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CT Radiation Exposure: An Overview

  • Radiation Exposure and Reduction (R Semelka, Section Editor)
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Abstract

Radiation used in CT examinations needs to be selected on image quality criteria, and also take into account the patient’s exposure. X-ray beam quality is controlled by the X-ray tube voltage (kV), and affects the X-ray beam penetration through a given patient as well as the contrast in the resultant image. CT radiation output can be characterized by the volume CTDI (CTDIvol), is controlled by tube output and CT pitch, and determines the random image noise (mottle). The total amount of radiation used to perform an examination is the dose length product (DLP), which is obtained by multiplying CTDIvol with the corresponding scan length, and is related to the corresponding patient radiation exposure. Optimal choices for CT X-ray beam characteristics (i.e., kV, CTDIvol, and DLP) need to take into account patient physical characteristics as well as the diagnostic imaging task at hand. Because CTDI metrics only describe the radiation incident on the patient, patient organ doses need to be obtained using conversion factors that account for patient size and examination scan length. Organ doses can be converted into organ risks, which can be summed to estimate the patient carcinogenic radiation risks. A 20-year-old adult weighing 75 kg, undergoing an abdominal pelvic CT examination [CTDIvol(L) 15 mGy & DLP 700 mGy-cm], has an estimated cancer induction risk of about 0.1 %. Practitioners need to understand radiation risks to be able to identify indicated examinations, where there is expected to be a net patient benefit, and to comply with the ALARA principle where unnecessary radiation is eliminated.

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Acknowledgments

The author would like to express his gratitude to R. Brad Abrahams DO for help with the artwork, and G. Don Frey PhD, Kent M Ogden PhD, and Sameer V. Tipnis PhD for useful discussions.

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  1. Department of Radiology and Radiological Science, Medical University of South Carolina (MUSC), Charleston, SC, 29425-3230, USA

    Walter Huda

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Huda, W. CT Radiation Exposure: An Overview. Curr Radiol Rep 3, 80 (2015). https://doi.org/10.1007/s40134-014-0080-x

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