Recording and post-processing speech signals from magnetic resonance imaging experiments

Resolution ‘scaling law’ in MRI of articular cartilage

Intracardiac echocardiography (ICE) is routinely used in many interventional procedures in cardiology. In these procedures ICE catheter is positioned with fluoroscopy guidance, which can be harmful due to ionizing X-ray radiation exposure. Positioning the ICE catheter using an interventional magnetic resonance imaging (MRI) system would enable procedures that are free of ionizing radiation, and complement MRI with its speed and image resolution. This paper presents a feasibility study of potential combination of these modalities demonstrating the visibility of a CMUT-based ICE catheter tip for positional guidance, minimum distortion of the MRI image, and the functionality of catheter components under high static and RF magnetic fields in MRI room.

In this paper, we present a method for the evaluation of the signal-to-noise ratio in magnetic resonance imaging (MRI) coils loaded with resonant ring metamaterial lenses, in the presence of a conducting phantom resembling human tissue. The method accounts for the effects of the discrete and finite structure of the metamaterial. Numerical computations are validated with experimental results, including laboratory measurements and MRI experiments.

Application of Magnetic Resonance Imaging to Study Pathophysiology in Brain Disease Models

We describe the design and construction of a laser-polarized Xe129 production and delivery system that is used in our in vitro and in vivo magnetic resonance imaging (MRI) experiments. The entire apparatus including lasers and optics, rapidly actuated valves, heating and cooling, and transport tubing lies in the high magnetic field environment of a 2 T MRI magnet. With approximately 7.5% Xe129 polarization, 157 cc atm of xenon gas is produced and stored as xenon ice every 5 min. Large quantities of polarized Xe129 can be obtained by cycling this process. The xenon is subsequently delivered in a controlled fashion to a sample or subject. With this device we have established the feasibility of using laser-polarized Xe129 as a magnetic tracer in MRI. This reliable, effective, and relatively simple production method for large volumes of Xe129 can be applied to other areas of research involving the use of laser-polarized noble gases.

Developing a non-invasive method to monitor the growth of tissue-engineered cartilage is of utmost importance for tracking the progress and predicting the success or failure of tissue-engineering approaches. Magnetic Resonance Imaging (MRI) is a leading non-invasive technique suitable for follow-through in preclinical and clinical stages. As complex tissue-engineering approaches are being developed for cartilage tissue engineering, it is important to develop strategies for true non-invasive MRI monitoring that can take into account contributions of the scaffold, cells and extracellular matrix (ECM) using MR parameters. In the current study, we present the preliminary MRI assessment of chondrogenic differentiation of human bone marrow derived stem cells seeded onto a specially designed osteochondral matrix system. We performed water relaxation times (T1 and T2) MRI measurements at 7, 14 and 28 days after cell seeding. The MRI experiments were performed for the tissue-engineered cartilage as well as for acellular scaffolds. We identified that the contribution of the scaffold is the dominant contribution in MR parameters of engineered cartilage and that it hinders observation of the tissue growth. An attempt is made to filter out this contribution, for the first time, in order to make a true observation of tissue growth using MRI.

In vivo detection of acute rat renal allograft rejection by MRI with USPIO particles

Less head motion during MRI under task than resting-state conditions

The synthesis of (octreotide–carboxymethyl–dextran)‐modified magnetic nanoparticles (CMD‐MNPs), which were characterized by FT‐IR, AFM, TEM and XRD, and magnetic hysteresis, is described. Magnetic Resonance Imaging (MRI) experiments were performed on a 1.5 Tesla Magnetom Vision machine. The internalization of CMD‐MNPs‐OC into pancreatic cancer cells Bx‐PC3 and colon cancer cells HCT‐116 were investigated by transmission electron microscopy (TEM) and magnetic resonance imaging (MRI). The nanoparticles can be recognized specifically, via the somatostatin receptor, and which can be used as a T2 MRI contrast agent. TEM and MRI results show that somatostatin receptor can deliver OC‐modified MNPs into the cytoplasm of a cancer cell line.

In this paper, a numerical analysis of the radio-frequency (RF) power requirements in magnetic resonance imaging (MRI) is presented at frequencies that span 200-362 MHz. This was performed utilizing an anatomically detailed human head model and a high-frequency RF coil utilized in high-field MRI systems. For axial slices through the brain region, it is demonstrated that the power required in order to obtain an average flip angle across the slice increases with frequency plateauing at a certain value, and then dropping as the frequency increases. The results demonstrate the significance of the electromagnetic interactions between the load and coil and their effects on the so important issue of power-frequency dependence in MRI.

Iron toxicity plays a key role in tissue damage in patients with iron overload, with induced heart failure being the main cause of death. T2*-weighted magnetic resonance imaging (MRI) has been established for evaluating myocardial iron overload with strong correlation with biopsy. The recently introduced dual-energy computed tomography (DECT) has the potential for evaluating iron overload without energy-dependent CT attenuation or tissue fat effects. This study investigates the performance of DECT for evaluating myocardial iron overload (based on images acquired at four different diagnostic imaging energies of 80, 100, 120, and 140 kVp) and compare the results to MRI T2* measurements based on DECT and MRI experiments on phantoms with calibrated iron concentrations. DECT showed high accuracy for evaluating iron overload compared to MRI T2* imaging, which might help in patient staging based on the degree of iron overload and independent of the implemented imaging energy.

A magnetic resonance imaging (MRI)-compatible device was developed to apply calibrated compression loads to the lumbar spine during imaging. Experiments were performed to establish a protocol to measure lumbar load-response and estimate muscle-force contribution to spinal load. To develop experimental methodology for direct study of lumbar spine response to compression load. Most lumbar MRI scans require subjects to lie relaxed and supine, but spinal stenosis has been demonstrated to increase during moderate compressive loading. Several devices have been used to load the spine during MRI, but they could not maintain and/or change calibrated loads during MRI experiments. Furthermore, artifact from viscoelastic creep during imaging was not considered. An MRI-compatible spine compression unit with pneumatic load elements was developed to produce calibrated compression loads. Young healthy men were loaded with 140% body weight for up to 10 minutes to establish an appropriate test protocol. Muscle force contribution to spinal load was estimated from electromyography experiments. The spine compression unit produced specified loads +/- 29 N (standard deviation). Spine viscoelastic creep reached steady state by 6.5 minutes, leaving 3.5 minutes for image acquisition. The subjects could support 1.0 body weight for the requisite 10 minutes. Muscle compressive force estimates were only 135 N during application of 1.4 x body weight external compression load; thus, internal muscle forces during supine spine compression could be neglected. The lumbar load/image protocol fits within the time constraints of creep deformation and subject endurance. These methods allow acute lumbar mechanical response measurements during loading.

Over almost five decades of development and improvement, Magnetic Resonance Imaging (MRI) has become a rich and powerful, non-invasive technique in medical imaging, yet not reaching its physical limits. Technical and physiological restrictions constrain physically feasible developments. A common solution to improve imaging speed and resolution is to use higher field strengths, which also has subtle and potentially harmful implications. However, patient safety is to be considered utterly important at all stages of research and clinical routine. Here we show that dynamic metamaterials are a promising solution to expand the potential of MRI and to overcome some limitations. A thin, smart, non-linear metamaterial is presented that enhances the imaging performance and increases the signal-to-noise ratio in 3T MRI significantly (up to eightfold), whilst the transmit field is not affected due to self-detuning and, thus, patient safety is also assured. This self-detuning works without introducing any additional overhead related to MRI-compatible electronic control components or active (de-)tuning mechanisms. The design paradigm, simulation results, on-bench characterization, and MRI experiments using homogeneous and structural phantoms are described. The suggested single-layer metasurface paves the way for conformal and patient-specific manufacturing, which was not possible before due to typically bulky and rigid metamaterial structures.

Magnetic Resonance Imaging (MRI) provides superior soft-tissue contrast in cancer diagnosis compared to other imaging modalities. However, the strong magnetic field inside the MRI bore along with limited scanner bore size poses significant challenges. Since current approaches in breast biopsy using MR images are primarily blind targeting approaches, it is necessary to develop an MRI-compatible robot that can avoid multiple needle insertions into the breast tissue. This MRI-compatible robotic system could potentially lead to improvement in the targeting accuracy and reduce sampling errors. A master–slave surgical system has been developed comprising a MRI-compatible slave robot which consists of one piezo motor and five pneumatic cylinders connected by long pneumatic transmission lines. The slave robot follows the configuration of the master robot, which provides an intuitive manipulation interface for the physician and operates inside the MRI bore to adjust the needle position and orientation and perform needle insertion tasks. Based on the MRI experiments using the slave robot, there was no significant distortion in the images, and hence the slave robot can be safely operated inside the MRI with minimal loss in signal-to-noise ratio (SNR). Ex vivo and in vivo experiments have been conducted to evaluate the performance of the master–slave surgical system.

Water and solute movement as any other transport processes through soil are influenced by the hydraulic properties of the soils. The heterogeneities of the soils imply heterogeneous spatial distribution of the hydraulic properties leading to heterogeneous distribution of soil water content. This may affects the water availability for plant growth, the groundwater contamination and nutrients losses within the root zone. The measurement techniques available today for the estimation of soil hydraulic parameters do not account for the heterogeneity of the sample and treat each measurement sample as a homogeneous representative volume. On the other side natural soils contain large heterogeneities mostly in terms of inclusions of different materials. Therefore the purpose of this study is to estimate soil hydraulic properties of a heterogeneous sample by combining classical multi‐step‐outflow (MSO) with magnetic resonance imaging (MRI) experiments. MSO experiments were performed on a sample filled with sand and sand‐clay mixture in a coaxial structure. During each pressure application MRI images at 4.7 T (200 MHz) were recorded using a pure phase‐encoding MRI sequence in order to provide information about the soil water content at specific locations within the coaxial sample. The recorded cumulative outflow and water content data were used as input data in the inversion of the MSO experiment. For the simulation and inversion of the MSO experiment we used the hydrological model HYDRUS‐2D3D in which the initial hydraulic parameters of the two materials were estimated based on CPMG‐T2 relaxation measurements on homogeneous sub‐samples. The results show conclusively that the combination of the two MRI and MSO methods leads to a unique estimation of the hydraulic properties of two materials simultaneously.