Two forms of calibration apply to the viewer. Image calibration assigns dimension to the pixels in the image. Monitor calibration assigns dimension to the monitors on which the images are displayed.
Image Calibration
Image calibration is necessary only for imaging modalities that do not provide enough information. In this case, pixel data uses measurement tools instead of millimeters. Calibration is required to convert pixel numbers to an accurate millimeter value.
On an ultrasound, the technologist uses screen captures, and image and measurement data are stored together. Therefore, this feature is seldom used.
The user is prompted to confirm monitor calibration when image calibration is required. If the monitor or display resolution has not changed, the user only needs to confirm the setting.
To perform image calibration, follow these steps:
Click Settings/Calibration/Image. A window appears showing the current pixel size information.
If numbers (other than zero) exist in the use DICOM calibration data field, the image object contains enough information.
If no information exists, select use manual setting data. Enter the horizontal and vertical pixel sizes, or click on add or change calibration rulers. The calibration rulers allow you to draw one or more rulers on the image and assign a length to each one. Using this information, the pixel sizes are calculated.
When the add or change calibration button is pressed, a full-screen window appears with an image display. The cursor becomes a ruler, similar to the linear measurement annotation tool.
Click, drag and release the mouse to place a ruler over the image. You will be prompted to enter a distance in millimeters.
Draw the ruler over an object in the image where you know the distance. For example, place the ruler over a measurement graph or lead ruler appearing in the image.
Pan and zoom the image to get a more accurate result by clicking on the buttons in the top left corner of the window. The more rulers you define at various angles, the more accurate the size calculations will be.
When finished, click on done. Return to the main calibration window, and choose to apply this setting to the present image, the series, the frame or the entire study.
Click finish.
Monitor Calibration
Even when image pixel size and spacing information is available, monitor information is sometimes necessary to render images correctly. Therefore, monitor calibration may be necessary and is only required once for each monitor.
To perform monitor calibration:
1. Click Settings/Calibration/Monitor. A notice appears explaining how to use the monitor calibration tool.
2. Click the checkbox indicating not to display this page again if desired.
3. Click on Next.
4. Hold a ruler up to the monitor.
5. Drag the horizontal and vertical rulers on the screen using the mouse until they reflect actual size.
6. Click OK when finished.