Search

A recent joint meeting was held on January 30, 2014, with the US Food and Drug Administration (FDA), National Cancer Institute (NCI), clinical scientists, imaging experts, pharmaceutical and biotech companies, clinical trials cooperative groups, and patient advocate groups to discuss imaging endpoints for clinical trials in glioblastoma. This workshop developed a set of priorities and action items including the creation of a standardized MRI protocol for multicenter studies. The current document outlines consensus recommendations for a standardized Brain Tumor Imaging Protocol (BTIP), along with the scientific and practical justifications for these recommendations, resulting from a series of discussions between various experts involved in aspects of neuro-oncology neuroimaging for clinical trials. The minimum recommended sequences include: (i) parameter-matched precontrast and postcontrast inversion recovery-prepared, isotropic 3D T1-weighted gradient-recalled echo; (ii) axial 2D T2-weighted turbo spin-echo acquired after contrast injection and before postcontrast 3D T1-weighted images to control timing of images after contrast administration; (iii) precontrast, axial 2D T2-weighted fluid-attenuated inversion recovery; and (iv) precontrast, axial 2D, 3-directional diffusion-weighted images. Recommended ranges of sequence parameters are provided for both 1.5 T and 3 T MR systems.

A Ku band coaxial high power microwave generator with a low magnetic field was investigated without mode competition in this paper. Mode competition is avoided physically by adopting a two-cavity extractor instead of a three-cavity extractor to eliminate the resonance between the modulation slow wave structure and the extractor slow wave structure at any unexpected frequency except the working frequency. Moreover, the efficiency of the device increases due to the separation process of energy extraction and electron collection by adopting the inner conductor collecting structure. Particle simulation results showed that when the magnetic flux density is 0.6 T, the diode voltage is 560 kV, and the diode current is 8 kA, we get 1.55 GW microwaves with an efficiency of 35% and a frequency of 14.7 GHz. Experimental investigation is carried out based on the physical design and simulation results. 1.0 GW microwaves are obtained, and the frequency is 14.8 GHz in the experiment when the magnetic flux density is 0.64 T, the diode voltage is 590 kV, and the diode current is 8.5 kA. No obvious hint of electron emission or bombardment is observed at the surface of the generator after 10 thousand pulses, and the advantage of this kind of generator working in a low magnetic field is proved. [ABSTRACT FROM AUTHOR]

We found that the start time in microwave generation of a relativistic backward wave oscillator (RBWO) for a slowly rising voltage pulse demonstrates a large jitter, which can be explained by the spread of explosive electron emission thresholds and plasma formation rates of the explosive emission cathode, and this large jitter is reduced greatly by a weak external RF signal. So, the effects of the emission threshold and plasma formation rate on the oscillation start time of a single RBWO and on the phase synchronization in two parallel RBWOs are investigated using particle-in-cell simulations. The 2D simulations show that a larger emission threshold and a faster plasma formation rate lead to a shorter start time due to the stronger shock excitation provided by the sharper beam current leading edge. For some special emission thresholds, the start time is abnormally long, which is due to the generation of other frequencies because of the shock excitation. The 3D simulations illustrate that with a larger emission threshold and a faster plasma formation rate, phase synchronization can be obtained in two parallel RBWOs even for a large voltage rise time. Therefore, we expect that by choosing the appropriate cathode emission threshold and plasma formation rate, it is possible to realize phase stabilization of an RBWO for a slowly rising voltage pulse even without an external RF signal. [ABSTRACT FROM AUTHOR]

Peroxisome proliferatoractivated receptor-[delta] (PPAR[delta]) activation results in upregulation of genes associated with skeletal muscle fatty acid oxidation and mitochondrial uncoupling. However, direct, noninvasive assessment of lipid metabolism and mitochondrial energy coupling in skeletal muscle following PPAR[delta] stimulation has not been examined. Therefore, in this study we examined the response of a selective PPAR[delta] agonist (GW610742X at 5 or 100 mg x [kg.sup.-1] x [day.sup.-1] for 8 days) on skeletal-muscle lipid metabolism and mitochondrial coupling efficiency in rats by using in vivo magnetic resonance spectroscopy (MRS). There was a decrease in the intramyocellular lipid-to-total creatine ratio as assessed by in vivo [1.sup.H]-MRS in soleus and tibialis anterior muscles by day 7 (reduced by 49 and 46%, respectively; P < 0.01) at the high dose. Following the [1.sup.H]-MRS experiment (day 8), [1-[sup.13]C]glucose was administered to conscious rats to assess metabolism in the soleus muscle. The relative fat-vs.-carbohydrate oxidation rate increased in a dose-dependent manner (increased by 52 and 93% in the 5 and 100 mg x [kg.sup.-1] x [day.sup.-1] groups, respectively; P < 0.05). In separate experiments where mitochondrial coupling was assessed in vivo (day 7), [sup.31]P-MRS was used to measure hindlimb ATP synthesis and [sup.13]C-MRS was used to measure the hindlimb tricarboxylic acid cycle flux ([V.sub.tca]), There was no alteration, at either dose, in mitochondrial coupling efficiency measured as the ratio of unidirectional ATP synthesis flux to [V.sub.tca]. Soleus muscle GLUT4 expression was decreased by twofold, whereas pyruvate dehydrogenase kinase 4, carnitine palmitoyl transferase 1a, and uncoupling protein 2 and 3 expression was increased by two- to threefold at the high dose (P < 0.05). In summary, these are the first noninvasive measurements illustrating a selective PPAR[delta]-mediated decrease in muscle lipid content that was consistent with a shift in metabolic substrate utilization from carbohydrate to lipid. However, the mitochondrial-energy coupling efficiency was not altered in the presence of increased uncoupling protein expression. peroxisome proliferator-activated receptor-[delta]; intramyocellular lipid; mitochondrial coupling; muscle

This paper studies the power handling capacity of the modes TM01 and TM02 in circumferentially corrugated waveguides through analytical research on the evolution of the field distribution and the corresponding dispersion with an overmoded ratio. As the overmoded ratio grows at the constant frequency, the total electric field of the volumetric wave, in which the amplitude of the axial electric field reaches its peak value on the central axis and declines along the r-axis, gradually concentrates toward the corrugated surface; the volumetric wave is then converted into a surface wave. Such conversion does not completely prevent, but weakens the enhancement of the power handling capacity caused by augmentation of the overmoded ratio. Moreover, due to the effect of the longitudinal mode transition, the power handling capacity of the modes TM01 and TM02 does not monotonically increase as the overmoded ratio grows with the constant frequency. Such longitudinal mode transition counteracts, to some extent, the enhancement of the power handling capacity caused by augmentation of the overmoded ratio. Even when the average radius of the corrugated waveguide is only a little larger than the cutoff radius of the required frequency, the power handling capacity decreases dramatically with augmentation of the overmoded ratio. A comparison between the different types of ripple demonstrates that a smaller corrugation pitch results in a lower power handling capacity. The advantage of the power handling capacity of the TM02 mode over that of the TM01 mode is proved by a careful comparison between the different cases. [ABSTRACT FROM AUTHOR]

We efficiently enhance the power capacity of klystron-like relativistic backward wave oscillators (RBWOs) with a TM021 mode extraction cavity. Theoretical analysis and simulation results are shown in detail. Theoretically, an electron cluster will be steadily decelerated in the whole region of the TM021 extraction cavity if the transiting time in the cavity approximates the period of microwaves. As a result, the energy of the electron beam will be efficiently extracted by the TM021 mode field. Due to the larger size, the electric field strength in a TM021 cavity can be much smaller than that in a TM020 cavity. In addition, once the extraction cavity breaks down, the emission electron will absorb less energy from the TM021 mode field than the TM020 mode field. In PIC simulations, for an X-band klystron-like RBWO with a frequency of 9.6 GHz and an output power of 2.3 GW, the maximum longitudinal electric field (Ez) in the extraction cavity decreases from 610 kV/cm to 320 kV/cm, when the TM020 extraction cavity is replaced with a TM021 extraction cavity. PIC simulation results agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]