Multiple sweep 3D ultrasound data

Sometimes the anatomical volume to be scanned is too wide to fit in a single ultrasound sweep. You may need to record one sweep, move the probe sideways a little, then record a second sweep in the reverse direction. Very wide target areas might require three or more sweeps. You must ensure that neighbouring sweeps overlap each other to some degree, otherwise useful data might fall in the gaps between the sweeps.

To record multiple sweep data, set the "Video rate" control on the Record task page to "Multiple gated". This is motion-gated acquisition with one difference: when you stop at the end of the first sweep, Stradwin waits for you to move the probe a little to the side and then hold the probe steady again: the system is now primed to record a second sweep. You can repeat this process to record as many sweeps as necessary to cover the target volume. Alternatively, if you record data in the normal way, stop recording, then re-start and record some more data within the same data set, each set of data will be treated as a separate sweep.

Stradwin has special facilities for visualising and processing multiple sweep data. The first step is to divide space into a number of partitions, with each partition associated with a particular sweep. You will see the partition dividers drawn in dark blue in Stradwin's various visualisation windows. You can adjust the positions of the dividers by dragging the "Multiple sweep partitioning" slider in the Reslice visualisation page. The ideal position for each divider is running down the middle of the overlap region between neighbouring sweeps. Setting the slider to values in the range 0 to 100 fine tunes the dividers' positions, while the adjacent checkbox can be used to disable the dividers altogether.

With the dividers properly positioned, data visualisation and analysis should proceed smoothly. The various reslice-type displays show data from only a single sweep in each partition, with dark blue lines marking the boundaries between partitions.

When drawing object contours, a fading blue strip indicates the partition boundary and which side of the boundary the current frame belongs to. Be sure to trace the contour up to the partition boundary and a little beyond it: Stradwin will then clip the contour to the correct partition. This way, large objects spanning several partitions can be segmented one partition at a time, then stuck together to form the whole, composite object. Stradwin knows how to add up each sweep's segmented volume to find the total object volume. Since both moving the "Multiple sweep partitioning" slider and performing pressure correction will change the positions of the dividers, object contours should only be drawn after either of these operations have been performed.

Finally, Stradwin performs any probe pressure correction one sweep at a time. A slider in the Pressure task page allows you to observe the correction in each sweep independently.