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X rays

X Rays and X ray procedures

Appropriateness and special situations

1. What are X rays and what do they do?

X rays are a form of electromagnetic radiation, as is visible light, but with some different characteristics. The important difference is that X rays can penetrate or pass through the human body and produce shadow-like images of structures such as bones, some of the organs, and signs of disease and injury.

A radiograph is a non-moving image and is like an ‘X ray photograph’. A fluoroscope is an X ray machine used by the doctor to see motion within the body and to observe certain diagnostic and treatment procedures that are being conducted within the body. Computed tomography (CT) also uses X rays to produce images.

Another characteristic of X rays that makes it different from light is that it carries much more energy and deposits a part of this energy within the body as it passes through.

The absorbed X ray energy has the potential to produce some biological effects within the tissue. The amount of X ray energy absorbed in the tissue is known as the radiation dose. Very large radiation doses are used in radiation oncology or therapy to stop the multiplication of cancer cells.

The very low radiation doses that are received during imaging procedures generally produce no adverse effects. However, it is appropriate to reduce the dose to the lowest amount that is necessary to produce the image quality that is required for a diagnosis.

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2. How safe are X rays?

For most diagnostic investigations, there will be no adverse effects from irradiation. Although there are many different types of radiation effect, those that can occur in diagnostic practice are only a few and their likelihood is very small. For example, the amount of radiation received in a simple X ray examination such as a chest X ray (radiograph) or a radiograph of the skull, abdomen, pelvic region, arms, shoulder or knees is quite low and is equivalent to less than one year of radiation exposure from natural sources. At these levels of radiation exposure, carcinogenic and genetic effects cannot be ruled out but remain only a theoretical possibility, as there is no practical evidence of such effects from any human studies to date.

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3. Which procedures are associated with higher radiations doses?

Computed tomography (CT) and interventional procedures, e.g. angiography and cardiac catheterisation can be associated with higher doses of radiation (about 100 to 1000 times more than chest X ray).

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4. What are the possible effects of radiation on my health?

Most diagnostic investigations will not have an adverse effect. However in procedures with higher doses, e.g. CT and interventional procedures and multiple exposures, there is a potential for biological effects. As the level of radiation exposure and the absorbed dose to the patient increases, the probability of effects increases almost linearly. Effects that have a threshold include skin redness, infertility, cataract and hair loss. Of these, infertility and cataract have not been reported in patients undergoing diagnostic and interventional procedures. Rarely, in interventional procedures requiring fluoroscopy times of one hour or more, some cases of radiation induced skin injuries (erythema) have been documented. For more information see radiation effect, stochastic effects, deterministic effects

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5. Are the effects of radiation additive?

The only effect from the radiation dose received during a diagnostic X ray or nuclear medicine examination that cannot be ruled out is a slightly increased risk of cancer. This risk increases with the magnitude of the dose and with the number of procedures.

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6. How much radiation is acceptable?

At the outset it must be emphasized that there are no prescribed limits on radiation doses to patients. This means that no amount of radiation is considered too much for a patient when the procedure is justified by the doctor. The doctor will consider the benefits versus the risk. There are well established guidelines and recommendations from a number of international organizations on this issue, which are based on scientific data. Every effort should be made to optimize the exposure to ionizing radiation using established principles ALARA. An examination that does not help medical management is inappropriate, no matter how small the dose.

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7. How do I know if the X ray facility is safe to perform the procedure?

A facility where X ray equipment is periodically tested and maintained by qualified staff adds to confidence. Appropriately qualified staff is essential and adds to quality. Radiation safety involves awareness and practice of patient dose management with due regard to image quality. Where available, accreditation of a facility by the appropriate organization or agency is generally recognized as an indication of approval.

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8. How will I know if I am getting the radiation dose that is needed and no more?

The following principles are helpful:

  • Each examination should be duly justified. This requires weighing the benefits and risks of the intended examination/procedure, with due consideration of alternative investigations that do not use ionizing  radiation (Justification)
  • Once justified, the examination should be performed with minimal radiation dose. This requires achieving adequate image quality while keeping the exposure as low as reasonably achievable (Optimization and ALARA principle)
  • Comparison of radiation dose imparted by the facility with regional, national or international reference levels
  • Avoiding unnecessary repeat examinations. However some repeat examinations are needed to monitor progress, particularly with cancer treatment.

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9. Can I avoid unnecessary repeat investigations?

You can help avoid unnecessary repeat investigations by keeping your previous X ray and scan films or discs safely and bringing them to consultations with your doctor. If films are stored in the hospital or kept electronically, it is helpful to tell your doctor when previous investigations took place. In the future electronic patient records and smart cards may be helpful for storing images of your previous investigations. Not all repeat investigations can be avoided as it is often necessary to perform an investigation again after treatment for cancer to ensure that it has been effective.


Procedure Effective Dose mSv Increased Risk of Cancer Equivalent Period of Natural Background
No Dose      
  • MRI
  • Ultrasound
Not defined/applicable Not known Not equivalent
Low Dose      
  • Chest X ray
  • Extremities
<0.1 One in a million Few days
Intermediate Dose      
  • IVP
  • Lumbar spine
  • Abdomen
  • CT head and neck
1 - 5 1 in 10,000 Few months to a few years
Higher doses      
  • Chest or abdomen CT
  • Nuclear cardiogram
  • Cardiac angiogram
  • Barium enema
5 - 20 1 in 2,000 Few years to several years

Natural background

2.4 - -

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10. Do I become radioactive after an X ray procedure?

No, This is not possible, X rays do not induce radioactivity.

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Appropriateness and special situations

11. How does my doctor select the most appropriate investigation/procedure for me?

Your doctor will be familiar with the appropriate investigations for common medical conditions and may have made use of accepted referral criteria such as those produced by the American College of Radiology, European Society of Radiology and the Royal College of Radiologists. In making this decision he will take into account your medical history, examination and other tests and also which investigations are locally available. This decision will, in part, be influenced by the radiation dose associated with the investigation and where possible, he will choose an alternative test with no radiation if one is available.

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12. What alternative investigations are available that do not use X rays or radioactivity?

Ultrasound and magnetic resonance imaging (MRI) do not use X rays or radioactivity. Ultrasound is particularly useful for examining the pelvis and abdomen, particularly in pregnancy and also for the breast, testes and soft tissues of the neck and limbs. Where available, MRI is increasingly used for scanning the head, spine and joints. As not all radiology departments will be able to offer these scans your doctor will be the best person to advise on the best investigation for you.

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13. How do doses and risk from nuclear medicine compare to X rays?

Most diagnostic investigations in nuclear medicine expose the patient to a small dose of radiation similar to the range of doses received from X ray investigations.

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14. Can I undergo X ray investigations while I am pregnant?

Yes, but with certain precautions. The aim is to minimize exposure of the unborn child. The unborn child is considered to be more sensitive than adults or children to potential adverse radiation effects. For many investigations such as X ray examinations of the head (including dental X rays), chest and limbs, where the unborn child is not in the direct X ray beam, the dose to the unborn child would be very low. These investigations can be conducted without concern provided there is medical justification. With these procedures the radiographer or technologist might provide you with some shielding to cover your pelvic region just as an added precaution. If a procedure is being considered in which the pelvic region and the unborn child will be in the direct path of the X ray beam, especially fluoroscopy or CT, which can produce a higher dose than plain X ray examinations, the doctor might consider delaying the procedure, using an alternative investigation such as ultrasound, or taking special actions to keep the dose to the unborn child as low as possible when the procedure is essential to the mother’s health. If you have additional questions, discuss these with your doctor.

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