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Am Fam Physician. 2021;103(1):42-50

Published online November 23, 2020.

This clinical content conforms to AAFP criteria for CME.

Author disclosure: No relevant financial affiliations.

The use of diagnostic radiography has doubled in the past two decades. Image Gently (children) and Image Wisely (adults) are multidisciplinary initiatives that seek to reduce radiation exposure by eliminating unnecessary procedures and offering best practices. Patients with an estimated glomerular filtration rate less than 30 mL per minute per 1.73 m2 may have increased risk of nephropathy when exposed to iodinated contrast media and increased risk of nephrogenic systemic fibrosis when exposed to gadolinium-based contrast agents. American College of Radiology Appropriateness Criteria can help guide specific diagnostic imaging choices. Noncontrast head computed tomography is the first-line modality when a stroke is suspected. Magnetic resonance imaging stroke protocols and computed tomography perfusion scans can augment evaluation and potentially expand pharmacologic and endovascular therapy timeframes. Imaging should be avoided in patients with uncomplicated headache syndromes unless the history or physical examination reveals red flag features. Cardiac computed tomography angiography, stress echocardiography, and myocardial perfusion scintigraphy (nuclear stress test) are appropriate for patients with chest pain and low to intermediate cardiovascular risk and have comparable sensitivity and specificity. Computed tomography pulmonary angiography is the preferred test for high-risk patients or those with a positive d-dimer test result, and ventilation-perfusion scintigraphy is reserved for patients with an estimated glomerular filtration rate less than 30 mL per minute per 1.73 m2 or a known contrast allergy. Computed tomography with intravenous contrast is preferred for evaluating adults with suspected appendicitis; however, ultrasonography should precede computed tomography in children, and definitive treatment should be initiated if positive. Ultrasonography is the first-line modality for assessing right upper quadrant pain suggestive of biliary disease. Mass size and patient age dictate surveillance recommendations for adnexal masses. Imaging should not be performed for acute (less than six weeks) low back pain unless red flag features are found on patient history. Ultrasonography should be used for the evaluation of suspicious thyroid nodules identified incidentally on computed tomography.

Estimates suggest that 30% of all U.S. health expenditures are a result of waste, with approximately $100 billion lost on overtreatment and low-value care; inappropriate radiography is a major component.1 The use of advanced imaging, including computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography, and nuclear medicine, has doubled in a 16-year period, accounting for 11% of allowed Medicare charges in 2018.2,3 Awareness of risks, benefits, and recommendations related to radiography enhances shared decision-making and reduces unnecessary testing.2,4

Clinical recommendationEvidence ratingComments
Follow reduced radiation protocols from the Image Wisely (adults) and Image Gently (children) initiatives, and use American College of Radiology Appropriateness Criteria when making diagnostic imaging decisions.816 CExpert opinion and longitudinal cohort studies
Prophylactic isotonic crystalloid volume expansion is recommended in patients with an eGFR less than 30 mL per minute per 1.73 m2 to prevent contrast-induced nephropathy.2128 CLarge retrospective propensity-matched studies demonstrate no significant effect; expert opinion and consensus guidelines still encourage hydration in these patients
An eGFR less than 30 mL per minute per 1.73 m2 is a relative contraindication for the use of gadolinium-based contrast agents.2931 CExpert opinion and consensus guidelines
Do not perform imaging in patients with primary headache disorders without new or progressive features who have normal neurologic examination findings.37,52,53 CExpert opinion and consensus guidelines
A clinical probability assessment tool should be used to determine pretest probability before performing imaging in patients with suspected pulmonary embolism. The Pulmonary Embolism Rule-out Criteria or d-dimer testing can be used to avoid unnecessary computed tomography pulmonary angiography in some low- or intermediate-risk patients.5760 CExpert opinion and well-designed randomized clinical trials with disease-oriented outcomes
Do not perform plain chest radiography in asymptomatic patients for preoperative evaluations or for baseline testing during hospitalization.42,52,72,73 CLarge meta-analysis of 20 trials with disease-oriented outcomes; expert opinion
Do not perform imaging in patients with acute (less than six weeks) low back pain and no red flag findings on history or physical examination.47,75,76 BNumerous randomized clinical trials and systematic reviews and meta-analyses
RecommendationSponsoring organization
Avoid using CT as the first-line imaging modality in the evaluation of suspected appendicitis in children. Ultrasonography should be performed first, with CT or magnetic resonance imaging considered in equivocal cases.American Academy of Pediatrics
Do not perform CT for evaluation of suspected appendicitis in children until after ultrasonography has been considered as an option.American College of Radiology
CT scans are not necessary in the routine evaluation of abdominal pain.American Academy of Pediatrics
Avoid CT scans of the head in emergency department patients with minor head injury who are at low risk based on validated decision rules.American College of Emergency Physicians
CT scans are not necessary in the evaluation of minor head injuries.American Academy of Pediatrics
Do not routinely obtain CT scans in children with mild head injuries.American Association of Neurological Surgeons and Congress of Neurological Surgeons

WHAT'S NEW ON THIS TOPIC

Diagnostic Imaging

The use of advanced imaging, including computed tomography, magnetic resonance imaging, ultrasonography, and nuclear medicine, has doubled in the past 16 years, accounting for 11% of 2018 allowed Medicare charges.

The Protecting Access to Medicare Act, which will be fully implemented as of January 1, 2022, requires clinicians to consult appropriate use criteria via a clinical decision support mechanism before ordering advanced diagnostic imaging services for Medicare Part B patients.

The proportion of personal radiation exposure attributed to medical sources rose from 5% in the 1980s to more than 50% by 2009, with computed tomography scans constituting 25% of all radiation exposure despite a decrease in radiation per scan.

The 2014 Protecting Access to Medicare Act (PAMA) requires clinicians to consult appropriate use criteria via a clinical decision support tool before ordering advanced diagnostic imaging services for Medicare Part B patients.5 Appropriate use criteria have been employed since 2018 as part of PAMA, but on January 1, 2020, the year-long education and operations testing period began. During this period, imaging orders that do not include use of a clinician decision support will still be performed and covered without payment consequences, although consultation with a clinical decision support mechanism is recommended. The Centers for Medicare and Medicaid Services extended this trial period for another year, until December 2021.6 The list of qualifying clinical decision support mechanisms was recently updated.6

PAMA will initially focus on eight areas: suspected or diagnosed coronary artery disease; suspected pulmonary embolism; traumatic and nontraumatic headache; hip pain; low back pain; shoulder pain, including suspected rotator cuff injury; suspected or diagnosed lung cancer (primary or metastatic); and neck pain. The program will be fully implemented as of January 1, 2022, after which payment consequences could result from failure to employ appropriate use criteria.5,7

Reduced radiation protocols from the Image Wisely (adults) and Image Gently (children) initiatives and American College of Radiology (ACR) Appropriateness Criteria should be used when making diagnostic imaging decisions.816 ACR Appropriateness Criteria cover 193 diagnostic imaging and interventional radiology topics, with 942 clinical variants and more than 1,680 clinical scenarios.17

Radiation Safety and Risk

Most data on cumulative ionizing radiation exposure and cancer incidence come from survivors of atomic tragedies and those working in the nuclear industry, reinforcing a dose response relative to cancer risk.810

Radiation dose can be measured in grays (Gy; a measure of absorbed dose) or sieverts (Sv; a measure of equivalent dose). Ionizing radiation exposure varies by type of imaging study (Table 1).18,19 The proportion of radiation exposures in the United States that is attributed to medical sources has risen from 5% in the 1980s to more than 50% in 2009, with CT scans constituting 25% of all exposures despite a decrease in radiation per scan.20 The estimated lifetime relative risk of developing cancer is 5% per Sv of radiation.12 Based on this, the U.S. Food and Drug Administration estimates that the risk of developing a fatal malignancy associated with one CT scan is approximately one out of 2,000.13 This risk is reliant on the patient's age at exposure, the organs exposed, the patient's sex, and other variables.

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