Question

A $74$-year-old man is brought to the emergency department due to the sudden onset of severe, diffuse abdominal pain that began $2$ hours ago. He reports nausea and one episode of non-bloody, non-bilious emesis. His medical history is significant for hypertension, type 2 diabetes mellitus, chronic kidney disease with a baseline serum creatinine of $1.7\text{ mg/dL}$, and paroxysmal atrial fibrillation. He was prescribed apixaban but admits to missing multiple doses over the past week. His temperature is $37.2^\circ\text{C}$ ($99.0^\circ\text{F}$), blood pressure is $145/88\text{ mm Hg}$, pulse is $118/\text{min}$ and irregularly irregular, and respirations are $22/\text{min}$. Pulse oximetry shows $96\%$ on room air. Physical examination reveals a patient in visible distress, writhing in pain on the stretcher. However, abdominal examination shows a soft, non-distended abdomen with only mild diffuse tenderness to deep palpation; there is no rebound, guarding, or rigidity. Bowel sounds are decreased. Laboratory studies show:

Leukocyte count: $18,500/\text{mm}^3$
Hemoglobin: $14.2\text{ g/dL}$
Platelet count: $210,000/\text{mm}^3$
Serum creatinine: $2.9\text{ mg/dL}$
Blood urea nitrogen: $48\text{ mg/dL}$
Serum lactate: $4.8\text{ mmol/L}$

Which of the following is the most appropriate next step in diagnostic imaging for this patient?