Minimizing radiation risk from diagnostic imaging

The recommended strategy for evaluation of PE begins with avoiding initiating the workup in no-risk patients (i.e., those with no dyspnea, no pleuritic pain, and no tachypnea). Next, avoid indiscriminant use of D-dimer testing, as the high rate of false-positives may lead to increased use of radiation.

In patients at low to intermediate risk in whom CT or VQ would be indicated, start with a high-sensitivity D-dimer test whenever available. A negative D-dimer can be considered as sensitive as VQ and more sensitive than CT as long as it is not one of the older assays and there are no conditions present that would cause a false-negative result.

If D-dimer is positive or deemed inappropriate, use VQ first when available, especially in younger patients who have normal chest x-ray and for whom alternate diagnoses are not a concern, or when there is a contraindication to IV contrast. A CT scan is advised when the patient is semi-unstable, when the chest x-ray is abnormal, or when such alternate conditions as aortic dissection are a consideration.

Abdominal, flank, and pelvic pain

Advances in CT scanning of the abdomen have revolutionized diagnosis of abdominal pain over the past few decades, most notably with improved sensitivity for important pathology (Table 3). Unfortunately, these advances, combined with the practice of defensive medicine, have led to inappropriate overuse of CT in patients with nonspecific abdominal pain, gastroenteritis, and dyspepsia. This overuse has led to increased cost, increased exposure to iodinated IV contrast, increased exposure to ionizing radiation, and delay in patient disposition.

Table 3. CT sensitivity for commonabdominal conditions

Making a diagnosis with CT scan is often relatively straightforward. Clinicians should be looking for instances in which the CT can be skipped. Consider three alternate approaches: ultrasound only, plain films only, and observation or therapeutic trials with no imaging.

Ultrasound only. Abdominal ultrasound, an imaging modality that lacks any ionizing radiation, already outperforms CT in a few scenarios. Ultrasound should be used preferentially—or at least initially—for right-upper-quadrant pain, pelvic pain, and abdominal pain in the pregnant patient. Ultrasound should also be considered initially in younger patients in whom ureteral stones or acute appendicitis is suspected.

In ureteral stone disease, ultrasound is 65% to 95% sensitive. Although not great, this sensitivity is acceptable as long as there is no concern for more serious conditions (i.e., AAA), as most stones pass on their own with time.¹⁴ If hematuria is present and the patient history is classic for a ureteral stone, imaging may be omitted altogether provided there is no suspicion for more serious disease based on risk factors and/or prior imaging showing a normal aorta.

For right-lower-quadrant pain, abdominal ultrasound is 80% to 95% sensitive and 86% to 98% specific for acute appendicitis in nonobese children.¹⁸ Abdominal ultrasound requires no IV, no prep time, and no radiation. It is the initial test of choice in children’s hospitals and should be the required initial test for evaluation of pediatric right-lower-quadrant pain when the primary rule-out is appendicitis.

Adequately trained sonographers and buy-in from hospital surgeons are critical for successful implementation of such a plan, but lack of either should by no means be seen as a reason to go straight to CT. Emergency and primary-care providers can use their influence to encourage technicians and general surgeons to use ultrasound to rule out appendicitis in children with right-lower-quadrant pain.

Plain films only. Plain films may be used instead of CT in a few fairly common emergency scenarios featuring bowel obstruction or perforation. If the patient appears acutely ill and may need to be rushed to the operating room, an abdominal series may be safer than CT since x-ray results are available more rapidly. If there is no CT queue and the clinician prefers noncontrast CT for this indication, CT may be almost as rapid.

Plain films may also be the study of choice when the patient is stable and suspicion for bowel obstruction is low, but vomiting and/or pain is present. Examples of such a scenario include suspected gastroenteritis in a patient who has had prior abdominal surgery and/or not much diarrhea, or a young patient with Crohn disease who has had multiple prior CTs for abdominal pain and vomiting. Plain films can help minimize radiation exposure without increasing the risk of missing a potentially surgical condition.

Observation or therapeutic trials with no imaging. Home observation for nonspecific abdominal pain with no or few red flags is a wise option in a majority of cases. A trial of antacids combined with carefully worded verbal and written aftercare instructions can prevent unnecessary radiation exposure and prolonged visits in most patients with nonspecific abdominal pain.

Conclusion

There are three relevant aspects of the Hippocratic Oath to consider in radiation stewardship:

• Place your patient’s interests before your own: It may be in the provider’s interest to do more testing, but not necessarily the patient’s.
• Respect the patient’s right to make decisions: Always discuss risks and benefits, which will help prevent legal problems if something is missed.
• Try to prevent as well as cure disease: Avoid unnecessary radiation, especially CT scanning, in younger low-risk patients.

CT scanning provides excellent imaging information that can help rule in or rule out a number of emergency medical conditions. On the other hand, disadvantages of CT include increased costs, increased visit times, increased waiting-room times, and increased radiation exposure that puts patients at higher risk for future cancers.

Clinical decision-making tools can help providers determine which patients require imaging. Alternate imaging modalities that use less radiation than CT (or no radiation at all) may be preferable under certain circumstances. Home observation may be a viable option for the right situation, but to minimize legal risks and maximize patient satisfaction, try to involve the patient in the decision-making process.

Brady Pregerson, MD, is a staff emergency physician at Cedars-Sinai Medical Center in Los Angeles and the editor-in-chief of EMresource.org. 


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