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R 1 correction in amide proton transfer imaging: indication of the influence of transcytolemmal water exchange on CEST measurements
Author(s) -
Li Hua,
Li Ke,
Zhang XiaoYong,
Jiang Xiaoyu,
Zu Zhongliang,
Zaiss Moritz,
Gochberg Daniel F.,
Gore John C.,
Xu Junzhong
Publication year - 2015
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.3428
Subject(s) - magnetization transfer , nuclear magnetic resonance , in vivo , chemistry , relaxation (psychology) , spin–lattice relaxation , proton , biophysics , materials science , magnetic resonance imaging , physics , biology , radiology , medicine , microbiology and biotechnology , quantum mechanics , neuroscience , nuclear quadrupole resonance
Amide proton transfer (APT) imaging may potentially detect mobile proteins/peptides non‐invasively in vivo , but its specificity may be reduced by contamination from other confounding effects such as asymmetry of non‐specific magnetization transfer (MT) effects and spin–lattice relaxation with rate R 1 (=1/ T 1 ). Previously reported spillover, MT and R 1 correction methods were based on a two‐pool model, in which the existence of multiple water compartments with heterogeneous relaxation properties in real tissues was ignored. Such simple models may not adequately represent real tissues, and thus such corrections may be unreliable. The current study investigated the effectiveness and accuracy of correcting for R 1 in APT imaging via simulations and in vivo experiments using tumor‐bearing rats subjected to serial injections of Gd‐DTPA that produced different tissue R 1 values in regions of blood–brain‐barrier breakdown. The results suggest that conventional measurements of APT contrast (such as APT* and MTR asym ) may be significantly contaminated by R 1 variations, while the R 1 ‐corrected metric AREX* was found to be relatively unaffected by R 1 changes over a broad range (0.4–1 Hz). Our results confirm the importance of correcting for spin–lattice relaxation effects in quantitative APT imaging, and demonstrate the reliability of using the observed tissue R 1 for corrections to obtain more specific and accurate measurements of APT contrast in vivo . The results also indicate that, due to relatively fast transcytolemmal water exchange, the influence of intra‐ and extracellular water compartments on CEST measurements with seconds long saturation time may be ignored in tumors. Copyright © 2015 John Wiley & Sons, Ltd.