How is the brain survival mechanism of localization for Tc DTPA primarily achieved?

• A. Active transport through neurons
• B. Passive diffusion due to disrupted blood-brain barrier
• C. Filtration from the bloodstream
• D. Compartmentalization

Answer: (B)

The mechanism by which technetium (Tc) DTPA localizes in the brain primarily occurs through passive diffusion, especially in situations where the blood-brain barrier is disrupted. This is particularly relevant in certain medical imaging scenarios, such as in cases of neurological disease or injury, where the integrity of the blood-brain barrier is compromised.

When the blood-brain barrier is disrupted, it allows for substances like Tc DTPA to passively diffuse into brain tissue more easily than they would under normal conditions. This diffusion is driven by a concentration gradient, where the concentration of Tc DTPA inside the brain will equilibrate with its concentration in the bloodstream. The localization observed with Tc DTPA can thus be attributed to this phenomenon of passive diffusion facilitated by the altered permeability of the blood-brain barrier.

In contrast, active transport is not the primary mechanism for Tc DTPA localization, as this radiopharmaceutical does not utilize energy-dependent transport systems typically found in neurons. Filtration from the bloodstream is more descriptive of renal function rather than central nervous system uptake. Compartmentalization refers to the distribution within different compartments of the body and is less relevant to the specific localization of this agent in brain tissue under the conditions described.