顎関節のX線写真計測に関する研究: 顎関節多層断層像重ね合わせ法およびその精度に関する検討

抄録

By means of the cephalometric selective lateral tomography (simultaneous multisection) of the temporomandibular joints (TMJs) in combination with the cephalometric axial projection, it would make possible to evaluate the inter- and intra-individual variation in the joint morphology, and on a longitudinal study of the TMJs, to evaluate quantitative changes in the TMJ bony structures, in mandibular position against the skull accompanied with various occlusal conditions and in the TMJ bony joint space resulted from the morphological change of the bony outline or change in occlusion, or both. However, in order to analyze these changes quantitatively, the reference points are necessary for the measurements on the multisection tomograms superimposed precisely.
In the present study, a method to superimpose multisection images and it's accuracy were examined and discussed as a fundamental study for establishment of the radiographic measurement of TMJ on the cephalometric selective lateral tomograms.
As the cassette for the multisection tomography (Optiplanimat) has only 5 layers (section interval 2mm) because of the mechanical interference, two tomographic exposures are required for an examination of the whole TMJ region, altering the tomographic depth. Then, we have to superimpose 10 tomograms as acurate as possible.
We devised a rectangular lead plate (140mm×160mm in size) as a reference marker, with a hole (0.5mm in diameter) at each corner, put it on the table in front of the cassette holder, and exposed x-ray on it before or after each tomographic examination. Referring the marks, multisection tomograms of each 5 layers would be superimposed with accuracy better than 0.1mm, respectively. But the images of 10 layers could not be superimposed by this way, for some mechanical factors of the tomographic apparatus and subtle movements of a subject between each tomographic series influenced on the accuracy of superimposition. From the reason, the section depth of two exposures was selected, in order that the same plane of a subject was projected on a film of each tomographic series. Then, the accuracy of superimposition of 10 images became better than 0.25mm based on this procedure.
Furthermore, each tomographic images were magnified twice as large as original one by utilizing a image filing system so that the tracing errors would be reduced and the accuracy improved.
As a result, the total accuracy of the method to superimpose multisection tomograms was considered to be better than 0.5mm.