Object ID: 00000018WIA301BC970GYZ
Topic ID: id_40026429 Version: 1.3
Date: Mar 25, 2022 4:11:04 PM

Add/Subtract images

About this task

The Add/Subtract application allows you to execute the following functions from the Add/Subtract screen:

Bind two series into a single series. This is useful for viewing pre- and post-contrast or T1 and T2 contrast series in a single series. The new series appears as a COMB series in the Patient List.
Add or subtract two series. This is useful for MRA exams. The new series appears as a PROC series in the Patient List.
Extract the minimum or maximum pixels from one or two sets of images. The new series appears as a PROC series in the Patient List.

CAUTION

Since “COMB” series contain images resulting from a combination of images from different locations in the patient’s body, the absolute anatomical coordinates accompanying these series (shown both in the Browser and on the displayed images) are not accurate. Only relative geometric measurements (i.e. distance, angle, or area) are accurate. Use these steps to create a new image set, for example add thin slices together or subtract pre/post contrast series. The resulting images are annotated with the day on which the addition/subtraction was performed.

Step-by-step instructions

From the header area of the screen, click the to open the Image Management work area.
From the exam area on the Patient List, select the desired exam.
When selecting image sets, consider the following:
- One or two sets of images must be selected.
- If only one set is selected, each operation performed produces one resulting image.
- If two sets are selected, images in the two sets are paired according to physical location in the patient’s body. Unpaired images in either set are ignored.
From the Session Apps list, click Add/Sub.
Figure 1. Session Apps list
- The Add/Subtract screen opens.
  Figure 2. Add/Subtract screen
From the Data Selector tab, select the desired series or set of images.
Click the left Select Set.
- If you are adding/subtracting two sets of images, select the second series or set of images and click the right Select Set.
- By default, equal weighting is applied to the two pixels in each pair, but you can change the weighting via the Ratio slider.
Click New Save Series.
Figure 3. Current and New Save series
- This action places images resulting from subsequent operations into a new series in the Patient List. If you do not select this option, the images are saved in the current saved series.
- Current Save Series: Displays the currents series and starting image number of the saved series. By default, images resulting from subsequent operations are added onto the end of the same series unless you click New Save Series.
Select desired Mode buttons.
Figure 4. Mode buttons
- Click Max to create a new series that finds the highest corresponding signal intensity values in the selected set or sets of images.
- Click + (plus) to create a new series that adds the image intensity values of the selected image sets.
- Click - (minus) to create a new series that subtracts the image intensity values of the selected image sets. For subtraction, click Accept Negative Pixels.
  - Subtracted images are scaled and do not represent a true pixel-by-pixel subtraction. They should not be used for quantitative measurements.
- Click Min to create a new series that finds the lowest corresponding signal intensity values in the selected set or sets of images.
- Click Bind to create a new series that consists of copies of the selected images from one or more existing series.
  - Bind is the only Add/Subtract option that allows you to add a series description.
Optional: Click Disable Normalization option box to perform a pixel by pixel addition or subtraction. The images are not normalized.
- Disable Normalization is available for both addition and subtraction.
- If Accept Negative Pixels is not selected the negative pixels are scaled to zero and the resultant images are clipped to 16 bit if they go beyond the bounds of 16 bit images.
- If both Accept Negative Pixels and Disable Normalization are selected, then Add/Subtract accepts input of negative pixels and performs a true pixel-by-pixel subtraction. A message is displayed if any overflow beyond the 16 bit image size occurs
Click = (equal).
- Each operation performed produces one resulting image per pair.
- When Add/Sub is performed, the resulting images are annotated with the day on which the addition/subtraction was performed.
- Clear Selection is used to erase the selections so that both Select Set buttons have no prior values associated with them.
Click Quit when you are finished with all Add/Subtract procedures.