A modular phantom and software to characterize 3D geometric distortion in MRI
Jordan M. Slagowski, Yao Ding, Manik Aima, Zhifei Wen, Clifton D. Fuller, Caroline Chung, J. Matthew Debnam, Ken-Pin Hwang, Mo Kadbi, Janio Szklaruk, Jihong Wang
MRI offers outstanding soft tissue contrast that may reduce uncertainties in target and organ-at-risk delineation and enable online adaptive image-guided treatment. Spatial distortions resulting from non-linearities in the gradient fields and non-uniformity in the main magnetic field must be accounted for across the imaging field-of-view to prevent systematic errors during treatment delivery. This work presents a modular phantom and software application to characterize geometric distortion (GD) within the large field-of-view MRI images required for radiation therapy simulation. The modular phantom is assembled from a series of rectangular foam blocks containing high-contrast fiducial markers in a known configuration. The modular phantom design facilitates transportation of the phantom between different MR scanners and MR-guided linear accelerators and allows the phantom to be adapted to fit different sized bores or coils. The phantom was evaluated using a 1.5T MR-guided linear accelerator (MR-Linac) and 1.5T and 3.0T diagnostic scanners. Performance was assessed by varying acquisition parameters to induce image distortions in a known manner. Imaging was performed using T1 and T2 weighted pulse sequences with 2D and 3D distortion correction algorithms and the receiver bandwidth (BW) varied as 250-815 Hz/pixel. Phantom set-up reproducibility was evaluated across independent set-ups. The software was validated by comparison with a non-modular phantom. Average geometric distortion was 0.94+/-0.58 mm for the MR-Linac, 0.90+/-0.53 mm for the 1.5 T scanner, and 1.15+/-0.62 mm for the 3.0T scanner, for a 400 mm diameter volume-of-interest. GD increased, as expected, with decreasing BW, and with the 2D versus 3D correction algorithm. Differences in GD attributed to phantom set-up were 0.13 mm or less. Differences in GD for the two software applications were less than 0.07 mm.
With the increasing complexity of external beam therapy, so-called "end-to-end" tests are intended to cover all steps from therapy planning to follow-up to fulfill the high demands on quality assurance. As magnetic resonance imaging (MRI) gains growing importance in the treatment process and established phantoms (such as the Alderson head) cannot be used for those tests, novel multimodality phantoms have to be developed. Here, we present a feasibility study for such a customizable multimodality head phantom. We used a set of patient CT images as the basis for the anthropomorphic head shape. Th…
Purpose: To develop bone material analogues that can be used in construction of phantoms for simultaneous PET/MRI systems. Methods: Plaster was used as the basis for the bone material analogues tested in this study. It was mixed with varying concentrations of an iodinated CT contrast, a gadolinium-based MR contrast agent, and copper sulfate to modulate the attenuation properties and MRI properties (T1 and T2*). Attenuation was measured with CT and 68Ge transmission scans, and MRI properties were measured with quantitative ultrashort echo time pulse sequences. A proof-of-concept skull was creat…
BigBrain-MR: a new digital phantom with anatomically-realistic magnetic resonance properties at 100-μm resolution for magnetic resonance methods development
This paper presents Contextual Fibre Growth (ConFiG), an approach to generate white matter numerical phantoms by mimicking natural fibre genesis. ConFiG grows fibres one-by-one, following simple rules motivated by real axonal guidance mechanisms. These simple rules enable ConFiG to generate phantoms with tuneable microstructural features by growing fibres while attempting to meet morphological targets such as user-specified density and orientation distribution. We compare ConFiG to the state-of-the-art approach based on packing fibres together by generating phantoms in a range of fibre configu…
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…
Objective: Accurate estimation of SAR is critical to safeguarding vulnerable patients who require an MRI procedure. The increased static field strength and RF duty cycle capabilities in modern MRI scanners mean that systems can easily exceed safe SAR levels for patients. Advisory protocols routinely used to establish quality assurance protocols are not required to advise on the testing of MRI SAR levels and is not routinely measured in annual medical physics quality assurance checks. This study aims to develop a head phantom and protocol that can independently verify global SAR for MRI clinica…
Low-Cost and Detunable Wireless Resonator Glasses for Enhanced Eye MRI with Concurrent High-Quality Whole Brain MRI
Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center（范德堡大学成像科学研究所，范德堡大学医学中心）；Department of Electrical and Computer Engineering, Vanderbilt University（范德堡大学电气与计算机工程系）；Philips（飞利浦）；Department of Biomedical Engineering, Vanderbilt University（范德堡大学生物医学工程系）；Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center（范德堡大学医学中心放射学与放射科学系）
Ultra high field (UHF) brain MRI has proved its value by providing enhanced SNR, contrast, and higher resolution derived from the higher magnetic field (B0). Nonetheless, with the increased B0 of UHF MRI, the transmit RF magnetic field (B1+) inhomogeneity also became one of the critical issues requiring attention. As the effective wavelength of RF becomes comparable or smaller than the dimension of the brain at B0 larger than 7 Tesla, the increased B1+ inhomogeneity of UHF MRI results in poor SNR and uneven contrast. While parallel transmission techniques (PTx) and high permittivity material (…
We investigated whether a combination of k-space undersampling and variable density averaging enhances image quality for low-SNR MRI acquisitions. We implemented 3D Cartesian k-space prospective undersampling with a variable number of averages for each k-line. The performance of this compressed sensing with variable-density averaging (CS-VDA) method was evaluated in retrospective analysis of fully sampled phantom MRI measurements, as well as for prospectively accelerated in vivo 3D brain and knee MRI scans. Both phantom and in vivo results showed that acquisitions using the CS-VDA approach res…
Objectives Studies that assess magnetic resonance imaging (MRI) induced radiofrequency (RF) heating of the tissue in the presence of an active electronic implant are mostly performed in horizontal, closed-bore scanners. Vertical, open-bore MRI systems have a 90° rotated magnet and generate a fundamentally different RF field distribution in the body, yet little is known about the RF heating of deep brain stimulation (DBS) systems in this class of scanners. Here, we investigated whether RF heating of DBS devices was significantly different in a vertical, open-bore MRI scanner compared to a horiz…
Purpose: Eddy currents might lead to image distortions in diffusion weighted echo planar imaging. A method is proposed to reduce their effects on double diffusion encoding (DDE) MRI experiments and the thereby derived microscopic fractional anisotropy (μFA) . Methods: The twice refocused spin echo scheme was adapted for DDE measurements. To assess the effect of individual diffusion encodings on the image distortions, measurements of a grid of plastic rods in water were performed. The effect of eddy current compensation on μFA measurements was evaluated in the brains of six healthy volunteers. …
Objective: Interventional MRI (i-MRI) is crucial for MR image-guided therapy. Current image reconstruction methods for dynamic MR imaging are mostly retrospective that may not be suitable for i-MRI in real-time. Therefore, an algorithm to reconstruct images without a temporal pattern as in dynamic imaging is needed for i-MRI. Methods: We proposed a low-rank and sparsity (LS) decomposition algorithm with framelet transform to reconstruct the interventional feature with a high temporal resolution. Different from the existing LS based algorithm, we utilized the spatial sparsity of both the low-ra…
Magnetic resonance imaging (MRI) is increasingly utilized for image-guided radiotherapy due to its outstanding soft-tissue contrast and lack of ionizing radiation. However, geometric distortions caused by gradient nonlinearity (GNL) limit anatomical accuracy, potentially compromising the quality of tumour treatments. In addition, slow MR acquisition and reconstruction limit the potential for real-time image guidance. Here, we demonstrate a deep learning-based method that rapidly reconstructs distortion-corrected images from raw k-space data for real-time MR-guided radiotherapy applications. We…
Intrafraction motion can play a pivotal role in the success of abdominal and thoracic radiation therapy. Hybrid magnetic resonance-guided radiotherapy systems have the potential to control for intrafraction motion. Recently, we introduced an MRI sequence capable of acquiring real-time cine imaging in two orthogonal planes (SOPI). We extend SOPI here to permit dynamic updating of slice positions in one plane while keeping the other plane position fixed. In this implementation, cine images from the static plane are used for motion monitoring and as image navigators to sort stepped images in the …
Hyperion-IID is a positron emission tomography (PET) insert which allows simultaneous operation in a clinical magnetic resonance imaging (MRI) scanner. To read out the scintillation light of the employed LYSO crystal arrays with a pitch of 1 mm pitch and 12 mm in height, digital silicon photomultipliers (DPC 3200-22, Philips Digital Photon Counting) (DPC) are used. The basic PET performance in terms of energy resolution, coincidence resolution time (CRT) and sensitivity as a function of operating parameters, such as the operating temperature, the applied overvoltage, activity and configuration…
Fast Electromagnetic and RF Circuit Co-Simulation for Passive Resonator Field Calculation and Optimization in MRI
Vanderbilt University（范德堡大学）；Vanderbilt University Medical Center（范德堡大学医学中心）；Middle Tennessee State University（中田纳西州立大学）；Oak Ridge National Laboratory（橡树岭国家实验室）
Background: Magnetic field inhomogeneities generate important geometric distortions in reconstructed echo-planar images. Various procedures were proposed for correcting these distortions on brain images; yet, few neuroimaging studies tailored and incorporated the use of these techniques in spinal cord diffusion MRI. Purpose: We present a comparative evaluation of distortion correction methods that use the reversed gradient polarity technique on spinal cord. We propose novel geometric metrics to measure the alignment of the reconstructed diffusion model with the apparent centerline of the spina…
Parallel imaging techniques have been widely used in high-field magnetic resonance imaging (MRI). Multiple receiver coils have been shown to improve image quality and allow accelerated image acquisition. Magnetic resonance imaging at ultra-low fields (ULF MRI) is a new imaging approach that uses SQUID (superconducting quantum interference device) sensors to measure the spatially encoded precession of pre-polarized nuclear spin populations at microtesla-range measurement fields. In this work, parallel imaging at microtesla fields is systematically studied for the first time. A seven-channel SQU…
Two-stage Respiratory Motion-resolved Radial MR Image Reconstruction Using an Interpretable Deep Unrolled Network
Soochow University（苏州大学）；The University of Queensland（昆士兰大学）；The Fifth Affiliated Hospital of Sun Yat-sen University（中山大学附属第五医院）；Philips Healthcare（飞利浦医疗）；Central South University（中南大学）；University of Sydney（悉尼大学）；Nanjing University（南京大学）
Fluorine-19 (19F) MRI of injected perfluorocarbon emulsions (PFCs) allows for the non-invasive quantification of inflammation and cell tracking, but suffers from a low signal-to-noise ratio and extended scan time. To address this limitation, we tested the hypothesis that a 19F MRI pulse sequence that combines a specific undersampling regime with signal averaging has increased sensitivity and robustness against motion artifacts compared to a non-averaged fully-sampled dataset, when both are reconstructed with compressed sensing. To this end, numerical simulations and phantom experiments were pe…
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
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 …
University of Auckland（奥克兰大学）；University of Leeds（利兹大学）；Auckland Bioengineering Institute（奥克兰生物工程研究所）；Institute of Environmental Science and Research（环境科学与研究所）；King's College London（伦敦国王学院）
4D-flow magnetic resonance imaging (MRI) is an emerging imaging technique where spatiotemporal 3D blood velocity can be captured with full volumetric coverage in a single non-invasive examination. This enables qualitative and quantitative analysis of hemodynamic flow parameters of the heart and great vessels. An increase in the image resolution would provide more accuracy and allow better assessment of the blood flow, especially for patients with abnormal flows. However, this must be balanced with increasing imaging time. The recent success of deep learning in generating super resolution image…
Physikalisch-Technische Bundesanstalt (PTB)（德国联邦物理技术研究院）；Berlin Center for Advanced Neuroimaging, Charite–Universitatsmedizin Berlin, Corporate Member of Freie Universitat Berlin, Berlin Institute of Health（柏林高级神经成像中心，柏林夏里特医科大学，柏林自由大学企业成员，柏林健康研究所）；Just Transition Center, Group C1, Martin-Luther-Universität Halle-Wittenberg（公正转型中心C1组，哈勒-维滕贝格马丁路德大学）；Open Source Imaging Initiative (OSI²) e.V.（开源影像倡议协会）；Helmut Schmidt University（赫尔穆特·施密特大学）
The fMRI community has made great strides in decoupling neuronal activity from other physiologically induced T2* changes, using sensors that provide a ground-truth with respect to cardiac, respiratory, and head movement dynamics. However, blood oxygenation level-dependent (BOLD) time-series dynamics are confounded by scanner artifacts, in complex ways that can vary not only between scanners but even, for the same scanner, between sessions. The lack of equivalent ground truth has thus far stymied the development of reliable methods for identification and removal of scanner-induced noise. To add…
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…
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…
We report decoupling of two closely located resonant dipole antennas dedicated for ultra-high field magnetic resonance imaging (MRI). We show that a scatterer slightly raised over the plane of antennas grants a sufficient decoupling even for antennas separated by very small gap (below 1/30 of the wavelength). We compare the operation of two decoupling scatterers. One of them is a shortcut resonant dipole and another is a split-loop resonator (SLR). Previously, we have shown that the SLR offers a wider operational band than the dipole and the same level of decoupling. However, it was so for an …
A No-Reference Medical Image Quality Assessment Method Based on Automated Distortion Recognition Technology: Application to Preprocessing in MRI-guided Radiotherapy
Beijing University of Posts and Telecommunications（北京邮电大学）；National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College（中国医学科学院北京协和医学院国家癌症中心/国家癌症临床医学研究中心/肿瘤医院）
In order to provide information for the use of radar in diagnostics a qualitative map of movements in the thorax has been obtained. This map was based on magnetic resonance image sequences of a human thorax during suspended respiration. The movements were measured using two distinct techniques. Segmentation provided measures of aorta dilatation and displacements, and image edge detection indicated other movements. The largest heart movements were found in the anterior and left regions of the heart with in-plane displacements on the order of 1 cm and which caused lung vessels displacements on t…
In Diffusion Tensor Imaging (DTI) or High Angular Resolution Diffusion Imaging (HARDI), a tensor field or a spherical function field (e.g., an orientation distribution function field), can be estimated from measured diffusion weighted images. In this paper, inspired by the microscopic theoretical treatment of phases in liquid crystals, we introduce a novel mathematical framework, called Director Field Analysis (DFA), to study local geometric structural information of white matter based on the reconstructed tensor field or spherical function field: 1) We propose a set of mathematical tools to p…
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 …
GE Global Research Center（GE全球研究中心）；Technische Universität München（慕尼黑工业大学）；INSERM（法国国家健康与医学研究院）；Université de Lorraine（洛林大学）；GE Healthcare（GE医疗）
To develop an efficient motion-compensated reconstruction technique for free-breathing cardiac magnetic resonance imaging (MRI) that allows high-quality images to be reconstructed from multiple undersampled single-shot acquisitions. The proposed method is a joint image reconstruction and motion correction method consisting of several steps, including a non-rigid motion extraction and a motion-compensated reconstruction. The reconstruction includes a denoising with the Beltrami regularization, which offers an ideal compromise between feature preservation and staircasing reduction. Results were …
Direct imaging of impressed dc currents inside the head can provide valuable conductivity information, possibly improving electro-magnetic neuroimaging. Ultra-low field magnetic resonance imaging (ULF MRI) at $μ$T Larmor fields can be utilized for current density imaging (CDI). Here, a measurable impact of the magnetic field $B_{J}$, generated by the impressed current density $J$, on the MR signal is probed using specialized sequences. In contrast to high-field MRI, the full tensor of $B_{J}$ can be derived without rotation of the subject in the scanner, due to a larger flexibility in the sequ…
In this work we introduce a new method that combines Parallel MRI and Compressed Sensing (CS) for accelerated image reconstruction from subsampled k-space data. The method first computes a convolved image, which gives the convolution between a user-defined kernel and the unknown MR image, and then reconstructs the image by CS-based image deblurring, in which CS is applied for removing the inherent blur stemming from the convolution process. This method is hence termed CORE-Deblur. Retrospective subsampling experiments with data from a numerical brain phantom and in-vivo 7T brain scans showed t…
Quantitative MRI (qMRI) methods allow reducing the subjectivity of clinical MRI by providing numerical values on which diagnostic assessment or predictions of tissue properties can be based. However, qMRI measurements typically take more time than anatomical imaging due to requiring multiple measurements with varying contrasts for, e.g., relaxation time mapping. To reduce the scanning time, undersampled data may be combined with compressed sensing reconstruction techniques. Typical CS reconstructions first reconstruct a complex-valued set of images corresponding to the varying contrasts, follo…
Department Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg（生物医学工程人工智能系，埃尔朗根-纽伦堡弗里德里希-亚历山大大学）；Department of Biomedical Engineering, The Ohio State University（生物医学工程系，俄亥俄州立大学）；Research & Clinical Translation, Magnetic Resonance, Siemens Healthineers AG（研究与临床转化，磁共振，西门子医疗有限公司）；Division of Cardiovascular Medicine, The Ohio State University（心血管医学系，俄亥俄州立大学）
Purpose: To separate the effects of magnetic susceptibility and chemical shift/exchange in a phantom with isotropic magnetic susceptibility. To generate a chemical shift/exchange-corrected quantitative susceptibility mapping (QSM) result. Theory and Methods: Magnetic susceptibility and chemical shift/exchange are the properties of a material. Both are known to induce the resonance frequency shift in MRI. In current QSM, the susceptibility is reconstructed from the frequency shift, ignoring the contribution of the chemical shift/exchange. In this work, a simple geometric approach, which average…
