Upgrading from a Prodigy to Prodigy Advance
Submitted by bbdg on Mon, 10/22/2007 - 10:14.
Dear John,
We updated from a GE Lunar prodigy to GE Lunar prodigy advance. Our phantoms before and after the change are within 1%. Now what? Can we compare our new to our old scans, using a new precision analysis to determine LSC, or should we use the old LSC, or do we need to adjust the new scan values based on the phantom variation?
Thanks, LK, M.D.?
my reply
The Prodigy and Prodigy Advance are basically the same with respect to hardware and analysis of the spine and hip.
The straight answer from the ISCD would be that if you perform phantom scans, and your agreement is within 1% you can upload the old database to the Advance and go on your merry way doing quantitative comparisons between scans taken on the old and new system.
The LSC used would be the same as your old since the technology didn’t change and thus you wouldn't expect a change in the precision. We have found this not to be true in some cases. We are preparing a manuscript comparing two seemingly identical technologies where the LSC dramatically went up.
For your case here are the important details.
1. You say a 1% difference between phantom results. Was this on the lunar QC spine phantom L1-L4 average? Was the difference consistent between each vertebrae? Let's say you observed a 0.5% difference in the average of 10 QC phantom scans for the L1-L4 BMD between the old and new system. And, that each of the vertebrae have a 0.5% difference, And that the phantom precision is similar on the new system as the old system, say within 0.001 g/cm2. And you reanalyzed 10 patients taken on the old system with the new system software and the results were unchanged. Then, I would say, use the same LSC. If you observe differences by vertebral level, that would point towards a nonlinearity that either means you need to get the unit fixed or do an invivo cross calibration.
2. If you do see a systematic difference between the old and new scanner on the phantom, you should have this removed by the service tech. Otherwise, it will affect your comparisons between old and new system scans.
Ok, I hope this helps John