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  1. Medical Imaging

Medical X-ray Imaging


Medical imaging has led to improvements in the diagnosis and treatment of numerous medical conditions in children and adults.

There are many types - or modalities - of medical imaging procedures, each of which uses different technologies and techniques. Computed tomography (CT), fluoroscopy, and radiography ("conventional X-ray" including mammography) all use ionizing radiation to generate images of the body. Ionizing radiation is a form of radiation that has enough energy to potentially cause damage to DNA and may elevate a person’s lifetime risk of developing cancer.

CT, radiography, and fluoroscopy all work on the same basic principle: an X-ray beam is passed through the body where a portion of the X-rays are either absorbed or scattered by the internal structures, and the remaining X-ray pattern is transmitted to a detector (e.g., film or a computer screen) for recording or further processing by a computer. These exams differ in their purpose:

  • Radiography - a single image is recorded for later evaluation. Mammography is a special type of radiography to image the internal structures of breasts.
  • Fluoroscopy - a continuous X-ray image is displayed on a monitor, allowing for real-time monitoring of a procedure or passage of a contrast agent (“dye”) through the body. Fluoroscopy can result in relatively high radiation doses, especially for complex interventional procedures (such as placing stents or other devices inside the body) which require fluoroscopy be administered for a long period of time.
  • CT - many X-ray images are recorded as the detector moves around the patient's body. A computer reconstructs all the individual images into cross-sectional images or “slices” of internal organs and tissues. A CT exam involves a higher radiation dose than conventional radiography because the CT image is reconstructed from many individual X-ray projections.



The discovery of X-rays and the invention of CT represented major advances in medicine. X-ray imaging exams are recognized as a valuable medical tool for a wide variety of examinations and procedures. They are used to:

  • noninvasively and painlessly help to diagnose disease and monitor therapy;
  • support medical and surgical treatment planning; and
  • guide medical personnel as they insert catheters, stents, or other devices inside the body, treat tumors, or remove blood clots or other blockages.

As in many aspects of medicine, there are risks associated with the use of X-ray imaging, which uses ionizing radiation to generate images of the body. Ionizing radiation is a form of radiation that has enough energy to potentially cause damage to DNA. Risks from exposure to ionizing radiation include:

  • a small increase in the possibility that a person exposed to X-rays will develop cancer later in life. (General information for patients and health care providers on cancer detection and treatment is available from the National Cancer Institute.)
  • tissue effects such as cataracts, skin reddening, and hair loss, which occur at relatively high levels of radiation exposure and are rare for many types of imaging exams. For example, the typical use of a CT scanner or conventional radiography equipment should not result in tissue effects, but the dose to the skin from some long, complex interventional fluoroscopy procedures might, in some circumstances, be high enough to result in such effects.

Another risk of X-ray imaging is possible reactions associated with an intravenously injected contrast agent, or “dye”, that is sometimes used to improve visualization.

The risk of developing cancer from medical imaging radiation exposure is generally very small, and it depends on:

  • radiation dose - The lifetime risk of cancer increases the larger the dose and the more X-ray exams a patient undergoes.
  • patient’s age - The lifetime risk of cancer is larger for a patient who receives X-rays at a younger age than for one who receives them at an older age.
  • patient’s sex - Women are at a somewhat higher lifetime risk than men for developing radiation-associated cancer after receiving the same exposures at the same ages.
  • body region - Some organs are more radiosensitive than others.

The above statements are generalizations based on scientific analyses of large population data sets, such as survivors exposed to radiation from the atomic bomb. One of the reports of such analyses is Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 (Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, National Research Council). While specific individuals or cases may not fit into such generalizations, they are still useful in developing an overall approach to medical imaging radiation safety by identifying at-risk populations or higher-risk procedures.

Because radiation risks are dependent on exposure to radiation, an awareness of the typical radiation exposures involved in different imaging exams is useful for communication between the physician and patient. (For a comparison of radiation doses associated with different imaging procedures see: Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog)

The medical community has emphasized radiation dose reduction in CT because of the relatively high radiation dose for CT exams (as compared to radiography) and their increased use, as reported in the National Council on Radiation Protection and Measurements (NCRP) Report No. 160. Because tissue effects are extremely rare for typical use of many X-ray imaging devices (including CT), the primary radiation risk concern for most imaging studies is cancer; however, the long exposure times needed for complex interventional fluoroscopy exams and resulting high skin doses may result in tissue effects, even when the equipment is used appropriately. For more information about risks associated with particular types of X-ray imaging studies, please see the CT, Fluoroscopy, Radiography, and Mammography web pages.

Balancing benefits and risks

While the benefit of a clinically appropriate X-ray imaging exam generally far outweighs the risk, efforts should be made to minimize this risk by reducing unnecessary exposure to ionizing radiation. To help reduce risk to the patient, all exams using ionizing radiation should be performed only when necessary to answer a medical question, treat a disease, or guide a procedure. If there is a medical need for a particular imaging procedure and other exams using no or less radiation are less appropriate, then the benefits exceed the risks, and radiation risk considerations should not influence the physician’s decision to perform the study or the patient's decision to have the procedure. However, the "As Low as Reasonably Achievable" (ALARA) principle should always be followed when choosing equipment settings to minimize radiation exposure to the patient.

Patient factors are important to consider in this balance of benefits and risks. For example:

  • Because younger patients are more sensitive to radiation, special care should be taken in reducing radiation exposure to pediatric patients for all types of X-ray imaging exams (see the Pediatric X-ray Imaging webpage).
  • Special care should also be taken in imaging pregnant patients due to possible effects of radiation exposure to the developing fetus.
  • The benefit of possible disease detection should be carefully balanced against the risks of an imaging screening study on healthy, asymptomatic patients (more information on CT screening is available on the CT webpage).

Information for Patients

X-ray imaging (CT, fluoroscopy, and radiography) exams should be performed only after careful consideration of the patient's health needs. They should be performed only when the referring physician judges them to be necessary to answer a clinical question or to guide treatment of a disease. The clinical benefit of a medically appropriate X-ray imaging exam outweighs the small radiation risk. However, efforts should be made to help minimize this risk.

Questions to ask your health care provider

Patients and parents of children undergoing X-ray imaging exams should be well informed and prepared by:

  • Keeping track of medical-imaging histories as part of a discussion with the referring physician when a new exam is recommended (see the Image Wisely/FDA Patient Medical Imaging Record card and "My Child's Medical Imaging Record" card from the Alliance for Radiation Safety in Pediatric Imaging).
  • Informing their physician if they are pregnant or think they might be pregnant.
  • Asking the referring physician about the benefits and risks of imaging procedures, such as:
    • How will the results of the exam be used to evaluate my condition or guide my treatment (or that of my child)?
    • Are there alternative exams that do not use ionizing radiation that are equally useful?
  • Asking the imaging facility:
    • If it uses techniques to reduce radiation dose, especially to sensitive populations such as children.
    • About any additional steps that may be necessary to perform the imaging study (e.g., administration of oral or intravenous contrast agent to improve visualization, sedation, or advanced preparation).
    • If the facility is accredited. (Accreditation may only be available for specific types of X-ray imaging such as CT.)

FDA information links for patients:

Extensive information is available on types of X-ray imaging exams, diseases and conditions where different types of X-ray imaging is used, and on the risks and benefits of X-ray imaging. The following web sites are not maintained by FDA:

Information for Health Care Providers

Principles of radiation protection: justification and optimization

As highlighted in its Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging, the FDA recommends that imaging professionals follow two principles of radiation protection of patients developed by the International Commission on Radiological Protection (Publication 103, The 2007 Recommendations of the International Commission on Radiological Protection; Publication 105, Radiological Protection in Medicine):

  1. Justification: The imaging procedure should be judged to do more good (e.g., diagnostic efficacy of the images) than harm (e.g., detriment associated with radiation induced cancer or tissue effects) to the individual patient. Therefore, all examinations using ionizing radiation should be performed only when necessary to answer a medical question, treat a disease, or guide a procedure. The clinical indication and patient medical history should be carefully considered before referring a patient for any X-ray examination.
  2. Optimization: X-ray examinations should use techniques that are adjusted to administer the lowest radiation dose that yields an image quality adequate for diagnosis or intervention (i.e., radiation doses should be "As Low as Reasonably Achievable" (ALARA)). The technique factors used should be chosen based on the clinical indication, patient size, and anatomical area scanned; and the equipment should be properly maintained and tested.

While the referring physician has the primary responsibility for justification and the imaging team (e.g. imaging physician, technologist, and medical physicist) has the primary responsibility for exam optimization, communication between the referring physician and imaging team can help ensure that the patient receives an appropriate exam at an optimal radiation dose. Facility quality assurance and personnel training with a focus on radiation safety are crucial for applying the principles of radiation protection to X-ray imaging exams.

Awareness and communication with the patient are essential to radiation protection. As highlighted in the National Council of Radiation Protection and Measurement's 2010 annual meeting on Communication of Radiation Benefits and Risks in Decision Making [proceedings published in Health Physics, 101(5), 497–629 (2011)], communicating about risks of radiation exposure with patients and especially parents of young children undergoing imaging exams poses special challenges. The Image Wisely and Image Gently campaigns, IAEA's Radiation Protection of Patients site, and other resources below provide tools that patients, parents, and healthcare providers can use to become better informed about the risks and benefits of medical imaging that uses ionizing radiation.

General recommendations

The FDA recommends that health care professionals and hospital administrators take special care to reduce unnecessary radiation exposure by following these steps:

  • Referring physicians should:
    • Become educated about radiation safety principles and how to communicate them to patients.
    • Discuss the rationale for the examination with the patient and/or parent to make sure they understand the benefits and risks.
    • Reduce the number of inappropriate referrals (i.e., improve justification of X-ray imaging exams) by:

1. determining if the examination is needed to answer a clinical question;

2. considering alternative examinations that use less or no radiation exposure, such as ultrasound or MRI, if medically appropriate; and

3. checking the patient's medical imaging history to avoid duplicate examinations.

  • Imaging teams (e.g., physician, radiologic technologist, medical physicist) should:
    • Receive training on radiation safety issues for particular equipment used at their facility, in addition to basic continuing education on this topic.
    • Develop protocols and technique charts (or use those available on the equipment) that optimize exposure for a given clinical task and patient group (see also the Pediatric X-ray Imaging webpage). Use dose reduction tools where available. If questions arise, ask the manufacturer for assistance on how to appropriately and safely use the device.
    • Implement regular quality control tests to ensure that equipment is functioning properly.
    • As part of a quality assurance program emphasizing radiation management, monitor doses to patients and check the facility doses against diagnostic reference levels, where available.
  • Hospital administrators should:
    • Ask about the availability of dose reduction features and design features for use with special patient groups (i.e. pediatric patients) when making purchasing decisions.
    • Assure appropriate credentials and training (emphasizing coverage of radiation safety) for medical personnel using X-ray imaging equipment.
    • Ensure that the principles of radiation protection are incorporated into the facility's overall quality assurance program.
    • Enroll their facility in an accreditation program for specific imaging modalities, where available.
Information for the referring physician

Unnecessary radiation exposure may result from medical imaging procedures that are not medically justified given a patient’s signs and symptoms, or when an alternative lower-dose examination is possible. Even when an exam is medically justified, without sufficient information about a patient’s medical imaging history, a referring physician might unnecessarily prescribe a repeat of an imaging procedure that has already been conducted.

Clinicians can manage justification through the use of evidence-based referral criteria to select the most appropriate imaging procedure for the particular symptoms or medical condition of a patient. Referral criteria for all types of imaging in general and for cardiac imaging in particular are provided, respectively, by the American College of Radiology and the American College of Cardiology. In addition, the Centers for Medicare & Medicaid Services is assessing the impact of appropriate use of advanced imaging services through use of decision support systems in its Medicare Imaging Demonstration, which is testing the use of automated decision support systems that incorporate referral criteria. The International Atomic Energy Agency has published information for Referring Medical Practitioners.

Another important aspect of justification is the use of screening guidelines. Information specific to CT is available on the CT webpage.

Information for the imaging team

Patient radiation dose is considered to be optimized when images of adequate quality for the desired clinical task are produced with the lowest amount of radiation considered to be reasonably necessary. A facility can use its quality assurance (QA) program to optimize radiation dose for each kind of X-ray imaging exam, procedure, and medical imaging task it performs. Patient size is an important factor to consider in optimization, as larger patients generally require a higher radiation dose than smaller patients to generate images of the same quality.

Note that there may be a range of optimized exposure settings, depending on the capabilities of the imaging equipment and the image quality requirements of the physician. Radiation exposure may be optimized properly for the same exam and patient size at two facilities (or on two different models of imaging equipment) even though the radiation exposures are not identical.

One important aspect of a QA program entails routine and systematic monitoring of radiation dose and implementation of follow-up actions when doses are considered to be anomalously high (or low). Here are the rudiments of QA dose monitoring and follow-up:

  1. Recording of modality specific dose indices, associated equipment settings, and patient habitus, obtained, for example, from data of the DICOM radiation dose structured report. [As a modality-specific example, CT dose indices are standardized as CTDIvol and dose-length product (DLP), and they are based on measurements in standardized dosimetry phantoms. In fluoroscopy, typical dose indices include reference air kerma and air kerma-area product.]
  2. Identification and analysis of dose-index values and conditions that consistently deviate from corresponding norms.
  3. Investigative follow-up of circumstances associated with such deviations.
  4. Adjustments of clinical practice and/or protocols to reduce (or possibly increase) dose, if warranted, while maintaining images of adequate quality for diagnosis, monitoring, or interventional guidance.
  5. Periodic reviews with respect to updating current norms or adopting new norms. Reviews can be based on practice trends over time, equipment operator or medical practitioner performance, or authoritatively established dose-index values associated with the most common exams and procedures.

Norms are referred to as “diagnostic reference levels” (DRLs), or simply "reference levels" for interventional fluoroscopy exams. They are established by national, state, regional, or local authorities, and by professional organizations. For a particular medical-imaging task and patient size group, a DRL is typically set at the 75th percentile (third quartile) of the distribution of dose-index values associated with clinical practice. DRLs are neither dose limits nor thresholds. Rather, they serve as a guide to good practice without guaranteeing optimum performance. Higher than expected radiation doses are not the only concern; radiation doses that are substantially lower than expected may be associated with poor image quality or inadequate diagnostic information. The FDA encourages the establishment of DRLs through the development of national dose registries.

Facilities can characterize their own radiation dose practices in terms of “local” reference levels, i.e., medians or means of the distributions dose-index values associated with the respective protocols they carry out. Local reference levels should be compared to regional or national diagnostic reference levels, where available, as part of a comprehensive quality assurance program. Such comparisons are essential to quality improvement activities. However, even when regional or national DRLs are not available for comparison, tracking dose indices within a facility can be of value in helping to identify exams with doses that fall far outside their usual ranges.

Because imaging practice and the patient population can vary amongst and within countries, each country or region should establish its own DRLs. While the focus of the list of resources below is on U.S. or more general guidelines from international radiation protection organizations, the references include a few examples of how other countries establish and use DRLs. Note that while the use of DRLs is voluntary in the U.S., it is a regulatory requirement in many European countries.

Resources related to diagnostic reference levels:

In addition to the references specific to diagnostic reference levels above, the following resources provide facility quality assurance and personnel training information important to radiation protection:

Other FDA publications relevant to promoting safety and quality in X-ray imaging among health care providers:

For more specific FDA resources, see also the webpages for the individual X-ray imaging modalities.

Regulations and guidelines pertaining to imaging facilities and personnel

Under the Mammography Quality Standards Act (MQSA), the FDA regulates personnel qualifications, quality control and quality assurance programs, and accreditation and certification of mammography facilities. The FDA also has regulations covering the safety and effectiveness and radiation control of all X-ray imaging devices (see the section "Information for Industry"). Individual states and other federal agencies regulate the use of the X-ray imaging devices through recommendations and requirements for personnel qualifications, quality assurance and quality control programs, and facility accreditation.

In accordance with Section 1834(e) of the Social Security Act as amended by the Medicare Improvements for Patients and Providers Act (MIPPA) of 2008, by January 1, 2012 freestanding advanced diagnostic imaging facilities (performing CT, MRI, nuclear medicine) that seek Medicare reimbursement must be accredited by one of three accreditation organizations (the American College of Radiology, the Intersocietal Accreditation Commission, or The Joint Commission) recognized by the Centers for Medicare & Medicaid Services (CMS). CMS has posted further information on Advanced Diagnostic Imaging Accreditation. This requirement does not apply to hospitals, which are subject to separate Medicare Conditions of Participation at 42 CFR 482.26 and 42 CFR 482.53, governing the provision of radiologic and nuclear medicine services, respectively. Information regarding CMS interpretive guidelines for these hospital regulations can be found in the State Operations Manual Appendix A- Survey Protocol, Regulations, and Interpretive Guidelines for Hospitals. A full list of CMS Internet-Only Manuals is also available.

Individual states have regulations and guidelines that apply to imaging facilities and personnel. The Conference of Radiation Control Program Directors (CRCPD) publishes Suggested State Regulations for the Control of Radiation, which may be voluntarily adopted by states. A number of states are updating their regulations and guidelines to improve radiation safety. In addition, professional organizations have published guidelines to ensure that facilities and state inspectors have the information they need to follow these regulations. Examples of such efforts include training for state CT inspectors run jointly by the American Association of Physicists in Medicine (AAPM) and CRCPD in May 2011 and recommendations of the California Clinical and Academic Medical Physicists (C-CAMP) on how to implement the new California dose reporting law (SB 1237).

The FDA worked with the Environmental Protection Agency and the federal Interagency Steering Committee on Radiation Standards (ISCORS) to develop and publicize the Federal Radiation Protection Guidance for Diagnostic and Interventional X-ray Procedures (FGR-14) on medical use of radiation in Federal facilities. While this comprehensive set of voluntary guidelines for pediatric and adult imaging was written for federal facilities, most of the recommendations are applicable to all X-ray imaging facilities and professionals.

Information for Industry

The FDA regulates manufacturers of X-ray imaging devices through the Electronic Product Radiation Control (EPRC) and the medical device provisions of the Federal Food, Drug, and Cosmetic Act. FDA specifies requirements related to these provisions through prescription of “regulations” or “rules,” which are mandatory, and it makes related recommendations through issuance of “guidance,” which is not mandatory.

Electronic Product Radiation Control (EPRC) requirements for manufacturers and assemblers

Manufacturers and assemblers of electronic radiation-emitting products sold in the United States are responsible for compliance with the radiological health regulations found in Title 21 of the Code of Federal Regulations (Subchapter J, Radiological Health).

Manufacturers of X-ray imaging systems are responsible for compliance with all applicable requirements of Title 21 Code of Federal Regulations (Subchapter J, Radiological Health) Parts 1000 through 1005:
1000 - General
1002 - Records and Reports
1003 - Notification of defects or failure to comply
1004 - Repurchase, repairs, or replacement of electronic products
1005 - Importation of electronic products

In addition, X-ray imaging systems must comply with radiation safety performance standards in Title 21 Code of Federal Regulations (Subchapter J, Radiological Health) Parts 1010 and 1020: Please see Medical X-ray Imaging Devices Conformance with IEC Standards Guidance for further information.
1010 - Performance standards for electronic products: general
1020.30 - Diagnostic x-ray systems and their major components
1020.31 - Radiographic equipment
1020.32 - Fluoroscopic equipment
1020.33 - Computed Tomography (CT) equipment

The following resources provide further information on radiation-emitting products, the EPRC provisions, and corresponding reporting requirements:

The following are guidance to FDA staff, but may also be valuable to industry subject to X-ray equipment inspections:

Medical device requirements for manufacturers of X-ray imaging devices

Medical X-ray equipment also must comply with the medical device regulations found in Title 21 of the Code of Federal Regulations (Subchapter H, Medical Devices). For more information about medical device requirements, see:

FDA-recognized standards

Through the Food and Drug Administration Modernization Act of 1997 (FDAMA), the FDA has formally recognized several standards related to X-ray imaging. When manufacturers submit pre-market notifications to the FDA for device clearance or approval, declarations of conformity to FDA-recognized standards may obviate the need for manufacturers to provide data supporting the safety and effectiveness covered by the particular recognized standards to which the devices conform. For more information see:

Reporting Problems to the FDA

Prompt reporting of adverse events can help the FDA identify and better understand the risks associated with the product. We encourage health care providers and patients who suspect a problem with a medical imaging device to file a voluntary report through MedWatch, the FDA Safety Information and Adverse Event Reporting Program.

Health care personnel employed by facilities that are subject to FDA's user facility reporting requirements should follow the reporting procedures established by their facilities.

Medical device manufacturers, distributors, importers, and device user facilities (which include many health care facilities) must comply with the Medical Device Reporting (MDR) Regulations of 21 CFR Part 803.

Required Reports for the Medical X-Ray Manufacturers

Industry Guidance - Documents of Interest

Other Resources


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