Radiation-free technology for spine and pelvis analysis After more than 20 years of research in Europe, the technology of body surface measurement by rasterstereography, combined with biomechanical modelling techniques, has produced a device for the fast, radiation-free evaluation and analysis of the spine and pelvis. This German device is used by universities and research clinics. It has also been utilized in, primarily private, chiropractic, orthopedic and dental clinics for diagnostics and for specifi c and interdisciplinary therapies. With the fi rst units produced for commercial use in 1996, this technology is now in its fourth generation. Four hundred and ninety units have been produced commercially and most of these are used in Germany. The high accuracy of this technology, used on scoliosis patients, was clinically confi rmed by Drerup et al (1997) and compared with customary thorax radiographs by Hackenberg et al (2003). ORIGIN AND SCIENTIFIC FOUNDATION OF THIS TECHNOLOGY The aspects of spinal deformity that have been researched extensively at many universities and research centres are the shape of the back, shape analysis of the body surface and techniques of body surface measurements. The objective driving this research in its early days – around 1980 – was to develop technologies and devices that would be complementary to radiology for the evaluation and monitoring of patients suffering from idiopathic scoliosis. The need for frequent follow-up evaluations during therapy, and the necessity to greatly reduce the overall radiation load during the duration of the therapy, were strong motivators to develop accurate and reliable devices. Among many research centres, the Institute for Experimental Biomechanics and the University Orthopedic Clinic at the University of Münster in Germany continuously develop a large body of research in this area. Research papers have been – and still are – produced by many of their professors, researchers and doctoral students. AN OPTICAL SYSTEM FOR SPINAL AND PELVIS ANALYSIS One of the ways to meet the objective of developing a radiation-free, fast, contactless and reliable device to complement X-ray measurement systems is to use the combination of 3-D-shape measurements and biomechanical modelling to reconstruct and display the spine structure and calculate the key spinal and pelvic parameters. (Figures 1 and 2, page 46) CAPTURING AND MEASURING THE DORSAL PROFILE (BACK SHAPE) White Light Raster Line Triangulation (WLRT) enables the scanning of objects in 3-D by projecting raster lines on their surfaces and by capturing these lines under a known and fi xed angle with a camera. (Figure 3) Based on triangulation algorithms, spatial co-ordinates of all raster points are calculated, resulting in a dense point cloud of randomly distributed points describing the measured surface. These data points are transformed to a regular grid by using interpolation, which will simplify further calculations. In this way the system captures and analyzes a body shape, statically or dynamically. Rasterstereography excels by its high precision – error margin = 0.1mm – and allows a radiation-free representation of the profi le. The speed of the measurement is fast at 0.04 seconds and the total dorsal surface is registered simultaneously. The recognition of the anatomical structure through the automatic identifi cation of anatomical landmarks on the body surface provides the basis for a reconstruction of the 3-D profi le of the dorsal surface. MATHEMATICAL CONSTRUCTION AND DISPLAY OF THE SPINE STRUCTURE The aim of capturing, measuring and analyzing the dorsal surface – back shape – is to obtain information about the 3-D shape of the vertebral column. It is well documented that the vertebral rotation is correlated to the surface rotation and this allows us to establish the relationship between the back shape and the shape of the spinal midline. In our case, the surface rotation is measured by the angle of the surface normal, or 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 estimated 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 generalization of the medial sagittal profi le. 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 analysis. 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 automatic recognition of four anatomical landmarks (vertebra prominens (VP), sacrum point (SP), right crista iliaca posterior superior (DR), and left crista iliaca posterior superior (DL) by means of the connected software provides the basis for a reconstruction of the three-dimensional profi le of the dorsal surface. 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-fi xed co-ordinate system both for radiography and for surface measurements. Furthermore, trunk length, trunk imbalance, pelvis inclination, 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 calculation of the surface normals. As a byproduct, the original measurement points are transformed into a regular square grid over the frontal (x-y) plane. The result of this procedure is presented in Figure 4B. WHAT DOES RASTERSTEREOGRAPHY OFFER THE CLINICIAN? Using a fast – 40-millisecond – high-defi nition 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 your screen and printed on the spot. Ideal for chiropractors, the rasterstereography provides clinical information to enhance your diagnostics and develop treatments, and document your treatment outcomes.