Very recently a new tool for the farrier and the veterinarian was introduced: it is a software system called Metron, from a company called EponaTech. Metron was specifically developed as an aid for farriers and vets to analyze the limb and feet angles. In particular, it is used in conjunction with photographs and/or radiographs of the equine foot. The most basic way to understand the software system is that it is a measuring and communication tool. It allows accurate measurements of lengths and angles in both photographs and radiographs, and gives a way to show these measurements overlaid on the original image so they are easy to understand.
The Features and Use of Metron A brief look at the features and method of using Metron will show that it much more than a simple drawing program for the mark-up of images. It was designed specifically for the horse.
Calibration of the Image In order to make accurate measurements in images, some care must be taken to calibrate each image. The software has been arranged to make this as easy as possible. In the case of a photograph of the foot, a scale marker – any object of known size – should be placed in the image. When the photograph is imported into Metron the user will be prompted to pick two points in the images which are a known distance apart, and to enter the distance between them. It is best if the scale marker is placed so that it lies in the plane of interest, for example, in the same plane as the plane of the sole of the foot, in the case of the photograph of the sole. Images without scale markers can still be used in Metron: angular measurements and ratiometric measurements will still be accurate, but length measurements will be approximate.
In the case of radiographs, existing radiographs with no special scaling information can easily be used, because the scaling can be done “after the fact”. An easy and popular method of digitizing a radiograph is to place it on a traditional lightbox, and then photograph it with a digital camera. Alternatively, a scanner with transparency capability may be used. When the radiograph is photographed or scanned, a scale marker of known size is placed on the lightbox, so the scale can be found later in Metron. When the radiograph is imported in Metron, the user enters the Film Focal Distance (the distance from the X-ray machine to the film, a value well-known to the radiographer) and also the Object Film Distance (the distance from the film to the center of the subject – in this case, the center of the bone column). Using these values, the Metron software computes accurate measurements in the image. This calibration compensates for the magnification normally seen in radiographs, and give measurements that are accurate in the plane of the bone column of the leg. Metron provides reasonable standard-practice defaults for these values, in case the information is not available, but accuracy is best when these values are known.
