Stradwin data sets are each stored in a pair of files. One file has the suffix '.sw' and contains the probe calibration, the 3D position of each frame and all the relevant configuration information. This is an ASCII text file which can be viewed using a simple text editor. The second file of each pair has the suffix '.sxi' and contains the image data in a binary format.
When you load a prerecorded data set, information is loaded from both these files. Stradwin temporarily changes the calibration and relevant configuration settings to match the settings when the data was recorded. The calibration and configuration settings revert to their previous values when you close the file or select the 'New' option from the file menu.
Detailed information on the format of Stradwin data files can be found here.
Stradwin template files contain probe calibration and configuration information to set up the system for recording with a particular probe at a particular depth setting. The configuration information sets up the controls on the images and positions configuration dialogs. When a template file is loaded, it permanently changes the values of the probe calibration parameters and configuration information within Stradwin.
Detailed information on the format of Stradwin template files can be found here.
This feature can be used either to export frames in one of a number of common image formats, or to create a new Stradwin data file with a reduced set of frames. The latter is useful if the recorded data contains frames which are of poor quality, for instance.
First enter the range of frames that you wish to export. This is a text field which operates in a similar manner to entering a range of pages when printing a document. You can specify individual frames, ranges of frames, ranges of frames with a defined number to skip, or any combination of these. The default is to export the currently displayed frame.
Stradwin then prompts for a file name and file type to save the data to. If an image format is selected, then the frames are saved as individual images to files in this format. If more than one frame has been selected, the file name used for each frame is appended with the number of the original frame. Hence a frame range of '1-2' and a file name of 'bscan.jpeg' will cause the data to be saved to files 'bscan1.jpeg' and 'bscan2.jpeg'.
If the selected format is 'Stradwin file', then the selected frames and any corresponding landmarks and object contours, as well as all associated configuration information, will be saved to a Stradwin file. In this case, the new Stradwin file is also loaded into Stradwin so that it becomes the current data set. If the existing data has not already been saved, Stradwin will warn that it may be lost before completing the export.
Stradwin data files only contain the original recorded B-scans or RF data. Since these are recorded as the ultrasound probe is moved by hand, they are neither regularly spaced nor parallel. The visualisation tools in Stradwin are optimised to work directly from such data, in order to maintain the highest possible resolution in every image. Outlining of objects in Stradwin is always performed in the original image frames, since the many artefacts common in ultrasound images are much better understood in these images.
By contrast, most general visualisation tools expect data to be arranged in a regularly spaced grid. The voxel export utility is provided to enable Stradwin data to be visualised in such tools. However, it should be noted that visualisations from voxelised data (other than those exactly aligned with the exported grid) will not be as precise as those available within Stradwin, and extreme care should be exercised when outlining objects in such data, since common ultrasound artefacts will appear in uncommon forms.
Voxel arrays are exported aligned to the current reslice, orthogonal or isocentre visualisation, whichever is selected. In the case of orthogonal visualisation, the alignment is with respect to the left of the two reslices. The width and height of each slice of data will be exactly the same as in the displayed reslice, and the number of slices will be chosen to cover the full extent of the 3D data. For the isocentre visualisation, the data will be exported in the current isocentre coordinates, whereas reslice and orthogonal visualisations will be exported in position sensor coordinates. Using the reslice visualisation, and setting the location with the 'Locate for minimum voxels' button, will ensure that all the data is exported in an orientation which minimises the size of the output data.
First select the resolution for the exported data. This can either be chosen as some integer multiple of the current image pixel width, or alternatively fixed slice separations of 1mm to 20mm can be selected. In each case, the approximate size of the exported data file is displayed.
Stradwin then prompts for a file name and file type to save the data to. If an image format is selected, then each slice is saved as individual images to files in this format. The file name used for each slice is appended with the number of the slice in the sequence. Hence a file name of 'voxels.jpeg' will cause the data to be saved to files 'voxels0.jpeg' etc.
If the selected format is 'Stradwin file', then the voxel array is saved in Stradwin format, where each new 'frame' actually corresponds to one slice from the voxelised data. The coordinate system is preserved, so a landmark placed on the original data will still appear in the same location in the voxel array data. Any current landmarks are also exported in addition to the data. If there are any current surfaces, the intersection of these surfaces with each slice is saved with the data. When the exported voxel array is re-loaded into Stradwin, these will appear as new object contours.