Motion Capture With AVT Cameras Makes Orthopedic Diagnosis Easier
Motion capture has become widely known for producing spectacular special effects and 3-D animation in motion pictures. However, this technology, which transfers a human actor’s motions onto a computer-generated figure, can be applied in many other fields. SIMI Reality Motion Systems GmbH of Munich, Germany provides innovative software and systems for motion capture applications, working not only with animation studios but also with competitive athletes, researchers and medical facilities who need precise tools for evaluation of motion sequences. With SIMI Motion, SIMI has developed a system for precisely evaluating a patient’s sequence of movements within the framework of orthopedic or neurologic diagnosis and treatment.
Diagnosis and treatment supervision
SIMI Motion is an analysis system for the dynamic, non-invasive diagnosis and monitoring of musculoskeletal dysfunction. The system analyzes video data from one or more digital cameras and generates crucial data such as joint angles, accelerations, axle symmetries, and joint torque or stress. Data can be compared with standard values in biomedical literature to identify possible dysfunctions.
The system is equipped with one (2-D version) or more (3D version) Pike F-032B fast digital cameras from Allied Vision Technologies. The cameras are connected to an ordinary desktop computer with an IEEE 1394b FireWire or a fiber optic interface. The test subject is outfitted with markings on crucial joints and then executes a particular sequence, such as taking a few normal steps, in front of the camera. The SIMI Motion Software analyzes the image data from the camera and derives the joint movements from the progression of the markings.
Graphic representations and easy-to-use tools simplify diagnosis for the physician who, thanks to this system, can quickly and precisely find the patient’s weak points. Thus, factors such as ambulation cycles and joint movements, translations or rotations can be examined in detail. Just as virtual 3-D figures can be brought to life in animation studios by actors, so can physicians get a moving 3-D model of the patient’s skeleton using the data provided by the system in order to better visualize the joint stress.
Particularly valuable for doctors is the system’s ability to synchronize with other medical measuring devices such as force plates, foot pressure measurement devices or electromyographs (EMGs). The data collected from all sides thus provides even greater precision.
Beyond mere diagnosis, archiving and comparison of data provide valuable assistance in treatment. Pre- and postoperative comparisons can be performed on patients, allowing for evaluation of the surgery’s success, and doctors can take measurements at regular intervals to check and document the progress of rehabilitation.
Scientists research treatments of the future
The SIMI Motion System using the AVT Pike has also been applied in basic research. Dr. Andrey Irintchev, Director of the Neuroscientific Research Laboratory of the ENT Clinic at the University of Jena Hospital (Germany), developed a method for scientifically measuring, comparing and documenting motor disruptions and particularly the healing processes corresponding thereto in laboratory mice. Dysfunction resulting from nerve or spinal cord damage, as well as possible treatment therapies, were studied.
Using his methodology, the scientist examined new treatment methods, such as the influence of electrical stimulation on the regeneration of nerves. At the moment, Dr. Irintchev is occupied with the genetics of motor healing processes: “We’re comparing normal mice with those carrying a mutated gene in order to determine whether certain proteins accelerate or retard the healing process.”
Andrey Irintchev’s method consists of capturing and analyzing a mouse’s gait along a beam. The animal can only move in one direction on a narrow, hanging beam, allowing the same sequence of movements to be compared repeated times. Thanks to SIMI’s motion analysis software, the movement sequences can be analyzed very exactly without marking the animal’s joints. “You can’t always do with mice what you can do with humans; mice legs are too short and the joints are too unclear, and their hair gets in the way of marking,” Irintchev explains. “For that reason, it’s very valuable for our work to be able to secure reliable results even without markings.” Yet another advantage of imaging is that it is non-invasive: animals can move freely and naturally, Irintchev says.
AVT Pike delivers 200 images per second
When Irintchev and his team began to develop a video-based analysis method years ago, they used an analog video camera and a conventional video recorder. The image quality, speed and further processing capabilities were too limited for such an ambitious project, so they turned to a professional digital camera. Still, at 100 images per second, they soon reached the limits of that technology. “Image rate and quality are key for the precision we need. For that reason, we finally decided on the Pike digital camera from Allied Vision Technologies, whose 200 fps speed and high image quality allowed us to analyze mouse movements with complete exactitude.”
The SIMI Motion Software analyzes the images and generates benchmark data such as certain joint angles or accelerations that are then statistically evaluated. “Thanks to our method using the SIMI software and the AVT cameras, we’re able to measure very slight deviations and to statistically account for what used to be mere empirical observation with data and numbers,” Andrey Irintchev reports. “This statistical evaluation of verifiably collected results is decisive in every discipline of scientific research, as only in this way can results be validated and conclusively proven”.