Introduction

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

There are many types – or modalities – of medical imaging procedures that are used on children, each of which uses different technologies and techniques. Computed Tomography (CT), fluoroscopy, and radiography (conventional X-ray) 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 for recording or further processing by a computer. These exams differ in their purpose:

1. Radiography – a single image is recorded for later evaluation.
2. 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, or “dye” through the body. Fluoroscopy can result in relatively high radiation doses, especially for interventional procedures (such as placing catheters, or other devices inside the body) which require fluoroscopy be administered for a long period of time.
3. CT – many X-ray images are recorded as the detector moves around the patient’s body. A computer reconstructs all the individual images of 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.

It is crucial to emphasized dose reduction in CT because of the relatively high doses of CT exams and their rapidly increased use.

How Much Radiation is used?

We all are exposed to small amounts of radiation daily from soil, rocks, building materials, air, water, and cosmic radiation. This is called naturally occurring background radiation. The radiation used in X-rays and CT scans has been compared to background radiation we are exposed to daily. This comparison may be helpful in understanding relative radiation doses to the patient.

Risk Vs Benefit

While the benefit of a clinically appropriate X-ray imaging exam generally far outweighs the risk, efforts should be made to reduce this risk by reducing unnecessary exposure to ionizing radiation. Ionizing radiation exposure to pediatric patients from medical imaging procedures is of particular concern because pediatric patients:

1. are more radio sensitive than adults (i.e., the cancer risk per unit dose of ionizing radiation is higher);
2. has a longer expected lifetime for any effects of radiation exposure to manifest as cancer; and
3. use of equipment and exposure settings designed for adults may result in excessive radiation exposure if used on smaller patients.

Benefit

X-ray imaging exams is recognized as a valuable medical tool for a variety of examinations and procedures including:

1. Using a multi-detector CT unit to examine children is faster than the older CT scanners, reducing the need for sedation and general anaesthesia.
2. CT scanning is painless, non-invasive and accurate.
3. A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time.
4. CT examinations are fast and simple; in emergency cases, they can show internal injuries and bleeding quickly enough to help save lives.
5. CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.
6. CT is less sensitive to patient movement than MRI.
7. CT can be performed if you have an implanted medical device of any kind, unlike MRI.
8. A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.
9. No radiation remains in a patient’s body after a CT examination.

Risk

The individual risk from a necessary imaging exam are generally quite small when compared to the benefit of helping with accurate diagnosis or intervention. Risks of X-ray imaging include risks of exposure to ionizing radiation and possible reactions to the intravenous contrast agent, or “dye” that is sometimes used to improve visualization. Types of radiation risks include:

1. Tissue effects such as cataracts, skin reddening, and hair loss, which occur at relatively high levels of radiation exposure and are very rare in children; and
2. A small increase in the possibility that a person exposed to X-rays will develop cancer later in life. Radiation-induced cancer risks depend on the radiation dose, the patient’s age at exposure, the sex of the patient (women are more radio sensitive than men), and the organ irradiated.

How Can The Risk Be Minimized?

There are ways to ensure that children are exposed to the smallest amount of radiation possible during an imaging study including:

1. Image when there is a clear medical benefit
2. Use the lowest amount of radiation for adequate imaging based on size of the child
3. Image only the indicated area
4. Avoid multiple scans
5. Use alternative diagnostic studies (such as ultrasound or MRI) when possible

Conclusion

The risks of ionizing radiation-induced cancers depend on the amount of radiation received, the organ irradiated, and the age and gender of the patient. While the cancer risk is higher for younger patients, the overall cancer risk is low for medical imaging exposures no matter what the age of the patient. If the X-ray procedure is medically necessary then the medical benefit will always exceed the cancer risk. Therefore, radiation risk estimates should not be factor into the decision in whether or not a particular exam should be performed for a particular patient. The decision of whether an X-ray imaging exam is justified needs to be made by the child’s physician based on the medical needs of that particular child and the information the exam could offer. If there is a medical need for a particular X-ray procedure and other exams using non ionizing radiation (e.g., ultrasound and MRI) or less radiation are unsuitable, radiation risk considerations should not influence the physician’s decision to do the study or the patient’s decision to have the procedure. However, radiation protection principles should always be followed when choosing equipment settings.

References

1. Pediatric X-ray Imaging. In Radiation-Emitting Products. Retrieved May 17, 2016 from http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/ucm298899.htm
2. Children’s (Pediatric) CT (Computed Tomography). Radiological Society of North America, Inc (RSNA). Retrieved June 7, 2016 from http://www.radiologyinfo.org/en/info.cfm?pg=pedia-ct
3. What Parents Should Know About CT Scans for Children: Medical Radiation Safety. Retrieved June 7, 2016 from http://www.imagegently.org/Portals/6/Parents/Image_Gently_8.5x11_Brochure2pg.pdf