Gradient Strength Research Articles

Minimization of eddy power loss in the cryostat for a z-gradient array coil driven by an arbitrary pulse sequence: An electromagnetic approach.

This paper presents a novel computational approach to optimize gradient array performance for a given pulse sequence. Specifically, we propose an electromagnetic (EM) approach that minimizes eddy losses within the cryostat while maintaining key performance parameters such as field linearity, gradient strength, and imaging region's dimension and position. High-resolution EM simulations on the cryostat's surface are deployed to compute the net EM fields generated by each element of a gradient array coil at different frequencies. The computed fields are stored and combined for each frequency to form a quadratic vector-matrix-vector computation. The overall time-average eddy power loss within the cryostat assembly for arbitrary pulse sequences is computed using frequency domain superposition. The proposed approach estimates and regulates eddy power losses within the cryostat assembly. When compared to the stray field minimization approach, it can achieve over twice the reduction in eddy power loss. The proposed approach eliminates the need to sample the stray fields on the cryostat surface, which the number and position of the samples would be challenging when designing tunable array coils with capabilities that disrupt field symmetries. Additionally, the loss calculation considers the entire cryostat assembly rather than just the inner cylindrical surface of the warm shield. Our findings highlight the efficacy of an on-the-fly tuning method for the development of high-performance whole-body gradient array coils, effectively mitigating eddy losses within the cryostat and minimizing stray fields outside the coil assembly. This approach proves particularly advantageous for array coils with variable feeding currents.

Damage mechanism and failure risk analysis of offshore pipelines subjected to impact loads from falling object, considering the soil variability

Trench and burial, as a primary and effective protection measurement for offshore pipelines from impact loads, has received much research attention recently. Previous studies were usually performed based on the assumption that the soil material was homogeneous with deterministic mechanical properties. The soil spatial variability, which is demonstrated to have significant influences on the soil capacity in marine geotechnical analysis, has not been included. This study was motivated to investigate the response of the buried pipelines subjected to the impact loads, with special address on the soil variability. Firstly, a three-dimensional random large deformation finite element analysis model was developed, which was implemented by the field variable (FV) technique to map the non-stationary random field (NSRF) into the verified Coupled Eulerian-Lagrangian (CEL) model (Hereafter referred to as FVRCEL). Then the FVRCEL model was integrated with the Monte-Carlo simulation (MCS) to obtain the statistical characteristics of the pipeline structural response. The failure mechanisms of the pipeline in the random soil with different fluctuation scales were investigated, and a parametric study was performed to identify the influential factors. Finally, the failure probability curves and surfaces were presented, providing clues for the pipeline safety design. The results revealed that in general, more than 50 % of the realized NSRF scenarios in the random analysis yielded more severe dent damage than the deterministic result, indicating that the latter would underestimate the damage degree, which was more pronounced when the increasing gradient of soil strength was high. The horizontal fluctuation scale had a remarkable influence on the pipeline damage behaviours and the corresponding statistical characteristics, of which the inner mechanisms were discussed. From the probabilistic perspective, at most an extra failure probability of 75 % would be suffered if the soil variability was ignored.

Rainfall Scouring Mechanism of the High-Speed Railway Subgrade Slope with Coarse-Grained Soil

The hydraulic erosion of the subgrade slope can lead to serious loss of filling materials and landslides, affecting stability. In particular, there is no quantitative consideration of the scouring calculation method for the design codes of High-Speed Railway Subgrade Slope (HRSS). This paper mainly focuses on the anti-erosion stability of HRSS with coarse-grained soil and analyzes the current research shortcomings. The scouring on the subgrade slope was analyzed by establishing an incipient flow velocity formula that optimized the derivation process and parameters. Compared with the two types of cases, the exactitude of the formula derivation is verified. Finally, combined with orthogonal grouping, a single-factor analysis was conducted on the slope gradient and soil shear strength. With the same particle size, the incipient flow velocity decreases with the increase of the slope gradient (29.7° – 45°). When the particle size is upwards of 0.1 mm, the slope gradient has a great impact on the incipient flow velocity. And as the slope gradient decreases, the acceleration of incipient flow velocity with the same particle size increases. The incipient flow velocity increases with the increase of C (Cohesion) or φ (internal friction angle). The value of φ influences more deeply in the particle size range of 0.1 – 20 mm, that is, to advance the resisting erosion capacity, the shear strength of the slope soil is encouraged to improve when designing slope protection measures.

Tectono‐Magmatic Evolution of Asymmetric Coronae on Venus: Topographic Classification and 3D Thermo‐Mechanical Modeling

AbstractVenus is the only other Earth‐sized planet in the Solar System but it does not exhibit evidence of plate tectonics that dominates geological processes on Earth. Surface deformation on Venus is mainly driven by mantle convection and plume‐lithosphere interactions, likely represented by the widespread development of the circular volcano‐tectonic features known as coronae. Here, we present a joint study of mission data analysis and 3D modeling of asymmetric coronae on Venus. We systematically analyze 155 of the largest coronae on Venus in terms of surface topography and morphology. We establish that 75% of those coronae are radially asymmetric, and further sub‐categorize them based on their adjacent topography. This analysis reveals that many asymmetric coronae are positioned at a topographic transition between a lowland and plateau (termed topographic margin). With state‐of‐the‐art 3D numerical models, we investigate the physical processes behind plume‐margin interactions on Venus. We find that several tectonic styles may be responsible for asymmetric coronae at topographic margins, including lowland‐sided subduction, plateau‐sided lithospheric dripping, and an embedded plume. The gradient in lithospheric strength across the topographic margin controls these tectonic styles, and larger gradients enhance lithospheric resurfacing and the lifetime of the coronae. We also find that the density increase associated with the basalt‐to‐eclogite phase change provides the extra negative gravitational force required for downgoing crust to be recycled into the mantle. The models presented in this study reproduce a wide set of asymmetrical corona features found on Venus and suggest that they are generally more long‐lived than symmetric coronae.

Energy efficiency optimization algorithm based on RIS and D2D for multi-user MIMO system

Reconfigurable Intelligent Surface (RIS) is composed of reconfigurable passive components, which can realize on-demand customization of wireless communication environment. Device-to-Device (D2D) communication is one of the essential technologies to improve the capacity and spectrum efficiency of network system. In this paper, we propose an energy efficiency optimization algorithm based on RIS and D2D assisted multi-user MIMO system. The purpose is to maximize the energy efficiency of the system by jointly optimizing subcarrier allocation, power allocation and passive beamforming at RIS. We first formulate the energy efficiency maximization problem with the constraints of different user rate, power, subcarrier allocation and phase. Since it is a non-convex problem, we use an alternating optimization (AO) algorithm to decouple it into three sub-problems. The solutions of these three sub-problems are solved by subcarrier allocation based on channel strength, SCA algorithm, Dinkelbach algorithm and Riemannian gradient algorithm respectively. Simulation results show that the proposed scheme can significantly improve the energy efficiency.

Diffusion MRI with free gradient waveforms on a high-performance gradient system: Probing restriction and exchange in the human brain

The dependence of the diffusion MRI signal on the diffusion time carries signatures of restricted diffusion and exchange. Here we seek to highlight these signatures in the human brain by performing experiments using free gradient waveforms designed to be selectively sensitive to the two effects. We examine six healthy volunteers using both strong and ultra-strong gradients (80, 200 and 300 mT/m). In an experiment featuring a large set of 150 gradient waveforms with different sensitivities to restricted diffusion and exchange, our results reveal unique and different time-dependence signatures in grey and white matter. Grey matter was characterised by both restricted diffusion and exchange and white matter predominantly by restricted diffusion. Exchange in grey matter was at least twice as fast as in white matter, across all subjects and all gradient strengths. The cerebellar cortex featured relatively short exchange times (115 ms). Furthermore, we show that gradient waveforms with tailored designs can be used to map exchange in the human brain. We also assessed the feasibility of clinical applications of the method used in this work and found that the exchange-related contrast obtained with a 25-minute protocol at 300 mT/m was preserved in a 4-minute protocol at 300 mT/m and a 10-minute protocol at 80 mT/m. Our work underlines the utility of free waveforms for detecting time dependence signatures due to restricted diffusion and exchange in vivo, which may potentially serve as a tool for studying diseased tissue.

Combined VHM bearing capacity of pile leg-mat foundation on marine clay seabed

The pile leg-mat foundation is a new type of jack-up wind power installation platform foundation. Since the foundation needs to bear the horizontal and bending moment loads caused by wind and waves for long period of time, the combined vertical, horizontal and moment (VHM) bearing capacity of the pile leg-mat foundation in the soft clay seabed is crucial in evaluating the safety of the jack-up platform. In this study, the effects of pile leg insertion depth L and the gradient of soil shear strength κ on the VHM bearing capacity of pile leg-mat foundation were analyzed. The numerical results indicate that the pile leg insertion depth significantly enhances the horizontal bearing capacity of the foundation. As the pile leg insertion depth increases, the horizontal load distribution of the foundation gradually shifts from the mat to the pile leg. However, the vertical and moment bearing capacity of the foundation is mainly provided by the mat and not significantly improved by the pile leg insertion depth. Based on the numerical results, the VHM failure envelope of the pile leg-mat foundation was established, and the method for assessing the bearing capacity of the pile-leg mat foundation was proposed.

Effect of powder milling on sintering behavior and monotonic and cyclic mechanical properties of Mo and Mo–Si lattices produced by direct ink writing

Molybdenum is a refractory metal regarded as a promising basis for producing high-temperature components. However, the potential of manufacturing molybdenum-based structures by direct ink writing (DIW) has not been explored. In this study, three-dimensional porous molybdenum (Mo) and molybdenum-silicon (Mo–Si) composite lattices were fabricated using DIW with non-milled and milled powders. The effects of Mo powder morphology (resulting from milling) and chemical composition (alloying Mo with 3 and 10 wt% of Si) on the microstructure, phase composition, and static and cyclic compression properties at room temperature were investigated. Lattices fabricated from commercial spherical Mo powder exhibited the highest intra-filament porosity. Conversely, lattices fabricated from milled Mo powder were denser and had higher compressive strength, offset stress, and quasi-elastic gradient. Alloying Mo with Si during sintering resulted in composite lattices with Mo + Mo3Si microstructure. A low content of Mo3Si slightly decreased monotonic compression properties but did not affect the cyclic compression response compared to Mo lattices made from milled powder. In contrast, a high content of Mo3Si produced quasi-brittle lattices with reduced compressive strength and increased damage accumulation during cyclic loading. The cyclic behavior of all lattices was characterized by a ratcheting-dominated stress-strain response. Lattices fabricated from milled Mo and milled Mo-3 wt.%Si powders demonstrated superior performance compared to those fabricated from commercial spherical Mo and milled Mo-10 wt%Si powders. The results suggest that using milled powders can enhance the mechanical reliability and promote the use of DIW as preferred additive manufacturing technology for the fabrication of Mo–Si composite lattices.

The available energy of trapped electrons: a nonlinear measure for turbulent transport

A collisionless plasma possesses a certain amount of ‘available energy’, which is that part of the thermal energy that can be converted into kinetic energy of plasma motion and electromagnetic fluctuations. In this paper we present a calculation of the available energy carried by trapped electrons in a slender non-omnigenous flux tube of plasma. This quantity is compared with gyrokinetic simulations of the nonlinear saturated radial energy flux resulting from turbulence driven by collisionless trapped-electron modes in various stellarators and a tokamak. The numerical calculation of available energy is fast and shows a strong correlation with the turbulent energy fluxes found in the gyrokinetic simulations. Indeed, the energy flux is found to be proportional to the available energy to the power of approximately $3/2$ , which is what one would expect from a simple argument. We furthermore investigate how available energy is distributed across different bounce wells, and it is found that deeply trapped electrons typically contribute most to the available energy. Finally, we investigate the dependence of available energy on gradient strength, and we find important differences between weakly and strongly driven regimes for stellarators and tokamaks.

The Mojave Section of the San Andreas Fault (California), 2: Pleistocene Records of Near‐Field Transpression Illuminate the Atypical Evolution of the Restraining “Big Bend”

AbstractWith an obliquity of ∼30° relative to plate motion direction, the ∼300‐km‐long Big Bend of the San Andreas Fault is one of the world's largest restraining bends. The 5–6 Ma (∼160 km of total displacement) longevity of this mechanically inefficient structure and the lack of evidence for associated widespread uplift both challenge existing models of transpression and bend evolution. We focus on the structurally simplest section of the Big Bend (the Mojave section of the San Andreas: MSAF) to characterize the pattern of near‐field (<5 km from the San Andreas trace) uplift over two different timescales. The topography of vertically deformed alluvial surfaces is used to demonstrate that near‐field uplift along the least oblique segment of the MSAF has been significant over the last ∼40 ka (∼1–2 mm/yr), and driven by slip on two oppositely dipping blind reverse faults. Topographic and structural analyses of the MSAF near‐field are conducted at the scale of the entire fault to show that, at least on the NE side of the MSAF, these blind structures coincide with the front of a fault‐parallel bedrock ridge with clear characteristics of a young transpressive ridge. Structural, sedimentary, and geomorphic arguments converge to suggest that these blind structures were activated ∼315 ka ago and record a Mid‐Pleistocene kinematic reorganization of the MSAF fault‐zone. This reorganization is tentatively interpreted as a shift in the mode of accommodation of the transpressive component of plate motion, in turn driven by the strike‐slip advection of crustal strength gradients along the Big Bend.

Physics-based and data-driven modeling for basal stability evaluation of braced excavations in natural clays

The design of fully braced excavation of underground works, whether in rural or urban areas, is important to ensure that the design of fully braced support is safe, particularly in determining the depth of excavation and inserting the length into the clay of the wall, as well as a proportional excavation width. This study investigates the undrained basal stability of fully braced excavation in anisotropic clays with linearly increasing shear strength with depth employing upper and lower bound finite element limit analysis under symmetry plane conditions based on the AUS failure criterion. The dimensionless variables were used to examine the stability number (N) and the failure mechanisms selected for this problem's practical analysis. There is an anisotropic strength ratio (re), depth-wide ratio (B/H), embedded wall depth ratio (D/H), and strength gradient factor (ρH/Suc0). This study proposes design charts and failure mechanisms for fully braced excavations based on finite element limit analysis. Moreover, the artificial neural network model (ANN) was used to establish the relationship between the investigated and output variables and to conduct sensitivity analysis. Therefore, the developed ANN formula is a pragmatic approach for geotechnical engineers to calculate the basal stability of the excavations.

Eddy current-induced artifact correction in high b-value ex vivo human brain diffusion MRI with dynamic field monitoring.

To investigate whether spatiotemporal magnetic field monitoring can correct pronounced eddy current-induced artifacts incurred by strong diffusion-sensitizing gradients up to 300 mT/m used in high b-value diffusion-weighted (DW) EPI. A dynamic field camera equipped with 16 1 H NMR field probes was first used to characterize field perturbations caused by residual eddy currents from diffusion gradients waveforms in a 3D multi-shot EPI sequence on a 3T Connectom scanner for different gradient strengths (up to 300 mT/m), diffusion directions, and shots. The efficacy of dynamic field monitoring-based image reconstruction was demonstrated on high-gradient strength, submillimeter resolution whole-brain ex vivo diffusion MRI. A 3D multi-shot image reconstruction framework was developed that incorporated the nonlinear phase evolution measured with the dynamic field camera. Phase perturbations in the readout induced by residual eddy currents from strong diffusion gradients are highly nonlinear in space and time, vary among diffusion directions, and interfere significantly with the image encoding gradients, changing the k-space trajectory. During the readout, phase modulations between odd and even EPI echoes become non-static and diffusion encoding direction-dependent. Superior reduction of ghosting and geometric distortion was achieved with dynamic field monitoring compared to ghosting reduction approaches such as navigator- and structured low-rank-based methods or MUSE followed by image-based distortion correction with the FSL tool "eddy." Strong eddy current artifacts characteristic of high-gradient strength DW-EPI can be well corrected with dynamic field monitoring-based image reconstruction.

Characterization of concomitant gradient fields and their effects on image distortions using a low-field point-of-care Halbach-based MRI system.

Concomitant gradient fields have been extensively studied at clinical field strengths. However, their effects have not yet been modeled for low-field point-of-care (POC) systems. The purpose of this work is to characterize the effects associated with concomitant fields for POC Halbach-array-based systems. The concomitant fields associated with a cylindrical gradient coils designed for a transverse and a signal model including the tilting effect of the effective magnetic field are derived. The formalism is used to simulate and predict concomitant field related distortions. A 46-mT Halbach-array-based system with a maximum gradient strength of 15 mT/m is used to verify the model using two-dimensional spin-echo sequences. The simulations and experimental results are in good agreement with the derived equations. The fundamental characteristics of the concomitant field equations are different to conventional MRI systems: Image distortions occur primarily in the transverse directions and a cross-term only exists when applying transverse gradient pulses simultaneously. The level of image warping in the frequency encoding direction is insignificant for the POC systems discussed here. However, when trying to achieve short echo-times by using strong phase encoding and readout-dephasing gradients, the combination can result in image warping and blurring which should be accounted for in image interpretation.

Metabolic engineering of Paracoccus denitrificans for dual degradation of sulfamethoxazole and ammonia nitrogen.

Sulfamethoxazole (SMX), as one of the most widely used sulfonamide antibiotics, has been frequently detected in the aqueous environment, posing potential risks to the environment and human health. Although microbial degradation methods have been widely applied, some issues remain, including low degradation efficiency and poor environmental adaptability. In this regard, constructing efficient degrading bacteria by metabolic engineering is an ideal solution to these challenges. In this study, we used Paracoccus denitrificans DYTN-1, a superior nitrogen removal environment strain, as chassis to construct an SMX degradation pathway, obtaining a new bacteria for simultaneous degradation of SMX and removal of ammonia nitrogen. In doing this, we first identified and characterized four native promoters of P. denitrificans DYTN-1 with gradient strength to control the expression of the SMX degradation pathway. After degradation pathway expression level optimization and FMN reductase optimization, SMX degradation efficiency was significantly improved. The constructed P. d-pIAB4-PCS-sutR strain exhibited superior co-degradation of SMX and ammonia nitrogen contaminants with degradation rates of 44% and 71%, respectively. This study could pave the way for SMX degradation engineered strain design and evolution of environmental bioremediation. IMPORTANCE The abuse of sulfamethoxazole (SMX) had led to an increased accumulation in the environment, resulting in the disruption of the structure of microbial communities, further disrupting the bio-degradation process of other pollutants, such as ammonia nitrogen. To solve this challenge, we first identified and characterized four native promoters of Paracoccus denitrificans DYTN-1 with gradient strength to control the expression of the SMX degradation pathway. Then SMX degradation efficiency was significantly improved with degradation pathway expression level optimization and FMN reductase optimization. Finally, the superior nitrogen removal environment strain, P. denitrificans DYTN-1, obtained an SMX degradation function. This pioneering study of metabolic engineering to enhance the SMX degradation in microorganisms could pave the way for designing the engineered strains of SMX and nitrogen co-degradation and the environmental bioremediation.

The effect of high-temperature ECAP on dynamic recrystallization behavior and material strength of 42CrMo steel

With the development of mechanical equipment towards long life and high reliability, the traditional heat treatment method is challenging to meet the high strength requirements of 42CrMo steel for mechanical equipment. High-temperature equal channel angular pressing (ECAP) of 42CrMo steel was carried out above austenite transformation temperature, and the microstructure and material strength of the specimen at different radial positions were characterized and tested. The dynamic recrystallization (DRX) kinetic model of 42CrMo steel was established. The distribution of strain, strain rate, temperature and DRX volume fraction in high-temperature ECAP was studied by coupling finite element software and DRX kinetic model, and the formation mechanism of microstructure and material strength difference was revealed. The results show that the different degrees of DRX caused by the uneven distribution of strain and strain rate on the specimen is the main reason for the gradient distribution of microstructure and material strength in the radial direction of the specimen. From the top to the bottom of the specimen, with the decrease of strain and strain rate, the degree of DRX increases continuously, the microstructure inhomogeneity decreases, the size of the martensite packets and blocks increases gradually, and the strength decreases gradually. The grain boundary strengthening caused by the decreased size of martensite packets and blocks is the main reason for the radial difference in material yield strength. Grain boundary strengthening and the coordinated deformation of geometrically necessary dislocations at the soft-hard grain interface of heterogeneous materials are the main mechanisms leading to the tensile strength gradient distribution. This study reveals the dynamic recrystallization behavior and material strength variation of high-temperature ECAP, which contributes to the qualification of the ECAP process and promotes the development of severe plastic deformation on the further strength enhancement of high-strength steel.

Research on the macro- and meso-mechanical properties of frozen sand mold based on Hertz-Mindlin with Bonding model

In this study, macro- and meso-mechanical properties of frozen sand molds were discussed based on the Hertz-Mindlin with Bonding (HMB) model. Plackett-Burman, steepest ascent, and central composite designs were utilized to propose a parameter calibration methodology. The effects of mesoscopic parameter variations on the compressive strength and average gradient of stress-strain were investigated through response surface method analysis. Results showed that the relative error between the simulated and measured repose angle is 3.1% under calibrated intrinsic contact parameters. The compressive strength and average stress-strain gradient primarily depend on the normal and shear stiffness per unit area, as well as the particle size and porosity of the silica sand. Furthermore, taking load-displacement curves of three frozen sand molds with different geometric characteristics as the target value, the reliability and effectiveness of the frozen sand mold HMB model were verified through uniaxial compression tests and discrete element simulations.

Transient and directional growth of supramolecular hydrogels through reaction–diffusion-mediated self-assembly for dynamic wet gluing

The growth of supramolecular structures in biological systems is usually featured by dynamics and directionality, yet remains a real challenge in synthetic scenarios. Here, we show our access to transient and directional growth of supramolecular hydrogels through a simple reaction–diffusion-mediated self-assembly strategy. Transient and directional propagation of acid/base gradients are achieved through the diffusions of acid and base from opposite directions followed by the neutralization reaction at their crossing of diffusional fronts. The propagating distance maxima and lifetimes of the gradients can be easily controlled by changing the contents of acid/base. By coupling pH-sensitive gelators to the reaction–diffusion system, transient and directional growth of supramolecular hydrogels with controlled width maxima and lifetimes is realized. The growing direction of the hydrogel fibers at the microscopic level is demonstrated to be dominated by the gradient strengths of the pH signals and gelators. We further leverage the dynamic and directional gelation at the wet interface of soft hydrogel substrates for a proof-of-concept application of dynamic wet gluing.

Real-time 31P NMR reveals different gradient strengths in polyphosphoester copolymers as potential MRI-traceable nanomaterials

Polyphosphoesters (PPEs) are used in tissue engineering and drug delivery, as polyelectrolytes, and flame-retardants. Mostly polyphosphates have been investigated but copolymers involving different PPE subclasses have been rarely explored and the reactivity ratios of different cyclic phospholanes have not been reported. We synthesized binary and ternary PPE copolymers using cyclic comonomers, including side-chain phosphonates, phosphates, thiophosphate, and in-chain phosphonates, through organocatalyzed ring-opening copolymerization. Reactivity ratios were determined for all cases, including ternary PPE copolymers, using different nonterminal models. By combining different comonomers and organocatalysts, we created gradient copolymers with adjustable amphiphilicity and microstructure. Reactivity ratios ranging from 0.02 to 44 were observed for different comonomer sets. Statistical ring-opening copolymerization enabled the synthesis of amphiphilic gradient copolymers in a one-pot procedure, exhibiting tunable interfacial and magnetic resonance imaging (MRI) properties. These copolymers self-assembled in aqueous solutions, 31 P MRI imaging confirmed their potential as MRI-traceable nanostructures. This systematic study expands the possibilities of PPE-copolymers for drug delivery and theranostics.

Gulf Stream Sea Surface Temperature Anomalies Associated With the Extratropical Transition of North Atlantic Tropical Cyclones

AbstractThis study investigates Gulf Stream (GS) sea surface temperature (SST) anomalies associated with the extratropical transition (ET) of tropical cyclones (TCs) in the North Atlantic. Composites of western North Atlantic TCs indicate that GS SSTs are warmer, and both large‐ and fine‐scale SST gradients are weaker than average, for TCs that begin the ET process but do not complete it, compared with TCs that do. Further analysis suggests that the associated fine‐scale GS SST gradient anomalies are related to atmospheric processes but not the same as those that are typically associated with the onset of ET. As sensible heat flux gradients and surface diabatic frontogenesis are shown to generally scale with the local SST gradient strength, these results suggest that knowledge of the fine‐scale GS SST gradient in the weeks prior to the arrival of a TC might potentially provide additional information regarding the likelihood of that system completing ET.

Correlation of Diffusion weighted MR Imaging and ADC values of hepatic metastasis of Gastrointestinal Stromal and Gastroenteropancreatic Neuroendocrine Tumors.

DWI and ADC-mapping was performed to analyze hepatic metastasis of GIST, GEP-NET. The objective of this study is to present hepatic metastasis of GIST and GEP-NET with Diffusion weighted MR imaging(DWI) and the Apparent diffusion coefficients (ADC) values of masses. 18 GIST patients and 8 GEP-NET patients were examined retrospectively. 11 males and 6 females were present in GIST group, 7 males to 5 females were involved in GEP-NET group. 18 primary GIST and 10 hepatic metastasis of GIST, 8 original GEP-NET and 19 hepatic metastasis of GEP-NET; total 55 GIST and GEP-NET masses were analysed by ADC mapping. MR images were acquired by 1,5 T MR units (32 mT/min gradient strength- Achieva; Philips Healthcare, Best, Netherlands and 32 channel GE Signa GE-Wisconsin-USA); by using a 4-8 channel standard phased-array torso XL coil, all images were evaluated by an Abdominal MRI experienced radiologist. DWI was performed in the transverse plane by using spin-echo-planar imaging sequence. No statistical differences were observed between GIST and GEP-NET patients according to age and gender variations. No significant statistical differences were observed according to the diameters and ADC values of GIST and GEP-NET patients. A significant statistical difference was observed between GIST and GEP-NET groups in terms of size of liver metastasis which was significantly higher in GIST patients. All three groups (GIST_Hep. MET, GEP-NET_Liver_Met and normal) were statistically differed according to ADC values. With the ROC curve analysis: Hepatic metastasis of GIST(n=10) and normal liver (n:47) had cut-off value for ADC: 0.925 under AUC: 0.939 with regard to ADC values and regarded 89.4 % Sensitivity, 100% Specificity, 100% PPV and 66.7% PPV. ROC curve of GEP NET_ Hepatic metastasis (n=19) group and normal liver (n:47) group presented cut-off value for ADC: 0.860 under AUC: 0.967 correlated to ADC values with 93.6 % sensitivity, 89.5% specificity, 95.7% PPV and 85% PPV. High cellular tumors resulted from liver metastasis of GIST and GEP-NET's, and a positive correlation was observed between ADC values and cellularity/differentiation ratios of metastatic masses.