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CiiS Lab
Johns Hopkins University
112 Hackerman Hall
3400 N. Charles Street
Baltimore, MD 21218
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Lab Director
Russell Taylor
127 Hackerman Hall
rht@jhu.edu
Last updated: 5/6/16 8:00AM
This project proposes new way of tracking technology by integration of the laser technology with the computer vision, and also piezoelectric effect. The goal of this project is to track a catheter using a stereo camera and applying laser spots on the patient surface, which can be seen by the stereo camera and generate a photoacoustic (PA) signal observed by the piezoelectric element. Preliminary results show reasonable repeatability of element localization.
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Photoacoustics is an acoustic wave generation by an absorption of light. The history of photoacoustic effect discovery starts from 1880 when Alexander Graham Bell observed it. The photoacoustic effect is broadly applied for using in various fields, especially medical field for spectroscopy. While the piezoelectric element is a device using the piezoelectric effect to measure changes in pressure, temperature or force by converting them to the electrical charge. Piezoelectric effect is used in many applications, such as detection of sound and generation of electronic frequency. When comparing to other guidance systems, the benefit of this project is that this method does not require any physical markers in order to create a coordinate transformation, also it does not need to have calibration processes because we can directly compute the coordinate transformation from the collected data. The significance of this project is to enable an innovation to track the tool in interventional photoacoustic system with no additional trackable markers and/or calibration processes.
2.1 Stereo camera point segmentation The goal of this approach is to locate the laser points in stereo camera images. Since we are dealing with multiple image frames, composed of either images with or without the laser point, the efficient segmentation method for those points is needed. Some characteristics of images are determined to be used as parameters of this segmentation method, such as intensity thresholds based on histogram of intensities, pixel size threshold, and shape filter.
2.2 System overview for PA signal acquisition The reason for this approach is to acquire the PA signal. We use the DAQ system to collect the signal. We not only use a filter to remove some unwanted feature noises from a signal before being sampled in the DAQ, but also apply the impedance matching design to improve the signal-to-noise ratio.
2.3 Trilateration method The reason for this approach is to acquire the location of piezoelectric element point or the location of catheter tip in this project. Trilateration is the method of calculating locations of points by measurement of distances, and applying the theory of geometry of circles and spheres.
2.4 Validation The reason for validation is to show that this system succeeds the project goals. We will use two methods to validate the system. One of them is “repeatability”: the result of calculation with different subsets of PA spots data should give the same location of catheter tip. Another method is “relative distance”: the results of calculation of at least two different set-up tip locations will be compared with known distance of those points. }
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