Facilities and Equipment

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The Biodynamics Lab houses a custom biplane radiography system.  This system is comprised of two 150 kVp constant-potential high-frequency cardiac cine-radiographic generators (EMD CPX-3100CV) driving 0.3/0.6 mm focal-spot x-ray tubes. These x-ray generators were customized by the manufacturer to provide short-duration pulses (down to 1 ms) at very high repetition rates (up to 180 Hz). The short-duration pulses allow us to collect radiographs of high-speed movements without motion blur.  Radiographic images are captured with two 40 cm image intensifiers (Thales, Inc.) optically coupled to synchronized high-speed video cameras (Phantom 10, Vision Research) that have the capability to collect images at 500 frames/s at 1800×1800 resolution with a 14-bit dynamic range.The biplane radiography system is highly flexible and can be arranged in a variety of configurations. This system is suspended by a custom overhead positioning gantry that allows us to easily and quickly move the system throughout the lab.  The X-ray tubes and image intensifiers translate along telescoping columns to adjust height, while the X-ray tubes and image intensifiers pivot in 5-degree increments to adjust the angle of incline/decline of the system.

 

Bertec’s dual-belt instrumented treadmill contains two side-by side 30×180 cm belts. The belts are driven by independent (but synchronized) motor systems, and each belt/motor is configured on a rigid platform supported by multi-axis load cells. This configuration enables assessment of three-dimensional foot-ground reaction forces (vertical, medial/lateral and anterior/posterior), applied torque and center-of-pressure location independently for each foot. This treadmill can be run in forward or reverse and inclined to simulate uphill or downhill running and walking. This system may also be run asynchronously to perturb gait.

 

Vicon Motion Capture System
This video-motion analysis system is used to capture whole-body movement. Prior to testing, lightweight, plastic reflective markers with a diameter of ~5-9 mm are attached to anatomical landmarks on each subject.  Movement of these markers is captured in three-dimensions using a 12-camera Vicon Vantage system. Overall body movements are typically captured with this system at 60 to 150 frames per second.  The Vicon system is synchronized to the biplane radiographic imaging system and instrumented treadmill, allowing for simultaneous collection of radiographs, ground reaction forces and overall body motion. C-Motion software – Visual3D is used for kinematic measurements using Vicon data.

 

Simpleware & Mimics are used for segmentation of MRI and CT scans to make subject-specific 3D models of bones and soft tissues. Custom software is then used to track the 3D bone model unto the dynamic x-ray images and to analyze bone kinematics.
Model-based tracking
The biplane radiographic imaging system is replicated within our computer.  The subject-specific 3D bone model, generated from CT, is placed within the system. Simulated x-rays pass through the bone model to create a digitally reconstructed radiograph (DRR).  The 3D bone model is moved in space until the DRR matches the original radiograph (see videos below).

 

 

 

3D matching process The 3D bone model is manually rotated and translated in 3D space until the DRR closely matches the original radiographs.  Once a close match is established, an automated optimization process is used to find the position and orientation that optimizes the correlation between the DRR and edge-enhanced radiographs.
Movement tracking The automated tracking process is repeated for each pair of simultaneous radiographs collected during the dynamic movement trial.  This process is repeated for each bone to be included in the analysis.  In contrast to edge-based or silhouette matching processes, we use a volumetric matching process.  This means the “interior” features of the bone can be used to improve the match between DRR and radiograph.  In this sequence, the pedicles and lateral masses, in addition to the external vertebral edges, are key for driving the matching process.

 

ZeroWire (Aurion srl, Milano, Italy) wireless surface electromyography (EMG) electrode/transmitters are used to collect the electrical activity of muscles with disposable Noraxon single electrodes.
OpenSim is used to create subject-specific models and simulations of the musculoskeletal system.
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Novel’s Pedar system is used to measure pressure distribution under the foot during dynamic movements. Participants are fitted with an elastic sensor insole (1.9 mm thickness) that is connected to a data logging pack via cables. Each Pedar insole is comprised of 100 discrete pressure sensors that can measure pressure on the foot during activities such as walking, running, hopping, pivoting and jumping. This technology is synchronized to our radiographic imaging system, treadmill and mocap systems and is used to characterize foot loading patterns for all lower body research studies within the lab.