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Objective: To establish an automated pipeline for post-processing of quantitative spin-lattice relaxation time constant in the rotating frame ($T_{1\rho}$) imaging of knee articular cartilage. Design: The proposed post-processing pipeline commences with an image standardisation procedure, followed by deep learning-based segmentation to generate cartilage masks. The articular cartilage is then automatically parcellated into 20 subregions, where $T_{1\rho}$ quantification is performed. The proposed pipeline was retrospectively validated on a dataset comprising knee $T_{1\rho}$ images of 10 healthy volunteers and 30 patients with knee osteoarthritis. Three experiments were conducted, namely an assessment of segmentation model performance (using Dice similarity coefficients, DSCs); an evaluation of the impact of standardisation; and a test of $T_{1\rho}$ quantification accuracy (using paired t-tests; root-mean-square deviations, RMSDs; and coefficients of variance of RMSDs, $CV_{RMSD}$). Statistical significance was set as p<0.05. Results: There was a substantial agreement between the subregional $T_{1\rho}$ quantification from the model-predicted masks and those from the manual segmentation labels. In patients, 17 of 20 subregions, and in healthy volunteers, 18 out of 20 subregions, demonstrated no significant difference between predicted and reference $T_{1\rho}$ quantifications. Average RMSDs were 0.79 ms for patients and 0.56 ms for healthy volunteers, while average $CV_{RMSD}$ were 1.97% and 1.38% for patients and healthy volunteers. Bland-Altman plots showed negligible bias across all subregions for patients and healthy volunteers. Conclusion: The proposed pipeline can perform automatic and reliable post-processing of quantitative $T_{1\rho}$ images of knee articular cartilage., Comment: Junru Zhong and Yongcheng Yao share the same contribution. Work was partially done when Yongcheng Yao and Siyue Li was with CUHK

This study evaluated a deep learning-based method using Deep Image Prior (DIP) to quantify triglyceride double bonds from chemical-shift encoded multi-echo gradient echo images without network training. We employed a cost function based on signal constraints to iteratively update the neural network on a single dataset. The method was validated using phantom experiments and in vivo scans. Results showed close alignment between measured and reference double bond values, with phantom experiments yielding a Pearson correlation coefficient of 0.96 (p = .0005). In vivo results demonstrated good agreement in subcutaneous fat. We conclude that Deep Image Prior shows feasibility for quantifying double bonds and fatty acid content from chemical-shift encoded multi-echo MRI.

Objective: Quantitative $T_1\rho$ imaging has potential for assessment of biochemical alterations of liver pathologies. Deep learning methods have been employed to accelerate quantitative $T_1\rho$ imaging. To employ artificial intelligence-based quantitative imaging methods in complicated clinical environment, it is valuable to estimate the uncertainty of the predicated $T_1\rho$ values to provide the confidence level of the quantification results. The uncertainty should also be utilized to aid the post-hoc quantitative analysis and model learning tasks. Approach: To address this need, we propose a parametric map refinement approach for learning-based $T_1\rho$ mapping and train the model in a probabilistic way to model the uncertainty. We also propose to utilize the uncertainty map to spatially weight the training of an improved $T_1\rho$ mapping network to further improve the mapping performance and to remove pixels with unreliable $T_1\rho$ values in the region of interest. The framework was tested on a dataset of 51 patients with different liver fibrosis stages. Main results: Our results indicate that the learning-based map refinement method leads to a relative mapping error of less than 3% and provides uncertainty estimation simultaneously. The estimated uncertainty reflects the actual error level, and it can be used to further reduce relative $T_1\rho$ mapping error to 2.60% as well as removing unreliable pixels in the region of interest effectively. Significance: Our studies demonstrate the proposed approach has potential to provide a learning-based quantitative MRI system for trustworthy $T_1\rho$ mapping of the liver.

Multi-parametric mapping of MRI relaxations in liver has the potential of revealing pathological information of the liver. A self-supervised learning based multi-parametric mapping method is proposed to map T$T_{1\rho}$ and T$_2$ simultaneously, by utilising the relaxation constraint in the learning process. Data noise of different mapping tasks is utilised to make the model uncertainty-aware, which adaptively weight different mapping tasks during learning. The method was examined on a dataset of 51 patients with non-alcoholic fatter liver disease. Results showed that the proposed method can produce comparable parametric maps to the traditional multi-contrast pixel wise fitting method, with a reduced number of images and less computation time. The uncertainty weighting also improves the model performance. It has the potential of accelerating MRI quantitative imaging.

$T_{1\rho}$ mapping is a promising quantitative MRI technique for the non-invasive assessment of tissue properties. Learning-based approaches can map $T_{1\rho}$ from a reduced number of $T_{1\rho}$ weighted images, but requires significant amounts of high quality training data. Moreover, existing methods do not provide the confidence level of the $T_{1\rho}$ estimation. To address these problems, we proposed a self-supervised learning neural network that learns a $T_{1\rho}$ mapping using the relaxation constraint in the learning process. Epistemic uncertainty and aleatoric uncertainty are modelled for the $T_{1\rho}$ quantification network to provide a Bayesian confidence estimation of the $T_{1\rho}$ mapping. The uncertainty estimation can also regularize the model to prevent it from learning imperfect data. We conducted experiments on $T_{1\rho}$ data collected from 52 patients with non-alcoholic fatty liver disease. The results showed that our method outperformed the existing methods for $T_{1\rho}$ quantification of the liver using as few as two $T_{1\rho}$-weighted images. Our uncertainty estimation provided a feasible way of modelling the confidence of the self-supervised learning based $T_{1\rho}$ estimation, which is consistent with the reality in liver $T_{1\rho}$ imaging., Comment: Provisionally accepted by Physics in Medicine and Biology

Purpose: To explore the usability and normal T1rho value of liver parenchyma with a novel single breathhold black blood single shot fast spin echo acquisition based liver imaging sequence. Materials and Methods: In total 19 health subjects (10 males, 9 females; mean age: 37.4 yrs; range: 23-54 yrs) participated in the study. 11 subjects had liver scanned twice in the same session to access scan-rescan repeatability. 12 subjects had liver scanned twice in two sessions with 7-10 days' interval to access scan-rescan reproducibility. MR was performed with a 3.0 T scanner with dual transmitter. The MR sequence allows simultaneous acquisition of 4 spin lock times (TSLs: 0ms, 10 ms, 30 ms, 50ms) in 10 second. Inherent black blood effect of fast spin echo and double inversion recovery were utilized to achieve blood signal suppression. Results: The technique demonstrated good image quality and minimal artifacts. For liver parenchyma, Bland-Altman plot showed the scan-rescan repeatability mean difference was 0.025 ms (95% limits of agreement: -1.163 to 1.213 ms), and intraclass correlation coefficient (ICC) was 0.977. The scan-rescan reproducibility mean difference was -0.075 ms (95% limits of agreement: -3.280 to 3.310 ms), and ICC was 0.820 which is better than the ICC of 0.764 of a previous bright blood multi-breath hold gradient echo acquisition technique. The liver T1rho value was 39.9 +/- 2.4 ms (range: 36.1 - 44.2 ms), which is lower than the value of 42.8=/-2.1 ms acquired with the previous bright blood technique. Conclusion: This study validated the application of a single breathhold black blood single shot fast spin echo acquisition based for human liver T1rho imaging. The lower liver parenchyma T1rho value and higher scan rescan reproducibility may improve of the sensitivity of this technique., Comment: Total 30 pages, 4 figures, 1 table

We have become increasingly aware of the fundamental importance of water, and aqueous alteration, on primitive solar-system bodies. All classes of astromaterials studied show some degree of interaction with aqueous fluids. We have direct observations of cryovolcanism of several small solar system bodies (e.g. Saturnian and Jovian moons), and indirect evidence for this process on the moons Europa, Titan, Ganymede, and Miranda, and the Kuiper Belt object Charon, and so are certain of the continuing and widespread importance of aqueous processes across the solar system. Nevertheless, we are still lacking fundamental information such as the location and timing of the aqueous alteration and the detailed nature of the aqueous fluid itself.

The nature and origin of extraterrestrial organic matter are still under debate despite the significant progress in the analyses and experimental approaches in this field over the last five decades. Xenolithic clasts are often found in a wide variety of meteorite groups, some of which contain exotic organic matter (OM). The Zag meteorite is a thermally-metamorphosed H ordinary chondrite. It contains a primitive xenolithic clast that has been proposed to have originated from Ceres, which was accreted to the Zag host asteroid after metamorphism. The cm-sized clast contains abundant large carbon-rich (mostly organic) grains or aggregates up to 20 microns. Such large OM grains are unique among astromaterials with respect to the size. Here we report organic and isotope analyses of a large (approx.10 microns) aggregate of solid OM in the Zag clast. The X-ray micro-spectroscopic technique revealed that the OM has sp2 bonded carbon with no other functional groups nor graphitic feature (1s-sigma exciton), and thus it is distinguished from most of the OM in carbonaceous meteorites. The apparent absence of functional groups in the OM suggests that it is composed of hydrocarbon networks with less heteroatoms, and therefore the OM aggregate is similar to hydrogenated amorphous carbon (HAC). The OM aggregate has high D/H and 15N/14N ratios, suggesting that it originated in a very cold environment such as the interstellar medium or outer region of the solar nebula, while the OM is embedded in carbonate-bearing matrix resulting from aqueous activities. Thus the high D/H ratio must have survived the extensive late-stage aqueous processing. It is not in the case for OM in carbonaceous chondrites of which the D/H ratio was reduced by the alteration via the D-H exchange of water. It indicates that both the OM precursors and the water had high D/H ratios, similar to the water in Enceladus. Our results support the idea that the clast originated from Ceres, or at least, a hydrovolcanically active body similar to Ceres, and further imply that Ceres originally formed in the outer Solar System and migrated to the main belt asteroid region as suggested by the "Grand tack" scenario.

We present in this study the effects of short-term heating on organics in the Tagish Lake meteorite and how the difference in the heating conditions can modify the organic matter (OM) in a way that complicates the interpretation of a parent body's heating extent with common cosmo thermometers. The kinetics of short-term heating and its influence on the organic structure are not well understood, and any study of OM is further complicated by the complex alteration processes of the thermally metamorphosed carbonaceous chondrites - potential analogues of the target asteroid Ryugu of the Hayabusa2 mission - which had experienced post-hydration, short-duration local heating. In an attempt to understand the effects of short-term heating on chondritic OM, we investigated the change in the OM contents of the experimentally heated Tagish Lake meteorite samples using Raman spectroscopy, scanning transmission X-ray microscopy utilizing X-ray absorption near edge structure spectroscopy, and ultra-performance liquid chromatography fluorescence detection and quadrupole time of flight hybrid mass spectrometry. Our experiment suggests that graphitization of OM did not take place despite the samples being heated to 900 degrees Centigrade for 96 hours, as the OM maturity trend was influenced by the nature of the OM precursor, such as the presence of abundant oxygenated moieties. Although both the intensity of the 1s-sigma σ* exciton cannot be used to accurately interpret the peak metamorphic temperature of the experimentally heated Tagish Lake sample, the Raman graphite band widths of the heated products significantly differ from that of chondritic OM modified by long-term internal heating.

Few traces of Earth's geologic record are preserved from the time of life's emergence, over 3,800 million years ago. Consequently, what little we understand about abiogenesis - the origin of life on Earth - is based primarily on laboratory experiments and theory. The best geological lens for understanding early Earth might actually come from Mars, a planet with a crust that's overall far more ancient than our own. On Earth, surface sedimentary environments are thought to best preserve evidence of ancient life, but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last approximately 2,500 million years or more. By the time oxygenic photosynthesis evolved on Earth, Mars had been a hyperarid, frozen desert with a surface bombarded by high-energy solar and cosmic radiation for more than a billion years, and as a result, photosynthetic surface life may never have occurred on Mars. Therefore, one must question whether searching for evidence of life in Martian surface sediments is the best strategy. This Perspective explores the possibility that the abundant hydrothermal environments on Mars might provide more valuable insights into life's origins.

C-class asteroids frequently exhibit reflectance spectra consistent with thermally metamor-phosed carbonaceous chondrites [1], or a mixture of phyllosilicate-rich material along with regions where they are absent [2]. One particularly important example appears to be asteroid 162173 Ryugu, the target of the Hayabusa 2 mission [1], although most spectra of Ryugu are featureless, suggesting a heterogeneous regolith [3]. Here we explore an alternative cause of dehydration of regolith of C-class asteroids - impact shock melting. Impact shock melting has been proposed to ex-plain some mineralogical characteristics of CB chondrites [4], but has rarely been considered a major process for hydrous carbonaceous chondrites [5]. Jbilet Winselwan (JW) is a very fresh CM breccia from Morocco, with intriguing characteristics. While some lithologies are typical of CM2s (Figure 1, top), other clasts show evidence of brief, though significant impact brecciation and heating. The first evidence for this came from preliminary petrographic and stable isotope studies [6,7]. We contend that highly-brecciated, partially-shocked, and dehydrated lithologies like those in JW dominate C-class asteroid regolith.

We requested and have been approved for 5 Hayabusa samples in order definitively establish the degree of shock experienced by the regolith of asteroid Itokawa, and to devise a bridge between shock determinations by standard light optical petrography, crystal structures as determined by synchrotron X-ray diffraction (SXRD), and degree of crystallinity as determined by electron back-scattered diffraction (EBSD). As of the writing of this abstract we are awaiting the approved samples. We propose measurements of astromaterial crystal structures and regolith processes. The proposed research work will improve our understanding of how small, primitive solar system bodies formed and evolved, and improve understanding of the processes that determine the history and future of habitability of environments on other solar system bodies. The results of the proposed research will directly enrich the ongoing asteroid and comet exploration missions by NASA, JAXA and ESA, and broaden our understanding of the origin and evolution of small bodies in the early solar system, and elucidate the nature of asteroid and comet regolith.

C-class asteroids frequently exhibit reflectance spectra consistent with thermally metamorphosed carbonaceous chondrites, or a mixture of phyllosilicate-rich material along with regions where they are absent. One particularly important example appears to be asteroid 162173 Ryugu, the target of the Hayabusa 2 mission, although most spectra of Ryugu are featureless, suggesting a heterogeneous regolith. Here we explore an alternative cause of dehydration of regolith of C-class asteroids - impact shock melting. Impact shock melting has been proposed to ex-plain some mineralogical characteristics of CB chondrites, but has rarely been considered a major process for hydrous carbonaceous chondrites.

Meteorites provide us with valuable insights into the conditions of the early solar system. Collisions often occur in our solar system that can result in materials accreting to other bodies as foreign clasts. These foreign pieces may have multiple origins that can sometimes be easily identified as a particular type of meteorite. It is important to interpret the origins of these clasts in order to understand dynamics of the solar system, especially throughout its early history. The Nice Model, as modified, proposes a reordering of planetary orbits that is hypothesized to have triggered the Late Heavy Bombardment. Clasts found within meteorites that came from objects in the solar system not commonly associated as an impactor could be indicative of such an event suggested by the Nice Model. Impacts also redistribute material from one region of an asteroid to another, and so clasts are found that reveal portions of the geological history of a body that are not recorded by typical samples. These would be cognate clasts. The goal of this investigation was to examine meteorites that had particularly interesting foreign and cognate clasts enclosed in them. We focus here on an unusual clast located in the ordinary chondrite, NWA 6925. This is one of three clasts analyzed during the LPI summer internship of Jessica Johnson.

C-class asteroids frequently exhibit reflectance spectra consistent with thermally metamor-phosed carbonaceous chondrites, or a mixture of phyllosilicate-rich material along with regions where they are absent. One particularly important example appears to be asteroid 162173 Ryugu, the target of the Hayabusa 2 mission, although most spectra of Ryugu are featureless, suggesting a heterogeneous regolith. Here we explore an alternative cause of dehydration of regolith of C-class asteroids impact shock melting. Impact shock melting has been proposed to explain some mineralogical characteristics of CB chondrites, but has rarely been considered a major process for hydrous carbonaceous chondrites. Jbilet Winselwan (JW) is a very fresh CM breccia from Morocco, with intriguing characteristics. While some lithologies are typical of CM2s, other clasts show evidence of brief, though significant impact brecciation and heating. The first evidence for this came from preliminary petrographic and stable isotope studies. We contend that highly-brecciated, partially-shocked, and dehydrated lithologies like those in JW dominate C-class asteroid regolith.

Recent reports of the DAWN spacecraft's observations of the surface of Ceres indicate that there are bright areas, which can be explained by large amounts of the Mg sulfate hexahydrate (MgSO4•6(H2O)), although the identification appears tenuous. There are preliminary indications that water is being evolved from these bright areas, and some have inferred that these might be sites of contemporary hydro-volcanism. A heat source for such modern activity is not obvious, given the small size of Ceres, lack of any tidal forces from nearby giant planets, probable age and presumed bulk composition. We contend that observations of chondritic materials in the lab shed light on the nature of the bright spots on Ceres

We requested and have been approved for 5 Hayabusa samples in order definitively establish the degree of shock experienced by the regolith of asteroid Itokawa, and to devise a bridge between shock determinations by standard light optical petrography, crystal structures as determined by synchrotron X-ray diffraction (SXRD), and degree of crystallinity as determined by electron back-scattered diffraction (EBSD) [1,2]. As of the writing of this abstract we are awaiting the approved samples. We propose measurements of astromaterial crystal structures and regolith processes. The proposed research work will improve our understanding of how small, primitive solar system bodies formed and evolved, and improve understanding of the processes that determine the history and future of habitability of environments on other solar system bodies. The results of the proposed research will directly enrich the ongoing asteroid and comet exploration missions by NASA, JAXA and ESA, and broaden our understanding of the origin and evolution of small bodies in the early solar system, and elucidate the nature of asteroid and comet regolith.

Meteorites play an integral role in understanding the history of the solar system. Not only can they contain some of the oldest material found in the solar system they also can contain material that is unique. Many lithologies are only found as foreign clasts within distinctly different host meteorites. In this investigation two foreign clasts within the meteorites, NWA6169 and NWA8330 were studied. The purpose of this investigation was to examine the mineralogy and petrography of the clasts within the samples. From there an identification and possible origin were to be inferred. NWA6169 is an unclassified ordinary chondrite that has a presumed petrologic type of L3. NWA8330 is a classified ordinary chondrite that has a petrologic type of LL3. Both meteorites were found to contain clasts that were similar; both modally were comprised of about 5% acicular graphite. Through SEM and Raman Spectroscopy it was found that they contained olivine, pyroxene, plagioclase, Fe-Ni sulfides, graphite, and metals. They were found to portray an igneous texture with relationships that suggest concurrent growth. Analytical microprobe results for NWA6169 revealed mineral compositions of Fa31-34, Fs23-83, and Ab7-85. For NWA8330 these were Fa28-32, Fs10-24, and Ab4-83. Only one similar material has been reported, in the L3 chondrite Krymka (Semenenko & Girich, 1995). The clast they described exhibited similar mineralogies including the unusual graphite. Krymka data displayed compositional values of Fa28.5-35.0 and Fs9-25.9. These ranges are fairly similar to that of NWA6169 and NWA8330. These samples may all be melt clasts, probably of impact origin. Two possibilities are (1) impact of a C-type asteroid onto the L chondrite parent asteroid, and (2) a piece of proto-earth ejected from the moon-forming collision event. These possibilities present abundant questions, and can be tested. The measurement of oxygen isotope compositions from the clasts should reveal the original source of the melt clasts. It may also be possible to perform Ar dating of the plagioclase present. Former analyses are now being performed.