Transverse Relaxation Constant Research Articles

Prediction of radiation necrosis in a rodent model using magnetic resonance imaging apparent transverse relaxation ()

Background and purpose. Radiation necrosis remains an irreversible long-term side-effect following radiotherapy to the brain. The ability to predict areas that could ultimately develop into necrosis could lead to prevention and management of radiation necrosis. Materials and Methods. Fischer 344 rats were irradiated using two platforms (micro-CT irradiator and x-Rad 225 IGRT) with radiation up to 30 Gy for the micro-CT and 40 Gy for the xRAD-224 to half the brain. Animals were subsequently imaged using a 9.4 T MRI scanner every 2–4 weeks for up to 28 weeks using a 7-echo gradient echo sequence. The apparent transverse relaxation constant () was calculated and retrospectively analyzed. Results. Animals irradiated with the low-dose rate micro-CT did not exhibit any symptoms or imaging changes associated with RN. Animals irradiated with the xRAD-225 exhibited imaging changes consistent with RN at week 24. Analysis of the coefficient within the lesion and hippocampus shows the potential for detection of RN up to 10 weeks prior to morphological changes. Conclusions. The ability to predict areas of RN and increases of within the hippocampus provides a method for long-term monitoring and prediction of RN.

Magnetic Resonance Monitoring of Disease Progression in mdx Mice on Different Genetic Backgrounds

Genetic modifiers alter disease progression in both preclinical models and subjects with Duchenne muscular dystrophy (DMD). Using multiparametric magnetic resonance (MR) techniques, we compared the skeletal and cardiac muscles of two different dystrophic mouse models of DMD, which are on different genetic backgrounds, the C57BL/10ScSn-Dmdmdx (B10-mdx) and D2.B10-Dmdmdx (D2-mdx). The proton transverse relaxation constant (T2) using both MR imaging and spectroscopy revealed significant age-related differences in dystrophic skeletal and cardiac muscles as compared with their age-matched controls. D2-mdx muscles demonstrated an earlier and accelerated decrease in muscle T2 compared with age-matched B10-mdx muscles. Diffusion-weighted MR imaging indicated differences in the underlying muscle structure between the mouse strains. The fractional anisotropy, mean diffusion, and radial diffusion of water varied significantly between the two dystrophic strains. Muscle structural differences were confirmed by histological analyses of the gastrocnemius, revealing a decreased muscle fiber size and increased fibrosis in skeletal muscle fibers of D2-mdx mice compared with B10-mdx and control. Cardiac involvement was also detected in D2-mdx myocardium based on both decreased function and myocardial T2. These data indicate that MR parameters may be used as sensitive biomarkers to detect fibrotic tissue deposition and fiber atrophy in dystrophic strains.

21.1 Tesla Magnetic Resonance Imaging Apparatus and Image Interpretation: First Report of a Scientific Advancement

Recent patents show that ultrahigh Magnetic field, Nuclear Magnetic Resonance (NMR) microscopy is emerging as bioimaging tool to study metabolic events and protein structure-functional characterization in the small animals and pure proteins in solutions. 900 MHz NMR magnet design characteristics were reviewed and imaging was done for high resolution rat skin, heart, mice kidney using NMR microscopy technique. Superparamagnetic iron-oxide bound avidin-polystyrene coated with anti-troponin (SPIOT) nanoparticles as imaging contrast agent was used to enhance contrast. 900 MHz NMR microscopy provides structural microscopic details and can detect the nanoparticle targeted heart muscle fiber orientation by deposits of nanoparticles. 900 MHz microscopy was done for imaging phantom, heart, skin, kidneys. Anti-troponin was bound with polymer coated avidin-iron oxide complex to inject in rat to image the excised heart. Fast spin echo and fast gradient echo imaging techniques were used for T2-weighted rat heart. After imaging, rat hearts were processed for histology. First time available 900 MHz NMR system was more suitable for longer data acquisition at room temperature with enhanced SNR, MR signal intensity, and high resolution in less time. The imager generated skin, kidney, and heart images with visible muscle fiber orientation and comparable with histology details. The present paper is an overview with available patents on 900 MHz NMR spectrometer to convert into microscopic imager to generate high MR signal intensity and high resolution images with possibility on 1000 MHz field. The imager was a suitable research tool for microscopy, protein structural characterization and drug therapeutic monitoring. Keywords: 900 MHz NMR, 21 Tesla imager, mice kidney, skin, rat heart, microscopy, NMR magnet design, metabolic events, MR visible water distribution mapping, transverse relaxation constants, fast data acquisition technique, quench reduction, Wide Bore Magnet Technology, superparamagnetic iron oxide magnetic nanoparticles, cardiac damage targeting techniques, animal microimaging coils

A13C and15N Solid-State NMR Study of Structural Disorder and Aurophilic Bonding in AuIand AuIIICyanide Complexes

Solid-state nuclear magnetic resonance has been used to study several cyanoaurates. Carbon-13 and nitrogen-15 NMR spectra of samples enriched with isotopically labeled 13C,15N cyanide ligands were recorded for stationary samples and samples spinning at the magic angle. Several salts of the dicyanoaurate(I) anion, M[Au(CN)2], where M = n-butylammonium, potassium, and thallium, were studied via solid-state NMR. A gold(III) cyanide, K[Au(CN)4], was also investigated. Carbon-13 and nitrogen-15 chemical shift tensors are reported for each salt, as are the measured 13C,15N direct dipolar coupling constants together with the related derived cyanide bond lengths, r(C,N). The value for r(C,N) in [(n-C4H9)4N][Au(CN)2], 1.17(5) A, was determined to be more realistic than a previously reported X-ray diffraction value of 1.03(4) A. Large 13C NMR line widths from Tl[Au(CN)2], 250-315 Hz, are attributed to coupling with 197Au (I = 3/2) and/or 203/205Tl (I = 1/2), as confirmed by measurements of the transverse relaxation constant, T2. Investigation of the carbon-13 chemical shifts for cyanide ligands bound to gold involved in a variety of metallophilic bonding environments demonstrates that the chemical shift is sensitive to metallophilic bonding. Differences in Au-Tl metallophilic bonding are shown to cause a difference in the isotropic carbon-13 chemical shift of up to 15.7 ppm, while differences in Au-Au aurophilic bonding are found to be responsible for a change of up to 5.9 ppm. The disordered polymeric material gold(I) monocyanide, AuCN, was also investigated using 13C and 15N SSNMR. Two-dimensional 13C,13C double-quantum dipolar-recoupling spectroscopy was used to probe connectivity in this material. The 13C NMR site multiplicity in AuCN is explained on the basis of sensitivity of the carbon-13 chemical shift to aurophilic bonding of the directly bonded gold atom. This assignment allows estimation of the position of the linear [-M-CN-]infinity chain's position with respect to the neighboring polymer chain. For the samples studied, a range of 7 +/- 2% to 25 +/- 5% of the AuCN chains are found to be "slipped" instead of aligned with the neighboring chains at the metal position.

A simulation based method to assess inversion algorithms for transverse relaxation data

NMR relaxometry is a very useful tool for understanding various chemical and physical phenomena in complex multiphase systems. A Carr-Purcell-Meiboom-Gill (CPMG) [P.T. Callaghan, Principles of Nuclear Magnetic Resonance Microscopy, Clarendon Press, Oxford, 1991] experiment is an easy and quick way to obtain transverse relaxation constant (T2) in low field. Most of the samples usually have a distribution of T2 values. Extraction of this distribution of T2s from the noisy decay data is essentially an ill-posed inverse problem. Various inversion approaches have been used to solve this problem, to date. A major issue in using an inversion algorithm is determining how accurate the computed distribution is. A systematic analysis of an inversion algorithm, UPEN [G.C. Borgia, R.J.S. Brown, P. Fantazzini, Uniform-penalty inversion of multiexponential decay data, Journal of Magnetic Resonance 132 (1998) 65–77; G.C. Borgia, R.J.S. Brown, P. Fantazzini, Uniform-penalty inversion of multiexponential decay data II. Data spacing, T2 data, systematic data errors, and diagnostics, Journal of Magnetic Resonance 147 (2000) 273–285] was performed by means of simulated CPMG data generation. Through our simulation technique and statistical analyses, the effects of various experimental parameters on the computed distribution were evaluated. We converged to the true distribution by matching up the inversion results from a series of true decay data and a noisy simulated data. In addition to simulation studies, the same approach was also applied on real experimental data to support the simulation results.

Transient signal changes in diffusion‐weighted stimulated echoes during neuronal stimulation at 3T

To develop a sensitive method for detecting minute transient signal changes that can arise due to variations in the extravascular apparent self-diffusion coefficient, D, during neuronal activation. A three-pulse sequence that reads out a moderately diffusion-weighted (DW) primary echo (PRE) and a heavily DW stimulated echo (STE) was employed to investigate whether small transient signal changes in extravascular D occur in response to a visual stimulus. Contributions to signal changes caused by subtle differences in the transient variations of the apparent transverse relaxation constant, T(2), between the PRE and STE were also quantified. On z-maps obtained from the STE, more voxels showed significant stimulus-related signal changes compared to maps of the PRE. The average maximum signal change of the STE was larger than that of the PRE. The observed increase in the relative signal change was independent of the strength of the diffusion weighting. The STE is more sensitive to neuronal activity than the PRE. The discrepancy between the two echoes does not arise from transient changes in D, but from subtle differences in stimulus-related variations of T(2) between the two echoes.

Relaxation characteristics of intracellular Na + as measured by double quantum filtered (DQf) NMR

We have measured the transverse relaxation rate constants depending on statistic field (B O) and the diffusion coefficient of 23Na + in an agar gel as a model of the intracellular Na +. We have estimated a binding site correlation time ( τ C ) and a quadrupole coupling constant (e 2qQ/h) on assumption of the discrete-exchange model. Transverse relaxation constants of “free Na +” (S free) in the agar gel were estimated from the self-diffusion coefficient of 23Na + in the agar gel using the observed relationship between the self-diffusion coefficient and the transverse relaxation rate constant of Na + in glycerol solution. As a result of minimization (r 2 = 0.98), the fraction of the 23Na + under the slow-motion condition (P b for 1% agar/1 M NaCl/water gel) was calculated as 9·10 −4. The values of e 2qQ/h and the correlation time were 1.0 MHz and 16 ns, respectively, and the calculated value of e 2qQ/h (1.0 MHz) lies in the reasonable range (0.2 MHz – 2 MHz).

A method for in vivo MR imaging of the short T2 component of sodium-23.

A magnetic resonance imaging pulse sequence featuring a short echo time of 3.6 ms is described and used clinically for in vivo imaging of sodium-23 in the human head. In living tissues, sodium exhibits at least two transverse relaxation constants, namely, (a) a short component T2s = 0.7-3.0 ms and (b) a long component T2e = 16-30 ms. Since our first in vivo imaging of sodium, an echo time of 10-15 ms has been used by us and by other investigators. This echo time is adequate for the observation of the long T2 component of sodium. However, a substantial fraction of the sodium, namely, the short T2 component, representing about 40%, has remained undetected by the imaging method with this echo time and is now observable by the new pulse sequence. The proposed method is a hybrid technique combining both projection reconstruction and Fourier encoding schemes. The projection reconstruction is used for the xy plane imaging while the Fourier encoding is used for slice separation. Sodium MR images of the human head produced with a short and a long TE are presented and analyzed. There is an increase in the MR signal and improved visibility of intraparenchymal sodium with the new scheme of short TE.

Determination of the apparent ratio of quaternary to tertiary aromatic carbon atoms in an anthracite coal by 13C- 1H dipolar dephasing n.m.r.

13C- 1H heteronuclear dipolar dephasing n.m.r. techniques allow discrimination between different chemical species contributing to the 13C n.m.r. spectra of complex hydrocarbons. Model compound studies show significantly different effective transverse relaxation constants for carboxyl and quaternary carbon atoms (≈200 μs), secondary and tertiary (≈20 μs), and primary carbon atoms (≈80 μs). Use of these effective relaxation data, together with appropriately timed windows in the continuous wave decoupling applied in standard cross-polarization-magic-angle spinning experiments on anthracite coal allow discrimination between aromatic tertiary and aromatic quaternary ring carbon atoms in this coal. Within the accuracy of experimental error, and of the structural modelling experiments herein reported, the use of the dipolar dephasing technique together with results of X-ray diffraction on coals allows a reasonable estimate to be made of the average number of condensed polynuclear rings in an ‘average molecule’ in the anthracite studied. Based on a model of pericondensed aromatic rings, this number lies between 33 and 45.

Two-Photon Echo and Excited State Photon Echo Methods to Determine the Transverse Relaxation Constants of Excitonic Molecules

Nonlinear optical methods to determine the transverse relaxation constants of excitonic molecules making use of two-photon echo and a new type of excited state photon echo are proposed. The two-photon echo is a seventh order nonlinear effect at the lowest and one needs three pulses to observe it, while the excited state photon echo is a fifth order nonlinear effect and requires four pulses. In these nonlinear optical methods we can satisfy the phase matching condition rather easily due to the large dispersion of excitonic polaritons. We can determine directly the transverse relaxation constants associated with the excitonic molecule from the correlation trace of the two-photon echo and the excited state photon echo.