Background: Parallel transmit (pTx) has introduced many benefits to MRI with regard to decreased specific absorption rates and improved transmit field homogeneity, of particular importance in applications at higher magnetic field strengths. PTx has also been proposed as a solution to mitigating dangerous RF induced heating of elongated conductive devices such as those used in cardiac interventions. In this work we present a system that can augment a conventional scanner with pTx, in particular for use in interventional MRI for guidewire safety. Methods: The pTx system was designed to work in-line with a 1.5T MRI while the RF synthesis and imaging control was maintained on the host MR scanner. The add on pTx system relies on the RF transmit signal, unblanking pulse, and a protocol driven trigger from the scanner. The RF transmit was split into multiple fully modulated transmit signals to drive an array of custom transceiver coils. The performance of the 8-channel implementation was tested with regards to active and real-time control of RF induced currents on a standard guidewire, heating mitigation tests, and anatomical imaging in a sheep torso. Results: The pTx system was intended to update RF shims in real-time and it was demonstrated that the safe RF shim could be determined while the guidewire is moved. The anatomical imaging demonstrated that heart anatomy and neighbouring structures can be fully imaged with the pTx system inline. Conclusion: We have presented the design and performance of a real-time feedback control pTx system capable of adding such capabilities to a conventional MRI with the focus guidewire imaging in cardiac interventional MRI applications.
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…
Shanghai Jiao Tong University（上海交通大学）；University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine（上海交通大学医学院附属瑞金医院）；KTH Royal Institute of Technology（瑞典皇家理工学院）；Mayo Clinic in Arizona（亚利桑那州妙佑医疗国际）；ShanghaiTech University（上海科技大学）
Interventional magnetic resonance imaging (i-MRI) for surgical guidance could help visualize the interventional process such as deep brain stimulation (DBS), improving the surgery performance and patient outcome. Different from retrospective reconstruction in conventional dynamic imaging, i-MRI for DBS has to acquire and reconstruct the interventional images sequentially online. Here we proposed a convolutional long short-term memory (Conv-LSTM) based recurrent neural network (RNN), or ConvLR, to reconstruct interventional images with golden-angle radial sampling. By using an initializer and C…
Faculty of Computer Science, Otto-von-Guericke University Magdeburg（马格德堡奥托·冯·格里克大学计算机科学学院）；Clinic for Radiology and Nuclear Medicine, University Hospital Magdeburg（马格德堡大学医院放射与核医学诊所）
Purpose: We aim to develop a robust 4D MRI method for large FOVs enabling the extraction of irregular respiratory motion that is readily usable with all MRI machines and thus applicable to support a wide range of interventional settings. Method: We propose a 4D MRI reconstruction method to capture an arbitrary number of breathing states. It uses template updates in navigator slices and search regions for fast and robust vessel cross-section tracking. It captures FOVs of 255 mm x 320 mm x 228 mm at a spatial resolution of 1.82 mm x 1.82 mm x 4mm and temporal resolution of 200ms. A total of 37 4…
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…
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 …
Transmitter arrays play a critical role in ultra high field Magnetic Resonance Imaging (MRI), especially given the advantages made possible via parallel transmission (pTx) techniques. One of the challenges in design and construction of transmit arrays has traditionally been finding effective strategies for decoupling elements of the transmit array. Here, we present the design of the first self-decoupled, loop-based transmit array for human brain MRI at 10.5T / 447MHz. We demonstrate, using full-wave electromagnetic simulations, effective decoupling of the transmit elements without requiring th…
In pTx MRI systems, the prediction of local SAR is based on numerical electromagnetic (EM) simulations and used to scale RF power to ensure FDA SAR limits are not exceeded. This prediction becomes more complex when superposition of E-fields from multiple coupled coils are employed in parallel transmission, each affected by dielectric and conductive properties of the human body. It was demonstrated that incorrect inductive coupling used in simulations of transmit array coil spatial excitation and SAR, leads to poor accuracy of predicted excitation and SAR, and more importantly from a safety per…
The purpose of this study was to develop a method for tissue elasticity imaging using tagged magnetic resonance imaging (MRI). First, we developed a cyclic pressure device that used air to remotely transmit the power to generate cyclic deformation in an object. The pressure induced by the cyclic pressure device was measured by MRI-compatible force sensors. Second, we developed a software to calculate Young's modulus from tagged MRI data using the harmonic phase (HARP) method and the finite element method (FEM). We also developed a software to extract tag-cross points from tagged MRI data. Fina…
We demonstrate an experimental method for direct 2D and 3D imaging of magnetic radio-frequency (rf) field distribution in metal-dielectric structures based on traveling wave (TW) magnetic resonance imaging (MRI) at ultra-high field (> 7T). The typical apparatus would include an ultra-high field whole body or small bore MRI scanner, waveguide elements filled with MRI active dielectrics with predefined electric and magnetic properties, and TW rf transmit-receive probes. We validated the technique by obtaining TW magnetic-resonance (MR) images of the magnetic field distribution of the rf modes of…
Purpose: Neurovascular MRI suffers from a rapid drop in B1+ into the neck when using transmit head coils at 7T. One solution to improving B1+ magnitude in the major feeding arteries in the neck is to use custom RF shims on parallel transmit (pTx) head coils. However, calculating such shims requires robust multi-channel B1+ maps in both the head and the neck, which is challenging due to low RF penetration into the neck, limited dynamic range of multi-channel B1+ mapping techniques, and B0 sensitivity. We therefore sought a robust large-dynamic-range pTx field mapping protocol, and tested whethe…
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
Over almost five decades of development and improvement, Magnetic Resonance Imaging (MRI) has become a rich and powerful, non-invasive technique in medical imaging, yet not reaching its physical limits. Technical and physiological restrictions constrain physically feasible developments. A common solution to improve imaging speed and resolution is to use higher field strengths, which also has subtle and potentially harmful implications. However, patient safety is to be considered utterly important at all stages of research and clinical routine. Here we show that dynamic metamaterials are a prom…
Purpose: Universal Pulses (UPs) are excitation pulses that reduce the flip angle inhomogeneity in high field MRI systems without subject-specific optimization, originally developed for parallel transmit (PTX) systems at 7T. We investigated the potential benefits of UPs for single channel (SC) transmit systems at 3T, which are widely used for clinical and research imaging, and for which flip angle inhomogeneity can still be problematic. Methods: SC-UPs were designed using a spiral nonselective k-space trajectory for brain imaging at 3T using transmit field maps (B1+) and off-resonance maps (B0)…
Cloud-Magnetic Resonance Imaging System: In the Era of 6G and Artificial Intelligence
Xiamen University（厦门大学）；Shanghai Electric Group CO., LTD（上海电气集团股份有限公司）；China Telecom Group（中国电信集团）；China Mobile Group（中国移动集团）；Xiamen University of Technology（厦门理工学院）
