by
Gus Iversen, Editor in Chief | March 11, 2016
From the March 2016 issue of HealthCare Business News magazine
So why not just swap out linear agents for macrocyclic agents? Unfortunately, that solution oversimplifies the problem. Radiologists must also factor in the relaxivity of an agent — which refers to how much must be administered to adequately produce the desired visual contrast.
“There is no agent, I believe, that is immune to having some retention in the body, it’s just not the way science or math works,“ says Kanal, “but there are significant differences in the amount or rate that they accumulate in a human after a certain number of doses of these agents.” As for the clinical significance of gadolinium accumulation? “As of today we simply do not know,” says Kanal.
Impacting utilizaion patterns
Kanal says his work as an emergency neuroradiology specialist has been drastically impacted by the knowledge that gadolinium can accumulate in the brain. “Every single day of my professional life I now find myself canceling studies that are requested with contrast where I don’t believe or agree that contrast is indicated,” he says.
The number of gadolinium-enhanced MR exams being conducted — both nationally and internationally — is decreasing, he says. When it is being administered, it is sometimes being done at a lower dose, and often affects the choice or what type/brand of agent is to be administered. “Which agents people are using is also changing,” says Kanal. “Just like we saw with NSF, there were massive changes with utilization patterns and which agents were used for what patients. We’re seeing people switching again based on the potential or theoretical concern of retaining more gadolinium in the patient’s bodies with some agents than with others.” As long as there are no good alternatives to gadolinium, however, it remains a vital part of the radiologist’s toolkit and Kanal doesn’t expect that to change any time soon.
More than meets the eye
The gadolinium that we can visualize is visible because it is interacting with water molecules in the brain, thereby shortening the tissue T1 and brightening its signal to become bright. According to Kanal, “That kind of gadolinium is almost across the board water soluble, but we do know there is also water-insoluble gadolinium in biopsies and autopsies — which very likely would not be visible on an MR image.” That means all the data that is being collected from MR images is potentially overlooking an undetectable quantity of retained tissue gadolinium that simply does not register in the scan. Through autopsies and biopsies, Kanal says work is being done to try and shed some light on that possibility.
“And we don’t even know what form it will be in,” says Kanal. “Is it in the form in which it had initially been injected? Did it disassociate and then re-form?” Further, accumulation in the brain is only part of this issue. It has been known for over a decade that gadolinium from at least some GBCAs is retained in the bone of patient recipients, and that the amount retained there is greater for at least some of the linear agents than from at least some of the macrocyclic agents. For now, according to Kanal, there are simply more questions than answers. Defining the medical implications of gadolinium accumulation — if indeed there are any — is a work in progress that researchers continue to chip away at every day.
Back to HCB News
