Attosecond microscopy —Advances and outlook

EAE/ASE Recommendations for Image Acquisition and Display Using Three-Dimensional Echocardiography

The use of ultrashort optical and X-ray pulses offers new opportunities to study fundamental interactions in materials exhibiting unconventional quantum states, such as stripes, charge density waves and high-temperature superconductivity. To understand the microscopic interdependence between these states a probe capable of discerning their interaction on the natural length and time scales is necessary. In this talk, I will present ultrafast resonant soft x-ray scattering results to track the transient evolution of nanoscale charge density wave correlations in the high temperature superconductor, YBa2Cu3O6+x. Ultrashort infrared pulses produce a non-thermal quench of the superconducting state while X-ray pulses detect the reaction of charge density waves. We observe a picosecond response, characterized by a large enhancement of spatial coherence of charge density waves, nearly doubling their correlation length, and a smaller increase of their amplitude. This ultrafast snapshot directly reveals the interaction between these quantum states on their natural timescales. It demonstrates that their competition manifests inhomogeneously, as disruption of nanoscale spatial coherence, indicating the role of superconductivity in stabilizing topological defects within charge density waves domains.

This reference is for an abstract only. A full paper was not submitted for this conference. Introduction The word "resolution" is often assumed to refer to the specific case of temporal resolution. In that regard, Kallweit & Wood (1982) observed that when two octaves of bandwidth are present, the limit of temporal resolution can be expressed as 1/(1.4 x FMAX). However, equally important is the issue of spatial resolution. One of the methods proposed by Berkhout (1984) for quantifying spatial resolution is via the use of the "spatial wavelet". Such wavelets demonstrate that better temporal resolution leads to better spatial resolution. A key point in this paper, though, is that this relationship works the other way too. That is, better spatial resolution leads to better temporal resolution. For instance, of great interest spanning from the Gulf of Mexico to the Red Sea is the exploration for reservoirs beneath salt. In order for the migration process to be able to produce high temporal frequencies in the images of reflections beneath salt, the corrugated nature of the top-salt boundary needs to be portrayed faithfully in the velocity model. However, if a smoothed version of that boundary is used instead (as would certainly be the case in the first round of tomography), the spatial resolution of the top salt is lost. This is what leads to a forfeiture of the subsalt temporal resolution. Binning requirements The formulas for spatial wavelets are computed from calculus via the analytic integration of continuous functions. However, seismic data are sampled in time and space, and the imaging calculations use discrete summations. This means the spatial resolution in real surveys is more limited than indicated by the spatial wavelets - and the limitation gets worse when the sampling is coarse. One of the key reasons for the loss of bandwidth with large midpoint bins is due to the anti-alias filtering of the migration operators that must be done. As discussed by Abma et al. (1999), such filtering is needed to prevent the generation of artifacts. The resolution implications are demonstrated in Figure 1. A depth-varying velocity function from an onshore survey was used to model diffractions from two closely spaced points in the zone of interest. Those diffractions were then migrated and stacked. The results from two candidate survey designs are shown. The macro designs were identical. However, the source and receiver intervals were selected to yield the 40-ft (12 m) and 80-ft (24 m) CMP bin dimensions in the two surveys respectively. We can see that the 40-ft CMP bin design clearly resolves the two points that are 200 ft (61 m) apart, but the 80-ft design does not. Also, analyses of spectra (not shown) reveal that the temporal bandwidth for the 40-ft case is better than that from the 80-ft scenario - again confirming the inter-relationship of temporal and lateral resolution. This situation is definitely shared in marine surveys too. Such examples not only demonstrate the benefits of the more detailed structural interpretation that can be obtained from small-bin surveys, they also demonstrate the more detailed identification of reservoir properties that can be derived from inversion. Coordinate accuracy requirements Of course hand-in-hand with the drive for greater spatial resolution should be the drive for greater accuracy in source and receiver coordinate information. That is understandably more challenging in the offshore case. To investigate this issue, modeling and subsequent migration tests similar to those performed for Figure 1 were executed for a marine survey design. A velocity function was used from a field where the target was 6130 m deep. After the modeling of the diffraction surfaces was performed, the source and receiver coordinates were perturbed. This caused the migration to be conducted with inaccurate coordinate information. Three scenarios are featured in Figure 2. The panel on the left is used for reference. In that case, the correct coordinates were used for the migration. The panel in the middle shows the results obtained when the receiver coordinates were perturbed using a Gaussian distribution characterized by a 3-m standard deviation. That is similar to the type of accuracy that is available from leading-edge acoustic positioning systems. The panel on the right shows the result when the standard deviation was 20 m. That is akin to the type of accuracy that was available in early surveys that relied solely on compasses for streamer navigation data. We can see that the loss of resolution induced by the 3-m inaccuracy is no great consequence. The two point diffractors that are separated by 30 m are easily resolved. However, those diffractors are not resolved when the standard deviation is 20 m. Note that in this exercise the bin dimensions are 5 m. So, the right-most panel in the figure demonstrates that small bins by themselves are not sufficient for good resolution. Accuracy in coordinates is required too. Enabling technologies Improved (temporal and spatial) resolution requires denser spatial sampling. This naturally implies that massively more shots (via continuous recording techniques) and/or higher channel counts are required in acquisition. Indeed such strategies would seem to be ideal for onshore programs in the Middle East and North Africa where the desert environments place minimal restriction on access. However, in other regions, topography, vegetation, infrastructure, and many other things often severely restrict where shot points can be placed. In those cases, the burden of denser spatial sampling would have to be placed primarily on the channel count. Whatever the case, the quest for better sampling also implies that each shot should ideally be a point (as in the case of a single vibrator) and each receiver should be recorded by a separate channel - otherwise there will be smearing of the signal. But this is not to say that it would be sufficient simply to use more channels and more computers. An order of magnitude increase in the number of live channels requires paradigm shifts in data QC, data transfer, and processing. It also requires improvements in things like positioning accuracy - as mentioned above. So assuming all hurdles are overcome, how many live channels would we like to have in each shot? Well frankly, most geophysicists would probably take all that they could get. Today, large "conventional" land and marine acquisition systems might have 4,000 to 5,000 channels. However, some single-sensor land systems have offered up to 30,000 live channels - with further advances to 150,000 channels recently launched. Similarly, marine singlesensor systems can record tens of thousands of live channels - with the main limitation being how many streamers can be towed by the vessel. Final Remarks What we have said here is that resolution is multifaceted. Good temporal resolution does not depend simply on how much high-frequency energy our seismic sources can pump into the ground. Good temporal resolution in the 3D migrated image also requires good spatial sampling. Good spatial sampling requires high channel counts. High channel counts require a paradigm shift in everything from QC procedures to final interpretation. Also, the very definition of "sampling" implies discrete sampling - not mixing. And finally, the big questions of course are just how small do the bins have to be, and how many channels are needed? In other words, what are the requirements in the field design that are needed to meet the requirements in resolution? Projects with which the authors have been involved employed bins as small as 3 m or so. Such density is certainly not yet required in most areas, but it might very well be appropriate for specific instances ranging from the SAGD programs of the heavy oil province in Canada to high-resolution surveys in heavily karsted zones of the Middle East. As a matter of practice, proper survey evaluation and design studies need be conducted to answer these field-specific questions. References Abma, R., Sun, J., & Bernitsas, N., 1999, Antialiasing methods in Kirchhoff migration: Geophysics, 64. 1783–1792 Berkhout, A. J., 1984, Seismic exploration - seismic resolution: a quantitative analysis of resolving power of acoustical echo techniques. Geophys. Press, London. Kallweit, R. S. & Wood, L. C. 1982. The limits of resolution of zero-phase wavelets. Geophysics. 47. 1035–1046.

Terminology of three-dimensional and four-dimensional ultrasound imaging of the fetal heart and other moving body parts.

We are living in a dynamic world, where all matter is in a vibrant process, whether it is a giant celestial body or a small atom. Being able to observe, analyze, and manipulate these dynamic processes is undoubtedly essential for scientific discoveries and technical innovations. The evolution of any physical quantity (e.g., displacement, mass, electromagnetic fields, intensity, phase, and spectra) with time gives rise to different time-varying phenomena—some are slow, some are fast, and some are ultrafast, in view of what human beings can sense. With the modern smartphone or camera, fast motions within the microsecond time scale can now be recorded in daily life. However, when we enter into the micro/nanoscale world, what happens often becomes ultrafast. For example, atomic diffusion occurs in a nanosecond (10–9s) time scale. Molecular rotation, charge transfer relaxation, and magnetization reversal happen in picoseconds (10–12s). Molecule and lattice vibrations can happen even faster, occurring in femtoseconds (10–15s). Looking into the depths of an atomic system, electrons move orders faster to the attosecond (10–18s), which is currently the fastest process that human beings can observe. Furthermore, when we explore the nucleus of an atom, we will find the ultrafast dynamics happening in zeptoseconds (10–21s). These ultrafast processes, which eventually govern the property of matter, need special pulsed probing sources, methods, and instruments to investigate. The related ultrafast technologies play important roles for research and applications in fundamental physics, chemistry, materials, biology, energy, and information science. Ultrafast science is a general term referring to a knowledge system to investigate and explore the phenomena and laws of ultrafast changes in the universe. It involves various disciplines including atom and molecule physics, condensed matter physics, mechanics, optics, chemistry, biology, material science, and information science. Thus, ultrafast science has developed rapidly in the past decades. The Nobel Prize in chemistry was awarded for femtosecond laser chemistry in 1999. The Nobel Prize in physics was awarded for optical frequency comb laser precision spectroscopy in 2005. The 2018 Nobel Prize in physics was awarded for ultrashort super-intense laser pulse technology—chirped pulse amplification. In the last 10 years, over 50,000 research articles have been published in over 1,000 journals, as analyzed by Web of Science using the keyword of “ultrafast.” However, there lacks a specific high-impact journal that focuses on ultrafast science. This is the motivation for launching the Ultrafast Science journal. After over 1 year of preparation and discussion with the American Association for the Advancement of Science (AAAS), we reached a consensus that ultrafast science is an emerging and important direction which covers very broad and leading research fields. In 2020, Ultrafast Science became a Science Partner Journal distributed by the AAAS in collaboration with Xi’an Institute of Optics and Precision Mechanics (XIOPM), which is one of the leading organizations in ultrafast science in China, from the Chinese Academy of Sciences (CAS). Ultrafast Science is an Open Access Journal which publishes top-quality original research articles, comprehensive reviews, and perspectives, reflecting significant advances, breakthroughs, and novel applications with considerable potential in ultrafast science and broad interest from scientific communities. Topics include but are not limited to ultrafast physics, ultrafast laser and application, ultrafast imaging, ultrafast spectroscopy, ultrafast measurement, ultrafast materials and devices, ultrafast terahertz photonics, ultrafast electronics, ultrafast chemical physics, and other ultrafast phenomena. Interdisciplinary research demonstrating how ultrafast technology advances physics, chemistry, biology, material science, and other disciplines is especially welcome. We are honored to serve as the founding Editors-in-Chief and are grateful to work with the members of the Editorial Board, which currently comprise around 40 famous scientists from all over the world, including Gerard Mourou, who was awarded the Nobel Prize in physics in 2018. We believe that Ultrafast Science will become a high-impact journal in the near future with all of your participation and contributions, and that the journal will grow with the continuous breakthroughs in the ultrafast frontier.

Background Myocardial deformation analyses using cardiovascular magnetic resonance feature tracking (CMR-FT) have incremental value in the assessment of cardiac function beyond volumetric analyses. Since guidelines do not recommend specific imaging parameters, we aimed to define optimal spatial and temporal resolutions for CMR cine images to enable reliable post-processing. Methods Intra- and inter-observer reproducibility was assessed in 12 healthy volunteers. Cine images were acquired with differing temporal (20, 30, 40 and 50 frames/cardiac cycle) and spatial resolutions (high in-plane 1.5x1.5mm through-plane 5mm, standard 1.8x1.8x8mm and low 3.0x3.0x10mm). CMR-FT analyses comprised left ventricular (LV) global longitudinal strain (GLS) and systolic strain rate (SRs) as well as LV circumferential and radial strains (GCS and GRS) and right ventricular (RV) GLS. Intra- and inter-observer reproducibility was assessed in all subjects. Results Temporal but not spatial resolution did impact absolute strain and SR. Maximum absolute changes between lowest and highest temporal resolution were as follows: 2.3% LV GLS, 2.2% GCS, 7.2% GRS, 1.7% RV GLS and 0.32s-1 SRs. Changes of time-integrated (strain) values occurred predominantly comparing 20 and 30 frames/cardiac cycle including LV GLS, GCS and GRS (p = 0.034, p = 0.008 and p = 0.034) in highest spatial resolution settings. In contrast, time-derivatives values (SRs) changed significantly from lower temporal resolutions to 40 frames/cardiac cycle and beyond (20 to 30 p = 0.002; 30 to 40 p = 0.018; 40 to 50 frames/cardiac cycle p = 0.075) in highest spatial resolution settings. Strain reproducibility was not affected by either temporal or spatial resolution. SRs variability as assessed by coefficient of variation decreased with higher temporal resolutions. Conclusion Temporal but not spatial resolutions significantly affect strain and SR in CMR-FT deformation analyses. Clinical CMR-FT strain and SR analyses require minimum temporal resolutions of 30 and 40frames/cardiac cycle, respectively to ensure precise quantification of myocardial function.

ObjectivesConventional perfusion-weighted MRI sequences often provide poor spatial or temporal resolution. We aimed to overcome this problem in head and neck protocols using a golden-angle radial sparse parallel (GRASP) sequence.MethodsWe prospectively included 58 patients for examination on a 3.0-T MRI using a study protocol. GRASP (A) was applied to a volumetric interpolated breath-hold examination (VIBE) with 135 reconstructed pictures and high temporal (2.5 s) and spatial resolution (0.94 × 0.94 × 3.00 mm). Additional sequences of matching temporal resolution (B: 2.5 s, 1.88 × 1.88 × 3.00 mm), with a compromise between temporal and spatial resolution (C: 7.0 s, 1.30 × 1.30 × 3.00 mm) and with matching spatial resolution (D: 145 s, 0.94 × 0.94 × 3.00 mm), were subsequently without GRASP. Instant inline-image reconstructions (E) provided one additional series of averaged contrast information throughout the entire acquisition duration of A. Overall diagnostic image quality, edge sharpness and contrast of soft tissues, vessels and lesions were subjectively rated using 5-point Likert scales. Objective image quality was measured as contrast-to-noise ratio in D and E.ResultsOverall, the anatomic and pathologic image quality was substantially better with the GRASP sequence for the temporally (A/B/C, all p < 0.001) and spatially resolved comparisons (D/E, all p < 0.002 except lesion edge sharpness with p = 0.291). Image artefacts were also less likely to occur with GRASP. Differences in motion, aliasing and truncation were mainly significant, but pulsation and fat suppression were comparable. In addition, the contrast-to-noise ratio of E was significantly better than that of D (pD-E < 0.001).ConclusionsHigh temporal and spatial resolution can be obtained synchronously using a GRASP-VIBE technique for perfusion evaluation in head and neck MRI.Key Points• Golden-angle radial sparse parallel (GRASP) sampling allows for temporally resolved dynamic acquisitions with a very high image quality.• Very low-contrast structures in the head and neck region can benefit from using the GRASP sequence.• Inline-image reconstruction of dynamic and static series from one single acquisition can replace the conventional combination of two acquisitions, thereby saving examination time.

Summary form only given. Increased interest in molecular imaging encouraged us to develop high resolution-high sensitivity PET (Positron Emission Tomograph) scanners as well as high field MRI (Magnetic Resonance Imaging), especially in the area of brain imaging. In the field of neuroimaging, both high molecular specificity and high spatial resolution are the essential requirements to meet the brain's delicate structures and neurochemical activities. In spite of these high molecular specificity and spatial resolution requirements of neuroimaging, actual molecular imaging have been limited in resolution due to several factors, such as the physical limitations involved in PET scanner design, i.e., spatial and temporal resolution and poor sensitivity of currently available low or intermediate field MRI. In the area of MRI, high spatial and temporal resolution have been the limited, especially for the low and intermediate high field MRI systems. More recent developments in this area are the emergence of the ultra high field (UHF) MRI such as 7.0 T. Unique features of these ultra high field MRI are the improved sensitivity which enable us to improve either temporal resolution or spatial resolution. For example, with 7.0 T MRI, one can improve spatial resolution as high as 200 /spl square/m or better so that neuroscientists can examine even the cortical laminae in the human brain in-vivo. In the field of PET development, recent developments include the brain dedicated high resolution PET scanner such as the HRRT (High Resolution Research Tomograph). This brain dedicated PET (HRRT) scanner is designed to meet the resolution requirement of human brain imaging with molecular specificity, that is as good as 2.5 mm fwhm. First time in history, together with the appearance of these new developments, i.e., UHF-MRI and HRRT-PET scanners, neuroscientists began to search for a brain dedicated high resolution-high sensitivity imaging scanner that can be used for the simultaneous imaging of both the morphological and molecular or neurochemical activities with substantially increased temporal and spatial resolution than what is available today, that is the molecular neuro-images of spatial resolution as high as 200 /spl square/m, the resolution that can be obtained only with the ultra high resolution MRI. This new hybrid PET-MRI scanner with HRRT-PET and UHF-MRI will provide us a fused PET-MRI image, the molecular specific high resolution image, that is a truly integrated image, both in space and time. Physical design concepts and potentials of this hybrid PET-MRI scanner in neuroscience applications will be discussed and some of the preliminary results will be presented.

Development of ultrafast table-top x-ray sources that can map various spin, orbital, and electronic configurations and reordering processes on their natural time and length scales is an essential topic for modern condensed matter physics as well as ultrafast science. In this work, we demonstrate spatiotemporally resolved resonant magnetic scattering (XRMS) to probe the inner-shell 4d electrons of a rare-earth (RE) composite ferrimagnetic system using a bright &gt; 200 e V soft x-ray high harmonic generation (HHG) source, which is relevant for future energy-efficient, high-speed spintronic applications. The XRMS is enabled by direct driving of the HHG process with power-scalable, high-energy Yb laser technology. The optimally phase-matched broadband plateau of the HHG offers a record photon flux ( &gt; 2 × 1 0 9 p h o t o n s / s / 1 % bandwidth) with excellent spatial coherence and covers the entire resonant energy range of RE’s N 4 , 5 edges. We verify the underlying physics of our x-ray generation strategy through the analysis of microscopic and macroscopic processes. Using a CoTb alloy as a prototypical ferrimagnetic system, we retrieve the spin dynamics, and resolve a fast demagnetization time of 500 ± 126 f s , concomitant with an expansion of the domain periodicity, corresponding to a domain wall velocity of ∼ 750 m / s . The results confirm that, far from cross-contamination of low-energy absorption edges in multi-element systems, the highly localized states of 4 d electrons associated with the N 4 , 5 edges can provide high-quality core-level magnetic information on par with what can be obtained at the M edges, which is currently accessible only at large-scale x-ray facilities. The analysis also indicates the rich material-, composition-, and probing-energy-dependent driving mechanism of RE-associated multicomponent systems. Considering the rapid emergence of high-power Yb lasers combined with novel nonlinear compression technology, this work indicates potential for next-generation high-performance soft x-ray HHG-based sources in future extremely photon-hungry applications on the table-top scale, such as probing electronic motion in biologically relevant molecules in their physiological environment (liquid phase), and advanced coherent imaging of nano-engineered devices with 5 ∼ 8 n m resolution.

BackgroundMyocardial deformation analyses using cardiovascular magnetic resonance (CMR) feature tracking (CMR-FT) have incremental value in the assessment of cardiac function beyond volumetric analyses. Since guidelines do not recommend specific imaging parameters, we aimed to define optimal spatial and temporal resolutions for CMR cine images to enable reliable post-processing.MethodsIntra- and inter-observer reproducibility was assessed in 12 healthy subjects and 9 heart failure (HF) patients. Cine images were acquired with different temporal (20, 30, 40 and 50 frames/cardiac cycle) and spatial resolutions (high in-plane 1.5 × 1.5 mm through-plane 5 mm, standard 1.8 × 1.8 x 8mm and low 3.0 × 3.0 x 10mm). CMR-FT comprised left ventricular (LV) global and segmental longitudinal/circumferential strain (GLS/GCS) and associated systolic strain rates (SR), and right ventricular (RV) GLS.ResultsTemporal but not spatial resolution did impact absolute strain and SR. Maximum absolute changes between lowest and highest temporal resolution were as follows: 1.8% and 0.3%/s for LV GLS and SR, 2.5% and 0.6%/s for GCS and SR as well as 1.4% for RV GLS. Changes of strain values occurred comparing 20 and 30 frames/cardiac cycle including LV and RV GLS and GCS (p < 0.001–0.046). In contrast, SR values (LV GLS/GCS SR) changed significantly comparing all successive temporal resolutions (p < 0.001–0.013). LV strain and SR reproducibility was not affected by either temporal or spatial resolution, whilst RV strain variability decreased with augmentation of temporal resolution.ConclusionTemporal but not spatial resolution significantly affects strain and SR in CMR-FT deformation analyses. Strain analyses require lower temporal resolution and 30 frames/cardiac cycle offer consistent strain assessments, whilst SR measurements gain from further increases in temporal resolution.

Abstract. The transfer of parameter sets over different temporal and spatial resolutions is common practice in many large-domain hydrological modelling studies. The degree to which parameters are transferable across temporal and spatial resolutions is an indicator of how well spatial and temporal variability is represented in the models. A large degree of transferability may well indicate a poor representation of such variability in the employed models. To investigate parameter transferability over resolution in time and space we have set up a study in which the Variable Infiltration Capacity (VIC) model for the Thur basin in Switzerland was run with four different spatial resolutions (1 km × 1 km, 5 km × 5 km, 10 km × 10 km, lumped) and evaluated for three relevant temporal resolutions (hour, day, month), both applied with uniform and distributed forcing. The model was run 3150 times using the Hierarchical Latin Hypercube Sample and the best 1 % of the runs was selected as behavioural. The overlap in behavioural sets for different spatial and temporal resolutions was used as an indicator of parameter transferability. A key result from this study is that the overlap in parameter sets for different spatial resolutions was much larger than for different temporal resolutions, also when the forcing was applied in a distributed fashion. This result suggests that it is easier to transfer parameters across different spatial resolutions than across different temporal resolutions. However, the result also indicates a substantial underestimation in the spatial variability represented in the hydrological simulations, suggesting that the high spatial transferability may occur because the current generation of large-domain models has an inadequate representation of spatial variability and hydrologic connectivity. The results presented in this paper provide a strong motivation to further investigate and substantially improve the representation of spatial and temporal variability in large-domain hydrological models.

Picosecond time resolved cathodoluminescence to study semiconductor materials and heterostructures

Dynamic contrast-enhanced (DCE) MRI has been widely used as a quantitative imaging method for monitoring tumor response to therapy. The simultaneous challenges of increasing temporal and spatial resolution in a setting where the signal from the much smaller voxel is weaker have made this MR technique difficult to implement in small-animal imaging. Existing protocols employed in preclinical DCE-MRI acquire a limited number of slices resulting in potentially lost information in the third dimension. This study describes and compares a family of four-dimensional (3D spatial + time), projection acquisition, radial keyhole-sampling strategies that support high spatial and temporal resolution. The 4D method is based on a RF-spoiled, steady-state, gradient-recalled sequence with minimal echo time. An interleaved 3D radial trajectory with a quasi-uniform distribution of points in k-space was used for sampling temporally resolved datasets. These volumes were reconstructed with three different k-space filters encompassing a range of possible radial keyhole strategies. The effect of k-space filtering on spatial and temporal resolution was studied in a 5 mM CuSO(4) phantom consisting of a meshgrid with 350-μm spacing and in 12 tumors from three cell lines (HT-29, LoVo, MX-1) and a primary mouse sarcoma model (three tumors∕group). The time-to-peak signal intensity was used to assess the effect of the reconstruction filters on temporal resolution. As a measure of heterogeneity in the third dimension, the authors analyzed the spatial distribution of the rate of transport (K(trans)) of the contrast agent across the endothelium barrier for several different types of tumors. Four-dimensional radial keyhole imaging does not degrade the system spatial resolution. Phantom studies indicate there is a maximum 40% decrease in signal-to-noise ratio as compared to a fully sampled dataset. T1 measurements obtained with the interleaved radial technique do not differ significantly from those made with a conventional Cartesian spin-echo sequence. A bin-by-bin comparison of the distribution of the time-to-peak parameter shows that 4D radial keyhole reconstruction does not cause significant temporal blurring when a temporal resolution of 9.9 s is used for the subsamples of the keyhole data. In vivo studies reveal substantial tumor heterogeneity in the third spatial dimension that may be missed with lower resolution imaging protocols. Volumetric keyhole imaging with projection acquisition provides a means to increase spatiotemporal resolution and coverage over that provided by existing 2D Cartesian protocols. Furthermore, there is no difference in temporal resolution between the higher spatial resolution keyhole reconstruction and the undersampled projection data. The technique allows one to measure complex heterogeneity of kinetic parameters with isotropic, microscopic spatial resolution.

Abstract: Generation of high spatial and temporal resolution LAI (leaf area index) products is challenging because higher spatial resolution remotely sensed data usually have coarse temporal resolutions and vice versa. In this study, a novel method that combining Kriging interpolation and Cressman interpolation was proposed to generate high spatial and temporal resolution LAI products by fusing Moderate Resolution Imaging SpectroRadiometer (MODIS) characterized by coarse spatial resolution and high temporal resolution and Gaofen-1 (GF-1) with fine spatial resolution and coarse temporal resolution. This method was applied to the Huangpu district of Guangzhou, Guangdong, China. The results showed that compared to field observation, the predicted values of LAI had an acceptable accuracy of 73.12%. Using Moran’s I index and Kolmogorov-Smirnov tests, it was found that the MODIS data were spatially auto-correlated and characterized by normal distributions. Scaling down the 1 km×1 km spatial resolution MODIS products to a spatial resolution of 30 m×30 m using point-Kriging resulted in a precision of 79.38% compared to the results at the same spatial resolution derived from an 8 m×8 m spatial resolution GF-1 image by scaling up using block-Kriging. Moreover, the regression models that accounts for the relationship between NDVI (Normalized Difference Vegetation Index) and LAI based on MODIS data obtained the determination coefficients ranging from 0.833 to 0.870. Finally, the data fusion and interpolation of MODIS and GF-1 data using Cressman method generated high spatial and temporal resolution LAI maps, which showed reasonably spatial and temporal variability. The results imply that the proposed method is a powerful tool to create high spatial and temporal resolution LAI products. Keywords: data fusion, MODIS, GF-1, LAI, spatiotemporal resolution, spatial interpolation, remote sensing DOI: 10.3965/j.ijabe.20160905.1777 Citation: Liu Z H, Huang R G, Hu Y M, Fan S D, Feng P H. Generating high spatiotemporal resolution LAI based on MODIS/GF-1 data and combined Kriging-Cressman interpolation. Int J Agric & Biol Eng, 2016; 9(5): 120－131.

PurposeAccurate identification of arterial feeders and draining veins is critical for treatment decision‐making in patients with intracranial high‐flow vascular lesions. Currently available MRI sequences lack the temporal and spatial resolution needed for this task. A novel time‐resolved pseudo‐continuous arterial spin labeling (ASL) angiography sequence with high spatial and temporal resolution was developed, and image quality metrics relevant to clinical performance were assessed.MethodsTen volunteers and eight patients with intracranial high‐flow vascular lesions underwent a brain MRI protocol, augmented with the new sequence with multi‐spoke (1–3) readouts and dynamic, sliding‐window reconstruction. For each of the acquisitions, image quality was assessed using a 5‐point Likert scale, as well as SNR and SNR efficiency. Spatial and temporal resolution and acquisition time were compared with standard‐of‐care sequences used to assess high‐flow vascular lesions.ResultsThe time‐resolved angiographic sequence achieved high isotropic spatial resolution (0.68 mm3), comparable to time of flight (TOF) MRA, but higher than that of contrast‐enhanced (CE)‐MRA, and a higher temporal resolution (200 ms) than CE‐MRA. Multi‐spoke acquisitions demonstrated a significant increase in SNR and SNR efficiency compared to single‐spoke acquisitions while maintaining an overall high image quality rating and at a 31% reduced scan time relative to the single‐spoke variant.ConclusionThis study demonstrated the clinical feasibility of a novel time‐resolved ASL sequence using a multi‐spoke 3D‐radial readout with a vessel‐signal optimized flip angle sweep. Sufficient SNR, superior spatial and temporal resolution to CE‐MRA, and a comparable spatial resolution to TOF MRA were achieved in a clinically reasonable acquisition time.