Image Analysis Systems Demystify The Secrets Of Motion

Motion analysis is the science (or art) of comparing sequential still images captured from photographing a body in motion, for the purpose of studying both the simple kinematics (the motions themselves) and the kinetics (the separate forces) involved. Originally developed in the early 1980s for use in sports medicine, motion analysis involves the recording of visual images of relatively large objects, such as the human body or an animal in movement, via a hardware-software system. Researchers can then analyze the recorded images separately or in sequence, or compare them to other single images or sequences, in order to detect patterns and make predictions. In the past five years, the applications for motion analysis systems have expanded far beyond uses in sports medicine. Scientists in such fields as orthopedics, kinesiology, general biology, the neurosciences, and bioengineering can benefit from this technique. Motion analysis can be used not only to determine more efficient training programs for athletes, but also, for example, to develop physical educational programs for victims of cerebral palsy or other debilitating conditions, to test the action of prosthetic devices, or to determine the evolution of locomotory patterns. Interpretation of visual images may be either automatic or digital. For automatic analysis, the object whose motion is analyzed is fitted with small reflective markers at strategic points - such as on the outer joint surfaces of the hip, knee, and ankle when one is analyzing the jumping motion of an athlete. Digitizing software (which is included with basic motion analysis system packages) detects each reflective spot in each captured frame, calculates the center of each "spot," and transforms its relative position into a data point, represented in either tabular or graphical form for analysis. For objects that are resistant to the reflective sticker approach (animal subjects, for example, or some neurological patients, whose random motions tend to dislodge the reflectors), captured images can be digitized manually. The researcher displays a single image on a video screen, moves a cursor in turn to the various points of interest (joints, most usually), and clicks a key or mouse to define a data point. Analyses can be done in two or three dimensions (requiring separate software modules), and can produce two- or three-dimensional graphics of the motion paths of selected points, such as the path of the ankle in a jumping man, or the flexion of a bear's foot during normal walking. Basic statistical routines to determine standard deviation and significance of variation in data are part of the software. Besides the type of large-body motion analysis described previously, the mathematical principles of motion analysis are also applied in computation to develop systems for robotic navigation, in development of computer vision, in target tracking, in traffic monitoring, in cloud and weather systems tracking, and in detection of biological cells' motions. Since investigations of this type tend to be either highly individualized or carried out under government auspices, there is not really any commercial software available for such purposes, though some investigators may adapt existing software or use commercial computation packages for the mathematical parts of their work. For an overview of current methods in this "finer-grained" type of motion analysis, an article by J.F. Vega-Riveros and K. Jabbour (IEEE Proceedings, Part I, 136:397-403) gives a good bibliography, including the names of many current researchers in the area. Most motion analysis systems have similar hardware components, though they may vary in flexibility or capacity, or in the analytical capabilities of the software component. These systems by and large are expensive; this is no small-ticket item. In some cases, though, the expense can be lessened if the purchaser already has some of the components available. Peak Performance Technologies Inc., 7388 S. Revere Pkwy., Suite 601, Englewood, Colo. 80112; (303) 799-8686 Motion Analysis Corp., 3650 N. Laughlin Rd., Santa Rosa, Calif. 95403; (707) 579-6500 Several other companies specialize in motion analysis in the United States, as do some in other countries, such as Oxford Metrics, in England; Selcom, in Sweden; and Northern Digital, in Canada. For the exact addresses of these firms, contact the Trade Board of each country. System prices vary, depending on complexity, but are all in the same approximate range as that described in the text. One of the most popular motion analysis systems is that supplied by Peak Performance Technologies Inc., headquartered in Englewood, Colo. The basic Peak Performance system consists of an ordinary video camera; a video camera recorder (VCR); an AT-class computer (IBM-compatible), either a 286 or a 386; two specialized boards that fit into slots on the computer's mother-board; and two video monitors. A normal, run-of-the-mill video camera captures images at approximately 60 frames per second (that is, 60 fields - or images - per second). The only proprietary parts of the system are the two specialized boards (which perform the image capture and transfer the images to and from the VCR) and the software modules necessary for different types of analysis. All other components are standard items that may be available in an existing laboratory setup, or may be purchased separately from other sources. Including all components, a basic system costs approximately $20,000. However, Peak Performance offers a university discount of approximately 30 percent, which makes the cost to academic users substantially less. Other systems can cost substantially more, though. Some studies (such as an analysis of the wing motion of a hummingbird) require variable-speed image capture rates, or those much faster than that achieved with ordinary cameras. Such high-speed motion picture cameras are quite expensive. Frame rates of up to 2,000 frames per second are available, but at a fairly high cost. Additional software modules for analysis beyond the standard system are also available, such as a module (from Peak Performance) that allows direct capture of analog data from a force platform or other motion transducer, without the necessity of interpreting visual images. Costs for a very sophisticated system can run as high as $60,000, which explains why motion analysis systems are commonly found only in large laboratories and research institutes. Motion Analysis Corp., another major vendor of motion analysis systems based in Santa Rosa, Calif., provides similar services to those offered by Peak Performance, though with a somewhat wider range of applications and prices. In addition to general-purpose systems and body-based applications, Motion Analysis provides specialized software and hardware for applications as diverse as spacesuit movement analysis for the National Aeronautics and Space Administration and sperm motility analysis for infertility specialists. Motion Analysis also sells both 2-D and 3-D systems; the two-dimensional systems are PC-based (based on an AT-class microcomputer), while the three-dimensional applications use a Sun workstation as the basic computer component. Like Peak Performance, Motion Analysis uses commercially available VCR equipment, ranging from standard to special high-speed cameras. The more expensive Motion Analysis systems are designed to use up to six separate cameras, for additional three-dimensional coverage. Prices for Motion Analysis systems are proportional. The com-pany's two-dimensional, PC-based systems begin at $30,000. (The firm will work with a customer who wishes to use pre-existing components, but warns that it is frequently easier and less expensive to buy a system "from scratch" than to try to integrate existing pieces.) The three-dimensional workstation based systems begin at $60,000, with additional charges for extra equipment and software, such as the phase-contrast microscope and analytical software used for sperm motility analysis. Diana J. Gabaldon is assistant research professor at the Center for Environmental Studies, Arizona State University, and editor of Science Software.

Image Analysis Systems Demystify The Secrets Of Motion

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