Multi-frequency harmonic arrays: initial experience with a novel transducer concept for nonlinear contrast imaging

Nonlinear contrast imaging modes such as second harmonic imaging (HI) and subharmonic imaging (SHI) are increasingly important for clinical applications. However, the performance of currently available transducers for HI and SHI is significantly constrained by their limited bandwidth. To bypass this constraint, a novel transducer concept termed multi-frequency harmonic transducer arrays (MFHA's) has been designed and a preliminary evaluation has been conducted. The MFHA may ultimately be used for broadband contrast enhanced HI and SHI with high dynamic range and consists of three multi-element piezo-composite sub-arrays (A-C) constructed so the center frequencies are 4f(A) = 2f(B) = f(C) (specifically 2.5/5.0/10.0 MHz and 1.75/3.5/7.0 MHz). In principle this enables SHI by transmitting on sub-array C receiving on B and, similarly, from B to A as well as HI by transmitting on A receiving on B and, likewise, from B to C. Initially transmit and receive pressure levels of the arrays were measured with the elements of each sub-array wired in parallel. Following contrast administration, preliminary in vitro HI and SHI signal-to-noise ratios of up to 40 dB were obtained. In conclusion, initial design and in vitro characterization of two MFHA's have been performed. They have an overall broad frequency bandwidth of at least two octaves. Due to the special design of the array assembly, the SNR for HI and SHI was comparable to that of regular B-mode and better than commercially available HI systems. However, further research on multi-element MFHA's is required before their potential for in vivo nonlinear contrast imaging can be assessed.     

Enhancing the acquisition efficiency of fast magnetic resonance imaging via broadband encoding of signal content

Current efficient magnetic resonance imaging (MRI) methods such as parallel-imaging and k-t methods encode MR signals using a set of effective encoding functions other than the Fourier basis. This work revisits the proposition of directly manipulating the set of effective encoding functions at the radiofrequency excitation step in order to increase MRI efficiency. This approach, often termed "broadband encoding," enables the application of algebraic matrix factorization technologies to extract efficiency by representing and encoding MR signal content in a compacted form. Broadband imaging equivalents of fast multiecho, parallel and k-t MRI are developed and analyzed. The potential of these techniques to increase the time efficiency of data acquisition is experimentally verified on a commercial MRI scanner using simple spin-echo imaging. A three-dimensional gradient-echo dynamic imaging application that demonstrates the potential benefits of this approach compared to the present state of the art for certain applications is also presented.     

Assessment of bone calcium and phosphorus content using micro X‐ray fluorescence spectrometry (μ‐EDXRF): effects of long‐term cadmium poisoning

This study assesses whether the concentrations of biologically important elements in bones are altered by long‐term consumption of cadmium (Cd)‐contaminated water. Heavy metal poisoning has significant impact on humans, and pollutants such as Cd are often found at high concentrations in waterways. Twelve Sprague Dawley rats consumed water with 50 p.p.m. Cd (Cd group), and another 12 consumed normal water (control group). Six subjects from each group were sacrificed after 2 weeks and the others after 4 weeks. Spectra were acquired from the femur by using the EDAX Eagle III micro‐XRF setup, and quantitative calculations were performed by using the fundamental parameter method to determine the concentrations of elements. A bone calcium/phosphorus concentration ratio (Ca/P) of 2.07 ± 0.001 is observed in the spectra from control subjects after 2 weeks and 2.07 ± 0.001 after 4 weeks. In Cd subjects, Ca/P after 2 weeks is 2.04 ± 0.001 and after 4 weeks is 1.97 ± 0.003. Statistically significant differences are obtained when comparing controls with Cd subjects at both time points and when comparing Cd subjects at both time points. Cadmium poisoning significantly affects bone Ca and P concentrations, increasing the likelihood of osteoporosis and other bone diseases. Copyright © 2016 John Wiley & Sons, Ltd.     

Broadband arrayed waveguide gratings on InP

Broadband arrayed waveguide gratings on InP are presented using a novel S-shape design. This design was utilized to accommodate the large free spectral range required for broadband operation. Four and eight channel AWGs with a wavelength channel spacing of 18 nm are discussed. The output peaks of the AWGs have a wide FWHM of 11 nm which provides insensitive operation to polarization, temperature fluctuations, and chromatic dispersion.     

Accounting for nonspecific enhancement in neuronal tract tracing using manganese enhanced magnetic resonance imaging

Manganese enhanced MRI (MEMRI) is an emerging technique for tracing neuronal pathways in vivo. However, manganese may leak into blood vessels or cerebrospinal fluid (CSF) after local injection and can be circulated to and taken up by brain regions that may not have connections to the targeted pathways. Comparing enhancement time courses after intranasal injection with intravenous infusion of MnCl₂ in rats, the early enhancements in the pituitary gland (Pit) and hippocampus indicate the contrasts in those regions in the olfactory tract-tracing experiment were caused by such systemic effects. Since the Pit has easy access to manganese from the blood and its signal is proportional to other brain regions after intravenous infusion, it was used as an internal reference for the systemic effects. Applying intensity normalization by the Pit signal to tract-tracing data from the olfactory bulb led to reduced contrast in the hippocampus. These results demonstrate that nonspecific enhancements in MEMRI tract-tracing studies may have to be taken into account and that normalization by the Pit signal can compensate these effects.     

Effect of signal intensity normalization on the multivariate analysis of spectral data in complex ‘real‐world’ datasets

Spectral signal intensities, especially in ‘real‐world’ applications with nonstandardized sample presentation due to uncontrolled variables/factors, commonly require additional spectral processing to normalize signal intensity in an effective way. In this study, we have demonstrated the complexity of choosing a normalization routine in the presence of multiple spectrally distinct constituents by probing a dataset of Raman spectra. Variation in absolute signal intensity (90.1% of total variance) of the Raman spectra of these complex biological samples swamps the variation in useful signals (9.4% of total variance), degrading its diagnostic and evaluative potential. Using traditional spectral band choices, it is shown that normalization results are more complex than generally encountered in traditionally designed sample sets investigating limited chemical species. We demonstrate that no choice of a single band proves to be appropriate for predicting all the reference parameters, instead requiring a tailored normalization routine for each parameter. Of the reference parameters studied in the chosen system, signals from pathogenic adducts in ocular tissues called advanced glycation endproducts were most prominent when normalizing about the 1550–1690 cm⁻¹ region of the spectrum (17.5% of total variance, compared with 0.3% for unnormalized), while prediction of pentosidine and gender were optimized by normalization about the 1570 (R² = 0.97 vs 0.57 for unnormalized) and 1003 cm⁻¹ (p < 0.0000001 vs p < 0.01 for unnormalized) bands, respectively. The data obtained point to the extreme sensitivity of multivariate analysis to signal intensity normalization. Some general guidelines for making appropriate band choices are given, including the use of peak‐finding routines. Copyright © 2008 John Wiley & Sons, Ltd.     

Adsorption and decomposition of NO on O-covered planar and faceted Ir(2 1 0)

We report on the adsorption and decomposition of NO on O-covered planar Ir(2 1 0) and nanofaceted Ir(2 1 0) with variable facet sizes investigated using temperature programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT). When pre-covered with up to 0.5 ML O, both planar and faceted Ir(2 1 0) exhibit unexpectedly high reactivity for NO decomposition. Upon increasing the oxygen coverage to 0.7 ML O, planar Ir(2 1 0) has little activity while faceted Ir(2 1 0) still remains active toward NO decomposition, although NO decomposition is completely inhibited when both surfaces are pre-covered by 1 ML O. NO molecularly adsorbs on O-covered Ir at 300 K. At low NO and oxygen coverage, NO adsorbs on the atop sites of planar Ir(2 1 0) while on the bridge and atop sites of faceted Ir(2 1 0) composed of (1 1 0) and {3 1 1} faces. No evidence for size effects in the decomposition of NO on O-covered faceted Ir(2 1 0) is observed for average facet size in the range 5-14 nm. Our findings should be of importance for development of Ir-based catalysts for NO decomposition under oxygen-rich conditions.     

Study of Strangeness Photoproduction on the Neutron in the Threshold Region

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K ⁰ with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K ⁰ + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K ₁, as ~ ?1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K ⁺ Λ.     

Quiescent Cosmological Singularities

The most detailed existing proposal for the structure of spacetime singularities originates in the work of Belinskii, Khalatnikov and Lifshitz. We show rigorously the correctness of this proposal in the case of analytic solutions of the Einstein equations coupled to a scalar field or stiff fluid. More specifically, we prove the existence of a family of spacetimes depending on the same number of free functions as the general solution which have the asymptotics suggested by the Belinskii–Khalatnikov–Lifshitz proposal near their singularities. In these spacetimes a neighbourhood of the singularity can be covered by a Gaussian coordinate system in which the singularity is simultaneous and the evolution at different spatial points decouples. Received: 17 January 2000 / Accepted: 27 November 2000