What tools are used to measure radiation exposure in diagnostic imaging?
For radiography and CT, phantoms are used to measure and calibrate the output of the x-ray tube  . Radiography phantoms are typically geometric structures composed of different materials, such as a combination of acrylic, aluminum, and Lucite. Some radiography phantoms also contain an air gap to simulate air-filled anatomic structures. Mammographic phantoms are composed of acrylic and designed to simulate specific compositions of breast tissue at particular compressed thicknesses. Cylinders of poly(methyl methacrylate) at specific diameters (10 cm, 16 cm, and 32 cm) are used for CT calibration; the different sizes are designed to simulate different body parts (16 cm for head; 32 cm for body) or patient sizes (10 cm and 16 cm for pediatric patients; 32 cm for adult patients). The CT phantoms have holes into which pencil ionization chambers can be inserted to measure CTDI 100 . Dose calibrators, special types of ionization chambers are used in nuclear medicine to measure the amount of radioactivity in a sample of isotope before it is administered to patients. Thermoluminescent dosimeters are incorporated into badges and rings and worn by all radiation workers to track occupational exposure. No devices exist to measure actual absorbed patient dose, and there are no means to directly measure internal organ dose. Monte Carlo simulations, computationally intensive mathematical models that simulate the patient and the type of radiation exposure, can be used to estimate organ doses. However, these estimates are dependent on assumptions made about the scanning equipment and the patient  . Some organ dose calculations use mathematical models of a hermaphrodite phantom, while others use anthropomorphic phantoms. This is an ongoing area of research as to development of more patient-specific models that can be used for organ dose calculation. As new imaging equipment is designed, the modeling of the scanner is updated to incorporate this information.