Magnetic Resonance Relaxation Times T1 Research Articles

Dual-Frequency Proton Spin Relaxation Measurements on Tissues From Normal and Tumor-Bearing Mice

Measurements of pulsed nuclear magnetic resonance relaxation times T1 and T2 were made at 2.7 MHz and 15 MHz on water protons in liver, kidney, spleen, muscle, and brain tissue from normal A.SW mice, and in the same tissues and tumors from A.SW mice developing MSWBS tumors (an ascites sarcoma) following dorsal sc implantation of tumor fragments. The measurement precision obtained from improved spectrometer design made it possible to show that T1 and T2 in all tissues except brain were increased by the presence of the tumor in the animal. The responses exhibited by T1 and T2 in liver and kidney were proportional to the size of the tumor. The smaller responses shown by T1 in spleen (15 MHz) and T1 and T2 in muscle (2.7 MHz) also showed a significant correlation with tumor size. The relaxation times for tumor (T1 at 2.7 MHz, T2 at 2.7 and 15 MHz) showed a significant negative correlation with tumor size: The times decreased as tumor size increased. The results were analyzed by use of the two-phase fast exchange model and were consistent with the effects expected if tissue water content increased and tumor water content decreased as tumor size increased. The analysis indicated that the effects arose primarily through changes in b, the fraction of water bound to fast exchange sites on the protein, with important modifications from changes in the correlation times Tc and Tm;Tr controlled the frequency that must be chosen for specific diagnostic applications.

Selfdiffusion studies in sodium iodide single crystals by NMR relaxation. (Ionic conduction)

Measurements of the nuclear magnetic resonance relaxation times T1, T1p, and T2 made on pure and Cd2+ doped single crystals of NaI, over a temperature range 385 to 900 K, are reported. The process responsible for relaxation is Na+ selfdiffusion. The cation migration enthalpy is found to be 0.45+or-0.02 eV, and the activation energy for the intrinsic diffusion process is found to be 1.6+or-0.05 eV, in good agreement with ionic conductivity and tracer selfdiffusion studies. An expression for T1p due to dipolar coupling between unlike spins is obtained, and is used to relate the T1p measurements to the sodium ion jump frequency. A comparison of the sodium ion jump frequency obtained from the relaxation time measurements, and from ionic conductivity measurements is made. This indicates that at high temperatures diffusion takes place predominantly via cation single vacancies. At lower temperatures impurity-vacancy complexes contribute to the relaxation indicating that the free and complexed vacancies have similar diffusion rates. At the lowest temperatures impurity precipitation takes place and the total concentration of Cd2+ as a function of temperature is calculated from the T1p measurements, and is in good agreement with that calculated from conductivity studies.

BINDING OF MN2+ TO NUCLEIC ACIDS.

Measurements of the nuclear magnetic resonance relaxation times T1 and T2 of the water protons in aqueous solutions of nucleic acids and magnetic metal ions allow one to determine details about the metal-ion binding. When Mn2+ is bound, the rotation of its hydration sphere becomes slower, so that its effectiveness in reducing the proton T1 from its value in pure water is enhanced. This relaxation enhancement has been measured for Mn2+ bound to DNA, RNA, synthetic polynucleotides, and E. coli ribosomes. Compared to water as unity, the enhancement factors range from 3.7 for polyuridylic acid to 16.7 for polyadenylic acid. The equilibrium constants for binding, and the concentration of binding sites have been calculated from the dependence of enhancement upon Mn2+ concentration.

Proton Magnetic Resonance in LiquidIso-Butyl Bromide

Proton magnetic resonance relaxation times T1 and T2 in liquid iso-butyl bromide [(CH3)2 CHCH2Br] have been measured at 21.5 × 106 c/s over the temperature range 110°K to 330°K. The results, together with others for T2 down to 90°K, are interpreted in terms of molecular motion of the molecule as a whole and of the methyl groups in it. This extremely wide temperature range without phase transitions allows a severe test of the validity of theories of nuclear relaxation in molecular substances. The correlation frequency as a function of temperature which ranges from 102c/s to 1011c/s is deduced and a remarkably good correlation with dielectric loss measurements is found. A distribution of correlation frequenices of molecular reorientation at low temperatures is confirmed and the effect of the more rapid reorientation of one methyl group is found. This is a case in which the nuclear resonance parameters are controlled principally by the motion of the molecule as a whole but are modified by an internal molecular motion which is considerably faster.

Frequency Dependence of Proton Spin Relaxation in Aqueous Solutions of Paramagnetic Ions

Magnetic resonance relaxation times T1 and T2 were measured for protons in aqueous solutions of Cr(H2O)6+++, Mn(H2O)x++, Co(H2O)x++, and Nd(H2O)x++ in the frequency range 2.7 to 28.7 Mc/sec. T1 was observed to decrease with decreasing frequency for the first two ions, but not the last two, while T2 was essentially constant for each ion. The abnormally large values of T1/T2 which have been previously reported appear as a result of the effect at high frequencies. Those observations are interpreted in terms of a theoretical model of the magnetic interaction between ion and proton in which a random thermal process is presumed to occur with a characteristic correlation time, τe, of 10—8 to 10—11 sec.