The development of a pH-sensitive contrast agent for NMR 1H imaging.
Fe(III)meso-tetra(4-sulfonatophenyl)porphine (Fe-TPPS4) has been investigated as a potential pH-sensitive nuclear magnetic resonance (NMR) proton image contrast agent. Relaxation rates (1/T1 and 1/T2) of water protons were measured as a function of pH and concentration of Fe-TPPS4 in phosphate-buffered isotonic saline. Transverse relaxation rates (1/T2) did not change appreciably with pH above 6.0. Longitudinal relaxation rates (1/T1) increased significantly between pH 7.75 and 5.75. This effect was more pronounced with the increasing concentration of Fe-TPPS4 from 0.1 to 1.5 mM and is attributed to a pH-dependent equilibrium between the high-spin (S = 5/2) Fe-TPPS4 monomer at low pH and the antiferromagnetically coupled mu-oxodimer O-(FeTPPS4)2 at high pH. The efficacy of this pH-dependent contrast agent is demonstrated in vitro.
Department of Neurology, Henry Ford Hospital, Detroit, Michigan 48202.
J A
JA
Helpern
J C
JC
Curtis
D
D
Hearshen
M B
MB
Smith
K M
KM
Welch
D003287:Contrast Media; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging; D008961:Models, Structural; D011166:Porphyrins
D003287:Contrast Media; D011166:Porphyrins; C016136:tetraphenylporphine sulfonate