Proton T1 Research Articles

T1-T2 Dual-modal MRI contrast agents based on superparamagnetic iron oxide nanoparticles with surface attached gadolinium complexes.

Dual-mode MRI contrast agents consisting of superparamagnetic iron oxide nanoparticle (SPION) cores and gadolinium ions associated with the ionic chitosan protecting layer were synthesized and studied. Gadolinium ions were introduced into the coating layer via direct complex formation on the nanoparticles surface, covalent attachment or electrostatically driven deposition of the preformed Gd complex. The modified SPIONs having hydrodynamic diameters ca. 100 nm form stable, well-defined dispersions in water and have excellent magnetic properties. Physiochemical properties of those new materials were characterized using e.g., FTIR spectroscopy, dynamic light scattering, X-ray fluorescence, TEM, and vibrating sample magnetometry. They behave as superparamagnetics and shorten both T1 and T2 proton relaxation times, thus influencing both r1 and r2 relaxivity values that reach 53.7 and 375.5 mM−1 s−1, respectively, at 15 MHz. The obtained materials can be considered as highly effective contrast agents for low-field MRI, particularly useful at permanent magnet-based scanners.

Dual responsive PNIPAM–chitosan targeted magnetic nanopolymers for targeted drug delivery

A dual stimuli sensitive magnetic hyperthermia based drug delivery system has been developed for targeted cancer treatment. Thermosensitive amine terminated poly-N-isopropylacrylamide complexed with pH sensitive chitosan nanoparticles was prepared as the drug carrier. Folic acid and fluorescein were tagged to the nanopolymer complex via N-hydroxysuccinimide and ethyl-3-(3-dimethylaminopropyl) carbodiimide reaction to form a fluorescent and cancer targeting magnetic carrier system. The formation of the polymer complex was confirmed using infrared spectroscopy. Gadolinium doped nickel ferrite nanoparticles prepared by a hydrothermal method were encapsulated in the polymer complex to form a magnetic drug carrier system. The proton relaxation studies on the magnetic carrier system revealed a 200% increase in the T1 proton relaxation rate. These magnetic carriers were loaded with curcumin using solvent evaporation method with a drug loading efficiency of 86%. Drug loaded nanoparticles were tested for their targeting and anticancer properties on four cancer cell lines with the help of MTT assay. The results indicated apoptosis of cancer cell lines within 3 h of incubation.

On the temperature dependence of several physicochemical properties for aqueous solutions of the ionic liquid 1-butyl-3-methylimidazolium methanesulfonate ([C4mim][MeSO3

The viscosity, conductivity, proton T1 relaxation, and the self-diffusion coefficients of cation, anion and water are presented for the binary system water–1-butyl-3-methylimidazolium methanesulfonate ([C4mim][MeSO3]) for the temperature and composition ranges of (298.15–343.14) K and ionic liquid mole fractions 0<xIL<0.5. The temperature dependence of these properties at fixed compositions was analyzed to obtain Arrhenius activation energies, which were found to be linearly dependent to xIL for xIL greater than about 0.15 for the self-diffusion coefficients, viscosity and proton T1 relaxation times (except for the water proton T1 relaxation times). The specific xIL dependencies of the various Arrhenius activation energies are qualitatively different from what was observed in a prior study of the water–1-ethyl-3-methylimidazolium methanesulfonate ([C2mim][MeSO3]) binary system [J. Mol. Liq. 160 (2011) 166–179]. In particular, the T1 relaxation behavior is markedly different und is discussed in detail along with other comparisons between these two water–IL binary systems.

NMR relaxation and exchange in metal–organic frameworks for surface area screening

We describe a robust screening technique that correlates the surface area of metal–organic frameworks to the proton T2 relaxation behavior of imbibed solvent at low field (13MHz). In frameworks with small pore sizes (<1nm) or strong solvent-framework interactions, diffusional exchange between the pore-confined and inter-particle solvent populations remains slow compared to the T2 of the pore-confined solvent, allowing for a direct porosity analysis of the T2 spectrum obtained from Laplace inversions. Increases in framework pore-size (>1nm) lead to corresponding increases in the rate of solvent exchange, as confirmed by T2 relaxation exchange (REXSY) experiments; increases in the pore size also increases the T2 of the pore-confined solvent. The combination of these two effects results in comparable rates of relaxation and exchange, which precludes the direct analysis of Laplace inversions. Thus, two- and three-site kinetics models were applied to extract porosity from relaxation decays, thereby improving the utility of the porosity screening tool.

Fe3+ ions anchored to Fe@O-MWCNTs as double impact T2 MRI contrast agents

Fe3+ ions were anchored via complexation onto the oxidized multiwall carbon nanotubes containing encapsulated iron-based nanoparticles (Fe@O-MWCNTs) yielding hybrids Fe(III)/Fe@O-MWCNTs for application as MRI contrast agents. After washing, no free Fe3+ ions were observed in the solution. A 120 mg Fe3+ was coordinated by each 1 gram of Fe@O-MWCNTs with a formation of stable hybrids. Relaxation times T1 and T2 of water protons were measured for the suspensions of hybrids. At 7.1 T relaxivity, r2 of Fe@O-MWCNT and Fe(III)/Fe@O-MWCNT was 25 and 35 s–1ml mg–1, respectively, whereas at 0.4 T r2-values were equal. Additionally, T1/T2 ratio was found in a range of 17–104, which is a promising value in the light of application of the proposed materials as potential T2 MRI contrast agents.

Exploiting parameter sparsity in model-based reconstruction to accelerate proton density and T2 mapping

T2 mapping is a powerful noninvasive technique providing quantitative biological information of the inherent tissue properties. However, its clinical usage is limited due to the relative long scanning time. This paper proposed a novel model-based method to address this problem. Typically, we directly estimated the relaxation values from undersampled k-space data by exploiting the sparse property of proton density and T2 map in a penalized maximum likelihood formulation. An alternating minimization approach was presented to estimate the relaxation maps separately. Both numerical phantom and in vivo experiment dataset were used to demonstrate the performance of the proposed method. We showed that the proposed method outperformed the state-of-the-art techniques in terms of detail preservation and artifact suppression with various reduction factors and in both moderate and heavy noise circumstances. The superior reconstruction performance validated its promising potential in fast T2 mapping applications.

In vivo proton T1 relaxation times of mouse myocardial metabolites at 9.4 T.

Proton magnetic resonance spectroscopy ((1) H-MRS) for quantitative in vivo assessment of mouse myocardial metabolism requires accurate acquisition timing to minimize motion artifacts and corrections for T1 -dependent partial saturation effects. In this study, mouse myocardial water and metabolite T1 relaxation time constants were quantified. Cardiac-triggered and respiratory-gated PRESS-localized (1) H-MRS was employed at 9.4 T to acquire signal from a 4-µL voxel in the septum of healthy mice (n = 10) while maintaining a steady state of magnetization using dummy scans during respiratory gates. Signal stability was assessed via standard deviations (SD) of zero-order phases and amplitudes of water spectra. Saturation-recovery experiments were performed to determine T1 values. Phase SD did not vary for different repetition times (TR), and was 13.1° ± 4.5°. Maximal amplitude SD was 14.2% ± 5.1% at TR = 500 ms. Myocardial T1 values (mean ± SD) were quantified for water (1.71 ± 0.25 s), taurine (2.18 ± 0.62 s), trimethylamine from choline-containing compounds and carnitine (1.67 ± 0.25 s), creatine-methyl (1.34 ± 0.19 s), triglyceride-methylene (0.60 ± 0.15 s), and triglyceride-methyl (0.90 ± 0.17 s) protons. This work provides in vivo quantifications of proton T1 values for mouse myocardial water and metabolites at 9.4 T.

The impact of alkali pretreatment and post-pretreatment conditioning on the surface properties of rice straw affecting cellulose accessibility to cellulases

Rice straw was pretreated with sodium hydroxide and subsequently conditioned to reduce the pH to 5–6 by either: (1) extensive water washing or (2) acidification with hydrochloric acid then water washing. Alkali pretreatment improved the enzymatic digestibility of rice straw by increasing the cellulose accessibility to cellulases. However, acidification after pretreatment reversed the gains in cellulose accessibility to cellulases and enzymatic digestibility due to precipitation of solubilized compounds. Surface composition analyses by ToF-SIMS confirmed a reduction in surface lignin by pretreatment and water washing, and suggested that acidification precipitated a chemically modified form of lignin on the surfaces of rice straw. The spin–spin relaxation times (T2) of the samples indicated increased porosity in alkali pretreated rice straw. The acidified pretreated rice straw had reduced amounts of water in the longer T2 proton pools associated with water in the pores of the biomass likely due to back-filling by the precipitated components.

In vivo T(2) relaxation time measurement with echo-time averaging.

The accuracy of metabolite concentrations measured using in vivo proton ((1) H) MRS is enhanced following correction for spin-spin (T2 ) relaxation effects. In addition, metabolite proton T2 relaxation times provide unique information regarding cellular environment and molecular mobility. Echo-time (TE) averaging (1) H MRS involves the collection and averaging of multiple TE steps, which greatly simplifies resulting spectra due to the attenuation of spin-coupled and macromolecule resonances. Given the simplified spectral appearance and inherent metabolite T2 relaxation information, the aim of the present proof-of-concept study was to develop a novel data processing scheme to estimate metabolite T2 relaxation times from TE-averaged (1) H MRS data. Spectral simulations are used to validate the proposed TE-averaging methods for estimating methyl proton T2 relaxation times for N-acetyl aspartate, total creatine, and choline-containing compounds. The utility of the technique and its reproducibility are demonstrated using data obtained in vivo from the posterior-occipital cortex of 10 healthy control subjects. Compared with standard methods, distinct advantages of this approach include built-in macromolecule resonance attenuation, in vivo T2 estimates closer to reported values when maximum TE ≈ T2 , and the potential for T2 calculation of metabolite resonances otherwise inseparable in standard (1) H MRS spectra recorded in vivo.

Bread staling: Effect of gluten on physico-chemical properties and molecular mobility

Three gluten enriched breads were produced (5% and 15% gluten samples where water was adjusted with farinograph determination, and a 15% sample with the same water amount of the control). The effect of gluten on bread staling (7 days) was evaluated, focussing on texture, amylopectin retrogradation, water status and 1H molecular mobility.The addition of gluten at higher levels (15%) resulted in breads, that retained higher softness, springiness and cohesiveness upon storage. Crumb moisture content was not affected by gluten but at a macromolecular level (DSC) 15% samples showed higher frozen water content. NMR measurements showed a significant effect of gluten on proton T2 relaxation time distributions, revealing a larger presence of protons strongly interacting with water and a more pronounced proton exchange with increasing storage time. The results suggested that, in the presence of gluten, a larger amount of water might be available to plasticize the crumb structure, resulting in a softer product.

Technical review, types of imaging, part 4--magnetic resonance imaging.

Technical review, types of imaging, part 4--magnetic resonance imaging.

Effects of Gadolinium Contrast Agent Administration on Automatic Brain Tissue Classification of Patients with Multiple Sclerosis

The administration of gadolinium contrast agent is a common part of MR imaging examinations in patients with MS. The presence of gadolinium may affect the outcome of automated tissue classification. The purpose of this study was to investigate the effects of the presence of gadolinium on the automatic segmentation in patients with MS by using the synthetic tissue-mapping method. A cohort of 20 patients with clinically definite multiple sclerosis were recruited, and the T1 and T2 relaxation times and proton density were simultaneously quantified before and after the administration of gadolinium. Synthetic tissue-mapping was used to measure white matter, gray matter, CSF, brain parenchymal, and intracranial volumes. For comparison, 20 matched controls were measured twice, without gadolinium. No differences were observed for the control group between the 2 measurements. For the MS group, significant changes were observed pre- and post-gadolinium in intracranial volume (-13 mL, P < .005) and cerebrospinal fluid volume (-16 mL, P < .005) and the remaining, unclassified non-WM/GM/CSF tissue volume within the intracranial volume (+8 mL, P < .05). The changes in the patient group were much smaller than the differences, compared with the controls, which were -129 mL for WM volume, -22 mL for GM volume, +91 mL for CSF volume, 24 mL for the remaining, unclassified non-WM/GM/CSF tissue volume within the intracranial volume, and -126 mL for brain parenchymal volume. No significant differences were observed for linear regression values against age and Expanded Disability Status Scale. The administration of gadolinium contrast agent had a significant effect on automatic brain-tissue classification in patients with MS by using synthetic tissue-mapping. The observed differences, however, were much smaller than the group differences between MS and controls.

Evaluation of The Effects Of Rheumatoid Arthritis On The Hard And Soft Tissue Components Of The Temporomandibular Joint By Using Magnetic Resonance Imaging

Background : Magnetic Resonance imaging (MRI) has been used to visualize the destructive effect of the Rheumatoid Arthritis ( RA) within the body joints , while Temporomandibular joint is often to be neglected. Aim of the study: observe the hard and soft tissue changes as well as the clinical involvement that may affect the TMJ in patients with longstanding RA. Patients and methods: 42 patients (84 TMJ’S), with mean age of (40.6 years) ranged from (28 to 63) years were divided into 2 groups; study (30) and control (12), all study group subjects consisted of patients with confirmed RA According to the criteria of American College Of Rheumatology (1987).Both groups have been examined clinically (at almustansiriya university/college of dentistry) and with MRI (at the MRI unit in alkadhmyia teaching hospital) in both sagital and coronal planes (open and close mouth) by the use of proton density and T2 weighted protocols. Results : The clinical involvement was present within (73.3%) of the study sample as the joint’s sounds was the predominant feature (80%) , masticatory muscle tenderness tenderness 70% , pain during function 58% ,morning stiffness 36.6% , deviation 43.3% while open bite was present in two cases (6.6%) , 33.3% of the RA patients had at least 3 clinical involvements , 26.6 % had at least 2 clinical involvement, uni-lateral involvement was present in 30% of RA patients, 5 subjects had only right side involvement and 4 patients had only left side involvement while bilateral involvement was present in 50% of RA patients. The mouth opening was significantly lowered (P<0.01) when compared with the control group.MRI findings was present in 80% of the study sample which lead to significant difference statistically when compared with the control group, the most common finding was the condylar head erosion (CHE), complete condylar destruction (score 4) was found in 2 RA patients, internal derangement 73.3%, meniscus perforation 73%, joint effusion 70%, increased joint space 66.6%, and osteophytes formation 60%, unilateral involvement was present in 53.3%, 5 subjects had right involvement only, and 7 subjects had left side involvement, while bilateral involvement was present in 46.7% . Key Words: Temporomandibular Joint, Rheumatoid Athritis , Magnatic Resonance Imaging , American College Of Rheumatology , Condylar Head Erosion.

T1 mapping in ischaemic heart disease

A unique feature of cardiac magnetic resonance is its ability to characterize myocardium. Proton relaxation times, T1, T2, and T2* are a reflection of the composition of individual tissues, and change in the presence of disease. Research into T1 mapping has largely been focused in the study of cardiomyopathies, but T1 mapping also shows huge potential in the study of ischaemic heart disease. In fact, the first cardiac T1 maps were used to characterize myocardial infarction. Robust high-resolution myocardial T1 mapping is now available for use as a clinical tool. This quantitative technique is simple to perform and analyse, minimally subjective, and highly reproducible. This review aims to summarize the present state of research on the topic, and to show the clinical potential of this method to aid the diagnosis and treatment of patients with ischaemic heart disease.

Reversible Cross-Linking, Microdomain Structure, and Heterogeneous Dynamics in Thermally Reversible Cross-Linked Polyurethane as Revealed by Solid-State NMR

Polyurethane material is widely utilized in industry and daily life due to its versatile chemistry and relatively easy handling. Here, we focused on a novel thermally reversible cross-linked polyurethane with comprehensive remarkable mechanical properties as reported in our recent work (Adv. Mater. 2013, 25, 4912). The microphase-separated structure and heterogeneous segmental dynamics were well revealed by T2 relaxometry experiments, which was also first utilized to in situ monitor the reversible cross-linking associated with Diels-Alder (DA) and retro-Diels-Alder (RDA) reactions. On the basis of T2 relaxometry results, we determined the actual temperature of the (R)DA reaction as well as the corresponding activation energies of the motion of soft segments. Besides, the roles of the temperature and cross-linker contents on the microdomain structure and dynamics are discussed in detail. It is found that the microphase separation is enhanced by the increase of temperature as well as the incorporation of cross-linkers. Also, the polyurethane samples are still thermal-stable even at a high temperature beyond the disassociation of the cross-linkages. Furthermore, Baum-Pines and three-pulse multiple-quantum NMR experiments are utilized to investigate the heterogeneous structures and dynamics of the mobile and rigid segments, respectively. Both the results obtained from the T2 relaxometry and multiple-quantum NMR experiments are in good agreement with the macroscopic mechanical properties of the polyurethane. Finally, it is also well demonstrated that proton T2 relaxometry combined with multiple-quantum NMR is a powerful method to study the heterogeneous structures and dynamics of a multiphase polymer system.

A Compressed Sensing Framework for Magnetic Resonance Fingerprinting

Inspired by the recently proposed magnetic resonance fingerprinting (MRF) technique, we develop a principled compressed sensing framework for quantitative MRI. The three key components are a random pulse excitation sequence following the MRF technique, a random EPI subsampling strategy, and an iterative projection algorithm that imposes consistency with the Bloch equations. We show that, theoretically, as long as the excitation sequence possesses an appropriate form of persistent excitation, we are able to accurately recover the proton density, T1, T2, and off-resonance maps simultaneously from a limited number of samples. These results are further supported through extensive simulations using a brain phantom.

Simultaneous dual contrast weighting using double echo rapid acquisition with relaxation enhancement (RARE) imaging

This work proposes a dual contrast rapid acquisition with relaxation enhancement (RARE) variant (2in1-RARE), which provides simultaneous proton density (PD) and T2 * contrast in a single acquisition. The underlying concept of 2in1-RARE is the strict separation of spin echoes and stimulated echoes. This approach offers independent weighting of spin echoes and stimulated echoes. 2in1-RARE was evaluated in phantoms including signal-to-noise ratio (SNR) and point spread function assessment. 2in1-RARE was benchmarked versus coherent RARE and a split-echo RARE variant. The applicability of 2in1-RARE for brain imaging was demonstrated in a small cohort of healthy subjects (n = 10) and, exemplary, a multiple sclerosis patient at 3 Tesla as a precursor to a broader clinical study. 2in1-RARE enables the simultaneous acquisition of dual contrast weighted images without any significant image degradation and without sacrificing SNR versus split-echo RARE. This translates into a factor of two speed gain over multi-contrast, sequential split-echo RARE. A 15% broadening of the point spread function was observed in 2in1-RARE. T1 relaxation effects during the mixing time can be neglected for brain tissue. 2in1-RARE offers simultaneous acquisition of images of anatomical (PD) and functional (T2 *) contrast. It presents an alternative to address scan time constraints frequently encountered during sequential acquisition of T2 * or PD-weighted RARE.

Ultrashort echo time MRI of pulmonary water content: assessment in a sponge phantom at 1.5 and 3.0 Tesla

We aimed to develop a predictive model for lung water content using ultrashort echo time (UTE) magnetic resonance imaging (MRI) and a sponge phantom. Image quality was preliminarily optimized, and the signal-to-noise ratio (SNR) of UTE was compared with that obtained from a three-dimensional fast gradient echo (FGRE) sequence. Four predetermined volumes of water (3.5, 3.0, 2.5, and 2.0 mL) were soaked in cellulose foam sponges 1.8 cm3 in size and were imaged with UTE-MRI at 1.5 and 3.0 Tesla (T). A multiple echo time experiment (range, 0.1-9.6 ms) was conducted, and the T2 signal decay curve was determined at each volume of water. A three-parameter equation was fitted to the measured signal, allowing for the calculation of proton density and T2*. The calculation error of proton density was determined as a function of echo time. The constants that allowed for the determination of unknown volumes of water from the measured proton density were calculated using linear regression. UTE-MRI provided excellent image quality for the four phantoms and showed a higher SNR, compared to that of FGRE. Proton density decreased proportionally with the decreases in both lung water and field strength (from 3.5 to 2.0 mL; proton density range at 1.5 T, 30.5-17.3; at 3.0 T, 84.2-41.5). Minimum echo time less than 0.6 ms at 1.5 T and 1 ms at 3.0 T maintained calculation errors for proton density within the range of 0%-10%. The slopes of the lines for determining the unknown volumes of water with UTE-MRI were 0.12±0.003 at 1.5 T and 0.05±0.002 at 3.0 T (P < 0.0001). In a sponge phantom imaged at 1.5 and 3.0 T, unknown volumes of water can be predicted with high accuracy using UTE-MRI.

A morphological interpretation of water chemical exchange and mobility in cellulose materials derived from proton NMR T2 relaxation

Proton T2 relaxation times of water in cellulosic fibres have been interpreted using a 3-term average model. Motional and chemical exchange contributions to relaxation show opposing temperature behaviour, enabling the use of Arrhenius analysis to determine proton exchange rates and water rotational correlation times. Both parameters vary dramatically with extent of hydration, with chemical exchange dominating relaxation at saturated water contents. Interpretations are based on a morphological model with two types of accessible cellulose, at void surfaces and internally within the cellulose phase. In native cellulose fibres, the presence of crystalline fibrils with low internal accessibility leads to rapid proton exchange at low moisture contents. Regenerated cellulose fibres typically have lower crystallinity and higher internal accessibility, which results in slower exchange as result of migration of water between void and internal environments. Exchange behaviour in regenerated fibres is highly dependent on structural organisation, which depends on the manufacturing process.

In vivo relaxation behavior of liver compounds at 7 tesla, measured by single‐voxel proton MR spectroscopy

To assess the proton T1 and T2 relaxation of in vivo hepatic water, choline and lipid resonances with possible J-coupling behavior of lipids in healthy volunteers at 7 Tesla (T). Relaxation measurements were conducted on corn oil phantoms and on the hepatic tissue of 11 healthy volunteers at 7 T using a surface coil and a STEAM sequence. T1 's were determined by monoexponential fitting, and T2 's by both monoexponential and enhanced-exponential fitting (empirically designed to consider J-coupling of lipid resonances). In vivo T1 's at 7 T were estimated as follows: water (4.70 ppm), 1362 ± 83 ms; methyl- (0.90 ppm), 1026 ± 162 ms; methylene- (1.30 ppm), 514 ± 25 ms; α-olefinic- (2.02 ppm), 488 ± 220 ms; α-carboxyl- (2.24 ppm), 476 ± 89 ms; diacyl- (2.77 ppm), 479 ± 260 ms group of lipid chains; and choline compounds (3.22 ppm), 1084 ± 52 ms. The T2 's calculated with enhanced fitting were as follows: water, 15 ± 2 ms; methyl-, 34 ± 10 ms; methylene-, 41 ± 8 ms; α-olefinic-, 44 ± 19 ms; α-carboxyl-, 39 ± 15 ms; diacyl-, 44 ± 5 ms group of lipid chains; and choline compounds, 32 ± 9 ms. An accurate knowledge of in vivo relaxation and J-coupling behavior will significantly improve the quantification of an extended number of resolved liver metabolites at 7 T.