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Ravinder Reddy - One of the best experts on this subject based on the ideXlab platform.

  • Compensation for Spin-lock artifacts using an off-resonance rotary echo in T1ρoff-weighted imaging
    Magnetic Resonance in Medicine, 2020
    Co-Authors: Walter R.t. Witschey, Arijitt Borthakur, Mark A. Elliott, Eric A. Mellon, Sampreet Niyogi, Chenyang Wang, Ravinder Reddy
    Abstract:

    The origin of image artifacts in an off-resonance Spin-Locking experiment is shown to be imperfections in the excitation flip angle. A pulse sequence for off-resonance Spin Locking is implemented that compensates for imperfections in the excitation flip angle through an off-resonance rotary echo. The off-resonance rotary echo alternates the frequency offset and phase of the RF transmitter during two Spin-Locking pulses of equal duration. The underlying theory is detailed, and MR images demonstrate the effectiveness of the technique in agarose gel phantoms and in in vivo human brain at 3T.

  • Spin-lock sodium MRI of the human brain: a preliminary study
    2020
    Co-Authors: David T. Pilkinton, Mark A. Elliott, Jeremy F. Magland, Ravinder Reddy
    Abstract:

    Introduction: Proton T1ρ MRI studies have shown that Spin-Locking can provide unique and clinically-useful contrast correlated to macromolecular content due to its ability to probe slow molecular motion (1). Although Spin-Locking spectroscopy of sodium has been investigated as a means to selectively detect sodium nuclei involved in slow molecular motion and anisotropic environments (2), to knowledge there is currently no literature reporting Spin-lock sodium MRI data. A large fraction of sodium ions in biological tissue are complexed to macromolecules through electrostatic binding sites and their interactions with the bound water fraction. Several disease states, e.g. stroke and osteoarthritis, involve substantial changes to motional characteristics of the complexed fraction of sodium Spins. Measurements of T2 or T2* are sensitive to slow motion only through the spectral density at zero frequency; slow dynamics are probed more efficiently through the application of a strong RF field near the kilohertz range (3). We hypothesize that Spin-lock sodium MRI will generate significant contrast based on macromolecular content in biological tissue due to its sensitivity to slow molecular motion. The purpose of this study was to characterize the effect of Spin-Locking in sodium MRI in agarose and human brain. Materials and Methods: A Spin-lock pulse cluster was used with a rotary echo Spin-lock pair and with frequency offset (Δω) equal to 200 Hz (Fig. 1). Spin-lock duration τ was set to 3 ms; high and low B1 amplitudes were performed corresponding to ω1 ≈ 465.4 and 116.4 Hz, respectively. A ramp-sampled 3D radial acquisition (ramp/total points = 12/64, BW/Px ≈ 500 Hx) with spirally distributed radial views was performed immediately after the last pulse with a dead time delay of 50 μs. RF spoiling with pseudorandom phase cycling was performed. An ultra-short echo (UTE) acquisition was also performed with the same α pulse and a TE=200 μs. All sequences had a TR=50 ms, and all were obtained at 3 Tesla Siemens Trio scanner. Phantoms of 1 M [Na+] of saline and 2, 4, and 8% agarose were imaged with UTE, 507 Hz Spin-lock, and 231 Hz Spin-lock with 2500 radial views. A healthy, 27 year-old male subject’s brain was imaged with the same three sequences and the same coil as with the agarose experiments, but with 25,000 radial views (scan time = 20.8 min). Brain images were intensity standardized using fluid signal from the ventricles and vitreous humor, and phantom images were standardized to the saline signal. Image intensities were evaluated from ROIs drawn in ImageJ (NIH). All image slices and their ROIs were coregistered and drawn manually. Brain scans were analyzed by drawing an ROI in the ventricular fluid and a large ROI in medial lobe of the axial slice in Fig. 2. The normalized tissue contrast was determined by subtracting the mean tissue ROI intensity from the mean fluid ROI intensity and dividing by the fluid ROI intensity (the standard deviations of the ROIs were carried through). Results: 3D radial sodium MRI scans using UTE and Spin-Locking in brain and agarose phantoms are shown in Fig. 2. Fig. 2A is the UTE sequence, and Fig. 2B and Fig. 2C are the high (507 Hz) and low (231 Hz) Spin-lock amplitude images, respectively. Standard intensities versus agarose concentration are shown in Fig. 3. The normalized tissue contrast values(measured as described above) were: 26.0 ± 2.6% for UTE, 28.2 ± 2.5% for 507 Hz, and 32.5 ± 2.7% for 231 Hz. Discussion: We have demonstrated that off-resonance Spin-lock sodium MRI is capable of providing contrast directly related to macromolecular content due to its sensitivity to Spins in slow molecular motion regimes. Agarose and tissue show substantially different sodium signal amplitudes under high and low amplitude Spin-lock pulses (Figs 2 and 3). Normalized tissue contrast showed a 4% greater decrease in amplitude in under 231 Hz Spin-lock versus 507 Hz. Although we are currently operating at the SAR limit, It may be possible to apply even higher amplitude pulses if TR is increased or the hard pulse is altered. In that case, it should be possible to further separate signal intensities of Spins at low frequencies so that a difference image could be made with signal almost entirely from motionally-restricted Spins. Although UTE produces more SNR than the Spin-lock sequence, it is much less sensitive to relaxation changes. While slow molecular motion can be probed with sequences weighting with T2 and T2* such as Spin echo and gradient echo, these suffer from a number of problems including SAR limits (180 deg refocusing pulses) and B0 imaging artifacts (gradient echo). Spin Locking produces less SAR than a refocusing pulse and is relatively insensitive to B0, while providing a sensitive means to probe relaxation induced changes. Since disease states correspond to changes primarily in sodium Spins complexed to macromolecules, we believe this technique could prove valuable as a biomarker for those pathologies. Future investigations will also investigate Spin-lock effects in heavily anisotropic environments, such as cartilage, where the observed signal changes under Spin-Locking are likely to be even greater in magnitude. References: (1) Witschey, et al. Magn Reson Med (2006), (2) Hancu, et al. Magn Reson Med (2002), (3) van der Maarel, Concepts Magn Reson Part A (2003)

  • A pulse sequence for rapid in vivo Spin-locked MRI.
    Journal of Magnetic Resonance Imaging, 2020
    Co-Authors: Arijitt Borthakur, Sridhar R Charagundla, Mark A. Elliott, Andrew J. Wheaton, Justin Hulvershorn, Eugene E. Gualtieri, Ravinder Reddy
    Abstract:

    T1P OR “Spin-LOCKED” MRI produces contrast unlike conventional T1-orT2-weighted images. Spin-Locking is achieved by the application of a low power on-resonance radiofrequency (RF) pulse to the magnetization in the transverse plane. The resulting MR signal decays with a time constant T1ρ and is dominated by processes that occur with a correlation time, τc, that is related to the amplitude of the Spin-lock (SL) pulse (γB1/2π), which typically ranges from zero to a few kilohertz. T1ρ is commonly referred to as the longitudinal relaxation time constant in the rotating frame. In biological tissues, T1ρ increases with higher B1 and approaches T2, the Spin-Spin relaxation time constant, as the amplitude of the SL pulse is reduced to zero. The sensitivity of T1ρ to low-frequency interactions facilitates the study of biological tissues in a manner that is unattainable by conventional T1- and T2-based MR methods. Consequently, T1ρ MRI has been used to investigate a variety of tissues such as breast, brain, and cartilage (1–3). Recently, T1ρ imaging has been employed to measure blood flow and oxygen metabolism and the effect of tracers such as H217O (4,5). These studies were performed using standard Spin-echo, turbo (fast) Spin-echo, or gradient-echo-based pulse sequences. There is substantial evidence demonstrating that the T1ρ relaxation time parameter is sensitive to the early detection of cerebral ischemia (6–8). Kettunen et al (9) revealed a linear dependence of T1ρ as a function of oxygen saturation in experiments performed in vitro. Dynamic studies such as these and others that involve imaging of flowing Spins such as that of blood would benefit from a fast T1ρ imaging technique that is able to acquire images in the order of tens of milliseconds. A method of rapid image acquisition is the echo planar imaging (EPI) technique (10,11). In its conventional form, the EPI pulse sequence consists of an excitation pulse that is followed by a train of gradient-echoes within a single pulse repetition time (TR), and is capable of generating images in tens of milliseconds. Here we present a method for acquiring T1ρ-weighted images in a time efficient manner by using SL pulses in a new pulse sequence called Spin-locked EPI (SLEPI). This sequence is used to determine T1ρ values in the human brain. Further, for the first time, we report the T1ρ of blood obtained in vivo. These measurements were possible because of the short image acquisition window offered by the new sequence. It is shown that the SLEPI sequence can significantly reduce susceptibility-induced artifacts during EPI acquisition, while maintaining image contrast similar to long echo time (TE) images.

  • investigation of chemical exchange at intermediate exchange rates using a combination of chemical exchange saturation transfer cest and Spin Locking methods cestrho
    Magnetic Resonance in Medicine, 2012
    Co-Authors: Feliks Kogan, Anup Singh, Mohammad Haris, Hari Hariharan, Ravinder Reddy
    Abstract:

    Proton exchange imaging is important as it allows for visualization and quantification of the distribution of specific metabolites with conventional MRI. Current exchange mediated MRI methods suffer from poor contrast as well as confounding factors that influence exchange rates. In this study we developed a new method to measure proton exchange which combines chemical exchange saturation transfer and T1ρ magnetization preparation methods (CESTrho). We demonstrated that this new CESTrho sequence can detect proton exchange in the slow to intermediate exchange regimes. It has a linear dependence on proton concentration which allows it to be used to quantitatively measure changes in metabolite concentration. Additionally, the magnetization scheme of this new method can be customized to make it insensitive to changes in exchange rate while retaining its dependency on solute concentration. Finally, we showed the feasibility of using CESTrho in vivo. This sequence is able to detect proton exchange at intermediate exchange rates and is unaffected by the confounding factors that influence proton exchange rates thus making it ideal for the measurement of metabolites with exchangeable protons in this exchange regime. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.

  • T1ρ-weighted MRI using a surface coil to transmit Spin-lock pulses
    Journal of Magnetic Resonance, 2004
    Co-Authors: Arijitt Borthakur, Sridhar R Charagundla, Andrew J. Wheaton, Ravinder Reddy
    Abstract:

    Abstract T 1 ρ -weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B 1 inhomogeneity. First, excitation with a spatially varying B 1 causes flip-angle artifacts and second, Spin Locking with an inhomogeneous B 1 results in non-uniform T 1 ρ contrast. In this study, we overcome the former complication with a specially designed Spin-Locking pulse sequence and we successfully obtain T 1 ρ -weighted images with a surface coil. In this pulse sequence, the Spin-lock pulse was divided into segments of equal duration and alternating phase. This “self-compensating” T 1 ρ -preparatory pulse sequence was analyzed and the effect of an inhomogeneous B 1 field was simulated using the Bloch equations. T 1 ρ -weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T 1 ρ -prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase Spin-lock pulse.

Robert Tycko - One of the best experts on this subject based on the ideXlab platform.

  • slice selection in low temperature dnp enhanced magnetic resonance imaging by lee goldburg Spin Locking and phase modulation
    Journal of Magnetic Resonance, 2020
    Co-Authors: Hsuehying Chen, Robert Tycko
    Abstract:

    Abstract Large enhancements in nuclear magnetic resonance (NMR) signals provided by dynamic nuclear polarization (DNP) at low temperatures have the potential to enable inductively-detected 1H magnetic resonance imaging (MRI) with isotropic spatial resolution on the order of one micron, especially when low temperatures and DNP are combined with microcoils, three-dimensional (3D) phase encoding of image information, pulsed Spin Locking during NMR signal detection, and homonuclear dipolar decoupling by Lee-Goldburg (LG) irradiation or similar methods. However, the relatively slow build-up of nuclear magnetization under DNP leads to very long acquisition times for high-resolution 3D images unless the sample volume or field of view (FOV) is restricted. We have therefore developed a method for slice selection in low-temperature, DNP-enhanced MRI that limits the FOV to about 50 μm in one or more dimensions. This method uses small-amplitude phase modulation of LG irradiation in the presence of a strong magnetic field gradient to invert Spin-locked 1H magnetization in the selected slice. Experimental results are reported, including effects of radio-frequency field inhomogeneity, variations in the amplitude of phase modulation, and shaped phase modulation.

  • sensitivity enhancement in structural measurements by solid state nmr through pulsed Spin Locking
    Journal of Magnetic Resonance, 2002
    Co-Authors: Aneta T Petkova, Robert Tycko
    Abstract:

    Abstract Free induction decay (FID) signals in solid state NMR measurements performed with magic angle Spinning can often be extended in time by factors on the order of 10 by a simple pulsed Spin Locking technique. The sensitivity of a structural measurement in which the structural information is contained in the dependence of the integrated FID amplitude on a preceding evolution period can therefore be enhanced substantially by pulsed Spin Locking in the signal detection period. We demonstrate sensitivity enhancements in a variety of solid state NMR techniques that are applicable to selectively isotopically labeled samples, including 13 C– 15 N rotational echo double resonance (REDOR), 13 C– 13 C dipolar recoupling measurements using the constant-time finite-pulse radio-frequency-driven recoupling (fpRFDR-CT) and constant-time double-quantum-filtered dipolar recoupling (CTDQFD) techniques, and torsion angle measurements using the double quantum chemical shift anisotropy (DQCSA) technique. Further, we demonstrate that the structural information in the solid state NMR data is not distorted by pulsed Spin Locking in the detection period.

V Sokolovsky - One of the best experts on this subject based on the ideXlab platform.

  • Spin Locking in liquid entrapped in nanocavities application to study connective tissues
    Journal of Magnetic Resonance, 2019
    Co-Authors: G B Furman, V Meerovich, V Sokolovsky
    Abstract:

    Abstract Study of the Spin-lattice relaxation in the Spin-Locking state offers important information about atomic and molecular motions, which cannot be obtained by Spin lattice relaxation in strong external magnetic fields. The application of this technique for the investigation of the Spin-lattice relaxation in biological samples with fibril structures reveals an anisotropy effect for the relaxation time under Spin Locking, T 1 ρ . To explain the anisotropy of the Spin-lattice relaxation under Spin-Locking in connective tissue a model which represents a tissue by a set of nanocavities containing water is used. The developed model allows us to estimate the correlation time for water molecular motion in articular cartilage, τ c = 30 μ s and the averaged nanocavity volume, V ≃ 5400 nm 3 . Based on the developed model which represents a connective tissue by a set of nanocavities containing water, a good agreement with the experimental data from an articular cartilage and a tendon was demonstrated. The fitting parameters were obtained for each layer in each region of the articular cartilage. These parameters vary with the known anatomic microstructures of the tissue. Through Gaussian distributions to nanocavity directions, we have calculated the anisotropy of the relaxation time under Spin Locking T 1 ρ for a human Achilles tendon specimen and an articular cartilage. The value of the fitting parameters obtained at matching of calculation to experimental results can be used in future investigations for characterizing the fine fibril structure of biological samples.

  • multiple pulse Spin Locking in nanofluids
    RSC Advances, 2015
    Co-Authors: G B Furman, V Meerovich, S D Goren, V Sokolovsky
    Abstract:

    We study the multiple-pulse Spin Locking dynamics of the nuclear Spins in a liquid or gas entrapped in nanosized cavities. Two cases are considered with the cavities being either in orientational order or isotropically disordered. The Spins inside the cavities are coupled by dipole–dipole interactions with the same interaction constant. It is shown that, under the high temperature approximation in a Spin system irradiated by a multiple-pulse sequence, the quasi-equilibrium state is established. An analytical expression is obtained describing the dependence of the steady-state magnetization on the structural parameters of a nanocavity and the characteristics of a gas or liquid confined in nanocavities. The relaxation process which follows the establishment of the equilibrium is considered. For the case of the orientationally ordered cavities, the analytical expression for the relaxation time is derived. When the nanocavities are isotropically disordered, the time dependence of the magnetization is numerically calculated. As shown for this case, the relaxation process is characterized by two time constants differing by two orders of magnitude. An advantage of the application of the multiple-pulse Spin Locking measurement method over the NMR cryoporometry technique is that the measurements of magnetization and its relaxation, along with the information about the cavity size, allow determination of the shape and orientation of the nanocavity.

John C Gore - One of the best experts on this subject based on the ideXlab platform.

  • Spin-lock imaging of early tissue pH changes in ischemic rat brain.
    NMR in Biomedicine, 2018
    Co-Authors: Zhongliang Zu, Aqeela Afzal, Hua Li, John C Gore
    Abstract:

    : We have previously reported that the dispersion of Spin-lattice relaxation rates in the rotating frame (R1ρ ) of tissue water protons at high field can be dominated by chemical exchange contributions. Ischemia in brain causes changes in tissue pH, which in turn may affect proton exchange rates. Amide proton transfer (APT, a form of chemical exchange saturation transfer) has been shown to be sensitive to chemical exchange rates and able to detect pH changes non-invasively following ischemic stroke. However, the specificity of APT to pH changes is decreased because of the influence of several other factors that affect magnetization transfer. R1ρ is less influenced by such confounding factors and thus may be more specific for detecting variations in pH. Here, we applied a Spin-Locking sequence to detect ischemic stroke in animal models. Although R1ρ images acquired with a single Spin-Locking amplitude (ω1 ) have previously been used to assess stroke, here we use ΔR1ρ , which is the difference in R1ρ values acquired with two different Locking fields to emphasize selectively the contribution of chemical exchange effects. Numerical simulations with different exchange rates and measurements of tissue homogenates with different pH were performed to evaluate the specificity of ΔR1ρ to detect tissue acidosis. Spin-lock and APT data were acquired on five rat brains after ischemic strokes induced via middle cerebral artery occlusions. Correlations between these data were analyzed at different time points after the onset of stroke. The results show that ΔR1ρ (but not R1ρ acquired with a single ω1 ) was significantly correlated with APT metrics consistent with ΔR1ρ varying with pH.

  • Spin-lock imaging of exogenous exchange-based contrast agents to assess tissue pH.
    Magnetic Resonance in Medicine, 2017
    Co-Authors: Zhongliang Zu, Hua Li, Xiaoyu Jiang, John C Gore
    Abstract:

    Purpose Some X-ray contrast agents contain exchangeable protons that give rise to exchange-based effects on MRI, including chemical exchange saturation transfer (CEST). However, CEST has poor specificity to explicit exchange parameters. Spin-lock sequences at high field are also sensitive to chemical exchange. Here, we evaluate whether Spin-Locking techniques can detect the contrast agent iohexol in vivo after intravenous administration, and their potential for measuring changes in tissue pH. Methods Two metrics of contrast based on R1ρ, the Spin lattice relaxation rate in the rotating frame, were derived from the behavior of R1ρ at different Locking fields. Solutions containing iohexol at different concentrations and pH were used to evaluate the ability of the two metrics to quantify exchange effects. Images were also acquired from rat brains bearing tumors before and after intravenous injections of iohexol to evaluate the potential of Spin-lock techniques for detecting the agent and pH variations. Results The two metrics were found to depend separately on either agent concentration or pH. Spin-lock imaging may therefore provide specific quantification of iohexol concentration and the iohexol-water exchange rate, which reports on pH. Conclusions Spin-lock techniques may be used to assess the dynamics of intravenous contrast agents and detect extracellular acidification. Magn Reson Med 79:298–305, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

  • dispersion of relaxation rates in the rotating frame under the action of Spin Locking pulses and diffusion in inhomogeneous magnetic fields
    Magnetic Resonance in Medicine, 2014
    Co-Authors: John T Spear, Zhongliang Zu, John C Gore
    Abstract:

    Purpose A method is described for characterizing magnetically inhomogeneous media and the spatial scales of intrinsic susceptibility variations within samples. The rate of Spin-lattice relaxation in the rotating frame, R1ρ, is affected by diffusion effects to a degree that depends on the magnitude of an applied Spin-Locking field. Appropriate analysis of the dispersion of R1ρ with Locking field may be used to characterize susceptibility variations in inhomogeneous tissues. Theory and Methods The contribution of diffusion to R1ρ is quantified by an analytic expression derived by analyzing of the effects of diffusion through periodic variations of magnetic susceptibility and is used to predict the effects of inhomogeneities in simple phantoms. The theory is further applied to imaging to derive parametric images that portray the dimensions of susceptibility inhomogeneities independent of their magnitude. Results Significant dispersion of R1ρ with Locking field was predicted and measured experimentally for suspensions of microspheres ranging from 1 to 90 μm in diameter. For scales of practical interest, these dispersion effects occur at much lower Locking fields than the range in which chemical exchange effects cause similar dispersion. Conclusion There is good agreement between theory and experiment, and the method has potential for quantitative tissue characterization and functional imaging. Magn Reson Med 71:1906–1911, 2014. © 2013 Wiley Periodicals, Inc.

  • Exchange-mediated contrast agents for Spin-lock imaging.
    Magnetic Resonance in Medicine, 2011
    Co-Authors: Jared G. Cobb, Ke Li, Daniel F. Gochberg, John C Gore
    Abstract:

    Measurements of relaxation rates in the rotating frame with Spin-Locking techniques are sensitive to substances with exchanging protons with appropriate chemical shifts. The authors develop a novel approach to exchange-rate selective imaging based on measured T1ρ dispersion with applied Locking field strength, and demonstrate the method on samples containing the X-ray contrast agent Iohexol with and without cross-linked bovine serum albumin. T1ρ dispersion of water in the phantoms was measured with a Varian 9.4-T magnet by an on-resonance Spin-Locking pulse with fast Spin-echo readout, and the results used to estimate exchange rates. The Iohexol phantom alone gave a fitted exchange rate of ∼1 kHz, bovine serum albumin alone was ∼11 kHz, and in combination gave rates in between. By using these estimated rates, we demonstrate how a novel Spin-Locking imaging method may be used to enhance contrast due to the presence of a contrast agent whose protons have specific exchange rates. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.

G B Furman - One of the best experts on this subject based on the ideXlab platform.

  • Spin Locking in liquid entrapped in nanocavities application to study connective tissues
    Journal of Magnetic Resonance, 2019
    Co-Authors: G B Furman, V Meerovich, V Sokolovsky
    Abstract:

    Abstract Study of the Spin-lattice relaxation in the Spin-Locking state offers important information about atomic and molecular motions, which cannot be obtained by Spin lattice relaxation in strong external magnetic fields. The application of this technique for the investigation of the Spin-lattice relaxation in biological samples with fibril structures reveals an anisotropy effect for the relaxation time under Spin Locking, T 1 ρ . To explain the anisotropy of the Spin-lattice relaxation under Spin-Locking in connective tissue a model which represents a tissue by a set of nanocavities containing water is used. The developed model allows us to estimate the correlation time for water molecular motion in articular cartilage, τ c = 30 μ s and the averaged nanocavity volume, V ≃ 5400 nm 3 . Based on the developed model which represents a connective tissue by a set of nanocavities containing water, a good agreement with the experimental data from an articular cartilage and a tendon was demonstrated. The fitting parameters were obtained for each layer in each region of the articular cartilage. These parameters vary with the known anatomic microstructures of the tissue. Through Gaussian distributions to nanocavity directions, we have calculated the anisotropy of the relaxation time under Spin Locking T 1 ρ for a human Achilles tendon specimen and an articular cartilage. The value of the fitting parameters obtained at matching of calculation to experimental results can be used in future investigations for characterizing the fine fibril structure of biological samples.

  • multiple pulse Spin Locking in nanofluids
    RSC Advances, 2015
    Co-Authors: G B Furman, V Meerovich, S D Goren, V Sokolovsky
    Abstract:

    We study the multiple-pulse Spin Locking dynamics of the nuclear Spins in a liquid or gas entrapped in nanosized cavities. Two cases are considered with the cavities being either in orientational order or isotropically disordered. The Spins inside the cavities are coupled by dipole–dipole interactions with the same interaction constant. It is shown that, under the high temperature approximation in a Spin system irradiated by a multiple-pulse sequence, the quasi-equilibrium state is established. An analytical expression is obtained describing the dependence of the steady-state magnetization on the structural parameters of a nanocavity and the characteristics of a gas or liquid confined in nanocavities. The relaxation process which follows the establishment of the equilibrium is considered. For the case of the orientationally ordered cavities, the analytical expression for the relaxation time is derived. When the nanocavities are isotropically disordered, the time dependence of the magnetization is numerically calculated. As shown for this case, the relaxation process is characterized by two time constants differing by two orders of magnitude. An advantage of the application of the multiple-pulse Spin Locking measurement method over the NMR cryoporometry technique is that the measurements of magnetization and its relaxation, along with the information about the cavity size, allow determination of the shape and orientation of the nanocavity.

  • Spin Locking and Spin lattice relaxation in a liquid entrapped in nanosized cavities
    Soft Matter, 2012
    Co-Authors: E. B. Feldman, G B Furman, S D Goren
    Abstract:

    We study the dynamics of the nuclear Spins in a liquid entrapped in nanosized cavities. This Spin system is like a solid system where all the Spins are coupled equally with the same interaction constant. It is shown that, under the high temperature approximation, the system is described by the two-temperature quasi-equilibrium density matrix. We find that the mixing rate W and the local dipolar field ωloc depend on the cavity size V, shape F, and cavity orientation, θ. For a large number of Spins N the rate W decreases as the inverse square root of the number of Spins, , and is proportional to the concentration of the molecules, C. The Spin–lattice relaxation rates, 1/T1ρ and 1/T1d, are proportional to C2/N. An NMR study of the dynamics of a Spin system allows extraction of the cavity size and shape, its orientation relative to the magnetic field, and the molecular concentration.