Selections in Scan Analysis

1 Update

The UPDATE selection will refresh the List Select display if new scan files have been created since the Scan Analysis Tool was started.

2 Scan Header

The SCAN HEADER selection will open a scrolling text window that contains the header text information contained in select scan file.

3 Cal Vectors

The CAL VETORS selection will open a window allowing you to select the calibration vectors in the selected scan file that you wish to view. After the selections are made, OK will process the data requests and display the results.

The resultant plots are auto-scaled, and in some cases, the range of data displayed is automatically set. This is to provide a reasonable initial view of the data. Always check the scale on the left-hand side of the plot displays. Cursor reporting of data value and channel numbers is provided.

The default selections are underlined in Table 1.

4 Aux Channels

This selection opens a window that allows you to select which of the auxiliary channels in the scan file you wish to look at, as well as the start and ending views to display. After the selections are made, OK processes the data requests and displays the results.

The resultant plots auto-scale, and in some cases the range of data displayed is automatically set. This is to provide a reasonable initial view of the data. Always check the scale on the left-hand side of the plot displays. Cursor reporting of data value and view numbers is provided.

The default selections are underlined in Table 2.

5 Z Axis Channels

This selection allows you to select the start and end views to display for the Z Axis Channel data. After the selections are made, OK will process the data and display the results.

6 Create MSD dd File

This will calculate a view averaged “super view” for the selected views and store the results in a separate file on the systems disk. The display will report the path and filename of the file just created. Once created, dd File can be viewed or compared with other files to check for specific operating characteristics.

7 Plot MSD

Provides a set of view summed means and standard deviation plots of a scan file. The plotter is started to display the means vectors and the standard deviation vectors, computed across the entire scan for each detector macro row. Four mean and standard deviation plot sets display in the window.

After Plot MSD is started, a window will allow you to select:

• Start View and EndView

• View Compression: Automatic, 2 to 1, 4 to 1

• Processing steps:

  1. Offset Correction: This processing step removes the signal bias introduced by the acquisition electronics from the scan data. This operation is performed on a channel-by-channel basis for each view.

  2. Primary Speed Correction (afterglow): This processing applies a correction value to each channel value to reduce the effect of scintillator afterglow from the detector cells.

  3. Reference Normalization: Makes use of unobstructed (not blocked by the patient) detector cells at the end of the detector to adjust for fluctuations in the x-ray beam and effects of aperture size and mA. In the case where the reference channels are blocked, the system uses an estimated value for the processing. The steps for reference normalizing the scan data involve:

     1. Offset correction for the reference channels.

     2. Dividing the offset corrected scan data by the averaged reference channels for each view.

  4. Convolved Data: This processing step mathematically filters the channel data to remove blurring effects that would occur when the views are back-projected. The effect is to “sharpen” each channel’s data value within the view. Without the convolution step, some of the x-ray attenuation data for a particular channel ends up in the channels on either side of that particular channel. Convolution puts that adjacent channel contribution back into the channel data that it should have been in to begin with.

Cursor reporting of data value and channel numbers is provided.

8 Plot VVC

The PLOT VVC selection provides Views-vs-Channels display of a grey scale representation for the selected scan file. Each view of data (or summed, compressed view) is represented on the display as a horizontal line. Each pixel in the line represents the data value for a particular channel from the DAS.

After VVC is activated, a window will allow you to select:

• Row (macro row) One of: 2A, 1A, 1B, 2B

• Start View and EndView

• Start Channel and End Channel

• View Compression: Automatic, 2 to 1, 4 to 1

• Processing steps:

  1. Offset Correction: This processing step removes from the scan data, the signal bias introduced by the acquisition electronics. This operation is performed on a channel-by-channel basis for each view.

  2. Primary Speed Correction (afterglow): This processing applies a correction value to each channel value to reduce the effect of scintillator afterglow from the detector cells.

  3. Reference Normalization: Makes use of unobstructed (not blocked by the patient) detector cells at the end of the detector to adjust for fluctuations in the x-ray beam and effects of aperture size and mA. In the case where the reference channels are blocked, the system uses an estimated value for the processing. The steps for reference normalizing the scan data involve:

     1. Offset correction for the reference channels.

     2. Dividing the offset corrected scan data by the averaged reference channels for each view.

  4. Convolved Data: This processing step mathematically filters the channel data to remove blurring effects that would occur when the views are back-projected. The effect is to “sharpen” each channel’s data value within the view. Without the convolution step, some of the x-ray attenuation data for a particular channel ends up in the channels on either side of that particular channel. Convolution puts that adjacent channel contribution back into the channel data that it should have been in to begin with.

     Once displayed, the window and level for the displayed data can be changed to better see variations in the data.

     CURSOR BEHAVIOR IN VVC

     Cross hair cursor reporting is provided for: Data Value, DAS Channel, Detector Channel, and View number. The cursor is moved across the display using the mouse.

     A selection box on the display allows selection of line cursors and box cursors, which allow the selection of a channel, view, or group of channels and views for plotting.

     The line and box cursors can be moved around the screen to view specific areas of interest. When the mouse pointer cursor is moved over a line cursor the mouse cursor will change to a four pointer arrow. Pressing the left mouse button allows you to ’drag’ the cursor across the display.

     For the box cursors, the box may be dragged using the left mouse button with the mouse cursor positioned over the box. The size and shape of the box can be changed by moving the mouse cursor over the Bottom or Right edges of the box. When over the Bottom or Right edges of the box you can press the left mouse button to drag the box edge up and down or left and right.

     With the channel and view cursors, the plotted data represent all channels for a selected view or all views for a selected channel.

     With the box cursors, the resulting plot is a view summed means and standard deviation plot for the selected views and channels.

9 Save Scan

This will save the selected scan file to a temporary disk location so that it can moved to MOD or transferred via ftp to another location.