How To Do A Sonogram of the Abdominal Aorta
Sonography of the abdominal aorta is one of the more commonly used applications of ultrasound. It is a straight-forward examination that can provide highly valuable diagnostic information as long as it is performed correctly.
This page provides step-by-step instructions for performing the examination, including patient preparation and equipment set-up. Please keep in mind that the protocol, or instructions, may vary slightly from one medical facility to another.
Sample Protocol for Sonography of Abdominal Aorta
Patients who will undergo sonography of the abdominal aorta must have nothing to eat or drink (be "NPO") for at least 4 hours prior to the examination in order to minimize gas in the stomach and intestines so that the aorta can be seen as clearly as possible. If possible, the patient really should be NPO for 8-12 hours. Examinations of this nature are usually scheduled for the early morning and the patient is instructed to not eat or drink anything after midnight the night before the exmaination. The timing of the examination is especially important for diabetic patients who must eat on a schedule in order to keep their blood sugar controlled.
The set up of the ultrasound equipment varies somewhat depending on the patient. The sonographer can use a transducer(probe) of a higher frequency on thin patients, while larger patients require a lower frequency transducer in order to get adequate penetration of the body with the ultrasound beam. Frequency is very important because sound waves of higher frequency result in better image resolution, but they have decreased penetration. As a rule, the sonographer uses the highest frequency possible in order to get the best resolution while still penetrating to the appropriate depth. In general, the following transducers and frequencies are used:
- Use a curvilinear probe (looks like a convex rectangle) if possible because it has a larger field of view and better resolution.
- If there is lots of bowel gas present, use a phased array probe which has a smaller footprint and better penetration. However, the resolution is not quite as good.
- Transducer frequencies range from 5 MHz for thin patients to 2.25MHz for very large patients.
- Choose the "Abdomen" or the "Aorta" machine preset which optimizes the computer settings for imaging of the aorta.
- Put the patient's identifying information (Name, Medical Record Number, etc) into the machine for future identification.
- Many clinics have the sonographer make notes regarding the patient's symptoms and history in the patient menu or on the monitor screen and document this information for the radiologist to utilize when interpreting the sonogram.
Performing the Aortic Sonogram
Patient Position: The patient should lie on the examination table on his or her back in the "supine" position.
Longitudinal Images: The following images should be obtained in the longitudinal plane with the sound beam parallel to the patient's vertical axis:
- Proximal Aorta (near the diaphragm)
- Mid Aorta (below the origin of the Superior Mesenteric Artery)
- Distal Aorta (including where the aorta bifurcates (splits) into the right and left Common Iliac Arteries)
- Right Iliac Artery (connect it to the distal aorta)
- Left Iliac Artery (connect it to the distal aorta)
The anterior-to-posterior dimension of the aorta and the common iliac arteries must be measured in these images. It is very important to keep the line of measurement perpendicular to the aortic walls so they are as accurate as possible. It is also very important to accurately label each of the sonographic images regarding the anatomy displayed.
Transverse Images: The following images should be obtained in the transverse plane with the sound beam perpendicular to the vertical axis of the patient's body:
- Proximal Aorta (near the diaphragm; superior to the celiac axis)
- Mid Aorta (inferior to the origin of the superior mesenteric artery)
- Renal Artery Origin (near the mid level, but demonstrating origin of at least one renal artery leaving the aorta)
- Distal Aorta (just superior to the bifurcation into the common iliac arteries)
- Bifurcation (demonstrating the proximal right and left common iliac arteries)
In these images, the vessels should be measured in the right-to-left dimension. The sonographer must be very careful to keep the probe perpendicular to the aorta so that the diameter is not overestimated.
The sonographer can also move the probe to the right lateral portion of the lower abdomen and aim the sound beam in a coronal plane to image the distal aorta and both common iliac arteries in a single image. This can be useful to demonstrate whether an aneurysm extends from the aorta down into one or both common iliac arteries.
Color Doppler may be used to demonstrate bloodflow within the aorta and/or common iliac arteries. Color Doppler works much like the weather radar; flow toward the transducer is colored red and flow away from the transducer is colored blue. The relative velocity of the blood flow is assigned different hues of red or blue with the slower flow being darker red or blue and the faster flow being assigned lighter hues heading toward yellow (on the red side) or green.
At a minimum, the longitudinal and transverse images listed above are documented in electronic or hard-copy format and become part of the patient's medical record.