PET-CT vs PET-MRI

Mayo in Rochester is doing a study of PET/MRI, comparing it with PET/CT for myeloma patients.  A standard full-body PET/CT gives a patient one of the largest doses of radiation of all the imaging procedures, but most of this is due to the CT, not the PET.  The CT is required because the PET doesn’t by itself provide enough information to determine where the bright spots from the PET are actually located.  PET doesn’t distinguish between bone and soft tissue – it just sees the radioactive sugar molecules that have been gobbled up by active cancer cells.

March 2015 – PET/MRI scanner
arrives at Charlton Building

MRI can see the bones and soft tissue, thereby providing a reference for the PET’s bright spots.  While CT uses X-ray technology to make its image, MRI does not, and contributes no radiation risk.  It’s noisy and maybe takes a little longer, but safer.

I don’t want to make too much of the risk of a PET/CT – some authorities would say that it increases the risk of a later cancer by at most 1 chance in 500 or 1000.  Contrast this with the natural incidence of fatal cancer in the U.S. population, about 1 chance in 5, so one CT or PET/CT is down in the noise.  Repeated CT’s add up, though, so Mayo seems to limit PET/CT’s to no more than one every six months, which makes it difficult to follow a patient’s myeloma.  Hopefully, PET/MRI can shorten that interval.

I’ve been waiting for months now to find out whether the lesion in my T5 is responding to the current study regimen, so in about two weeks I will participate in the PET/CT – PET/MRI comparison study.  I really want this to work, for my own sake and for all other myeloma patients.