| Fig. 1
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.
| Fig. 2
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)
Capturing and measuring the dorsal profile (back shape)
| Fig. 3
| Fig. 4A
The recognition of the anatomical structure through the automatic identification of anatomical landmarks on the body surface provides the basis for a reconstruction of the 3-D profile 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.
| Fig. 4B
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 profiles. A symmetry point, in turn, is defined by that point which divides the profile 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 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 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 profile of the dorsal surface.
| Fig. 5
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?
| Fig. 6
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.
Rasterstereography is contactless, radiation-free and non-intrusive and allows chiropractors to perform multiple scans of each patient – e.g., before and immediately after an adjustment – and a typical report will offer the capability to compare four sets of results taken at different dates.
A complement to your radiology equipment, rasterstereography does not require any licence or special building construction permit, nor any lengthy training for its accurate and repeatable operation.
A typical report is shown in Figure 5. This system is an ideal tool for chiropractors, as it allows multiple radiation-free scans tha contain key information on the spine and pelvis complex of each patient. With rasterstereography, chiropractors can first perform a detailed evaluation, to help determine a treatment plan, and then monitor and document, the progress of this treatment plan. This is demonstrated in Figure 6. Patients can receive updates of the progress of their treatment and can also easily be handed a copy of their scans for their own records.
Various applications for rasterstereo-graphy technology have been developed and are currently being investigated in clinical situations. In the months to come, results from these investigations will be collated and available to chiropractors who may be interested in incorporating this device into their diagnostic regimes.
(Canadian Chiropractor is pleased to have been offered the opportunity to update our readers with results from clinical trials with this technology – which is new to Canada – in another issue later in 2008. Please look for more on rasterstereography in our September issue.)
Drerup B, Hierholzer E, Ellger B. Shape analysis of the lateral and frontal projection of spine curves assessed from rasterstereographs. In: Sevastik JA, Diab KM, eds. Research Into Spinal Deformities. 1st ed. Amsterdam, The Netherlands: lOS Press; 1997:271-275.
Hackenberg L, Hierholzer E, Potzl W, Götze G, Liljenqvist U. Rasterstereographic back shape analysis in idiopathic scoliosis after posterior correction and
fusion. Clin Biomech.2003;18:883-889.
Hackenberg L, Hierholzer E, Potzl W, Götze C, Liljenqvist U. Rasterstereographic back shape analysis in idiopathic scoliosis after anterior correction and fusion. Clin Biomech. 2003;18:1-8.
Turner-Smith AR, Harris JD, Houghton GR, Jefferson RJ. A method for analysis of back shape in scoliosis. J Biomech. 1988;21(6):497-509.
Jean-Pierre Gibeault, PEng, is the founder and CEO of Biometrix Medica. He graduated from Queen’s University with a degree in electrical engineering and has been involved in scientific instrumentation throughout his career. Headquartered in Canada, his companies deliver medical products and equipment in the Americas and Scandinavia.