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The linear array exam of the duodenum is an excellent way to see the CBD and pancreatic head. The anatomy is difficult to understand since the endoscope image is tipped into the C‐sweep of the duodenum, and then the image plane is swept in various angles, resulting in a cross‐sectioning of the CBD and pancreatic duct (PD). The image planes employed can be appreciated from observing the models in the video. The cross‐sections obtained can be positioned to first give a longitudinal view of the CBD and both longitudinal views and cross‐sections of the portal vein and SMV.

Figure 1.5 Visible Human Model of an image plane that is in the location in which radial array endoscopic ultrasound (EUS) generates the “stack sign”, in which the portal vein, common bile duct (CBD), and pancreatic duct are in the same field. A probe in orange is shown going into the proximal duodenum. The superior mesenteric vein (SMV) is also shown.

Figure 1.6 The cross‐sectional anatomy within the plane shown in Figure 1.3. The common bile duct (CBD), pancreatic duct (PD), and portal vein are all in the same field (“stack sign”).

Figure 1.7 Visible Human Model with a plane that is in a location similar to what can be generated during linear array endoscopic ultrasound (EUS), showing the relative position of the gastroduodenal artery, pancreatic duct (PD), hepatic artery, and common bile duct (CBD).

As seen in the first part of Video 1.6, if the endoscope is in the second part of the duodenum, the bile duct goes to the ampulla away from the transducer and the liver is towards the transducer. If the endoscope is in the duodenal bulb, as shown in the second part of the video, the liver is away from the transducer.

The GDA drapes over the portal vein and can be found most readily using Doppler. Figure 1.7 shows a model and Figure 1.8 the resultant cross‐section where the GDA can be found.