15

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 4 ) sensitiv ity . AJNR: 15, November 1994 RADIATION EXPOSURE 1803 TABLE 3: Operator equivalent doses Number Operator Equivalent Dose, mSv Patient Diagnosis of DSA F-Time, min L L L Studies Glabella Neck Neck* Shoulder protector. F -time indicates time of fluoroscopy; AVF, arteriovenous fistula; C-dAVF, dural AVF of the cavernous sinus; AVM, arteriovenous malformation; P-dAVF, dural AFV of the posterior fossa; and STA-AN , aneurysm of the superficial temporal artery. * Inside the protector. eterization in a patient with a brain arteriovenous malformation. In this examination, 120 films ( 40 each in the anteroposterior and lateral views, and 20 each in the right and left anterior oblique views) were obtained with a standard angiographic unit with biplane rapid serial changers. The x-ray tube was always placed to the left side of the patient when the lateral-view films were obtained. The operator was in the room during the fluoroscopic examination but went out of the room during the film angiogram. Digital subtraction angiography was not performed in this patient. Results The total time for the endovascular procedure was more than 3 hours in every patient. The number of digital subtraction angiography examinations per patient ranged from 1 0 to 44 (21.1 :±: 10.0, mean :±: 1 SO). The fluoroscopic examination time ranged from 30 to 99 minutes (72.6 :±: 23.8 minutes). Operator Equivalent Doses The operator equivalent doses ranged from 0 .02 to 0.88 mSv at the glabella (representing the lens dose), 0 .06 to 1.1 mSv at the neck outside the thyroid protector, 0 to 0.09 mSv at the neck inside the protector, 0 to 0.2 mSv at the left shoulder inside the protector, 0.09 to 1.99 mSv at the ulnar aspect of the left upper arm, 0.05 to 3.55 mSv at the back of the left hand, and 0 to 0.49 mSv at the pubis (Table 3). The relationship of the equivalent dose for each area to the fluoroscopy time (Fig 2) and to the number of digital subtraction angiography studies (Fig 3) was examined. Although no significant relationship was found, the doses at the glabella, the neck outside the protector, and the left arm showed some tendency to increase with both the fluoroscopy time and the number of digital subtraction angiography studies. The correlation coefficients for the dose and fluoroscopy time were .35 for the glabella, .30 for the neck outside the protector, and .35 for the arm, and those for the dose and the number of digital subtraction angiography studies were .47, .25, and .40, respectively. Patient Equivalent Doses The patient equivalent doses ranged from 3.1 to 136 mSv at the glabella , 13 to 5441 mSv at the right temporal area , 4 to 186 mSv at the left temporal area , 0 .1 to 51 mSv at the neck, and 0 to 0.62 mSv at the pubis (Table 4). The dose at the right temporal area was much higher than at the left side in all the patients except one , be – cause the x-ray tube was usually placed to the right side of the patient during the lateral-view examination.