PURPOSE: 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. MATERIALS AND 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). CONCLUSION: The full 3S2X model allows accurate estimation of K(trans), v(e), and v(p) and rates of water proton exchange.
PURPOSE: 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. MATERIALS AND 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). CONCLUSION: The full 3S2X model allows accurate estimation of K(trans), v(e), and v(p) and rates of water proton exchange.
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