Imaging methods

Ultrasound scanning (USS) is the initial investigation of choice for examining the organs of the upper abdomen. A 3.5 MHz probe provides good depth penetration and resolution. However, lower frequency transducers may be necessary in larger patients. A distinct advantage of USS is that tissues can be examined in nonorthogonal planes and, when combined with the modern small transducer heads, organs can be examined through small anatomical windows, e.g. between the ribs. Intraoperative USS, using a 5 MHz probe, is often used for the assessment of surgical resectability of liver masses when the extent of the lesion could not be clearly demonstrated by other imaging methods.

The sonographer should not only examine the liver but use its excellent acoustic properties to obtain optimal views of the retroperitoneal organs, e.g. the pancreas. By changing the position of the probe and altering the position of the liver relative to other organs (e.g. breath holding), an acoustic window to the upper abdomen is created.

Doppler USS is used routinely to examine the blood flow to the organs to the upper abdomen. The coeliac axis, superior mesenteric artery and portal venous system are all amenable to study using pulsed wave real time Doppler scanning. Examination of these vessels demonstrates the velocity and direction of blood flow, as changes in these parameters are of great importance in the assessment of patients with liver disease and portal hypertension.

Computed tomography (CT) and contrast enhanced CT (CECT) demonstrate the organs of the upper abdomen in the axial plane.