Automated correction of unwanted phase jumps in reference signals which corrupt MRSI spectra after eddy current correction

A commonly applied step in the postprocessing of gradient localized proton MR spectroscopy, is correction for eddy current effects using the water signal as a reference. However, this method can degrade some of the metabolite signals, in particular if applied on proton MR spectroscopic imaging data. This artifact arises from the water reference signal in the presence of a second signal which resonates close to the main water resonance. The interference of both resonances will introduce jumps in the phase of the reference time domain signal. Using this phase for eddy current correction will result in a ringing artifact in the frequency domain of the metabolite signal over the whole frequency range. We propose a moving window correction algorithm, which screens the phase of reference signals and removes phase jumps in time domain caused by interference of signals from multiple spin systems. The phase jumps may be abrupt or gradually distributed over several time data points. Because the correction algorithm only corrects time data points which contain phase jumps, the phase is minimally disrupted. Furthermore, the algorithm is automated for large datasets, correcting only those water reference signals which are corrupted. After correction of the corrupted reference signals, normal eddy current correction may be performed. The algorithm is compared with a method which uses a low-pass filter and tested on simulated data as well as on in vivo proton spectroscopic imaging data from a healthy volunteer and from patients with a brain tumor.     

The multiple hydrogen location near a α-Fe vacancy

The interaction between 10 hydrogen atoms and a α-Fe structure having a vacancy (V) has been studied using a cluster model and a semi-empirical theoretical method. The energy of the system was calculated by the atom superposition and electron delocalization molecular orbital method. The electronic structure was studied using the concept of density of states and crystal orbital overlap population curves.For the study of a sequential absorption, the hydrogen atoms were positioned in their energy minima configurations, near to the tetrahedral sites neighboring the vacancy, except the last H atom that was located far from the vacancy. The energy difference for H agglomeration was also computed. The vacancy-H_n complexes become less stable than VH species for more than three hydrogen's.The changes in the electronic structure of Fe atoms near the vacancy were also analyzed. The interactions mainly involve Fe 3d and 4s atomic orbitals. The contribution of Fe p orbitals is much less important. The Fe-Fe bond weakened as new Fe-H and H-H pairs were formed. The effect of H atoms is limited to its first Fe neighbors. The detrimental effect of H atoms on the Fe-Fe bonds can be related to the mechanism for embrittlement in α-Fe.     

High-resolution imaging without iteration: a fast and robust method for breast ultrasound tomography

Breast ultrasound tomography has the potential to improve the cost, safety, and reliability of breast cancer screening and diagnosis over the gold-standard of mammography. Vital to achieving this potential is the development of imaging algorithms to unravel the complex anatomy of the breast and its mechanical properties. The solution most commonly relied upon is time-of-flight tomography, but this exhibits low resolution due to the presence of diffraction effects. Iterative full-wave inversion methods present one solution to achieve higher resolution, but these are slow and are not guaranteed to converge to the correct solution. Presented here is HARBUT, the hybrid algorithm for robust breast ultrasound tomography, which utilizes the complementary strengths of time-of-flight and diffraction tomography resulting in a direct, fast, robust and accurate high resolution method of reconstructing the sound speed through the breast. The algorithm is shown to produce accurate reconstructions with realistic data from a complex three-dimensional simulation, with masses as small as 4 mm being clearly visible.     

Distribution and behavior of some radionuclides associated with the Trinity nuclear test

The activities of ¹³³Ba, ¹³⁷Cs, ¹⁵²Eu, ¹⁵⁴Eu, ¹⁵⁵Eu, ²³⁹Pu, and ²⁴¹Am were determined by gamma spectroscopy on the largest sample set (n = 49) of bulk trinitite to date. The range in activity for all isotopes is large. For example, the activity of ²⁴¹Am (normalized to the time of detonation) ranges between 1 and 42 Bq/g. Comparison of activities for isotopes derived from the device, ²⁴¹Am versus ¹³⁷Cs, ¹⁵⁵Eu, and ²³⁹Pu, indicate positive trends. Correlations were not observed between the activities of the soil-derived activation products ¹⁵²Eu and ¹⁵⁴Eu and the radioisotopes from the device. The calculated ratio of fission products (¹⁵⁵Eu/¹³⁷Cs) is 0.012 ± .006 (1σ, n = 3), which is lower than predicted for the thermal neutron-induced fission of ²³⁹Pu (~0.03). This discrepancy may be attributed to the spontaneous fission of the natural U tamper resulting in mixing between fission products from ²³⁹Pu and ²³⁵U. The spatial distribution of the trinitite samples relative to ground zero has been modeled based on the activity of ¹⁵²Eu. The calculated distances do not correlate with any of the activities for the radioisotopes investigated here, and suggest a relatively homogeneous distribution. However, trinitite samples with the highest activities for ¹³⁷Cs, ²³⁹Pu, and ²⁴¹Am yield the shortest calculated distances of 50–60 m away from ground zero.