X-Ray Motion Analysis
- What is X-Ray?
- What is X-Ray analysis?
- What is an image intensifier?
- What are the types of X-Ray imaging?
- What are the tracking techniques in X-Ray motion analysis?
- How is X-Ray analysis conducted?
- What are the applications of X-Ray motion analysis?
What is X-Ray?
X-rays are electromagnetic radiations having wavelength ranging from 10-8 – 10-11 m (frequencies between 3×1019 and 3×1016 Hz). X-Rays are used for nullifying cancer cells, in X-Ray machines, motion analysis, radiotherapy, computed tomography, projectional radiography, etc.
What is X-Ray Motion analysis?
X-Ray motion analysis refers to the process of tracking the motion of objects or bodies with the help of X-rays. In this technique, the object to be analyzed is placed in the center of the X-ray beam for imaging by using an image intensifier or a high-speed camera. This allows to record high-quality videos of object motion sampled many times per second. X-Ra motion analyzing technology can be varied in terms of X-Ray settings for visualizing specific structures in a body, such as bones or cartilage. Measuring skeletal motion is of great importance in the study of vertebrate energetics, motor control, and biomechanics.
What is an image intensifier?
Image intensifiers: An image intensifier is a device that works with X-rays for “real-time” processes like contrast studies of the hollow organs by fluoroscopy or for the procedures of angiography. The conversion of X-Rays into visible light occurs at very high intensity compared to fluorescent screens.
What are the types of X-Ray imaging?
Planar: Planar imaging allows to track the motion of objects in a two-dimensional plane of the X-ray. This is performed by a camera and a single X-Ray emitter. The motion analysis is conducted parallel to the camera’s imaging plane so that the motion of the object can be tracked accurately. The imaging is performed in the sagittal plane for gait analysis so that one can achieve highly accurate tracking of large movements. Nowadays, methods have been invented for analyzing all the 6 degrees of freedom of motion from a planar X-ray and a model of the object to be tracked.
These instruments can work as direct digital detectors i.e. they can directly convert x-ray photons into electrical charges that form a digital image. In indirect digital detectors, the x-ray photons are first transformed into visible light and then into electrical signals. Both the indirect and direct digital detectors are capable of detecting and transforming the resultant electronic signal to a digital image by utilizing thin-film transistors.
Biplanar: Biplanar imaging allows to track the motion of objects expanding to a 3-D volume of the imaging plane of the X-ray. This is performed by a camera and two X-Ray emitters. The imaging occurs at the intersection of two X-ray beams. For this reason, the total size is limited by the area of the X-ray emitters. This technique is not feasible at times as there is only one X-ray emitter available most of the time.
What are the tracking techniques in X-Ray motion analysis?
There are two types of tracking techniques in X-Ray motion analysis:
- Markered: The markered tracking technique uses reflective markers for capturing images. The marker chosen should be opaque in the given X-ray image. Markers are either placed on the subject’s skin or implanted in the subject’s bones, for tracking the motion of the underlying bones. These markers are then tracked with respect to the X-ray camera(s) and the motion observed is mapped to the local anatomical bodies.
- Markerless: With modern technology, it is now possible to track motion without using radio-opaque markers. The object to be analyzed can be overlaid on the images of the X-ray video at each frame with the help of a 3-D model of the object. The orientation of the 3D model of the object is tracked with respect to the X-ray camera(s). The motion observed is mapped to the standard anatomical movements with the help of a local coordinate system.
How is X-Ray analysis conducted?
In the case of planar X-Ray imaging, the movement of the markers is tracked by using specialized software. The software can either be manually controlled or automatically for locating the objects for each frame of the video. The automatic tracking, however, requires manual supervision for obtaining optimum results. The tracking results are then implemented on the local anatomical bodies.
In case of biplanar X-Ray imaging also, the movement of the markers are tracked by using specialized software. Similar to planar imaging, the software can either me manually controlled or automatically for locating the objects for each frame of the video. However, in biplanar imaging, tracking needs to be performed on both video frames simultaneously. in this case both the X-ray cameras require to be calibrated with the help of an object of known volume. The tracking results are then implemented on the local anatomical bodies.
What are the applications of X-Ray motion analysis?
X-Ray motion analysis is used for
- Measuring the kinematics of the lower limbs in human gait analysis.
- Performing joint torque analysis by a combination of X-ray motion analysis with force platforms.
- Quantifying osteoarthritis in the knee.
- Estimating the contact areas of knee cartilage.
- Analyzing the results of rotator cuff repair by observing the images of the shoulder joint.
- Analyzing animal locomotion.
- Analyzing moving morphologies like pig mastication, and motion of the temporomandibular joint in rabbits.
- Recording the bone motion obscured by soft tissue.
- Measuring skeletal motion.
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