Comparison between MRI, microbiology and histology in evaluation of antibiotics in a murine model of thigh infection

Although in vivo magnetic resonance imaging (MRI) is rapidly becoming a recognised tool in experimental pharmacological research, at the best of our knowledge, scarce application in the field of antibacterial drug research has been reported so far. In this last field, animal models of bacterial infections are used to test the efficacy of novel compounds. In this paper we have explored the potential usefulness of MRI in monitoring the chronological evolution of experimental bacterial infections and the effect of different therapeutic treatments. A murine model of thigh infection induced byStaphylococcus aureus has been used and the efficacy of vancomycin and imipenem/cilastatin has been tested. Three groups of infected animals were studied by microbiology, histology and MRI methods. The results obtained show that in vivo MRI data are highly consistent with microbiological and histological data, allowing, similarly to these commonly used techniques, the efficacy of different antibacterial treatments to be quantified. Our findings suggest that MRI could be used to assess the efficacy of new chemical entities in antibacterial pharmacological research. The advantages of MRI, as a non invasive technique, in comparison with commonly used microbiological and histological methods are discussed.     

31P MR spectroscopy and in vitro markers of oxidative capacity in type 2 diabetes patients

Background: Skeletal muscle mitochondrial function in type 2 diabetes (T2D) is currently being studied intensively. In vivo ³¹P magnetic resonance spectroscopy (³¹P MRS) is a noninvasive tool used to measure mitochondrial respiratory function (MIFU) in skeletal muscle tissue. However, microvascular co-morbidity in long-standing T2D can interfere with the ³¹P MRS methodology. Aim: To compare ³¹P MRS-derived parameters describing in vivo MIFU with an in vitro assessment of muscle respiratory capacity and muscle fiber-type composition in T2D patients. Methods: ³¹P MRS was applied in long-standing, insulin-treated T2D patients. ³¹P MRS markers of MIFU were measured in the M. vastus lateralis. Muscle biopsy samples were collected from the same muscle and analyzed for succinate dehydrogenase activity (SDH) and fiber-type distribution. Results: Several ³¹P MRS parameters of MIFU showed moderate to good correlations with the percentage of type I fibers and type I fiber-specific SDH activity (Pearson’s R between 0.70 and 0.75). In vivo and in vitro parameters of local mitochondrial respiration also correlated well with whole-body fitness levels (VO _2peak) in these patients (Pearson’s R between 0.62 and 0.90). Conclusion: Good correlations exist between in vivo and in vitro measurements of MIFU in long-standing insulin-treated T2D subjects, which are qualitatively and quantitatively consistent with previous results measured in healthy subjects. This justifies the use of ³¹P MRS to measure MIFU in relation to T2D.     

Versatile coil design and positioning of transverse-field RF surface coils for clinical 1.5-T MRI applications

Clinical MRI/MRS applications require radio frequency (RF) surface coils positioned at an arbitrary angle with respect to B₀. In these experimental conditions the standard circular loop (CL) coil, producing an axial RF field, shows a large signal loss in the central region of interest (ROI). We demonstrate that transverse-field figure-of-eight (FO8) RF surface coils design are not subject to the same amount of signal loss in the central ROI as loop coils when their orientations are changed. The 1.5-T CL and FO8 prototypes (diameter = 10 cm) were built on Plexiglas using copper strips (width = 4 mm, thickness = 100 m). The two linear elements of the FO8 coil were 1 cm apart. Axial spoiled gradient echo (SPGR) images of a phantom containing doped water were acquired with the coil plane at =0°, 45°, and 90°. As increases, the CL images show, in the central ROI, a signal that decreases from a maximum value to zero. Whereas the FO8 images show, in the same ROI, a signal that varies little from the maximum value (20%). Optimized FO8 coils can be oriented with the coil plane positioned along any direction with respect to B₀ without significant signal loss. Transverse RF coil design should be useful for clinical MRS studies and also for parallel imaging techniques where versatile RF coils disposed along arbitrary directions are required.     

Quantitative T 2 measurement of a single voxel with arbitrary shape using pinwheel excitation and CPMG acquisition

Objective The aim of this study is to present a new approach for making quantitative single-voxel T ₂ measurements from an arbitrarily shaped region of interest (ROI), where the advantage of the signal-to-noise ratio (SNR) per unit time of the single-voxel approach over conventional imaging approach can be achieved. Materials and methods Two-dimensional (2D) spatially selective radiofrequency (RF) pulses are proposed in this work for T ₂ measurements based on using interleaved spiral trajectories in excitation k-space (pinwheel excitation pulses), combined with a summed Carr–Purcell Meiboom–Gill (CPMG) echo acquisition. The technique is described and compared to standard multi-echo imaging methods, on a two-compartment water phantom and an excised brain tissue. Results The studies show good agreement between imaging and our method. The measured improvement factors of SNR per unit time of our single-voxel approach over imaging approach are close to the predicted values. Conclusion Measuring T ₂ relaxation times from a selected ROI of arbitrary shape using a single-voxel rather than an imaging approach can increase the SNR per unit time, which is critical for dynamic T ₂ or multi-component T ₂ measurements.     

Investigation on the design and synthesis of new systems of BNT-based lead-free piezoelectric ceramics

Three primary differences between BNT- and PZT-based ceramics were analyzed from the composition and the active component of the materials. Based on the analysis the authors’ group developed the new idea of the design of the multiple complex in the A-site ions of BNT compounds. (Bi_0.5Na_0.5)²⁺, Bi³⁺ and Na⁺ in the ABO₃ structure are defined as A-site, A₁-site and A₂-site ions, respectively, and A, A₁ and A₂-site ions can be simultaneously or singly substituted partially by alkaline-earth metal ions, metal ions with +3 valence and metal ions with +1 valence, respectively. Under this consideration, Several new systems of Bi_0.5Na_0.5TiO₃ (abbreviated as BNT)-based lead-free piezoelectric ceramics were proposed. These ceramics can be prepared by conventional ceramic techniques and have excellent piezoelectric performance. Among these materials, Bi_0.5(Na_1−x−y K _x Li _y )_0.5TiO₃ possesses higher piezoelectric constant (d ₃₃ = 230 pC/N), higher electromechanical couple factor (k _p = 0.40), larger remanent polarization (P _r = 38.9 μC/cm²) and a better P-E hysteresis loop until about 200^∘C. This work was supported by the projects of NSFC (50410179), (50572066), and (59972020), and NAMMC (2001-AA325060).     

Effect of Cr2O3 addition on the microstructure and electrical properties of Mn-Ni-Co oxides NTC thermistors

The as-sintered Mn_1.1Ni_1.4Co_0.5O₄ crystallized in the solid solution of cubic spinel Mn-Ni-Co oxides, along with a small amount of the cubic spinel Ni-rich oxide phase. On the other hand, the Cr-substituted Mn_1.1Ni_1.4 Co_{0.5− x} Cr _x O₄ (0.07 ≤x ≤q 0.35) showed a single phase of cubic spinel Mn-Ni-Co-Cr oxides. This indicates that the substituted Cr suppressed the decomposition in the oxides. In addition, the Cr hindered the grain growth during sintering and increased the porosity. The electrical resistivity, the B _25/85 constant, and the activation energy of the Mn_1.1Ni_1.4Co_{0.5− x} Cr _x O₄ NTC thermistors increased with increasing Cr content. It is demonstrated that the Cr-substituted Mn_1.1Ni_1.4Co_{0.5− x} Cr _x O₄ NTC thermistors provided a variety of electrical properties, depending on the composition.     

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.