When a child comes in to the clinic after a fall with pain in an extremity, as a nurse practitioner you know what to do. You order an X-ray of the affected area, right? Sometimes, however, selecting the appropriate diagnostic test isn't so simple. Ultimately, test selection depends on the condition(s) you are looking for or trying to rule out as determined by the patient's history and physical exam. If you're not quite sure what to order and when, here are some general differences between common diagnostic imaging tools which may help you make a decision.