USING SIMULATED RADIOGRAPHIC IMAGES TO TEST THE ACCURACY OF AN UPPER CERVICAL X-RAY ANALYSIS SYSTEM.
Edward F. Owens, MS, DC, Life College, Marietta, GA
INTRODUCTION
The value of X-ray analysis for producing listings for chiropractic
adjustment has been questioned frequently in the literature. The
reliability of x-ray marking systems for the cervical spine has been
tested several times with generally promising results. Yet to be
established is how well any upper cervical x-ray analysis predicts the
actual positions of the skull and vertebrae with respect to each other.
Grostic (1) used a model consisting of a dry skull with a movable
atlas mounted beneath it to test the accuracy of the atlas laterality
measure. The preliminary results showed very good agreement between
actual and measured values. Grostic suggested the need for further
studies to test the accuracy of rotational misalignments as well as the
interrelationship between atlas rotation and laterality. The goal of
this paper is to test the accuracy of the Grostic upper cervical
analysis by comparing analysis findings to known misalignments displayed
on simulated radiographs generated by a computer model.
METHODS
Simulated radiographs have been generated using 3D
Studio rendering and animation software (Autodesk, Inc.) on an MS-DOS
compatible computer. The rendering software is first used to position a
three-dimensional digitized model of the human skull and cervical
spine. The model can be viewed from different viewpoints, and rendered
with a semitransparent material to produce a fair likeness of a cervical
radiograph. While the modeled bones have no internal trabecular
structure, the surface models do well represent many of the commonly
used reference points for cervical x-ray analysis.
In positioning the model, individual bones can be precisely rotated and
translated to simulate misalignments of the atlas and axis. Renderings
then represent radiographs of known misalignments. The rendering can
be viewed on screen or printed on paper using a laser printer. Each
rendering is generated at 2560x1920 pixels and takes two and one half
hours to render (using a 486 DX2 running at 66 mHz).
For this study, five sets of simulated radiographs were generated,
including Nasium, Vertex and Lateral views. These were sent to three
chiropractors in practice locally for analysis. The simulated
radiographs were coded so that none of the investigators knew the actual
misalignments present.
RESULTS
At the time of this writing, the results of the
x-ray analyses are not yet available. The analysis results will be
statistically evaluated for inter-examiner reliability and then compared
to the known values to determine accuracy.
REFERENCES
(1) Grostic JD, Marshall WG. Accuracy of an upper cervical measuring
system: A validity study. Proceeding 1992 ICSM, Chicago, IL, pg 146-7.