A Three-Dimensional Virtual Simulator for Teaching Bitewing Radiography
Embed Size (px)
Transcript of A Three-Dimensional Virtual Simulator for Teaching Bitewing Radiography
Volume 117, Number 5 Abstracts e421OOOO ABSTRACTS
Objectives & Hypotheses The purpose of this study is to analyze and compare the way novice clinicians (dental students) and experts (certified oral and maxillofacial radiologists) examine panoramic images using an eye-tracking device. We hypothesize that the experts require less time and fewer eye movements than dental students in examining panoramic images.
Preliminary Results Some students use a back-and-forth approach to image review, comparing the right and left sides, while others simply look at the image in a circular manner. Still, others used a combination of both methods, depending on the region they are looking at. Unfortunately, a small portion of them seem to simply not have a standard approach when searching a panoramic radiograph, which explains the large areas that they simply do not look at. The quantitative data reveals that the observers spent more time, made more fixations, and covered more distance when looking at the normal and “subtle” images. Also, we found similar results for the areas of interest (AOIs), as long as the observers identified them. A recurrent finding was that observers spent considerable time looking at the midline region, most likely at the ghost shadow of the spine, when no abnormalities are easily visible. This is most likely caused by the lack of experience of the observers with panoramic radiographs.
References 1. Suwa K, Furukawa A and Matsumoto T. Analyzing the eye
movement of dentists during their reading of CT images. Odontology 2001;89:54-61.
2. Manning D, Ethell S, Donovan T and Crawford T. How do radiologists do it? The influence of experience and training on searching for chest nodules. Radiography 2006;12:134-142.
3. Krupinski EA. Visual scanning patterns of radiologists searching mammograms. Academic Radiology 1993;3:137-144.
4. Dreiseitl S, Pivec M and Binder M. Differences in examination characteristics of pigmented skin lesions: Results of an eye tracking study. Artificial Intelligence in Medicine 2012;54:201-205.
Influence of Experience and Training in the Examination Pattern of Panoramic Radiographs: Results of a Pilot Study
Turgeon DP, Pharoah MJ, Perschbacher SE, Lam EWN Faculty of Dentistry, University of Toronto, Canada
Future Directions Power calculations show the need for approximately 40 participants in each group (novice clinicians and experts). Once this number of participants is recruited, we hope to see obvious differences between the two groups. A feedback session will be provided to the students to show them how they performed. We also hope to be able to use the information gathered from the expert group to improve the way we teach how to search strategies and interpretation of panoramic images.
(A) Cumulative Heat Map for 4 Subjects Colour scale of gaze duration Background
Panoramic radiographs are complicated tomographic images containing many important anatomical structures. Since these images are used commonly by general dentists and specialists alike, it is vital that students learn to competently differentiate normal from abnormal, and make interpretations that “make sense” so that patient care is optimized. Understanding how students and experts interpret images may enable us to develop better approaches in how we teach dental students.
Materials & Methods We identified 20 panoramic images, and asked a panel of certified oral and maxillofacial radiologists to classify them as being normal or abnormal, and the areas of interest (AOIs) as obvious, intermediate, or subtle depending on their abilities to localize the abnormality. We used a RED-m (SensoMotoric Instruments, Tetlow, Germany) eye-tracking system, mounted on a 17-inch laptop. The panoramic images were displayed in a randomized fashion using the system software. This first stage of data collection consisted of ten 4th year dental students at the University of Toronto, and the following types of data were collected:
1. Time elapsed to identify the AOI (s). 2. Duration of the first eye fixation on the AOI (s). 3. Number of fixations of the AOI. 4. Duration of the fixations of the AOI (s). 5. Number of revisits to the AOI. 6. Total distance covered on the image. (cm). 7. Total number of fixations of the image. 8. Total duration of image examination (s).
Ethics approval was granted by the University of Toronto Health Sciences Research Ethics Board.
Figure 1 Figure 2 Figure 3 Figure 4
Variable Normal Obvious (AOI 1)
Obvious (AOI 2)
Obvious (AOI 3)
Obvious (AOI 4) Intermediate Subtle
Time elapsed to identify the AOI (s) 18.1 ± 5.1 9.9 ± 1.8 6.2 ± 3.3 18.6 ± 3.6 15.0 ± 5.9 29.5 ± 6.9 Duration of the first eye fixation on the AOI (s) 0.3 ± 0.1 0.4 ± 0.1 0.3 ± 0.0 0.3 ± 0.1 0.2 ± 0.0 0.2 ± 0.0 Number of fixations of the AOI 15 ± 4 31 ± 8 33 ± 8 2 ± 1 29 ± 6 3 ± 1 Duration of the fixations of the AOI (s) 5.2 ± 1.3 11.7 ± 3.1 12.0 ± 2.7 0.9 ± 0.3 10.7 ± 1.8 1.0 ± 0.3 Number of revisits to the AOI 9 ± 3 15 ± 4 13 ± 4 1 ± 1 11 ± 2 1 ± 1 Total distance covered on the image (cm) 778.5 ± 124.8 765 ± 199 655 ± 130 1165 ± 241 Total number of fixations of the image 182 ± 34 227 ± 60 153 ± 32 234 ± 42 Total number of saccades 193 ± 34 2367 ± 59 163 ± 31 247 ±42 Total duration (s) 69.1 ± 10.2 85.5 ± 20.7 62.1 ± 10.8 81.2 ± 13.0
Figure 1. Normal image.
Figure 2. Abnormal and “obvious”.
Figure 3. Abnormal and “intermediate”.
Figure 4. Abnormal and “subtle”.
(B) Original Image (C) Scan Path for a Single Subject Showing all the fixations (circles) and saccades (lines)
A B C
Mean eye-tracking data for the four images (± SE)
1. Chadwick BL, Dummer PH. Factors affecting the diagnostic quality of bitewing radiographs: a review. Br Dent J 1998;184:80-4.
2. Lateef F. Simulation-based learning:Just like the real thing. J Emerg Trauma Shock 2010;3:348-52.
The objective of this project is to develop a computer-based, three-dimensional simulator to teach the principles of x-ray beam positioning for bitewing radiography. This simulator will provide real-time image results to the user and be accessible from anywhere via a computer.
Many errors can occur while acquiring intraoral radiographs, creating adverse effects on the diagnostic value of the resultant image. Proficiency in bitewing radiography requires an understanding of how horizontal and vertical x-ray beam angulations as well as central ray positioning, affect the projection of patient anatomy on the x-ray sensor1. Current teaching methods involve the use of mannequins and is restricted to being performed in a clinic setting. The biggest limitation of practicing on mannequins is the time delay between irradiation and image acquisition. This lack of immediate feedback leaves the learner unsure of why an error has occurred and what would be required to correct it. Virtual simulation can be used to compensate for these limitations2.
This program’s effectiveness as a learning tool will be evaluated by dental students in an intervention study. Ideally, utilizing this simulation in conjunction with standard teaching techniques will yield more diagnostically relevant radiographs. Once its usefulness is shown, the program will be expanded to teach other intraoral radiographic techniques including periapicals and occlusals.
Acknowledgements Andrea Cormier, James Fiege and Dr. Ernest Lam
A Three-Dimensional Virtual Simulator for Teaching Bitewing Radiography Thang T, Cash M, Perschbacher SE
Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada M5G 1G6
Opening Page From the opening page , users may select either the
right premolar or left molar bitewing module.
Methods and Materials
Using MATLAB (The MathWorks, Inc. Massachusetts, USA) and a patient CT volume, multiple radiographs were simulated from an array of horizontal and vertical angulations. 3D models were developed from the same patient CT volume through the combined use of OsiriX (Pixmeo SARL, Geneva, Switzerland) and Maya (Autodesk, Inc., California, USA). The final program, built in Unity (Unity Technologies, California, USA) incorporates the radiographic images and the 3D virtual models into one graphic user interface. Unity was chosen for its ability to create and manipulate 3D environments, giving the user the greatest chance of visualizing a three-dimensional concept from a two-dimensional computer monitor. Vertical Angulation
As the vertical angulation is adjusted, the images change accordingly. Errors such as poor cusp overlap, distortion and off-centering of the occlusal
plane can be produced. A selected vertical angulation may be locked.
Horizontal Angulation As the user adjusts the horizontal angulation, the resulting images
change accordingly. Overlap can be produced when non-ideal angles are selected.
Central Ray Positioning As the user moves the tube-head bodily, the relationship of the central ray of the x-ray beam, relative to the image receptor, changes. Cone
cuts are produced when the central ray is incorrectly positioned.
Graphic User Interface The full GUI of the right premolar view module which consists of,
clockwise from top left, a “cone” view, scene overview, saved radiographs and current radiograph.
Horizontal: 70° Horizontal: 80° Horizontal: 50°
Instructional Overlay The overlay provides module instructions and is accessed
when the ‘I’ key is held.
Scene Overview Perspectives The user can interact with the scene by rotating, moving or zooming the perspective to visualize the relationship between the jaws and the tube-
head. Pre-set views are also available.
Vertical: +30° Vertical: +10° Vertical: -10°
Saving and Recalling Past Radiographs
The user is able to save up to four radiographs (smaller frames).
These radiographs can be dragged into the larger frames to be compared side-by-side. Furthermore, when clicked, the x-ray
tube-head returns to the location at which the radiograph was acquired.
This grants the user the ability to correlate radiographic changes with changes in x-ray tube-head positioning.
As shown in this example, the horizontal angulation selected for Image 1 produces overlapping interproximal contacts. The more
posterior horizontal beam angulation selected for Image 3 successfully opens the contacts.
Correspondence: Trevor Thang ( [email protected] )