Ideas and Comments About New Virtual Grids
From someone who knows

With CR and DR, one of the biggest reasons for image artifacts comes from grids and improper alignment and grid cut-off. Essentially, the manufacturers of DR products want the grids out of the exposure process to lessen the artifacts issues. This problem is even more pronounced as techniques continue to drop with faster RS values of the new DR detectors (600-800 speed). Less mAs means less mAs to cover up exposure technique errors. Even a grid-cut-off of 10-15% can have damaging effects upon image quality in terms of artifacts and noise. In the old F/S screen days, a 10-15% degree of grid-cut-off was not seen, many times. because there was enough exposure to the image to cover up the cut-off.

There are several vendors of this technology. Philips created the first one about 4-5 years ago and marketed it as their “SkyFlow”product.  Carestream calls their product SmartGrid, Canon calls theirs Scatter Correction, Konica-Intelligent Grid, Fuji-Virtual Grid.

All are intended to do the same thing. Create a grid-like image when no grid was used.

These products fall into a new category known as: grid-replacement software or grid-substitution software. This is not to be confused with grid-suppression software which is designed to remove objectionable grid lines from the image.

The grid substitution software is indeed software and works as a post-processing feature using the equalized histogram that has been re-scaled.

It is a frequency processing process much like look-up-tables work to give the image a customized look.

The vendor community will likely not agree on a standardized “look” and an acceptable grid ratio. Currently, Konica and their Intelligent Grid software emulates a 6:1 grid ratio.

After several conversations with a couple of vendors as to the effectiveness of this software they indicated that is seems to work best for chests but is not well suited for all abdomen images. It’s to be expected that this will change and improve in the years ahead, as they get better with their software platforms and database of acceptable image appearances. This can be a lengthy and arduous process.

For more discussion of this new feature reference the 6th ed of Carlton, Adler, and Balac’s text, Principles of Radiographic Imaging: An Art and a Science.

Randy Griswold, M.P.A., RTR

Radiology Program Faculty in Green Bay, WI