3 Direct Measurement Techniques


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3 Direct Measurement Techniques

  1. 1. direct Measurement Techniques Dr. Amal HM. Ibrahim Professor of Physical Therapy aebrahim123@hotmail.com
  2. 2. Goniometers10/28/2011 aebrahim123@hotmail.com
  3. 3. Goniometers  A goniometer is a special name given to the electrical potentiometer that can be attached to measure a joint angle.  One arm of the goniometer is attached to one limb segment and the other to the adjacent limb segment.  The axis of goniometer is aligned to the joint axis10/28/2011 aebrahim123@hotmail.com
  4. 4. Goniometers  A constant voltage is applied across the outside terminals, and the wiper arm moves to pick off a fraction of the total voltage.  The fraction of the voltage depends on the joint angle, θ.  Note that the voltage proportional to θ requires a potentiometer whose resistance varies linearly with θ.10/28/2011 aebrahim123@hotmail.com
  5. 5. Goniometers  Potentiometers: A potentiometric element is attached to a joints rotation point. The potentiometers electrical resistance can be used to determine the angle between the joints.  These types of electrogoniometers are somewhat bulky and restrict patient movement10/28/2011 aebrahim123@hotmail.com
  6. 6. Advantages of Electrogoniometer  A goniometer is inexpensive.  Output signal is available immediately for recording or conversion into a computer.10/28/2011 aebrahim123@hotmail.com
  7. 7. Disadvantages of Electrogoniometer1. Relative angular data are given, not absolute angles, thus severely limiting diagnostic value.2. It may require an excessive length of time to fit and align.3. If a large number are fitted, movement can be encumbered by the straps and cables.4. More complex goniometers are required for joints which do not move as hinge joint. 10/28/2011 aebrahim123@hotmail.com
  8. 8. Agreement between an electrogoniometer and motion analysis system measuring angular velocity of the knee during walking after strokeV.M. Pomeroy a,∗, E. Evansa, J.D. Richards- Physiotherapy 92 (2006) 159–165  Objectives: There is a need to measure quality of movement to assess effectiveness of physical therapy interventions after stroke. Knee angular velocity may be a sensitive measure of change in performance of movement during functional activity, but not all clinical centers have access to a movement analysis laboratory.  The aim of this study was to investigate the concurrent validity of using an electrogoniometer and a laboratory-based movement analysis system (Vicon Motion Systems Ltd, Oxford, UK) to measure knee angular velocity.10/28/2011 aebrahim123@hotmail.com
  9. 9. Agreement between an electrogoniometer and motion analysis system measuring angular velocity of the knee during walking after strokeV.M. Pomeroy a,∗, E. Evansa, J.D. Richards- Physiotherapy 92 (2006) 159–165  Design: Prospective agreement study.  Setting : Movement analysis laboratory.  Participants: Fifteen adult volunteers (mean age 55.6 years) at least 6 months after stroke and able to walk at least 4.5m indoors.  Interventions: Kinematic data were collected simultaneously from the electrogoniometer and TheVicon system whist subjects walked forwards in the laboratory.10/28/2011 aebrahim123@hotmail.com
  10. 10. Agreement between an electrogoniometer and motion analysis system measuring angular velocity of the knee during walking after stroke V.M. Pomeroy a,∗, E. Evansa, J.D. Richards- Physiotherapy 92 (2006) 159–165  Main outcome measures:  Electrogoniometer and Vicon data were filtered.  Angular velocity was calculated for both sets of data, and the values for peak flexion and peak extension velocity for each stride were extracted for each subject trial.10/28/2011 aebrahim123@hotmail.com
  11. 11. Agreement between an electrogoniometer and motion analysis system measuring angular velocity of the knee during walking after stroke V.M. Pomeroy a,∗, E. Evansa, J.D. Richards- Physiotherapy 92 (2006) 159–165  Results : The intraclass correlation coefficient (ICC) and lower 95% confidence interval was 0.90 (0.87) for peak flexion angular velocity and 0.92 (0.8), and 0. 9 for peak extension angular velocity. The limits of agreement were −50.64 to 80.28 ◦/second for peak flexion angular velocity and −30.59 to 86.27 ◦/ second for peak extension angular velocity.  Conclusions: Despite high ICC values, the limits of agreement were wide. These data indicate that the Vicon system and an electrogoniometer may not be used interchangeably to measure knee angular velocity in stroke subjects.10/28/2011 aebrahim123@hotmail.com
  12. 12. Movement Analysis using VICON computer generated image10/28/2011 aebrahim123@hotmail.com
  13. 13. Motion Analysis Lab  An adult male types a paragraph as motion data is collected to evaluate motor performance during typing.10/28/2011 aebrahim123@hotmail.com
  14. 14. accelerometers
  15. 15. accelerometers  An accelerometer is a device that measures acceleration.  Most accelerometers are nothing more than force transducers designed to measure the reaction forces associated with a given acceleration.  If the acceleration of the limb segment is a and the mass inside the accelerometer is m, then the force exerted by the mass is F= ma10/28/2011 aebrahim123@hotmail.com
  16. 16. accelerometers  The force is measured by force transducer, usually a strain gauge or piezoresistive type.  The mass is accelerated against a force transducer which produces a signal voltage, V, which is proportional to the force, and since m is known and constant, then V is also proportional to the acceleration10/28/2011 aebrahim123@hotmail.com
  17. 17. accelerometers  The acceleration can be toward or away from the face of the transducer; this is indicated by a reversal in sign of the signal.  In the most movement there is no guarantee that the acceleration vector will act at right angles to the force of the force transducer.  The accelerometer measures the aⁿ component.  Nothing is known about a t or a unless a triaxial accelerometer is used.10/28/2011 aebrahim123@hotmail.com
  18. 18. accelerometers  Advantages 1- output signal is available immediately for recording or conversion to a computer.  Disadvantages 1-Acceleration signal is relative to its position on the limb segment. 2- Cost can be excessive if a large number are used. 3- If a large number are used they can encumber movement. 4- Many types are quit sensitive to shock and are easily broken.10/28/2011 aebrahim123@hotmail.com
  19. 19. Imaging Measurement Techniques
  20. 20. Imaging measurement techniques  There are many types of imaging systems that could be used:  1- Movie camera.  2- Television.  3- Multiple exposure.  4- Optoelectric10/28/2011 aebrahim123@hotmail.com
  21. 21. Film Acquisition With the development of photography, it became possible to capture image sequences which reveal details of human and animal locomotion that are not noticeable by watching the movement with the naked eye.10/28/2011 aebrahim123@hotmail.com
  22. 22. Video Camera System Although much early research was done using film cameras, the widespread application of gait analysis to humans with pathological conditions such as cerebral palsy, Parkinsons disease, and neuromuscular disorders, began in the 1970s with the availability of video camera systems. A video camera is a camera used for electronic motion picture acquisition, initially developed by the television industry but now common in other applications as well. 10/28/2011 aebrahim123@hotmail.com
  23. 23. Hi Cam Intensified Camera  A gated intensified high-speed camera that records images up to 100.000 fps, at high time resolution. Also offers single photon detection. Fast moving objects are recorded sharply by shuttering the image10/28/2011 aebrahim123@hotmail.com
  24. 24. Hi Speed Camera  Ultra-compact high-speed camera with 1,3 megapixels at 1.000 fps.10/28/2011 aebrahim123@hotmail.com
  25. 25. Basic Lens Optics  A simple converging lens is one which creates an inverted image in focus. The typical focal length is 25 mm10/28/2011 aebrahim123@hotmail.com
  26. 26. Basic simple lens type  There are TWO basic simple lens types:  CONVEX or POSITIVE lenses will CONVERGE or FOCUS light and can form an IMAGE  CONCAVE or NEGATIVE lenses will DIVERGE (spread out) light rays10/28/2011 aebrahim123@hotmail.com
  27. 27. Camera lens  This complex lens has 6 simple lens elements  A professional TV zoom lens used to broadcast sports could have 40 elements.10/28/2011 aebrahim123@hotmail.com
  28. 28. f-stop sitting and field of focus  The amount of light entering the lens is controlled by lens opening, which is measured by its f-stop setting (f means fraction of lens aperture opening).  f-stop (or f-number) is a measurement of the size of the aperture (opening) of the camera iris. If the aperture is wider, more light enters the lens and the picture is brighter.  The larger the opening, the lower the f-stop setting.10/28/2011 aebrahim123@hotmail.com
  29. 29. f-stop sitting and field of focus  F-stops can be a little confusing at first as the numbers do not behave as you would expect. Higher f-stop numbers indicate a smaller aperture diameter - in other words, as the iris opening decreases in size the f- stop number increases.  Example: a lens may have the following settings: 22,16,11,8,act, f/22 is 1/22 of the lens diameter and f/11 is 1/11 of the lens diameter. Thus f/11 lets in four times the light that f/22 does.10/28/2011 aebrahim123@hotmail.com
  30. 30. f-stop sitting and field of focus  F-stop settings are normally written with a forward slash like so: f/16. Common f-stops are:  f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22.  Note that a small f-stop (large aperture) results in a small depth of field and a larger f-stop (smaller aperture) gives a large depth of field.10/28/2011 aebrahim123@hotmail.com
  31. 31. f-stop sitting and field of focus  The amount of light entering the lens is controlled by the lens opening which is measured by its f-stop sitting (f means fraction of lens aperture opening).  The larger the opening the lower the f- stop sitting.10/28/2011 aebrahim123@hotmail.com
  32. 32. f-stop sitting and field of focus  to keep the lighting requirements to a minimum it is obvious that the lens should be opened as wide as possible to a low f setting.10/28/2011 aebrahim123@hotmail.com
  33. 33. Cinematography  Many different sizes of movie cameras are available.  8mm 16mm, 35mm, and 70mm cameras.  16 mm cameras are reasonable compromise and most high speed camera.10/28/2011 aebrahim123@hotmail.com
  34. 34. Cinematography  There are several types of 16mm either spring driven or motor driven (by batteries or AC source).  The type of the film required depends on the lighting available.  The ASA rating is a measure of the “speed” of the film; the higher the rating, the less light required to get the same exposure.10/28/2011 aebrahim123@hotmail.com
  35. 35. Cinematography  Higher ASA ratings are available and are good for a qualitative assessment of movement, especially fast moving sport.  The higher ASA films introduces inaccuracies in quantitative analyses.10/28/2011 aebrahim123@hotmail.com
  36. 36. Cinematography The shutter speed of the camera  Shutter speed is the amount of time the shutter remains open to allow light to reach a digital camera sensor. Shutter speed is measured in seconds, or fractions of seconds.  The higher the frame rate, the less time is available to expose the film.  Most high speed cameras have rotating shutters that open once per revolution for a period of time to expose a new frame of unexposed film.10/28/2011 aebrahim123@hotmail.com
  37. 37. Cinematography  Example: at 60 frames/sec using a 3 factor shutter the exposure time is 1/180 sec. the amount of light entering will be the same as a normal (still) camera set to a speed of 1/180 sec.10/28/2011 aebrahim123@hotmail.com
  38. 38. Television  The television has a fixed frame rate .  The name given to each television image is a field ranged 60 field/sec (USA) and 50 field/sec (Europe).  Television has a high enough field rate for most movements, but too low for a quantitative analysis of rapid athletic events.  The advantage of television is the capability for instant reply, which serves both as a quality control check and as an initial qualitative assessment.10/28/2011 aebrahim123@hotmail.com
  39. 39. Multiple Exposure  It is economical and simplest imaging system.  It uses a still camera in a darkened room with its shutter open for the entire time of the event.  a bright flashing light (strobe light) illuminates the subject for few milliseconds at a regular interval (say 20 times/sec).10/28/2011 aebrahim123@hotmail.com
  40. 40. Multiple Exposure  Reflective strips or markers are placed on the subject, and once every flash a new exposure is made on the film.10/28/2011 aebrahim123@hotmail.com
  41. 41. Multiple Exposure  Reflective strips or markers are placed on the subject, and once every flash a new exposure is made on the film.  Over a period of a few seconds the film is re-exposed many times, but each time with the body in a new position.10/28/2011 aebrahim123@hotmail.com
  42. 42. Multiple Exposure advantagesThis technique is not expensive.Give rapid assessment if a Polaroid type camera is used.10/28/2011 aebrahim123@hotmail.com
  43. 43. Multiple Exposure  Disadvantages  There is overlapping of the images on top of each other, so the assessment are limited to crude measures as ROM.  Due to the need of darken room and limited field of view of a fixed camera, the technique have restricted applications.  The flashing strop light can be very distracting to the subject.10/28/2011 aebrahim123@hotmail.com
  44. 44. Optoelectric Technique  Two types of system have evolved: 1- Selspot technique which requires the subject to wear special light on each desired anatomical landmark. The lights are flashed sequentially and the location (x,y) of the light flash is picked up on a special camera.10/28/2011 aebrahim123@hotmail.com
  45. 45. Optoelectric Technique  The location of the image of the light flash gives two signals, one indicating the x coordinate of the image , the other indicating the y coordinate.  As each light flashes in sequence a series of x and y coordinate signals are fed to the tape recorder or high speed computer.10/28/2011 aebrahim123@hotmail.com
  46. 46. 10/28/2011 aebrahim123@hotmail.com
  47. 47. Motion analysis lab  Experimental set-up during motion capture of typing styles10/28/2011 aebrahim123@hotmail.com
  48. 48. Cameras in motion analysis lab10/28/2011 aebrahim123@hotmail.com
  49. 49. 10/28/2011 aebrahim123@hotmail.com
  50. 50. Clinical movement analysis lab10/28/2011 aebrahim123@hotmail.com
  51. 51. 10/28/2011 aebrahim123@hotmail.com
  52. 52. Reflected marks10/28/2011 aebrahim123@hotmail.com
  53. 53. 10/28/2011 aebrahim123@hotmail.com
  54. 54. Movement AnalysisMovement analysis has now become an important clinical tool to diagnose movement disorders. Specialist physicians are able to diagnose problems by inspecting the pattern of ground reaction forces, the nature of anatomical joint angles, joint torques and power. However, an estimation of muscle forces during a gait cycle will give precise information for the treatment of gait pathologies, particularly, in surgical cases.10/28/2011 aebrahim123@hotmail.com
  55. 55. Questions??????10/28/2011 aebrahim123@hotmail.com