3D Gynecologic Ultrasound Tutorial

Preparation
Image Acquisition
Optimization
Navigation
Interpretation

Once attention has been given to the steps of preparation above, data acquisition is relatively easy.
As the probe head scans through the angle of acquisition to acquire the volume, both the patient and practitioner should move as little as possible (including holding their breath) to minimize movement artifact. This is the only key to acquisition - as little movement as possible.
You may now choose to select a new quality or angle of acquisition and repeat, or change your area of interest altogether and collect another volume.

With the volume acquired and saved either to a network server, local machine, or optical disc, image optimization can take place either with software on the US machine or more commonly on a PC equipped with rendering software such as GE's 4D View.
There are 6 basic rendering algorithms which can be applied to the volume. Any two of these algorithms can be used at one time, and they can be applied in a percentage gradient - so there are infinite possibilities. Each of these algorithms govern how a 2D image is rendered. The software passes a virtual ray through the 3D volume of data at the user defined plane of intersection or render view direction, and as the "ray" passes through a 3D voxel of data, a 2D pixel is recorded for the reconstructed 2D image. The color (or level of gray) and opacity of this pixel is defined by the rendering algorithm or combination of rendering algorithms used:
   1. Surface texture - The first gray area above the selected threshhold which is encountered beyond a hypoechoic area (such as amniotic fluid or fluid in a cyst or saline in the uterine cavity) is rendered so that the surface of a structure interfacing with the hypoechoic area is rendered.
   2. Surface smooth - Similar to surface texture, but the gray values of adjacent pixels are averaged to create a smoother image.
   3. X-ray mode - The gray values in all of the voxels the ray passes through are averaged together to determine the resulting gray value of the pixel.
   4. Gradient/Light mode - The gray values rendered are based upon the distance of the pixel from the rendering starting point, so that close structures are brighter gray than far away structures.
   5. Transparency maximum - The highest valued gray along the ray is displayed in the pixel.
   6. Transparence minimum - The lowest valued gray along the ray is displayed in the pixel.
A newer technique being employed is called volume inversion which dislays cystic structures as echogenic and the grayscale areas become transparent. This has the benefit of allowing all cystic areas, such follicular cysts, to be seen at once by making the  solid areas transparent. This would also allow a hydrosalpinx, for example, to be seen in one view, regardless of its tortuosity, and aids greatly in the diagnosis of cystic structures. This mode could also be used with SIS to create a 3D view of the distended uterine cavity.

Moving through the volume of data is done through translation or rotation.
Translation means to move through one plane layer by layer of slice by slice.
Rotation is to move through a plane angularly along any of the axises through the volume.
Point Correlation is used to rotate around a fixed point, usually a yellow dot, in all of the planes. Thus, if the correlation dot is placed at the focus of anatomy under investigation it should produce the best 3D image.
Unnecessary data or images obstructing the view of the desired anatomy can be removed with a feature called Magic Cut or the Electronic Scalpel. This allows this user to cut away noncontributory data from the volume and clean up the image.