10.5 T MRI static field effects on human cognitive, vestibular, and physiological function

A 128-channel receive array with enhanced signal-to-noise ratio performance for 10.5T brain imaging

PURPOSE

To develop and characterize a 128-channel head array for brain imaging at 10.5 T, evaluate signal-to-noise ratio (SNR) relative to ultimate intrinsic SNR (uiSNR) and lower field strengths, and demonstrate human brain anatomical and functional imaging with this unique magnetic field and high-channel-count array.

METHODS

The coil consists of a 16-channel self-decoupled loop transmit/receive (16Tx/Rx) array with a 112-loop receive-only (Rx) insert. Interactions between the 16Tx/Rx array and the 112Rx insert were mitigated using coaxial cable traps placed every 1/16 of a wavelength on each feed cable, locating most preamplifier boards outside the transmitter field, and miniaturizing those placed directly on individual coils.

RESULTS

The effect of the 112Rx insert on the circumscribing 16Tx/Rx array was minimized, leading to similar transmit field maps obtained experimentally with and without the 112Rx array in place and by electromagnetic simulations of the 16Tx/Rx array alone. The 128-channel array captured 77% of uiSNR centrally. Significantly higher 1/g-factor values across the whole brain was achieved compared with 7 T. Excellent SNR, high parallel-imaging performance, and minimal Tx-Rx interactions collectively facilitated acquisition of high-quality, high-resolution, proof-of-concept functional and anatomical images, including with power-demanding sequences in the human brain.

CONCLUSIONS

Counterintuitive to expectations based on magnetic fields less than or equal to 7 T, the higher channel counts provided SNR gains centrally, capturing about 80% uiSNR. The fraction of uiSNR achieved centrally in 64Rx, 80Rx, and 128Rx arrays suggested that a plateau was being reached at 80%. At this plateau, B0-dependent SNR gains for 10.5 T relative to 7 T were approximately linear to quadratic for the periphery and the center, respectively.

Vascular mechanoreceptor magnetic activation, hemodynamic evidence and potential clinical outcomes

There is sufficient proof that static magnetic fields (SMFs) of different parameters have a significant effect on the cardiovascular system. The sometimes contradictory, opposite-directional nature of SMF's hemodynamic effect generates uncertainty; therefore, an explanation of the underlying mechanisms is required. Following SMF selective carotid baroreceptors or microvascular net exposure, both high and low blood pressure (BP)/vascular tone starting conditions showed a return to normal. Beyond the previous descriptions of SMF's simple hemodynamic results, the current study aims to clarify the physiology of the SMF BP/vascular tone normalizing effects. The examination of available literature and hemodynamic tracings provided strong evidence that mechanoreceptor magnetic activation is concealed behind SMF vascular tone adjustment (increasing or decreasing as needed), filling in the knowledge gap regarding SMF opposite directional vascular tone normalizing outcomes. It has been proposed that cytoskeletal actin filament rearrangement, mechanically-gated Ca2+ influx, and nitric oxide (NO) activity may strengthen SMF's vascular mechanoreceptor sensing/regulation ability, modifying BP and vascular tone features in a hemodynamic normalizing pattern. It is suggested that baro/mechanoreceptor magnetic activation physiology is a unique mechanism of the magneto-cardiovascular interaction with substantial potential for cardiovascular protection.

Exploring in vivo human brain metabolism at 10.5 T: Initial insights from MR spectroscopic imaging

INTRODUCTION

Ultra-high-field magnetic resonance (MR) systems (7 T and 9.4 T) offer the ability to probe human brain metabolism with enhanced precision. Here, we present the preliminary findings from 3D MR spectroscopic imaging (MRSI) of the human brain conducted with the world's first 10.5 T whole-body MR system.

METHODS

Employing a custom-built 16-channel transmit and 80-channel receive MR coil at 10.5 T, we conducted MRSI acquisitions in six healthy volunteers to map metabolic compounds in the human cerebrum in vivo. Three MRSI protocols with different matrix sizes and scan times (4.4 × 4.4 × 4.4 mm³: 10 min, 3.4 × 3.4 × 3.4 mm³: 15 min, and 2.75×2.75×2.75 mm³: 25 min) were tested. Concentric ring trajectories were utilized for time-efficient encoding of a spherical 3D k-space with ∼4 kHz spectral bandwidth. B0/B1 shimming was performed based on respective field mapping sequences and anatomical T1-weighted MRI were obtained.

RESULTS

By combining the benefits of an ultra-high-field system with the advantages of free-induction-decay (FID-)MRSI, we present the first metabolic maps acquired at 10.5 T in the healthy human brain at both high (voxel size of 4.4³ mm³) and ultra-high (voxel size of 2.75³ mm³) isotropic spatial resolutions. Maps of 13 metabolic compounds (aspartate, choline compounds and creatine + phosphocreatine, γ-aminobutyric acid (GABA), glucose, glutamine, glutamate, glutathione, myo-inositol, scyllo-inositol, N-acetylaspartate (NAA), N-acetylaspartylglutamate (NAAG), taurine) and macromolecules were obtained individually. The spectral quality was outstanding in the parietal and occipital lobes, but lower in other brain regions such as the temporal and frontal lobes. The average total NAA (tNAA = NAA + NAAG) signal-to-noise ratio over the whole volume of interest was 12.1± 8.9 and the full width at half maximum of tNAA was 24.7± 9.6 Hz for the 2.75 × 2.75 × 2.75 mm³ resolution. The need for an increased spectral bandwidth in combination with spatio-spectral encoding imposed significant challenges on the gradient system, but the FID approach proved very robust to field inhomogeneities of ∆B0 = 45 ± 38 Hz (frequency offset ± spatial STD) and B1+ = 65 ± 11° within the MRSI volume of interest.

DISCUSSION

These preliminary findings highlight the potential of 10.5 T MRSI as a powerful imaging tool for probing cerebral metabolism. By providing unprecedented spatial and spectral resolution, this technology could offer a unique view into the metabolic intricacies of the human brain, but further technical developments will be necessary to optimize data quality and fully leverage the capabilities of 10.5 T MRSI.

RF coil design strategies for improving SNR at the ultrahigh magnetic field of 10.5T

PURPOSE

Toward pushing the boundaries of ultrahigh fields for human brain imaging, we wish to evaluate experimentally achievable SNR relative to ultimate intrinsic SNR (uiSNR) at 10.5T, develop design strategies toward approaching the latter, quantify magnetic field-dependent SNR gains, and demonstrate the feasibility of whole-brain, high-resolution human brain imaging at this uniquely high field strength.

METHODS

A dual row 16-channel self-decoupled transmit (Tx) and receive (Rx) array was developed for 10.5T using custom Tx/Rx switches. A 64-channel receive-only array was built to fit into the 16-channel Tx/Rx array. Electromagnetic modeling and experiments were used to define safe operational power limits. Experimental SNR was evaluated relative to uiSNR at 10.5T and 7T.

RESULTS

The 64-channel Rx array alone captured approximately 50% of the central uiSNR at 10.5T, while an identical array developed for 7T captured about 76% of uiSNR at 7T. The 16-channel Tx/80-channel Rx configuration brought the fraction of uiSNR captured at 10.5T to levels comparable to the 64-channel Rx array at 7T. SNR data displayed an approximateB 0 2 $$ {\mathrm{B}}_0^2 $$ dependence over a large central region when evaluated in the context of uiSNR. Whole-brain, high-resolutionT 2 * $$ {\mathrm{T}}_2^{\ast } $$ -weighted and T1-weighted anatomical and gradient-recalled-echo BOLD-EPI functional MRI images were obtained at 10.5T for the first time with such an advanced array.

CONCLUSION

We demonstrated the ability to approach the uiSNR at 10.5T over the human brain, achieving large SNR gains over 7T, currently the most commonly used ultrahigh-field platform. Whole-brain, high-resolution anatomical and EPI-based functional MRI data were obtained at 10.5T, illustrating the promise of greater than 10T fields in studying the human brain.

Modelling of coronary artery stenosis and study of hemodynamic under the influence of magnetic fields

Investigating magnetic blood flow characteristics through arteries and micron-size channels for clinical therapies in biomedicine is becoming increasingly important with the rise of point-of-care diagnostics devices. A computational fluid dynamics (CFD) investigation is conducted to explore blood flow within a coronary artery affected by an elliptical stenosis near the artery wall under the influence of a magnetic field. The novelty of our study is the integration of Navier-Stokes and Maxwell's equations to calculate body forces on fluid flow, coupled with the application of magnetic fields both longitudinally and vertically, and the use of the Carreau-Yasuda model to analyse non-Newtonian blood rheology. Blood flow is modelled by solving the incompressible continuity and momentum equations, considering laminar and non-Newtonian properties, with the finite element-based solver COMSOL Multiphysics. The CFD model is validated using previously published analytical and computational data. This study investigates the effects of magnetic fields on blood flow through stenotic arteries with 25 %, 35 %, and 50 % stenosis, examining how the magnetic field and its orientation impact variations in velocity profiles, pressure drop, and wall shear stress (WSS). Our results show that magnetic fields can effectively manipulate blood flow, causing acceleration or deceleration depending on field direction. Significant changes in hemodynamics are observed, particularly at 50 % arterial stenosis, highlighting the profound impact of stenosis on flow characteristics. Compared to healthy arteries, the velocity change in stenosed arteries increased by 16.5 %, 29.4 %, and 62.1 % for 25 %, 35 %, and 50 % stenosis, respectively. The findings advance experimental models of blood flow in magnetic fields, highlighting the critical importance of regulating blood velocity and pressure. These insights are particularly valuable for developing drug delivery systems and magnetic-driven blood pumps.

In vivo imaging of the human brain with the Iseult 11.7-T MRI scanner

The understanding of the human brain is one of the main scientific challenges of the twenty-first century. In the early 2000s, the French Atomic Energy Commission launched a program to conceive and build a human magnetic resonance imaging scanner operating at 11.7 T. We have now acquired human brain images in vivo at such a magnetic field. We deployed parallel transmission tools to mitigate the radiofrequency field inhomogeneity problem and tame the specific absorption rate. The safety of human imaging at such high field strength was demonstrated using physiological, vestibular, behavioral and genotoxicity measurements on the imaged volunteers. Our technology yields T2 and T2*-weighted images reaching mesoscale resolutions within short acquisition times and with a high signal and contrast-to-noise ratio.

A 128-channel receive array with enhanced SNR performance for 10.5 tesla brain imaging

Purpose

To develop and characterize the performance of a 128-channel head array for brain imaging at 10.5 tesla and evaluate the potential of brain imaging at this unique, >10 tesla magnetic field.

Methods

The coil is composed of a 16-channel self-decoupled loop transmit/receive array with a 112-loop receive-only (Rx) insert. Interactions between the outer transmitter and the inner 112Rx insert were mitigated using coaxial cable traps placed every 1/16 of a wavelength on each feed cable, locating most preamplifier boards outside the transmitter field and miniaturizing those placed directly on individual coils.

Results

The 128-channel array described herein achieved 77% of ultimate intrinsic SNR in the center of the brain. Transmit field maps obtained experimentally on a phantom with and without the receive array were similar and matched EM simulations, leading to FDA approval for human imaging. Anatomical and functional data, including with power demanding sequences, were acquired successfully on human volunteers.

Conclusions

Counterintuitive to expectations based on magnetic fields ≤7T, the higher channel counts provided SNR gains centrally, capturing ∼80% uiSNR. Fraction of uiSNR achieved centrally in 64Rx, 80Rx, and 128Rx arrays suggested that a plateau was being reached at 80%. At this plateau, linear to approximately quadratic B 0 dependent SNR gains for the periphery and the center, respectively, were observed for 10.5T relative 7T.

Performance of receive head arrays versus ultimate intrinsic SNR at 7 T and 10.5 T

PURPOSE

We examined magnetic field dependent SNR gains and ability to capture them with multichannel receive arrays for human head imaging in going from 7 T, the most commonly used ultrahigh magnetic field (UHF) platform at the present, to 10.5 T, which represents the emerging new frontier of >10 T in UHFs.

METHODS

Electromagnetic (EM) models of 31-channel and 63-channel multichannel arrays built for 10.5 T were developed for 10.5 T and 7 T simulations. A 7 T version of the 63-channel array with an identical coil layout was also built. Array performance was evaluated in the EM model using a phantom mimicking the size and electrical properties of the human head and a digital human head model. Experimental data was obtained at 7 T and 10.5 T with the 63-channel array. Ultimate intrinsic SNR (uiSNR) was calculated for the two field strengths using a voxelized cloud of dipoles enclosing the phantom or the digital human head model as a reference to assess the performance of the two arrays and field depended SNR gains.

RESULTS

uiSNR calculations in both the phantom and the digital human head model demonstrated SNR gains at 10.5 T relative to 7 T of 2.6 centrally, ˜2 at the location corresponding to the edge of the brain, ˜1.4 at the periphery. The EM models demonstrated that, centrally, both arrays captured ˜90% of the uiSNR at 7 T, but only ˜65% at 10.5 T, leading only to ˜2-fold gain in array SNR in going from 7 to 10.5 T. This trend was also observed experimentally with the 63-channel array capturing a larger fraction of the uiSNR at 7 T compared to 10.5 T, although the percentage of uiSNR captured were slightly lower at both field strengths compared to EM simulation results.

CONCLUSIONS

Major uiSNR gains are predicted for human head imaging in going from 7 T to 10.5 T, ranging from ˜2-fold at locations corresponding to the edge of the brain to 2.6-fold at the center, corresponding to approximately quadratic increase with the magnetic field. Realistic 31- and 63-channel receive arrays, however, approach the central uiSNR at 7 T, but fail to do so at 10.5 T, suggesting that more coils and/or different type of coils will be needed at 10.5 T and higher magnetic fields.

RF coil design strategies for improving SNR at the ultrahigh magnetic field of 10.5 Tesla

Purpose

To develop multichannel transmit and receive arrays towards capturing the ultimate-intrinsic-SNR (uiSNR) at 10.5 Tesla (T) and to demonstrate the feasibility and potential of whole-brain, high-resolution human brain imaging at this high field strength.

Methods

A dual row 16-channel self-decoupled transmit (Tx) array was converted to a 16Tx/Rx transceiver using custom transmit/receive switches. A 64-channel receive-only (64Rx) array was built to fit into the 16Tx/Rx array. Electromagnetic modeling and experiments were employed to define safe operation limits of the resulting 16Tx/80Rx array and obtain FDA approval for human use.

Results

The 64Rx array alone captured approximately 50% of the central uiSNR at 10.5T while the identical 7T 64Rx array captured ∼76% of uiSNR at this lower field strength. The 16Tx/80Rx configuration brought the fraction of uiSNR captured at 10.5T to levels comparable to the performance of the 64Rx array at 7T. SNR data obtained at the two field strengths with these arrays displayed dependent increases over a large central region. Whole-brain high resolution T 2 * and T 1 weighted anatomical and gradient-recalled echo EPI BOLD fMRI images were obtained at 10.5T for the first time with such an advanced array, illustrating the promise of >10T fields in studying the human brain.

Conclusion

We demonstrated the ability to approach the uiSNR at 10.5T over the human brain with a novel, high channel count array, achieving large SNR gains over 7T, currently the most commonly employed ultrahigh field platform, and demonstrate high resolution and high contrast anatomical and functional imaging at 10.5T.

Changes in tissue sodium concentration and sodium relaxation times during the maturation of human knee cartilage: Ex vivo 23 Na MRI study at 10.5 T

PURPOSE

To evaluate the influence of skeletal maturation on sodium (23 Na) MRI relaxation parameters and the accuracy of tissue sodium concentration (TSC) quantification in human knee cartilage.

METHODS

Twelve pediatric knee specimens were imaged with whole-body 10.5 T MRI using a density-adapted 3D radial projection sequence to evaluate 23 Na parameters: B1 + , T1 , biexponentialT 2 * $$ {\mathrm{T}}_2^{\ast } $$ , and TSC. Water, collagen, and sulfated glycosaminoglycan (sGAG) content were calculated from osteochondral biopsies. The TSC was corrected for B1 + , relaxation, and water content. The literature-based TSC (TSCLB ) used previously published values for corrections, whereas the specimen-specific TSC (TSCSP ) used measurements from individual specimens. 23 Na parameters were evaluated in eight cartilage compartments segmented on proton images. Associations between 23 Na parameters, TSCLB  - TSCSP difference, biochemical content, and age were determined.

RESULTS

From birth to 12 years, cartilage water content decreased by 18%; collagen increased by 59%; and sGAG decreased by 36% (all R2  ≥ 0.557). The shortT 2 * $$ {\mathrm{T}}_2^{\ast } $$ (T 2 * S $$ {{\mathrm{T}}_2^{\ast}}_{\mathrm{S}} $$ ) decreased by 72%, and the signal fraction relaxing withT 2 * S $$ {{\mathrm{T}}_2^{\ast}}_{\mathrm{S}} $$ (fT 2 * S $$ {{\mathrm{fT}}_2^{\ast}}_{\mathrm{S}} $$ ) increased by 55% during the first 5 years but remained relatively stable after that. TSCSP was significantly correlated with sGAG content from biopsies (R2  = 0.739). Depending on age, TSCLB showed higher or lower values than TSCSP . The TSCLB  - TSCSP difference was significantly correlated withT 2 * S $$ {{\mathrm{T}}_2^{\ast}}_{\mathrm{S}} $$ (R2  = 0.850),fT 2 * S $$ {{\mathrm{fT}}_2^{\ast}}_{\mathrm{S}} $$ (R2  = 0.651), and water content (R2  = 0.738).

CONCLUSION

TSC and relaxation parameters measured with 23 Na MRI provide noninvasive information about changes in sGAG content and collagen matrix during cartilage maturation. Cartilage TSC quantification assuming fixed relaxation may be feasible in children older than 5 years.

Effects of ultra-high field MRI environment on cognitive performance in healthy participants

INTRODUCTION

Ultra-high field MRI (UHF MRI) is rapidly becoming an essential part of our toolbox within health care and research studies; therefore, we need to get a deeper understanding of the physiological effects of ultra-high field. This study aims to investigate the cognitive performance of healthy participants in a 7 T (T) MRI environment in connection with subjectively experienced effects.

METHODS

We measured cognitive performance before and after a 1-h 7T MRI scanning session using a Digit Symbol Substitution Test (DSST) in 42 subjects. Furthermore, a computer-based survey regarding the subjectively experienced effects in connection with the MRI examination was distributed. Similarly, two DSSTs were also performed by a control group of 40 participants.

RESULTS

Even though dizziness was the strongest sensory perception in connection to the MRI scanning, we did not find any correlation between dizziness and cognitive performance. Whilst the control group improved (p=<0.001) on their second DSST the MRI group showed no significant difference (p=0.741) in the DSST before and after MRI scanning.

CONCLUSION

Transient effect on cognition after undergoing MRI scanning can't be ruled out as the expected learning effect on the DSST was not observed.

IMPLICATIONS FOR PRACTICE

Increasing understanding of the possible adverse effects may guide operators in performing UHF MRI in a safe way and with person-centered care. Furthermore, it can guide researchers in setting up research protocols to minimize confounding factors in their fMRI studies due to the transient adverse effects of the UHF environment.

11.4 T ultra-high static magnetic field has no effect on morphology but induces upregulation of TNF signaling pathway based on transcriptome analysis in zebrafish embryos

As magnetic resonance imaging (MRI) scanners with ultra-high field (UHF) have optimal performance, scientists have been working to develop high-performance devices with strong magnetic fields to improve their diagnostic potential. However, whether an MRI scanner with UHF poses a risk to the safety of the organism require further evaluation. This study evaluated the effects of 11.4 Tesla (T) UHF on embryonic development using a zebrafish model. Multiple approaches, including morphological parameters, physiological behaviors, and analyses of the transcriptome at the molecular level, were determined during 5 days after laboratory-controlled exposure from 6 hour post fertilization (hpf) to 24 hpf. No significant effects were observed in embryo mortality, hatching rate, body length, Left-Right patterning, locomotor behavior, etc. RNA-sequencing analysis revealed up-regulated tumor necrosis factor (TNF) inflammatory factors and activated TNF signaling pathways in the 11.4 T exposure group. The results were further validated using qPCR. Our findings indicate that although UHF exposure under 11.4 T has no effect on the development of zebrafish embryos, it has specific effects on the immune response that require further investigation.

Germany's journey toward 14 Tesla human magnetic resonance

Multiple sites within Germany operate human MRI systems with magnetic fields either at 7 Tesla or 9.4 Tesla. In 2013, these sites formed a network to facilitate and harmonize the research being conducted at the different sites and make this technology available to a larger community of researchers and clinicians not only within Germany, but also worldwide. The German Ultrahigh Field Imaging (GUFI) network has defined a strategic goal to establish a 14 Tesla whole-body human MRI system as a national research resource in Germany as the next progression in magnetic field strength. This paper summarizes the history of this initiative, the current status, the motivation for pursuing MR imaging and spectroscopy at such a high magnetic field strength, and the technical and funding challenges involved. It focuses on the scientific and science policy process from the perspective in Germany, and is not intended to be a comprehensive systematic review of the benefits and technical challenges of higher field strengths.

Radiofrequency antenna concepts for human cardiac MR at 14.0 T

OBJECTIVE

To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx).

MATERIALS AND METHODS

RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B₁⁺) uniformity and efficiency in the heart of the human voxel model. B₁⁺ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR_10g) were examined at 7.0 T and 14.0 T.

RESULTS

At 14.0 T static pTx revealed a minimum B₁⁺_ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR_10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B₁⁺_ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B₁⁺_ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR_10g < 5.25 W/kg.

DISCUSSION

MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.

Commissioning of the Iseult CEA 11.7 T whole-body MRI: current status, gradient-magnet interaction tests and first imaging experience

OBJECTIVES

The Iseult MRI is an actively shielded whole-body magnet providing a homogeneous and stable magnetic field of 11.7 T. After nearly 20 years of research and development, the magnet successfully reached its target field strength for the first time in 2019. This article reviews its commissioning status, the gradient-magnet interaction test results and first imaging experience.

MATERIALS AND METHODS

Vibration, acoustics, power deposition in the He bath, and field monitoring measurements were carried out. Magnet safety system was tested against outer magnetic perturbations, and calibrated to define a safe operation of the gradient coil. First measurements using parallel transmission were also performed on an ex-vivo brain to mitigate the RF field inhomogeneity effect.

RESULTS

Acoustics measurements show promising results with sound pressure levels slightly above the enforced limits only at certain frequency intervals. Vibrations of the gradient coil revealed a linear trend with the B₀ field only in the worst case. Field monitoring revealed some resonances at some frequencies that are still under investigation.

DISCUSSION

Gradient-magnet interaction tests at up to 11.7 T are concluded. The scanner is now kept permanently at field and the final calibrations are on-going to pave the road towards the first acquisitions on volunteers.

The Promise of Magnetic Resonance Imaging in Radiation Oncology Practice in the Management of Brain, Prostate, and GI Malignancies

Magnetic resonance imaging (MRI) has a key role to play at multiple steps of the radiotherapy (RT) treatment planning and delivery process. Development of high-precision RT techniques such as intensity-modulated RT, stereotactic ablative RT, and particle beam therapy has enabled oncologists to escalate RT dose to the target while restricting doses to organs at risk (OAR). MRI plays a critical role in target volume delineation in various disease sites, thus ensuring that these high-precision techniques can be safely implemented. Accurate identification of gross disease has also enabled selective dose escalation as a means to widen the therapeutic index. Morphological and functional MRI sequences have also facilitated an understanding of temporal changes in target volumes and OAR during a course of RT, allowing for midtreatment volumetric and biological adaptation. The latest advancement in linear accelerator technology has led to the incorporation of an MRI scanner in the treatment unit. MRI-guided RT provides the opportunity for MRI-only workflow along with online adaptation for either target or OAR or both. MRI plays a key role in post-treatment response evaluation and is an important tool for guiding decision making. In this review, we briefly discuss the RT-related applications of MRI in the management of brain, prostate, and GI malignancies.

Evaluating the biological safety on mice at 16 T static magnetic field with 700 MHz radio-frequency electromagnetic field

OBJECTIVES

This study evaluated the associated biological effects of radio-frequency (RF) exposure at 16 T magnetic resonance imaging (MRI) on mice health.

MATERIAL AND METHODS

A total of 48 healthy 8-week-old male C57BL/6 mice were investigated. A 16 T high static magnetic field (HiSMF) was generated by a superconducting magnet, and a radiofrequency (RF) electromagnetic field for hydrogen resonance at 16 T (700 MHz) was transmitted via a homemade RF system. The mice were exposed inside the 16 T HiSMF with the 700 MHz RF field for 60 min, and the body weight, organ coefficients, histomorphology of major organs, and blood indices were analyzed for the basal state of the mice on day 0 and day 14. The Heat Shock Protein 70 (HSP70), cyclooxygenase 2 (COX2), and interleukin- 6 (IL-6) were used to evaluate the thermal effects on the brain. Locomotor activity, the open field test, tail suspension test, forced swimming test, and grip strength test were used to assess the behavioral characteristics of the mice.

RESULTS

The 16 T HiSMF with 700 MHz RF electromagnetic field exposure had no significant effects on body weight, organ coefficients, or histomorphology of major organs in the mice. On day 0, the expressions of HSP70 and COX2 in the brain were increased by 16 T HiSMF with 700 MHz RF electromagnetic field exposure. However, the expression of HSP70, COX2, and IL-6 had no significant difference compared with the sham group on day 14. Compared with the sham groups, the meancorpuscularvolume (MCV) on day 0 and the total protein (TP) on day 14 were increased significantly, whereas the other blood indices did not change significantly. The 16 T HiSMF with 700 MHz RF electromagnetic field exposure caused the mice to briefly circle tightly but had no effect on other behavioral indicators.

CONCLUSIONS

In summary, 16 T HiSMF with 700 MHz RF electromagnetic field exposure for 60 min did not have severe effects on mice.

Effects of High Magnetic Fields on the Diffusion of Biologically Active Molecules

The diffusion of biologically active molecules is a ubiquitous process, controlling many mechanisms and the characteristic time scales for pivotal processes in living cells. Here, we show how a high static magnetic field (MF) affects the diffusion of paramagnetic and diamagnetic species including oxygen, hemoglobin, and drugs. We derive and solve the equation describing diffusion of such biologically active molecules in the presence of an MF as well as reveal the underlying mechanism of the MF’s effect on diffusion. We found that a high MF accelerates diffusion of diamagnetic species while slowing the diffusion of paramagnetic molecules in cell cytoplasm. When applied to oxygen and hemoglobin diffusion in red blood cells, our results suggest that an MF may significantly alter the gas exchange in an erythrocyte and cause swelling. Our prediction that the diffusion rate and characteristic time can be controlled by an MF opens new avenues for experimental studies foreseeing numerous biomedical applications.

7 Tesla and Beyond: Advanced Methods and Clinical Applications in Magnetic Resonance Imaging

ABSTRACT

Ultrahigh magnetic fields offer significantly higher signal-to-noise ratio, and several magnetic resonance applications additionally benefit from a higher contrast-to-noise ratio, with static magnetic field strengths of B0 ≥ 7 T currently being referred to as ultrahigh fields (UHFs). The advantages of UHF can be used to resolve structures more precisely or to visualize physiological/pathophysiological effects that would be difficult or even impossible to detect at lower field strengths. However, with these advantages also come challenges, such as inhomogeneities applying standard radiofrequency excitation techniques, higher energy deposition in the human body, and enhanced B0 field inhomogeneities. The advantages but also the challenges of UHF as well as promising advanced methodological developments and clinical applications that particularly benefit from UHF are discussed in this review article.

Non-Invasive Analysis of Human Liver Metabolism by Magnetic Resonance Spectroscopy

The liver is a key node of whole-body nutrient and fuel metabolism and is also the principal site for detoxification of xenobiotic compounds. As such, hepatic metabolite concentrations and/or turnover rates inform on the status of both hepatic and systemic metabolic diseases as well as the disposition of medications. As a tool to better understand liver metabolism in these settings, in vivo magnetic resonance spectroscopy (MRS) offers a non-invasive means of monitoring hepatic metabolic activity in real time both by direct observation of concentrations and dynamics of specific metabolites as well as by observation of their enrichment by stable isotope tracers. This review summarizes the applications and advances in human liver metabolic studies by in vivo MRS over the past 35 years and discusses future directions and opportunities that will be opened by the development of ultra-high field MR systems and by hyperpolarized stable isotope tracers.

Occupational exposure to electromagnetic fields in magnetic resonance environment: an update on regulation, exposure assessment techniques, health risk evaluation, and surveillance

Magnetic resonance imaging (MRI) is one of the most-used diagnostic imaging methods worldwide. There are ∼50,000 MRI scanners worldwide each of which involves a minimum of five workers from different disciplines who spend their working days around MRI scanners. This review analyzes the state of the art of literature about the several aspects of the occupational exposure to electromagnetic fields (EMF) in MRI: regulations, literature studies on biological effects, and health surveillance are addressed here in detail, along with a summary of the main approaches for exposure assessment. The original research papers published from 2013 to 2021 in international peer-reviewed journals, in the English language, are analyzed, together with documents published by legislative bodies. The key points for each topic are identified and described together with useful tips for precise safeguarding of MRI operators, in terms of exposure assessment, studies on biological effects, and health surveillance.

Long-term behavioral effects observed in mice chronically exposed to static ultra-high magnetic fields

PURPOSE

The primary goal of this study was to investigate whether chronic exposures to ultra-high B₀ fields can induce long-term cognitive, behavioral, or biological changes in C57BL/6 mice.

METHODS

C57BL/6 mice were chronically exposed to 10.5-T or 16.4-T magnetic fields (3-h exposures, two exposure sessions per week, 4 or 8 weeks of exposure). In vivo single-voxel ¹ H magnetic resonance spectroscopy was used to investigate possible neurochemical changes in the hippocampus. In addition, a battery of behavioral tests, including the Morris water-maze, balance-beam, rotarod, and fear-conditioning tests, were used to examine long-term changes induced by B₀ exposures.

RESULTS

Hippocampal neurochemical profile, cognitive, and basic motor functions were not impaired by chronic magnetic field exposures. However, the balance-beam-walking test and the Morris water-maze testing revealed B₀ -induced changes in motor coordination and balance. The tight-circling locomotor behavior during Morris water-maze tests was found as the most sensitive factor indexing B₀ -induced changes. Long-term behavioral changes were observed days or even weeks subsequent to the last B₀ exposure at 16.4 T but not at 10.5 T. Fast motion of mice in and out of the 16.4-T magnet was not sufficient to induce such changes.

CONCLUSION

Observed results suggest that the chronic exposure to a magnetic field as high as 16.4 T may result in long-term impairment of the vestibular system in mice. Although observation of mice may not directly translate to humans, nevertheless, they indicate that studies focused on human safety at very high magnetic fields are necessary.