Window Level

The most commonly used image enhancement tool in PACS systems is the Window Level adjustment. Due to this reason, the window level tool is always available through the right mouse button. If the user presses the mouse wheel and moves the mouse up/down, the image will zoom in/out respectively. Holding down the right mouse button and moving the cursor also activates the tool. This activation is indicated by the change of the mouse cursor icon.

Moving the mouse vertically changes the window center (Level) value. Moving the mouse horizontally adjusts the window width (Window) value. The actual window and level values currently being applied to the image are visible in the image annotations found on the bottom left corner of the image.

The level value is denoted by the C value, while the window value is denoted by the W value. These values update in real time when the mouse is moved up or down.

The Window Level tool can also be activated as the main tool by selecting it from the toolbar. At that point the mouse cursor icon changes permanently and the window level values can be modified using either the left or right mouse button.

Although it is nice to have the ability to change the window and level values on the fly, quite often it is not necessary. Simply applying preset window level values to the images, will display the images in the optimal state. Window Level presets available for the current study are accessible through the pull down arrow associated with the Window Level tool in the toolbar as well as through the Image Right Click Menu.

Choosing any of the presets from the list will automatically apply that preset to the current series of images. Only presets applicable to the currently open study are visible in the list. This list can be modified by the system admin. Presets can be removed or added, and existing presets can be modified if they do not correspond to the values used at your facility.

Another way to quickly switch between presets is to use the Home and End keys to scroll through the list of available presets. Pressing the Home key while a viewport is selected will change the window and level values of that viewport to the previous setting in the list. The End key will change the window and level values to the next setting in the list.

Note: When the preset you select from the list includes color mapping on NM/PT images, then the WL/WW is applied to the entire frameset even if only specific images in the frameset are selected.

The Auto option can be used to allow the system to apply the optimal window preset for that image as determined by a software algorithm. The Auto window can be applied at any time by hitting the F5 key. The other presets in the list are mapped to the shortcut keys defined by the user in Windows Presets. These shortcut key assignments can be modified by the user. If shortcut keys have been assigned by the user, they are visible in the list of presets.

If you will like to adjust the sensitivity of the mouse when using the window level tool, or to enter a very specific window and center value combination that is not associated with any preset, you can do this through the Window Settings dialog. This dialog is opened by clicking the Settings option in the list of window presets or by clicking on the drop-down menu for the Window Level tool and selecting the Settings menu item.

Entering a Center and Width value into the fields and clicking OK, will apply that value to the images. If you find the mouse too sensitive, or not sensitive enough in regards to its motion, you can adjust the window level values by modifying the Sensitivity track bar. The lower the Sensitivity value, the more the mouse cursor will have to travel to change the window or level value. Similarly, the higher the value, the less movement will be necessary to alter the window level.

The Enable window level ROI checkbox allows for Window Level to be performed in a Region of Interest. Once you release the mouse, it gets applied over the whole image. This is particularly useful for large images as it will speed up the adjustment of the Window Level, but can be configured as required.

The Mouse Move Up options can be used to increase or decrease the brightness when the mouse is moved vertically.

The Mouse Move Right option can be used to increase or decrease the contrast range when the mouse is moved sideways.

Selecting the Sigmoid option from the window level drop-down list provides the ability to toggle between linear and sigmoid window and level settings. Sigmoid window and level is used specifically for x-ray images such as DX, MG, and CR.

Note that when the Sigmoid window level preset is enabled for a GE MG image, VOI LUT is removed. If you disable Sigmoid, it would not revert the image to the initial state as the presentation state is no longer available. You can assign the default presentation state to revert the image to its initial state. This limitation can only be experienced with GE MG images. For other modalities, disabling the Sigmoid preset reverts the image back to its earlier state.

Clamped Window/Level - The Clamped Window/Level mode will be automatically turned on for NM modality (SOP Class UID 1.2.840.10008.5.1.4.1.1.20) and PT modality (SOP Class UID 1.2.840.10008.5.1.4.1.1.128), excluding Secondary Capture (1.2.840.10008.5.1.4.1.1.7) and turned off when other modality images are activated. However, this automatic behavior will be disabled when you explicitly select the clamped Window/Level tool. Once you select this tool, the tool is applied across all the images in the Image Viewer. The Clamped Window/Level tool changes the mode of windowing behavior for the selected viewport(s) between changing the window center and width, or adjustment of the upper value of the window with the lower limit clamped to zero.