Ultrasound uses sound waves to image structures within the body. A detailed survey of the abdominal organs can be done to diagnose the cause of symptoms a patient may be having. Ultrasound may be used in conjunction with other imaging modalities to obtain a more detailed diagnosis.
Imaging Modalities
There are several modalities that can be used to examine the abdomen. X-ray and computed tomography (CT) use X-rays to obtain images. X-ray produces general images that may show a subtle soft-tissue mass. CT gives clear, detailed images. Magnetic resonance imaging (MRI) uses magnetism to produce detailed images. Ultrasound uses sound waves and is a safer and more affordable alternative to the other modalities, which is why it is often used as a first step to finding abdominal masses or other problems.
Patient Preparation
The abdomen is filled with small and large bowel. The bowel is often fill with gas, especially after eating. Ultrasound cannot be used to see through gas, so the patient is asked to fast for eight hours prior to the ultrasound exam. The gallbladder must be filled during the ultrasound, and it fills with bile during a fast. When digesting food, the gallbladder contracts and squeezes the bile out to aid in the digestion of fats.
Frequency
Different frequencies of ultrasound are used depending on how deep the sound waves must travel into the body. Lower ultrasound frequencies are used for abdominal ultrasound. Generally, five megahertz is sufficient, but a range of two to seven megahertz may be used. The sonographer may press hard on the abdomen with the camera to displace fat and bowel, allowing for better imaging of the abdominal organs.
Protocol
Abdominal ultrasound is used to evaluate specific organs. A series of pictures is taken in two planes for each organ. One plane is called longitudinal, and is an image splice in the head-to-toe direction. Transverse is the side-to-side plane. The organs imaged are the pancreas, liver, gallbladder and spleen. The liver and spleen are measured. The gallbladder wall and common bile duct are measured. Kidneys often are not imaged and are evaluated during a renal ultrasound.
Patient Positioning
The patient generally starts out lying on his back, called the supine position. The gallbladder will be evaluated while the patient is in the supine and left lateral decubitus positions. The left lateral decubitus position is when the patient lies on his left side. The patient may be asked to lie on his right side, right lateral decubitus position, when imaging the spleen. This causes the bowel to fall toward the right side and away from the spleen so it can be seen better using ultrasound.
Tags: lateral decubitus, sound waves, abdominal organs, decubitus position, decubitus position when, detailed images
