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Atlas of Human Body Ultrasound Scanning_ Methods and Diagnostic Applications ( PDFDrive ).pdf
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9  Abdominal Vascular Scanning

351

 

 

4.4\ Doppler Spectrum

of the Superior Mesenteric

Artery

SMA

Ao

Fig. 9.16  Doppler spectrum of the superior mesenteric artery

4.4.1\ Scanning Method

The start of the SMA is the place to get a Doppler spectrum. The gate should be placed at the brightest region, and the angle correction line should be the same as the true blood flow direction.

4.4.2\ Section Structure

Long-axis view of the SMA and Ao.

4.4.3\ Measurement Method and Normal Value

If the patient is fasted, the Doppler spectrum of the SMA is a triphasic wave with an average PSV of 119.6 ± 22.8 cm/s. After a meal, there is a remarkable increase in the PSV; 45 min after a meal, the PSV may be as high as twice the basic level; at the same time, the pattern of the spectrum may be biphasic without a reverse wave.

4.4.4\ Clinical Application Value

A PSV ≥275 cm/s at the stenosis is used to diagnose an SMA stenosis above 70%; in the case of a severe stenosis, there is no early diastolic reverse wave if the patient is fasted and there is no remarkable increase in the PSV after a meal.

4.4.5\ Notice

An SMA stenosis of less than 70% is usually asymptomatic with no remarkable increase in the PSV. An increase in the PSV is the main parameter for diagnosis of mesenteric ischemia; other parameters such as the spectrum pattern, diastolic blood flow changes, and changes in blood flow before and after a meal have limited clinical ­significance. The PSV ratio of the SMA and Ao has no significance.