Question

A $64$-year-old man is evaluated in the emergency department for severe right upper quadrant abdominal pain, nausea, and dark urine that began $24$ hours ago. He has a history of essential hypertension, type 2 diabetes mellitus, and profound sensorineural hearing loss for which he underwent bilateral cochlear implant placement $5$ years ago. His temperature is $37.4^\circ\text{C}$ ($99.3^\circ\text{F}$), blood pressure is $138/85 \text{ mm Hg}$, and pulse is $88\text{ /min}$. Physical examination reveals scleral icterus and tenderness to palpation in the right upper quadrant without guarding or rebound. Laboratory studies show:

Leukocyte count: $9,500\text{ /mm}^3$
Total bilirubin: $2.8 \text{ mg/dL}$
Direct bilirubin: $2.0 \text{ mg/dL}$
Alkaline phosphatase: $310 \text{ U/L}$
Aspartate aminotransferase (AST): $145 \text{ U/L}$
Alanine aminotransferase (ALT): $160 \text{ U/L}$

Right upper quadrant transabdominal ultrasound demonstrates multiple echogenic foci with posterior acoustic shadowing in the gallbladder. The common bile duct is dilated at $9 \text{ mm}$, but the distal portion is obscured by overlying bowel gas, and no ductal stones are visualized.

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