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Scanners

Discussion in 'Biomechanics, Sports and Foot orthoses' started by bkelly11, Feb 24, 2009.

  1. bkelly11

    bkelly11 Active Member


    Members do not see these Ads. Sign Up.
    Looking for some testimonials.

    Different types
    Portability
    cost effective
    reliability
    different opinions

    Any information much appreciated.

    Seems to be the future???
     
  2. Admin2

    Admin2 Administrator Staff Member

  3. Phil Wells

    Phil Wells Active Member

    Brian

    You get what you pay for.
    I have access to a 3D Photogrammetry scanner for under £2000 but as it is a line of sight system, you really only get the plantar surface. I also have access to another scanner costing £20 k which has perfect image capture but takes over a minute.
    If want to look at the images they produce, try and get an .stl file viewer off the web and I'll send you images from them if it helps.

    Cheers

    Phil
     
  4. bkelly11

    bkelly11 Active Member

    I'll ask the IT boys on monday and get back to you
     
  5. joejared

    joejared Active Member

    Photogrammetry doesn't suggest a strongly accurate 3D scan. It's a nice word though. I have a few new customers and veteran customers using my scanner, and of which, Ultrex Podiatric Laboratories is likely to give a most shining testimonial as to its accuracy and how it has improved their business. I myself have been taking special pleasure out of replacing veteren customers' $8000.00 contact digitizing system with my own, knowing full well the stylus alone pays for the cost of manufacturing of 2 true 3D LPi (http://en.wikipedia.org/wiki/Line-plane_intersection) based scanners. If the potential vendor cannot explain briefly the science of their technology, question the merits of their product.
     
  6. Joe:

    I would like to know more about these technologies, as I'm sure that many other Podiatry Arena members would. It would be helpful for us if you could give us some more basic information about the different types of scanner systems along with photos, illustrations, etc so we can better understand the technology. What makes one system better than another system? What are the limitations and benefits of each system? What type of orthoses can be made using one vs another system? What is your tolerance for error in scanning with each system?

    Even though this is a lot of work, if you do a nice job on it, it will not only help many of us understand the technology better but will also reflect very positively on you and certainly will reward you and your company in the long run. I respect your opinion on this subject. It would be most helpful if you could start a new thread with the title: Pros and Cons of Different Foot Scanning Systems.
     
  7. joejared

    joejared Active Member

    Much of various technology has been discussed already in this thread
    . However, here's some basics, only discussing non-contact scanners. A white light scanner, however reliable can be used to calculate the angle of incidence (maximum specular reflectivity) relative to a ccd (camera), which can be used in theory to provide a 3D location using a similar equation to LPi, but in my opinion is not a reliable or quantifiable axiom. Different feet have different reflective properties, and my own work in the mid 90's left me dissillusioned with that thought. Also, and to understand diffusion of light, take a light source, say at 1 foot away, and measure the amplitude off of a photo sensor. Now move 2 feet away from the source. The light will be 1/4 of its output at 1 foot away. Mathematically, amplitude of a light source an area measurement and the light has diffused the square of the difference in distance. Some would use this change in amplitude to suggest a difference in distance, and further would try to suggest that it is true 3D. In theory, it sounds nice, but is vulnerable to any changes in the environment, and not a stable concept from object to object. If a bar laser is involved, odds are LPi is also, which suggests at least an accurate and known science in scanning.

    As for what makes one system better than another, it really depends on the pilot (operator), to be brutally honest. I have had mixed experiences training people to use my system, and I'm pretty sure this is common from one system to the next. In terms of flexibility to perform various tasks, I'm pretty sure it's at the top of the list. In terms of user friendliness and how well documented it is, it's probably closer to the bottom of the list. Delcam produces a nice device, but they've yet to make the jump to the custom orthotics that are really necessary to reflect products based on a patient's foot. Sharpshape is mostly human driven, and slowed down greatly to avoid patent infringement, and hasn't made any real advance in technology in years. The most blatent weakness in Sharpshape is the inability to scan a blue biofoam cast without first 'treating' the surface with something like baby powder or paint/plaster.

    I don't know that I can fully quantify the relative error of my own scanner, but I'm relatively confident that the depth accuracy is +-0.25 mm (0.090") non-accumulative For depth measurement, my output has subpixel resolution, which makes it difficult to provide more accurate answers for depth. For any scan line, accuracy is about +-0.01", given what a pixel means relative to real space. This will be improved in version 1B, which will bring the camera about 3 inches closer to the foot and use about 50% more pixels in the same region of real space. As for cumulative error as it is also converted into a polynomnial regression very quickly in the cast correction process, the new scanner greatly surpasses the Poluhemus wand method of digitizing a cast, simply because the points are evenly distributed throughout the foot, and because one human element has been eliminated. One member here is using my scanner and will probably come forward once their system is setup completely to produce orthotics, but one promising quality I see out of this person is what company they consider imitating. David Smith works for the same company. :D

    For anatomical reference points, being within +0mm/-5mm seems to be sufficient(No more than 1/4" proximal), although most users of my system are within 2mm in the selection of the reference points and an error proximal usually is insignificant for both the 1st and 5th metatarsal, unless it is a gross error. Setting the scanner asside except for the acquisition of data points, this is one element that still involves the human factor. The only anatomical point that seems the most difficult to identify would be the 5th metatarsal, especially on semi-weight bearing scans and biofoams. Dr. Spooner already pointed out, however, that there was a weakness in the region medial and distal of the heel as the arch climbs both laterally and longitudinally. I believe I have improved on the filters to minimize this critical loss of data.

    This doesn't sound like a bad idea, but I do believe the results should be quantifiable according to a standard set of casts/positives and let the reader review and express input on them. I'd be happy to convert any data that is either stl, sharpeshape raw format, or otherwise convertable to a dxf format for comparison and present them both online or email them to other labs in dxf format for view in standard drafting programs, in much the same format as I've shown a couple here on my drawings page. I think it should be left to the reader to decide but also think the input shouldn't be inappropriately biased by my own opinion. Each participating test location would have to acknowedge failure to scan a cast unmodified, as would be common for those incapable of scanning objects that are blue in color, rather than modify the test data. Organized properly, we could send such sample data from lab to lab and ultimately come up with a set of data that should be sufficient to provide a real comparison.

    As for the basics of scanning, a good solid plantar surface is necessary, although a full volumetric scan showing the top surface and calcaneous could be beneficial at some point. As long as forefoot deformity is known (Angle of the calcaneous relative to the forefoot along the longitudinal axis), a plantar surface is all that is absolutely necessary to make a good quality functional orthosis, and keeps the entry cost for new systems down.
     
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