Novel inductively coupled ear-bars (ICEs) to enhance restored fMRI signal from susceptibility compensation in rats.

Functional magnetic resonance imaging faces inherent challenges when applied to deep-brain areas in rodents, e.g. entorhinal cortex, due to the signal loss near the ear cavities induced by susceptibility artifacts and reduced sensitivity induced by the long distance from the surface array coil. Given the pivotal roles of deep brain regions in various diseases, optimized imaging techniques are needed. To mitigate susceptibility-induced signal losses, we introduced baby cream into the middle ear. To enhance the detection sensitivity of deep brain regions, we implemented inductively coupled ear-bars, resulting in approximately a 2-fold increase in sensitivity in entorhinal cortex. Notably, the inductively coupled ear-bar can be seamlessly integrated as an add-on device, without necessitating modifications to the scanner interface. To underscore the versatility of inductively coupled ear-bars, we conducted echo-planner imaging-based task functional magnetic resonance imaging in rats modeling Alzheimer's disease. As a proof of concept, we also demonstrated resting-state-functional magnetic resonance imaging connectivity maps originating from the left entorhinal cortex-a central hub for memory and navigation networks-to amygdala hippocampal area, Insular Cortex, Prelimbic Systems, Cingulate Cortex, Secondary Visual Cortex, and Motor Cortex. This work demonstrates an optimized procedure for acquiring large-scale networks emanating from a previously challenging seed region by conventional magnetic resonance imaging detectors, thereby facilitating improved observation of functional magnetic resonance imaging outcomes.

Precise stellarator quasi-symmetry can be achieved with electromagnetic coils.

Magnetic fields with quasi-symmetry are known to provide good confinement of charged particles and plasmas, but the extent to which quasi-symmetry can be achieved in practice has remained an open question. Recent work [M. Landreman and E. Paul, Phys. Rev. Lett. 128, 035001, 2022] reports the discovery of toroidal magnetic fields that are quasi-symmetric to orders-of-magnitude higher precision than previously known fields. We show that these fields can be accurately produced using electromagnetic coils of only moderate engineering complexity, that is, coils that have low curvature and that are sufficiently separated from each other. Our results demonstrate that these new quasi-symmetric fields are relevant for applications requiring the confinement of energetic charged particles for long time scales, such as nuclear fusion. The coils' length plays an important role for how well the quasi-symmetric fields can be approximated. For the longest coil set considered and a mean field strength of 1 T, the departure from quasi-symmetry is of the order of Earth's magnetic field. Additionally, we find that magnetic surfaces extend far outside the plasma boundary used by Landreman and Paul, providing confinement far from the core. Simulations confirm that the magnetic fields generated by the new coils confine particles with high kinetic energy substantially longer than previously known coil configurations. In particular, when scaled to a reactor, the best found configuration loses only 0.04% of energetic particles born at midradius when following guiding center trajectories for 200 ms.

Application of high-density 2D receiver coil arrays for improved SNR in prostate MRI.

PURPOSE: To study if adaptive image receive (AIR) receiver coil elements can be configured into a 2D array with high (>45% by diameter) element-to-element overlap, allowing improved SNR at depth (0.7-1.5× element diameter) versus conventional (20%) overlap. METHODS: An anterior array composed of twenty 10-cm diameter elements with 45% overlap arranged into a 4 × 5 grid and a similar 3 × 7 twenty-one-element posterior array were constructed. SNR and g-factor were measured in a pelvic phantom using the new high-density (HD) arrays (41 total elements) and compared to vendor AIR-based arrays (30 total elements) with conventional overlap. T2-weighted fast-spin-echo (T2SE) images acquired using both arrays were compared in 20 subjects. SNR was estimated in vivo. Results were compared blindly by three uroradiologists using a five-point scale. Images using the HD arrays were also compared to a set of images acquired over a range of acceleration factors (R = 2.0, 2.5, 3.0) with the conventional arrays. RESULTS: SNR within the phantom was on average 15% higher for R = 1.0, 1.5, and 2.0 using the HD arrays. Across the 20 subjects SNR within the prostate was 11% higher and assessed radiologically as significantly higher (p < 0.001) for the HD versus conventional arrays. At all acceleration factors the new HD arrays outperformed the conventional arrays (p ≤ 0.01), allowing increased R for similar SNR. CONCLUSION: AIR elements can be configured into 2D arrays with high (45%) element-to-element overlap, consistently providing increased SNR at depth versus arrays with conventional (20%) overlap. The SNR improvement allows increased acceleration in T2SE prostate MRI.

The restricted SAR protocol: A method to assess MRI coil prototypes in an unconditionally safe manner.

PURPOSE: Testing an RF coil prototype on subjects involves laborious verifications to ensure its safety. In particular, it requires preliminary electromagnetic simulations and their validations on phantoms to accurately predict the specific absorption rate (SAR). For coil design validation with a simpler safety procedure, the restricted SAR (rS) mode is proposed, enabling representative first experiments in vivo. The goal of the developed approach is to accelerate the transition of a custom coil system from prototype to clinical use. METHODS: The restricted specific absorption rate (SAR) (rS) mode imposes a radical limitation on the transmitted RF power based on a worst-case scenario of local RF power absorption. The limitations used are independent of the SAR spatial distribution, making this approach unconditionally safe. The developed rS protocol contains the sequences required for coil evaluation and satisfies the imposed rS conditions. It provides a quantitative characterization of the coil transmission and reception profiles and a qualitative evaluation of the anatomical images. Protocol validation was performed on commercial and pre-industrial prototype coils on a small cohort of healthy volunteers. RESULTS: The proposed rS protocol enables coil evaluation within an acquisition time compatible with common clinical protocol duration. The total time of all evaluation steps does not exceed 17 min. At the same time, the global SAR remains 100 times less than the International Electrotechnical Commission safety limit for played sequences. CONCLUSION: The rS protocol allows characterizing and comparing coil prototypes on volunteers without extensive electromagnetic calculations and phantom validations in an unconditionally safe way.

Effect of MR head coil geometry on deep-learning-based MR image reconstruction.

PURPOSE: To investigate whether parallel imaging-imposed geometric coil constraints can be relaxed when using a deep learning (DL)-based image reconstruction method as opposed to a traditional non-DL method. THEORY AND METHODS: Traditional and DL-based MR image reconstruction approaches operate in fundamentally different ways: Traditional methods solve a system of equations derived from the image data whereas DL methods use data/target pairs to learn a generalizable reconstruction model. Two sets of head coil profiles were evaluated: (1) 8-channel and (2) 32-channel geometries. A DL model was compared to conjugate gradient SENSE (CG-SENSE) and L1-wavelet compressed sensing (CS) through quantitative metrics and visual assessment as coil overlap was increased. RESULTS: Results were generally consistent between experiments. As coil overlap increased, there was a significant (p < 0.001) decrease in performance in most cases for all methods. The decrease was most pronounced for CG-SENSE, and the DL models significantly outperformed (p < 0.001) their non-DL counterparts in all scenarios. CS showed improved robustness to coil overlap and signal-to-noise ratio (SNR) versus CG-SENSE, but had quantitatively and visually poorer reconstructions characterized by blurriness as compared to DL. DL showed virtually no change in performance across SNR and very small changes across coil overlap. CONCLUSION: The DL image reconstruction method produced images that were robust to coil overlap and of higher quality than CG-SENSE and CS. This suggests that geometric coil design constraints can be relaxed when using DL reconstruction methods.

Comparison of tight-fitting 7T parallel-transmit head array designs using excitation uniformity and local specific absorption rate metrics.

PURPOSE: We model the performance of parallel transmission (pTx) arrays with 8, 16, 24, and 32 channels and varying loop sizes built on a close-fitting helmet for brain imaging at 7 T and compare their local specific absorption rate (SAR) and flip-angle performances to that of birdcage coil (used as a baseline) and cylindrical 8-channel and 16-channel pTx coils (single-row and dual-row). METHODS: We use the co-simulation approach along with MATLAB scripting for batch-mode simulation of the coils. For each coil, we extracted B1 + maps and SAR matrices, which we compressed using the virtual observation points algorithm, and designed slice-selective RF shimming pTx pulses with multiple local SAR and peak power constraints to generate L-curves in the transverse, coronal, and sagittal orientations. RESULTS: Helmet designs outperformed cylindrical pTx arrays at a constant number of channels in the flip-angle uniformity at a constant local SAR metric: up to 29% for 8-channel arrays, and up to 34% for 16-channel arrays, depending on the slice orientation. For all helmet arrays, increasing the loop diameter led to better local SAR versus flip-angle uniformity tradeoffs, although this effect was more pronounced for the 8-channel and 16-channel systems than the 24-channel and 32-channel systems, as the former have more limited degrees of freedom and therefore benefit more from loop-size optimization. CONCLUSION: Helmet pTx arrays significantly outperformed cylindrical arrays with the same number of channels in local SAR and flip-angle uniformity metrics. This improvement was especially pronounced for non-transverse slice excitations. Loop diameter optimization for helmets appears to favor large loops, compatible with nearest-neighbor decoupling by overlap.

Radiation damping at clinical field strength: Characterization and compensation in quantitative measurements.

PURPOSE: In any MR experiment, the bulk magnetization acts on itself, caused by the induced current in the RF receiver circuit that generates an oscillating damping field. This effect, known as "radiation damping" (RD), is usually weak and, therefore, unconsidered in MRI, but can affect quantitative studies performed with dedicated coils that provide a high SNR. The current work examined RD in a setup for investigations of small tissue specimens including a quantitative characterization of the spin-coil system. THEORY AND METHODS: A custom-made Helmholtz coil (radius and spacing 16 mm) was interfaced to a transmit-receive (Tx/Rx) switch with integrated passive feedback for modulation or suppression of RD similar to preamplifier decoupling. Pulse sequences included pulse-width arrays to demonstrate the absence/ presence of RD and difference techniques employing gradient pulses or composite RF pulses to quantify RD effects during free precession and transmission, respectively. Experiments were performed at 3T in small samples of MnCl2 solution. RESULTS: Significant RD effects may impact RF pulse application and evolution periods. Effective damping time constants were comparable to typical T2 * times or echo spacings in multi-echo sequences. Measurements of the phase relation showed that deviations from the commonly assumed 90° angle between the damping field and the transverse magnetization may occur. CONCLUSION: Radiation damping may affect the accuracy of quantitative MR measurements performed with dedicated RF coils. Efficient mitigation can be achieved hardware-based or by appropriate consideration in the pulse sequence.

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 approximate B 0 2 $$ {\mathrm{B}}_0^2 $$ dependence over a large central region when evaluated in the context of uiSNR. Whole-brain, high-resolution T 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.

Computational methods for the estimation of ideal current patterns in realistic human models.

PURPOSE: To introduce a method for the estimation of the ideal current patterns (ICP) that yield optimal signal-to-noise ratio (SNR) for realistic heterogeneous tissue models in MRI. THEORY AND METHODS: The ICP were calculated for different surfaces that resembled typical radiofrequency (RF) coil formers. We constructed numerical electromagnetic (EM) bases to accurately represent EM fields generated by RF current sources located on the current-bearing surfaces. Using these fields as excitations, we solved the volume integral equation and computed the EM fields in the sample. The fields were appropriately weighted to calculate the optimal SNR and the corresponding ICP. We demonstrated how to qualitatively use ICP to guide the design of a coil array to maximize SNR inside a head model. RESULTS: In agreement with previous analytic work, ICP formed large distributed loops for voxels in the middle of the sample and alternated between a single loop and a figure-eight shape for a voxel 3-cm deep in the sample's cortex. For the latter voxel, a surface quadrature loop array inspired by the shape of the ICP reached 87 . 5 % $$ 87.5\% $$ of the optimal SNR at 3T, whereas a single loop placed above the voxel reached only 55 . 7 % $$ 55.7\% $$ of the optimal SNR. At 7T, the performance of the two designs decreased to 79 . 7 % $$ 79.7\% $$ and 49 . 8 % $$ 49.8\% $$ , respectively, suggesting that loops could be suboptimal at ultra-high field MRI. CONCLUSION: ICP can be calculated for human tissue models, potentially guiding the design of application-specific RF coil arrays.

Linear Bloch-Siegert phase-encoded low-field MRI: RF coils, pulse sequence, and image reconstruction.

Conventional B 0 $$ {B}_0 $$ gradient systems have several weaknesses including high cost and bulk. As a step towards addressing these while providing new degrees of freedom for spatial encoding and system design in Magnetic Resonance Imaging (MRI), a radio frequency (RF) gradient encoding system and pulse sequence for phase encoding using the Bloch-Siegert (BS) shift were developed. Optimized BS spatial encoding coils with bucking windings (counter-wound loops) were designed and constructed, along with compatible homogeneous imaging coils for excitation and signal reception. Two coil systems were developed: one for phantom imaging and a second for human wrist imaging. BS phase-encoded imaging and BS RF pulse simulations were performed. Pulse sequences were designed for linear stepping in k-space and implemented on a 47.5-mT scanner to image resolution phantoms in both coil setups. Reconstructions were performed using both the full B 1 + $$ {B}_1^{+} $$ -based encoding fields for each BS pulse amplitude and using inverse discrete Fourier transforms. A B 0 $$ {B}_0 $$ gradient was used for frequency encoding during signal readout, and the third axis was projected. Specific absorption ratio (SAR) calculations were performed for the wrist coil to determine the safety of BS-based RF encoding for B 0 $$ {B}_0 $$ fields in the low field MRI regime. The optimized RF spatial encoding coils resulted in higher linearity ( R 2 = 0.9981 $$ {R}^2=0.9981 $$ and 0.9921 in the phantom and wrist coils, respectively) than coils used in previous work. The phantom and wrist imaging coils were validated in simulations and experimentally to produce a peak B 1 + = 1.35 $$ {B}_1^{+}=1.35 $$ G and 0.8 G with 12-W input power, respectively, in the field-of-view (length = 11 cm) used for imaging. Nominal imaging resolutions of 5.22 and 7.21 mm were, respectively, achieved by the two-coil systems in the RF phase-encoded dimension. Coil systems, pulse sequences, and image reconstructions were developed for linear RF phase encoding using the BS shift and validated using a 47.5-mT open low field scanner, establishing a key component required for B 0 $$ {B}_0 $$  gradient-free imaging at low B 0 $$ {B}_0 $$  field strengths.

Signal-to-noise ratio versus field strength for small surface coils.

The increasing signal-to-noise ratio (SNR) is the main reason to use ultrahigh field MRI. Here, we investigate the dependence of the SNR on the magnetic field strength, especially for small animal applications, where small surface coils are used and coil noise cannot be ignored. Measurements were performed at five field strengths from 3 to 14.1 T, using 2.2-cm surface coils with an identical coil design for transmit and receive on two water samples with and without salt. SNR was measured in a series of spoiled gradient echo images with varying flip angle and corrected for saturation based on a series of flip angle and T1 measurements. Furthermore, the noise figure of the receive chain was determined and eliminated to remove instrument dependence. Finally, the coil sensitivity was determined based on the principle of reciprocity to obtain a measure for ultimate SNR. Before coil sensitivity correction, the SNR increase in nonconductive samples is highly supralinear with B0 1.6-2.7, depending on distance to the coil, while in the conductive sample, the growth is smaller, being around linear close to the surface coil and increasing up to a B0 2.0 dependence when moving away from the coil. After sensitivity correction, the SNR increase is independent of loading with B0 2.1. This study confirms the supralinear increase of SNR with increasing field strengths. Compared with most human measurements with larger coil sizes, smaller surface coils, as mainly used in animal studies, have a higher contribution of coil noise and thus a different behavior of SNR at high fields.

Lung Tensioning Device Coil Treatment in Patients with Severe Emphysema: A Prospective Safety and Feasibility Trial (EFFORT).

INTRODUCTION: Currently, there is a lack of bronchoscopic lung volume reduction options that do not depend on fissure integrity. Endobronchial coils have been extensively studied to address this need but exhibited variable patient response and have been discontinued. Lung tension device (LTD) coils represent the next-generation coil treatment. This study aimed to evaluate safety, feasibility, and efficacy of LTD-coil treatment. METHODS: Patients with advanced emphysema and hyperinflation were enrolled at two European sites. LTD-coils (Free Flow Medical, Fremont, CA, USA) were implanted in the two most destructed lobes, as determined by quantitative CT analysis, in two separate procedures. The primary endpoint was 3-month follow-up after the last treatment. RESULTS: Fourteen patients (50% male, median age 64 years, FEV1 23%predicted, RV 249%predicted) received LTD-coil treatment: 12 received bilateral and 2 unilateral treatment. Six serious respiratory adverse events occurred within the initial 3 months posttreatment, including one device-associated death. Treatment significantly reduced in- and expiratory volume of the treated lobes (-410 [-710, -340], p = 0.004 and -650 [-730, -190] mL, p < 0.001, respectively) and improved quality of life (SGRQ total score -4.6 [-21.0, -2.6], p < 0.001). However, at a group level, no significant improvements in pulmonary function or 6-min walk distance were observed. Responder rates ranged from 18% to 54% for the different endpoints. CONCLUSION: This first-in-human study shows that the new LTD-coil procedure is feasible with a safety profile comparable to the previous coil treatment. While the treatment effectively reduced lobar volume and modestly improved quality of life up to 3 months' follow-up, at a group level it did not significantly enhance pulmonary function or exercise capacity.

The possible influence of third-order shim coils on gradient-magnet interactions: an inter-field and inter-site study.

OBJECTIVE: To assess the possible influence of third-order shim coils on the behavior of the gradient field and in gradient-magnet interactions at 7 T and above. MATERIALS AND METHODS: Gradient impulse response function measurements were performed at 5 sites spanning field strengths from 7 to 11.7 T, all of them sharing the same exact whole-body gradient coil design. Mechanical fixation and boundary conditions of the gradient coil were altered in several ways at one site to study the impact of mechanical coupling with the magnet on the field perturbations. Vibrations, power deposition in the He bath, and field dynamics were characterized at 11.7 T with the third-order shim coils connected and disconnected inside the Faraday cage. RESULTS: For the same whole-body gradient coil design, all measurements differed greatly based on the third-order shim coil configuration (connected or not). Vibrations and gradient transfer function peaks could be affected by a factor of 2 or more, depending on the resonances. Disconnecting the third-order shim coils at 11.7 T also suppressed almost completely power deposition peaks at some frequencies. DISCUSSION: Third-order shim coil configurations can have major impact in gradient-magnet interactions with consequences on potential hardware damage, magnet heating, and image quality going beyond EPI acquisitions.

Magnetoelastic standing waves induced in UO2 by microsecond magnetic field pulses.

Magnetoelastic dilatometry of the piezomagnetic antiferromagnet UO2 was performed via the fiber Bragg grating method in magnetic fields up to 150 T generated by a single-turn coil setup. We show that in microsecond timescales, pulsed-magnetic fields excite mechanical resonances at temperatures ranging from 10 to 300 K, in the paramagnetic as well as within the robust antiferromagnetic state of the material. These resonances, which are barely attenuated within the 100-µs observation window, are attributed to the strong magnetoelastic coupling in UO2 combined with the high crystalline quality of the single crystal samples. They compare well with mechanical resonances obtained by a resonant ultrasound technique and superimpose on the known nonmonotonic magnetostriction background. A clear phase shift of π in the lattice oscillations is observed in the antiferromagnetic state when the magnetic field overcomes the piezomagnetic switch field H[Formula: see text] T. We present a theoretical argument that explains this unexpected behavior as a result of the reversal of the antiferromagnetic order parameter at Hc.

Long-term outcome of endovascular treatment for indirect carotid-cavernous fistulas.

OBJECTIVE: Endovascular treatment (EVT) is the primary approach used to treat indirect carotid-cavernous fistulas (CCFs). In this study, the authors evaluated the immediate and long-term efficacy and safety of different endovascular techniques for indirect CCFs. METHODS: The databases of two endovascular centers were retrospectively reviewed to collect the patients with indirect CCFs treated using endovascular techniques between 2013 and 2023. Demographics, clinical presentation, CCF features, EVT characteristics, and clinical and radiological outcomes were evaluated and analyzed. The analysis was performed to compare the clinical and radiological data between different endovascular approaches and different embolic materials. RESULTS: Ninety-eight patients were included in the study. EVT was successful in 95 patients (96.9%). Immediate complete obliteration of the CCF was achieved in 93.9% of patients, with 98% undergoing embolization with liquid embolic agents (LEAs) and 95.6% undergoing coiling alone. Complete CCF obliteration was higher in the transvenous than in the transarterial approach (94.3% vs 75%, p = 0.010). At ≥ 6 months follow-up, complete CCF obliteration was achieved in all patients (100%). The rate of procedure-related complications was higher following LEAs than with coiling alone (32.0% vs 15.6%). New cranial nerve (CN) palsy was diagnosed in 26.0% and 2.2% after embolization with LEAs and coiling alone, respectively (p = 0.001), with complete CN palsy recovery in 78.6%. Procedure-related intracranial hemorrhage occurred in 3 patients (3.1%). Two patients experienced an ischemic stroke following Onyx migration into the internal carotid artery. Ocular symptoms improved in 93% (83/89) of the patients who were followed. CONCLUSIONS: In this study, complete obliteration of an indirect CCF was achieved in more than 90% of patients. Despite the occurrence of some new postprocedural ocular CN palsy, ocular symptoms improved in most patients in long-term follow-up. The transvenous approach was the most effective method for treating the indirect CCF. Coiling was safer than LEAs for the embolization of the indirect CCF.

The jailed coiling technique: An endovascular solution for saccular aneurysms with suboptimal fixation sites.

OBJECTIVE: To evaluate the midterm results of patients with saccular aneurysms treated with the jailed coiling technique. METHODS: A retrospective review of 17 patients treated with the jailed coiling technique over a 7 year period, between 2018 and 2024 at our institution. Treatment entails placing an endograft across the neck of the saccular aneurysm followed by coiling of the aneurysm through an extraluminal catheter. Debranching procedures of the aortic arch were performed when necessary in order to create a sealing zone of >5 mm. Data collected included demographics, anatomical features of the lesions and sealing zones, indication for intervention, method of treatment and technical success, sac expansion, and reinterventions. RESULTS: 17 patients (median age 69, 14 males) were treated for saccular aneurysms with short, suboptimal sealing zones (aortic arch 13, distal thoracic aorta 2, celiac trunk 1, brachiocephalic artery 1). Among the aortic arch aneurysms, six required preoperative debranching procedures of the aortic arch in order to create a short landing zone of 5 mm, making them eligible for the procedure. Technical success was obtained in all patients. One perioperative mortality occurred. Mean follow-up among those treated for arch aneurysms was 32 months (range 1-71 months). One patient who was treated for an aortic arch aneurysm had a persistent endoleak. No sac enlargement was observed. None of the patients required interventions and none experienced aneurysm related mortality. CONCLUSION: The jailed coiling technique is a safe and effective method to treat saccular arterial aneurysms with suboptimal, short sealing zones. It can be utilized for saccular aneurysms located within the aortic arch and for aneurysms located in other locations where coiling or stent grafting is not an option. The procedure can be performed with minimal morbidity with a high percentage of success. Long term durability of the repair needs to be determined.

Real-world data to support post-market safety and performance of embolization coils: evidence generation from a medical device manufacturer and data institute partnership.

BACKGROUND: Recognizing the limitations of pre-market clinical data, regulatory authorities have embraced total product lifecycle management with post-market surveillance (PMS) data to assess medical device safety and performance. One method of proactive PMS involves the analysis of real-world data (RWD) through retrospective review of electronic health records (EHR). Because EHRs are patient-centered and focused on providing tools that clinicians use to determine care rather than collecting information on individual medical products, the process of transforming RWD into real-world evidence (RWE) can be laborious, particularly for medical devices with broad clinical use and extended clinical follow-up. This study describes a method to extract RWD from EHR to generate RWE on the safety and performance of embolization coils. METHODS: Through a partnership between a non-profit data institute and a medical device manufacturer, information on implantable embolization coils' use was extracted, linked, and analyzed from clinical data housed in an electronic data warehouse from the state of Indiana's largest health system. To evaluate the performance and safety of the embolization coils, technical success and safety were defined as per the Society of Interventional Radiology guidelines. A multi-prong strategy including electronic and manual review of unstructured (clinical chart notes) and structured data (International Classification of Disease codes), was developed to identify patients with relevant devices and extract data related to the endpoints. RESULTS: A total of 323 patients were identified as treated using Cook Medical Tornado, Nester, or MReye embolization coils between 1 January 2014 and 31 December 2018. Available clinical follow-up for these patients was 1127 ± 719 days. Indications for use, adverse events, and procedural success rates were identified via automated extraction of structured data along with review of available unstructured data. The overall technical success rate was 96.7%, and the safety events rate was 5.3% with 18 major adverse events in 17 patients. The calculated technical success and safety rates met pre-established performance goals (≥ 85% for technical success and ≤ 12% for safety), highlighting the relevance of this surveillance method. CONCLUSIONS: Generating RWE from RWD requires careful planning and execution. The process described herein provided valuable longitudinal data for PMS of real-world device safety and performance. This cost-effective approach can be translated to other medical devices and similar RWD database systems.

Use of the Perturbing Sphere Method for the Estimation of Radiofrequency Coils' Efficiency in Magnetic Resonance Applications: Experience from an Electromagnetic Laboratory.

Radiofrequency (RF) transmitter and receiver coils are employed in in magnetic resonance (MR) applications to, respectively, excite the nuclei in the object to be imaged and to pick up the signals emitted by the nuclei with a high signal-to-noise ratio (SNR). The ability to obtain high-quality images and spectra in MR strongly depends on the RF coil's efficiency. Local coil efficiency can be estimated with magnetic field mapping methods evaluated at a fixed point in space. Different methods have been described in the literature, divided into electromagnetic bench tests and MR techniques. In this paper, we review our experience in designing and testing RF coils for MR in our electromagnetic laboratory with the use of the perturbing sphere method, which permits coil efficiency and magnetic field mapping to be estimated with great accuracy and in a short space of time, which is useful for periodic coil quality control checks. The method's accuracy has been verified with simulations and workbench tests performed on RF coils with different surfaces and of different volumes. Furthermore, all the precautions taken to improve the measurement sensitivity are also included in this review, in addition to the various applications of the method that have been described over the last twenty years of research in our electromagnetic laboratory.

Machine Learning for the Design and the Simulation of Radiofrequency Magnetic Resonance Coils: Literature Review, Challenges, and Perspectives.

Radiofrequency (RF) coils for magnetic resonance imaging (MRI) applications serve to generate RF fields to excite the nuclei in the sample (transmit coil) and to pick up the RF signals emitted by the nuclei (receive coil). For the purpose of optimizing the image quality, the performance of RF coils has to be maximized. In particular, the transmit coil has to provide a homogeneous RF magnetic field, while the receive coil has to provide the highest signal-to-noise ratio (SNR). Thus, particular attention must be paid to the coil simulation and design phases, which can be performed with different computer simulation techniques. Being largely used in many sectors of engineering and sciences, machine learning (ML) is a promising method among the different emerging strategies for coil simulation and design. Starting from the applications of ML algorithms in MRI and a short description of the RF coil's performance parameters, this narrative review describes the applications of such techniques for the simulation and design of RF coils for MRI, by including deep learning (DL) and ML-based algorithms for solving electromagnetic problems.

Assemblies of Coaxial Pick-Up Coils as Generic Inductive Sensors of Magnetic Flux: Mathematical Modeling of Zero, First and Second Derivative Configurations.

Coils are one of the basic elements employed in devices. They are versatile, in terms of both design and manufacturing, according to the desired inductive specifications. An important characteristic of coils is their bidirectional action; they can both produce and sense magnetic fields. Referring to sensing, coils have the unique property to inductively translate the temporal variation of magnetic flux into an AC voltage signal. Due to this property, they are massively used in many areas of science and engineering; among other disciplines, coils are employed in physics/materials science, geophysics, industry, aerospace and healthcare. Here, we present detailed and exact mathematical modeling of the sensing ability of the three most basic scalar assemblies of coaxial pick-up coils (PUCs): in the so-called zero derivative configuration (ZDC), having a single PUC; the first derivative configuration (FDC), having two PUCs; and second derivative configuration (SDC), having four PUCs. These three basic assemblies are mathematically modeled for a reference case of physics; we tackle the AC voltage signal, VAC (t), induced at the output of the PUCs by the temporal variation of the magnetic flux, Φ(t), originating from the time-varying moment, m(t), of an ideal magnetic dipole. Detailed and exact mathematical modeling, with only minor assumptions/approximations, enabled us to obtain the so-called sensing function, FSF, for all three cases: ZDC, FDC and SDC. By definition, the sensing function, FSF, quantifies the ability of an assembly of PUCs to translate the time-varying moment, m(t), into an AC signal, VAC (t). Importantly, the FSF is obtained in a closed-form expression for all three cases, ZDC, FDC and SDC, that depends on the realistic, macroscopic characteristics of each PUC (i.e., number of turns, length, inner and outer radius) and of the entire assembly in general (i.e., relative position of PUCs). The mathematical methodology presented here is complete and flexible so that it can be easily utilized in many disciplines of science and engineering.