Room light will fog the phosphor plate: FALSE
By now, I'm sure that we have all used a CR cassette that has worn-out latches and springs. Due to the way some manufacturers construct their photostimulable phosphor plates, they can slide right out of the cassette and onto the floor, leaving the device holding the latent image susceptible to room light and/or dirt and scratches. You pick up the PSP from the floor, and what do you do?
Let me reassure you by saying that your image will not be fogged at all like it would have been with film/screen. In fact, a mistake like that with film/screen would completely ruin your image no questions asked; no need to run it through the processor to check... it would go straight to the repeat bin. You can freely process it without fear of image fog, although you're going to want to clean your screen before re-inserting it into the cassette.
So why isn't the PSP affected by room light? When compared to film/screen, the plate does not respond to the lower frequency of room light like film does. In fact, in order to see any radiographic density at all, the plate has to be ionized, which releases electrons from the valence band and sends them to the electron traps within the PSP (click here for more information on how the CR Image Plate works). Room light is simply not going to cause ionization of the plate.
I can hear what you are thinking already... "but why is it called 'photo' stimulable if it doesn't respond to light?" When a high frequency light source, like that of a laser seen in the previously mentioned post, this frees the electron traps of their charge and in turn, releases energy - some of it in the form of light. But this has the opposite effect of fog... here's how the relationships mesh together:
The higher the x-radiation exposure to the plate, the more electrons are released from the valence band and collected into the electron traps. The more electrons collected in the trap, the higher signal received during processing for that particular region of the image. The higher signal received, the greater the density displayed (darker pixel values).
The release of the electrons from the image plate by the laser scanner will actually reduce the amount of charge collected in the trap, therefore reducing density. If you read the whole post I referred to above, there is a very cool lab experiment that can be performed to display this concept with a laser-pen for the instructors out there that are reading this.
So a few minutes of exposure to room light will not fog your radiograph, and exposure to high-intensity laser or fluorescent light will actually decrease density on your final image. The most common ways you will see fog on your image receptor is if you have your image plate in the x-ray room during an exposure, leaving it exposed to scatter radiation (click here to learn about CR Image Plate Response to Scatter), or if you neglect to erase your image plates over long periods of not being used - most manufacturers recommend erasing the plates daily, or at least every 48 hours.
Additional posts in this series:
CR Myths #1 - An Increase in Exposure Creates an Increase in Density
CR Myths #2 - Radiographic Image Contrast is Controlled by kVp
By now, I'm sure that we have all used a CR cassette that has worn-out latches and springs. Due to the way some manufacturers construct their photostimulable phosphor plates, they can slide right out of the cassette and onto the floor, leaving the device holding the latent image susceptible to room light and/or dirt and scratches. You pick up the PSP from the floor, and what do you do?
Let me reassure you by saying that your image will not be fogged at all like it would have been with film/screen. In fact, a mistake like that with film/screen would completely ruin your image no questions asked; no need to run it through the processor to check... it would go straight to the repeat bin. You can freely process it without fear of image fog, although you're going to want to clean your screen before re-inserting it into the cassette.
So why isn't the PSP affected by room light? When compared to film/screen, the plate does not respond to the lower frequency of room light like film does. In fact, in order to see any radiographic density at all, the plate has to be ionized, which releases electrons from the valence band and sends them to the electron traps within the PSP (click here for more information on how the CR Image Plate works). Room light is simply not going to cause ionization of the plate.
I can hear what you are thinking already... "but why is it called 'photo' stimulable if it doesn't respond to light?" When a high frequency light source, like that of a laser seen in the previously mentioned post, this frees the electron traps of their charge and in turn, releases energy - some of it in the form of light. But this has the opposite effect of fog... here's how the relationships mesh together:
The higher the x-radiation exposure to the plate, the more electrons are released from the valence band and collected into the electron traps. The more electrons collected in the trap, the higher signal received during processing for that particular region of the image. The higher signal received, the greater the density displayed (darker pixel values).
The release of the electrons from the image plate by the laser scanner will actually reduce the amount of charge collected in the trap, therefore reducing density. If you read the whole post I referred to above, there is a very cool lab experiment that can be performed to display this concept with a laser-pen for the instructors out there that are reading this.
So a few minutes of exposure to room light will not fog your radiograph, and exposure to high-intensity laser or fluorescent light will actually decrease density on your final image. The most common ways you will see fog on your image receptor is if you have your image plate in the x-ray room during an exposure, leaving it exposed to scatter radiation (click here to learn about CR Image Plate Response to Scatter), or if you neglect to erase your image plates over long periods of not being used - most manufacturers recommend erasing the plates daily, or at least every 48 hours.
Additional posts in this series:
CR Myths #1 - An Increase in Exposure Creates an Increase in Density
CR Myths #2 - Radiographic Image Contrast is Controlled by kVp
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