[Basic study for the measurement of the bone mineral density of the calcaneus by using the radiographic contrast].

We performed a fundamental study for the measurement of the bone mineral density (BMD) of the calcaneus by using the radiographic contrast (RC). The RC of the bone radiography is proportional to the product of the thickness of the bone H(b), the gradient of the image detector system and the difference of the linear attenuation coefficient between the bone and the soft tissue. Therefore, the radiographic contrast per unit bone thickness (RC/H(b)) can be used as a good measure of the BMD. Though the linearity of RC/H(b) is maintained for x-rays with the monochromatic energy spectrum, the energy spectrum of the x-rays employed in clinical examinations is continuous. The relationship between RC/H(b) value and BMD value was examined by two kinds of added filter (Al with 5 mm and 15 mm thickness) and two kinds of bone phantoms (the phantom with 1 cm and 4 cm thickness, which is made by a bone equivalent material). The experimental results obtained from the 1 cm bone phantom indicated an approximately linear relationship. However, the experimental results obtained from the 4 cm bone phantom indicated a non-linear relationship due to the beam hardening. Therefore, the estimation of the calcaneus BMD value in clinical practice is performed by using the relationship between RC/H(b) and BMD values obtained from experimental results for the bone phantom with 4 cm thickness.

[Experimental study of the influence on pacemakers of X-rays from angiocardiography equipment].

We performed an experimental study of the influence on pacemakers (PM) of X-rays from the angiocardiography equipment. (1) We used one PM of DDD mode in this study. (2) The PM was irradiated under two exposure levels: one the standard dose and the other the maximum dose in the angiocardiography study situation. (3) We set the pacing lead wires to the bilateral atria and ventricles in Irnich's human body model. (4) We set two irradiation fields, one with a lead block on the PM and the other without the lead block. The result showed that when the PM was included in the irradiation field and the exposure level was of the maximum dose, the influence of irradiation on the PM was that of level 2 as classified by a research report by the Ministry of Internal Affairs and Communications. The absorbed dose of the PM was 93.4 mGy under these conditions. We confirmed that radiation dose does not affect a pacemaker with pacing lead wire. However, it acts on the generator of the PM owing to the direct photoelectric effect. When there were many dose rates (or total radiation dose), an obstacle occurred.