Visible Human Project® female surface based computational phantom (Nelly) for radio-frequency safety evaluation in MRI coils

Quantitative modeling of specific absorption rate and temperature rise within the human body during 1.5 T and 3 T MRI scans is of clinical significance to ensure patient safety. This work presents justification, via validation and comparison, of the potential use of the Visible Human Project (VHP) derived Computer Aided Design (CAD) female full body computational human model for non-clinical assessment of female patients of age 50–65 years with a BMI of 30–36 during 1.5 T and 3 T based MRI procedures. The initial segmentation validation and four different application examples have been identified and used to compare to numerical simulation results obtained using VHP Female computational human model under the same or similar conditions. The first application example provides a simulation-to-simulation validation while the latter three application examples compare with measured experimental data. Given the same or similar coil settings, the computational human model generates meaningful results for SAR, B1 field, and temperature rise when used in conjunction with the 1.5 T birdcage MRI coils or at higher frequencies corresponding to 3 T MRI. Notably, the deviation in temperature rise from experiment did not exceed 2.75° C for three different heating scenarios considered in the study with relative deviations of 10%, 25%, and 20%. This study provides a reasonably systematic validation and comparison of the VHP-Female CAD v.3.0–5.0 surface-based computational human model starting with the segmentation validation and following four different application examples.

Design and Implementation of Split-Leg Type Elliptical Whole-Body Birdcage RF Coil at 1.5 T MRI

The feasibility and the development of a four-port elliptical birdcage radio frequency (RF) coil for generating a homogenous RF magnetic (B1) field is presented for a space-constrained narrow-bore magnetic resonance imaging (MRI) system. Optimization was performed for the elliptical birdcage RF coil by adjusting the position and the structure of the legs to maximize the B1+-field uniformity. Electromagnetic (EM) simulations based on RF coil circuit co-simulations were performed on a cylindrical uniform phantom and a three-dimensional human model to evaluate the B1+-field uniformity, the transmission efficiency, and the specific absorption rate (SAR) deposition. An elliptical birdcage RF coil was constructed, and its performance was evaluated through network analysis measurements such as S-parameters and Q-factor. Quadrature transmit and receive MRI experiments were conducted using both phantom and in vivo human for validation. The EM simulation results indicate reasonable B1+-field uniformity and transmission efficiency for the proposed elliptical birdcage RF coil. The signal-to-noise ratio and the flip angle maps of the uniform phantom and the in vivo human MR images acquired using an elliptical birdcage (62 cm × 58 cm) were similar to those of a commercial circular birdcage (diameter, 58 cm), thereby indicating acceptable performance. In conclusion, the proposed split-type asymmetric elliptical birdcage RF coil is useful for whole-body MRI applications and can be used for imaging larger human subjects comfortably in a spacious imaging space.

Design of a Dual-Purpose Patch Antenna for Magnetic Resonance Imaging and Induced RF Heating for Small Animal Hyperthermia

The popularity of patch antennas in magnetic resonance imaging (MRI) has reduced because of the large size required for patch antennae to resonate. Since the size of the patch antenna is associated with the wavelength and the wavelengths that are used in MRI are substantially large, large antennas are used. Methods of reducing patch antenna sizes have been proposed; however, these methods reduce the penetration depth and uniformity. In this study, we reduced the area of the patch antenna by 30% by folding the ground and patch planes in a zigzag pattern. The patch antenna produced two main resonant modes. The first mode produced a uniform magnetic field that was used for MRI. The second mode produced a strong and focused electric (|E|)-field, which was used for radiofrequency (RF) heating. Furthermore, we explored the use of a combination of two patch antennas aligned along the z-axis to provide a circular uniform magnetic flux density (|B1|) field at 300 MHz, which corresponds to the Larmor frequency in the 7T MRI system. In addition, the patch antenna configuration will be used for RF heating hyperthermia operating at 1.06 GHz. The target object was a small rat with insertion of colon cancer. Using the proposed configuration, we achieved |B1|-field uniformity with a standard deviation of 3% and a temperature increment of 1 °C in the mimic cancer tissue.

The Influence of Radio-Frequency Transmit Field Inhomogeneities on the Accuracy of G-ratio Weighted Imaging

G-ratio weighted imaging is a non-invasive, in-vivo MRI-based technique that aims at estimating an aggregated measure of relative myelination of axons across the entire brain white matter. The MR g-ratio and its constituents (axonal and myelin volume fraction) are more specific to the tissue microstructure than conventional MRI metrics targeting either the myelin or axonal compartment. To calculate the MR g-ratio, an MRI-based myelin-mapping technique is combined with an axon-sensitive MR technique (such as diffusion MRI). Correction for radio-frequency transmit (B1+) field inhomogeneities is crucial for myelin mapping techniques such as magnetization transfer saturation. Here we assessed the effect of B1+ correction on g-ratio weighted imaging. To this end, the B1+ field was measured and the B1+ corrected MR g-ratio was used as the reference in a Bland-Altman analysis. We found a substantial bias (≈-89%) and error (≈37%) relative to the dynamic range of g-ratio values in the white matter if the B1+ correction was not applied. Moreover, we tested the efficiency of a data-driven B1+ correction approach that was applied retrospectively without additional reference measurements. We found that it reduced the bias and error in the MR g-ratio by a factor of three. The data-driven correction is readily available in the open-source hMRI toolbox (www.hmri.info) which is embedded in the statistical parameter mapping (SPM) framework.

Water Injection Operation Readiness of BB Field Redevelopment

BB field complex redevelopment is an integrated development under PETRONAS Enhanced Oil Recovery (EOR) project. BB fields are producing fields operated by PETRONAS Carigali Sendirian Berhad (PCSB). The BB fields redevelopment is a project to redevelop both B1 and B2 fields and to enable EOR implementation in the B1 field. The B1 redevelopment includes the EOR implementation through immiscible water alternating gas (IWAG), infill drilling, and safeguarding of no further activity (NFA) production. The B1 redevelopment also incorporates some provisions for the B2 field to secure gas supply for B1 IWAG. The B2 redevelopment focuses on safeguarding B2 NFA production. The redevelopment consists of three main elements, 1) EOR IWAG that involves injector well drilling at a new IWAG injection wellhead platform, 2) infill drilling at existing platforms and 3) safeguarding of NFA. Surface facilities scope includes installing a new Central Processing Platform (CPP) for B1 field, wellhead platforms, and intra-field pipelines. The CPP includes 60 kbpd water injection plant capacity, gas compression, gas-liquid separation, and produced water treatment. Modification in the B2 field is to flow gas from the B2 field to the B1 field. Operational readiness is crucial to ensure that the integrated project is executed smoothly. Two cases for changes are new technology deployment for water injection module (WIM) and people capability. It is a big challenge to achieve an effective start-up with minimum delay. There are some important aspects considered includes operation philosophy, Health Safety and Environment (HSE), and collaborative working environment (CWE) implementation. It is important to ensure improving oil recovery through infill and IWAG. Best practices in operation readiness of an integrated project that have many challenges that include process, people, and technology. These best practices may be replicated in any other projects by other companies/operators.

Design of a Coplanar Interlayer Gapped Microstrips Arrangement for Multi-Nuclei (1H, 19F, 31P, and 23Na) Applications in 7T MRI

Seven Tesla Magnetic Resonance (MR) systems can obtain high quality anatomical images using protons (1H) and can be used for multinuclear imaging and MR spectroscopy. These imaging modes can also obtain images and metabolic information using other nuclei, such as 19F, 31P, and 23Na. Here, we present an RF coil unit using a microstrip capable of resonating at four frequencies: 300 (1H), 280 (19F), 121 (31P), and 78 (23Na) MHz. The RF unit consists of a single feeding port and four lines that resonate and run a current at their respective frequency. We used the gapped microstrip concept to isolate each conducting line and interleaved the dielectric materials used for each line, thereby reducing the coupling between them. We also analyzed this design using electromagnetic (EM) simulations, and found that the quad tuned arrangement produced low coupling between adjacent current lines and achieved a uniform |B1| field in the z-y plane.

Three-Line Microstrip Array for Whole-Body MRI System at 7 T

This paper proposes the use of a triple-line microstrip array for transmitting a magnetic field (|B1+|) into the whole body for magnetic resonance applications at ultra-high field strength, such as 7 T. We explored some technologies that can potentially be applied for whole-body 7 T magnetic resonance imaging, as there is ongoing research on this topic. The triple-line microstrip transmission line (t-MTL) array consists of 32 channels. Each channel has a t-MTL, comprising a main conductor line and two adjacent coupled lines. The adjacent lines are not connected directly to the source. This configuration resulted in increased intensity and a centered |B1+|-field. We compared the proposed structure and some reference radiofrequency (RF) transmitters, such as a patch antenna, using a magnet bore as a waveguide and a whole-body birdcage coil. We evaluated the performance of the t-MTL using cylindrical phantoms. We computed the |B1+|-field from each RF transmitter inside a 3D human model containing more than 200 tissues. We compared their uniformity and field intensity and proposed a t-MTL array that yielded better performance. The proposed design also showed a lower specific absorption rate compared with a patch antenna.