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#### Adding and measuring the Elliptical Region of Interest (ROI)

You can define an Elliptical region of interest (ROI), and measure its pixel intensity parameters, area, and perimeter. Pixel intensity enables you to determine the tissue type of the ROI. See Use of the pixel intensity values. Elliptical ROI is exclusively used in CT studies.

Values that you can measure

The following table describes the values that you can measure for the Elliptical ROI.

Value | Meaning
Average | The average pixel intensity values within the Elliptical ROI, in Hounsfield Units (HU) or Optical Density (OD).
Area | The area of the Elliptical ROI.
Min/Max | The minimum and maximum pixel intensity values within the Elliptical ROI, in Hounsfield Units (HU) or Optical Density (OD).
Perimeter | The perimeter of the Elliptical ROI.
Std Dev | The standard deviation pixel intensity values within the Elliptical ROI, in Hounsfield Units (HU) or Optical Density (OD).

Step 1: Select the Elliptical ROI tool

To select the tool:

| 1. | Click the Annotate icon on the main toolbar.

| 2. | Click the Elliptical ROI tool on the Annotation Control Panel.

For other ways to select the tool, see Selecting an annotation tool.

Step 2: Adjust the Elliptical ROI tool properties (if necessary)

For an overview of annotation properties, see Setting the annotation properties.

To adjust the tool properties:

| 1. | Select the check boxes that correspond to the types of values you want to display. For a description, see Values that you can measure.

| 2. | Follow steps 1 and 2 of Step 2: Adjust the Distance tool properties (if necessary).

Step 3: Draw and measure the Elliptical ROI

To measure an Elliptical ROI:

| 1. | Drag the mouse pointer diagonally across the area of the image where you want the ellipse to appear.

| 2. | Release the mouse button.

An Elliptical ROI is displayed with the values.

Note: If the area and perimeter of the Elliptical ROI contains no measurement unit, calibrate the scale. See Calibrating the measurement scale.

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