Single Point Imaging Research Articles

Abstract 384: T cell infiltration into tumors induced by DPX-Survivac combination immunotherapy demonstrated by PET/MRI imaging in an orthotopic ovarian cancer model

Abstract Introduction: Epithelial ovarian cancers are highly aggressive and often diagnosed at late stages. To date, a limited number of these patients benefit from immunotherapies, and recurrent ovarian cancer remains an area of unmet medical need. Novel immunotherapies that generate and drive activated T cells into tumors, such as DPX-Survivac, represent a promising approach. To better understand the underlying mechanisms of action of this novel immunotherapy and how it may correlate with clinical outcomes, we used an orthotopic ovarian cancer model and a dual approach using molecular imaging to track immune cells in vivo followed by biological assays. Methods: Humanized transgenic mice (HLA-A2.1-/HLA-DR1; H-2 class-I/II knockout) were implanted with 104 syngeneic mouse ovarian surface epithelial cells in the left ovarian bursa and were either untreated or treated with DPX-Survivac, intermittent low dose cyclophosphamide and anti-PD-1. The CD8+ cytotoxic T cells (CTLs) and myeloid cells (MCs) were isolated from disease matched mice, cultured in vitro, loaded with superparamagnetic iron oxide (SPIO) nanoparticles, and injected i.v. in recipient mice. The next day, recipient mice were injected with 500µCi of 18F-fluorodeoxyglucose and imaged by magnetic resonance (MRI) and positron emission tomography (PET). Anatomical images and tumor volumes were collected with a balance steady-state free precession sequence, cells were semi-quantified using R2* maps from a multi-echo single point imaging sequence (TurboSPI) and tumor metabolism was assessed by simultaneous acquisition of PET. Mice were imaged days 41, 49, and 56 post-implant. CTLs and MCs were characterized by flow cytometry (FC) before injection into recipient mice. Following imaging completion, tumors and lymph nodes (LN) were assayed for tumor infiltrating lymphocytes. Ascites were analyzed for tumor cell to lymphocyte content by FC. Results: PET/MRI images showed that the combination immunotherapy significantly decreased primary tumor burden and improved survival rates. The recruitment of isolated CTLs and MCs was detected in both tumors and LNs. CTL recruitment to tumors was increased in mice receiving combination immunotherapy while MCs recruitment was decreased. CTLs were recruited at a higher rate to the DPX-Survivac draining LN than tumor draining LN and MCs were equally recruited to both. The expression of checkpoint inhibitor molecules on CTL did not appear to vary with treatment. CTLs from treated mice expressed higher rates of Ki67 (a proliferative marker) than CTLs from untreated mice. The treatment increased the lymphocyte:tumor cell ratio within the tumors of treated animals and included a population of CD8/CD4 double positive (DP) T cells. Differences in tumor infiltrating lymphocyte phenotype correlated with tumor burden. Conclusions: DPX-Survivac combination immunotherapy induces the recruitment of CD8+ T cells into tumors, resulting in tumor control in an orthotopic ovarian cancel model. Citation Format: Marie-Laurence Tremblay, Caitrin Sobey-Skelton, Hailey Wyatt, Victoria Gonzalez, Andrea Nuschke, Christa Davis, Alecia Mackay, Kim Bobbit, Andrea West, Barbara Vanderhyden, Genevieve Weir, Alexandra Merkx-Jacques, Kimberly Brewer, Marianne Stanford. T cell infiltration into tumors induced by DPX-Survivac combination immunotherapy demonstrated by PET/MRI imaging in an orthotopic ovarian cancer model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 384.

Rapid single scan ramped hybrid-encoding for bicomponent T2* mapping in a human knee joint: A feasibility study.

The purpose of this study is to determine the feasibility of using a single scan ramped hybrid-encoding (RHE) method for rapid bicomponent T2* analysis of the human knee joint. The proposed method utilizes RHE to acquire ultrashort echo time (UTE) and subsequent gradient echo images at 16 different echo times ranging between 40 μs and 30 ms in a single scan. In the proposed RHE technique, UTE imaging was followed by acquisition of 14 gradient recalled echo images, where an additional UTE image was obtained within the first readout by oversampling single point imaging (SPI) encoding. The single scan RHE method with a 9-minute scan time was performed on human cadaveric knee joints from six donors and in vivo knee joints from four healthy volunteers at 3 T. A bicomponent signal model was used to characterize the short T2* and long T2* water components. Mean bicomponent T2* parameters for patellar tendon, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL) and meniscus were calculated. In the experimental results, the RHE technique provided bicomponent T2* parameter estimations of tendon, ACL, PCL and meniscus, which were similar to previously reported values in the literature. In conclusion, the proposed single scan RHE technique provides rapid bicomponent T2* analysis of the human knee joint with a total scan time of less than 9 minutes.

Stokes flow due to point torques and sources in a spherical geometry

Singularity representations of the Stokes flow due to point torques and sources in a spherical geometry are derived. Both rigid spheres with no slip and spherical bubbles are considered. Surprisingly, for an axisymmetric torque with no slip the solution consists of a single point image torque, similar to point charges in electrostatics.

Establishing an effective offset‐dependent velocity model by ray tracing and its application in Kirchhoff time migration

ABSTRACTConventional Kirchhoff prestack time migration based on the hyperbolic moveout can cause ambiguity in laterally inhomogeneous media, because the root mean square velocity corresponds to a one‐dimensional model under the horizontal layer assumption; it does not include the lateral variations. The shot/receiver configuration with different offsets and azimuths should adopt different migration velocities as they contribute to a single image point. Therefore, we propose to use an offset‐vector to describe the lateral variations through an offset‐dependent velocity corresponding to the difference in offset from surface points to the image point. The offset‐vector is decomposed into orthogonal directions along the in‐line and cross‐line directions so that the single velocity can be expressed as a series of actual velocities. We use a simple Snell's law‐based ray tracing to calculate the travel time recorded at the image point and convert the travel time to an equivalent velocity corresponding to a pseudo‐straight ray. The double‐square‐root equation using such an equivalent velocity in the offset‐vector domain is non‐hyperbolic and asymmetrical, which improves the accuracy of the migration. Numerical examples using the Marmousi model and a wide azimuth field data show that the proposed method can achieve reasonable accuracy and significantly enhances the imaging of complex structures.

High-resolution characterization of nanoparticle transport in heterogeneous porous media via low-field nuclear magnetic resonance

Understanding the transport of nanoparticles (NPs), including nanoscale zero-valent iron (nZVI) particles, through water-saturated porous media has important implications for many natural and engineered systems. For the first time, we use spin-echo single point imaging (SE-SPI) of low-field Nuclear Magnetic Resonance (LF-NMR) to monitor nanoparticle transport through a heterogeneous porous medium. The ability of this method to provide information of nano- to micro-scale pore structure and to monitor transient processes is verified by a transport experiment using modified nZVI particles. Early breakthrough of the NP front and large amount of residual NPs (27% of the iron was retained in the core) were observed in the experiment. These observations were due to the presence of preferential flow paths and dead-end pores as demonstrated by micro X-ray Computed Tomography (μCT) imaging. Spatial and temporal data provided by this method enabled numerical simulations to quantify the impacts of spatial heterogeneity in pore structure on NP transport in terms of transport parameters. The simulation that captures the spatial heterogeneity by explicitly considering four regions of distinct porosities outperforms the model assuming a homogeneous pore structure. The maximum of residual sum of squares reduced from 0.328 to 0.138 when considering the impact of pore structure. The transport parameters vary significantly among different regions. For example, in the lowest porosity region of this sandstone, colloid dispersion (D) is 0.10 cm2/min instead of 0.20 cm2/min in the most connected region, while the attachment (kac) increased from 0.007 to 0.025 min−1. Overall, SE-SPI imaging is shown to be an important tool in refining transport processes of NPs in heterogeneous porous media with application to constrain complex natural systems.

Mapping of fatty acid composition with free-breathing MR spectroscopic imaging and compressed sensing.

Nonalcoholic fatty liver disease (NAFLD) is a growing health problem, and a major challenge in NAFLD management is identifying which patients are at risk of progression to more serious disease. Simple measurements of liver fat content are not strong predictors of clinical outcome, but biomarkers related to fatty acid composition (ie, saturated vs. unsaturated fat) may be more effective. MR spectroscopic imaging (MRSI) methods allow spatially resolved, whole‐liver measurements of chemical composition but are traditionally limited by slow acquisition times. In this work we present an accelerated MRSI acquisition based on spin echo single point imaging (SE‐SPI), which, using appropriate sampling and compressed sensing reconstruction, allows free‐breathing acquisition in a mouse model of fatty liver disease. After validating the technique's performance in oil/water phantoms, we imaged mice that had received a normal diet or a methionine and choline deficient (MCD) diet, some of which also received supplemental injections of iron to mimic hepatic iron overload. SE‐SPI was more resistant to the line‐broadening effects of iron than single‐voxel spectroscopy measurements, and was consistently able to measure the amplitudes of low‐intensity spectral peaks that are important to characterizing fatty acid composition. In particular, in the mice receiving the MCD diet, SE‐SPI showed a significant decrease in a metric associated with unsaturated fat, which is consistent with the literature. This or other related metrics may therefore offer more a specific biomarker of liver health than fat content alone. This preclinical study is an important precursor to clinical testing of the proposed method.MR‐based quantification of fatty acid composition may allow for improved characterization of non‐alcoholic fatty liver disease. A spectroscopic imaging method with appropriate sampling strategy allows whole‐liver mapping of fat composition metrics in a free‐breathing mouse model. Changes in metrics like the surrogate unsaturation index (UIs) are visible in mice receiving a diet which induces fat accumulation in the liver, as compared to a normal diet; such metrics may prove useful in future clinical studies of liver disease.

Inversion recovery UTE based volumetric myelin imaging in human brain using interleaved hybrid encoding.

Direct myelin imaging can improve the characterization of myelin-related diseases such as multiple sclerosis. In this study, we explore a novel method to directly image myelin using inversion recovery-prepared hybrid encoding (IR-HE) UTE MRI. The IR-HE sequence uses an adiabatic inversion pulse to suppress the long T2 white matter signal, followed by 3D dual-echo HE utilizing both single point imaging and radial frequency encoding, for which the subtraction image between 2 echoes reveals the myelin signal with high contrast. To reduce scan time, it is common to obtain multiple spokes per IR. Here, we invented a novel method to improve the HE, adapted for the multi-spoke IR imaging-termed interleaved HE-for which single point imaging encoding is interleaved between radial frequency encodings near nulling point to allow more efficient IR-signal suppression. To evaluate the proposed approach, a computer simulation, myelin phantom experiment, an ex vivo experiment with a cadaveric multiple sclerosis brain, and an in vivo experiment with 8 healthy volunteers and 13 multiple sclerosis patients were performed. The computer simulation showed that IR-interleaved HE allows for improved contrast of myelin signal with reduced imaging artifacts. The myelin phantom experiment showed IR-interleaved HE allows direct imaging of myelin lipid with excellent suppression of water signal. In the ex vivo and in vivo experiments, the proposed method demonstrated highly specific imaging of myelin in white matter of the brain. IR-interleaved HE allows for time-efficient, high-contrast direct myelin imaging and can detect demyelinated lesions in multiple sclerosis patients.

Night-light Image Restoration Method Based on Night Scattering Model for Luojia 1-01 Satellite.

Aiming at solving the degradation problem of Luojia 1-01 night-light remote sensing images, the main reason for the “glow” phenomenon was analyzed. The APSF (Atmospheric Point Spread Function) template of night-light image was obtained from atmospheric source scattering. The template was used as the initial value in the regularization restoration model in this paper. Experiments were carried out using single point and regional images. The results demonstrate that the estimated APSF and restoration results of the method are better than those from other methods, and the image quality is improved after restoration.

Noise suppression by controlling the sparsity of the point spread function in interferenceless coded aperture correlation holography (I-COACH).

Interferenceless coded aperture correlation holography (I-COACH) is an incoherent opto-digital technique for imaging 3D objects. In I-COACH, the light scattered from an object is modulated by a coded phase mask (CPM) and then recorded by a digital camera as an object digital hologram. To reconstruct the image, the object hologram is cross-correlated with the point spread function (PSF)-the intensity response to a point at the same object's axial location recorded with the same CPM. So far in I-COACH systems, the light from each object point has scattered over the whole camera area. Hence, the signal-to-noise ratio per camera pixel is lower in comparison to the direct imaging in which each point is imaged to a single image point. In this work, we consider the midway between the camera responses of a single point and of a continuous pattern over the entire camera area. The light in this study is focused onto a set of dots randomly distributed over the camera plane. With this technique, we show that there is a PSF with a best number of dots, yielding an image with a maximum product of the signal-to-noise ratio and the image visibility and a maximum value of structural similarity.

Simultaneous T2* mapping of 14N- and 15N-labeled dicarboxy-PROXYLs using CW-EPR-based single-point imaging.

This article reports a method of simultaneous T2* mapping of 14N- and 15N-labeled dicarboxy-PROXYLs using 750-MHz continuous-wave electron paramagnetic resonance (CW-EPR) imaging. To separate the spectra of 14N- and 15N-labeled dicarboxy-PROXYLs under magnetic field gradients, an optimization problem for spectral projections was formulated with the spatial total variation as a regularization term and solved using a local search based on the gradient descent algorithm. Using the single-point imaging (SPI) method with spectral projections of each radical, simultaneous T2* mapping was performed for solution samples. Simultaneous T2* mapping enabled visualization of the response of T2* values to the level of dissolved oxygen in the solution. Simultaneous T2* mapping applied to a mouse tumor model demonstrated the feasibility of the reported method for potential application to in vivo oxygenation imaging.

15 N MRI of SLIC-SABRE Hyperpolarized 15 N-Labelled Pyridine and Nicotinamide.

Magnetic Resonance Imaging (MRI) is a powerful non-invasive diagnostic method extensively used in biomedical studies. A significant limitation of MRI is its relatively low signal-to-noise ratio, which can be increased by hyperpolarizing nuclear spins. One promising method is Signal Amplification By Reversible Exchange (SABRE), which employs parahydrogen as a source of hyperpolarization. Recent studies demonstrated the feasibility to improve MRI sensitivity with this hyperpolarization technique. Hyperpolarized 15 N nuclei in biomolecules can potentially retain their spin alignment for tens of minutes, providing an extended time window for the utilization of the hyperpolarized compounds. In this work, we demonstrate for the first time that radio-frequency-based SABRE hyperpolarization techniques can be used to obtain 15 N MRI of biomolecule 1-15 N-nicotinamide. Two image acquisition strategies were utilized and compared: Single Point Imaging (SPI) and Fast Low Angle SHot (FLASH). These methods demonstrated opportunities of high-field SABRE for biomedical applications.

Ultrashort Echo Time Quantitative Susceptibility Mapping (UTE-QSM) of Highly Concentrated Magnetic Nanoparticles: A Comparison Study about Different Sampling Strategies.

The ability to accurately and non-invasively quantify highly concentrated magnetic nanoparticles (MNPs) is desirable for many emerging applications. Ultrashort echo time quantitative susceptibility mapping (UTE-QSM) has demonstrated the capability to detect high iron concentrations. In this study, we aimed to investigate the effect of different sampling trajectories on the accuracy of quantification based on MNPs acquired through UTE-QSM. A phantom with six different MNP concentrations was prepared for UTE-QSM study with different UTE sampling trajectories, including radial acquisition, continuous single point imaging (CSPI), and Cones with four different gradient stretching factors of 1.0, 1.2, 1.4, and 1.6. No significant differences were found in QSM values derived from the different UTE sampling strategies, suggesting that the UTE-QSM technique could be accelerated with extended Cones sampling.

Feasibility and accuracy of single time point imaging for renal dosimetry following 177Lu-DOTATATE (\u2018Lutate\u2019) therapy

BackgroundThis study aims to assess both feasibility and accuracy of renal dosimetry imaging protocols in patients receiving Lutate therapy for neuroendocrine tumours (NETs), when data acquisition over multiple days is not possible on all cycles.MethodPatients who had received a full 4 cycles of Lutate therapy with complete imaging at each cycle were included. Imaging consisted of quantitative SPECT/CT of the kidneys at 4, 24 and 96–120 h post injection. Renal absorbed dose was calculated for each data set, and in addition, five alternative methods were explored for comparison. Method 1: a patient average clearance time (t1/2 average) derived from the first half of contributing patient data was used to estimate absorbed dose for subsequent patients based on 4 h imaging alone; method 2: t1/2 average was applied to subsequent patients on 24 h imaging alone; method 3: a patient-specific clearance rate (t1/2 patient) was determined from complete image data of cycle 1 and applied subsequently to remaining cycles using 4 h image data alone; method 4: t1/2 patient was applied to 24 h imaging alone in subsequent cycles; method 5: the 120 h data was estimated on subsequent cycles based on the cycle 1 fraction of injected activity (%IA) at 24 and 120 h.ResultsTwenty treatments from 18 patients, resulting in 80 cycles of therapy, were analysed. The measured average renal absorbed dose per cycle of treatment was 0.38 ± 0.19 Gy/GBq when derived from full imaging data. The use of t1/2 average applied to a single time point led to large deviations of dose estimates from true values (on average 59% and 30%, when using 4 h data and 24 h data, respectively). The use of complete image data on cycle 1 and the derivation of t1/2 patient led to improved dose estimates, with an average deviation from true values of 13% and 2% when using 4 h data only and 24 h data only, respectively. The use of a 120 h %IA derived from cycle 1 led to an average deviation from true dose estimates of 14%.ConclusionIn instances where demands on both patients and facilities make multiple time point data acquisition impractical, renal dosimetry is best derived through complete imaging at cycle 1 only followed by a single 24 h imaging time point on subsequent cycles, assuming no significant changes in renal function during the time course of therapy.

True phase quantitative susceptibility mapping using continuous single-point imaging: a feasibility study.

In this study, we explore the feasibility of a new imaging scheme for quantitative susceptibility mapping (QSM): continuous single-point imaging (CSPI), which uses a pure phase encoding strategy to achieve true phase imaging and improve QSM accuracy. The proposed CSPI is a modification of conventional SPI to allow acquisition of multiple echoes in a single scan. Immediately following a phase encoding gradient, the free induction decay is continuously sampled with extremely high temporal resolution to obtain k-space data at a fixed spatial frequency (i.e., at a fixed k-space coordinate). By having near-0 readout duration, CSPI results in a true snapshot of the transverse magnetization at each TE. Additionally, parallel imaging with autocalibration is utilized to reduce scan time, and an optional temporal averaging strategy is presented to improve signal-to-noise ratio for objects with low proton density or short T2* decay. The reconstructed CSPI images were input to a QSM framework based on morphology enabled dipole inversion. In an experiment performed using iron phantoms, susceptibility estimated using CSPI showed high linearity (R2 = 0.9948) with iron concentration. Additionally, reconstructed CSPI phase images showed much reduced ringing artifact compared with phase images obtained using a frequency encoding strategy. In an ex vivo experiment performed using human tibia samples, estimated susceptibilities ranged from -1.6 to -2.1 ppm, in agreement with values reported in the literature (ranging from -1.2 to -2.2 ppm). We have demonstrated the feasibility of using CSPI to obtain true phase images for QSM.

A study of MR signal reception from a model for a battery cell

Number of NMR/MRI studies on batteries is rapidly increasing in the past decade. As the test batteries designed for the studies contain metal parts such as electrodes and lead wires as well as other conductive parts (electrolyte), which all present obstacles for good MR signal reception, understanding of the role of battery design and of battery interactions with magnetic field is of a key importance for a successful performance of the experiments. For the study, five different samples mimicking a real battery cell were made. All the samples had two parallel copper electrodes separated by a gel layer, however, they differed in electrode thickness, gel conductivity and separation between the electrodes. The samples were inserted in an MRI magnet in different orientations with respect to magnetic fields B0 and B1 and scanned with the spin-echo and single point imaging methods in 2D and 3D (spin-echo only). The performed experiments confirmed that the main reason for poor MR signal reception from a test battery are RF-induced eddy currents. These were found stronger with the sample with the smaller distance between the electrodes. The effect of RF-induced eddy currents was efficiently suppressed when the sample was oriented with the electrodes parallel to the B1 field. However, in the orientation there were still susceptibility effects that caused a signal voiding in a narrow region near the electrodes. The susceptibility effects were found lower with the sample with thin electrodes and the non-conductive gel. The results of the study can help optimizing test battery and capacitor designs for NMR/MRI experiments.

High-efficiency and high-accuracy digital speckle correlation for full-field image deformation measurement

Many works around the digital speckle correlation (DSC) are to improve the computational efficiency and measurement accuracy in recent years. This work aims to improve the efficiency and accuracy of DSC for both single-point and full-field points used in mechanical properties test of materials. For this purpose, first, a subpixel initial guess for the inverse compositional Gauss–Newton algorithm (IC-GN) with the first-order shape function is introduced for single-point image registration. Then, with the aid of strategy of subset image edge extend interpolation (SIEEI), the efficiency and accuracy of full-field displacement and deformation measurement are improved simultaneously. The SIEEI is employed to reduce mean squared difference errors caused by traditional bicubic interpolation algorithm. Comparative studies between the traditional IC-GN algorithm and the proposed algorithms are presented using simulated speckle images and CCD images. The proposed method achieves more executive efficiency and more accuracy for single-point and full-field points image registration. The computational efficiency of the proposed algorithms increases 7.5% for full-field registration using CCD images. The mean of squared difference errors of the SIEEI method is less than the traditional bicubic interpolation algorithm. The presented approach shows great potentials for challenging application, such as mechanical properties test of materials.

EPR-based oximetric imaging: a combination of single point-based spatial encoding and T1 weighting.

Spin-lattice relaxation rate (R1 )-based time-domain EPR oximetry is reported for in vivo applications using a paramagnetic probe, a trityl-based Oxo71. The R1 dependence of the trityl probe Oxo71 on partial oxygen pressure (pO2 ) was assessed using single-point imaging mode of spatial encoding combined with rapid repetition, similar to T1 -weighted MRI, for which R1 was determined from 22 repetition times ranging from 2.1 to 40.0 μs at 300 MHz. The pO2 maps of a phantom with 3 tubes containing 2 mM Oxo71 solutions equilibrated at 0%, 2%, and 5% oxygen were determined by R1 and apparent spin-spin relaxation rate ( R2*) simultaneously. The pO2 maps derived from R1 and R2* agreed with the known pO2 levels in the tubes of Oxo71. However, the histograms of pO2 revealed that R1 offers better pO2 resolution than R2* in low pO2 regions. The SDs of pixels at 2% pO2 (15.2 mmHg) were about 5 times lower in R1 -based estimation than R2*-based estimation (mean ± SD: 13.9 ± 1.77 mmHg and 18.3 ± 8.70 mmHg, respectively). The in vivo pO2 map obtained from R1 -based assessment displayed a homogeneous profile in low pO2 regions in tumor xenografts, consistent with previous reports on R2*-based oximetric imaging. The scan time to obtain the R1 map can be significantly reduced using 3 repetition times ranging from 4.0 to 12.0 μs. Using the single-point imaging modality, R1 -based oximetry imaging with useful spatial and oxygen resolutions for small animals was demonstrated.

Exploring a carbonate reef reservoir – nuclear magnetic resonance and computed microtomography confronted with narrow channel and fracture porosity

The complexity of hydrocarbon reservoirs, comprising numerous moulds, vugs, fractures and channel porosity, requires a specific set of methods to be used in order to obtain plausible petrophysical information. Both computed microtomography (μCT) and nuclear magnetic resonance (NMR) are nowadays commonly utilized in pore space investigation. The principal aim of this paper is to propose an alternative, quick and easily executable approach, enabling a thorough understanding of the complicated interiors of the carbonate hydrocarbon reservoir rocks. Highly porous and fractured Zechstein bioclastic packstones from the Brońsko Reef, located in West Poland were studied. Having examined 20 thin sections coming from two different well bores, 10 corresponding core samples were subjected to both μCT and NMR experiments. After a preliminary μCT-based image analysis, 9.4 [T] high-field zero echo time (ZTE) imaging, using a very short repetition time (RT) of 2 [μs] was conducted. Taking into consideration the risk of internal gradients' generation, the reliability of ZTE was verified by 0.6 [T] Single Point Imaging (SPI), during which such a phenomenon is much less probable. Both narrow channels and fractures of different apertures appeared to be common within the studied rocks. Their detailed description was therefore undertaken based on an additional tool – the spatially-resolved 0.05 [T] T2 profiling. According to the obtained results, ZTE seems to be especially suitable for studying porous and fractured carbonate rocks, as little disturbance to the signal appears. This can be confirmed by the SPI, indicating the negligible impact of the internal gradients on the registered ZTE images. Both NMR imaging and μCT allowed for locating the most porous intervals including well-developed mouldic porosity, as well as the contrasting impermeable structures, such as the stylolites and anhydrite veins. The 3D low-field profiling, in turn, showed the fracture aperture variations and contributed to the recognition of pore geometry. Analogously, the authors believe that such a spatially-resolved profiling could also be successfully implemented to study unconventional reservoirs. Finally, it has been concluded that although it is possible to investigate the connectivity of a given pore space solely using μCT, a detailed labeling process might turn out to be too time consuming and require a sound experience in that field. Therefore it is proposed to follow a preliminary μCT modeling by the direct and non-invasive set of NMR experiments.

ZTE MRI in high magnetic field as a time effective 3D imaging technique for monitoring water ingress in porous rocks at sub-millimetre resolution

Zero echo time magnetic resonance imaging (ZTE MRI) at 9.4T was used to assess the local distribution of water in dolomite rocks under different saturation conditions. The results were compared with the industry standard Single Point Imaging (SPI) at 0.6T. 3D maps of the local amount of water saturating heterogeneous rock were obtained from the imaging data, and correlated with the corresponding structural images from high resolution micro-CT (μCT). The method can be applicable in the investigation of spatial kinetics of water saturation processes in porous, heterogeneous rocks where imaging methods based on spin echo, such as RARE, have failed due to short T2, while SPI is often impractical due to its long acquisition time.

Image systems for the reaction field inside spheroidal dielectric objects and applications

Charges inside a dielectric object embedded in a dissimilar dielectric medium polarize the surrounding medium, which in turn makes a contribution, called the reaction field, to the electric field inside the object. In this work, we develop complete image systems for the reaction field inside a prolate or oblate spheroidal dielectric object embedded in an infinite dissimilar dielectric medium. In either case, an image system consists of a point image and a symmetric surface image over an exterior confocal spheroid that passes through the point image. As an application, the point image is applied into the generalized image charge solvation model (GICSM) and is tested in simulations of liquid water, and the results are analyzed in comparison with those obtained from the ICSM simulation as references. The results indicate that, for both the prolate and oblate cases, the single point image charge approximation for the reaction field inside the dielectric cavity of the model is good enough for the GICSM to faithfully reproduce typical static and dynamic properties of the liquid water at least when the spheroidal cavity has relatively small eccentricity.