The ultrasound transducer produces an image of the narrow plane of tissue beneath it. The transducer of most open ultrasound probes is perpendicular to the cord and handle and is therefore described as having a “left” and “right” side (Fig. 16.2). The laparoscopic probe is oriented such that the transducer is in line with the shaft. The distal tip of the device is termed the “toe” and the proximal end of the transducer the “heel” (Fig. 16.3). The image on the ultrasound screen can be manipulated in regard to the “left-right” orientation viewed on the screen. Thus, the toe portion of the image can be on the right-hand side of the screen or on the left. This applies in a similar manner to an open probe. It is at the operator’s discretion as to which orientation to choose, and the preferred view will depend on how each individual visually processes the spatial relationship seen on the screen [8]. Either orientation is acceptable, but it is critically important to know the orientation prior to beginning a scan for accurate planning and execution of biopsy or ablation. The recommended technique for determining orientation of the probe is to place only the tip of the laparoscopic probe, or one side of the open probe, in contact with the tissue and then look at the screen to determine which side of the tissue is being projected (Fig. 16.4a, b). The orientation is now known and the image can then be reversed as needed.

The laparoscopic transducer can be flexed up and down as well as left to right. This allows for great flexibility in scanning an organ’s contour. Rigid laparoscopic ultrasound devices are available, but the limitations of movement make them inadequate for full hepatic ultrasound. A common pitfall is to place the transducer in contact with the tissue and then rotate the transducer head while stationary in order to scan the tissue. This results in large amounts of deep tissue scanned, but very little tissue scanned on the surface. Figure 16.5 shows the result of rotating the transducer head without moving across the tissue (Fig. 16.5). When this maneuver is performed sequentially at different positions along a path, it is very easy to think that all tissue along the path has been scanned. However, in reality this is not the case. Figure 16.6 illustrates how a superficial lesion can be missed entirely by placing the transducer in two positions and rotating while remaining in place (Fig. 16.6). Therefore, the recommended technique for scanning is to move the transducer over the tissue while keeping it parallel to the tissue. In this way, an equal amount of deep and superficial tissue will be visualized, reducing the chance of missed lesions at any depth (Fig. 16.7). With an open ultrasound probe, this error is easier to avoid by keeping the ultrasound probe flat on the tissue of interest.

There are circumstances when moving an ultrasound probe smoothly over the surface of an organ is not possible. For example, a cirrhotic liver is very challenging to transduce accurately because it is difficult to get all points of the transducer touching the surface at one time. This can be overcome with a “standoff” technique where saline solution is used to submerge the liver (Figs. 16.8 and 16.9). The ultrasound transducer can then be positioned above the surface without the loss of image quality that would result from transmission through air. This can also be very useful for superficial lesions located around corners. Figure 16.10 demonstrates the standoff technique allowing visualization of a lesion that would be difficult to access with a flexed ultrasound transducer (Fig. 16.10)

Regardless of the tissue scanning method employed, it is important that it be methodical and complete. With any organ, a scanning technique can follow anatomic landmarks within the tissue, such as vasculature, or can be performed in a standardized fashion along the surface of the organ. For liver ultrasound, two different approaches are recommended. The portal vasculature can be followed in a “pedicle” technique, or the surface of the liver can be followed in a “lawnmower” fashion. These techniques will be described for the liver in this section, but other organs in the abdomen can be scanned with similar techniques requiring only small modifications for anatomy.