What approaches are available to reduce exposure to imaging radiation dose?
Many simple modifications can decrease unnecessary radiation exposure to patients. The first and most important consideration is: Does the study need to be done? If there is a modality that does not require ionizing radiation (such as ultrasonography [US] or magnetic resonance imaging [MRI]) that would provide equivalent or better diagnostic information, it should be performed instead. Each modality—radiography, fluoroscopy, CT, and nuclear medicine techniques—has unique dose reduction techniques. In radiography, dose reduction is best achieved by properly configuring the imaging study: correctly positioning the patient, aligning the x-ray tube with the detector, adding or removing the grid as appropriate, and using collimation. Dose reduction in fluoroscopy can be achieved by using the “last image hold” feature, which retains the last low-dose exposure on the display screen after the x-ray tube has been turned off. If there is a finding of interest on this exposure, a full-dose image can be acquired. In addition, only turning on the x-ray tube incrementally rather than leaving it on continuously significantly reduces patient radiation exposure. Minimizing the distance between the x-ray tube, patient, and image intensifier can also decrease radiation exposure. For long interventional procedures, periodically readjusting the angle of the x-ray tube can decrease the risk of skin injury. In CT, simple adjustments like centering the patient in the scanner bore, setting the scan region to not include anatomy beyond the region of interest, minimizing the number of image acquisitions, and adjusting the scan parameters for patient size can all decrease radiation exposure. Recent technological advancements such as x-ray tube current modulation, x-ray tube voltage optimization, iterative reconstruction (an alternative to filtered back-projection for reconstructing images from the raw CT data), dual-energy scanning, larger detectors, and more powerful x-ray tubes have also enabled dramatic decreases in the amount of radiation used to image patients  . The most technologically advanced CT scanners currently available can perform chest CT examinations at effective doses only slightly higher than those of a frontal and lateral chest radiographic examination. In nuclear medicine studies, using only as much radiotracer as is necessary for diagnosis can help decrease radiation exposure. One salient example of this is perfusion-only scintigraphy, which is sometimes performed in pregnant patients with suspected pulmonary embolism. The extra radiation exposure from a second dose of radiotracer used for a ventilation scan is eliminated, and a decreased dose of radiotracer is used for the perfusion scan. All the techniques described above can be implemented in adult and pediatric patients. However, it is also critical when imaging pediatric patients to use pediatric protocols instead of adult protocols.