Diffusion-weighted MRI: influence of intravoxel fat signal and breast density on breast tumor conspicuity and apparent diffusion coefficient measurements

Promising recent investigations have shown that breast malignancies exhibit restricted diffusion on diffusion-weighted imaging (DWI) and may be distinguished from normal tissue and benign lesions in the breast based on differences in apparent diffusion coefficient (ADC) values. In this study, we assessed the influence of intravoxel fat signal on breast diffusion measures by comparing ADC values obtained using a diffusion-weighted single shot fast spin-echo sequence with and without fat suppression. The influence of breast density on ADC measures was also evaluated. ADC values were calculated for both tumor and normal fibroglandular tissue in a group of 21 women with diagnosed breast cancer. There were systematic underestimations of ADC for both tumor and normal breast tissue due to intravoxel contribution from fat signal on non–fat-suppressed DWI. This ADC underestimation was more pronounced for normal tissue values (mean difference=40%) than for tumors (mean difference=27%, P<.001) and was worse in women with low breast tissue density vs. those with extremely dense breasts (P<.05 for both tumor and normal tissue). Tumor conspicuity measured by contrast-to-noise ratio was significantly higher on ADC maps created with fat suppression and was not significantly associated with breast density. In summary, robust fat suppression is important for accurate breast ADC measures and optimal lesion conspicuity on DWI.     

An efficient non-iterative algorithm to estimate the apparent diffusion coefficient of water molecules in the magnetic resonance diffusion imaging experiments

Many studies have shown that the magnetic resonance signal decay with an extend range of diffusion weighting(b-factor)is a bi-exponential attenuation in the diffusion-weighted magnetic resonance imaging experiments in vivo.Based on this feature and the two-compartmental model,we propose a twice-linear-fitting(TLF)algorithm to estimate the apparent diffusion coefficient(ADC)of the water molecules instead of the commonly used iterative Levenberg–Marquardt(LM)method.The TLF algorithm consists of two liner fitting steps to estimate the fast and the slow apparent diffusion coefficients and their sizes,respectively.It is unnecessary to guess the initial values in the whole fitting process.The time consumption of the TLF algorithm is much less than that of the iterative LM method.Moreover,the TLF algorithm may avoid the extraneous solutions,which often deteriorates the results of the LM method.Compared with the iterative fitting method,the TLF algorithm is a reliable and timeefficient approach to estimate the ADC of water molecules in vivo in magnetic resonance diffusion-weighted imaging experiments.     

Reply to the comment from Mamedov

Here, I present the reply to the comments from Mamedov regarding numerical solution of Bloch–Gruneisen function to determine the contribution of electron–phonon interaction in polycrystalline superconductor. Reply to the comments from Mamedov is discussed one by one.     

高压下石墨超硬相的电阻率测量

采用高压下精确的原位电阻率测量技术,利用高浓度硼掺杂的金刚石薄膜制备微电路,在0～34 GPa测量石墨的电阻率随压力的变化规律.结果表明:在第一和第二个压力循环中,石墨超硬相电阻率不连续变化,分别出现在15.1 GPa和17.9 GPa;相存在的最低压力为8 GPa.     

应用激发极化中间梯度测量法勘查金及多金属盲矿体

研究激发极化中间梯度法在深切割地貌区勘查金及多金属盲矿体.根据深切割区地形、地貌变化大的复杂地质环境条件,现场实验、优选测量方法,有针对性布设激电测量装置;以金及多金属矿化体的横向、纵向电性参数理论变化规律,结合地质勘查基础成果综合研究.确定单一、多层盲矿体的走向、倾向、埋深的变化特点,为布置工程勘查提供准确的依据.     

Enhancement of electrical properties due to Cr substitution in Co-ferrite nanoparticles synthesized by two chemical techniques

Nanocrystalline cobalt ferrites with nominal composition CoCr_xFe_2−xO₄ ranging from x=0.0 to 0.5 with step increment of 0.25 were prepared by sol–gel auto combustion and chemical co-precipitation techniques. A comparative study of structural, electrical and magnetic properties of these ferrites has been measured using different characterization techniques. Structural and micro-structural studies were measured using X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy and atomic force microscopy. Crystallite sizes of the series are within the range of 12–29±2 nm. Lattice parameters decrease by increasing Cr³⁺ concentration. FTIR confirms the presence of two lattice absorption bands. DC electrical resistivity increases to a value of ∼10¹⁰ Ω-cm with increase in Cr³⁺ concentration, but the most significant increase is in samples prepared by sol–gel combustion. Dielectric properties have been measured as a function of frequency at room temperature. Dielectric loss decreases to 0.1037 and 0.0108 at 5 MHz for chemical co-precipitation and sol–gel combustion, respectively. Impedance measurements further helped in analyzing the electrical properties and to separate the grain and grain boundary resistance effects using a complex impedance analysis. Magnetic parameters were studied using a vibrating sample magnetometer in the applied field of 10 kOe. The saturation magnetization decreased from 63 to 10.8 emu/gm with increase in Cr³⁺ concentration.     

正丁醇在N,N-二甲基甲酰胺+水溶液中的体积性质

测定了２９８。１５Ｋ时正丁醇＋Ｎ，Ｎ－二甲诺甲酰胺（ＤＭＦ）＋水三元系的密度求出正丁醇在ＤＭＦ＋水混合溶剂中的表观摩尔体积。观察２到：⑴Φ＾０．Ｅ～ｆｍ与ＶＤＭＦ＾Ｅ～ｆｍ之间存在相似变化关系，其中Φ２＾０．Ｅ为正丁醇的过量无限稀释表观摩尔体积，ＶＥＭＦ＾Ｅ为ＤＭＦ＋水二元系中ＤＭＦ的过量偏摩尔体积，ｆｍ为混合溶剂中ＤＭＦ的摩尔分数。⑵Ｂ１～ｆｍ与０６２１２＾０．Ｅ～ｆｍ之间存的反向变化关系。Ｂ１     

A large hydrothermal reservoir beneath Taal Volcano (Philippines) revealed by magnetotelluric observations and its implications to the volcanic activity

Taal Volcano is one of the most active volcanoes in the Philippines. The magnetotelluric 3D forward analyses indicate the existence of a large high resistivity anomaly (∼100 Ω·m) with a volume of at least 3 km × 3 km × 3 km, which is capped by a conductive layer (∼10 Ω·m), beneath the Main Crater. This high resistivity anomaly is hypothesized to be a large hydrothermal reservoir, consisting of the aggregate of interconnected cracks in rigid and dense host rocks, which are filled with hydrothermal fluids coming from a magma batch below the reservoir. The hydrothermal fluids are considered partly in gas phase and liquid phase. The presence of such a large hydrothermal reservoir and the stagnant magma below may have influences on the volcano’s activity. Two possibilities are presented. First, the 30 January 1911 explosion event was a magmatic hydrothermal eruption rather than a base-surge associated with a phreato-magmatic eruption. Second, the earlier proposed four eruption series may be better interpreted by two cycles, each consisting of series of summit and flank eruptions.     

Electrical resistivity of the alkaline earth metals Ca,Sr and Ba in the 50–300K temperature region

The computed values of the temperature dependent electrical resistivity is presented for the alkaline earth metals Ca, Sr and Ba. Numerical values of the mean free paths obtained using a finite mean free path approach is also reported. The structure factor has been evaluated using experimental values for the phonon spectra while local model potentials were used for the form factors. Our numerical results compare favourably with experiments.     

Electrical resistivity of dilute,interacting fermions

A first-principles calculation of the initial decay of a current-carrying state is used to infer the electrical resistivity ofinteracting fermions (electrons or holes). This approach is useful when it is impractical to apply the Kubo formalism.