MRI assessment of BBB permeability

Question 1

dynamic imaging of tracer

Answer 1

1. Inject marker
2. Tract marker over time using MRI
3. Assess BBB disruption location

Question 2

PET and BBB

Answer 2

• Use of radiopharmacon (radiotracer) = radioactive nuclide + pharmacon
• Detection of receptor binding, cell internalisation, i.e. active transport

Question 3

CT and BBB

Answer 3

• Use of iodinated (I) contrast agent to attenuate x-rays
• Detection of tight-junction breakdown, BBB leakage (passive paracellular transport)

Question 4

MRI and BBB

Answer 4

• Use of gadolinium (Gd) contrast agent to enhance water signal
• Detection of tight-junction breakdown, BBB leakage(passive paracellular transport)
• Measured leakage rate is the product of permeability (P) and microvascular surface area (S), and may be dependent on blood flow (F)
• Measured leakage is subtle and noisy

Question 5

MRI contrast - BBB

Answer 5

• Gadolinium is paramagnetic, thus changes locally the magnetic field
• Chelate means “claw” the chelate surrounds an ion (make a cage)
• A chelate of gadolinium occupies all available space around the ion, except one
• Water molecules exchange in and out of that one spot
• When in that spot, the spins have an extremely short T1, which accelerates the overall relaxation rate, shortening T1 of tissue –> high visibility
• At high doses also shortens T2 but T1 predominates
• Relation between MRI signal and gado concentration [Gd] is non-linear in general for low concentrations it is nearly linear