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Imaging the extracellular pH of tumors by MRI after injection of a single cocktail of T 1 and T 2 contrast agents
Author(s) -
Martinez Gary V.,
Zhang Xiaomeng,
GarcíaMartín María L.,
Morse David L.,
Woods Mark,
Sherry A. Dean,
Gillies Robert J.
Publication year - 2011
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.1701
Subject(s) - gadolinium , chemistry , diethylenetriaminepentaacetic acid , nuclear magnetic resonance , in vivo , extracellular , lanthanide , spin–lattice relaxation , relaxation (psychology) , chelation , analytical chemistry (journal) , pentetic acid , relaxometry , magnetic resonance imaging , nuclear medicine , spin echo , chromatography , ion , inorganic chemistry , medicine , biochemistry , physics , microbiology and biotechnology , organic chemistry , nuclear quadrupole resonance , biology , radiology
The extracellular pH (pH e ) of solid tumors is acidic, and there is evidence that an acidic pH e is related to invasiveness. Herein, we describe an MRI single‐infusion method to measure pH e in gliomas using a cocktail of contrast agents (CAs). The cocktail contained gadolinium–1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraaminophosphonate (GdDOTA‐4AmP) and dysprosium–1,4,7,10‐tetraazacyclododecane‐ N , N ′, N ′′, N ′′′‐tetrakis(methylenephosphonic acid) (DyDOTP), whose effects on relaxation are sensitive and insensitive to pH, respectively. The Gd‐CA dominated the spin–lattice relaxivity Δ R 1 , whereas the Dy‐CA dominated the spin–spin relaxivity Δ R 2 *. The Δ R 2 * effects were used to determine the pixel‐wise concentration of [Dy] which, in turn, was used to calculate a value for [Gd] concentration. This value was used to convert Δ R 1 values to the molar relaxivity Δ r 1 and, hence, pH e maps. The development of the method involved in vivo calibration and measurements in a rat brain glioma model. The calibration phase consisted of determining a quantitative relationship between Δ R 1 and Δ R 2 * induced by the two pH‐independent CAs, gadolinium–diethylenetriaminepentaacetic acid (GdDTPA) and DyDOTP, using echo planar spectroscopic imaging (EPSI) and T 1 ‐weighted images. The intensities and linewidths of the water peaks in EPSI images were affected by CA and were used to follow the pharmacokinetics. These data showed a linear relationship between inner‐ and outer‐sphere relaxation rate constants that were used for CA concentration determination. Nonlinearity in the slope of the relationship was observed and ascribed to variations in vascular permeability. In the pH e measurement phase, GdDOTA‐4AmP was infused instead of GdDTPA, and relaxivities were obtained through the combination of interleaved T 1 ‐weighted images ( R 1 ) and EPSI for Δ R 2 *. The resulting r 1 values yielded pH e maps with high spatial resolution. Copyright © 2011 John Wiley & Sons, Ltd.