Surface Coil Research Articles

Body Interventional MRI for Diagnostic and Interventional Radiologists: Current Practice and Future Prospects.

Clinical use of MRI for guidance during interventional procedures emerged shortly after the introduction of clinical diagnostic MRI in the late 1980s. However, early applications of interventional MRI (iMRI) were limited owing to the lack of dedicated iMRI magnets, pulse sequences, and equipment. During the 3 decades that followed, technologic advancements in iMRI magnets that balance bore access and field strength, combined with the development of rapid MRI pulse sequences, surface coils, and commercially available MR-conditional devices, led to the rapid expansion of clinical iMRI applications, particularly in the field of body iMRI. iMRI offers several advantages, including superior soft-tissue resolution, ease of multiplanar imaging, lack of ionizing radiation, and capability to re-image the same section. Disadvantages include longer examination times, lack of MR-conditional equipment, less operator familiarity, and increased cost. Nonetheless, MRI guidance is particularly advantageous when the disease is best visualized with MRI and/or when superior soft-tissue contrast is needed for treatment monitoring. Safety in the iMRI environment is paramount and requires close collaboration among interventional radiologists, MR physicists, and all other iMRI team members. The implementation of risk-limiting measures for personnel and equipment in MR zones III and IV is key. Various commercially available MR-conditional needles, wires, and biopsy and ablation devices are now available throughout the world, depending on the local regulatory status. As such, there has been tremendous growth in the clinical applications of body iMRI, including localization of difficult lesions, biopsy, sclerotherapy, and cryoablation and thermal ablation of malignant and nonmalignant soft-tissue neoplasms. Online supplemental material is available for this article. ©RSNA, 2021.

Role of MRI in the evaluation of spinal trauma

Aim: Role of MRI in the Evaluation of Spina Trauma. Material and methods: The present prospective observational study was on 50 patients with clinical suspicion of spinal trauma referred to Department of Radio diagnosis, from OPD/IPD of C.S.S.Hospital, Subharti Medical College, Meerut. After obtaining clinical history relevant clinical examination was done. MRI examinations were done on GE – Signa HDe contour GE 1.5 Tesla Feiloversikt, whole body MR scanner with sense surface coil and then evaluation of M R Imaging was done by using different pulse sequences. The findings were viewed in the light of complete clinical and radiographic data. Results: 78%, subjects were male, hence there was male preponderance with age group of 31-40 years with compression fracture in 72% & retropulsion of vertebral body. Spinal cord oedema was found among78% with maximum no of cases, having cord oedema >3 cm. AIS grade A, B, C, D and E was found among 20%, 20%,16%, 22% and 22% of cases respectively. Sensory & Motor loss in 24% & 74% of cases. Sensory loss was corresponded with level of spinal cord oedema & level of vertebrae fracture. Discussion: MRI plays a crucial role in evaluating and detecting spinal trauma. Subtle bone marrow, soft-tissue, and spinal cord abnormalities, which may not be apparent on other imaging modalities, can be readily detected on MRI. Early detection often leads to prompt and accurate diagnosis, expeditious management, and avoidance of unnecessary procedures. The depiction of parenchymal SCI on MRI not only correlates well with the degree of neurologic deficit, but it also bears significant implications in regard to prognosis and potential for neurologic recovery. Conclusion: With this study we concluded that MRI findings in spinal trauma correlate with the clinical findings according to ASIA impairment scale and can be helpful to clinician in predicting the outcome.

Inductively Coupled Intraoral Flexible Coil for Increased Visibility of Dental Root Canals in Magnetic Resonance Imaging.

Accurate visualization of dental root canals is vital for the correct diagnosis and subsequent treatment. This work assesses the improvement of a dedicated new coil for dental magnetic resonance imaging (MRI) in comparison to conventional ones in terms of signal-to-noise ratio (SNR) and visibility. A newly developed intraoral flexible coil was used to display dental roots with MRI, and it provides improved sensitivity with a loop design and size adjusted to a single tooth anatomy. Ex vivo and in vivo measurements were performed on a 3 T clinical MR system, and results were compared with conventional head and surface coil images. Additional comparison was performed with a modified fast spin echo sequence and a constructive interference in steady-state sequence. Ex vivo, an SNR gain of 6.3 could be achieved with the intraoral flexible coil setup, and higher visibility down to 200 μm was possible, whereas the external loop coil is limited to 400 μm. In vivo measurements in a volunteer resulted in an SNR gain of up to 4.5 with an improved delineation of the root canals, especially for the branch tissue splitting of the mesial root canal into mesial-buccal and mesial-lingual. In summary, we showed the feasibility of implementing a wireless coil approach with readily available dental practice materials for sealing and placement. Highly improved MRI scans can be acquired within clinically feasible scan times, and this might provide additional medical findings to supplement available x-ray images.

Flexible Segmented Surface Coil Resonator for In Vivo EPR Measurements in Human Subjects

Flexible Segmented Surface Coil Resonator for In Vivo EPR Measurements in Human Subjects

Network and Field Analysis of Koch Snowflake Fractal Geometry Radiofrequency Coils for Sodium MRI

Sodium is one of the most abundant physiological cations and is a key element in many cellular processes. It has been shown that several pathologies, including degenerative brain disorders, cancers, and brain traumas, express sodium deviations from normal. Therefore, sodium magnetic resonance imaging (MRI) can prove to be valuable for physicians. However, sodium MRI has its limitations, the most significant being a signal-to-noise ratio (SNR) thousands of times lower than a typical proton MRI. Radiofrequency coils are the components of the MRI system directly responsible for signal generation and acquisition. This paper explores the intrinsic properties of a Koch snowflake fractal radiofrequency surface coil compared to that of a standard circular surface coil to investigate a fractal geometry’s role in increasing SNR of sodium MRI scans. By first analyzing the network parameters of the two coils, it was found that the fractal coil had a better impedance match than the circular coil when loaded by various anatomical regions. Although this maximizes signal transfer between the coil and the system, this is at the expense of a lower Q, indicating greater signal loss between the tissue and coil. A second version of each coil was constructed to test the mutual inductance between the coils of the same geometry to see how they would behave as a phased array. It was found that the fractal coils were less sensitive to each other than the two circular coils, which would be beneficial when constructing and using phased array systems. The performance of each coil was then assessed for B1+ field homogeneity and signal. A sodium phantom was imaged using a B1+ mapping sequence, and a 3D radial acquisition was performed to determine SNR and image quality. The results indicated that the circular coil had a more homogeneous field and higher SNR. Overall while the circular coil proved to generate a higher signal-to-noise ratio than the fractal, the Koch coil showed higher versatility when in a multichannel network which could prove to be a benefit when designing, constructing, and using a phased array coil.

A Novel Energy Harvesting Circuit for RF Surface Coils in the MRI System.

RF surface coils are commonly used as receivers in Magnetic Resonance Imaging (MRI) systems to acquire sensitive signals from the human body. These coils rely on cables for power and transferring information from the patient to the computer for processing. Higher image quality and faster scan times are possible by using an array of surface coils, and there is a constant need for high-density surface coil arrays. Each array element utilizes at least three cables and, increasing the number of elements in the array also increases the number of cables, making the cable bundle bulkier. This makes the placement of cables complicated for the operators and may cause patient harm when improperly positioned. Wireless technologies can eliminate cables, and this paper proposes a novel design for harvesting the ambient RF energy present during the transmit phase of the MRI system operation. After introducing the surface coil's building blocks, the importance of the decoupler as a mechanism for safety and image quality is detailed. The paper presents the analysis and design of an RF energy harvesting circuit that couples to the decoupler circuit. Its performance is tested both in simulation and the Philips Ingenia 3.0 T MRI system. The results show that the circuit successfully harvests energy, up to 1 W, during the MRI's transmit phase without any adverse effects on the decoupler or surface coil. To make energy harvesting (EH) beneficial, a new GaN -based FET switch that consumes low power is also proposed.

Design, simulation, and test of surface and volume radio frequency coils for 13C magnetic resonance imaging and spectroscopy.

Hyperpolarized 13C Magnetic Resonance (MR) is a promising technique for in vivo non-invasive assessment of metabolism in humans. Despite the considerable signal increase provided by hyperpolarization techniques, the low molar concentration of derivate 13C metabolites gives rise to technological limits in terms of data quality. The development of dedicated radio frequency coils, capable of providing a large field of view with high signal-to-noise ratio data, is thus a fundamental task. This work describes the design, simulation, and test of a surface and a volume coil, both designed to be integrated with a clinical scanner for hyperpolarized 13C studies in small animal models, with the purpose to provide a detailed characterization and comparison of their performance. In particular, coil inductance was evaluated with analytical calculation, while the magnetostatic theory was employed for coils magnetic field pattern estimation. Workbench tests permitted us to characterize coil performance in terms of quality factor and efficiency. Additionally, this Tutorial summarizes the acquisition experience for the reconstruction of 13C spectroscopic maps in phantom using the two designed coils and a 3T MR clinical scanner. We believe that this Tutorial could be interesting for graduate students and researchers in the field of magnetic resonance coil design and development, especially for 13C studies.

Study of MRI Transmit/Receive Coils for 7T/300 MHz Application

A new type of high frequency RF Microstrip surface coil (transmit/receive) was proposed for Magnetic Resonance Imaging (MRI) applications at 7T /300 MHz. Planar RF Microstrip surface coil is formed from the ring resonator loaded with inductor (via) and an interdigital capacitor on a substrate. A detailed simulation study is carried out on this proposed RF Microstrip surface coil detector and its characteristics (resonant frequency, Signal to noise ratio (SNR) and specific absorption rate) comparing with the conventional loop coil detector in the frequency range of 300 MHz/7T for MRI application.

“WHAT MRI CAN DO IN SUSPECTED NON-DEGENRATIVE CASES OF COMPRESSIVE MYELOPATHY”

BACKGROUND: Compressive Myelopathy is described as the spinal cord compression either from outside or within the cord itself. Compression may be due to Herniated disc, post traumatic compression by fracture / displaced Vertebra, epidural hemorrhage / abscess or Epidural / Intradural (Intramedullary and Extramedullary) neoplasm. Study aimed to to study the role of MRI in evaluation of compressive myelopathy MATERIAL & METHOD: It is a cross sectional observational study conducted during Jan 2019 to June 2020 in patients presenting to the Department of Radiodiagnosis with features of compressive myelopathy at Sharda Hospital, SMS&R. Total of 30 patients who fullled inclusion criteria and provided the informed consent. Philips Achieva 3.0T MRI. Standard surface coils and body coils, were used for cervical, thoracic and Lumbar spine for acquisition of images was used to assess the compressive myelopathy. RESULTS: In present study, total of 30 patients were included in the present study. Among them 20 were males and 10 were female with the ratio of 2:1 showing the male predominance. The mean age of the patients was found to be 39.23 years. Extra dural compartment was the most commonly involved (n=26). POTTs (n=12) and TM (n=11) were most common located in extradural compartment, followed by metastasis (n=2). (p<0.001) CONCLUSION: MRI was able to successfully classify the spinal tumor based on Extradural / Intradural position and evaluate the integrity of the spinal cord, intervertebral disks and ligament following acute spinal trauma.

Magnetic resonance imaging-guided lumbar nerve root infiltrations: optimization of an in-house protocol

BackgroundFor the treatment of radicular pain, nerve root infiltrations can be performed under MRI guidance in select, typically younger, patients where repeated CT exams are not desirable due to associated radiation risk, or potential allergic reactions to iodinated contrast medium.MethodsFifteen 3 T MRI-guided nerve root infiltrations were performed in 12 patients with a dedicated surface coil combined with the standard spine coil, using a breathhold PD sequence. The needle artifact on the MR images and the distance between the needle tip and the infiltrated nerve root were measured.ResultsThe distance between the needle tip and the nerve root was 2.1 ± 1.4 mm. The visual artifact width, perpendicular to the needle long axis, was 2.1 ± 0.7 mm. No adverse events were reported.ConclusionThis technical note describes the optimization of the procedure in a 3 T magnetic field, including reported procedure time and an assessment of targeting precision.

A local multi-transmit coil combined with a high-density receive array for cerebellar fMRI at 7 T.

The human cerebellum is involved in a wide array of functions, ranging from motor control to cognitive control, and as such is of great neuroscientific interest. However, its function is underexplored in vivo, due to its small size, its dense structure and its placement at the bottom of the brain, where transmit and receive fields are suboptimal. In this study, we combined two dense coil arrays of 16 small surface receive elements each with a transmit array of three antenna elements to improve BOLD sensitivity in the human cerebellum at 7 T. Our results showed improved B 1 + and SNR close to the surface as well as g‐factor gains compared with a commercial coil designed for whole‐head imaging. This resulted in improved signal stability and large gains in the spatial extent of the activation close to the surface (<3.5 cm), while good performance was retained deeper in the cerebellum. Modulating the phase of the transmit elements of the head coil to constructively interfere in the cerebellum improved the B 1 +, resulting in a temporal SNR gain. Overall, our results show that a dedicated transmit array along with the SNR gains of surface coil arrays can improve cerebellar imaging, at the cost of a decreased field of view and increased signal inhomogeneity.

Bioactive refinement for endosaccular treatment of intracranial aneurysms.

Endovascular treatment is the first-line therapy for most intracranial aneurysms; however, recanalisation remains a major limitation. Developments in bioengineering and material science have led to a novel generation of coil technologies for aneurysm embolisation that address clinical challenges of aneurysm recurrence. This review presents an overview of modified surface coil technologies and summarises the state of the art regarding their efficacy and limitations based on experimental and clinical results. We also present potential perspectives to develop biologically optimised devices.

The Value of 3 Tesla Field Strength for Musculoskeletal Magnetic Resonance Imaging.

Musculoskeletal magnetic resonance imaging (MRI) is a careful negotiation between spatial, temporal, and contrast resolution, which builds the foundation for diagnostic performance and value. Many aspects of musculoskeletal MRI can improve the image quality and increase the acquisition speed; however, 3.0-T field strength has the highest impact within the current diagnostic range. In addition to the favorable attributes of 3.0-T field strength translating into high temporal, spatial, and contrast resolution, many 3.0-T MRI systems yield additional gains through high-performance gradients systems and radiofrequency pulse transmission technology, advanced multichannel receiver technology, and high-end surface coils. Compared with 1.5 T, 3.0-T MRI systems yield approximately 2-fold higher signal-to-noise ratios, enabling 4 times faster data acquisition or double the matrix size. Clinically, 3.0-T field strength translates into markedly higher scan efficiency, better image quality, more accurate visualization of small anatomic structures and abnormalities, and the ability to offer high-end applications, such as quantitative MRI and magnetic resonance neurography. Challenges of 3.0-T MRI include higher magnetic susceptibility, chemical shift, dielectric effects, and higher radiofrequency energy deposition, which can be managed successfully. The higher total cost of ownership of 3.0-T MRI systems can be offset by shorter musculoskeletal MRI examinations, higher-quality examinations, and utilization of advanced MRI techniques, which then can achieve higher gains and value than lower field systems. We provide a practice-focused review of the value of 3.0-T field strength for musculoskeletal MRI, practical solutions to challenges, and illustrations of a wide spectrum of gainful clinical applications.

A 16-Channel 13C Array Coil for Magnetic Resonance Spectroscopy of the Breast at 7T.

Considering the reported elevation of ω-6/ω-3 fatty acid ratios in breast neoplasms, one particularly important application of 13C MRS could be in more fully understanding the breast lipidome's relationship to breast cancer incidence. However, the low natural abundance and gyromagnetic ratio of the 13C isotope lead to detection sensitivity challenges. Previous 13C MRS studies have relied on the use of small surface coils with limited field-of-view and shallow penetration depths to achieve adequate signal-to-noise ratio (SNR), and the use of receive array coils is still mostly unexplored. This work presents a unilateral breast 16-channel 13C array coil and interfacing hardware designed to retain the surface sensitivity of a single small loop coil while improving penetration depth and extending the field-of-view over the entire breast at 7T. The coil was characterized through bench measurements and phantom 13C spectroscopy experiments. Bench measurements showed receive coil matching better than -17 dB and average preamplifier decoupling of 16.2 dB with no evident peak splitting. Phantom MRS studies show better than a three-fold increase in average SNR over the entirety of the breast region compared to volume coil reception alone as well as an ability for individual array elements to be used for coarse metabolite localization without the use of single-voxel or spectroscopic imaging methods. Our current study has shown the benefits of the array. Future in vivo lipidomics studies can be pursued. Development of the 16-channel breast array coil opens possibilities of in vivo lipidomics studies to elucidate the link between breast cancer incidence and lipid metabolics.

FC 054FUNCTIONAL SODIUM MAGNETIC RESONANCE IMAGING OF THE HUMAN KIDNEY

Abstract Background and Aims Maintenance of a cortico-medullary concentration gradient (CMG) required for urine concentration, is one of most important tubular function. However, we are lacking of functional tubular parameters to explore this function. The only tool available to assess it currently, is urinary osmolarity that is an indirect and nonspecific maker of CMG. In this study, we explore the ability of 23NaMRI in measuring 1) the dynamics of CMG for the first time compared to urinary osmolarity after a water load 2) the CMG in kidney disease. Method We conducted an exploratory pilot study for 10 healthy controls with water load then 5 cardiorenal patients with kidney disease. 1) Healthy controls were asked to be fasting since midnight. Urines sample were collected to measure fasting osmolarity and a first MRIscan were performed to acquire baseline anatomical and sodium images. Once the baseline was completed, healthy participants were asked to ingest water (15 mL/kg) within 15 minutes. Four subsequent sodium pictures were acquired an hour after water ingestion. Urine samples were obtained after each sodium acquisition every 15 min during one hours. 2) Cardiorenal patients underwent an MRI scan, provided a spot urine sample and have blood work collected. All MR experiments were carried out on a GE MR750 3T (GE Healthcare, WI). A custom-built two-loop (18cm in diameter) butterfly radiofrequency surface coil tuned for 23Na frequency (33.786 MHz) was used to acquire renal 23Na images. Results Mean age of the 10 healthy controls was 41.8 ± 15.3 years, mean body mass index (BMI) was 24.3 ± 3.8 kg/m2. Mean water intake was 1092 ± 233 mL, total water excreted was 1250 ± 301 mL . Mean age of the 5 cardiorenal patients was 76.6 ± 12.2 years, mean BMI was 28.1 ± 6.9 kg/m2. eGFR was 54 ± 37 mL/min/1.73m2. Urinary osmolarity was 498 ± 145 mosm/L and medulla/cortex ratio was 1.35 ± 0.11. Sodium imaging was successfully acquired in all volunteers. In the morning fasting, medulla/cortex ratio was 1.55 ± 0.11 regarding to a urinary osmolarity to 814 ± 121 mosm/L. Mean ± SD fasting urinary osmolarity dropped significantly to 73 ± 14 mosm/L for maximal dilution, p=0.001. Mean medulla/cortex ratio dropped significantly to 1.31 ± 0.09 mosm/L for maximal dilution, p=0.002. Figure 1 displays changes of 23NaMRI pictures before (A) then 1h (B), 1H15 (C), 1h30 (D) and 1h45 (E) after a water load. Urinary osmolarity and medulla/cortex ratio are significantly correlated, r=0.54, p=0.0001. We measured corticomedullary gradient in cardiorenal patient with different level of eGFR to show the ability and feasibility to measure this gradient in pathological settings. We were able to measure medulla/cortex ratio in patients with CKD with a mean SNR of 20.45 ± 9.45. Conclusion We explored CMG dynamically every 15 min and we were able to discriminate significant changes after a water load. We were also able to provide efficient 23NaMRI pictures in cardiorenal patients with kidney disease. CMG exploration would provide a relevant assessment of tubular dysfunction independently of glomerular alteration and thus could be of prognostic value.

Advances in magnetic resonance imaging of orbital disease

Magnetic resonance imaging (MRI) is increasingly used by the orbital surgeon to aid in the diagnosis, surgical planning, and monitoring of orbital disease. MRI provides superior soft tissue detail compared with computed tomography or ultrasound, and advancing techniques enhance its ability to highlight abnormal orbital pathology. Diffusion-weighted imaging is a specialized technique that uses water molecule diffusion patterns in tissue to generate contrast signals and can help distinguish malignant from benign lesions. Steady-state free precession sequences such as Constructive Interference in Steady-State (CISS) and Fast Imaging Employing Steady-state Acquisition (FIESTA) generate highly detailed, 3-dimensional reconstructed images and are particularly useful in distinguishing structures adjacent to cerebral spinal fluid. Magnetic resonance angiography can be used to characterize vascular lesions within the orbit. New developments in magnetic field strength as well as the use of orbital surface coils achieve increasingly improved imaging resolution.

Millimeter-Wave Band Resonator with Surface Coil for DNP–NMR Measurements

In this study, we developed a surface coil with a meanderline shape for nuclear magnetic resonance (NMR) combined with a Fabry–Perot resonator (FPR) for millimeter-wave band electron-spin resonance (ESR). Our goal was to perform both NMR and ESR measurements with high sensitivity, in particular for thin samples, such as a silicon wafer. We measured NMR signals using a variety of meanderline coil shapes and determined the optimal turn number of the meanderline as well as the clearance length between the lines. The FPR consisted of spherical and flat mirrors, where the latter was constructed of a thin gold layer with the meanderline underneath. We observed that the meanderline provided high sensitivity when the gold layer was sufficiently thin at approximately 16 nm. We also measured millimeter-wave ESR from a thin sample of phosphorous-doped silicon with the developed FPR with the meanderline.

Wearable and Elastic Surface Coil for 1H Magnetic Resonance Imaging

Wearable and elastic surface coil using a conductive and stretchable textile for magnetic resonance imaging (MRI) of breast was designed. A high-conductive silver thread was woven with elastofiber to create two elastic textile coils. Three phantoms with varying sizes and a resolution plate were also designed to validate the coil performance. Signal-to-noise ratios (SNRs) were calculated for the phantoms with different planar cuts. Resolution plate hole diameter of 6 mm was clearly discernible on axial MR images. Despite its canonical circular geometry, the wearable and elastic textile coil with one channel only was successful. The elastic coil can improve clinical applications of MRI with larger filling factor and may provide better patient comfort.

Metamaterial-Inspired Radiofrequency (RF) Shield With Reduced Specific Absorption Rate (SAR) and Improved Transmit Efficiency for UHF MRI.

To prevent the interferences between radiofrequency (RF) coils and other components in the magnetic resonance imaging (MRI) system such as gradient coils, it is essential to place an RF shield between the RF coils and gradient coils. However, the induced currents on conventional RF shields have negative influences on the RF coil performance. To reduce these influences, metamaterial absorbers (MA), a class of metamaterials exhibiting nearly unity absorption rate for the incident electromagnetic fields, can be employed for the design of a novel RF shield. However, the adoption of metamaterials in MRI systems is usually problematic because of the bulkiness of the metamaterial structure. In this work, capacitors and metallic interconnectors are used to miniaturize the MA so that the unit MA cell can operate at the Larmor frequencies of 7T and 9.4T MRI and stay compact. This MA-RF shield is used to improve the transmit efficiency of RF surface coils and reduce the specific absorption rate (SAR) in the region of interest (ROI). It is successfully demonstrated by simulations and experiments that, compared with conventional RF shield structure, the transmit efficiency can be enhanced by more than 32% and the peak SAR value can be reduced by 22% using the MA-RF shield. Moreover, it is observed that the transmit field penetration is improved when the surface coil is used with the MA-RF shield. This proof-of-concept study suggests a new practical way for the utilization of metamaterials in ultra-high field MRI applications.

Implantable NMR Microcoils in Rats: A New Tool for Exploring Tumor Metabolism at Sub-Microliter Scale?

The aim of this study was to evaluate the potential of a miniaturized implantable nuclear magnetic resonance (NMR) coil to acquire in vivo proton NMR spectra in sub-microliter regions of interest and to obtain metabolic information using magnetic resonance spectroscopy (MRS) in these small volumes. For this purpose, the NMR microcoils were implanted in the right cortex of healthy rats and in C6 glioma-bearing rats. The dimensions of the microcoil were 450 micrometers wide and 3 mm long. The MRS acquisitions were performed at 7 Tesla using volume coil for RF excitation and microcoil for signal reception. The detection volume of the microcoil was measured equal to 450 nL. A gain in sensitivity equal to 76 was found in favor of implanted microcoil as compared to external surface coil. Nine resonances from metabolites were assigned in the spectra acquired in healthy rats (n = 5) and in glioma-bearing rat (n = 1). The differences in relative amplitude of choline, lactate and creatine resonances observed in glioma-bearing animal were in agreement with published findings on this tumor model. In conclusion, the designed implantable microcoil is suitable for in vivo MRS and can be used for probing the metabolism in localized and very small regions of interest in a tumor.