In vivo localized1 H spectroscopy of the rat eye at 7 T: preliminary studies

Preliminaryin vivo proton spectroscopic studies of the posterior chamber of the rat eye have been undertaken at 7 T. The Spatial and Chemical shift encoded Excitation (SPACE) localization sequence was used to acquire signals from 10-µl voxels and demonstrate the presence of metabolites associated with the vitreous humor, lens, retina, and the optic nerve. LocalizedT ₂ andT ₁ measurements of water in the vitreous humor indicate a relatively fluid environment. Susceptibility maps are used to demonstrate the difficulties ofin vivo spectroscopic investigations in the anterior regions of the eye. Comments are made concerning the implications for spectral resolution in these regions.     

Magnetic resonance imaging at 1.5 T with immunospecific contrast agent in vitro and in vivo in a xenotransplant model

Object: Demonstrating the feasibility of magnetic resonance imaging (MRI) at 1.5 T of ultrasmall particle iron oxide (USPIO)-antibody bound to tumor cells in vitro and in a murine xenotransplant model. Methods: Human D430B cells or Raji Burkitt lymphoma cells were incubated in vitro with different amounts of commercially available USPIO-anti-CD20 antibodies and cell pellets were stratified in a test tube. For in vivo studies, D430B cells and Raji lymphoma cells were inoculated subcutaneously in immunodeficient mice. MRI at 1.5 T was performed with T1-weighted three-dimensional fast field echo sequences (17/4.6/13°) and T2-weighted three-dimensional fast-field echo sequences (50/12/7°). For in vivo studies MRI was performed before and 24 h after USPIO-anti-CD20 administration. Results: USPIO-anti-CD20-treated D430B cells, showed a dose-dependent decrease in signal intensity (SI) on T2*-weighted images and SI enhancement on T1-weighted images in vitro. Raji cells showed lower SI changes, in accordance to the fivefold lower expression of CD20 on Raji with respect to D430B cells. In vivo 24 h after USPIO-anti-CD20 administration, both tumors showed an inhomogeneous decrease of SI on T2*-weighted images and SI enhancement on T1-weighted images. Conclusions: MRI at 1.5 T is able to detect USPIO-antibody conjugates targeting a tumor-associated antigen in vitro and in vivo.     

DynamicT 1 studies of gadolinium uptake in brain tumors using LL-EPI

Using ultrafastT ₁ mapping (LL-EPI), the uptake from a bolus injection of Gd-DO3A (ProHance) into the sagittal sinus and a brain tumor has been monitored. The measurement of absoluteT ₁ removes the possible error in uptake curves created fromT ₁-weighted sequences caused by changes inT ₂ ^* and simplifies the calculation of ProHance concentration. The LL-EPI sequence has an acquisition time of 1.2 s and is repeated every 4 s to obtain uptake curves with a high temporal and spatial resolution. Optimization of the LL-EPI sequence has been performed to obtain a precision of 5% over theT ₁ range 0.3–1.2 s.     

Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T

The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T₁- and T₂-weighted MR imaging was performed to follow tumor growth. T₁-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T₂-weighted images.Measurements of T₁ and T₂ relaxation times were performed with inversion recovery FLASH and Carr–Purcell–Meiboom–Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T₁ and T₂ of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T₁ relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment.     

Imaging lung function using rapid dynamic acquisition of <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript>-maps during oxygen enhancement

This paper describes imaging of lung function with oxygen-enhanced MRI using dynamically acquired T ₁ parameter maps, which allows an accurate, quantitative assessment of time constants of T ₁-enhancement and therefore lung function. Eight healthy volunteers were examined on a 1.5-T whole-body scanner. Lung T ₁-maps based on an IR Snapshot FLASH technique (TE = 1.4 ms, TR = 3.5 ms, FA = 7 ^∘) were dynamically acquired from each subject. Without waiting for full relaxation between subsequent acquisition of T ₁-maps, one T ₁-map was acquired every 6.7 s. For comparison, all subjects underwent a standard pulmonary function test (PFT). Oxygen wash-in and wash-out time course curves of T ₁ relaxation rate (R ₁)-enhancement were obtained and time constants of oxygen wash-in (w _in) and wash-out (w _out) were calculated. Averaged over the whole right lung, the mean w _out was 43.90 ± 10.47 s and the mean (w _in) was 51.20 ± 15.53 s, thus about 17% higher in magnitude. Wash-in time constants correlated strongly with forced expired volume in one second in percentage of the vital capacity (FEV₁ % VC) and with maximum expiratory flow at 25% vital capacity (MEF25), whereas wash-out time constants showed only weak correlation. Using oxygen-enhanced rapid dynamic acquisition of T ₁-maps, time course curves of R ₁-enhancement can be obtained. With w _in and w _out two new parameters for assessing lung function are available. Therefore, the proposed method has the potential to provide regional information of pulmonary function in various lung diseases.     

Estimation of metabolite <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript> relaxation times using tissue specific analysis,signal averaging and bootstrapping from magnetic resonance spectroscopic imaging data

Object A novel method of estimating metabolite T ₁ relaxation times using MR spectroscopic imaging (MRSI) is proposed. As opposed to conventional single-voxel metabolite T ₁ estimation methods, this method investigates regional and gray matter (GM)/white matter (WM) differences in metabolite T ₁ by taking advantage of the spatial distribution information provided by MRSI. Material and methods The method, validated by Monte Carlo studies, involves a voxel averaging to preserve the GM/WM distribution, a non-linear least squares fit of the metabolite T ₁ and an estimation of its standard error by bootstrapping. It was applied in vivo to estimate the T ₁ of N-acetyl compounds (NAA), choline, creatine and myo-inositol in eight normal volunteers, at 1.5 T, using a short echo time 2D-MRSI slice located above the ventricles. Results WM-T _1,NAA was significantly (P < 0.05) longer in anterior regions compared to posterior regions of the brain. The anterior region showed a trend of a longer WM T ₁ compared to GM for NAA, creatine and myo-Inositol. Lastly, accounting for the bootstrapped standard error estimate in a group mean T ₁ calculation yielded a more accurate T ₁ estimation. Conclusion The method successfully measured in vivo metabolite T ₁ using MRSI and can now be applied to diseased brain.     

Effects of functional electrical stimulation in denervated thigh muscles of paraplegic patients mapped with T 2 imaging

OBJECT: Functional electrical stimulation (FES) for paraplegic patients, with the long-term goal of ultimately restoring muscle function, is associated with several positive effects: improvement of blood circulation, skin condition, peripheral trophism and metabolism, prophylaxis against decubitus ulcer and better physical fitness. Since fibres of denervated muscles (lacking a supplying nerve) need to be activated directly, the fraction of elicited muscle tissue follows the geometric distribution of the electrical field, which can be simulated using electrophysiological computer models. Experimental validation of these results, however, has not yet been established. MATERIALS AND METHODS: We acquired T (2) parameter images using a multislice multi-spin-echo MR sequence before and immediately after FES in nine denervated paraplegic patients and three healthy subjects in order to visualise the geometric distribution of activation by electrically induced muscle stimulation in denervated versus innervated (healthy) thigh muscle. RESULTS AND CONCLUSION: After realigning and normalisation, maps of relative T (2) increase were calculated. The results demonstrate that the spatial distribution of short-term effects of FES of denervated muscle tissue of paraplegic patients who regularly perform FES can be visualised by T (2) parameter images. This may be used to refine models of the electrical field of FES in muscle and fibre activation in the future.     

Gas sensors: New materials and processing approaches

To satisfy demands for detecting chemicals in the environment, versatile sensors are required to detect a rapidly growing range of chemical species. In this paper, focus is directed on progress being made to develop temperature-independent oxygen sensors based on the perovskite solid solution system SrTi_1−x Fe _x O_3−δ,and on improving the sensitivity of thin film gas sensors integrated on Si-based self heated substrates. A novel strategy to produce macroporous films with high surface area for enhanced chemical activity is described, and how this processing strategy results in markedly improved sensitivity of gas sensors based on a novel material, CaCu₃Ti₄O₁₂, is demonstrated.     

Sintering and compositional effects on the microwave dielectric characteristics of Mg(Ta1−x Nb x )2O6 ceramics with 0.25 ≦ x ≦ 0.35

1,500 °C−sintered MgTa₂O₆ ceramic exhibits microwave dielectric characteristics of ɛ _r = 30.5, Q × f = 56,900 GHz, and τ _f = 28.3 ppm/°C, whereas 1,400 °C-sintered MgNb₂O₆ ceramic exhibits microwave dielectric characteristics of ɛ _r = 21.7, Q × f = 89,900 GHz, and τ _f = −68.5 ppm/°C. In order to find the dielectric resonators with τ _f value close to 0 ppm/°C, the effects of sintering condition and composition on the microwave dielectric characteristics of Mg(Ta_1−x Nb _x )₂O₆ ceramics (0.25 ≦ x ≦ 0.35) prepared under sintering temperature of 1,300–1,450 °C are investigated. The results show that as the sintering temperature increases from 1,300 to 1,450 °C, the ɛ _r, Q × f and τ _f values of Mg(Ta_1−x Nb _x )₂O₆ ceramics all increase and saturate at 1,450 °C. On the other hand, as the Nb₂O₅ content decreases, the τ _f values of Mg(Ta_1−x Nb _x )₂O₆ ceramics will shift to near 0 ppm/°C. The optimized sintering conditions and composition to obtain the Mg(Ta_1−x Nb _x )₂O₆ dielectrics with τ _f close to 0 ppm/°C are sintering temperature of 1,450 °C, sintering duration of 4 h, and composition of x = 0.25, which exhibits the microwave dielectric characteristics of ɛ _r = 27.9, Q × f = 33,100 GHz, and τ _f = −0.7 ppm/°C.     

Magnetic properties of iron-based materials (nitrogen interstitially modified 1:12 compounds and Fe3B-Nd) for low rare-earth bonded magnets

Hard magnetic properties of nitrogen interstitially modified NdM_xFe_12-xN_y compounds and Fe₃B-based ultra-fine crystalline Nd? Fe? Co? T? B alloys of low Nd content of 3 to 5 at. % are studied. The nitrogen-modified compounds have been prepared via the rapid solidification route and the mechanical alloying route both followed by gas nitrogenation using N₂. The Fe₃B-based materials have been prepared by means of rapid solidification and crystallization treatment. The latter materials appear promising as the base material for high-remanence, easy-to-magnetize bonded magnets with small temperature coefficients of remanence. Typical magnetic properties of compaction isotropic bonded magnets produced from this material are B_r = 0.80 T, H_cJ = 350 kA/m, and (BH)_max = 60.5 kJ/m³.     

Application of LCModel for quality control and quantitative in vivo1H MR spectroscopy by short echo time STEAM sequence

The linear combination of model spectra (LCModel) calculation of a parameter for long-term quality control,k _T, was introduced, representing the ratio of the temporal and nominal intensities of CH₃ groups of lactate and acetate in a quality control phantom. This procedure is a part of the quality assurance of the scanner using fully automatic measurement and calculation ofk _T parameters, and utilizing Shewhart regulation control charts for continuous evaluation of the magnetic resonance (MR) scanner setting. The application of thek _T parameter for the correction of in vivo data increases the precision of molar concentration determination by about 4%. This was tested by the quantitative in vivo MR determination of the molar concentrations of 13 prominent metabolites (N-acetylaspartate (NAA),N-acetylaspartylgutamate, creatine and phosphocreatine (Cr), choline-containing compounds (Cho), myo-inositol, scyllo-inositol., γ-aminobutyric acid, glutamine, glutamate, glucose, lactate, alanine, taurine) in the white matter and hippocampus of the brain in groups of volunteers, using a short echo time stimulated echo acquisition mode sequence (echo time =10 ms) and the LCModel technique. The repeatability of the measurement of prominent metabolites such as NAA, Cr and Cho was found to be around 10% (relative standard deviation,n=6); precision in a group of volunteers (n=20 and 28, respectively) was in the range of approximately 13–20%. For other metabolites, which are measured with a lower signal-to-noise ratio, the precision can be much lower.