Final answer:
The first imaging modality used for a patient with acute pancreatitis is usually an abdominal ultrasound to detect potential gallstones and other abnormalities. If necessary, a CT scan with contrast dye may follow for more detailed imaging.
Step-by-step explanation:
When a patient comes in with acute pancreatitis, the first imaging modality typically used is abdominal ultrasound. This non-invasive test can identify gallstones, which might block the outflow of pancreatic fluids, and can also show the presence of a pancreatic pseudocyst or an abscess. If further detailed imaging is required, other modalities such as Computed tomography (CT) scan with contrast dye might be employed, which can provide detailed images of the pancreas and help assess complications such as fluid collections or abscesses.