T1 Relaxation Processes Research Articles

Role of Contrast in MR Imaging.

Magnetic resonance (MR) contrast agents have been widely used over the last 3 decades in routine clinical practice. Paul Lauterbur recognized the presence of these contrast agents, which act as paramagnetic catalysts that accelerate the T1 relaxation process. The first MR contrast agent to be approved for clinical use was in 1988, and since then, it is estimated that 200 million doses have been administered worldwide. These contrast agents have diverse clinical as well as research applications, involving almost all the body organs. This review will cover some existing as well as many new applications that have emerged over the last few decades. MR imaging now has the potential of being used to monitor enzymatic activity, gene expression, metal ion homeostasis, and cell death in vivo. In future, newer contrast agents will develop and become commercially available, expanding the current clinical applications of MR contrast media.

On the generation of a foam film during a topological rearrangement

AbstractT1 topological rearrangement, i.e. switching of neighbouring bubbles in a liquid foam, is the elementary process of foam dynamics, and it involves film disappearance and generation. It has been studied extensively as it is crucial in foam rheology or foam collapse. T1 dynamics depends mainly on the surfactants used to generate the foam, and several models taking into account surface viscosity and/or elasticity have been proposed. By performing experiments in a cubic assembly of films, we go a step forward in this global analysis and investigate experimentally the mechanism of formation of the new film. In particular, the flow velocity field is probed by particle tracking and the film thickness is measured by light absorption and interferometric measurements. Two limit behaviours for the film are reported: it may (i) undergo an homogeneous extension, or (ii) resist elongation and remain at rest, new film being created from liquid exchange with connecting meniscus. Both T1 dynamics and film thickness are shown to depend on the competition between these two behaviours. Interestingly, their balance is set by the surfactant solution used, but it is also shown to vary during a single T1 relaxation process.

Tissue Characterization of Intracranial Tumors by MR Imaging

The main purpose of this in vivo study was to provide a detailed description of the T1- and T2-relaxation processes in intracranial tumors at 1.5 T. A total of 100 patients were investigated. Optimal experimental conditions were carefully observed, including the use of long TR values. T1 determination was based on a partial saturation inversion recovery sequence covering 12 or 6 data points. T2 determination involved a multiple spin echo sequence with 32 echoes. Calculations included biexponential analysis of the 12-point T1 data and all T2 data obtained. The results were evaluated in accordance with histopathology. The T1- and the T2-relaxation times of the prevailing tumor types were significantly different (p less than 0.0005). However, biologic scatter and overlap between tumor types were considerable. In particular, no discrimination between benign and malignant tumor growth was possible. Biexponential evaluation did not increase the specificity, although a biexponential relaxation behavior was recognized in 37% of the T2 curves. The results indicate that tissue heterogeneity is responsible for most of the scatter in the relaxation times. It is concluded that tissue characterization by MR imaging, based solely on relaxation time measurements, seems to be of no value in the differentiation of intracranial tumors.

Changes in T1 relaxation processes in the bone marrow following treatment in children with acute lymphoblastic leukemia

Magnetic resonance imaging (MRI) and T1 relaxation time measurements of the vertebral bone marrow were performed in 11 children with acute lymphoblastic leukemia (ALL) at diagnosis. Nine of the children were re-examined after chemotherapeutic treatment. The results were compared with histological data from bone marrow biopsies obtained in close association to the MR examinations. Ten age matched children were examined as a control group. A 1.5 Tesla whole body scanner was used for the measurements. The pretreatment T1 relaxation times of the bone marrow were significantly prolonged, compared to the age matched controls. After chemotherapy the T1 relaxation times of the children with ALL decreased significantly towards or into the normal range. A significant correlation was found between the T1 relaxation time and the content of malignant blast cells in the bone marrow.

In Vivo Measurements of the T1 Relaxation Processes in the Bone Marrow in Patients with Myelodysplastic Syndrome

Nine patients with myelodysplastic syndrome (MDS) were examined with magnetic resonance imaging and in vivo T1 relaxation time measurements of the vertebral bone marrow in a 1.5 tesla whole body scanner. Two patients underwent transformation to acute myeloid leukemia and were evaluated at follow-up examinations. At the time of diagnosis the T1 relaxation times of the vertebral bone marrow were significantly prolonged compared with normal values. The T1 relaxation times of the vertebral bone marrow in patients with MDS showed significantly lower values compared with patients with acute leukemia and did not differ from patients with polycythemia vera.

Evaluation of Biexponential Relaxation Behaviour in the Human Brain by Magnetic Resonance Imaging

Quantitative estimation of individual biologic components in relaxation curves obtained in vivo may increase the specificity of tissue characterization by magnetic resonance imaging. In this study, the potential of biexponential curve analysis was evaluated in T1 and T2 measurements on the human brain at 1.5 tesla. Optimal experimental conditions were carefully observed, including the use of long TR values and a very small voxel size. T1 determination was based on a 12-points partial saturation inversion recovery pulse sequence. T2 determination involved a multiple spin echo sequence with 32 echoes. No genuine biexponentiality was demonstrated in the T1 and T2 relaxation processes of white matter, cortical grey matter, or cerebrospinal fluid. Thus, a monoexponential model seems adequate for description of the relaxation behaviour in these cases. Furthermore, the results suggest that the accuracy of the measurements may not be critically dependent on the voxel size employed.

In Vivo Measurements of the T1 Relaxation Processes in the Bone Marrow in Patients with Myelodysplastic Syndrome

Nine patients with myelodysplastic syndrome (MDS) were examined with magnetic resonance imaging and in vivo T1 relaxation time measurements of the vertebral bone marrow in a 1.5 tesla whole body scanner. Two patients underwent transformation to acute myeloid leukemia and were evaluated at follow-up examinations. At the time of diagnosis the T1 relaxation times of the vertebral bone marrow were significantly prolonged compared with normal values. The T1 relaxation times of the vertebral bone marrow in patients with MDS showed significantly lower values compared with patients with acute leukemia and did not differ from patients with polycythemia vera.

High-resolution 1H NMR spectroscopy in the diagnosis of breast cancer.

Surgical specimens from 22 patients with infiltrating ductal carcinoma of the breast were analyzed by high-resolution 1H NMR spectroscopy at 80 and 300 MHz. Results were compared with those obtained from 9 benign (proliferative dysplasia without atypia) breast samples. NMR spectra at 80 MHz showed well-resolved water and lipid peaks so it was possible to calculate specific T1 and T2 relaxation times. The longitudinal T1 relaxation process of the water was found to be properly represented by a monoexponential function, whereas the transverse T2 decay was well accounted for by a biexponential model. Relaxation time measurements of the water were found to be a valuable tool in breast tissue characterization, in particular (a) mean T1 values from malignant and control populations are well distinguished (P less than 0.0008); (b) mean T2 values of both fast and slow components from the two populations are statistically different (P less than 0.0001) and no overlap exists in the distributions of the second component. Three-hundred-megahertz spectra allowed a detailed analysis of the lipidic component of the sample: malignant tumors were found to present in the region 1.3-1.2 ppm a species characterized by a very slow transverse relaxation time (T2 = 200-1000 ms).

In vivo determination of T1 and T2 in the brain of patients with severe but stable multiple sclerosis.

In vivo measurements of relaxation processes in multiple sclerosis (MS) lesions by magnetic resonance imaging (MRI) may be important for evaluation of the disease activity in individual MS plaques. To obtain information of presumably chronic plaques, 10 patients with severe, but stable MS were investigated, using a whole-body superconductive MR scanner, operating at 1.5 T. By employing 12-point (or 6-point) partial saturation inversion recovery (PSIR) and 32-echo multiple spin-echo sequences we measured T1 and T2 in MS plaques, white matter, and cortical gray matter. We also focused on the issue, whether T1 and T2 relaxation processes in fact were monoexponential. T1 and T2 in plaques were found to cover a wide range, which could be explained only by inherent biophysical dissimilarity of the plaques, possibly due to differences in disease activity, edema and gliosis. T1 appeared monoexponential in all the plaques, but in seven cases T2 showed biexponential behavior. This was found to be most pronounced near the cerebrospinal fluid of the ventricles, probably caused by partial volume effects or increased free water content. The T2 of apparently normal white matter was significantly longer in MS patients than in healthy subjects.

Dielectric and C-13 NMR relaxation in solutions of the sulphone copolymers and terpolymers of but-2-ene and of but-1-ene.

Abstract We describe studies made with a time domain system of the high frequency dielectric relaxation of solutions in chloroform and in dioxane of the polyolefins sulphones of but-2-ene and but-1-ene, and of the terpolymers of intermediate composition. The correlation times for transverse dipole relaxation are compared with the values obtained here or elsewhere by dynamic NMR means for the hydrocarbon segments of the main chain in the same solvents. Solvent viscosity is not an important factor controlling segmental motions. In chloroform the high frequency motions of the chains rich in 1-olefin units have similar dipole and NMR correlation times, which is consistent with the simple helical model of the terpolymers, but in the less polar dioxane a specific solvent effect may sufficiently disrupt dipole ordering to produce a different chain dynamics. The dielectric measurements indicate a wide range of correlation times for dipole movement. Differences between the dielectric and NMR correlation times in the disordered chains may arise from a greater sensitivity of the NMR T1 relaxation process to the high frequency components in the spectral distribution function.

In vitro proton T1 and T2 studies on rat liver: analysis of multiexponential relaxation processes.

At 37 degrees C and 20 MHz, the T1 and T2 proton relaxation processes in intact rat liver tissue are multiexponential functions which in the majority of cases were decomposed into a major (alpha* approximately 90%, T1* = 374 ms, T2* = 58 ms) and a minor (alpha** approximately 10%, T1** = 130 ms, T2* = 181 ms) component. Both, T1 and T2, are temperature-dependent with a temperature shift of delta T1 = 1.5 ms/degrees C and delta T2 = 0.5 ms/degrees C, respectively. Storage of liver tissue at 4 degrees C and 37 degrees C led to remarkable changes of the T1 and T2 values. For T2 these changes occurred after a shorter storage time than for T1, but they are more pronounced for T1. To avoid such influences the relaxation measurements were performed within one hour after excision of the tissue. Even at 4 degrees C, long-term storage (greater than 3 h) must be avoided. A method for the quantitative determination of the fat content in liver based on multiexponential analysis of the T1 relaxation process was evaluated employing mixtures of triolein with liver homogenate. Triolein is a two-component system with T1* = 144 ms (alpha* = 62%) and T1** = 355 ms (alpha** = 38%). Finally, liver-specific protocol conditions were defined for in vitro relaxation studies.

Proton Spin Lattice Relaxation in Vinylidene Fluoride/Trifluoroethylene Copolymer I. Vinylidene Fluoride 72 mol% Copolymer

The proton spin lattice relaxation times T1 of drawn films of a VDF/TrFE copolymer (VDF 72 mol%) were measured for various values of γ, which was the angle between the magnetic field and the draw direction of the film, and for different Larmor frequencies ω, over a temperature range from −23 to 130°C. Three kinds of T1 relaxation processes were observed below the Curie temperature (Tc), around Tc, and at a certain temperature in the paraelectric phase. The curve of ln T1 against reciprocal temperature 1/T was linear for the relaxation process in the paraelectric phase. The T1 became larger as the frequency ω and the angle γ increased.The formulation of T1 in the paraelectric phase for the oriented copolymer was derived, using the non-exponential correlation function which describes a one dimensional diffusion motion of conformational defects along the chain. The existence of the 1-D diffusion motion of the conformation defect was confirmed by a reasonable agreement between the theoretical and experimental results.

Dynamics of a N × K‐Level Molecule Coupled to a Thermal Reservoir

AbstractThe influence of intermolecular elastic (T2 processes) and inelastic (T1 processes) interactions on the population relaxation and phase relaxation of a specific molecular mode is studied in terms of a two mode model. Therein one mode (K‐level system) is assumed to undergo T1 and T2 relaxation processes as a consequence of its coupling to a thermal reservoir while the second mode (N‐level system) is not explicitly damped but is coupled to the first one. The quantum statistical equations of motion for the coupled two‐mode system are solved numerically with a special integration scheme in which the damping is considered in first order and the coupling of the modes in infinite order. Energy relaxation and dephasing of the N‐level system are studied as functions of the external relaxation behaviour and of the coupling between the modes. A dynamical decoupling of the two modes is found with decreasing intermolecular dephasing times T2.

Vibrational relaxation in a structurally disordered organic solid: Temperature dependence of Raman active phonons in p-bromochlorobenzene and p-dichlorobenzene

A theoretical discussion is presented to show that for a highly delocalized phonon motion, the line shapes derived from disorder and from vibrational relaxation due to anharmonic phonon–phonon scattering are both approximately Lorentzians. The linewidths obtained from disorder and vibrational relaxation are additive. A temperature dependence of the linewidth can be used to identify the mechanism and obtain the rate of vibrational relaxation. An experimental study is presented on the lowest frequency Raman active phonon of p-bromochlorobenzene which in the solid state shows an orientational disorder. The result is compared with that on the corresponding phonon in the isomorphic p-dichlorobenzene crystal which does not involve any orientational disorder. Experimental findings are in agreement with the theoretical predictions. The experimental study shows that in p-bromochlorobenzene at 2° K, the line broadening due to disorder is almost an order of magnitude larger than that due to anharmonic phonon–phonon scattering. Yet the overall line shape is a Lorentzian and the two linewidths are additive. The temperature dependence reveals that in both p-bromochlorobenzene and p-dichlorobenzene the mechanism of line broadening involves a T1-relaxation process in which the optical phonon decays into two phonons of half its frequency by cubic anharmonic interactions.