In choosing an imaging modality, the emergency physician attempts to optimize diagnostic accuracy, rapidity of testing, patient safety, and expense. Prudent medical decision making begins with a deliberate history and physical examination yielding a reasonable differential diagnosis. The list of pathology to be excluded directs what imaging is pursued.

The chest radiograph (CXR) serves as a fast initial study for most thoracic complaints. The CXR exposes the patient to minimal radiation and does not necessarily require travel out of the ED. These advantages can contribute to overuse however.

The ventilation/perfusion (V/Q) scan was once the prevailing study for the evaluating pulmonary embolism, but the pulmonary scintigram has been widely supplanted by MDCT. Limitations of the V/Q scan include radiation exposure and handling radio nuclides, lengthy image acquisition time, transport of patients to areas where close monitoring is challenging, and frequent difficulty in study interpretation, especially in patients without a normal chest x-ray.²³

MDCT provides excellent detail of the aorta and pulmonary vasculature with scans acquired in a single breath-hold.²¹ MDCT may reveal alternate diagnoses. As new ED designs incorporate CT scanners within the department, transport times and risks of decompensation away from the ED are minimized. Risks of IV contrast administration include renal impairment and allergic reaction, though these effects have been mitigated by newer generations of ionic contrast agents.

Echocardiography (ECHO) is particularly useful in patients too unstable to leave the resuscitation room. ECHO may detect right ventricular dilitation suggestive of pulmonary embolism or confirm aortic dissection without radiation. Diagnostic accuracy is operator dependent.⁵⁰

Magnetic Resonance Imaging (MRI) provides excellent detail of thoracic pathology without radiation. This use in ED patients is often limited by prolonged image acquisition, distance from the clinical area, and expense.^51,52 Another limitation of MRI is that it can not be used in patients with implaned devices such as pacemakers and automatic inplantable cardioverter defibrillators.