Fast and accessible T2 mapping using off-resonance corrected DESPOT2 with application to 3D prostate.

PURPOSE: Most T1 and T2 mapping take long acquisitions or needs specialized sequences not widely accessible on clinical scanners. An available solution is DESPOT1/T2 (Driven equilibrium single pulse observation of T1/T2). DESPOT1/T2 uses Spoiled gradient-echo (SPGR) and balanced Steady-State Free Precession (bSSFP) sequences, offering an accessible and reliable way for 3D accelerated T1/T2 mapping. However, bSSFP is prone to off-resonance artifacts, limiting the application of DESPOT2 in regions with high susceptibility contrasts, like the prostate. Our proposal, DESPO+, employs the full bSSFP and SPGR models with a dictionary-based method to reconstruct 3D T1/T2 maps in the prostate region without off-resonance banding. METHODS: DESPO+ modifies the bSSFP acquisition of the original variable flip angle DESPOT2. DESPO+ uses variable repetition and echo times, employing a dictionary-based method of the full bSSFP and SPGR models to reconstruct T1, T2, and Proton Density (PD) simultaneously. The proposed DESPO+ method underwent testing through simulations, T1/T2 phantoms, and on fourteen healthy subjects. RESULTS: The results reveal a significant reduction in T2 map banding artifacts compared to the original DESPOT2 method. DESPO+ approach reduced T2 errors by up to seven times compared to DESPOT2 in simulations and phantom experiments. We also synthesized in-vivo T1-weighted/T2-weighted images from the acquired maps using a spin-echo model to verify the map's quality when lacking a reference. For in-vivo imaging, the synthesized images closely resemble those from the clinical MRI protocol, reducing scan time by around 50% compared to traditional spin-echo T1-weighted/T2-weighted acquisitions. CONCLUSION: DESPO+ provides an off-resonance insensitive and clinically available solution, enabling high-resolution 3D T1/T2 mapping and synthesized T1-weighted/T2-weighted images for the entire prostate, all achieved within a short scan time of 3.6 min, similar to DESPOT1/T2.

High precision orientation mapping from 4D-STEM precession electron diffraction data through quantitative analysis of diffracted intensities.

The association of scanning transmission electron microscopy (STEM) and detection of a diffraction pattern at each probe position (so-called 4D-STEM) represents one of the most promising approaches to analyze structural properties of materials with nanometric resolution and low irradiation levels. This is widely used for texture analysis of materials using automated crystal orientation mapping (ACOM). Herein, we perform orientation mapping in InP nanowires exploiting precession electron diffraction (PED) patterns acquired by an axial CMOS camera. Crystal orientation is determined at each probe position by the quantitative analysis of diffracted intensities minimizing a residue comparing experiments and simulations in analogy to x-ray structural refinement. Our simulations are based on the two-beam dynamical diffraction approximation and yield a high angular precision (∼0.03°), much lower than the traditional ACOM based on pattern matching algorithms (∼1°). We anticipate that simultaneous exploration of both spot positions and high precision crystal misorientation will allow the exploration of the whole potentiality provided by PED-based 4D-STEM for the characterization of deformation fields in nanomaterials.

Experimental model for the description of the behaviour of a 9-mm projectile at a target.

Analysis of crime scenes involving single-fire-gun projectiles requires the determination of the direction of arrival of a projectile at the target and other factors to reconstruct events. The movement of a projectile can be analyzed by applying Euler's equations to a solid symmetrical rigid body. The present work starts from a Newtonian reformulation of these equations to show that, in the presence of a gravitational field, the system can be expressed with a complex variable nonlinear equation, where the inclusion of small nutation variables allows us to find possible solutions. As a particular case, we analyzed the movement of a 9-mm projectile fired from distances greater than 1 m to demonstrate that the direction of arrival of the projectile at the target cannot be traced by a stick placed in the target hole, as is usually performed in crime investigations. A series of shots were fired from distances varying between 1 m and 7 m. Impact data were recorded on Riemann planes of projection for the description of nutation and precession motions, allowing the observation of the motion dynamics of the projectile. We show that the direction of arrival at the target can be determined approximately from the analysis of the nutation and precession curves through Riemann planes of projection. The results presented in this work will allow more accurate judgements to be made in judicial investigations.

Monitoring electrochemical reactions in situ using steady-state free precession (13)C NMR spectroscopy.

All attempts to use in situ(13)C NMR in spectroelectrochemical studies, using static cells and unlabeled substrates, have failed due to the very long average time (several hours). In this paper, we demonstrated that steady-state free precession (SSFP) pulse sequence can enhance signal to noise ratio and reduces the average time of (13)C NMR signals by more than one order of magnitude. The results showed that each (13)C NMR spectrum during the electrochemical reduction of 9-chloroanthracene, in a static cell, can be acquired in eleven minutes. This short averaging time allowed the analysis of the reaction every 30min during 3h. The phase and truncation anomalies present in SSFP spectra were minimized using Traff apodization function and Krylov basis diagonalization method (KBDM).

Innermost stable circular orbits and epicyclic frequencies around a magnetized neutron star / Órbitas circulares marginalmente estables y frecuencias epicíclicas alrededor de una estrella de neutrones magnetizada / Órbitas circulares marginalmente estáveis e frequencias epicicloidais nas proximidades de uma estrela de neutrons magnetizada

El formalismo de la relatividad general es usado para calcular el radio de la órbita marginalmente estable (ROME), las frecuencias kepleriana, de Lense-Thirring, de precesion y oscilación de los movimientos radiales y verticales, de una partícula de prueba neutra que orbita el plano ecuatorial de una estrella de neutrones magnetizada. El espacio tiempo alrededor de la estrella se modela por medio de la solución seis paramétrica derivada por Pachón et al. (2012). Se concluye que la presencia del campo magnético de la fuente tiene efectos apreciables en las cantidades físicas mencionadas arriba y, por tanto, su inclusión es necesaria si se desea describir con más exactitud los procesos físicos que ocurren en la vecindad de este tipo de estrellas tales como la dinámica de discos de acreción. Los resultados presentados aquí también sugieren que la presencia de campos magnéticos intensos pueden introducir correcciones apreciables en, por ejemplo, las predicciones de la masa de estrellas de neutrones hechas con base en el modelo de precesión relativista.

A full-relativistic approach is used to compute the radius of the innermost stable circular orbit (ISCO), the Keplerian, frame-dragging, precession and oscillation frequencies of the radial and vertical motions of neutral test particles orbiting the equatorial plane of a magnetized neutron star. The space-time around the star is modelled by the six parametric solution derived by Pachón et al. (2012) It is shown that the inclusion of an intense magnetic field, such as the one of a neutron star, have non-negligible effects on the above physical quantities, and therefore, its inclusion is necessary in order to obtain a more accurate and realistic description of physical processes, such as the dynamics of accretion disks, occurring in the neighbourhood of this kind of objects. The results discussed here also suggest that the consideration of strong magnetic fields may introduce non-negligible corrections in, e.g., the relativistic precession model and therefore on the predictions made on the mass of neutron stars.

O formalismo da relatividade geral é usado para calcular o raio da órbita marginalmente estável (ROME), as frequencias keplerianas de Lense Thirring, precessao e oscilaçao de movimentos radiais e verticais, de uma partícula de prova neutra em órbita equatorial de uma estrela de neutrón magnetizada. O espaço-tempo ao redor da estrela é modelado por meio da soluçao seis paramétrica derivada por Pachón et al. (2012). Conclui-se que a presença do campo magnético da fonte tem efeitos apreciáveis nas quantidades físicas mencionadas acima e, portanto, a sua inclusão é necessária se se deseja descrever com mais exatidão os processos físicos que ocorrem na vizinhança deste tipo de estrelas tais como a dinâmica dos discos de acreção. Os resultados apresentados também sugerem que a precessão de campos magnéticos intensos podem introduzir correcções apreciáveis em, por exemplo, as predições da massa da estrela de neutróns feitas com base nos modelos de precessão relativista.

Single-Breathhold Four-Dimensional Assessment of Left Ventricular Morphological and Functional Parameters by Magnetic Resonance Imaging Using the VAST Technique.

INTRODUCTION: The accurate and reproducible assessment of cardiac volumes, function, and mass is of paramount importance in cardiology. In the present study we sought to determine whether the 3D cine-magnetic resonance (MR) technique, using the variable asymmetric sampling in time (VAST) approach, provided an accurate assessment of LV functional parameters when compared with the conventional 2D cine-MR technique. METHODS: A total of 43 consecutive patients referred for a CMR examination for clinical reasons and 14 healthy volunteers were included in the study. Cine images were acquired using a steady-state free precession pulse sequence. Two different multiphase acquisitions were performed: conventional 2D cine-MR and 3D cine-MR. The short-axis cine images acquired by both cine-MR techniques were used for the quantitative assessment of LV end-diastolic, end-systolic and stroke volumes, LV mass and ejection fraction. RESULTS: All CMR examinations were completed successfully, with both cine-MR imaging techniques yielding interpretable diagnostic results in all patients. Regarding the quantitative assessment, Bland-Altman analyses demonstrated a good agreement between the measurements of both cine-MR techniques for all LV parameters. In addition, the agreement between 2D and 3D cine-MR techniques for the qualitative assessment of LV global function was perfect (kappa = 1.0, P<0.001) for the two observers in consensus. The assessment performed by the third independent observer also demonstrated very good agreement (kappa = 0.88, P<0.001). CONCLUSION: The single breathhold 3D cine-MR technique provides an accurate and reproducible quantitative assessment of LV volumes, mass and function when compared with the conventional 2D cine-MR method.