Ultrasound assessment of flow-mediated dilation

Abstract

Developed in 1992, the flow-mediated dilation test is now the most commonly used noninvasive assessment of vascular endothelial function in humans. Since its inception, scientists have refined their understanding of the physiology, analysis, and interpretation of this measurement. Recently, a significant growth of knowledge has added to our understanding and implementation of this clinically relevant research methodology. Therefore, this tutorial provides timely insight into recent advances and practical information related to the ultrasonic assessment of vascular endothelial function in humans.

Figure 1

Schematic of the essential elements for the ultrasound assessment of FMD.

Figure 2

The image quality of B-mode images using different frequency linear probes. A) 6 MHz, B) 9 MHz, C) 10 MHz, and D) 12 MHz. The magnification illustrates both the intima to intima (I-I) and the media to media (M-M) interfaces. Note: Although there is definitely a visible layer among all images above, using at least a 10 MHz probe offers a very clear identification of the endothelium.

Figure 3

The determination of blood velocity and blood flow using different placements of the Doppler sample gate. A) Outer, B) Middle, C) Inner. Note: the difference in velocity and blood flow among the different placements of the sample gate.

Figure 4

The relationships between flow-mediated dilation (FMD) and different assessments of shear rate to be considered when normalizing FMD. A) FMD vs. peak shear, B) FMD vs. shear AUC until peak diameter, C) FMD vs. total shear AUC for the entire 2 minutes. Inlays for each panel illustrate the corresponding shear rate (shaded) used in the analysis.