A possible improvement in the resolution of proton spin relaxation for the study of cancer at low frequency.

Available results indicate that the water proton spin-lattice relaxation time resolution, defined as [T1(tumorous) -T1(healthy)]/T1(tumorous), may increase if relaxation time is measured at 2 rather than at 30 MHz.

Proton spin-spin relaxation study of molecular dynamics and proteoglycan hydration in articular cartilage.

Spin-spin relaxation of proton magnetization in natural and deuterated articular cartilage is reported over a range of hydration. Information about macromolecular dynamics is deduced and a hydration stabilized macromolecular regime identified. There is good correspondence between NMR results and cartilage stoichiometry. A new measure for hydration of proteoglycans is found.

Design of a high-power NMR probe for low-temperature studies.

A low-temperature, high-power NMR probe head design is described which eliminates the problem of electric arc discharge commonly experienced during radiofrequency pulse cycling in a helium environment. A polychlorotrifluoroethylene (Kel-F) coil former, fitted with a solenoid coil, is heat-shrunk onto stainless-steel flanges and spot-welded inside a stainless-steel probe head assembly connected to a hollow coaxial transmission-line probe shaft. By this means, the sample coil and all high-voltage elements can effectively be isolated in a vacuum, while at the same time permitting good thermal contact between the sample and cryogenic gas. This design was used in NMR studies in the 4.6 K < or = T < or = 77 K temperature range for RF pulse durations < or = 50 ms (and longer for low RF amplitudes) and amplitudes up to approximately 60 G.

Spectroscopy from proton spin magnetization evolution in their rotating frame: A study of small tunneling splitting.

The time evolution of proton Zeeman magnetization in the rotating frame at exact resonance, omega = omega(0), is evaluated for an isolated tunneling methyl group CH(3). The Fourier transform of this evolution in time is calculated and both its real and imaginary components are presented. It is shown that the real component does not depend significantly on the strength of the preparation pulse when the tunneling splitting of the methyl rotator ground state is less than 100 kHz. It is also found that the imaginary component of the transform is inversely proportional to the strength of the preparation RF pulse. This is a consequence of the partial dephasing of proton spins during the preparation pulse. The results of the calculation compare well with the experimental spectra of CH(3)CD(2)I.

Tunneling spectroscopy from magnetization evolution in a tilted rotating frame of nuclear spins.

The time evolution of the proton Zeeman magnetization in the rotating frame at the magic angle theta(M) = cos(-1)(1/3) is calculated for an isolated tunneling methyl group and its Fourier transform is given. The calculation compares well with the experimental spectra of CH(3)CD(2)I and methylmalonic acid. It is shown that Fourier transform spectroscopy of the magnetization evolution in a tilted RF frame represents an excellent alternative to the analogous experiment performed at exact resonance, resulting in improved resolution and a much better signal-to-noise ratio.

Micro magnetic resonance imaging of water uptake by glass ionomer cements.

OBJECTIVES: The purpose of the present study was: 1) to visualize the water penetration into glass ionomer cement samples prepared in two different setting modes as a function of time, and 2) to assess the potential use of micro magnetic resonance imaging by studying penetration processes. METHODS: An encapsulated form of resin-modified glass ionomer cement (Fuji II LC, GC) was used in this study. The mixed cement was syringed into quartz tubes (4 mm ID x 10 mm long). Half of the samples were radially exposed to a light source for 120 s; the other half were allowed to set chemically in a photographic darkroom. One hour after the start of mixing, samples were extruded from the quartz tubes, immediately immersed in distilled water, and stored at 37 degrees C. Eight specimens were prepared with each setting mode and imaged at different times. Micro magnetic resonance imaging was performed on a Bruker Biospec System equipped with micro-imaging utilities. A spin echo technique was used. A small tube containing a mixture of normal and deuterated water was added as a standard to which the signals from the samples were normalized. The average signal, as calculated by the image processing software from each region, was divided by the signal from the standard sample to obtain the normalized intensity. The results were analyzed by a Student's t-test. RESULTS: After 24 h of immersion, water diffused 1 mm into the chemical-cured material and approximately 0.5 mm in the light-cured samples. After 96 h, the water had reached the center of all chemical-cured samples but not of the light-cured samples. After 192 h, water had reached the center of the cylinders of both groups of samples. SIGNIFICANCE: MRI microscopy is a good method for monitoring the water permeability of glass ionomer cements. The technique is nondestructive thus, the process can be followed on the same sample without destroying it. By using some special imaging techniques, refinement of the method will be possible.

Proton spin-spin relaxation study of hydration of a model nanopore.

The hydration pattern of controlled pore glass, with pore diameter of 237 A, was investigated using nuclear magnetic resonance. Water proton spin-spin relaxation decay curves were monitored and modeled as two-component exponential decays as a function of hydration. The results are consistent with a geometric model involving a surface water layer and a bulk-like liquid fraction in the form of a plug. The amount of surface water increases as the sample hydrates, until hydration reached approximately a monolayer, at which point a water plug starts to form in the pore, and grow in length at the expense of the surface layer. The results are also analyzed in terms of, and compared to, a recently developed puddle pore-filling model [S.G. Allen, et al. J. Chem. Phys. 106 (1997) 7802-7809].

Nuclear magnetic resonance multiwindow analysis of proton local fields and magnetization distribution in natural and deuterated mouse muscle.

The proton free-induction decays, spin-spin relaxation times, local fields in the rotating frame, and spin-lattice relaxation times in the laboratory and rotating frames, in natural and fully deuterated mouse muscle, are reported. Measurements were taken above and below freezing temperature and at two time windows on the free-induction decay. A comparative analysis show that the magnetization fractions deduced from the different experiments are in good agreement. The main conclusion is that the resolution of the (heterogeneous) muscle nuclear magnetic resonance (NMR) response is improved by the multiwindow analysis.

Origin of the nonexponentiality of the water proton spin relaxations in tissues.

An attempt to explain the nonexponential recovery of the water proton spin magnetization in tissues is presented. The origin of this effect is the nonhomogeneity of the material and the distribution of slow diffusion correlation times. This proposal is based on a dispersion study of the tissue water proton spin relaxation time in the rotating frame.

NMR spectroscopy of heterogeneous solid-liquid mixtures. Spin grouping and exchange analysis of proton spin relaxation in a tissue.

An attempt to resolve the complicated proton NMR signal of a heterogeneous material is presented. Lung tissue is used to illustrate the approach to this problem, which is based on resolving the total proton magnetization into components according to their relaxation times. This procedure is utilized at both low and high magnetic fields. These results are then correlated and analyzed for the effect of exchange between spin groups. For example, the total proton NMR signal of lung tissue is shown to arise from three interacting proton groups: protons on solid macromolecules, bound water protons, and bulk water protons. The dynamics of water is modeled to satisfy the dispersivity and the values of the relaxation parameters obtained considering the effect of exchange. It is proposed that this approach is generally applicable.

Nuclear magnetic resonance study of mammalian cell water influence of water content and ionic environment.

The water proton spin-lattice relaxation time (T(1)) in mammalian cells and tissues has been measured as a function of external ion concentration and total cell water content. The results can be interpreted in terms of changes in the fractions of bound and unbound water, and changes in the coordination shells of macromolecules due to alterations in macromolecular configuration caused by changes in salt molarity and the amount of water. It is shown that the direct effect of the ions (Na(+), K(+), Li(+), Cl(-)) on structuring cellular water, i.e., into ion coordination shells, is small; the main effect of these ions on cellular water structure is an indirect one, resulting from their capability of changing macromolecular coordination shells.

Nuclear magnetic resonance analysis of water in natural and deuterated mouse muscle above and below freezing.

Measurements of absolute proton signal intensities, free induction decays, spin-spin relaxation times, and local fields in the rotating frame in natural and fully deuterated mouse muscle at five temperatures in the range 293-170 K are reported. The analysis is carried out at three time windows on the free induction decay. The contribution to the magnetization from protons on large molecules and water are analyzed.

Monitoring structural changes of liquids frozen in nanopores.

Less dense packing of molecules in frozen liquids confined to cylindrical glass pores was observed to depend on pore size. This conclusion was derived by monitoring the rotational tunneling of methyl protons, which reside on studied molecules, with nuclear magnetic resonance. For example, the tunneling frequency of dimethyl sulfide and propionic acid at 10 K was observed to be larger in pores than in bulk. This is interpreted as being due to a decrease in the hindering potential. In another type of tunneling spectrum which is due to methyl-methyl interaction, observed in acetyl acetone at 10 K, the splitting decreases as the pores become smaller. It is demonstrated that in both types of materials the shifts of the methyl tunneling splittings in pores are the result of the reduced intermolecular interaction in the pore core region. This in turn indicates that the unit cell size of liquids frozen in nanopores is slightly increased. The increase is largest in smallest pores.

Determination of curing time in visible-light-cured composite resins of different thickness by electron paramagnetic resonance.

The irradiation time of a visible-light-activated composite necessary to achieve full polymerization throughout the material was studied. Curing-time dependence on the thickness of the material was also investigated. To monitor the visible light-activation effect, the free radical concentration was measured as a function of irradiation time. If the composite sample is less than 0.5 mm thick and exposed to light for a time interval recommended by the manufacturer, full radical concentration is indeed created uniformly. This is not the case in thicker samples. Electron paramagnetic resonance (EPR) was used to monitor the concentration of free radicals in the samples. The number of radicals was monitored as a function of irradiation time during which the radicals were generated in samples 0.5, 0.8, 2.0, 3.0 and 5.0 mm thick. An EPR X-band spectro-meter was used to detect the free radical spectra. The number of free radicals per unit mass as a function of irradiation time shows that 60% of the maximum concentration of radicals in a 1 mm sample is reached in 24 s curing time, while in thicker samples it takes hundreds of seconds. On the basis of the experiments, a depth and irradiation time-dependent radical concentration model was developed. This model shows that a 2.0 mm thick sample is cured at the bottom side if irradiated for 60 s. It is proposed that the measure of the degree of polymerization in composite materials should be the polymerization of the bottom layer of the sample which is modelled from the number of free radicals generated in the sample.

NMR spin grouping and correlation exchange analysis. Application to low hydration NaDNA paracrystals.

The NMR spin-grouping technique is applied to low hydration oriented fibers of NaDNA to study the role of exchange in determining the apparent (observed) spin relaxation of the system. The analysis proceeds in three steps: first, the apparent proton relaxation is measured at high fields, with both selective and nonselective inversion pulse sequences, and in the rotating frame. The spin-grouping technique is used in all spin-lattice relaxation measurements to provide the optimum apparent relaxation characterization of the sample. Next, all apparent results are analyzed for exchange. In this analysis the results from the high field and rotating frame experiments (which probe the exchange at two different time scales) are correlated to determine the inherent (or true) spin relaxation parameters of each of the proton groups in the system. The results of selective inversion T1 measurements are also incorporated into the exchange analysis. Finally, the dynamics of each spin group are inferred from the inherent relaxation characterization. The low hydration NaDNA structure is such that the exchange between the protons on the water and those on the NaDNA is limited, a priori, to dipolar mixing. The results of the exchange analysis indicate that the dipolar mixing between water and NaDNA protons is faster than the spin diffusion within the NaDNA proton group itself. The spin-diffusion on the macromolecule is the bottleneck for the exchange between the water protons and the NaDNA protons. The water protons serve as the relaxation sink both at high fields and in the rotating frame for the total NaDNA-water spin bath. The inherent relaxation of the water is characteristic of water undergoing anisotropic motion with a fast reorientational correlation time about one axis (5 X 10(-10) less than or equal to tau r less than or equal to 8 X 10(-9)S) which is about three orders of magnitude slower than that of water in the bulk; and a slow tumbling correlation time for this axis (1.5 x 10(-7) less than or equal to tau t less than or equal to 8 x 10(-7)S) which is two orders of magnitude slower yet.

Proton T1 study of coverage parameter changes in tissues from tumor-bearing mice.

measurements of water proton spin-lattice relaxation time, T1, at 20 and -15 degrees C have been performed in spleen, kidney, liver, and muscle tissues from tumor-bearing mice, as well as in tumors grown in their dorsal subcutaneous tissues. All mice used were either from the C3H/HeJ or BALB/c strain. At - 15 degrees C the T1's of tissues of a given type from tumor-bearing and healthy mice are essentially the same. It is shown that in spleen the increased T1 from tumor-bearing mice can only be explained in terms of a large change in the water coverage parameter of macromolecules. In liver, muscle, and tumors the increased water content accounts for the changes in T1, while kidney represents an intermediate case.

Modeling of proton spin relaxation in muscle tissue using nuclear magnetic resonance spin grouping and exchange analysis.

NMR spin relaxation experiments performed on healthy mouse muscle tissue at 40 MHz and 293 K are reported. The spin-lattice relaxation experiments were performed using different combinations of selective and nonselective radio frequency pulses. Relaxation experiments in the rotating frame at H1 = 10, 5 and 1 G are also reported. The experimental results were analyzed using the spin-grouping method, which yields the sizes of the resolved magnetization components as well as their T2's and T1's (or T1p's) for the nonexponential relaxation functions. These results were analyzed further for the exchange between different spin groups. It has been found that to explain all of these experimental data it was necessary to use a four-compartment model of the muscle tissue that consists of a lipid spin group, a "solid-like" spin group (mainly proteins), a "bulk water" spin group and a "bound water" spin group. The chemical exchange rate between "bulk" and "bound" water was found to be 29 +/- 9s-1 at room temperature. The exchange rate between the bound water and the solid moderator was estimated to be approximately 500 s-1.