A 28-year-old woman comes to clinic because of 5 days of painful lumps on her legs and low-grade fever. She reports fatigue and aching in her ankles and knees. Examination shows multiple 2–4 cm, tender, erythematous, warm nodules on the anterior shins bilaterally without ulceration. Lungs are clear to auscultation, and she denies cough or shortness of breath. The physician suspects a reactive inflammatory skin disease. Which of the following is the most appropriate initial imaging study to evaluate for an associated underlying condition?

(A photograph of the lesions is shown.)