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In a lateral-view examination , the x-ray tube was almost always placed to the right side of the patient because of the design of our x-ray device. Digital subtraction angiography was always performed with manual injection of contrast medium and at the frame rate of 3 frames per second, and at each digital subtraction angiography examination a total of 15 to 25 frames were collected in most cases. The operator performed the endovascular procedure while seated on a chair at the right side of the patient. The local exposure dose was measured with thermoluminescence dosimeters (Kasei Optonix, Tokyo, Japan) composed of Mg2Si04 (Tb), each covered by a holder with a sensitivity compensation filter (holder F). The detection limits of this thermoluminescence dosimeter system are 0.1 mR and 100 R. The sensitivity of each thermoluminescence dosimeter and the thermoluminescence dosimeter reader were calibrated with a radiation source (radium226; Kasei Optonix), and residua l radiation energy of each thermoluminescence dosimeter was removed by placing it in an a nnealing oven (Kasei Optinix). Thermoluminescence dosimeters were attached to seven areas on the operator and five areas on the patient. The areas in the operator were glabella outside the spectacles, representing the eye lens, the midline of the neck inside and outside of the thyroid protector, the left shoulde r inside the protector, the ulnar a spect of the left upper arm, the back of the left hand, and the pubis. In the patients, thermoluminescence dosimeter were atta ched to the glabella, the right and left temporal a reas (a round the pterion), the midline of the neck, and the pubis. Immediately after the operation, each the rmoluminescence dosimeter was removed from the Holder-F, avoiding exposure to fluorescent light, and inserted into the thermoluminescence dosimeter reader AJNR: 15, November 1994 TABLE 2: Conversion coefficients from the radiation dose to the 70 ~-tm equivalent dose at each photon energy of X-ray source Photon Energy, keY f70 .,_m fx 7 0 1-Lm 10 8.12 0.930 15 8.51 0.0974 20 8.92 1.02 30 10.4 1.19 40 12.0 1.38 50 13.3 1.52 (Kyokko thermoluminescence dosimeter Reader 2500, Kasei Optonix) . The exposure dose was automatically calculated from the luminescent dose of the thermoluminescence dosimeter. The equivalent dose (H70,_..m, in millisieverts) of the skin was calculated by the formula: H70,_..m = f7o,_..m X fx70 X Px where f70 is a conversion factor from the Mm ' M m radiation dose to H70,_..m; fx70,_..m is a conversion factor from Px to the radiation dose; and Px is the dose measured by the thermoluminescence dosimeter reader for the areas other than the glabella . As shown in Table 2 , the coefficients 10.4 and 1.19 were used for f70,_..m and fx7 o,_..m, respectively, because the estimated effective photon energy of our x-ray device is about 30 keV. The equivalent dose (H3mm• in millisieverts) of the lens (eye) was calculated by the formula : H3mm = f3mm X fx3mm X Px, where f3mm is a conversion factor from the radiation dose to H3mm; fx3mm is a conversion factor from Px to the radiation dose; and Px is the dose measured by the thermoluminescence dosimeter reader for the glabella . The coefficients of f3mm and fx3mm were those used for f70,_..m and fx70,_..m in the preceding equation. Doses exceeding 100 R were calibrated according to the dose-characteristic curve for this thermoluminescence dosimeter (Fig 1 ), because supralineality (overestimation) is observed in this range. In the comparative study, the equivalent doses were measured by the same method during routine diagnostic four-vessel study (film angiography) by transfemoral cathsensitivity 3 2 10 ........ 100 Radiation dose (R) v / 1000 Fig 1. Dose characteristic curve of thermoluminescence dosimeter (Mg2Si0
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