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(source anterior to patient, image intensifier posterior to patient, patient supine) results in an exposure approximately four times greater to the operator's head, neck, and upper extremities.5 Additionally, these areas are far more difficult to shield than the area below the waist. Obtaining oblique views will also have an impact on the scattered radiation dose. The right anterior oblique view will result in significantly more scatter to an operator standing on the patient's left than the left anterior oblique view.10 The image intensifier should be positioned as close as possible to the patient. This reduces scatter by allowing for a lower entrance exposure and also results in a sharper image. Pulse mode fluoroscopy at rates of 15 to 30 frames per second or lower greatly reduces exposure, compared with continuous mode. A larger image intensifier mode requires less radiation than a smaller one. The radiation dose approximately doubles with each successively smaller image intensifier setting.11 Large image intensifier sizes should be used whenever possible. The excessive use of high level or cineacquisition mode should be avoided. The amount of radiation produced by the fluoroscope depends on the energy used to generate the beam as determined by the milliamperes and kilovolts. The milliampere setting controls the number of photons produced.11 Low milliamperes produce a mottled image that can be eliminated by increasing the milliamperes at the cost of higher radiation. The kilovolt control determines the penetration of the beam and image contrast. For most fluoroscopic units the milliampere and kilovolt settings are determined by an automatic brightness control, which sets the values using feedback from the image obtained. However, where these are not set, the use of higher kilovolt and lower milliampere techniques will reduce exposure while not greatly affecting image quality. Increasing the fluoroscopy voltage from 75 to 96 kV can decrease the entrance dose by 50%.12 A heavier patient will require greater radiation energy to penetrate the tissues with a consequent increase in radiation exposure to the patient and staff. We found increased doses in heavier patients, although the amount is difficult to quantify because of variability in the amount of high-level fluoroscopy used in each case. Although collimation of fluoroscopic units is regulated by federal law, the ratio of the field of view to the total exposed area is not 1:1. Granger et al13 evaluated 18 fluoroscopic units from different manufacturers and of different ages and found that only 67% of the units met federal compliance standards. The measured difference between the total exposed area and the field of view ranged from 22% to 48% for units not in compliance and from 5% to 32% for units in compliance. This excess-exposed area increases the radiation dose and reduces image contrast and quality. After the units were serviced, a 40% average reduction in beam area was achieved, and 100% of the units met compliance standards. All fluoroscopes should undergo at least biannual inspection and calibration as required by law. Although automatic collimation is part of all current systems, reducing the field size by means of manual collimation will greatly decrease exposure and has the added benefit of enhancing image quality by reducing stray radiation. Lindsay et al7 found that by collimating the field of image during radiofrequency catheter-ablation procedures, the radiation dose to the patient and staff was reduced by 40%. Antiscatter grids mounted in front of the input screen decrease the amount of scatter reaching the image intensifier and improve image quality. They also greatly increase both the required radiation to obtain a satisfactory image and the backscatter to the patient and staff.14 Removal of these
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