Fig. 9.22  Measurement of the AC and AT in different types of normal spectrum

5.6.1\ Scanning Method

On the coronal section of the kidney, the velocity measurements of the segmental and interlobar arteries are accurate because both arteries run toward the probe with a low echo–flow angle. In the case of a main renal artery stenosis, there is no jet flow at the level of the interlobar artery, so it can be used as a regular position to evaluate the downstream spectrum pattern. If the spectrum of the interlobar artery is hard to acquire, the segmental artery can be used as a substitute. Measurements of the arcuate and interlobar arterial spectrums are not reliable.

5.6.2\ Section Structure

There are four types of normal renal artery spectrum: early systolic peak higher than late systolic peak (a); early systolic peak lower than late sys-

tolic peak (b); absence of early systolic peak (c); and absence of late systolic peak (d).

5.6.3\ Measurement Method and Normal Value

For measurement of the AC and AT, the cursors should be placed at the beginning of the systolic phase and the end point of the early systolic peak (see the arrowheads in Fig. 9.22 a–d); if the latter point is hard to determine, the cursor should be placed at the highest point of the spectrum.

5.6.4\ Clinical Application Value

The AC and AT of the downstream spectrum can be used as indirect parameters to diagnose a renal artery stenosis. When the main renal artery is hard to measure, the downstream spectrum patterns are helpful for analysis of an upstream renal artery stenosis.