T2 Components Research Articles

Ultrashort TE chemical shift imaging (UTE‐CSI)

A fundamental modification to the conventional chemical shift imaging (CSI) method is described that improves the imaging of species with short T2's (i.e., less than approximately 2 ms). This approach minimizes the delay before each k-space point is collected. This results in different time delays, T(d), for different free induction decay (FID) acquisitions in k-space. On a clinical 1.5 T system this yields an effective delay due to transmit/receive switching of 70 micros and an echo time (TE) from the center of the excitation pulse to the center of k-space of 170 micros, as compared with 1-2 ms for conventional CSI techniques. Using this method, the signal decay before acquisition is greatly reduced, thus enabling imaging of species with very short T2)(e.g., 200 micros) and increasing the signal-to-noise ratio (SNR) of species with intermediate T2. Increases in the SNR of the short T2 components of 23Na in the heart, and 31P acquisitions of bone are about 27% and 400%, respectively, compared to an optimized conventional CSI approach. The imperfections of this approach are also described, and the magnitude of the resultant image artifacts is quantified for different practical imaging situations. These artifacts were not found to be significant in the described applications. This new method allows us to obtain information on short T2 components without degrading the image quality from long T2 components.

Intracellular manganese ions provide strong T1 relaxation in rat myocardium.

The efficacy of manganese ions (Mn2+) as intracellular (ic) contrast agents was assessed in rat myocardium. T1 and T2 and Mn content were measured in ventricular tissue excised from isolated perfused hearts in which a 5-min wash-in with 0, 30, 100, 300, or 1000 microM of Mn dipyridoxyl diphosphate (MnDPDP) was followed by a 15-min wash-out to remove extracellular (ec) Mn2+. An inversion recovery (IR) analysis at 20 MHz revealed two T1 components: an ic and short T1-1 (650-251 ms), and an ec and longer T1-2 (2712-1042 ms). Intensities were about 68% and 32%, respectively. Tissue Mn content correlated particularly well with ic R1-1. A two-site water-exchange analysis of T1 data documented slow water exchange with ic and ec lifetimes of 11.3 s and 7.5 s, respectively, and no differences between apparent and intrinsic relaxation parameters. Ic relaxivity induced by Mn2+ ions in ic water was as high as 56 (s mM)(-1), about 8 times and 36 times higher than with Mn2+ aqua ions and MnDPDP, respectively, in vitro. This value is as high as any reported to date for any synthetic protein-bound metal chelate. The increased rotational correlation time (tauR) between proton and electron (Mn2+) spins, and maintained inner-sphere water access, might make ic Mn2+ ions and Mn2+ -ion-releasing contrast media surprisingly effective for T1-weighted imaging.

Magnetic resonance imaging of the Achilles tendon using ultrashort TE (UTE) pulse sequences

AIM: To assess the potential value of imaging the Achilles tendon with ultrashort echo time (UTE) pulse sequences.MATERIALS AND METHODS: Four normal controls and four patients with chronic Achilles tendinopathy were examined in the sagittal and transverse planes. Three of the patients were examined before and after intravenous gadodiamide.RESULTS: The fascicular pattern was clearly demonstrated within the tendon and detail of the three distinct fibrocartilaginous components of an “enthesis organ” was well seen. T2* measurements showed two short T2* components. Increase in long T2 components with reduction in short T2 components was seen in tendinopathy. Contrast enhancement was much more extensive than with conventional sequences in two cases of tendinopathy but in a third case, there was a region of reduced enhancement.CONCLUSION: UTE pulse sequences provide anatomical detail not apparent with conventional sequences, demonstrate differences in T2* and show patterns of both increased and decreased enhancement in tendinopathy.

Regional variations in normal brain shown by quantitative magnetization transfer imaging.

A quantitative magnetization transfer imaging (qMTI) study, based on a two-pool model of magnetization transfer, was performed on seven normal subjects to determine, on a regional basis, normal values for the pool sizes, exchange, and relaxation parameters that characterize the MT phenomenon. Regions were identified on high-resolution anatomical scans using a combination of manual and automatic methods. Only voxels identified as pure tissue at the resolution of the quantitative scans were considered for analysis. While no left/right differences were observed, significant differences were found among white-matter regions and gray-matter regions. These regional differences were compared with existing cytoarchitectural data. In addition, the pattern and magnitude of the regional differences observed in white matter was found to be different from that reported previously for an alternative putative MRI measure of myelination, the 10-50-ms T2 component described as myelin water.

Pulse NMR Study of Refrigerated Cooked Rice and Comparison with Physicochemical Properties

The behavior of water molecules in refrigerated cooked rice was examined by measuring spin-spin relaxation time T2 using a pulse NMR spectrometer. T2 decay curve was analyzed using two-component and non-linear regression analysis and the presence of three kinds of water components with different T2 were revealed. In the case of fresh cooked rice, the observed T2 and the relative population were 0.9 ms (short T2) and 13%, 26 ms (intermediate T2) and 76%, and 200 ms (long T2) and 11%, respectively. The short T2 component was ascribed to the water molecules hydrated directly on the starch molecules. Intermediate T2 component was dominant and ascribed to the water molecules accommodated in the starch matrix inside the rice grain. The mobility of water molecules was suppressed remarkably during the storage at 0°C while it was almost independent of the refrigerated storage below −18°C. The long T2 component was ascribed to those grains accommodated in the surface luster film that was formed in the initial stage of the cooking process and composed of low molecular weight polysaccharides. The relaxation property observed by NMR was well consistent with the physicochemical properties.

Computational and NMR Analyses for the Identification of Bound Water Molecules in Ribonuclease T1

A structural characterization of bound water molecules in ribonuclease T1 (RNase T1) was carried out by nuclear magnetic resonance spectroscopy and molecular dynamics simulation. Amide protons of residues Trp59, Leu62, Tyr68 and Phe100 were found to cross-relax with protons of bound waters. Molecular dynamics simulations of the 120 water molecules observed in the free form of the crystal structure indicate that these amide protons donate hydrogen bonds to the less mobile water molecules. Hydrogen-bonded chains of the water molecules that are identified in the simulation study are located in the hairpin-like loop of RNase T1, comprising residues 62 to 76. The temperature factors of the observed water molecules in the crystal structure are very low, indicating that these bound waters are intrinsic components of RNase T1.

Application of independent component analysis to magnetic resonance imaging for enhancing the contrast of gray and white matter

An application of independent component analysis (ICA) was attempted to develop a method of processing magnetic resonance (MR) images to extract physiologically independent components representing tissue relaxation times and achieve improved visualization of normal and pathologic structures. Anatomical T1-weighted, T2-weighted and proton density images were obtained from 10 normal subjects, 3 patients with brain tumors and 1 patient with multiple sclerosis. The data sets were analyzed using ICA based on the learning rule of Bell and Sejnowski after prewhitening operations. The three independent components obtained from the three original data sets corresponded to (1) short T1 components representing myelin of white matter and lipids, (2) relatively short T1 components representing gray matter and (3) long T2 components representing free water. The involvement of gray or white matter in brain tumor cases and the demyelination in the case of multiple sclerosis were enhanced and visualized in independent component images. ICA can potentially achieve separation of tissues with different relaxation characteristics and generate new contrast images of gray and white matter. With the proper choice of contrast for the original images, ICA may be useful not only for extracting subtle or hidden changes but also for preprocessing transformation before clustering and segmenting the structure of the human brain.

Magnetic resonance imaging of the liver with ultrashort TE (UTE) pulse sequences.

To assess the feasibility of imaging the liver in volunteers and patients with ultrashort echo time (UTE) pulse sequences. Seven normal controls as well as 12 patients with biopsy-proven generalized liver disease and three patients with focal disease were examined using pulse sequences with initial TEs of 0.08 msec followed by three later echoes, with or without frequency-based fat suppression. T(2)* values were calculated from regions of interest in the liver. Good image quality was obtained in each subject. There was a highly significant difference in the mean T(2)* values between the normal controls and patients with generalized liver disease (P = 0.001). T(2)* was significantly decreased in hemochromatosis (P = 0.002) and increased in cirrhosis (P = 0.04), compared with controls. T(2)* also correlated with functional status assessed by Child's grade (P = 0.001). A hepatocellular carcinoma showed reduced short T(2) components in the region of thermal ablation and evidence of a subcapsular hematoma which were not apparent with conventional imaging. Imaging of the liver with UTE sequences showed good image quality and tolerance of abdominal motion. T(2)* was specifically correlated with the presence of hemochromatosis, cirrhosis, and functional grade. Imaging of short T(2) relaxation components may provide useful information in disease.

Magnetic resonance: an introduction to ultrashort TE (UTE) imaging.

The background underpinning the clinical use of ultrashort echo-time (UTE) pulse sequences for imaging tissues or tissue components with short T2s is reviewed. Tissues properties are discussed, and tissues are divided into those with a majority of short T2 relaxation components and those with a minority. Features of the basic physics relevant to UTE imaging are described including the fact that when the radiofrequency pulse duration is of the order T2, rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad line-width of short T2 components are also discussed including their partial saturation by off-resonance fat suppression pulses as well as multislice and multiecho imaging. The need for rapid data acquisition of the order T2 is explained. The basic UTE pulse sequence with its half excitation pulse and radial imaging from the center of k-space is described together with options that suppress fat and/or long T2 components. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, and periosteum as well as brain, liver, and spine are illustrated. Short T2 components in all of these tissues may show high signals. Possible future developments are outlined as are technical limitations.

Another approach to protons with constricted mobility in white matter: pilot studies using wideline and high-resolution NMR spectroscopy.

We report a new approach for the identification of an independent method of studying the semi-solid pool of protons, i.e., protons with constrained motion as a result of being bound to lipid and protein matrices. These protons cannot be observed using conventional imaging techniques since their transverse relaxation times are much shorter than the minimum echo times that are currently available on clinical scanners. In this pilot study, in vitro multicomponent transverse relaxation experiments were made on human white matter slices, fixed in formalin (7 normal and 5 with multiple sclerosis). The transverse relaxation decay curves were multiexponential and were decomposed to yield three primary components. The shortest T(2) component that we obtained (a component too short to be seen by in vivo methods) was of the order of microseconds. We hypothesize that this might correspond to the macromolecular pool of lipid protons trapped within the myelin sheaths. To our knowledge, this is the first attempt at extracting this ultra short T(2) component from human white matter. Subsequently, an attempt was made to directly detect the lipid protons in a proton NMR spectrum and, if possible, measure their concentration in some of the tissues, using the technique of magic angle spinning.

Time-Resolved Electron Paramagnetic Resonance Study of the First Excited Triplet States of Dibenzocycloheptadienylidene and Diphenylmethylene Derivatives

Transient triplet electron paramagnetic resonance (EPR) spectra of dibenzocycloheptadienylidene (DBC) and substituted diphenylmethylenes were observed in a rigid glassy matrix at low temperatures. On excitation with the wavelength of the T−T transition of DBC, polarized EPR spectra due to the both ground (T0) and excited (T1) states were observed at a short delay time (180 ns) after the laser pulse. The T1 components in the spectrum decayed faster than the other and diminished at 1 μs after the laser pulse irradiation. The remaining signals after the decay of the T1 state were unambiguously assigned to the T0 state, taking into account the steady-state (SS) EPR results. From analysis of the spectrum of the short-lived triplet species, the zero-field splitting (ZFS) parameters, |D| = 0.201 and |E| = 0.008 cm-1, were determined for the T1 state directly. The parameters obtained were comparable to those of the T1 state of diphenylmethylene (DPM). The polarization patterns of the transient spectra match well with interpretation as anisotropic intersystem crossing induced by the spin−orbit couplings between the Sn and the triplet states. On the basis of the results of magnetophotoselection experiments, we also confirmed that the principal axes in the T0 and T1 states did not differ significantly from each other. The behavior of the methyl-substituted DPM resembles that of DPM and DBC, indicating that the methyl group does not affect the photophysical and photochemical properties of the T0 and T1 states. Although the SS EPR spectra were observed for the T0 state of substituted DPM derivatives, the chemical properties of the excited states were affected by substitution of electron-donating (OCH3) or -withdrawing (CN) groups.

パルス法ＮＭＲによる最近のゴム研究

Pulsed NMR, which is used for measuring spin-spin relaxation time, T2, and spin-lattice relaxation time, T1, has a unique advantage over other techniques because it can provide direct information on molecular motion and volume fraction of each component in the composites1), 3), 4), 20), 25), 60). Rubber-Carbon black interactions are very important to study the reinforcement of rubbers. The T2 signal of the bound rubber was resolved into two components, short T2 component and long T2 component. In a two-phase model for interpreting the reinforcement, one phase was the immobilized rubber layer around carbon blacks, and the other was the rubber away from the filler surface1), 29), 34), 36), 60) On the other hand, Folland and co-workers3), 4) suggested that unfilled isoprene rubber crosslinked by irradiation consisted of two components such as network structures and non-network structures. Recently, Noguchi and co-workers48) reported the results from a pulsed NMR spectroscopy with Hahn echo method for EPDM specimens and their relations with the dynamic fatigue behaviors. The retention of stress under fatigue for peroxide-crosslinked EPDM filled with carbon black, calcium-carbonate, or silica, tended to decrease as the network T23), 4) became longer and the non-network fraction became larger. This result suggests the relationships between the fatigue behavior and the non-network fraction as well as the molecular mobility of the network component.

Computed tomography and magnetic resonance imaging for noninvasive coronary angiography and plaque imaging: current and potential future concepts.

Atherothrombosis is a systemic disease of the vessel wall that causes distinct clinical manifestations, depending on the affected circulatory bed and the characteristics of the individual lesions.1 These lesions may be quite heterogeneous.1 Thus, the clinical manifestations of atherothrombosis of the coronary arteries, of the arteries supplying the central nervous system, of the aorta, and of the peripheral circulation can be significantly different. Disruption-prone plaques in the coronary arteries, the so-called “vulnerable plaques,” tend to have a thin fibrous cap (cap thickness ≈65 to 150 μm) and a large lipid core (American Heart Association [AHA] plaque type IV-Va). Acute coronary syndromes often result from disruption of a modestly stenotic vulnerable plaque, not visible by x-ray angiography, which results in a thrombotic complication (AHA plaque type VI). During its evolution, a type Va plaque may also become fibrotic (AHA plaque type Vc) or calcified (AHA plaque type Vb).2,3⇓ In contrast to coronary artery vulnerable plaques characterized by high lipid content and a thin fibrous cap, high-risk plaques of the carotid arteries tend to be fibrotic and severely stenotic.3 ### Imaging of Atherothrombotic Disease Because there is striking heterogeneity in the composition of human atherothrombotic plaques, even within the same individual, reliable noninvasive imaging tools that can detect early atherothrombotic disease in the various regions and characterize the composition of the plaques are clinically desirable.3 Such imaging tools would improve our understanding of the pathophysiological mechanisms underlying atherothrombotic processes and allow us to better risk-stratify the disease. Additionally, such tools may permit optimal tailoring of treatment and allow direct monitoring of the vascular response. Presently, a number of imaging modalities are employed to study atherosclerosis; most identify luminal diameter or stenosis, wall thickness, and plaque volume.3 Two noninvasive imaging modalities, computed tomography and MRI, have been introduced to the study …

Biexponential T2 Relaxation Time Analysis of the Brain

To measure T2 relaxation times of normal white and gray matter using a novel CPMG sequence and investigate if any correlation exists between magnetization transfer ratio (MTR) and T2 relaxation-related parameters. Seventeen normal volunteers participated on this study. A single-slice 32-echo sequence was used to calculate the T2 relaxation time of frontal and occipital white matter and cortical gray matter. T2 relaxation analysis included monoexponential and biexponential fitting whereas an F test was used to determine if biexponential fitting was statistically more accurate than monoexponential fitting. Short and long T2 constants were calculated as well as the signal fractions of each pool. MTR calculations were based on a three-dimensional gradient echo (3D FFE) proton density weighted sequence with and without an on-resonance composite prepulse. MTR and T2 relaxation times were calculated and linear regression analysis was applied. Biexponential fitting was more accurate comparing with monoexponential fitting in all WM and GM regions (F > 2.47, P < 0.01). Mean values of short T2 constant for frontal white matter (fWM), occipital white matter (oWM) and gray matter (GM) were 8.10, 9.36, and 22.23 milliseconds, respectively, whereas the mean values of long T2 constant were 85.1, 93.02, and 118.72 milliseconds, respectively. Mean restricted water percentages (RWP)-corresponding to the signal fraction of the protons with short T2-for the fWM, oWM, and GM were 22.01%, 23.36%, and 18.7%. Mean free water percentages (FWP)-corresponding to the signal fraction of the protons with long T2-for the fWM, oWM and GM were 77.99%, 76.64%, and 81.3%. Mean MTR values for fWM, oWM and GM were 68.4%, 68.2%, and 61.3%, respectively. No significant correlation was found in fWM and oWM between MTR and RWP, short and long T2 components while a moderate correlation existed in GM between MTR and RWP (r = 0.57; P = 0.02), MTR and short T2 component (r = -0.69; P = 0.004) and MTR and long T2 component (r = -0.62; P = 0.012). Two proton pools with different T2 decay characteristics can be separated in normal gray and white matter when using a multiecho sequence with short echo spacing. MTR and T2 relaxation times were significantly correlated in gray matter and the combination of both types of measurements may be helpful in studying myelin related disorders.

パーオキサイド架橋ＥＰＤＭの構造と動的特性に関する研究 第１報 動的粘弾性とパルス法ＮＭＲによるＥＰＤＭのパーオキサイド架橋構造の考察

The network structure of peroxide-crosslinked ethylene-propylene-diene rubber (EPDM) was examined by dynamic mechanical analysis and 1H pulsed NMR. The loss tangent (tanδ) hardly changed with the increase of the crosslinking density (νe) in the glass transition region (<0°C). However, in the higher temperature region, a broad tanδ peak was observed for less crosslinked systems. This relaxation was thought to be connected with the entanglement of long dangling chain ends. The tanδ values at 150°C decreased with the increase of νe. The signal of spin-spin relaxation time (T2) was resolved into three components. The three components respectively correspond to the molecules surrounding crosslinking points, molecules between crosslinking points, and non-network molecules such as dangling chains and end-chains. The increase of νe reduced the molecular mobility of each T2 component, and decreased the fraction of component with the longest T2 consisting of dangling chains. The fraction of each T2 component showed good correlation with tanδ values at 150°C independent of the kinds of fillers.

2H NMR spin relaxation study of the soft segment motion in alternating ethylene–propylene copolymers

AbstractWe synthesized three partially deuterated polymer samples, namely a poly(ethylene‐alt‐propylene) (EP) alternating copolymer, a poly(styrene‐b‐EP) diblock copolymer (SEP) and a poly(styrene‐b‐EP‐b‐styrene) triblock copolymer (SEPS). The 2H spin–lattice relaxation time, T1, of EP soft segments above their glass transition temperature was measured by solid‐state 2H NMR spectroscopy. It was found that the block copolymers had a fast and a slow T1 component whereas EP copolymer had only a fast component. The fast T1 components for SEP and SEPS are similar to the T1 value of EP above ca 20°C. The slow T1 component for SEP and SEPS exhibited a minimum at 60°C and approached the value of the fast component near the Tg of polystyrene. The motional behavior of the EP units for SEP is similar to that of SEPS over the entire range of temperature. Copyright © 2001 John Wiley &amp; Sons, Ltd.

A phenomenological theory of possible sequences of ferrotoroidal phase transitions in boracites

A phenomenological theory of the sequence of two second-order phase transitions with close temperatures is considered; such transitions occur in the Ni-Br boracite. The thermodynamic potential is written as a function of polarization Pi, magnetization Mi, and toroidal moment Ti vectors and fields Ei and Hi; Ti is treated as an order parameter. It is assumed that only one coefficient of Ti2passes through zero as T decreases. The possibility of a sequence of two proper ferrotoroidal phase transitions along the T1 and T2 components is demonstrated. Spontaneous Ti, Pi, and Mi vector values and equations for susceptibility tensors (dielectric χij = dPi/dEj, magnetic kij = dMi/dHj, and magnetoelectric αij = dPi/dHj = dMj/dEi) were obtained for three phases. Some of these values have well-defined anomalies in the vicinity of transitions. All possible sequences of ferrotoroidal phase transitions in boracites are considered. Depending on two potential coefficient values, these sequences may consist of one, two, or three such transitions.

Magnetization transfer of water T2 relaxation components in human brain: implications for T2-based segmentation of spectroscopic volumes

Biexponential T2 relaxation of the localized water signal can be used for segmentation of spectroscopic volumes. To assess the specificity of the components an iterative relaxation measurement of the localized water signal (STEAM, 12 echo times, geometric spacing from 30 ms to 2000 ms) was combined with magnetization transfer (MT) saturation (40 single lobe pulses, 12 ms duration, 1440° nominal flip angle, 1 kHz offset, repeated every 30 ms). Voxels including CSF were examined in parietal cortex and periventricular parietal white matter (10 each), as well as 13 voxels in central white matter and 16 T1-hypointense non-enhancing multiple sclerosis lesions without CSF inclusion. Biexponential models (excluding myelin water) were fitted to the relaxation data. In periventricular VOIs the component of long T2 (1736 ± 168 ms) that is attributed to CSF was not affected by MT. In cortical VOIs this component had markedly shorter T2’s (961 ± 239 ms) and showed both attenuation and prolongation with MT, indicating contributions from tissue. MS lesions and central WM showed a second tissue component of intermediate T2 (160–410 ms). In white matter similar MT attenuation indicated strong exchange between the two tissue components, prohibiting segmentation. In MS lesions, however, markedly less MT of the intermediate component was found, which is consistent with decreased cellularity and exchange in a region that is large compared to diffusion motion.

Different magnetization transfer effects exhibited by the short and long T2 components in human brain

Different magnetization transfer effects exhibited by the short and long T2 components in human brain

Structural and Dynamic Study of Ethylene−Vinyl Alcohol Copolymer Gels by 1H Pulse NMR and Solid-State 13C NMR

1H pulse NMR and solid-state 13C NMR spectra of ethylene−vinyl alcohol copolymer (EVOH) gels were measured as a function of ethylene content, and furthermore, the 13C spin−lattice relaxation times (T1) and the 1H spin−spin relaxation times (T2) have been measured, to elucidate the structure and dynamics of the mobile and immobile regions in the gels. From the 1H pulse NMR experimental results, it is found that the 1H T2 signal is mainly composed of two or three kinds of components with different molecular motions. The long T2 component is assigned to correspond to the mobile region, which comes from the un-cross-linked region, the short T2 component corresponds to the immobile region, which comes from the cross-linked region, and the intermediate T2 component corresponds to the intermediate region between the mobile and immobile regions, which comes from the vicinity of the cross-linked region in the EVOH gel. Furthermore, from the solid state 13C NMR experimental results, it is found that the formation of hydrogen bonds between the hydroxyl groups in vinyl alcohol parts of EVOH copolymers with high vinyl alcohol fraction and the formation of hydrophobic interactions between the methylene groups in ethylene parts of EVOH copolymers with high ethylene fraction contributes to its gel formation.