BACKGROUND. Artery diameter is typically measured with the ultrasound probe longitudinally (LONG) aligned. There has been recent interest in performing measures with cross-sectional (CSA) alignment to improve sensitivity and reliability measurements. However, it is unknown if pressure and tilt of the probe influence the measures differently. The purpose of our study was to examine the effect of probe pressure and tilt on measurements taken in LONG vs. CSA. METHODS. A blood vessel phantom was used for all measurements. At time point 1 the phantom artery was imaged in LONG with zero pressure (NP), light pressure (LP), and moderate pressure (MP). The pressure was quantified by the investigator’s discretion. After pressure images were obtained, the best image of the artery in the LONG view was taken and assigned an angle of 0o. Using a digital inclinometer secured to the ultrasound probe, 2 images were taken at probe angles of 0o, 5o, 10o, and 15o. Following LONG, pressure and angle measurements were imaged using CSA. At time point 2, on a separate day, images were repeated at the same 3 pressures and 4 different angles in both LONG and CSA. Artery diameters (cm) for LONG and artery areas (cm2) for CSA were obtained using ImageJ. Averages were calculated at each pressure and angle for LONG and CSA. RESULTS. The mean diameter taken in LONG across both days for NP, LP, and MP were 0.557, 0.522, and 0.475, respectively. We converted these diameters to area (A) for each pressure (A= 0.243, 0.214, and 0.177). The mean CSA across both days for NP, LP, and MP were 0.218, 0.198, and 0.182, respectively. The mean diameters taken in LONG for each angle were 0.509, 0.509, 0.490, and 0.448, for 0o, 5o, 10o, and 15o, respectively (A= 0.204, 0.205, 0.191, and 0.162). The mean CSA across both days for each angle were 0.205, 0.209, 0.212, and 0.239 for 0o, 5o, 10o, and 15o, respectively. DISCUSSION. LONG measurements were more influenced by probe pressure and tilt compared to CSA, meaning that CSA measurements may be better suited for vascular testing protocols requiring assessments of arterial size, such as flow-mediated dilation (FMD) where the ability to detect even small changes in diameter is desired. Future studies could strengthen these findings by comparing arterial size at rest and during exercise and possibly FMD using both methods in humans.

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