Keywords:  Image Manipulation, rotate, flip, zoom, Loupe, Annotation, Invert, LUT, Presentation State, WW, LVL
Image Manipulation

Image Manipulation:  These features apply to the presentation of the individual images.  These manipulations can be saved and/or recalled using the DICOM Presentation State.

Window Width and Level (WW/LVL):  These features are sometimes called, incorrectly, contrast and brightness.  The contrast/brightness parameters are really influenced by the setting on the monitor and typically impact the hardware settings.  The window width allows a device to select a subset of a dynamic range that is often larger than the device can handle or display.  For example, a CT image might be represented in 12 bits, having a dynamic range of 4096 different values.  The human eye can distinguish at most different levels.  By squeezing all 4096 values into 200 values, it would resulting a significant loss of information.  By taking a subset of the information and mapping it to the available output levels, e.g., 256 gray values, the human eye can then differentiate between the structures.

The Level parameter identifies the center of the mapped information.  Some images have multiple WW/LVL values stored in their header.  For example, a CT of the chest might have a bone and lung window, the selection on the view station of predefined, preferably-configured presets is a requirement, in case this information is not available in the header.  A "revert to stored or previous value" of the WW/LVL feature is needed as well, in case a physician happens to steer his WW/LVL feature is needed as well, in case a physician happens to steer his WWLVL controls out of range.

Rotate/Flip:  These features are often required for C, whereby an image plate might contain an image that is acquired in a "landscape" mode, while the display assumes it is in a portrait mode.  Ideally, the information in the image header would instruct the application software to display it correctly; however, a technologist might have forgotten to enter it or entered it incorrectly.

Invert:  In some cases, inverting the image to create a "negative" can help a physician to better identify certain pathology.  It is not used that often because most radiologists are not used to looking at "negative images" because in the traditional film world it is not commonly used (except for fluoroscopy exams).  However, an orthopedic specialist might want to use this feature to help identify small fractures in bones or track the placement of a tube in the lungs, which is very common for ICU exams.

Zoom, Pan, Loupe   These features are all basically enlargements of the image.  Zoom increases the size of the image, pan allows the center reference point to be changed, and the loupe allows for enlarging only a small area, keeping the remainder of the image intact.

Image Annotation and Screen Annotation:  Annotation can be text, markers such as arrows, freehand drawings, etc.  Image annotation is tied to the actual image and will (supposedly) change with the image manipulation features such as zoom, flip, rotate, etc.  They are mostly used to identify findings in the image.  Screen annotations are not necessarily related to any particular area in the image but could contain general comments and are displayed, for example, on the bottom of the screen, not subject to any image manipulations.

Look Up Table Support:  CR and DR images in particular, often have a Look Up Table (LUT) included in the image header to provide for matching the display of the image with a particular "look" or to comply with a certain standard such as the DICOM Grayscale Standard Display Function (GSDF).  Suppose a CR device sends the LUT with an image, assuming that it will be applied, and the receiver does not support the LUT application.  The image will most likely look quite different than expected.  Therefore, LUT support should be provided for applying a different LUT, depending on the image type.

Presentation State Storage:  The Presentation State is a DICOM information object that stores image manipulations.  If a radiologist manipulates the image presentation, e.g., flips an image, applies a zoom, and adds annotation, this particular presentation needs to be preserved.  The DICOM Presentation State allows this to be kept in a standard manner.  This allows a radiologist to apply the saved presentation again upon retrieval, as well as allowing for another physician to see it.  This feature is part of the IHE Consistent Presentation of Images profile.

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