Design of a Novel Otoscopy Trainer

University of California - San Diego

MAE 156B CAPSTONE Project

Spring 2022

Figure 1: Final Otoscopy Task Trainer Design

Overview

Background

Otoscopy, commonly known as ear exams, is a medical procedure performed by doctors to inspect the ear for any abnormalities or signs of infections. Doctors use a tool called an otoscope which shines a light in the ear and has a magnification lens. During these ear inspections, doctors inspect the tympanic membrane, also known as the eardrum, and look for a cone of light reflecting from the eardrum and the malleus bone structure. Typical signs of infection include dilated blood vessels, thickening or bulging of the eardrum, and a malleus or cone of light that is not defined.

Figure 2: Otoscopy Exam

Objective

The purpose of this project is to develop a novel otoscopy skills trainer to help improve the ear exam skills of medical students and residents. Dr. Helen Wang and Dr. Lawrence Ma, pediatricians of the UC San Diego Health Department, identified that many students are struggling with performing ear exams due to a lack of experience and confidence. Therefore, this otoscopy task trainer includes an otoscope with position tracking capabilities that helps medical students identify which areas within the ear to inspect without causing any discomfort or pain to patients as well as how far into the ear canal to go and what to be looking for. Moreover, by giving the students a method to practice, this increases their confidence when conducting actual ear exams.

Theoretical Model

Figure 3: Position Tracking Using Magnet Sensors

In this model, the magnetic flux density detected from the magnet sensor is related to the distance and the orientation of the magnet through a magnetic constant, K.

Figure 4: Orientation Tracking Using Inertial Measurement Unit (IMU)

An IMU consists of a 3D accelerometer and 3D gyroscope that measures the external force and angular velocity experienced by the sensor, respectively. By implementing a discrete time complementary filter as shown above, measurements from the gyroscope and accelerometer can be converted to a measurement of angular displacement.

Final Design

Figure 5: Magnetic Sensor Layout

Magnetic Sensing

Three magnetometers are placed in plane with one another. By taking readings of the magnetic flux density from each of these four sensors, there is sufficient information to determine the local position of the magnet inside of the otoscope handle in cartesian coordinates (x,y,z). Furthermore, this magnet position can be translated to find the position of the otoscope tip by using translation matrices.

An IMU is a sensor that with a 3D accelerometer and 3D gyroscope, which track the acceleration and angular velocity experienced by the sensor, respectively. Using this information alongside a complimentary filter, readings from an IMU can be translated to changes in the rotation angle about three orthogonal axes. Similar to the magnet sensor, the rotation experienced by the IMU can be translated to a corresponding rotation in the otoscope tip through translation and rotation matrices.

Graphical User Interface

Through the incorporation of magnetometers (magnet sensors) and inertial measurement unit (IMU), the position of the otoscope tip in 6 degrees of freedom (DOF) was simulated in MATLAB.

The ear mold is stationary in this simulation, however the otoscope, represented by red dots, moves freely in space and is updated every 55 ms.

Figure 6: MATLAB GUI illustrating otoscope outside of the ear canal

Results

Position Tracking Accuracy

Average Position Error: 2.72 mm

Orientation Tracking Accuracy

Average Orientation Error: 3.55 degrees

Challenges

The targeted accuracy for position tracking and orientation tracking were <0.5 mm and <5 degrees, respectively. While the orientation tracking error met the specified requirement with an average error of only 3.55 degrees, the position tracking accuracy was relatively far from the specified requirement with an average position error of 2.72 mm. This large amount of error can be attributed to a poor model of the magnetic tracking system and magnetic interference that may arise from surrounding devices.

Recommendations for the Future

One way to improve the model of the magnetic tracking system would be to incorporate an interpolation method that would provide a specific magnetic flux density reading from each magnetometer as the otoscope moves to each unique location in the system. This method would generate a "look-up table" that can characterize each possible position that the otoscope could be at, therefore improving precision and accuracy. Additionally, the incorporation of an electromagnet that emits a magnetic field at a certain frequency would be advantageous over a permanent magnet because the signal could be filtered from all other magnetic disturbances in the surrounding area. Consequently, this would generate a magnetic sensor reading with less noise and would also improve the precision of the system.