The image source configuration dialog is used to select and configure the image acquisition facilities. The top menu lists what, if any, image acquisition hardware has been detected. If Stradwin has not found video or RF capture facilities, you will need to fix this using the information on the installation page. Unlike the driver for the position sensor, it is not possible to fix this problem from within Stradwin.
The next four sliders control the cropping of recorded image data. Two sliders set the width and height of the acquired image. Immediately below them are two further sliders that set the horizontal and vertical offsets of the recorded image from the top left hand corner of the image returned by the video card. Note that any change to these offset values will change your probe calibration. You must therefore recalculate the calibration and save it to an appropriate template file if you change these offsets. As a general rule, it is best to try and get your image cropping right before performing probe calibration. Note that cropping can also be set by clicking and dragging in the review window with the 'select region' tool.
The 'auto crop video' button, if enabled, allows the previous four sliders to be set automatically such that you can see all of the available ultrasound data. Currently, this button is only enabled when you are using the Gage Compuscope, Sonix, Terason or ULA-OP image acquisition drivers.
When Stradwin records colour Doppler data, it classifies pixels as greyscale or colour on-the-fly, and stores each pixel as an appropriately coded byte. For a pixel to be classified as coloured, its red and blue chroma values must differ by a certain amount: this threshold is the first parameter which you can set. Since colour is not well defined for very dark pixels, the pixel's luminance value must also exceed a certain threshold for the pixel to be classified as coloured: this is the second parameter which you can set. In practice, you will need to set these parameters once for your particular ultrasound machine and frame grabbing card, and then save them in your template files for later recall.
The easiest way to set the parameters is to observe their effect on the live image. When this image most closely matches the picture you see on the ultrasound machine's screen, you have set the parameters correctly.
Note that the control to select whether data is recorded as greyscale or Doppler is on the recording task page.
There are also some additional controls when recording RF data. These are only relevant when using a Gage CompuScope connected to raw RF signals from the ultrasound machine, a Sonix or Terason ultrasound machine recording RF data, or a ULA-OP scanner recording IQ data.
The 'Use probe' selection box allows you to select a probe configuration file. These files have the filenames 'probe*.cfg', where * can be anything. Stradwin will search for any such files in the data directory or the same directory as the executable, and present a list of the probe names from the configurations which have been found in the selection box.
The next line controls the sample rate, which can be either 50MHz, 100MHz, 200MHz 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. The next line tells Stradwin 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.
Note that the control to select whether data is recorded as RF or B-scans is on the recording task page.
The 'Driver-specific controls' button pops up low-level controls specific to the particular image source. For video sources, these include a 'Source type' and 'Standard' selector, to choose between physical video input connectors, and whether the input video standard is PAL or NTSC. Sometimes the 'Source type' selector gets the wrong input, in which case you can override it using the 'Input number' selector (Linux only). Under Windows, some direct show video devices do not allow the input and standard to be set individually, and instead provide their own controls to do so. In this case, the 'Source type' and 'Standard' selections are not available, but Stradwin instead shows the video device's own dialog for setting these features.
When interfacing to a Sonix, the controls are different according to the particular interface in use:
When interfacing to a Terason, the controls consist of a single drop-down list allowing selection of configurations which have previously been saved by the Terason system.
When using a Gage Compuscope, there are controls for the acquisition of timing signals, which tell Stradwin when to sample the RF signal. The default behaviour is to acquire the timing automatically from Channel B at the start of the first acquisition. If you need to do single channel acquisition (for instance when using an external clock, or a high sampling rate), the timing must be acquired before the acquisition, by first connecting the timing signal to Channel A, then pressing the 'A' button. The 'B' button can be used to acquire the timing signal from Channel B as a one-off operation.
There are also various controls for setting the trigger levels and impedances of the RF timing signals. If the timing is not expected to be repeatable for each frame (for example when using the Gage CompuScope with a VisualSonics systems), the 'percentage variation' slider can be set to a value higher than zero. This will cause Stradwin to update the RF timing on-the-fly, at the cost of a slightly reduced frame rate. See the description of RF signals for more information.
When using a ULA-OP system, there is a drop-down list for selecting a beamforming scheme. See the description of probe configuration files for more details on defining beamforming schemes. There is then a slider to control the depth of scan by setting the number of IQ sample pairs to acquire. The 'Update scanner' button must be pressed whenever either of these controls is changed. This may take several seconds while the ULA-OP is reprogrammed. The remaining controls can be changed while running live without needing to use the update button. The sliders allow adjustment of the pulse repetition frequency (line frequency) and the time gain compensation. The TGC controls define a linear function with an initial gain at depth zero and a gradient in dB/cm.