Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering最新文献

{"title":"SQUID-Based Magnetic Resonance Imaging at Ultra-Low Field Using the Backprojection Method","authors":"Qingqian Guo, Chang-yu Ma, Xin Zhang, Yajie Xu, Meisheng Fan, P. Yu, Tao Hu, Yan Chang, Xiao-dong Yang","doi":"10.1155/2020/8882329","DOIUrl":"https://doi.org/10.1155/2020/8882329","url":null,"abstract":"Ultra-low field magnetic resonance imaging (ULF MRI) is an effective imaging technique that applies the ultrasensitive detector of superconducting quantum interference device (SQUID) sensor to detect the MR signal at a microtesla field range. In this work, we designed and developed a SQUID-based ULF MRI system with a frequency-adjustable measurement field, the performance of which was characterized via water phantoms. In order to enhance the MR signals, a 500 mT Halbach magnet was used to prepolarize the magnetization of the sample prior to excitation. The signal-to-noise-ratio (SNR) of the spin-echo- (SE-) based pulse sequence can reach up to 70 in a single scan. The images were then reconstructed successfully by using the maximum likelihood expectation maximization (MLEM) algorithm based on the backprojection imaging method. It was demonstrated that an in-plane resolution of 1.8 × 1.8 mm2 can be achieved which indicated the feasibility of SQUID-based MRI at the ULF.","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"28 1","pages":"1-11"},"PeriodicalIF":0.9,"publicationDate":"2020-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86763216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Capacitive versus Overlap Decoupling of Adjacent Radio Frequency Phased Array Coil Elements: An Imaging Robustness Comparison When Sample Load Varies for 3 Tesla MRI.","authors":"Michael J Beck, Dennis L Parker, J Rock Hadley","doi":"10.1155/2020/8828047","DOIUrl":"10.1155/2020/8828047","url":null,"abstract":"<p><p>Phased array (PA) receive coils are built such that coil elements approximate independent antenna behavior. One method of achieving this goal is to use an available decoupling method to decouple adjacent coil elements. The purpose of this work was to compare the relative performance of two decoupling methods as a function of variation in sample load. Two PA receive coils with 5 channels (5-ch) each, equal outer dimensions, and formed on 12 cm diameter cylindrical phantoms of conductivities 0.3, 0.6, and 0.9 S/m were evaluated for relative signal-to-noise ratio (SNR) and parallel imaging performance. They were only tuned and matched to the 0.6 S/m phantom. Simulated and measured axial, sagittal, and coronal 5-ch PA coil SNR ratios were compared by dividing the overlap by the capacitive decoupled coil SNR results. Issues related to the selection of capacitor values for the two decoupling methods were evaluated by taking the ratio of the match and tune capacitors for large and small 2 channel (2-ch) PA coils. The SNR ratios showed that the SNR of the two decoupling methods were very similar. The inverse geometry-factor maps showed similar but better overall parallel imaging performance for the capacitive decoupled method. The quotients for the 2-ch PA coils' maximum and minimum capacitor value ratios are 3.28 and 1.38 for the large and 3.28 and 2.22 for the small PA. The results of this paper demonstrate that as the sample load varies, the capacitive and overlap decoupling methods are very similar in relative SNR and this similarity continues for parallel imaging performance. Although, for the 5-ch coils studied, the capacitive decoupling method has a slight SNR and parallel imaging advantage and it was noted that the capacitive decoupled coil is more likely to encounter unbuildable PA coil configurations.</p>","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"2020 ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8640609/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39693100","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The \"Loopole\" Antenna: A Hybrid Coil Combining Loop and Electric Dipole Properties for Ultra-High-Field MRI.","authors":"Karthik Lakshmanan, Martijn Cloos, Ryan Brown, Riccardo Lattanzi, Daniel K Sodickson, Graham C Wiggins","doi":"10.1155/2020/8886543","DOIUrl":"10.1155/2020/8886543","url":null,"abstract":"<p><strong>Purpose: </strong>To revisit the \"loopole,\" an unusual coil topology whose unbalanced current distribution captures both loop and electric dipole properties, which can be advantageous in ultra-high-field MRI.</p><p><strong>Methods: </strong>Loopole coils were built by deliberately breaking the capacitor symmetry of traditional loop coils. The corresponding current distribution, transmit efficiency, and signal-to-noise ratio (SNR) were evaluated in simulation and experiments in comparison to those of loops and electric dipoles at 7 T (297 MHz).</p><p><strong>Results: </strong>The loopole coil exhibited a hybrid current pattern, comprising features of both loops and electric dipole current patterns. Depending on the orientation relative to B₀, the loopole demonstrated significant performance boost in either the transmit efficiency or SNR at the center of a dielectric sample when compared to a traditional loop. Modest improvements were observed when compared to an electric dipole.</p><p><strong>Conclusion: </strong>The loopole can achieve high performance by supporting both divergence-free and curl-free current patterns, which are both significant contributors to the ultimate intrinsic performance at ultra-high field. While electric dipoles exhibit similar hybrid properties, loopoles maintain the engineering advantages of loops, such as geometric decoupling and reduced resonance frequency dependence on sample loading.</p>","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"2020 ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8207246/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39248406","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermal Effects Associated with RF Exposures in Diagnostic MRI: Overview of Existing and Emerging Concepts of Protection","authors":"J. S. van den Brink","doi":"10.1155/2019/9618680","DOIUrl":"https://doi.org/10.1155/2019/9618680","url":null,"abstract":"Apart from magnetic attraction risks, the primary biophysical concern associated with MRI is radiofrequency heating of the human body and associated discomfort, health deterioration, or potential burns. This paper reviews experimental data and numerical modeling of systemic (core and brain) temperature and local thermal effects associated with diagnostic MRI exposures at 1.5T (64 MHz) and 3.0T (128 MHz). Allowable temperatures and duration of systemic exposure are established based on knowledge of (short-term) human thermobiology. Longer term effects related to DNA damage or altered cellular pathways are not covered in this review. Updated limits are proposed for core temperature increase (≤1.3°C) and for Specific Absorption (<4 kJ/kg). The potential use of thermal dose (CEM43) for local thermal protection is described, and previously proposed exposure limit values are evaluated against available data from current MRI practice. Gaps in knowledge are identified, and recommendations for additional research are provided.","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"10 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90496079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Inherent Geometry Correction for Diffusion EPI Using the Reference Echoes as Navigators","authors":"J. S. van den Brink, J. Koonen","doi":"10.1155/2019/4139726","DOIUrl":"https://doi.org/10.1155/2019/4139726","url":null,"abstract":"Diffusion-weighted EPI has become an indispensable tool in body MRI. Geometric distortions due to field inhomogeneities are more prominent at large field–of–view and require correction for comparison with T2W TSE. Several known correction methods require acquisition of additional lengthy scans, which are difficult to apply in body imaging. We implement and evaluate a geometry correction method based on the already available non phase-encoded EPI reference data used for Nyquist ghost removal. The method is shown to provide accurate and robust global geometry correction in the absence of strong, local phase offsets. It does not require additional time for calibrations and is directly compatible with parallel imaging methods. The resulting images can serve as improved starting point for additional geometry correction methods relying on feature extraction and registration.","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"179 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2019-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77776229","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-channel helical-antenna inner-volume RF coils for ultra-high field MR scanners","authors":"Pranav S. Athalye,&nbsp;Milan M. Ilić,&nbsp;Pierre-Francois van de Moortele,&nbsp;Andrew J. M. Kiruluta,&nbsp;Branislav M. Notaroš","doi":"10.1002/cmr.b.21405","DOIUrl":"10.1002/cmr.b.21405","url":null,"abstract":"<p>RF coil design for human ultra-high field (7 T and higher) magnetic resonance (MR) imaging is an area of intense development, to overcome difficult challenges such as RF excitation spatial heterogeneity and low RF transfer efficiency into the spin system. This article proposes a novel category of multi-channel RF volume coil structures at both 7 T and 10.5 T based on a subject-loaded multifilar helical-antenna RF coil that aims at addressing these problems. In some prior applications of helix antennas as MR RF coils at 7 T, the imaged sample was positioned outside the helix. Here, we introduce a radically different approach, with the inner volume of a helix antenna being utilized to image a sample. The new coil uniquely combines traveling-wave behavior through the overall antenna wire structure and near-field RF interaction between the conducting elements and the imaged tissues. It thus benefits from the congruence of far- and near-field regimes. Design and analysis of the novel inner-volume coils are performed by numerical simulations using multiple computational electromagnetics techniques. The fabricated coil prototypes are tested, validated, and evaluated experimentally in 7-T and 10.5-T MR human wide bore (90-cm) MR scanners. Phantom data at 7 T show good consistency between numerical simulations and experimental results. Simulated <i>B</i>₁⁺ transmit efficiencies, in T/√W, are comparable to those of some of the conventional and state-of-the-art RF coil designs at 7 T. Experimental results at 10.5 T show the scalability of the helix coil design.</p>","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"48B 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2019-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.b.21405","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82530811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"OpenForce MR: A low-cost open-source MR-compatible force sensor","authors":"Francesco Santini,&nbsp;Oliver Bieri,&nbsp;Xeni Deligianni","doi":"10.1002/cmr.b.21404","DOIUrl":"10.1002/cmr.b.21404","url":null,"abstract":"<p>Measuring the force exerted by muscles during dynamic MR acquisition (either imaging or spectroscopy) provides important information for the standardization of the exercise performed in the scanner and is therefore important for reproducible results in musculoskeletal imaging. However, existing commercial solutions for such measurements are often very expensive and impractical. In this work, a novel, open-source, versatile force sensor made of non-magnetic, off-the-shelf components is presented. The sensor is based on four aluminum Wheatstone bridge load cells enclosed in a custom-built aluminum frame. These cells are connected to an Arduino microcontroller for data acquisition and serial communication with a host computer, on which a dedicated program visualizes and logs the recorded force in real time. All components were chosen to be compatible with the MR environment, commercially available, and low cost. The sensor was calibrated with a commercial dynamometer and subsequently tested in multiple MR acquisition scenarios (static morphological imaging, cine imaging during contraction, velocity-encoded imaging). The sensor correctly recorded data during all tested sequences, without cross-interference between the MR and the force acquisitions. Minor susceptibility artifacts are visible in the immediate vicinity of the sensor, but they did not impair the evaluation of the muscle of interest. In conclusion, the development of a low-cost, MR-compatible force sensor is feasible, and its usage does not interfere with MR acquisition. The full specifications of the sensor, including hardware design, firmware and host software are publicly released as open-source for the potential benefit of the whole community.</p>","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"48B 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2019-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.b.21404","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73329165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Traveling-wave meets standing-wave: A simulation study using pair-of-transverse-dipole-ring coils for adjustable longitudinal coverage in ultra-high field MRI","authors":"Xinqiang Yan,&nbsp;John C. Gore,&nbsp;William A. Grissom","doi":"10.1002/cmr.b.21402","DOIUrl":"10.1002/cmr.b.21402","url":null,"abstract":"<p>At ultrahigh fields (<i>B</i>₀ ≥ 7T), it is challenging to cover a large field of view using single-row conventional RF coils (standing wave resonators) due to the limited physical dimensions. In contrast, traveling wave approaches can excite large fields of view even using a relatively simple hardware setup, but suffer from poor efficiency and high local specific absorption rate in non-imaged regions. In this study, we propose and numerically analyze a new coil which combines the concept of traveling wave and standing wave. The new coil consists of a pair of transverse dipole rings (PTDR) whose separation is adjusted according to the desired imaging coverage. The PTDR coil was validated using electromagnetic simulations in phantoms and human leg models, which showed that coverage can be as long as 60 cm. When the coverage of the PTDR coil was shortened to 20 cm to cover the knees only, it's transmit and specific absorption rate efficiencies were 84% and 37% higher than those of the 50 cm coverage, respectively.</p>","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"48B 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2019-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.b.21402","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84161180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coupled actuators with a mechanically synchronized phase during MR elastography: A phantom feasibility study","authors":"Wiebke Neumann,&nbsp;Vanessa R. Lehnart,&nbsp;Yannik Vetter,&nbsp;Andreas Bichert,&nbsp;Lothar R. Schad,&nbsp;Frank G. Zöllner","doi":"10.1002/cmr.b.21403","DOIUrl":"10.1002/cmr.b.21403","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Introduction</h3>\u0000 \u0000 <p>Magnetic resonance elastography (MRE) is an MR imaging method for the quantification of spatial stiffness of soft tissues using mechanically induced dynamic shear waves. In some applications, the penetration of shear waves can be limited through attenuation and shadowing of the waves. In order to increase the actuator performance, we present a dual driver approach to compensate for shear wave attenuation and to achieve better coverage over the entire region of interest.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Materials and Methods</h3>\u0000 \u0000 <p>(a) We designed pneumatic turbines that created a sinusoidal centrifugal force due to an eccentric weight. Two turbines were connected in-phase with each eccentric weight having the same angular position relative to its pivot point. (b) We developed a tissue elasticity mimicking abdominal phantom. (c) The phantom served as a test object to investigate the feasibility to generate shear waves at two surface origins with the dual actuator system and to compare it against a single actuation setup.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results and Discussion</h3>\u0000 \u0000 <p>A stable phase relationship of the shear waves generated by the turbines was achieved as the positions of the eccentric weights were mechanically fixed. The abdominal phantom yielded sufficient MR signal. Liver and rib cage were clearly visible in MR imaging. The shear waves generated by the dual turbine propagated through the region of interest. Our turbine design is reproducible through 3D printing and can be integrated into existing clinical equipment for 1.5 T and 3 T scanners.</p>\u0000 </section>\u0000 </div>","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"48B 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2019-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.b.21403","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82199915","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"NMR Concepts","authors":"","doi":"10.1002/cmr.b.21390","DOIUrl":"https://doi.org/10.1002/cmr.b.21390","url":null,"abstract":"","PeriodicalId":50623,"journal":{"name":"Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering","volume":"48B 2","pages":""},"PeriodicalIF":0.9,"publicationDate":"2018-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/cmr.b.21390","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"137778811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}