Advanced RF Controls

The Advanced RF Controls Window

This window allows you to control the way in which RF data is acquired, and how the displayed image is calculated from this data.

The top section controls acquisition of RF data. The 'Use probe' selection box allows you to select one of 26 probe configuration files. These files have the filenames 'probeA.cfg' to 'probeZ.cfg'. Stradx will search for any such files in the same directory as the executable, and present a list of configurations which have been found in the selection box. Once a file has been selected, the name of the probe (from the configuration file) will be displayed next to the control.

The next line controls the sample rate, which can be either 50MHz, 100MHz or Ext. (when using an external clock), so long as this is supported by the CompuScope input board. The external clock rate is set from the probe configuration file - this must be within the allowed range for single channel acquisition. Following this is the scale (in cm/pixel) for the B-scan display. The next line tells Stradx how many foci are being used and which is the shallowest focus: this determines how many RF pulses are expected for each vector (or B-scan column), and which part of each vector will be used in constructing the B-scan. See the description of RF signals for more information.

The Advanced RF Controls Window

The final line in this section controls the acquisition of timing signals, which tells Stradx when to sample the RF signal. When sampling at 50MHz or 100MHz, the timing is acquired automatically from Channel B (at 50MHz) at the start of each acquisition. If using an external clock, the timing must be acquired before the acquisition (see the figure above), by first connecting the timing signal to Channel A. Acquiring timing from Channel A is also more accurate for the 100MHz sampling rate, since in this case the timing is acquired at the same rate as the RF signal is sampled. Once again, see the description of RF signals for more information. Note that none of the controls in this section can be changed after the data has been acquired.

The following section controls how the acquired RF data is processed to generate the B-scans. If the data is being recorded as raw RF, then 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.

Review window based on RF data

The first selection box controls the type of display: 'Envelope' generates the usual B-scan display, for instance as shown above. There are also two other options, 'Phase' and 'Frequency'. The former displays the phase of the analytic RF signal, and the latter displays the rate of change of phase, which is related to the instantaneous frequency of the signal. The image below shows an example of frequency display from the same data as above.

Review window showing phase difference of RF data

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 select a smaller frequency range. These filters are defined and named in the probe configuration file. The user can select from the filters defined in the configuration file by using the 'Process RF with' selection box. 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 result in 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 'Envelope' display is selected. The image below is an example of a compounded B-scan.

Review window based on compounded RF data

The final line in this section controls the gain (first slider) and offset (second slider) of the log calculation used in displaying the 'Envelope'. These sliders have no effect on the other types of display.

All the controls can be returned to their default values by pressing the 'Set default RF controls' button. Note that, if you have already acquired some RF data, only those controls which can be legally changed are affected by this action.