CHAPTER 17

Image Gently Approach to Pediatric Imaging

Jane S. Kim, MD; Lindsay S. Baron, MD; and Benjamin H. Taragin, MD

Overuse of medical imaging is a growing problem in the United States, with financial and medical repercussions. The primary care physician must often decide what, if any, imaging is appropriate for a particular patient. In many situations, clinical assessment and physical examination are adequate for diagnosis. In some instances, however, imaging provides vital information that cannot be adequately obtained from other sources. Patients and their families may also insist on diagnostic imaging based on the belief that the more technologically advanced the evaluation, the better the care.

Approximately 370 million studies using diagnostic radiation are performed annually in the United States (Figure 17.1). The most dramatic increase has been in the use of computed tomography (CT). In 1982, 1 million CT scans were performed in the United States. In 2006, 67 million CT scans were performed, with an estimated 4 to 7 million of these performed in children. In response, many concerned health professionals and radiologists gathered to create the national Image Gently Campaign, with a focus on minimizing the use of diagnostic radiation when possible and using appropriate pediatric imaging for children in the United States. Because of the widespread attention and highly concerted efforts of the organizations involved in this effort, several recent studies have observed a slight downward trend in CT use for pediatric patients in the United States. Because of the substantial variation among different imaging practices, however, the opportunity exists for continual improvement.

Basic Concepts

Diagnostic radiology examinations that use ionizing radiation include plain radiography, fluoroscopy, CT, and nuclear medicine. Ionizing radiation may cause damage to DNA molecules. Children are more radiosensitive than adults secondary to children’s growth of rapidly proliferating cells and longer life span. Certain organs are more radiosensitive than others, and children in particular are at an increased risk for breast cancer, thyroid cancer, and leukemia.

Figure 17.1. Charts showing the United States annual per capita effective radiation dose from various sources. Upper: Chart for 1980. Lower: Chart for 2006.

Abbreviation: Bkd, background.

Reprinted with permission from Mettler FA Jr, Bhargavan M, Faulkner K, et al. Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources—1950-2007. Radiology. 2009;253(2): 520–531, with permission.

One of the most common ways to measure radiation dose is by the effective dose, measured in sieverts, which takes into account all the exposed tissues and the relative radiosensitivity of each organ. The effective dose also provides a way to compare radiation dose across different imaging modalities. For example, for children 1 CT scan of the chest imparts an effective dose equivalent to up to 150 chest x-rays (Table 17.1).

The ALARA Principle

In recent years, increasing attention has been paid to and research done on patient radiation exposure from diagnostic imaging. Much of this concern stems from data derived from survivors of the atomic bombs used in World War II. The radiation dose to each survivor was calculated based on each individual’s distance from ground zero, and more than 50,000 of these patients were followed for more than 50 years. The data showed an increased cancer risk for many of the survivors. Based on this observation, a mathematical model was created which states that the risk of cancer proceeds in a linear fashion without threshold (Figure 17.2). According to this model, even a small amount of radiation increases the risk of cancer. Current estimates vary concerning diagnostic radiation and the risk of cancer. Based on research by multiple radiation biologists, the American College of Radiology (ACR) estimates that for adults, 1 fatal cancer is induced for every 1,000 CT scans performed. The risk is higher in children, with 1 fatal cancer occurring for every 500 to 1,000 CT scans performed. This figure is superimposed on the national cancer incidence of 42%.

^a Natural background radiation is 3 mSv per year.

Abbreviations: CT, computed tomography; GI, gastrointestinal; PA, posteroanterior.

Derived from the Image Gently Alliance and the Society for Pediatric Radiology.

Figure 17.2. Graphic representation of the relative risk of contracting cancer in atomic bomb survivors. The dashed curves represent 61 standard error for the smoothed curve. The straight line is the linear risk estimate computed from the range 0–2 Sv. Because of an apparent distinction between distal and proximal zero-dose cancer rates, the unity baseline corresponds to zero-dose survivors within 3 km of the bombs. The horizontal dotted line represents the alternative baseline if the distal survivors were not omitted.

Reprinted with permission from Pierce DA, Preston DL. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res. 2000;154(2):178–186.

This research spurred the founding of the Image Gently Campaign, which stresses a multifaceted approach that is intended to minimize radiation exposure to children. The campaign has brought together 60 medical and professional organizations representing more than 700,000 imaging specialists from the fields of pediatrics, radiology, physics, and radiology technology. The as low as is reasonably achievable principle (ALARA principle) is based on the notion that any amount of radiation exposure, no matter how small, can increase the chance of negative biologic effects. The aim of the ALARA principle is to balance the goals of minimizing the amount of radiation while obtaining sufficient imaging quality, resulting in accurate diagnostic information.

The Role of the Radiologist

The pediatrician can often determine whether any imaging study is needed based on the history and physical examination. In some conditions (eg, acute trauma), imaging is important to assess the nature and extent of the injury. In other conditions, such as infectious processes (eg, cough, symptoms of sinusitis), medical management is warranted initially before any imaging is performed.

Communication and coordination between medical specialists and radiologists is often helpful. When in doubt, a call to the local radiologist, regardless whether that person is a dedicated pediatric radiologist, can guide the specialist in determining which test is reasonable for a specific patient. Radiologists have many means by which to tailor examinations to minimize radiation. The first step often involves asking whether nonionizing diagnostic examinations, such as ultrasonography or magnetic resonance (MR) imaging, can be performed to answer the same diagnostic question. In particular, ultrasonography often can be used as a screening examination to evaluate conditions that can be clarified with other studies that involve radiation if needed. For certain indications, MR imaging is a great alternative to CT; however, in some cases, the need for sedation and other risks of MR imaging may outweigh the risks of CT. Radiologists are also required to monitor equipment and study protocols to ensure radiation dosage does not exceed the recommended range. All commercial CT scanners used in the United States include multiple methods to adjust the radiation dose. A low-dose technique should be used whenever appropriate. Newer-generation CT scanners use a significantly decreased dose while maintaining imaging quality. Breast and gonadal shielding can offer additional protection to children.

Resources for Physicians and Parents

The ACR has established appropriateness criteria for imaging of specific medical conditions and presentations; these criteria were coauthored by clinicians and radiologists. The criteria are available free online and can be downloaded and incorporated into computerized ordering and electronic health record systems (https://www.acr.org/Clinical-Resources/ACR-Appropriateness-Criteria).

The Image Gently website (www.imagegently.org) offers educational materials for parents to help them understand the risks and benefits of diagnostic imaging and the associated radiation. The website also has printable child imaging history cards for parental use to track all diagnostic radiation examinations performed on their child (Figure 17.3).

Figure 17.3. Child imaging history card on which parents can record their child’s exposure to imaging studies.

Borrowed with permission from the Image Gently® Alliance.

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