©Walter Rasmussen, R.D.C.S.
The abdominal aorta runs parallel to the inferior vena cava and in most cases is easily found by angling the face of the transducer from the inferior vena cava slightly toward the left side of the abdomen. In some instances, a long segment of the abdominal aorta can be recorded, while in others, only a few centimeters will be visible. As in all of the abdominal views, having the patient take in and retain a deep breath will in most cases, greatly improve the image. Patients with obesity, tight, spherical abdomens or post-abdominal surgery can be very difficult to image and a notation should be made if the abdominal aorta is not visualized.
The abdominal aorta is located in such close proximity to the inferior vena cava that distinguishing characteristics must sometimes be carefully observed so that the two are not confused. One method for distinguishing the abdominal aorta from the inferior vena cava is to look at the Pulsed Doppler characteristics. After placing the sample volume within the vessel, the abdominal aorta will contain regular, pulsatile blood flow that is connected to each systolic contraction represented by the ECG signal. On the other hand, the inferior vena cava will demonstrate slow, irregular blood flow which changes velocity and even direction with respiration.
Color Doppler can also help to distinguish between the abdominal aorta and the inferior vena cava, although it is less dependable than pulsed wave Doppler when the signal is weak, flow reversal is present or blood flow is slow. In each of these situations observations of the timing of blood flow with the ECG can be of assistance.
Above: Color Doppler of the abdominal aorta will help to assess for flow reversal in aortic regurgitation and false lumen in abdominal aortic dissection.
PW Doppler of the abdominal aorta is used to detect blood flow reversal in patients with severe aortic regurgitation. Note the consistent connection of blood
flow to the ECG signal. When performing PW Doppler of this area, try to place the sample volume as parallel to flow as possible. If necessary, slide the transducer superiorly or inferiorly to achieve more parallel Doppler angle to flow.
The Sample Volume placement on top is preferred because it is more parallel to blood flow than on the lower image and will reveal more accurate blood flow characteristics.
Angle Correction in Echocardiography
Generally, angle correction is not used in Echocardiography because gross distortion of the blood flow can take place and can result in confusing and misleading images.
For the abdominal aorta, the assumed angle cannot be accurately determined and can make other blood flow look like aortic blood flow.