In order to obtain the basic data for the risk estimation of dental X-ray diagnostic examinations, the absorbed doses in some organs mainly involved in the causation of stocha-stic and non-stochastic effects were determined with an ionization chamber and a thermo-luminescent dosimeter, using an average woman RANDO phantom. The dose determinations were made on the eyes, thyroids, submandibulae, the lungs, the stomach, the female breast, the red marrow and the gonads for the intra-oral dental examinations and the orthopanto-mographic examinations. The resultant organ doses are tabulated in the unit of a current-time product of 10 m As. The measurements showed the large variations in doses received caused by the different beam directions for the intra-oral examinations. For example, the doses in the submandibulae ranged from 10.5 to 360 mrad/sec depending on the beam direction and the X-ray tube voltage used.

抄録全体を表示

Possibility of bone mineral assessment with dual energy radiographic densitometry method was examined by means of model experiment.
In this method, X-ray penetration ratios through the object at two different energies are measured by using radiographic densitometry and substituted to a first order simultaneous equation whoes constances are mass attenuation coefficients of the two different energy X-rays for bone mineral and soft tissue. The bone mineral content is obtained as a solution of the equation.
The result can be obtained in forms of two dimensional information with high specific resolution, with no necessity of bolus. Therefore, this method is expected to provide, in future, much valuable informations in the region of maxillofacial diagnosis.
X-ray penetration ratios are obtained from comparison between the film density in the image of the object and that of the reference material wedge whoes composition and density are not only precisely defined but also adjusted approximately equal to those of the object, in orde to compensate the lack of reproducibility of X-ray irradiation, the effect of scattered photons and the fluctuation of film speed due to film processing condition.
In the present study, X-ray beams were monochronized by means of tin and tungsten filters in order to reduce the hardening effect of beam quality in the object, so that high accuracy could be obtained in case of using an ordinally diagnostic X-ray generator.
Bone models were made of mixture 3Ca ₃ (PO ₄) ₂·CaCO ₃ and methyl-methacrylate so as to adjust the effective atomic number of them to that of bone. These models were wedge shaped because analyses were simple.
Object in the present exiperiment were composed of the bone models mentioned above and an acrylic resin wedge as soft tissue equivalent layer. Amount of calcium salt was measured with accuracy of ± 0.1 g/cm ² at a point of 3 g/cm ² total layer.
Causes of error were analyzed and it was suggested that higher accuracy could be possible provided a X-ray generator with uniform field of more monochromatic beam and a homogenous reference wedge were used.
Factors and parameters necessary in case of in-vivo measurment were theoritically discussed and it was pointed out that mass attenuation coefficient for collagen, fat and other tissues, and mass of those tissues exsist in the measurement area should be measured as well as accurate values of mass attenuation coefficient for bone mineral and muscle.
Possibility of triple energy technique was also theoretically discussed and little could be expected for improvement in accuracy.

抄録全体を表示

here have been many persons suffering from TMJ disorders with varying symptoms in temporo-mandibular joints (TMJ). Many devices for the X-ray examination have been made for the detection of the morphological changes in the osseous components of TMJ, and more than scores of radiographic methods have been reported. Panoramic radiography has. been also utilized to find out the morphological changes in osseous TMJ, as this kinds of machine have been developed. However, the panoramic methods seem to be rarely used in routine x-ray diagnosis of the TMJ, notwithstanding the fact that the method has a suitable angle of the x-ray beam for the osseous articular surface of the TMJ.
The purpose of this study is to establish the more useful and effective radiographic methods for the x-ray examination of TMJ by orthopantomography.
Experiments were performed as follows to investigate the role of orthopantomographyin x-ray examination of TMJ.
1. The locus of the rotation center, and the width and the center of the image layer of Panoramax 100-20 R were examined utilizing a test chart devised by the authors. Use ful parts of the image layer were selected on the basis of the relative positional relationship between the image layer and ear rods.
2. Various parts of the condylar head, articular fossa and articular eminence of the five dry skulls with different shape and different angle of the long axis of condylar head were marked with 0.5 mm copper wire. They were positioned on the selected image layer nd were examined by Panoramax 100-20 R. Then, the effects of the morphological variations of the TMJ to the radiographic image were examined and discussed. The anatomical landmarks of the TMJ were confirmed in the radiograms.
3. The investigation was carried out theoretically, whether the sharp images of dental arch and TMJ can be obtained on one film. The theoretical considerations were followed by the experiments on a dry skull.
4. Furthermore, this method was applied to several patients. As the results of a series of experiments and practices, it was found that the lateral part of the articular eminence and the most parts of the condylar head except medial one third were detected clearly with conventional orthopantomographic image of teeth.
It was evidenced that this orthopantomographic method was useful and effective in radiography for TMJ arthrotic patients, because the articular surface of the condylar head was projected tangenitially, that is, the outline of the image of condylar head was formed by a part of articular surface of osseous condylar head. Moreover, as TMJ was projected from antero-medial direction, there was minimum superimposition.

抄録全体を表示