Impact of Depth and ROI Size on the Reliability of SWE Measurement

ROI Size in 2D-SWE

According to WFUMB (2024), in 2D-SWE, the ROI (measurement box) should be at least 10 mm. Unlike p-SWE, where the ROI size is fixed, in 2D-SWE it can be adjusted (Ferraioli et al., 2018). The ROI should ideally be placed closer to the center of the field of view (FOV) as measurement errors often occur at the FOV boundaries (Ferraioli et al., 2018).

Depth of ROI Placement

According to WFUMB (2024), the measurement box in liver studies should be positioned 15–20 mm below the capsule. The 2D-SWE field of view can be shifted closer to the capsule provided reverberation artifacts are avoided.

The key physical constraint is the energy distribution of the ARFI push pulse: in most ultrasound systems, the push pulse peak is achieved at a depth of 4–4.5 cm from the transducer, which is the optimal zone for measurements. At a depth of 6–7 cm, the push pulse weakens, limiting adequate shear wave generation (WFUMB, 2024).

The EFSUMB Course Book (Sporea et al., 2018) recommends placing the ROI at a depth of more than 2 cm but not deeper than 8 cm. According to Bamber et al. (2013), shear wave speed can be measured to a depth of approximately 8 cm.

ROI Placement Relative to Structures

The ROI should be placed in an area free of large blood vessels, bile ducts, and mass lesions (WFUMB, 2024; ACR/SRU, 2024; Sporea et al., 2018). Measurements are performed during neutral breath-hold (WFUMB, 2024).

Number of Measurements and Quality Control

Operator Training

According to EFSUMB (Dietrich et al., 2017), a novice is recommended to perform at least 50 supervised 2D-SWE measurements to achieve stable results; an experienced operator demonstrates higher reproducibility over time.