Effect of Respirophasic Displacement of the Inferior Vena Cava on Size Measurement in 2-D Ultrasound Imaging

Objective: Volume status assessment of a patient by ultrasound (US) imaging of the inferior vena cava (IVC) is important for the diagnosis and prognosis of various clinical conditions. In order to improve the clinical investigation of IVC, which is mainly based on unidirectional US (in M-mode), automated processing of 2-D US scans (in Bmode) has enabled tissue movement tracking on the visualized plane and can average this in various directions. However, IVC geometry outside of the visualized plane is not under control and could result in errors that have not yet been evaluated. Methods: We used a method that integrates information from long- and short-axis IVC views (simultaneously acquired in the X-plane) to assess challenges in IVC diameter estimations using 2-D US scans in eight healthy subjects. Results: Relative movements between the US probe and IVC induced the following problems when assessing IVC diameter via 2-D view: a median error (i.e., absolute difference with respect to diameter measured in the X-plane) of 17% using 2-D US scans in the long-axis view of the IVC affected by medio-lateral displacements (median: 4 mm); and a median error of 7% and 9% when measuring the IVC diameter from a short-axis view in the presence of pitch angle (median: 0.12 radians) and cranio-caudal movement (median: 15 mm), respectively. Conclusion: Relative movements in the IVC that are out of view of B-mode scans cannot be detected, which results in challenges in IVC diameter estimation.