Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 53, Issue 2, Pages 282-293Publisher
WILEY
DOI: 10.1002/mrm.20340
Keywords
vascular permeability; MRI; water exchange; dynamic contrast; blood-brain barrier; enhancement; magnetic resonance contrast agent
Funding
- NCI NIH HHS [2PO1 CA59827, 1R21CA96965-01] Funding Source: Medline
- NHLBI NIH HHS [1R01 HL70023-01A1] Funding Source: Medline
- NINDS NIH HHS [1R21 NS42742, 1R01-NS38540, 1PO1-NS 23393] Funding Source: Medline
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Water exchange across capillary walls couples intra- and extravascular (IV-EV) protons and their magnetization. A bolus i.v. injection of an extracellular MRI contrast agent (MRCA) causes a large increase in the spin-lattice relaxation rate, R-1, of water protons in the plasma and blood cells within the capillaries and changes the effective relaxation rate R-1eff in tissue via IV-EV water exchange. An analysis of the effect of plasma-red cell and IV-EV water exchange on the MRI-measured influx and permeability of capillaries to the MRCA is presented and focused on the brain and the blood-brain barrier. The effect of arrival of a bolus of an MRCA in the capillary on the relaxation rate R-1eff in tissue via IV-EV water exchange occurs more rapidly than the MRCA uptake in tissue and can dominate the initial time curve of the R-1eff change before the MRCA uptake in tissue becomes significant. This raises the possibility that (tissue dependent) IV-EV rate of exchange of water molecules can affect estimates of MRCA transfer constant. We demonstrate that an approach that considers IV-EV water exchange and uses the theoretical model of blood-brain tracer distribution developed by Patlak et al. (J Cereb Blood Flow Metab 1983;3:1-7) can lead to an accurate estimate of the MRI-determined influx rate constant of the MRCA and to an underestimation of the tissue blood volume. (C) 2005 Wiley-Liss, Inc.
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