An ultrasound device synchronized with a motion analysis system works by combining the high-resolution imaging capabilities of ultrasound with the real-time tracking capabilities of a motion analysis system. The ultrasound device is used to produce images of the body, while the motion analysis system tracks and records the movements of specific joints, muscles, or other body parts.
Traditional motion capture systems are based on optical technology, using cameras and reflective markers to capture human motion. However, the measurement accuracy can be affected by factors such as light, marker shifts and shadows. On the other hand, ultrasound technology can provide more accurate biomechanical data, which can monitor muscle and bone movements in real time and help evaluate joint kinematics and dynamics.
To eliminate the limitations of each technology and improve the accuracy/ reliability of the data, two systems are synchronized so that the images captured by the ultrasound device are accurately aligned with the movements being tracked by the motion analysis system.
This combination allows:
- Personalize parameters such as muscle paths or muscle lever arms
- Characterize the displacements of muscle fascicles and musculotendinous junction involved in motor tasks
- Medical professionals to observe the internal structures of the body in real-time as they move and respond to different stimuli
- Have better understanding of the movement of a patient's muscular and skeletal systems
- Identify movement disorders and incoordination
- Develop more targeted rehabilitation programs
In a clinical setting, an ultrasound device synchronized with a motion analysis system may be used to study the movement of joints and muscles during physical therapy or rehabilitation.
In order to synchronize ultrasound with motion analysis system, we have 2 problems that needs to be solved:
1) Temporal calibration: To calculate the temporal offset between the tracking from Polaris and the video stream from the ultrasound. This step needs to be done if we use a different motion capture system, a different video stream device or if we use a different ultrasound device.
2) Spatial calibration: To calculate the transform matrix between the markers attached to the probe and the ultrasound image. This step needs to be done if using a different ultrasound probe, if the marker holder moved or if the setting of the probe, such as depth, changed. In other words compute Image-to-Probe transformation, by following the blue arrows:
- ImageToStylusTip: Defined manually by mouse-clicking on the Image
- StylusTipToStylus: Computed by using pivot calibration
- StylusToProbe: Computed by PLUS software using the position tracker