Here we propose double-coil setup to allow high signal-to-noise ratio broad-range heteronuclear magnetic resonance imaging experiments: two independent coils, one of them tuned to $^{1}$H frequency to perform anatomical $^{1}$H imaging, and another one, metamaterial-inspired coil, tuned to the X-nucleus frequency. In this work our goal was to design a broad-range X-nuclei coil to cover $^{2}$H, $^{11}$B, $^{13}$C, $^{23}$Na, $^{7}$Li and $^{31}$P nuclear magnetic resonance frequencies, and to combine it with $^{1}$H coil in one setup. The system was designed for 11.7 T scanner, i.e., with 76-203 MHz frequency tuning range for the X-nuclei and tuned to 500 MHz for the proton coil. X-nuclei coil operates via excitation of the fundamental eigenmode of an array of parallel non-magnetic wires. The excitation of the array is provided via non-resonant feeding loop inductively coupled to the resonator. In order to tune the X-coil over such a wide range, both structural capacitance and inductance of the coil were made variable; narrow range tuning of the $^{1}$H coil is achieved via conventional tuning-matching circuit. Here, the design principle and setup tunability were investigated in simulations and experimentally.
We looked for a biological analogy to developed an improved surface coil to acquire magnetic resonance images. Nature offers engineering solutions that can be exploited to improve the performance of devices, such as MRI RF coils. In this paper, we proposed a coil layout based on flower petal patterns for UHF MRI at 15.2 T. This particular configuration offers the possibility to use a different number of petals and shapes. The petal resonator coil and the magnetron coil have similar layouts, which have proved to outperform the popular circular coil. Phantom images were acquired with our coil pr…
In this paper we propose, design and test a new dual-nuclei RF-coil inspired by wire metamaterial structures. The coil operates due to resonant excitation of hybridized eigenmodes in multimode flat periodic structures comprising several coupled thin metal strips. It was shown that the field distribution of the coil (i.e. penetration depth) can be controlled independently at two different Larmor frequencies by selecting a proper eigenmode in each of two mutually orthogonal periodic structures. The proposed coil requires no lumped capacitors for tuning and matching. In order to demonstrate the p…
Background: Prostate cancer is one of the most common forms of cancer found in males making early diagnosis important. Magnetic resonance imaging (MRI) has been useful in visualizing and localizing tumor candidates and with the use of endorectal coils (ERC), the signal-to-noise ratio (SNR) can be improved. The coils introduce intensity inhomogeneities and the surface coil intensity correction built into MRI scanners is used to reduce these inhomogeneities. However, the correction typically performed at the MRI scanner level leads to noise amplification and noise level variations. Methods: In t…
A volume coil with squared slots-end ring was developed to attain improved sensitivity for imaging of rat's brain at 7 T. The principles of the high cavity resonator for the low-pass case and the law of Biot-Savart were used to derive a theoretical expression of the coil sensitivity. The slotted-end ring resonator showed a theoretical 2.22-fold improvement over the standard birdcage coil with similar dimensions. Numerical studies were carried out for the electromagnetic fields and specific absorption rates for our coil and a birdcage coil loaded with a saline-filled cylindrical phantom and a d…
University of Calgary（卡尔加里大学）；Hotchkiss Brain Institute, University of Calgary（卡尔加里大学霍奇基斯脑研究所）；Foothills Medical Center（山麓医学中心）；Radboud University Medical Center（拉德堡德大学医学中心）；Netherlands Cancer Institute（荷兰癌症研究所）；University of Amsterdam（阿姆斯特丹大学）；Amsterdam UMC（阿姆斯特丹大学医学中心）；University of Campinas（坎皮纳斯大学）
Deep-learning-based brain magnetic resonance imaging (MRI) reconstruction methods have the potential to accelerate the MRI acquisition process. Nevertheless, the scientific community lacks appropriate benchmarks to assess MRI reconstruction quality of high-resolution brain images, and evaluate how these proposed algorithms will behave in the presence of small, but expected data distribution shifts. The Multi-Coil Magnetic Resonance Image (MC-MRI) Reconstruction Challenge provides a benchmark that aims at addressing these issues, using a large dataset of high-resolution, three-dimensional, T1-w…
In this paper we design and construct gradient coils for a Halbach permanent magnet array magnetic resonance (MR) scanner. The target field method, which is widely applied for the case of axial static magnetic fields, has been developed for a transverse static magnetic field as produced by a Halbach permanent magnet array. Using this method, current densities for three gradient directions are obtained and subsequently verified using a commercial magneto-static solver. Stream functions are used to turn the surface current densities into wire patterns for constructing the gradient coils. The mea…
Magnetic resonance imaging systems rely on signal detection via radiofrequency coil arrays which, ideally, need to provide both bendability and form-fitting stretchability to conform to the imaging volume. However, most commercial coils are rigid and of fixed size with a substantial mean offset distance of the coil from the anatomy, which compromises the spatial resolution and diagnostic image quality as well as patient comfort. Here, we propose a soft and stretchable receive coil concept based on liquid metal and ultra-stretchable polymer that conforms closely to a desired anatomy. Moreover, …
University of Minnesota（明尼苏达大学）；University of Florida（佛罗里达大学）；MIT-IBM Watson AI Lab, IBM Research（MIT-IBM沃森人工智能实验室，IBM研究院）
Although deep learning (DL) has received much attention in accelerated MRI, recent studies suggest small perturbations may lead to instabilities in DL-based reconstructions, leading to concern for their clinical application. However, these works focus on single-coil acquisitions, which is not practical. We investigate instabilities caused by small adversarial attacks for multi-coil acquisitions. Our results suggest that, parallel imaging and multi-coil CS exhibit considerable instabilities against small adversarial perturbations.
Objective: Concurrent excitation and acquisition in MRI is a method to acquire MRI signal from tissues with very short transverse relaxation time. Since transmit power is many orders of magnitude larger than receive signal, a weak coupling dominates the MR signal during CEA. Thus, appropriate decoupling between transmit and receive coils is required. In this study, two controllable decoupling designs are investigated for achieving isolation between coils. Methods: A modified version of isolation concept used in the full-duplex radios in communication systems is applied to acquire MRI signal us…
Design and performance of a Toroidal RF Volume Coil with Intrinsic Electromagnetic Interference Rejection for low-field Portable Halbach-Based MRI Systems
We develop a novel next generation light-weight highly flexible pediatric coil array, combine it with a high-density pediatric posterior array or conventional posterior phased array, and determine feasibility of pediatric clinical use. A highly flexible 16 element MRI receiver coil was constructed with low-profile noise controlling preamplifiers that minimized reactive and resistive coupling. Element decoupling was assessed in flat and highly flexed states. With IRB approval and informed consent and assent, 24 consecutive subjects undergoing torso or extremity MRI were prospectively recruited.…
A wearable, stretchable radio-frequency coil for extremity imaging in low-field MRI systems
The Institute for Instrumentation in Molecular Imaging (I3M), CSIC–Universitat Politècnica de València（分子成像仪器研究所（I3M），西班牙瓦伦西亚理工大学）；C.J. Gorter MRI Center, Department of Radiology, Leiden University Medical Center（莱顿大学医学中心放射科 C.J. Gorter 磁共振中心）；PhysioMRI Tech
Birth of the Coil: another Milestone towards a fully reproducible low-field MRI scanner for head-imaging
Istituto Nazionale di Ricerca Metrologica (INRiM)（意大利国家计量研究所）；Institute of Biomedical Imaging, Graz University of Technology（格拉茨工业大学生物医学成像研究所）；Physikalisch-Technische Bundesanstalt (PTB) Braunschweig and Berlin（德国联邦物理技术研究院）；Universidad Comunera（科穆内拉大学）；University of Alberta（阿尔伯塔大学）；Cross Cancer Institute（交叉癌症研究所）
In this contribution we present numerical and experimental results of a parametric quantitative study of radiative dipole antennas in a phased array configuration for efficient body magnetic resonance imaging at 7T via parallel transmission. For magnetic resonance imaging (MRI) at ultrahigh fields (7T and higher) dipole antennas are commonly used in phased arrays, particularly for body imaging targets. This study reveals the effects of dipole positioning in the array (elevation of dipoles above the subject and inter-dipole spacing) on their mutual coupling, $B_1^{+}$ per $P_{acc}$ and $B_1^{+}…
The coaxial cables commonly used to connect RF coil arrays with the control console of an MRI scanner are susceptible to electromagnetic coupling. As the number of RF channel increases, such coupling could result in severe heating and pose a safety concern. Non-conductive transmission solutions based on fiber-optic cables are considered to be one of the alternatives, but are limited by the high dynamic range ($>80$~dB) of typical MRI signals. A new digital fiber-optic transmission system based on delta-sigma modulation (DSM) is developed to address this problem. A DSM-based optical link is pro…
In this work a mu=-1 metamaterial (MM) lens for magnetic resonance imaging (MRI) is demonstrated. MRI uses surface coils to detect the radiofrequency(RF) energy absorbed and emitted by the nuclear spins in the imaged object. The proposed MM lens manipulates the RF field detected by these surface coils, so that the coil sensitivity and spatial localization is substantially improved. Beyond this specific application, we feel that the reported results are the experimental confirmation of a new concept for the manipulation of RF field in MRI, which paves the way to many other interesting applicati…
Standard coils can cause inhomogeneities due to the standing wave patterns at ultra high field MRI. This B1 inhomogeneity can be overcome using the travelling-wave MRI (twMRI) approach. The ma- jority of twMRI research has been done with clinical MRI scanners at 7T or above. More recently, this concept has been also used with animal MRI systems, using circular-cross section waveguides and dielectric materials for both type of scanners. We have demonstrated that twMRI can be used at 3 T with clinical systems and a parallel-plate waveguide. Here, we investigated the use of a parallel- plate wave…
Microsoft Research（微软研究院）；University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；University of Minnesota（明尼苏达大学）；Stanford University（斯坦福大学）；Duke University（杜克大学）；New York University（纽约大学）
Improving speed and image quality of Magnetic Resonance Imaging (MRI) via novel reconstruction approaches remains one of the highest impact applications for deep learning in medical imaging. The fastMRI dataset, unique in that it contains large volumes of raw MRI data, has enabled significant advances in accelerating MRI using deep learning-based reconstruction methods. While the impact of the fastMRI dataset on the field of medical imaging is unquestioned, the dataset currently lacks clinical expert pathology annotations, critical to addressing clinically relevant reconstruction frameworks an…
In parallel magnetic resonance imaging (pMRI), to find a joint solution for the image and coil sensitivity functions is a nonlinear and nonconvex problem. A class of algorithms reconstruct sensitivity encoded images of the coils first followed by the magnitude only image reconstruction, e.g. GRAPPA. It is shown in this paper that, if only the magnitude image is reconstructed, there exists a convex solution space for the magnitude image and sensitivity encoded images. This solution space enables formulation of a regularized convex optimization problem and leads to a globally optimal and unique …
It is well known that magnetic resonance imaging (MRI) at 7 Tesla (7T) and higher magnets can provide much better signal sensitivity compared with lower field strengths. However, variety of commercially available ultra-high-field MRI coils are still limited, due to the technical challenges associated with wavelength effect, such as flip angle inhomogeneity and asymmetric transmit and receive RF field patterns. We aimed to develop a passive RF shimming technique using an inductively coupled RF resonator array to improve brain MRI at 7T, focusing of cerebellum. Method: an inductively coupled RF …
High impedance RF coils, such as self-decoupled coils, reduce the electromagnetic coupling between the coil elements and eliminates the use of complex decoupling technologies. Although the high impedance design promises excellent decoupling between the coil elements, it also results in high electric fields across the RF coil, leading to potential safety problems during imaging. It also causes B1 field asymmetry, ultimately leading to difficulties in imaging quantification. In this study, we propose and investigate using a high dielectric sheet to reduce the electric fields across the coil and …
Increasing imaging speed is of utmost importance in in-vivo magnetic resonance imaging (MRI). With simultaneous multi-slice (SMS) MRI we can simultaneously acquire several slices of an object, which allows for higher undersampling factors compared to single- or conventional multi-slice measurements by exploiting axial coil sensitivity information. In this thesis, we give a short introduction to the physical principles of MRI, cover the basics of a FLASH based SMS MRI sequence and perform tests to verify its accuracy: We check the fidelity of the slice distance as well as the flip angle and con…
The analytical expression for the signal-to-noise ratio of a slotted surface coil with an arbitrary number of slots was derived using the quasi-static approach. This surface coil based on the vane-type magnetron tube. To study the coil perfomance, the theoretical signal-to-noise ratio predictions of this coil design were computed using a different number of slots. Results were also compared with theoretical results obtained for a circular coil with similar dimensions. It can be appreciated that slotted surface coil performance improves as the number of coils increases and, outperformed the cir…
With a hybrid MEG--MRI device that uses the same sensors for both modalities, the co-registration of MRI and MEG data can be replaced by an automatic calibration step. Based on the highly accurate signal model of ultra-low-field (ULF) MRI, we introduce a calibration method that eliminates the error sources of traditional co-registration. The signal model includes complex sensitivity profiles of the superconducting pickup coils. In ULF MRI, the profiles are independent of the sample and therefore well-defined. In the most basic form, the spatial information of the profiles, captured in parallel…
Theory of a high impedance coil (HIC) - a cable loop antenna with a modified shield - is discussed comprehensively for both in transmitting and receiving regimes. Understanding a weakness of the previously reported HIC in transmitting regime, we suggest another HIC which is advantageous in both transmitting and receiving regimes compared to a conventional loop antenna. In contrast with a claim of previous works, only this HIC is a practical transceiver HIC. Using the perturbation approach and adding gaps to both shield and inner wire of the cable, we tune the resonance frequency to be suitable…
Purpose: To design a low-cost, portable permanent magnet-based MRI system capable of obtaining in vivo MR images within a reasonable scan time. Methods: A discretized Halbach permanent magnet array with a clear bore diameter of 27 cm was designed for operation at 50 mT. Custom built gradient coils, radiofrequency coil, gradient amplifiers and radiofrequency amplifier were integrated and tested on both phantoms and in vivo. Results: Phantom results showed that the gradient non-linearity in the y- and z-directions was less than 5% over a 15 cm field-of-view and did not need correcting. For the x…
In phase-contrast magnetic resonance imaging (PC-MRI), spin velocity contributes to the phase measured at each voxel. Therefore, estimating velocity from potentially wrapped phase measurements is the task of solving a system of noisy congruence equations. We propose Phase Recovery from Multiple Wrapped Measurements (PRoM) as a fast, approximate maximum likelihood estimator of velocity from multi-coil data with possible amplitude attenuation due to dephasing. The estimator can recover the fullest possible extent of unambiguous velocities, which can greatly exceed twice the highest venc. The est…
Netherlands Cancer Institute（荷兰癌症研究所）；qurAI group（qurAI团队）；University of Amsterdam（阿姆斯特丹大学）
Magnetic Resonance Imaging can produce detailed images of the anatomy and physiology of the human body that can assist doctors in diagnosing and treating pathologies such as tumours. However, MRI suffers from very long acquisition times that make it susceptible to patient motion artifacts and limit its potential to deliver dynamic treatments. Conventional approaches such as Parallel Imaging and Compressed Sensing allow for an increase in MRI acquisition speed by reconstructing MR images from sub-sampled MRI data acquired using multiple receiver coils. Recent advancements in Deep Learning combi…
Multi-shot echo planar imaging (msEPI) is a promising approach to achieve high in-plane resolution with high sampling efficiency and low T2* blurring. However, due to the geometric distortion, shot-to-shot phase variations and potential subject motion, msEPI continues to be a challenge in MRI. In this work, we introduce acquisition and reconstruction strategies for robust, high-quality msEPI without phase navigators. We propose Blip Up-Down Acquisition (BUDA) using interleaved blip-up and -down phase encoding, and incorporate B0 forward-modeling into Hankel structured low-rank model to enable …
Real-time magnetic resonance imaging (MRI) poses unique challenges related to the speed of data acquisition and to the degree of undersampling necessary to achieve this speed. This Master's thesis introduces and evaluates two pre-processing approaches for these problems: Coil compression to reduce the data volume and a channel selection algorithm to reduce streak artifacts which arise as a consequence of undersampling. Both approaches are tested on real data covering anatomical imaging of the head and of the heart.
At high magnetic field strengths (> 4 T), the propagation wave vector of the excitation field B1 can no longer be ignored as the wavelength becomes commensurate or smaller than the imaging field of view (FOV), particularly for high dielectric media. The emergence of this propagation wave vector renders the excitation field variant in both time and space. In this paper, the propagation of RF excitation waves in a high field vertical NMR system is demonstrated for the first time with an appropriate screened dielectric waveguide excited by a simple loop coil to enable below cutoff propagation for…
Contrast agents with a strong $R_1$ dispersion have been shown to be effective in generating target-specific contrast in MRI. The utilization of this $R_1$ field dependence requires the adaptation of a MRI scanner for fast field-cycling (FFC). Here, we present the first implementation and validation of FFC-MRI at a clinical field strength of 3 T. A field-cycling range of $\pm$100 mT around the nominal $B_0$ field was realized by inserting an additional insert coil into an otherwise conventional MRI system. System validation was successfully performed with selected iron oxide magnetic nanoparti…
'Coil design' is an inverse problem in which arrangements of wire are designed to generate a prescribed magnetic field when energized with electric current. The design of gradient and shim coils for magnetic resonance imaging (MRI) are important examples of coil design. The magnetic fields that these coils generate are usually required to be both strong and accurate. Other electromagnetic properties of the coils, such as inductance, may be considered in the design process, which becomes an optimization problem. The maximum current density is additionally optimized in this work and the resultan…
Magnetic Particle Imaging (MPI) is a novel and versatile imaging modality developing towards human application. When up-scaling to human size, the sensitivity of the systems naturally drops as the coil sensitivity depends on the bore diameter. Thus, new methods to push the sensitivity limit further have to be investigated to cope for this loss. In this paper a dedicated surface coil for mice is developed, improving the sensitivity in cerebral imaging applications. Similar to MRI the developed surface coil improves the sensitivity due to the closer vicinity to the region of interest. With the d…
Optically-powered Low Power Low Noise Amplifiers for MRI
Division of Medical Physics, Department of Diagnostic and Interventional Radiology, Medical Center – University of Freiburg, Faculty of Medicine – University of Freiburg（弗赖堡大学医学院医学中心诊断与介入放射学系医学物理分部）；Microsystems for Biomedical Imaging Group, Department of Microsystems Engineering, University of Freiburg（弗赖堡大学微系统工程学院生物医学成像微系统小组）
