RF display

The RF display configuration dialog is used to control how recorded (or live) RF data is converted to a displayable form, for instance a B-scan. If the data is being recorded as RF, these parameters will not affect what is stored, only how it is displayed. Hence, they can be changed after acquisition. If the data is being stored as B-scans rather than RF, then these parameters control what is stored, and will not affect subsequent display.

The first selection box controls the type of display:

B-scan

This is the conventional B-scan display of log-weighted signal envelope.

Phase

This is a display of the phase of the analytic RF signal, where 0 to 360 degrees is mapped to a linear range from black to white.

Strain

This displays the relative strain by comparing two images, used to highlight areas which are harder or softer than the surrounding tissue. See 2D and 3D strain imaging for more information.

To the right of this selection box, there is a '+ B-scan' check box. Checking this box will cause an additional B-scan to be displayed in the review window to the right of the normal image. Note that this is only possible if Stradwin is recording RF data, rather than just B-scans.

In order to generate such displays from the RF data, the acquired RF signal is first converted to analytic form, which is a complex representation in which the magnitude gives the response, and the argument the phase of the received RF signal. To do this, the signal is filtered by a pair of matched filters, which can be chosen to cover the whole frequency range of the signal or to select a smaller frequency range. These filters are defined and named in the probe configuration file. The 'Using filter' selection box allows the user to select from the filters defined in the configuration file. The selected filter affects all types of display.

The final 'compounding' filter is a special case: if this is selected, the RF data will be processed with a sequence of filters of varying centre frequency, and the results averaged. This can give an increase in signal-to-speckle ratio, at the cost of a reduction in axial resolution. Use of the 'compounding' filter only makes sense if the 'B-scan' display is selected.

The next three controls in this dialog control the dynamic range in dB (first slider), offset in dB (second slider) and gamma value (third slider). These are used in the log calculation when displaying the 'B-scan'. These sliders have no effect on the other types of display.

After this control is a slider which can be used to increase the persistence, i.e. the amount of averaging over a series of B-scans. Setting this slider to '1' will disable persistence. In this case all B-scans will be created from one set of RF vectors only. The final slider controls the scale, in mm per pixel, at which the RF data is converted to a displayable image.

The last row of checkboxes control which steering angles are in use when recording steered RF data.