29. LUT
Look Up Table (LUT)
Each anatomic area has a LUT
Used to adjust contrast and density
Other terms that may be used for this from
various vendors (don’t need to memorize
them, just tellin’ you)
Contrast rescaling
Contrast processing
Gradation processing
Tone scaling
30. LOOK UP TABLE (LUT)
Linear LUT
Black
Saturation
White
Saturation
Black Shirt
Facial Tones
* No Detail in Black Areas
* High Contrast
* Only Detail in White
Areas can be seen
* No Detail in White Areas
* Low Contrast
* Only Detail in Black
Areas can be seen
One more concept in the image processor that is critical. It’s called the LUT. It stands for lookup table. The situation here is that if we take this picture and we say “Let’s take a look at how much of the image is black and how much is white and how much is gray”. This is a little fancy curve, it’s called a histogram. What you see is all the blacks are down here. This is a lot of her shirt down here. And this is the gray area. In fact, these are most of the facial tones. If you want to reproduce this image exactly as it was taken on the image intensifier, you want the whole thing to be linear. Every time you put this energy in, you want the exact out. Again, like anything else, I can play with this lookup table and say “Forget about the blacks. Everything that’s below this curve let’s make black. Because what I really want to do is I want to see the shades of gray in this white area”. Or I can do the reverse. I can say “Forget about all the white stuff. I want to see the shades of gray in here”. Now, why would anybody in their right mind want to do this? Easy. Radiography is a game of shades of gray. That’s all the radiologist is doing. He wants to see a little bit of a calcification here, a little bit of air in the lung here. It’s always a game of the shades of gray. So, the more you can take his area of interest and stretch it out for him, he’s going to be a happy camper. And he’s willing to compromise that the other areas are going to be bad. Look at this original image here. You’d say “That’s the image I’d want”. Can you tell me what kind of sweater she’s got on. Look at the ribbing. So, we might say, we’re not interested in her face and her hair, but we’re interested in the shades of gray in the vest, or in the cardiac or mediastinum in the medical world. So, the point here is that by varying lookup tables, we can actually also vary the ability to see varying shades of gray. This image processor can play games with low pass, high pass, or lookup tables to create images that are just spectacular, or garbage if you happen to set it up wrong.