McMaster technology takes stock of valuable medical metal
An innovative device developed at McMaster University could answer some of the key questions that have been fueling controversy amongst radiologists about the safety of some of the world’s most widely used and effective imaging contrast agents.
This dispute centres on the rare earth metal gadolinium, whose paramagnetic properties have made it a workhorse of medical imaging. When combined with chelates and injected into the bloodstream, it generates magnetic resonance imaging data for a picture of an individual’s heart function as well as highlighting regions where abnormal tissue growth — usually cancer — are occurring.
Surgeons regularly rely on gadolinium-based drugs for detailed pre-operative assessments of a patient’s condition and worldwide hundreds of millions of people have undergone such diagnostic treatments. In spite of this longstanding record of safe and highly beneficial use, about a decade ago radiologists began to link these drugs to the deaths of some patients, primarily due to kidney problems. This problem has since been eliminated by adding a preliminary test of an individual’s kidney function to screen candidates for the procedure.
What persisted, however, was a small cohort of people who suffered a variety of other health problems that appear to be related to gadolinium, although the specific link to the metal remains unclear. A group of about 145 self-identified subjects have made public statements about the issue, which took on Hollywood proportions last fall, when Gena Norris, wife of action film star Chuck Norris, filed a lawsuit against 11 companies that manufacture gadolinium drugs. Her claim describes a litany of ailments, including abdominal pain, tremors, weak muscles, low body temperature and weight and hair loss.
How those symptoms may be related to the presence of gadolinium remains an open question, one that continues to nag Fiona McNeill, a professor in McMaster's Department of Radiation Science.
“There’s some information but really not enough to connect those dots,” she says.
She has spent much of her career developing ways of tracking all manner of toxins that can plague the human body, from chlorides and cobalt to aluminum and lead. “If it has the potential to poison you I’m interested in it and we build devices to study that,” she says.
The goal in each case has been to pin down precisely the amounts of these agents that can be found in the body. For gadolinium, clinicians had not been expecting any amount at all, since the metal should be completely flushed out of a patient’s system with the chelates.
“But we’ve started to realize that there is a small percentage that is retained,” she points out. “This implies that the gadolinium is detaching from the chelate.”
Michelle Lord, a doctoral student working with McNeill, designed an instrument to measure the amount of gadolinium in bone. This invention combines X-ray fluorescence detectors with a gamma ray source, all pointed in the same direction. When this array is mounted next to a target, such as a subject’s leg, the gamma rays activate signals from any gadolinium in the bone, which are then captured by the X-ray detector.
The equipment package is portable and Lord has calibrated it to take standardized measurements in less than an hour, with an accompanying radiation dose that is about 100 times less than a typical chest X-ray. She and McNeill introduced this benign, non-invasive approach in a recent article for the journal Radiology, where they expressed their hope that it could lead a practical means of understanding what is happening with people who appear to react negatively to gadolinium drugs.
According to McNeill, that understanding will start with the basic data about who has this metal in their body and how much, then correlate that information with other factors, such as genetic markers or some other health condition.
“My goal would be that we find a way to screen out those people who are potentially at risk,” she concludes.