allowed the viewer to localize the cross-section after each clue, or anatomical structure, was displayed. This maximises the information to us, the developers, as we design the tests. The viewer continued the identification process till all clues were exhausted.
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Figure 1: Cross-section through the thorax with some anatomical structures visible.
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CLUE PRESENTATION The clues consisted of the oudine of the cross-section and the individual anatomic structures. The outline was the first clue. Other clues were presented in random order, each in its anatomically correct location with respect to the outline. After each clue, the user was required to identify the cross-section by specifying a slice location and the upper and lower boundary of the range of possible locations (a confidence interval).
RESULTS There was no question that the anatomist could identify the cross-section and its location. He derived information from many features of the clues. From the outline of the cross-section, he could identify the abdominal or thoracic nature of the slice. Within the thorax, the presence or absence of breast contours and their shape, allowed him to locate the slice to the upper, middle or lower third of the thorax. All this information was obtained before a single anatomic structure was displayed.
A clue editor was designed in SuperEdit, with dialog interfaces programmed in Pascal. It allows presentation of the clues in any predetermined sequence or in a computerselected random sequence. Preparation includes making the clue invisible when the test begins and specifying the location at which the clue should be displayed. Accurate coordinate location is necessary because clues may be shifted from their anatomical location during editing.
Anatomic structures were identified by their shape and location. Details of their shape were used to analyze whether the upper or lower end of the structure was being seen. Many subtle features of spatial relations between structures were also used. For example, whether the medial edge of the lung extended anterior to the heart or not could also indicate the level of the cross-section. The location of each cross-section was determined early in the sequence of clue presentation. Subsequent clues were used to confirm the selected location and, sometimes, to narrow the confidence range.
USER RESPONSE INTERFACE The user sees an image of the human body with thirty horizontal sections indicated by parallel, horizontal lines. The interface allows the user to point-and-click on the image of the body to specify a cross-section's location. By clicking on one of two arrows, the user can choose locations above or below the one first selected. When the user selects a location for the cross-section, a confidence bar is visible beside the image. The top and bottom locations of this bar are also adjusted by clicking on their respective up and down arrows. Once these adjustments are complete, the user clicks on a "confirm" button to indicate that the selections should be accepted. A new clue is presented until all the clues are exhausted. The user is allowed to view the image of the complete slice before proceeding to the next slice. In this test, the user receives no feedback regarding the correctness of the response.
Feedback obtained during this test is being used to modify some of the clues and their presentation. However, the basic nature of the test was acceptable to the subject. DISCUSSION A system was designed to test the ability to recognize and locate anatomical cross-sections. The computer was used to prepare the data, present the test and track the user's responses. The nature of the test was such that it could be prepared, presented and used much more easily on the computer than on paper. The system was used successfully by an anatomist.
TRACKING THE USER The user's responses are collected in a text format. The clue number and each confirmed response (cross-section location, upper and lower bounds) are stored for each slice viewed. These responses can be output for automatic entry into analysis programs such as Excel.
Additional tests are being conducted. In our first test, the performance of an anatomist, a fourth-year medical student and a first-year medical student will be compared to determine if the test differentiates between degrees of anatomical expertise. In subsequent tests, the performance of first-year students on this test and on conventional anatomy tests will be compared to determine if this test is a reliable predictor of anatomical knowledge.
PRELIMINARY TEST Our experiment was to determine if this test was one that could be performed successfully by an experienced anatomist, and to obtain qualitative feedback about their perception of the test's usefulness.
References 1. Stevens R.H., Kwak A.R. and McCoy J.M. (1989): Implementation of computer-based problem solving examinations for testing preclinical students in immunology.Proceedings of the 13th Annual Symposium on Computers Applications in Medical Care, 920-23.
The subject was asked to identify the slice location and range of uncertainty of the location. He was also asked to verbalize his thoughts including what he thought each clue was, what inference procedure he was using, and how much information each clue supplied in allowing him to identify a cross-section and its location.
2. Peterson R.R. (1982): A Cross-sectional Approach to Anatomy, published by R.R.Peterson.
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