Figure 4A frontal (x-y) plane. The result of this proce- dure is presented in Figure 4B. Figure 3 horizontal component. To do this, the high sampling density and resolution provided by rasterstereography is essential. The calculated construction of the spinal midline requires three inputs: 1. The line of the spinous process. The line of the spinous processes is esti- mated by the symmetry line of the back. The symmetry line (solid line in Figure 4A) is composed of the symmetry points of the horizontal profi les. A symmetry point, in turn, is defi ned by that point which divides the profi le into two halves with minimum lateral symmetry (with respect to surface curvature). For the model, we assume the symmetry line to be a representation of the line of the spinous processes and it is a gen- eralization of the medial sagittal profile. 2. Surface rotation. As mentioned above, we measure surface rotation by the horizontal component of the direction of the surface normal. From any grid point in Figure 4A, components of the surface normal are known from curvature analy- sis. On the symmetry line these values are calculated by interpolation. In Figure 4B, the surface normals are represented by bars erected on the symmetry line. As the results show, it is reasonable to assume that the horizontal component of the normal angle is equal to vertebral rotation. 3. Anatomical landmarks. An auto- matic recognition of four anatomical land- marks (vertebra prominens (VP), sacrum point (SP), right crista iliaca posterior su- perior (DR), and left crista iliaca posterior superior (DL) by means of the connected software provides the basis for a reconstruc- tion of the three-dimensional profi le of the dorsal surface. www.canadianchiropractor.ca The landmarks are used for skeletal reference of the surface data. In particular, the vertebra prominens landmark is used as the origin of a body-fixed co-ordinate system both for radiography and for sur- face measurements. Furthermore, trunk length, trunk imbalance, pelvis inclination, WHAT DOES RASTERSTEREOGRAPHY OFFER THE CLINICIAN? Using a fast – 40-millisecond – high-defini- tion optical measurement of the surface of the back of your patient, rasterstereography produces graphical, clinical and analytical information about the spine, the pelvis and the posture. It takes only 40 milliseconds to do a scan and the results are available immediately on Figure 4B and similar parameters may be determined from these landmarks. In Figure 4A the landmarks are represented by black dots. Curvature analysis is combined with an algorithm for data smoothing and calcula- tion of the surface normals. As a byproduct, the original measurement points are trans- formed into a regular square grid over the your screen and printed on the spot. Ideal for chiropractors, the raster- stereography provides clinical information to enhance your diagnostics and develop treatments, and document your treatment outcomes. Continued on Page 46 CANADIAN CHIROPRACTOR | FEBRUARY 2008 • 33
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