Gd retention co-efficients. More than biphasic or triphasic Gd elimination patterns.

Prior reports have described proposed biphasic and triphasic elimination patterns for Gd from the body. These have focused on the attributes of the GBCA agents themselves. Macrocyclic GBCAs for example having a faster and more simple elimination pattern than linear.

In this posting I synthesize concepts I have previously written on. Characteristics of the individual also are critical: the varying retention coefficients of different organ and tissue spaces. In broad terms I often have written that bone retention is more durable than soft tissue, including skin, brain, liver, other organs. Likely many different spaces are involved. Each organ likely has its own retention coefficient (also altered by disease) so liver, different from brain, different from skin, etc. More importantly even within organs, localization in a perivascular location has lower retention than deep extracellular matrix (ECM). To the extent that Gd is intracellular, this is more durable than extracellular. Gd in fibrosis is likely similar in durability to bone, as a major separate disease centered reservoir.

A direct analogy to this is how the evaluation of radiation measurement from x-rays and gamma-rays. has evolved. In early days of Radiology, measurement considered just dose of the emitted energy forms (measured in RADs), to in modern times the evaluation of radiation experienced by the tissues (milliSieverts), with each organs system considered separately in advanced analysis.

Using this, then there is likely not just a bi- or triphasic elimination pattern (focused on the agent) but also combined with host tissue retention coefficients. In normal and diseased states.

So elimination is not really just triphasic, but centiphasic (100) or more.

All that considered I always return to focusing on the forest, and do not get caught up by the 100 different trees. Le Chatelier's principle is critical to managing the different reservoirs' retentions. So I treat the forest, not individual trees, but recognize that those trees exist. The trees however may effect the nuances of treatment.

If Gd is making a person sick, the treatment is to remove the responsible substance, regardless if removal is centiphasic.