Theory of heterogeneous relaxation in compartmentalized tissues.
A new model of compartmentalized relaxation--that which occurs for spins (protons) exchanging between compartments of different relaxation rates--is presented. This model generalizes previous ones by allowing spatially dependent relaxation within compartments. Solutions for the diffusion-Bloch equations are found via an efficient numerical technique known as the generalized moment expansion, and they agree well with the solutions to the standard two-site exchange equations (TSEE) for many typical situations. Specific models are developed for liposomes, red blood cells, capillaries, and arteries with respect to applied contrast agents. A parameter derived from tissue characteristics is introduced to predict the nature of the solutions. A new method is proposed for using contrast agents to detect capillaries, which exploits their high surface-to-volume ratio relative to the other elements of the vasculature.
Barsky
D
D
Department of Biophysics, University of Illinois at Urbana/Champaign, Urbana, USA.
Pütz
B
B
Schulten
K
K
D001158:Arteries; D002196:Capillaries; D003287:Contrast Media; D004912:Erythrocytes; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological
D003287:Contrast Media; D008081:Liposomes