title: Impact of transvascular and cellular-interstitial water exchange on dynamic contrast-enhanced magnetic resonance imaging estimates of blood to tissue transfer constant and blood plasma volume.
abstract: OBJECTIVE
  To examine the effect of transvascular (k(be)) and cellular-interstitial water protons exchange (k(ie)) in estimates of the blood-to-tissue contrast agent transfer rate constant (K(trans)), interstitial volume fraction (v(e)), and blood plasma volume fraction (v(p)) using a full three-site two exchange (3S2X) model.
  
  
  METHODS
  Using the Bloch-McConnell equations, magnetic resonance imaging (MRI) signal arising from a 3S2X system was derived for the T(1)-weighted spoiled gradient-recalled echo (SPGR) pulse sequence. To model the effects of k(be) and k(ie) on estimates of R(1), the MRI-measured arterial input function, the different sets of values of kinetic parameters: K(trans), v(e), and v(p) and water protons exchange rates, k(be) and k(ie), were used. To calculate the tissue water protons R(1), the signal evolving from a 3S2X model was set to a monoexponential function. By comparing the estimated K(trans), v(e), and v(p) with their simulated model truth values, the impact of k(be) and k(ie) on K(trans), v(e), and v(p) was evaluated.
  
  
  RESULTS
  v(p) was strongly underestimated and K(trans) and v(e) were much less influenced by k(be), when k(ie) was held constant. When k(be) was held constant, the k(ie) had a significant effect on K(trans) and v(e) and less effect on v(p).
  
  
  CONCLUSIONS
  The full 3S2X model allows accurate estimation of K(trans), v(e), and v(p) and rates of water proton exchange.
authors.affiliation: Department of Radiology, Molecular Imaging Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. Ramesh.Paudyal@uphs.upenn.edu
authors.forename: Ramesh
authors.initials: R
authors.lastname: Paudyal
authors.forename: Harish
authors.initials: H
authors.lastname: Poptani
authors.forename: Kejia
authors.initials: K
authors.lastname: Cai
authors.forename: Rong
authors.initials: R
authors.lastname: Zhou
authors.forename: Jerry D
authors.initials: JD
authors.lastname: Glickson
mesh_terms: D001158:Arteries / Q000378:metabolism*; D001811:Blood Volume Determination / Q000379:methods*; D001834:Body Water / Q000378:metabolism*; D003198:Computer Simulation; D003287:Contrast Media / Q000493:pharmacokinetics; D019786:Gadolinium DTPA / Q000493:pharmacokinetics*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008955:Models, Cardiovascular; D010953:Plasma Volume
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA