[Measurement of the Dose Rate Using Dosimeters in Interventional Radiology and Its Difficulty].

In equipment used for interventional radiology (IVR), automatic exposure control (AEC) is incorporated to obtain the X-ray output suitable for the treatment of targeted lesions. For the AEC, users select a region as the signal sensing region (measuring field, MF) in the flat panel detector; MFs with various sizes and shapes were pre-defined and prepared in the system. The aim of this study was to examine the change of measured dose rate with the selection of MFs, the type of dosimeters (the ionization chamber dosimeter and the semiconductor dosimeter), and the dosimeter placement relative to the direction of X-ray tube (from cathode to anode). The IVR equipment was Allura Xper FD20/10 (Philips Medical Systems), and six kinds of built-in MFs were used. It was found that dose rate measured by the ionization chamber dosimeter showed a variation of -2 mGy/min with the MFs and the ionization chamber dosimeter placement. The dose rate measured by the semiconductor dosimeter showed more variation than the ionization chamber dosimeter. The change of dose rate with the dosimeter placement would be caused by the MF overlapping the dosimeter which would affect the AEC (the X-ray output). Also, the change of dose rate with the dosimeter placement was considered to be related to the heel effect of the X-ray beam. When performing dose rate measurements, we should notice that the selection of MFs, the type of dosimeters, and the dosimeter placement would affect the measured values.

[Ultrasonographic study of the hip joint in infants].

We performed ultrasonography screening for the hip joint in 145 infants between January 2003 and January 2004 at Nakajo-machi in Niigata Prefecture. This ultrasonographic study was conducted by Graf's method. The method could discriminate normal hip joints and was able to visualize 11 abnormal hip joints as well. All abnormal hip joints were dysplastic. This method is more useful than x-ray examination for infants, since the cartilaginous femoral head and the soft tissues around the hip could be clearly visualized. As a result, ultrasonography appears to be a useful screening method for congenital dislocation of the hip joint, without the hazard of radiation caused by x-rays.