Direct Linear Transformation for the Measurement of In-Situ Peripheral Nerve Strain During Stretching
January 12th, 2024
This protocol implements a stereo-imaging camera system calibrated using direct linear transformation to capture three-dimensional in-situ displacements of stretched peripheral nerves. By capturing these displacements, strain induced at varying degrees of stretch can be determined informing the stretch injury thresholds that can advance the science of stretch-dependent nerve repair.
To begin, acquire three clear acrylic plexiglass square sheets. On each sheet, create a grid and mark at least 10 points, ensuring a minimum of 30 points across the 3D control volume on the X, Y and Z coordinate planes. Stack the sheets at different heights to capture the maximum height of the intended recording.
Using a digitizer equipped with a foot pedal, digitize all points on the 3D control volume. Establish the origin of the 3D control cube and define the positive X and Y directions to obtain X, Y, and Z coordinates. On the digitizer software interface, set the origin and positive X and Y axes respectively on the reference frame.
Open a new Excel worksheet to save the X, Y, and Z coordinates of the control volume. Then on the digitizer software interface, set the format strings to Excel to store the coordinates on the 3D control volume. As the X, Y and Z coordinates are digitized using the digitizer and foot pedal, they're recorded onto an open Excel sheet.
To document them, open an Excel sheet and save the coordinates as a csv file. To begin, run the MATLAB code to split the stretched nerve displacement videos into left and right camera files. Click Run to initiate the DLTdv7m22 GUI.
The DLTdv7 Controls window will appear enabling options like project, load project and quit. To start a new project, click New Project on the DLTdv7 Controls window. In the dialogue box, select 2 to indicate the use of 2 video files for tracking marker trajectories.
Choose the first video file from the left camera view and click Open. Then select and open the second video file from the right camera view. After selecting both video files, click Yes to confirm that they were calibrated using DLT.
Select the appropriate DLT coefficients csv file from the camera system and click open. Upon loading video files, the DLTdv7 controls are enabled, and the new project button changes to recompute 3D points, while the load project button changes to save. Then in the DLTdv7 Controls window, verify that the frame number is set to 1.
The current point is 1 and the auto track mode is off. Ensure that Update All Videos, DLT Visual Feedback and Show 2D Tracks are selected. In video 1, place 0.1 precisely at the center of the insertion marker.
Use the keyboard shortcuts to adjust the points'position for accuracy. In video 2, a blue, epipolar line guides the placement of 0.1 on the insertion marker. Use the keyboard shortcuts to adjust the points'position, aligning it with the center of the insertion marker.
Next, use the add a point function in the DLTdv7 Controls to track each tissue marker sequentially, then click Add a Point and place 0.2 on marker 2 in video 1. Using the blue epipolar line and keyboard shortcuts, place 0.2 on marker 1 in video 2. Continue adding and placing points on both videos from the insertion to the clamp.
After placing all initial points in both videos, set the frame number to 1 and ensure the current point is also set to 1 in the DLTdv7 Controls. Change the auto track mode to Auto Advance. The auto track predictor to Extend Kalman in the DLTdv7 Controls.
Begin tracking 0.1 in video 1, zoom in or out as needed for precision. Click through each frame until reaching the failure point or the video's end. After completion, reset to frame 1 and switch to 0.2 in the DLTdv7 Controls.
Tracked points will show distinct colors for easy identification. To track all points in video 1, click through each frame until reaching the failure point or video end. In video 2, use the blue epipolar line for tracking points, referencing video 1.
On the DLTdv7 Controls window, return the frame number to 1. Set the current point to 1 and begin tracking point one's trajectory in video 2. After tracking is complete in video 1 and video 2, click Export Points on the DLTdv7 Controls window to export the X, Y, and Z coordinates of the tracked points.
Select the desired direct relocation to save the output files. Set the name for the output files in another dialogue box. Then select the save format to flat.
After that, select No in another dialogue box to decide on calculating the 95%confidence interval. Confirm the export and saving of data, indicating that 4 output files are exported to the chosen directory. Click Save Project in the DLTdv7 Controls window to save the current project in the same directory as the output files.
Run a custom MATLAB code to import the tracked 3D marker trajectories in X, Y, and Z dimensions. Enter specific details like the rupture time and number of tracked points. Select the X, Y, Z point CSV file containing the 3D trajectories.
Choose a directory to save the output plots and the xls file with comprehensive data on time, length, change in length and strain. Then use the given equations to calculate length, change in length and percent strain.
Overview
This protocol implements a stereo-imaging camera system calibrated using direct linear transformation to capture three-dimensional in-situ displacements of stretched peripheral nerves. By capturing these displacements, strain induced at varying degrees of stretch can be determined informing the stretch injury thresholds that can advance the science of stretch-dependent nerve repair.
Key Study Components
Area of Science
- Neuroscience
- Biomechanics
- Imaging Techniques
Background
- Understanding nerve stretch and injury is crucial for developing repair strategies.
- Three-dimensional imaging provides insights into nerve mechanics.
- Calibrated imaging systems enhance measurement accuracy.
- Strain thresholds can inform clinical practices in nerve repair.
Purpose of Study
- To capture and analyze in-situ displacements of peripheral nerves.
- To determine strain thresholds during nerve stretching.
- To advance the understanding of stretch-dependent nerve repair mechanisms.
Methods Used
- Acquisition of clear acrylic sheets for grid marking.
- Digitization of points in a 3D control volume.
- Calibration of the stereo-imaging camera system.
- Analysis of strain induced by varying degrees of nerve stretch.
Main Results
- Successful capture of three-dimensional displacements of nerves.
- Identification of strain thresholds related to nerve stretching.
- Insights into the mechanics of stretch-induced nerve injury.
- Potential applications in improving nerve repair techniques.
Conclusions
- The calibrated stereo-imaging system effectively measures nerve displacements.
- Findings contribute to the understanding of nerve stretch injuries.
- Research supports advancements in clinical nerve repair strategies.
