BACKGROUND: Internal jugular vein (IJV) congestion occurs during spaceflight. Historically, IJV distension on the International Space Station (ISS) has been quantified using single slice cross-sectional images from conventional 2D ultrasound with remote guidance. Importantly, the IJV is an irregular shape and highly compressible. Consequently, conventional imaging is susceptible to poor reproducibility due to inconsistent positioning, insonation angle, and hold-down pressure, especially when controlled by novice sonographers (i.e., astronauts). Recently, a motorized 3D ultrasound was launched to the ISS that mitigates angulation errors and has a larger design, allowing for more consistent hold-down pressure and positioning. This short communication compares IJV congestion measured with 2D vs. 3D methods during spaceflight.METHODS: IJV was measured prior to and following a 4-h venoconstrictive thigh cuff countermeasure. Data were acquired from three astronauts approximately halfway through their 6-mo missions.RESULTS: The 2D and 3D ultrasound results were not congruent in all astronauts. 3D ultrasound confirmed that the countermeasure reduced IJV volume in three astronauts by approximately 35%, whereas 2D data were more equivocal. These results indicate that 3D ultrasound provides less error-prone quantitative data.DISCUSSION: These data are the first to compare 2D and 3D methods during spaceflight in the same participants by using a known countermeasure that reduces IJV congestion. The current results demonstrate that 3D ultrasound should be the preferred imaging method when trying to measure venous congestion in the IJV, and that 2D ultrasound results should be interpreted with caution.Patterson C, Greaves DK, Robertson A, Hughson R, Arbeille PL. Motorized 3D ultrasound and jugular vein dimension measurement on the International Space Station. Aerosp Med Hum Perform. 2023; 94(6):466-469.