X-ray Fluorescence

X-ray fluorescence is a technique that had been developed and used to detect the presence of lead in bones. More recently this technique has been described for Gadolinium, another heavy metal that also goes to bone. All research on GDD is to be commended.

There are a couple of critical considerations though regarding this technique:

1. Heteogeneity of deposition between cortical and trabecullar bone has been desxcribed with lead, and there is also variability between bones, and various physiologic states can have an impact. All this would be true with Gd.

2. With lead, the question that x-ray fluorescence answers, is lead present? This is of value where uncertainty of lead intake occurs. This however is not the case with Gd, unlike with lead, where even whether lead has been ingested is uncertain, we know with Gd that Gd is present, because we know if the patient has had a GBCA injection, and we even know the dose. So we have controlled knowledge of Gd, which is never the case with environmental exposures to heavy metals, such as lead.

3. Many patients with GDD have extremely little Gd left in their body. Examples are disease development after a single administration of a macrocyclic agent such as Dotarem or Gadavist, where the amount of Gd deposited in bone is likely infinitesimally small, and beneath the detection limit of the modality. The basis of the disease is primarily the autoimmune type disease that has been elicited by the GBCA, rather than the amount of Gd left behind.

4. X-ray fluorescence could be very helpful in the future if it can separately isolate different heavy metals, and if it can be used as a measuring tool to determine how much Gd has been removed from bone (for example following chelation).

In my opinion, x-ray fluorescence is an interesting tool, but as currently used does not seem to show any value for sufferers. There may be future applicability as a noninvasive tool to see how much Gd is being removed from bone.