Magnetic Resonance Imaging Apparatus Research Articles

MRI insight on multiphase flow in hydrate-bearing sediment and development mechanism of hydrate seal

Gas and water migration through the hydrate-bearing sediment are characteristic features in marine gas hydrate reservoirs worldwide. However, there are few experimental investigations on the effect of water-gas flow on the gas hydrate reservoir. In this study, gas-water migration in gas hydrate stability zone (GHSZ) was investigated visually employing a high-resolution magnetic resonance imaging (MRI) apparatus, and the formation of hydrate seal was experimentally investigated. Results revealed that normal flow of gas-water at the low flow rate of 1–0.25 mL/min will induce the hydrate reformation. Conversely, higher gas-water flow rates (at 2–0.5 and 4–1 mL/min) need higher reservoir pressure to induce the hydrate reformation. In addition, the hydrate reformation during the gas-water flow process produced the hydrate seal, which can withstand an over 9.0 MPa overpressure. This high overpressure provides the development condition for the underlying gas and/or water reservoir. A composite MRI image of the whole hydrate seal was obtained through the MRI. The pore difference between hydrate zone and coexistence zone produces a capillary sealing effect for hydrate seal. The hydrate saturation of hydrate seal was more than 51.6%, and the water saturation was more than 19.3%. However, the hydrate seal can be broken through when the overpressure exceeded the capillary pressure of the hydrate seal, which induced the sudden drop of reservoir pressure. This study provides a scientific explanation for the existence of high-pressure underlying gas below the hydrate layer and is significant for the safe exploitation of these common typical marine hydrate reservoirs.

Characteristics of Ultrasound and Magnetic Resonance Imaging of Normal Testes and Epididymis Besides Angiography of Testicular Artery in Dromedary Camel.

Decreasing male fertility encouraged the investigators to innovate accurate diagnostic non-invasive methods for detection of changes in the testicular parenchyma. Ultrasonography (US) has the potential to be used in this manner for decades, but magnetic resonance imaging (MRI) is still of limited application in animals for this purpose. The current study was designed to describe appearances and quantitative MRI attributes of the normal testes, epididymis besides angiography of testicular artery in camels. About 30 apparently healthy male dromedary camels aged 8–14 years were slaughtered during the rutting season. Immediately after slaughtering, the male gonads (n = 30 pairs of testicles and epididymis) were subjected to morphometric evaluation using a Vernier caliper and ultrasound scanning. Epididymial sperms were evaluated for motility, vitality and abnormality. MRI was performed for testes (n=16) by using a 1.5T Excite-II MRI apparatus of Sigma. Radiography and angioarchitecture of testicular artery (n=24) were done. Camel testicular length, width, and depth showed non-significant differences between a Vernier caliper or sonar. The MRI results revealed that both the testis and epididymis have homogenously intermediate signal (T1) and testes have hyperintense signal, with slightly lower signal in the epididymis (T2). In conclusion, both the ultrasonography and MRI techniques, with each respective computer-assisted imaging, could be used to detect the histomorphological changes of the camels' testicles. However, US imaging remains the first diagnostic technique for evaluating the reproductive health in men for its lower cost and accuracy. MRI is beneficial when the sonograms are inconclusive and/or equivocal. It shows the examined tissues in greater anatomical details compared to ultrasonography. Further studies are needed to compare between characteristics of US and MRI of normal testes and epididymis with testicular artery angiography in living camel during rut season and non-rut season and between normal healthy and affected diseased genitalia.

Control of Indentation of a Needle into the Brain Phantom Tissue Using a Piezoelectric Drive

Currently, stereotaxic brain surgery is an actively developing branch of medicine. During these operations, a special needle is inserted into the brain through a hole in the skull. This needle is moved in the brain tissue so that its tip reaches a certain point, after which the necessary medical manipulation is performed (for example, taking a puncture). To ensure accurate positioning of the needle, it is advisable to monitor the process of such operations using the magnetic resonance imaging apparatus. This puts restrictions on the type of actuators that can be used to drive the needle. The paper considers the problem of controlling the penetration of a cylindrical needle into a phantom of the brain where the control force is generated using a piezoelectric drive (PED). To describe the interaction of the needle with the tissue, a phenomenological model is proposed, under which it is assumed that the phantom tissue is a viscoelastic and plastic material, and also demonstrates relaxation properties. When describing forces acting on the lateral surface of the needle from the side of the tissue, the presence of dry friction is taken into account. The proposed model contains a number of parameters that are identified based on experiments carried out at the NCKU (Taiwan). In these experiments, a standard biopsy needle was inserted into a phantom made from agar-agar solution, and the position of the needle and the force acting on it from the tissue were registered. It is shown that the experimental results are in good agreement with the calculations in the context of the model. An algorithm for controlling the needle by setting the frequency of excitation of the probe is proposed. The aim of the control is to introduce the needle to a given depth at a given constant speed, and then hold the needle at this depth. During the process, it is required to avoid overshooting in speed and position. Numerical simulation has been carried out. The effect of the feedback parameters on the nature of the process is investigated. It is shown that the proper choice of parameters allows for avoiding the overshooting.

Identifying export markets for Indian medical devices

Purpose Medical device industry in India is a niche sector with few key players but it possesses huge potential for both domestic and international trade. In recent years, a number of regulatory relaxations have been provided to medical device manufacturers in India to enhance production and further trade especially exports. Though the industry is highly dependent on imports, the purpose of this paper is to identify key medical devices using the revealed comparative advantage, which can be exported from India by identifying new markets. Design/methodology/approach For the selected medical devices, India’s exports to the world and the newly identified markets are forecasted using the autoregressive integrated moving average model of regression. Findings It is seen that three major medical devices emerge to be the ones where India has the capacity and potential to manufacture and export. These medical devices are electro-cardiographs, magnetic resonance imaging apparatus and oscilloscopes and oscillographs being exported to the USA, Australia; China and the USA, respectively, which is rising in recent years. Research limitations/implications As the forecasted values indicate that there is an increasing potential in exports from India to the world of the selected medical devices, there is an urgent need to develop this industry and enhance exports from India. Very few studies have been carried out to examine and forecast exports from specific sectors or industries which is the need of the hour now. Originality/value The paper also provides suggestions to exporters and policymakers on leveraging the future export potential of selected medical devices.

Dynamics of the meniscus underweight-loading conditions: an investigation using upright magnetic resonance imaging

Objectives:Meniscal morphology underweight-loading conditions remains unknown, because weight loading is rarely performed during magnetic resonance imaging (MRI). We focused on the weight-loading condition and developed an upright MRI. This study aimed to investigate the shift of the medial and lateral meniscus in healthy adults under both fully weight loaded and unloaded conditions, using both supine and upright MRI.Methods:Eighteen volunteers (13 men and 5 women) without previous knee complaints underwent an MRI of the right knee. The mean age of the subjects was 21.8±3.1 years. The examination was performed in three positions: supine, double-leg upright (DLU), and single-leg upright (SLU). The knees were fully extended in each position. For both the supine and upright examinations, we used a special MRI apparatus (Gravity MRI, Hitachi, Japan) that is capable of imaging in any position with a static magnetic field strength of 0.4 T (Figure). T1-weighted images were obtained in both coronal and sagittal planes with a slice thickness of 2 mm. The medial or lateral, anterior and posterior shifts of both the medial and lateral meniscus were measured, against the tibial wedge. The medial and lateral meniscal shift rates were measured as assessment items under each condition. The shift rate was defined as the proportion of the measured meniscal shift compared to the overall width of the medial and lateral meniscus. The MRI reference section on the sagittal plane was the midpoint of the medial or lateral femoral condyle. On the coronal plane, the reference point was the midpoint of the medial and lateral tibial condyle. The measurement items were compared in all three imaging positions using analysis of variance and multiple comparison tests, with statistical significance set at P < 0.05.Results:We show the results from the analysis of the dynamics of the medial and lateral meniscus in Table. The difference among the three conditions for the medial shift rate of the medial meniscus was significant. The medial shift rate was significantly greater in the DLU and SLU positions than in the supine position (supine: 7.3±5.8% vs. DLU: 20.0±8.8 % (P<0.01), supine vs. SLU: 21.5±7.6% (P<0.01), DLU vs. SLU (P=0.7)). No significant differences were observed for the anterior and posterior shift rates of the medial meniscus (anterior: P=0.6, posterior: P=0.4). In the lateral meniscus, the lateral shift rate was significantly greater in the SLU position than in the supine position, but no significant difference was observed in the DLU position (supine: -1.2±11.8% vs. DLU: 2.7±11.1 % (P=0.2), supine vs. SLU: 4.5±10.8% (P=0.04), DLU vs. SLU: P=0.7). Both anterior and posterior shift rates in the lateral meniscus were significantly greater in DLU and SLU positions than in the supine position (anterior/ supine: -20.6±14.3% vs. DLU: -14.7±12.2% (P<0.01), supine vs. SLU: -8.9±14.9% (P<0.01), DLU vs. SLU: P=0.3, posterior/ supine: -78.0±19.6% vs. DLU: -63.7±18.7 % (P<0.01), supine vs. SLU: -57.8±19.2% (P<0.01), DLU vs. SLU: P=0.4).Conclusions:Under upright weight-loading conditions, the medial meniscus showed only medial shift, whilst the lateral meniscus was seen to shift in lateral, anterior, and posterior directions. No significant difference was observed between the DLU and SLU shift rates in both the medial and lateral meniscus in healthy adults. We believe that this result will be useful when considering loading and rehabilitation following meniscal repair.Table.The results of medial and lateral shift among supine, DLU and SLUMeniscal shiftrate on MRIShift directionSupineDLUSLUP-value Medial shift (%)7.3 ± 5.820.0 ± 8.821.5 ± 7.6<0.01Medial meniscusAnterior shift (%)33.8 ± 5.935.1 ± 7.333.1 ± 7.60.61 Posterior shift (%)-25.3 ± 8.5-27.1 ± 9.6-26.8 ± 8.20.41 Lateral shift (%)-1.2 ± 11.82.7 ± 11.14.5 ± 10.80.05Lateral meniscusAnterior shift (%)-20.6 ± 14.3-14.7 ± 12.2-8.9 ± 14.9<0.01 Posterior shift (%)-78.0 ± 19.6-63.7 ± 18.7-57.8 ± 19.20.001

A 100-m Sprint Time Is Associated With Deep Trunk Muscle Thickness in Collegiate Male Sprinters.

Introduction: One reason athletes train their trunk muscles is that the body's trunk stability has been shown to prevent injury. However, the relationship between body trunk muscle thickness, particularly that of deep muscles, and athletic performance remains to be clarified.Purpose: We aimed to explore the relationship between 100-m sprint performance and the sizes of the trunk stabilizing muscles, the psoas major muscle (PM), transversus abdominis (TA), and multifidus muscle (MM), in collegiate sprinters.Methods: Fourteen male sprinters belonging to a university athletics club participated in this study. The thicknesses of the TA and MM were measured using an ultrasonic diagnostic apparatus (ProSound C3; Aloka, Tokyo, Japan). The cross-sectional area of the PM was assessed by a magnetic resonance imaging apparatus (Vantage Elan; Toshiba Medical Systems, Tokyo, Japan). The relationship between these anthropometric parameters and the 100-m sprint time was analyzed by Spearman's correlation coefficient, multi- regression analysis, and the change-point regression model.Results: The sizes (mean ± SD) of the muscles were: PM, 43.074 ± 7.35 cm2; TA, 4.36 ± 0.72 mm; and MM, 3.99 ± 0.48 cm. The mean 100-m sprint time was 11.00 ± 0.48 s. Spearman's correlation analysis revealed that the 100-m sprint time had a significant moderate negative correlation with TA (ρ = −0.691, p < 0.01) and a low negative but not significant correlation with MM (ρ = −0.327, p = 0.28), whereas PM did not show a significant or in-negligible correlation. The change-point regression model found the change-points in the 100-m sprint time and the thickness of the TA and MM at 4.70 mm (95% CI: 4.00–5.43 mm) and 3.84 cm (95% CI: 3.28–4.31 cm), respectively. The sprint time decreased with an increase in the thickness of the muscles up to the change-points, whereas it did not change even if the muscles became thicker than the change-points. The change-points were consistently observed when the thickness of the muscles was normalized by body mass.Conclusion: Sprint performance for 100-m was found to be associated with TA and MM thickness in a biphasic manner. As muscle thickness increased, the sprint time decreased, followed by a plateau phase.

Composition and acoustic properties in a cartilage phantom

In this study, a cartilage phantom that can be used for verifications and calibrations of not only magnetic resonance imaging (MRI) apparatus but also ultrasonic diagnosis equipment for cartilage diagnosis in the future was fabricated. Acoustic properties of the phantom fabricated for MRI apparatus evaluation were measured, and it was verified whether the acoustic properties of the phantom are close to those of the normal cartilage, which are set as the target values. In addition, as the fundamental physical properties of the cartilage phantom, the Young’s modulus and the density were also measured. As a result, a cartilage phantom that satisfies target values of transverse relaxation time (T2) and apparent diffusion coefficient (ADC), and a target value of speed of sound (SOS) could be fabricated.

Detection and Evaluation of Low Contrast Resolution of Magnetic Resonance Imaging Apparatus Based on Magphan Phantom

Based on the Magphan phantom,a baseline value of low contrast resolution was established,and the stability of the imaging performance of the system was monitored.Drift and correction were found in time to give full play to the performance of the device. The general test evaluation method for low-contrast resolution was not suitable for the characteristics of long-term monitoring equipment performance changes,and the test evaluation of low-contrast resolution that incorporates the t-test method in statistical principle was proposed. By analyzing and evaluating the test results of the low contrast resolution of the standard water model image,and verifying the correctness of the evaluation method,according to the correct test method,the test statistic value was used as the low contrast resolution value of the MRI equipment to test the t boundary of the region.The value was used as a baseline value for low contrast resolution to establish a long-term stable quality assurance system. In this paper,the data of the low contrast resolution test on Magphan phantom was in line with practical experience,therefore the test method of low contrast resolution was verified.The baseline value of the indicator can be established based on the detection and evaluation method of low contrast resolution based on phantom,then to ensure the stability of the imaging performance of the system.

Research and application of magnetic resonance coordinate transformation method for brain control technology of carp robots

To solve the problem of precise positioning of carp brain tissue coordinates, it is proposed in this paper for a method for transforming the coordinates of magnetic resonance imaging of carp brain tissue into the coordinates of electrode implantation using a brain stereotaxic apparatus. In this study, the 3.0T magnetic resonance imaging instrument was used to scan the carp brain. We independently established the three-dimensional positioning coordinate system of the brain, the three-dimensional coordinate assistance system of skull surface and the three-dimensional coordinate assistance system in brain tissue. After two coordinate transformations, the magnetic resonance image coordinates of the brain electrodes implantation sites were converted into the three-dimensional stereotactic coordinate system to guide the electrodes implantation. The experimental groups were divided into two groups, A and B. Group A was the group of magnetic resonance imaging apparatus combining with the brain stereotaxic apparatus, and group B was the group of brain atlas combining with the brain stereotaxic apparatus. Each group had 20 tails of carps ( n = 20). This two methods were used to implant the electrodes into the cerebellar motor area. The underwater experiments of the carp robots were carried out to test the two methods. The results showed that the accuracy of the implanted electrodes were 90% in group A and 60% in group B. The success rate of group A was significantly higher than that of group B ( P < 0.05). Therefore, the new method in this paper can accurately determine the coordinates of carp brain tissue.

Magnetic resonance imaging after cochlear implants

IntroductionMost cochlear implants are currently compatible with magnetic resonance imaging (MRI) up to 3 T. Nevertheless, this does not completely eliminate the risk of serious accidents. Implant displacements and other adverse events with compatible implants have been reported in the literature. Case reportsAmong the six patients who had MRI after receiving implants at our center, we report three cases with adverse events related to the examination. The first case was complicated by magnet displacement with partial demagnetization. The second case showed total demagnetization, which necessitated removal and reimplantation of the implant. The third case involved severe pain sensation which disrupted the MRI scan. The smallest artifact was found with 3D MRI angiography, and largest artifact was found with diffusion and T2 FLASH. DiscussionMoving the patient into the MRI apparatus must be supervised by an otorhinolaryngology specialist or an experienced radiologist. It is important to consider the magnetic field directions, so that angle between the implant magnetic fields and the MRI B0 always remains less than or equal to 90°. In addition, we recommend the use of an “arrow drawing” to facilitate the orientation of the magnetic field directions. Furthermore, to prevent magnet displacement, we recommend systematic use of a protective splint in addition to bandaging.

MRI experiments for introductory physics

The introductory physics classroom has long educated students about the properties of the atom and the nucleus. But absent from these lessons has been an informed discussion of magnetic resonance imaging (MRI) and its parent science nuclear magnetic resonance (NMR). Physics teachers should not miss the opportunity to instruct upon this highly relevant application of modern physics, especially with so many of our students planning to pursue a career in medicine. This article provides an overview of the physics of MRI and gives advice on how physics teachers can introduce this topic. Also included are some demonstration activities and a discussion of a desktop MRI apparatus that may be used by students in the lab or as a demo.

Low-temperature magnetic resonance imaging with 2.8 μm isotropic resolution

We demonstrate the feasibility of high-resolution 1H magnetic resonance imaging (MRI) at low temperatures by obtaining an MRI image of 20 μm diameter glass beads in glycerol/water at 28 K with 2.8 μm isotropic resolution. The experiments use a recently-described MRI apparatus (Moore and Tycko, 2015) with minor modifications. The sample is contained within a radio-frequency microcoil with 150 μm inner diameter. Sensitivity is additionally enhanced by paramagnetic doping, optimization of the sample temperature, three-dimensional phase-encoding of k-space data, pulsed spin-lock detection of 1H nuclear magnetic resonance signals, and spherical sampling of k-space. We verify that the actual image resolution is 2.7 ± 0.3 μm by quantitative comparisons of experimental and calculated images. Our imaging approach is compatible with dynamic nuclear polarization, providing a path to significantly higher resolution in future experiments.

Robustness of spatio-temporal regularization in perfusion MRI deconvolution: An application to acute ischemic stroke.

The robustness of a recently introduced globally convergent deconvolution algorithm with temporal and edge-preserving spatial regularization for the deconvolution of dynamic susceptibility contrast perfusion magnetic resonance imaging is assessed in the context of ischemic stroke. Ischemic tissues are not randomly distributed in the brain but form a spatially organized entity. The addition of a spatial regularization term allows to take into account this spatial organization contrarily to the sole temporal regularization approach which processes each voxel independently. The robustness of the spatial regularization in relation to shape variability, hemodynamic variability in tissues, noise in the magnetic resonance imaging apparatus, and uncertainty on the arterial input function selected for the deconvolution is addressed via an original in silico validation approach. The deconvolution algorithm proved robust to the different sources of variability, outperforming temporal Tikhonov regularization in most realistic conditions considered. The limiting factor is the proper estimation of the arterial input function. This study quantified the robustness of a spatio-temporal approach for dynamic susceptibility contrast-magnetic resonance imaging deconvolution via a new simulator. This simulator, now accessible online, is of wide applicability for the validation of any deconvolution algorithm. Magn Reson Med 78:1981-1990, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

The experience of using magnetic resonance imaging of the uterus and its appendages as an alternative to X-ray hysterosalpingography

Determination of the diagnostic capabilities of magnetic resonance imaging of the uterus and its appendages (MRHSG) on devices with the induction of the magnetic field 3 Tesla (T) as an alternative to the classic X-ray hysterosalpingography, accompanied by a significant radiation dose to the patient. During the period from April 2015 to February 2016 12 MRHSG was conducted using magnetic resonance imaging apparatus Verio Magnetom 3T, Siemens company (Diagnostic Center "BarsMed", Kazan, Russia). We used neutral and not giving adverse reactions contrast agent – carbon dioxide. The pelvic organs – the uterus and fallopian tubes – represent the zone of interest. Analysis of the data showed that MRHSG on the apparatus with the induction of the magnetic field of 3 T is a highly informative method in the diagnosis of tubal patency, allowing fully assess the state of the pelvic organs on the whole and identify pathology. The absence of radiation exposure and contraindications associated with intolerance to iodinated contrast agents and other side effects differs MRHSG from the traditional X-ray method and makes MRHSG to be an alternative secure method of diagnosis, which has a number of advantages described in the article. MRHSG on the apparatus with the induction of the magnetic field of 3 T in diagnosis of obstruction of the fallopian tubes and the visualization of the uterus and appendages diseases can be optimal and safe alternative to the X-ray hysterosalpingography, which accompanied with radiation exposure and is a number of side effects.

Abstract IA11: Perfusion MRI: A potential biomarker of tumor response in clinical trials

Abstract This presentation will show an overview of perfusion MRI for in vivo imaging of solid cancers and emerging evidence supporting the use of this technique to monitor response to anticancer therapy is discussed. The noninvasive nature and high image resolution of Magnetic Resonance Imaging (MRI) makes it the preferred modality for in vivo imaging and disease monitoring of most solid cancers. While conventional MRI provides important anatomic information on the tumor and surrounding tissue, it reveals fewer insights on the metabolic and hemodynamic status and function of the tumor. With the advent of antiangiogenic agents that are not directly cytotoxic, there is an urgent need for clinical trials to incorporate advanced imaging analyses that goes beyond traditional and formalized imaging-based response criteria – usually by assessing tumor load after contrast agent administration. Blockade of vascular endothelial growth factors (VEGF) results in decreased vascular permeability and reduced tumor contrast enhancement on conventional MRI, artificially boosting radiographic response rates. Unfortunately, the high response rates do not always translate into prolonged survival [1]. The negative results of several recent late-phase trials suggest that first-line administration of antiangiogenic therapies in unselected patient groups is probably not the best approach, owing to diversity in cancer biology and natural history. Identification of a subset of cancer patients most likely to benefit from therapy and understanding the underlying mechanisms that separate these responding patients from non-responders are of high priority. According to the National Cancer Institute imaging response criteria [2], developing and validating clinical trial-acceptable advanced imaging methods can lead to smaller clinical trials with fewer patients by earlier and more-focused response assessments; faster regulatory approvals, and by this, earlier use of new drugs in clinical care. Dynamic contrast-enhanced MRI, or perfusion MRI, may help address the limitations of conventional imaging methods in antiangiogenic trials and complement these imaging exams with information on vascular permeability, blood flow and blood volume, among others. A large number of retrospective human studies show consistent reductions in abnormal vascular permeability after antiangiogenic therapy in a range of cancer types [3]. Small studies of brain tumor patients treated with VEGFR inhibitors also show a transient normalization of inefficient blood flow in a selected group of patients and suggest that vascular normalization may be a mechanism for improved delivery of adjuvant therapy and prolonged survival [4]. Similar data on changes in relative blood volume also show a sensitive, yet more complex response to VEGFR inhibition [5]. These efforts are followed by the recent introduction of MRI-based measurements of tumor vessel caliber and relative tissue oxygen saturation in clinical trial data [6]. These measurements are made possible using MR images sensitive to the vessel-size-related scale of magnetic field inhomogeneities created by blood and contrast agents flowing through the vessels. Most, if not all major manufacturers of MRI apparatus now provide these dedicated image protocols. Collectively, perfusion MRI may provide the clinical decision maker with a battery of complementary parameters capable of identifying the initial response, duration and end of the vascular remodeling period following antiangiogenic therapy and thereby enable early identification of patients most likely to benefit from targeted therapies.

Micron-scale magnetic resonance imaging of both liquids and solids

We describe and demonstrate a novel apparatus for magnetic resonance imaging (MRI), suitable for imaging of both liquid and solid samples with micron-scale isotropic resolution. The apparatus includes a solenoidal radio-frequency microcoil with 170μm inner diameter and a set of planar gradient coils, all wound by hand and supported on a series of stacked sapphire plates. The design ensures efficient heat dissipation during gradient pulses and also facilitates disassembly, sample changes, and reassembly. To demonstrate liquid state 1H MRI, we present an image of polystyrene beads within CuSO4-doped water, contained within a capillary tube with 100μm inner diameter, with 5.0μm isotropic resolution. To demonstrate solid state 1H MRI, we present an image of NH4Cl particles within the capillary tube, with 8.0μm isotropic resolution. High-resolution solid state MRI is enabled by frequency-switched Lee–Goldburg decoupling, with an effective rotating frame field amplitude of 289kHz. At room temperature, pulsed gradients of 4T/m (i.e., 170Hz/μm for 1H MRI) are achievable in all three directions with currents of 10A or less. The apparatus is contained within a variable-temperature liquid helium cryostat, which will allow future efforts to obtain MRI images at low temperatures with signal enhancement by dynamic nuclear polarization.

Dynamic stability characteristics of fluid flow in CO2 miscible displacements in porous media

The dynamic stability characteristics of fluid flow in miscible displacement processes were investigated by using a magnetic resonance imaging apparatus and simulated by a lattice-Boltzmann method at elevated pressures.

Magnetic resonance imaging analysis on the in-situ mixing zone of CO2 miscible displacement flows in porous media

The in-situ mixing zone represents dynamic characteristics of CO2 miscible displacement flows, which is important for carbon dioxide enhanced oil recovery (CO2-EOR) projects. However, the migration characteristics of the in-situ mixing zone under reservoir conditions has been neither well studied nor fully understood. The in-situ mixing zone with the flowing mixture of supercritical CO2 and n-decane (nC10) was investigated by using a magnetic resonance imaging apparatus at a reservoir condition of 8.5 MPa and 37.8 °C in porous media. The experimental results showed that the CO2-frontal velocity was larger than the mixing-frontal velocity. The mixing zone length was linearly declined in the miscible displacement process. And the declining rate of the mixing zone length was increased with injection rate. It indicates that the mixing zone length is not constant in a vertically stable CO2 misible displacement and a volume contraction due to phase behavior effects may occur. Then, an error function based on the convection-dispersion equation was fitted with CO2 miscible displacement experiments. The error function was well fitted both at a series of fixed core positions and a series of fixed displacement times. Furthermore, the longitudinal dispersion coefficients (Klx and Klt) and the longitudinal Peclet numbers (Ped and PeL) were quantified from the fitting results. The evolutions of the longitudinal dispersion coefficient were reduced along the displacement time. And the declining rate was increased with injection rate. And with proceeding, the longitudinal dispersion coefficient was tending towards stability and constant. But the evolutions of the longitudinal Peclet numbers were increased along the displacement time. And the increasing rate was increased with injection rate.

The value of neurosurgical and intraoperative magnetic resonance imaging and diffusion tensor imaging tractography in clinically integrated neuroanatomy modules: A cross‐sectional study

Neuroanatomy is considered to be one of the most difficult anatomical subjects for students. To provide motivation and improve learning outcomes in this area, clinical cases and neurosurgical images from diffusion tensor imaging (DTI) tractographies produced using an intraoperative magnetic resonance imaging apparatus (MRI/DTI) were presented and discussed during integrated second-year neuroanatomy, neuroradiology, and neurosurgery lectures over the 2008-2011 period. Anonymous questionnaires, evaluated according to the Likert scale, demonstrated that students appreciated this teaching procedure. Academic performance (examination grades for neuroanatomy) of the students who attended all integrated lectures of neuroanatomy, was slightly though significantly higher compared to that of students who attended these lectures only occasionally or not at all (P=0.04). Significantly better results were obtained during the national progress test (focusing on morphology) by students who attended the MRI/DTI-assisted lectures, compared to those who did so only in part or not at all, compared to the average student participating in the national test. These results were obtained by students attending the second, third and, in particular, the fourth year (P≤0.0001) courses during the three academic years mentioned earlier. This integrated neuroanatomy model can positively direct students in the direction of their future professional careers without any extra expense to the university. In conclusion, interactive learning tools, such as lectures integrated with intraoperative MRI/DTI images, motivate students to study and enhance their neuroanatomy education.

TUNING THE NOISE IN MAGNETIC RESONANCE IMAGING TO MAXIMIZE NONLINEAR INFORMATION TRANSMISSION

We demonstrate a new instance of useful-noise effect or stochastic resonance, occurring in magnetic resonance imaging (MRI). Based on the physics of signal–noise coupling specific to MRI, we establish the possibility of regimes where nonlinear post-processing can benefit from an increase in the level of the noise present in the MRI apparatus. The validation is obtained by both theoretical analysis and experimental observations. We especially show that the beneficial tuning of the noise can be practically achieved by controlling the bandwidth of the sampling receiver of the MRI apparatus. These results constitute a nontrivial extension of stochastic resonance in the domain of images, arising here with a signal–noise coupling in MRI which is distinct from the purely additive or multiplicative couplings previously investigated in the framework of useful-noise effect.