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Table 1 Summary of EOD measurement by 3D TVS

From: Towards more accurate measurement of edge to os distance in low-lying placenta using three dimensional transvaginal ultrasound: an innovative technique

Volume acquisition
 1. Reference plane: The mid-sagittal view of the cervix.
 2. Acquisition box and angle: adjusted to include the upper part of the cervix and the lower uterine segment containing the lower placental edge.
Volume display
 1. Plane A:
  a. The IO is centered in the plane.
  b. The reference point is positioned at the IO.
  c. Rotation around the z-axis to make the IO at the lowest level in the lower uterine segment.
 2. Plane B:
  a. The reference point is positioned in the middle of the upper edge of the cervical canal.
  b. Rotation around the z-axis to make the IO at the lowest level in the lower segment.
 3. Plane C:
  a. The reference point is positioned in the middle of the IO.
  b. Rotation around the z-axis to get the IO parallel to the y-axis.
 4. Plane A:
  a. Rotation 360° around the y-axis.
  b. Measure the shortest distance between the lower placental edge and the reference point (center of IO).