Hi Wendy,

Exposure Index with some eqipment can change by cropping the image. I question the validity and sensitivity of that system in quantifying the energy input for a given image, but obviously this example indicates some irregularity in the system.

DR transmits its signal upon completion of the exposure, so I assume you are talking about CR using a portable imaging plate. There are some differences in the CR Technologies across the manufacturers. They are in essence devices that convert X-Rays to stored electron energy levels within the crystal lattice, or Pixels, of the phosphor which covers the Plate.

The phosphor is scanned by a laser in a very fine grid pattern across the entire surface. Like the "gun" in a cathode ray tube type TV, the laser hits every Pixel which gives of a flash of light proportional to the X-Ray energy absorbed by it. Later technologies function more like a Photo Copier.

The position and intensity measurements are compiled to produce the image data we then view on the monitors after a whole lot more post processing, which is automatic.

Some "fading" or leakage of electron energy is possible and the time between Exposure and Reading can concievably result in loss of Data. But HOW MUCH?????

Try this out for yourself. Expose a plate at a fixed FFD, kV, mAs through a stepwedge or the like.

Process it immediately. Same plate, take another exposure and process it in 10 minutes. Repeat the process for 20, 30 & 40 minutes. Or take the exposure and set the Imaging Plate aside, where no-one will use it, note the time and process it in an hour or 2.

You may be able to visually compare the images or overlay a histogram across matched areas and compare.

This may also be a valid QA exercise to judge the aging and deterioration of the Imaging Plates to determine when to replace them.

Regards

Gary Allbutt

3  out of 3 found this valuable. Do you find this valuable? Do you?