Standard Coil Research Articles

Systematic Analysis of the Improvements in Magnetic Resonance Microscopy with Ferroelectric Composite Ceramics.

The spatial resolution and signal-to-noise ratio (SNR) attainable in magnetic resonance microscopy (MRM) are limited by intrinsic probe losses and probe-sample interactions. In this work, the possibility to exceed the SNR of a standard solenoid coil by more than a factor-of-two is demonstrated theoretically and experimentally. This improvement is achieved by exciting the first transverse electric mode of a low-loss ceramic resonator instead of using the quasi-static field of the metal-wire solenoid coil. Based on theoretical considerations, a new probe for microscopy at 17 T is developed as a dielectric ring resonator made of ferroelectric/dielectric low-loss composite ceramics precisely tunable via temperature control. Besides the twofold increase in SNR, compared with the solenoid probe, the proposed ceramic probe does not cause static-field inhomogeneity and related image distortion.

Design and Modeling of a Radiofrequency Coil Derived from a Helmholtz Structure

This paper focuses on radiofrequency (RF) coils that can produce a high electromagnetic field homogeneity to be used for magnetic resonance imaging (MRI) applications. The proposed structure is composed of four wire loops symmetrically located on an ellipsoidal surface. The main objective of this work is to improve field homogeneity compared to a standard Helmholtz coil. Numerical simulation was carried out to assess the RF electromagnetic field behavior of the proposed coil. Different electrical modeling and simulations were investigated, particularly the study of the whole modeling of the proposed structure taking into account all the couplings between the loops. The proposed coil was evaluated and compared with the standard Helmholtz coil. Simulation and experimental results confirmed the good performance of the developed coil in terms of electromagnetic field homogeneity, efficiency, sensitivity, and quality factor.

Long-Term Single-Center Retrospective Follow-Up After Embolization of Pulmonary Arteriovenous Malformations Treated Over a 20-year Period: Frequency of Re-canalization with Various Embolization Materials and Clinical Outcome.

The present study is a register-based observational study of an unselected consecutive patient cohort with pulmonary arteriovenous malformations (PAVMs) from a single national hereditary hemorrhagic telangiectasia and PAVM embolization center. The aim was to investigate the frequency of re-embolizations and the clinical outcome after embolization with the use of different embolization materials further, to define which PAVM morphology and size of feeding arteries that most often were re-embolized, and to estimate the clinical outcome of the patients including those that were re-embolized. The population was included from 1996 until 2016 and was made up of a total of 136 patients with 322 PAVMs. Median follow-up was 38.3 (0.3-241 months). The re-embolization rate was 9.3%. None of the PAVMs treated with detachable silicone balloons were re-embolized, while 4.5% treated with vascular plugs and 11.7% treated with coils were re-embolized (p=0.07). In total, 16/74 complex PAVMs were re-embolized compared with 14/248 simple PAVMs. In big-sized feeding arteries ≥ 6mm, 16/112 were re-embolized compared with 14/210 with smaller-sized feeding arteries. Out of the 30 re-embolized PAVMs, 23 resulted in a successful clinical outcome. Our results suggest that standard coils probably should not be the first choice for embolization of PAVMs, and vascular plug alone or in combination with coils might be a better primary option for embolization in these patients. Level 3A, non-randomized case controlled cohort/follow-up study.

Modular Coiled Flow Inverter with Narrow Residence Time Distribution for Process Development and Production

AbstractThe ideal plug flow reactor is a common model with narrow residence time distribution in reaction engineering. This contribution explains a design strategy of a coiled flow inverter (CFI) with narrow residence time and flexible adjustable process conditions. The design space diagram illustrates the design limits of inner diameter and coil diameter on the base of dimensionless numbers. Standard coil tube diameters allow for rational design of a limited number of devices. The reactor performance diagram enables the facile scale‐up and adaption of new process conditions with the CFI with economic boundary conditions.

Metamaterial Zeroth-Order Resonator RF Coil for Human Head: Preliminary Design for 10.5 T MRI

The objective is to develop a highly efficient RF head coil on a thin substrate for the ultra-high magnetic field MRI systems. The metamaterial zeroth-order resonator is investigated for this purpose. Simulation and experimental results are provided for an eight-channel M-ZOR-based RF coil in comparison with a standard high performance eight-channel dipole-based RF coil for the 10.5 T MRI system. Each element is 18 cm (approximately a quarter of a wavelength λ0) long, identical, evenly spaced along the circumference of the cylindrical phantom, loaded with dielectric material, and referred to as an inverted metamaterial zeroth-order resonator. The resonator elements are open circuited, matched, and tuned to 447.06 MHz with the phantom. An unloaded to loaded Q-factor ratio of 2.97 is obtained from the scattering matrix of the proposed design. The length independent nature of the proposed design and the flexibility of the lumped elements have provided an optimized element with a substrate thickness of roughly 3 mm (λ0/200). With the proposed design, there is a similar RF magnetic field strength (B1+) to SAR ratio with a reduced 10 g averaged SAR of 2.892 for the same input power compared to that of a dipole coil. This could make the coil acceptable for the clinical high-quality imaging.

Numerical Simulations of Realistic Lead Trajectories and an Experimental Verification Support the Efficacy of Parallel Radiofrequency Transmission to Reduce Heating of Deep Brain Stimulation Implants during MRI

Patients with deep brain stimulation (DBS) implants may be subject to heating during MRI due to interaction with excitatory radiofrequency (RF) fields. Parallel RF transmit (pTx) has been proposed to minimize such RF-induced heating in preliminary proof-of-concept studies. The present work evaluates the efficacy of pTx technique on realistic lead trajectories obtained from nine DBS patients. Electromagnetic simulations were performed using 4- and 8-element pTx coils compared with a standard birdcage coil excitation using patient models and lead trajectories obtained by segmentation of computed tomography data. Numerical optimization was performed to minimize local specific absorption rate (SAR) surrounding the implant tip while maintaining spatial homogeneity of the transmitted RF magnetic field (B1+), by varying the input amplitude and phase for each coil element. Local SAR was significantly reduced at the lead tip with both 4-element and 8-element pTx (median decrease of 94% and 97%, respectively), whereas the median coefficient of spatial variation of B1+ inhomogeneity was moderately increased (30% for 4-element pTx and 20% for 8-element pTx) compared to that of the birdcage coil (17%). Furthermore, the efficacy of optimized 4-element pTx was verified experimentally by imaging a head phantom that included a wire implanted to approximate the worst-case lead trajectory for localized heating, based on the simulations. Negligible temperature elevation was observed at the lead tip, with reasonable image uniformity in the surrounding region. From this experiment and the simulations based on nine DBS patient models, optimized pTx provides a robust approach to minimizing local SAR with respect to lead trajectory.

Abstract WP139: MRI Evaluation and Functional Assessment of Brain Injury Improvement After 3K3A-Activated Protein C Treatment for Murine White Matter Stroke

Introduction: Subcortical white matter stroke (WMS) accounts for 25% of all incidences of stroke and results in severe motor and cognitive disability. WMS stands as the second leading cause of dementia and is notably prevalent in older adults. Activated protein C (APC), a plasma serine protease with potent antithrombotic and cell-signaling activities, was engineered to reduce bleeding risk while retaining normal cell-signaling activities (anti-inflammatory, anti-apoptotic, and neuroregenerative, etc. activities). The engineered variant, 3K3A-APC, is neuroprotective in preclinical models of ischemic stroke with large infarcts involving common large arteries and gray matter. A multicenter Phase 2 randomized clinical trial enrolled 110 patients to assess the safety, pharmacokinetics, and efficacy of human recombinant 3K3A-APC in acute ischemic stroke patients following endovascular treatments (NCT02222714). Methods: In this new study, a murine WMS was induced by the vasoconstrictor N5-(1-iminoethyl)-L-ornithine, dihydrochloride (L-Nio) by injection into the subcortical white matter ventral to the mouse forelimb motor cortex using the Neurostar motorized ultra-precise small animal stereotaxic instrument. Mice received intravenously 0.2 mg/kg recombinant murine 3K3A-APC or saline at 4, 24, 48 and 72 h after L-Nio. Then MRI scans were performed using a 7T PET/MRI scanner (MR Solutions) and a standard quadrature coil at 1 and 7 days after the stroke. Results: Both MRI and histological results showed that 3K3A-APC significantly reduced the lesion volume, increased the viability of oligodendrocytes and neurons, and protected against blood brain barrier damage at 1 and 7 days after stroke. Behavioral tests showed that 3K3A-APC improved functional recovery. Conclusions: These results demonstrated that 3K3A-APC might be an effective treatment for white matter stroke.

Energy efficiency analysis in office building through thermal modelling

Malaysia is hot and humid country with high temperature and humidity. The air conditioning systems that have huge energy consumption are an essential component in daily life. The aims of this research are to build a building thermal HVAC model, which could predict the amount of energy consumption required to get the comfort level using eQUEST and purpose energy saving methods. In the model the different physical properties of the building, weather, and internal load, HVAC system, operating strategies and schedules taken to account. From the result, huge energy used for space cooling resulting low room temperature outside the range of Malaysian Standard MS1525. Among the purposed method, packaged VAV DX coil air conditioning system has the most energy saving on the building’s overall energy consumption following by roof and wall insulation (24°C) indoor temperature, standard VAV CW coil air conditioning system, and daylight control with low e glass. The energy reduction range from 6.0% to 21.2%. This study are significant to study and improve the building energy efficiency.

Penumbra Occlusion Device for neurovascular vessel sacrifice: Feasibility and application

PurposeThe purpose of this study is to describe the use of the Penumbra Occlusion Device (POD), which is a coil with an enhanced anchor segment, along with standard coils for carotid and vertebral artery sacrifice, and to assess its feasibility, safety, and efficacy. MethodsThis is a retrospective chart review of patients with vessel sacrifices who were treated using POD. For the procedure, a balloon test occlusion was performed prior to permanent arterial sacrifice. Following this, a POD was deployed followed by subsequent angiography to confirm occlusion. Secondary PODs or standard coils were deployed as necessary. ResultsA total of 5 internal carotid arteries and 5 vertebral arteries were treated in 10 patients. The mean vessel diameter of the vessel sacrificed was 4 mm (range 2.9–7.7 mm). The total mean number of coils required for vessel sacrifice was 7 (range 3–17). The mean number of PODs used for vessel sacrifice was 2.4 (range, 1–6). The mean number of additional standard coils used was 4.1 (range, 0–13). 9/10 (90%) parent arteries were successfully occluded. One patient had slow flow distal to the occluded segment. One (10%) of the patients had a delayed ischemic event. There were no immediate periprocedural complications including coil migrations or vessel dissections. 6/10 patients had follow-up imaging and no patients developed recanalization during the follow-up period. ConclusionParent vessel sacrifice using a combination of PODs and standard coils appear to be a feasible, safe and effective alternative to the traditional vessel sacrifice techniques.

Testing the Medina embolization device in experimental aneurysms.

The Medina embolization device (MED) is a novel, braided self-expanding endovascular device designed to occlude aneurysms by constructing an in situ intrasaccular flow diverter. Although a single device can be positioned at the neck of simple spherical in vitro aneurysms, the best way to occlude more complex in vivo aneurysms (using multiple MEDs or a combination of MEDs and platinum coils) is currently unknown. Fifty-two aneurysms of 3 different types were created in 31 canines, yielding 48 patent aneurysms. Treatments were randomly allocated by drawing lots: group 1, MEDs alone (n = 16); group 2, MEDs plus standard platinum coils (n = 16); and group 3, control aneurysms treated with coils alone (n = 16). Angiographic results were scored and compared immediately following treatment completion and at 3 months. Specimens were photographed and the extent of neointimal closure of the aneurysmal neck scored, followed by histopathological analyses. Angiographic scores of 0 or 1 (occlusion or near occlusion) were initially obtained in 2 of 16 (12.5%, 95% CI 1.6%-38.3%) group 1 (MEDs alone), 3 of 16 (18.7%, 95% CI 4%-45.6%) group 2 (MEDs plus coils), and 10 of 16 (62.5%, 95% CI 35.4%-84.8%) group 3 (coils alone) aneurysms (p = 0.005). At 3 months, scores of 0 or 1 were found in 11 of 16 (68.7%, 95% CI 41.3%-89.0%) group 1, 9 of 16 (56.2%, 95% CI 29.9%-80.2%) group 2, and 8 of 16 (50%, 95% CI 24.7%-75.3%) group 3 aneurysms (p = 0.82). Neointimal scores were similar for the 3 treated groups (p = 0.66). Endovascular treatment of experimental aneurysms with MEDs or MEDs and coils showed angiographic occlusion and neointimal scores at 3 months that were similar to those achieved with standard platinum coiling.

Awake Rat Brain Functional Magnetic Resonance Imaging Using Standard Radio Frequency Coils and a 3D Printed Restraint Kit.

Functional magnetic resonance imaging (fMRI) is a powerful noninvasive tool for studying spontaneous resting state functional connectivity (RSFC) in laboratory animals. Brain function can be significantly affected by generally used anesthetics, however, rendering the need for awake imaging. Only a few different awake animal habituation protocols have been presented, and there is a critical need for practical and improved low-stress techniques. Here we demonstrate a novel restraint approach for awake rat RSFC studies. Our custom-made 3D printed restraint kit is compatible with a standard Bruker Biospin MRI rat bed, rat brain receiver coil, and volume transmitter coil. We also implemented a progressive habituation protocol aiming to minimize the stress experienced by the rats, and compared RSFC between awake, lightly sedated, and isoflurane-anesthetized rats. Our results demonstrated that the 3D printed restraint kit was suitable for RSFC studies of awake rats. During the short 4-day habituation period, the plasma corticosterone concentration, movement, and heart rate, which were measured as stress indicators, decreased significantly, indicating adaptation to the restraint protocol. Additionally, 10 days after the awake MRI session, rats exhibited no signs of depression or anxiety based on open-field and sucrose preference behavioral tests. The RSFC data revealed significant changes in the thalamo-cortical and cortico-cortical networks between the awake, lightly sedated, and anesthetized groups, emphasizing the need for awake imaging. The present work demonstrates the feasibility of our custom-made 3D printed restraint kit. Using this kit, we found that isoflurane markedly affected brain connectivity compared with that in awake rats, and that the effect was less pronounced, but still significant, when light isoflurane sedation was used instead.

Transcranial Magnetic Stimulation: Design of a Stimulator and a Focused Coil for the Application of Small Animals

Transcranial magnetic stimulation (TMS) is a non-invasive, safe, effective, and food and drug administration approved treatment for major depressive disorder. TMS relies on time-varying magnetic fields to induce an electric field in the brain, resulting in depolarization or hyperpolarization of the neurons. Recently, there has been extensive research to improve the magnetic coil design, effectiveness of TMS treatment, and improvement in the computer modeling of human brains, yet little development is reported on the TMS pulse generators and coil design for small animals. TMS pulse generators, or stimulators, are the circuits which provides pulse current to drive the inductive coils (TMS coils), used to generate time-varying magnetic fields. Commercial TMS stimulators are expensive and have limitations of using standard and non-customizable coils. These stimulators do not support small inductive loads, which require high-current capabilities. Furthermore, the commercial animal coil stimulates the entire body of a mouse, as they are designed for large animals. In this paper, the authors present the design of a small sized TMS stimulator and a focused coil for the application on small animals such as mice. The proposed TMS stimulator will have the potential of handling small inductive loads enabling stimulation of specific regions within the mouse brain.

Compact Design of a Hydraulic Driving Robot for Intraoperative MRI-Guided Bilateral Stereotactic Neurosurgery

In this letter, we present an intraoperative magnetic resonance imaging (MRI)-guided robot for bilateral stereotactic procedures. Its compact design enables robot's operation within the constrained space of standard imaging head coil. magnetic resonance (MR) safe and high-performance hydraulic transmissions are incorporated. A maximum stiffness coefficient of 24.35 N/mm can be achieved with transmission fluid preloaded at 2 bar. Sufficient targeting accuracy (average within ≤1.73 mm) has been demonstrated in a simulated needle insertion task of deep brain stimulation. A novel MR-based wireless tracking technique is adopted. It is capable of offering real-time and continuous (30-40 Hz) three-dimensional (3-D) localization of robotic instrument under the proper MR tracking sequence. It outperforms the conventional method of using low-contrast passive fiducials that can only be revealed in the MR image domain. Two wireless tracking units/markers are integrated with the robot, which are two miniaturized coil circuits in size of 1.5 × 5 × 0.2 mm 3 , fabricated on flexible thin films. A navigation test was performed under the standard MRI settings in order to visualize the 3-D localization of the robotic instrument. MRI compatibility test was also carried out to prove the minimal interference to MR images of the presented hydraulic robotic platform.

Embolisation of pulmonary arteriovenous malformations - case series.

PurposePulmonary arteriovenous malformations (PAVM) are the direct communications between the pulmonary arteries and veins. These malformations can cause serious complications, and most of these patients should be treated. Herein we present our experience in the treatment of 18 cases of PAVM, treated with endovascular embolisation.Material and methodsEighteen patients with PAVMs underwent endovascular embolisation during a five-year period. Eight were male and 10 were female, with ages ranging from 16 to 65 years. Standard steel coils and vascular plug were used for embolisation.ResultsEmbolisation was successful in 17 of 18 patients. Coiling was used in 10 patients, vascular plug in five, and both materials in two patients. All symptomatic patients with successful embolisation lost all their symptoms after treatment. Control angiography after embolisation showed a closure of AV shunt without migration of embolic material in all patients. Post-embolisation syndrome developed in four patients and late onset of pleural pain in three patients. There was no connection between pleural reaction and type of PAVM and embolic material.ConclusionsEndovascular PAVM treatment is a minimally invasive, highly successful method with a low rate of only transitory complications.

A Dedicated 36-Channel Receive Array for Fetal MRI at 3T.

Due to a lack of fetal imaging coils, the standard commercial abdominal coil is often used for fetal imaging, the performance of which is limited by its insufficient coverage, element number, and Signal-to-noise ratio (SNR). In this paper, a dedicated 36-channel coil array, of which size can best fit the body sizes of pregnancy gestation from 20 to 37+ weeks, was designed for fetal imaging at 3T. SNR with full phase encoding and G-factor denoted as noise amplification for parallel imaging were quantitatively evaluated by phantom studies. Compared with a commercial abdominal coil array, the proposed 36-channel fetal array provides not only SNR improvements in full phase encoding (with 10% in the region where the whole fetal body was located, and up to 40% in the edge region where the fetal brain and heart may appear) but also an augmented parallel imaging capability and remarkable SNR improvements at high acceleration factors.

Assessment of hepatic and cardiac iron overload in thalassemia patients by magnetic resonance imaging: Our experience in Alexandria University

Aim of the studyThe aim of this study was to assess the utility of MRI as a non-invasive technique for grading of the hepatic and cardiac iron overload in Thalassemia patients in a cohort of patients in Alexandria, Egypt. Patients and methodsThe study included 80 known patient with Thalassemia on repeated blood transfusion referred from internal medicine department (hematology unit) to the radiology department at Alexandria main university hospital. A 1.5-Tesla MR scanner was used (Achieva; Philips Medical Systems, the Netherlands) equipped with a standard five-element synergy cardiac coil. ResultsThe myocardial iron overload among our cases were as follow: 73 cases (91.3%) with no overload, 5 cases (6.3%) with mild overload, one case (1.3%) with moderate overload and also only one case (1.3%) with sever iron overload. The hepatic iron overload among the studied cases were as follow: 20 patients (25%) with no overload, two patients (2.5%) were upper normal overload, 9 cases (11.3%) with mild overload, 47 patients (58.8%) with moderate overload and only two patients (2.5%) with sever overload. ConclusionMost thalassemia major patients in our study, who had no regular chelation therapy, had hepatic iron overload, less frequently myocardial iron overload.

Insertable biplanar gradient coils for magnetic resonance microscopy: theoretical minimization of power dissipation for different fabrication methods

High-resolution magnetic resonance microscopy (MRM) demands strong gradient magnetic fields to be driven rapidly by a set of three gradient coils. However, due to their small size, gradient coils for MRM are typically limited by resistive heating, especially since standard coil design methods for minimizing power dissipation do not account for certain fabrication constraints, which leads to suboptimal coils and low duty cycles. In this paper, a method is presented for designing insertable biplanar gradient coils that exhibit genuine minimum power dissipation, in which important geometrical parameters that define the intended fabrication method are included in the optimization. A survey of different coil types is presented and it is shown that for wire-wound coils, considerable reductions in dissipated power (21 ± 9%) and increases in efficiency (23 ± 16%) are possible compared to the corresponding standard minimum power designs.

Wireless deep-subwavelength metamaterial enabling sub-mm resolution magnetic resonance imaging

A wireless deep-subwavelength metamaterial architecture is proposed, modeled and demonstrated for a high-resolution magnetic resonance imaging (HR-MRI) application that is miniaturized to be resonant at approximately λ0/1500 dimensions. The proposed structure has the adjustable resonance frequency from 65 MHz to 5.5 GHz for the sub-cm footprint area (8 mm × 8 mm for this study) and provides a quality factor (Q-factor) of approximately 80 in free space for 123 MHz of operation. This structure consists of a cross-via metallized partial-double-layer metamaterial, sandwiching a dielectric thin film; this structure strongly localizes the electric field in this film and has a highly capacitive metal overlay that allows for a wide range of frequency adjustment. Although the achieved resonance frequencies enable a large number of applications, as a proof-of-concept demonstration, we experimentally showed the operation of this wireless metastructure in HR-MRI to highlight its precise frequency adjustment and signal-to-noise-ratio (SNR) improvement capabilities. The proposed metamaterial was found to maintains high Q-factors despite loading with a body-mimicking lossy phantom. The experimental results indicated that the proposed metastructure can be used as an SNR-enhancing device offering 15-fold SNR enhancements that allows for imaging of objects as small as 200 μm in diameter in its vicinity, at an unprecedented level of resolution at the given DC field using standard head coils. As a result of its deep-subwavelength miniaturization accompanied by reasonable Q-factor with outstanding resonance frequency adjustment capability, this class of metastructure is proved to be an excellent candidate for in vivo medical applications.

MR Performance in the Presence of a Radio Frequency-Penetrable Positron Emission Tomography (PET) Insert for Simultaneous PET/MRI.

Despite the great promise of integrated positron emission tomography (PET)/magnetic resonance (MR) imaging to add molecular information to anatomical and functional MR, its potential impact in medicine is diminished by a very high cost, limiting its dissemination. An RF-penetrable PET ring that can be inserted into any existing MR system has been developed to address this issue. Employing optical signal transmission along with battery power enables the PET ring insert to electrically float with respect to the MR system. Then, inter-modular gaps of the PET ring allow the RF transmit field from the standard built-in body coil to penetrate into the PET fields-of-view (FOV) with some attenuation that can be compensated for. MR performance, including RF noise, magnetic susceptibility, RF penetrability through and $B_{1}$ uniformity within the PET insert, and MR image quality, were analyzed with and without the PET ring present. The simulated and experimentally measured RF field attenuation factors with the PET ring present were -2.7 and -3.2 dB, respectively. The magnetic susceptibility effect (0.063 ppm) and noise emitted from the PET ring in the MR receive channel were insignificant. $B_{1}$ homogeneity of a spherical agar phantom within the PET ring FOV dropped by 8.4% and MR image SNR was reduced by 3.5 and 4.3 dB with the PET present for gradient-recalled echo and fast-spin echo, respectively. This paper demonstrates, for the first time, an RF-penetrable PET insert comprising a full ring of operating detectors that achieves simultaneous PET/MR using the standard built-in body coil as the RF transmitter.

Poster Number: NR 28 - Sham Validation in Transcranial Magnetic Stimulation

Introduction: Devising sham treatment for repetitive Transcranial Magnetic Stimulation (rTMS) studies has been problematic. A reliable sham coil needs to produce cutaneous electric stimulation, and noise related to electrical discharge indistinguishable from the active coil. Initially investigators used to tilt the coil 45 to 90 degrees from the scalp to produce a sham treatment, which enabled both subjects and TMS operators to know the treatment allocation. Later investigators used scalp electrodes to mimic the cutaneous sensation associated with treatment. We used Neurostar Xplor system in a double blind sham controlled rTMS protocol for the management of apathy in patients with Alzheimer's dementia. The Neurostar Xplor system consists of Xplor standard treatment coil, a blinded active coil, a blinded sham coil, a quick release hub, enhanced coil connector, coil cart and the acoustic blinding hardware. Our objective was to assess the integrity of the sham treatment by recording subject's, caregiver's and operator's perception of whether they think that the subject received sham or active treatment. We further checked if the perception of coil assignment had an impact on outcomes.