DXA after MRI and CT
Submitted by bbdg on Fri, 10/26/2007 - 11:57.
Dear Dr.
We have some discussions going on in the hospital ... about the influence of mri-scans on subsequent dxa-scans.
Do you have any idea or do you know some manuscripts that can clear out if there is any influence of performing a mri-scan immediately followed by a dxa-scan?
And we have the same discussing about the influence of qct-scans (with > or without contrast) on dxa-scan results?
With best regards,
H B, MD
Wait 10-14 days...
Dear Dr B,
Contrast agents for MRI, such as Gadolinium, have a very high atomic number and density relative to other soft tissue. To a DXA system, it looks like bone when at full concentration. Barium contrast for CT also has a very high atomic number and is dense at full concentration. Any residual concentration of these contrasts in the DXA scan regions of interests will cause artifacts. A well-trained DXA technologist will rejetct the scan for reasons of having untrustworthy accuracy.
At full concentration, the contrast in the blood vessels superimposes on the bone in the projectional image causing an increase in bone density in that region. At lower concentrations, it can make the soft tissue look leaner and account too much attenuation to the total soft tissue, reducing the DXA measure of bone density.
Therefore, one should wait about 5-7 half-lives of the contrasts in the body, but most centers have a general guideline of waiting 10-14 days after any radioisotope or contrast procedure to make the processing of patients easier.