System for and method of radio frequency emission mitigation from an MRI scanner

Abstract

An apparatus for controlling electromagnetic (EM) radiation emitted from a magnetic resonance imaging (MRI) system having a magnet assembly having a superconducting magnet and a radio frequency (RF) shield includes an RF birdcage body coil positioned in the magnet assembly proximate to an inner radius of the RF shield and configured to apply one or more RF excitation pulses, at least one radiation control array positioned in the magnet assembly and configured to control EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses, and a processor device coupled to the RF birdcage coil and the at least one radiation control array and configured to control current waveforms provided to the RF birdcage body coil and to the at least one radiation control array.

Description

MGH 2024-162-02 Q&B 125141.04905SYSTEM FOR AND METHOD OF RADIO FREQUENCY EMISSION MITIGATION FROM AN MRI SCANNERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on, claims priority to, and incorporates herein by reference in its entirety U.S. Serial No. 63 / 722,842 filed November 20, 2025, and entitled “System for and Method of Radio Frequency Emission Mitigation from an MRI Scanner."STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] N / AFIELD

[0003] The present disclosure relates generally to magnetic resonance imaging (MRI) and, more particularly, to systems and methods for mitigation of electromagnetic radiation from an MRI system.BACKGROUND

[0004] Magnetic resonance imaging (MRI) is among the most powerful diagnostic tools, yet its widespread use remains constrained by high installation costs. The substantial siting cost for MRI forms a major barrier to broader MRI access, significantly contributing to the overall expense of installing these systems. Current MRI scanners almost universally require a specialized room lined with conductive material referred to as a Faraday shielded room or RF cabin which: 1) eliminates or blocks external electromagnetic (EM) interference during signal reception that would otherwise be detected by the scanner’s receive system and introduce artifacts in the image and 2) prevent RF radiation (or EM radiation) from kilowatt level transmit circuitry of the scanner itself from interfering with sensitive nearby equipment in, for example, the hospital. The infrastructure required to accommodate a conventional superconducting MRI system in a clinical setting can nearly double overall installation cost, with the Faraday-shielding representing one of the costliest components.MGH 2024-162-02 Q&B 125141.04905

[0005] Eliminating the need for a traditional RF-shielded cabin (Faraday cage) in clinical MRI could considerably reduce installation cost and complexity, enabling deployment in diverse settings. However, this necessitates both a reduction in the electromagnetic (EM) radiation emitted by the RF body transmit system and an attenuation of EM interference (EMI) detected by the RF receive system. Considerable progress has been made in mitigating receive-side interference (which can be referred to as “the receive problem”) using external detection coils and post-processing strategies, potentially reducing the need for Faraday shielding. For example, several recent efforts have shown that “the receive problem” can be solved using an external antenna to detect the incoming contaminant waves to allow their digital removal from the image However, much less effort has addressed transmit-side emissions (which can be referred to as the “transmit problem), which are critical for EM-compatibility.

[0006] It would be desirable to provides systems and methods for providing radiation mitigation so that an MRI system can meet safety standards without requiring Faraday-shielding.SUMMARY

[0007] In accordance with an embodiment, an apparatus for controlling electromagnetic (EM) radiation emitted from a magnetic resonance imaging (MRI) system having a magnet assembly having a superconducting magnet and a radio frequency (RF) shield includes an RF birdcage body coil positioned in the magnet assembly proximate to an inner radius of the RF shield and configured to apply one or more RF excitation pulse, at least one radiation control array positioned in the magnet assembly and configured to control EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses and a processor device coupled to the RF birdcage coil and the at least one radiation control array and configured to control current waveforms provided to the RF birdcage body coil and to the at least one radiation control array.

[0008] In accordance with another embodiment, a magnetic resonance imaging (MRI) system includes a magnet system configured to generate a polarizing magnetic field about at least a portion of a subject, a gradient system including a plurality of gradient coils configured to apply at least one magnetic gradient field to the polarizing magnetic field, a radio frequency (RF) system including an RF shield and an RF birdcage body coil positioned proximate to an inner surface of the RF shield and configured to apply one or more RF excitation pulses to theMGH 2024-162-02 Q&B 125141.04905 subject, at least one radiation control array configured to control EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses, and a computer system. The computer system is programmed to direct the plurality of magnetic gradient coils, the RF birdcage body coil, to perform a pulse sequence, and direct the at least one radiation control array to apply one or more RF pulses.

[0009] In accordance with another embodiment, a method for generating a magnetic resonance (MR) image of a subject using a magnetic resonance imaging (MRI) system without Faraday shielding and having a parallel transmit (pTx) array includes receiving, using the MRI system, a set of parameters for a parallel transmit excitation configured to control EM radiation generated by the MRI system during transmission of one or more RF excitation pulses, performing, using the MRI system including the parallel transmit array, a pulse sequence comprising the parallel transmit excitation to acquire magnetic resonance (MR) data from the subject, and generating, using a processor device, an image of the subject using the acquired MR data.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements.

[0011] FIG. 1 is a block diagram of an example magnetic resonance imaging (MRI) system in accordance with an embodiment;

[0012] FIG. 2 is a simplified perspective view of an example magnet assembly of an MRI system in accordance with an embodiment;

[0013] FIG. 3 is a perspective view of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment;

[0014] FIGs. 4A and 4B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment;

[0015] FIG. 5A and 5B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment;MGH 2024-162-02 Q&B 125141.04905

[0016] FIGs. 6A an 6B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment;

[0017] FIG. 7 is perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using parallel transmission (pTx) in accordance with an embodiment;

[0018] FIGs. 8A and 8B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using parallel transmission (pTx) in accordance with an embodiment;

[0019] FIG. 9 illustrates a method for generating a magnetic resonance (MR) image of a subject using a magnetic resonance imaging (MRI) system without Faraday shielding and parallel transmission (pTx) electromagnetic (EM) radiation control in accordance with an embodiment; and

[0020] FIG. 10 is a block diagram of an example computer system in accordance with an embodiment.DETAILED DESCRIPTION

[0021] FIG. l is a block diagram of an example magnetic resonance imaging (MRI) system in accordance with an embodiment. MRI system 100 that may incorporate an apparatus for mitigation of RF emission described herein and may be used to perform the methods described herein. In some embodiments, the disclosed systems and methods may be designed to accompany the MRI system 100. The MRI system 100 includes an operator workstation 102, which may include a display 104, one or more input devices 106 (e.g., a keyboard and mouse), and a processor 108. The processor 108 may include a commercially available programmable machine running a commercially available operating system. The operator workstation 102 provides the operator interface that facilitates entering scan parameters (e.g., a scan prescription) into the MRI system 100. The operator workstation 102 may be coupled to different servers, including, for example, a pulse sequence server 110, a data acquisition server 112, a data processing server 114, and a data store server 116. The operator workstation 102 and the servers 110, 112, 114, and 116 may be connected via a communication system 140, which may include any suitable network connection, whether wired, wireless, or a combination of both.MGH 2024-162-02 Q&B 125141.04905

[0022] The pulse sequence server 110 functions in response to instructions provided by the operator workstation 102 to operate a gradient system 118 and a radiofrequency (“RF”) system 120. Gradient waveforms for performing a prescribed scan are produced and applied to the gradient system 118, which excites gradient coils in an assembly 122 to produce the magnetic field gradients Gx, Gy, and Gzthat are used for spatially encoding magnetic resonance signals. The gradient coil assembly 122 forms part of a magnet assembly 124 that includes a polarizing magnet 126 and a whole-body RF coil 128 and / or a local coil (not shown). The magnet assembly 124 surrounds a bore 125 in which a subject 123 may be positioned for performing a scan. The magnet assembly 124 and bore 125 have a service end 127 and a patient end 129. In some embodiments, the magnet assembly 124 may also include an RF shield (not shown) that can be positioned around the Rf coil 128.

[0023] RF waveforms are applied by the RF system 120 to the RF coil 128, or a separate local coil, to perform the prescribed magnetic resonance pulse sequence. Responsive magnetic resonance signals detected by the RF coil 128, or a separate local coil, are received by the RF system 120. The responsive magnetic resonance signals may be amplified, demodulated, filtered, and digitized under direction of commands produced by the pulse sequence server 110. The RF system 120 includes an RF transmitter for producing a wide variety of RF pulses used in MRI pulse sequences. The RF transmitter is responsive to the prescribed scan and direction from the pulse sequence server 110 to produce RF pulses of the desired frequency, phase, and pulse amplitude waveform. The generated RF pulses may be applied to the whole-body RF coil 128 or to one or more local coils or coil arrays.

[0024] The RF system 120 also includes one or more RF receiver channels. Each RF receiver channel includes an RF preamplifier that amplifies the magnetic resonance signal received by the coil 128 to which it is connected, and a detectorthat detects and digitizes the I and Q quadrature components of the received magnetic resonance signal. The magnitude of the received magnetic resonance signal may, therefore, be determined at any sampled point by the square root of the sum of the squares of the I and Q components:M = l2+ Q2(1) and the phase of the received magnetic resonance signal may also be determined according to the following relationship:MGH 2024-162-02 Q&B 125141.04905(p = tan1). (1)

[0025] The pulse sequence server 110 may receive patient data from a physiological acquisition controller 130. By way of example, the physiological acquisition controller 130 may receive signals from a number of different sensors connected to the patient, such as electrocardiograph (“ECG”) signals from electrodes, or respiratory signals from a respiratory bellows or other respiratory monitoring device. Such signals are typically used by the pulse sequence server 110 to synchronize, or “gate,” the performance of the scan with the subject’s heartbeat or respiration.

[0026] The pulse sequence server 110 may also connect to a scan room interface circuit 132 that receives signals from various sensors associated with the condition of the patient and the magnet system. Through the scan room interface circuit 132, a patient positioning system 134 can receive commands to move the patient to desired positions during the scan.

[0027] The digitized magnetic resonance signal samples produced by the RF system 120 are received by the data acquisition server 112. The data acquisition server 112 operates in response to instructions downloaded from the operator workstation 102 to receive the real-time magnetic resonance data and provide buffer storage, such that no data is lost by data overrun. In some scans, the data acquisition server 112 passes the acquired magnetic resonance data to the data processor server 114. In scans that require information derived from acquired magnetic resonance data to control the further performance of the scan, the data acquisition server 112 may be programmed to produce such information and convey it to the pulse sequence server 110. For example, during pre-scans, magnetic resonance data may be acquired and used to calibrate the pulse sequence performed by the pulse sequence server 110. As another example, navigator signals may be acquired and used to adjust the operating parameters of the RF system 120 or the gradient system 118, or to control the view order in which k-space is sampled. In still another example, the data acquisition server 112 may also process magnetic resonance signals used to detect the arrival of a contrast agent in a magnetic resonance angiography (“MRA”) scan. For example, the data acquisition server 112 may acquire magnetic resonance data and process it in real-time to produce information that is used to control the scan.

[0028] The data processing server 114 receives magnetic resonance data from the data acquisition server 112 and processes it in accordance with instructions downloaded from the operator workstation 102. Such processing may include, for example, reconstructing two-MGH 2024-162-02 Q&B 125141.04905 dimensional or three-dimensional images by performing a Fourier transformation of raw k-space data, performing other image reconstruction algorithms (e.g., iterative or back-projection reconstruction algorithms), applying fdters to raw k-space data or to reconstructed images, generating functional magnetic resonance images, or calculating motion or flow images.

[0029] Images reconstructed by the data processing server 114 are conveyed back to the operator workstation 102 for storage. Real-time images may be stored in a data base memory cache (not shown in FIG. 1), from which they may be output to operator display 104 or a display 136. Batch mode images or selected real time images may be stored in a host database on disc storage 138. When such images have been reconstructed and transferred to storage, the data processing server 114 notifies the data store server 116 on the operator workstation 102. The operator workstation 102 may be used by an operator to archive the images, produce films, send the images via a network to other facilities, or post-processing of the acquired MR data or reconstructed images.

[0030] The MRI system 100 may also include one or more networked workstations 142. By way of example, a networked workstation 142 may include a display 144, one or more input devices 146 (e.g., a keyboard and mouse), and a processor 148. The networked workstation 142 may be located within the same facility as the operator workstation 102, or in a different facility, such as a different healthcare institution or clinic.

[0031] The networked workstation 142 may gain remote access to the data processing server 114 or data store server 116 via the communication system 140. Accordingly, multiple networked workstations 142 may have access to the data processing server 114 and the data store server 116. In this manner, magnetic resonance data, reconstructed images, or other data may be exchanged between the data processing server 114 or the data store server 116 and the networked workstations 142, such that the data or images may be remotely processed by a networked workstation 142. This data may be exchanged in any suitable format, such as in accordance with the transmission control protocol (TCP), the internet protocol (IP), or other known or suitable protocols.

[0032] FIG. 2 is simplified perspective view of an example magnet assembly of an MRI system in accordance with an embodiment. Magnet assembly 200 includes a superconducting magnet 202, a whole-body radio frequency (RF) birdcage coil (BC), and an RF shield 206 Various other elements of the magnet assembly 200 are emitted from FIG. 3 for simplicity. The magnet assembly surrounds a bore in which a subject 208 can be positioned for an MRI scan. TheMGH 2024-162-02 Q&B 125141.04905 magnet assembly has a service end 212 and a patient end 210 which has an opening to facilitate the positioning of the subject in the bore. In the example magnet assembly 200 shown in FIG. 3, the magnet 202, RF BC body coil 204 and RF shield 206 are cylindrical. The RF shield 206 is positioned within an inner diameter of the magnet 206 and surrounds the RF BC body coil 204 which is positioned within an inner diameter of the RF shield 206. In some embodiments, the RF BC body coil 204 can be a high pass BC body coil and operated in a circular polarization (CP) mode. A controller (or processor device) such as, for example, pulse sequence service 110 and operator workstation 102 shown in FIG. 1, can be used to operate the RF BC body coil 204 to apply (or transmit) RF pulses (e.g., RF excitation pulses) of a desired frequency, phase, and pulse amplitude waveform for a prescribed pulse sequence. During a scan, the RF BC body coil can emit EM radiation (or RF radiation or transmit radiation) while applying (e.g., a transmit mode) the RF pulses as part of the MR pulse sequence. Current international safety standards, such as IEC 60601-1-2 and CISPR-11, impose strict limits on the peak E-field or H-field radiated at a lO-meter radius (depending on the operating frequency). For example, in 0.5T MRI systems, this limit is set at 8.5 dBpA / m for the peak H-field at 10-m distance (peak-Hiom) and the limit is set to below 1 mV / m for the peak E-field at 10-m distance (peak-Eiom) during 3T imaging. Both of these regulations limit the electromagnetic (EM) radiation emitted by the MRI scanner into the world by limiting the radiation amplitude on the 10-meter sphere.

[0033] As mentioned, typically an MRI scanner (e.g., MRI system described above with respect to FIGs. 1 and 2 typically requires a Faraday shielded room which can be one of the most expensive siting requirements for a conventional scanner. The present disclosure describes systems, apparatus and methods for controlling or mitigating electromagnet (EM) radiation (or RF radiation) emitted by a radio frequency (RF) transmit system (e.g., an RF body transmit coil) of an MRI system without Faraday shielding (e.g., a Faraday shielded room or Faraday cage). In some embodiments, one or more radiation control arrays (RCAs) can be included in a magnet assembly of the MRI system and can be configured to control (e.g., minimize, reduce, cancel) the EM radiation emitted by the RF transmit system as described further below with respect to FIGs. 3-6B. In some embodiments, a parallel transmit (pTx) array can be used as an alternative to an RF body transmit coil and configured, for example, for EM radiation, flip angle, and Specific Absorption Rate (SAR) control as described further below in FIGs. 7-9.MGH 2024-162-02 Q&B 125141.04905

[0034] FIG. 3 is a perspective view of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment. In FIG. 3, a magnet assembly can include a magnet 302 and an RF shield 304 disposed within an inner radius of the magnet 302. In some embodiments, the magnet 302 can be a cylindrical superconducting magnet and the RF shield 304 can be a cylindrical RF shield. The magnet assembly also include an RF birdcage body coil 306 disposed within an inner radius of the RF shield 304. In FIG. 3, a subject 308 is illustrated positioned within a bore of the magnet assembly. To control or mitigate EM radiation (or RF radiation) emitted by the RF birdcage body coil 306 during operation (e.g., transmission of EF excitation pulses), a radiation control array (RCA) can advantageously be included in the magnet assembly. In the embodiment illustrated in FIG. 3, the RCA is a parallel transmit (pTx) array. In some embodiments, the parallel transmit array can be, for example, a 25-channel loop parallel transmit array. As shown in FIG. 3, the parallel transmit array 314 can be positioned around the subject’s feet proximate to the patient’s end 310 of the magnet assembly bore. In some embodiments, an electromagnetic (EM) absorber 316 can be placed at a service end 312 of the magnet assembly bore. The EM absorber 316 can, for example, include 5 layers 320, 322, 324, 326, 328 of high-dielectric materials optimized for graded interference impedance matching. Accordingly, the EM absorber 316 can be configured to provide passive mitigation of EM radiation from the RF birdcage body coil.

[0035] A top view 330 and a side view 340 illustrate the plurality of pTx loops 332 of the parallel transmit array 314 positioned around the subject 308. In some embodiments, the pTx channel of the parallel transmit array 314 can be decoupled. In some embodiments, the parallel transmit array 314 can advantageously be used to minimize the EM radiation generated during operation of the RF birdcage body coil 306. In some embodiments, the parallel transmit array 314 can be used to control (or minimize or reduce) the EM radiation emitted by the RF birdcage body coil so that it is below a predetermined threshold. For example, in some embodiments the predetermined threshold can be a safety standard of limit, for example, the IEC 60601-1 -2 and CISPR-11 limits on the peak E-field (peak-Eiom) or H-field (peak-Hiom) radiated at a 10-meter radius. In some embodiments, the RF pulses (e.g., RF shimming pulses, RF excitation pulses) applied by the parallel transmit array 314 (e.g., by pTx loops 332) can be optimized to both reduce the EM radiation (e.g., below the predetermined threshold such as a regulatory limit) generated by the RF birdcage body coil during a scan as well as provide sufficient imagingMGH 2024-162-02 Q&B 125141.04905 characteristic (e.g., sufficient flip angle excitations within the subject 308). In some embodiments, the RF pulses applied by the parallel transmit array 314 can be designed to optimize the transmit field (or field patterns) both inside and outside the subject 308. For example, the RF pulses applied by the parallel transmit array 314 can be jointly optimized to produce both uniform and efficient fields inside the subject 308 (for imaging purposes) and low peak E-field on the regulatory 10-meter radius surface (for EM radiation mitigation). In some embodiments, known optimization techniques for parallel transmission can be used to optimize the RF pulses applied by the parallel transmit array 314. In some embodiments, a pulse optimization process can be performed on a computer system such as operator workstation 102 shown in FIG. 1 or computer system 1000 shown in FIG. 10.

[0036] FIGs. 4A and 4B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment. In FIG. 4A, a magnet assembly can include a magnet 402 and an RF shield 408 disposed within an inner radius of the magnet 402. In some embodiments, the magnet 402 can be a cylindrical superconducting magnet and the RF shield 508 can be a cylindrical RF shield. The magnet assembly also include a first RF birdcage body coil 404, BC1, disposed within an inner radius of the RF shield 408. In FIG. 4A, a subject 412 is illustrated positioned within a bore of the magnet assembly. To control or mitigate EM radiation (or RF radiation) emitted by the first RF birdcage body coil 404 during operation (e.g., transmission of RF excitation pulses), a radiation control array (RCA) can advantageously be included in the magnet assembly. In the embodiment illustrated in FIG. 4A, the RCA is a second RF birdcage body coil 406, BC2 disposed outside of the RF shield 408. Accordingly, the first RF birdcage body coil 404 is located inside the RF shield 408 and the second RF birdcage body coil 406 is located outside the RF shield 408. The second RF birdcage body coil 406 has a larger diameter than the first RF birdcage body coil 404. The embodiment illustrated on FIG. 4A is a dual birdcage configuration and the second RF birdcage body coil 406 is a “mirrored” birdcage coil. In some embodiments, the first RF birdcage body coil 404 can be a circularly polarized (CP) driven high-pass body birdcage coil and can be the primary imaging coil. FIG. 4B illustrates the mirrored birdcage configuration including the first RF birdcage body coil 404 and the second (“mirrored”) RF birdcage body coil 406. Also illustrated in FIG. 4B are two input ports 420, 422 of the first RF birdcage body coil 404 and two input ports 424, 426 of the second RF birdcage body coil 406.MGH 2024-162-02 Q&B 125141.04905

[0037] In some embodiments, an electromagnetic (EM) absorber 410 can be placed at a service end 416 of the magnet assembly bore. The EM absorber 410 can be, for example, a 5-layer, isotropic half-sphere formed of high-dielectric materials. Accordingly, the EM absorber 410 can be configured to provide passive mitigation of EM radiation from the RF birdcage body coil.

[0038] Advantageously, the second RF birdcage body coil 406 can be optimized to minimize the EM radiation produced by the first RF birdcage body coil 404 during operation of the first RF birdcage body coil 404. In one example, in some embodiments, the second RF birdcage body coil 406 can be used to control (or minimize or reduce) the EM radiation emitted by the first RF birdcage body coil 404 so that it is below a predetermined threshold. For example, in some embodiments the predetermined threshold can be a safety standard of limit, for example, the IEC 60601-1-2 and CISPR-11 limits on the peak E-field (peak-Eiom) or H-field (peak-Hiom) radiated at a 10-meter radius. In some embodiments, the capacitors of the second RF birdcage body coil 406 can be optimized. The second RF birdcage body coil 406 can be optimized to, for example, reduce far-field radiation (e.g., peak-Eiom) while minimally affecting spin-excitation in the image field-of-view. For example, the second In some embodiments, known optimization techniques for RF pulse design can be used to optimize the RF pulses applied by the second RF birdcage body coil 406 406 can be configured to cancel surface currents and EM radiation. In some embodiments, RF pulses applied by the second RF birdcage body coil 406 can be optimized to both reduce the EM radiation (e.g., below the predetermined threshold such as a regulatory limit) generated by the RF birdcage body coil during a scan as well as provide sufficient imaging characteristic (e g., sufficient flip angle excitations within the subject 408). In some embodiments, known optimization techniques for birdcage coil capacitors can be used to optimize the capacitors of the second RF birdcage body coil 406. In some embodiments, known optimization techniques for RF pulse design can be used to optimize the RF pulses applied by the second RF birdcage body coil 406. In some embodiments, an optimization process can be performed on a computer system such as operator workstation 102 shown in FIG. 1 or computer system 1000 shown in FIG. 10.

[0039] FIG. 5A and 5B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment. In FIG. 5A, a magnet assembly can include a magnet 502 and an RF shield 508 disposed within an inner radius of the magnet 502. In some embodiments, the magnet 502 can beMGH 2024-162-02 Q&B 125141.04905 a cylindrical superconducting magnet and the RF shield 508 can be a cylindrical RF shield. The magnet assembly also include a first RF birdcage body coil 504, BC1, disposed within an inner radius of the RF shield 508. In FIG. 5A, a subject 512 is illustrated positioned within a bore of the magnet assembly. To control or mitigate EM radiation (or RF radiation) emitted by the first RF birdcage body coil 504 during operation (e.g., transmission of RF excitation pulses), a radiation control array (RCA) can advantageously be included in the magnet assembly. In the embodiment illustrated in FIG. 5A, the RCA is a second RF birdcage body coil 506, BC2 disposed inside of the RF shield 508 and a predetermined distance toward a patient end 514 of the magnet assembly bore and away from the position of the first RF birdcage body coil 504. However, there is an overlap between the first RF birdcage body coil 404 and the second RF birdcage body coil 306 as illustrated in FIGs, 5 A and 5B. The second RF birdcage body coil 506 has a larger diameter than the first RF birdcage body coil 504. The embodiment illustrated in FIGs. 5A and 5B is a dual birdcage configuration and the second RF birdcage body coil 506 is a “overlapping” birdcage coil. In some embodiments, the first RF birdcage body coil 504 can be a circularly polarized (CP) driven high-pass body birdcage coil and can be the primary imaging coil. FIG. 5B illustrates the overlapping birdcage configuration including the first RF birdcage body coil 504 and the second, overlapped, RF birdcage body coil 506. Also illustrated in FIG. 5B are two input ports 520, 522 of the first RF birdcage body coil 504 and two input ports 524, 526 of the second RF birdcage body coil 506.

[0040] In some embodiments, an electromagnetic (EM) absorber 510 can be placed at a service end 516 of the magnet assembly bore. The EM absorber 510 can be, for example, a 5-layer, isotropic half-sphere formed of high-dielectric materials. Accordingly, the EM absorber 510 can be configured to provide passive mitigation of EM radiation from the RF birdcage body coil.

[0041] Advantageously, the second RF birdcage body coil 506 can be optimized to minimize the EM radiation produced by the first RF birdcage body coil 504 during operation of the first RF birdcage body coil 504. In one example, in some embodiments, the second RF birdcage body coil 506 can be used to control (or minimize or reduce) the EM radiation emitted by the first RF birdcage body coil 504 so that it is below a predetermined threshold. For example, in some embodiments the predetermined threshold can be a safety standard of limit, for example, the IEC 60601-1-2 and CISPR-11 limits on the peak E-field (peak-Eiom) or H-field (peak-Hiom) radiated at a 10-meter radius. In some embodiments, the overlapping first RF birdcage body coil 504 andMGH 2024-162-02 Q&B 125141.04905 second RF birdcage body coil 506 can null their mutual inductance. The second RF birdcage body coil 406 can be optimized to, for example, reduce far-field radiation (e.g., peak-Eiom) while minimally affecting spin-excitation in the image field-of-view. In some embodiments, known optimization techniques for RF pulse design can be used to optimize the RF pulses applied by the second RF birdcage body coil 506 can be configured to cancel surface currents and EM radiation. In some embodiments, RF pulses applied by the second RF birdcage body coil 506 can be optimized to both reduce the EM radiation (e.g., below the predetermined threshold such as a regulatory limit) generated by the RF birdcage body coil during a scan as well as provide sufficient imaging characteristic (e g., sufficient flip angle excitations within the subject 508). In some embodiments, known optimization techniques for RF pulse design can be used to optimize the RF pulses applied by the second RF birdcage body coil 506. In some embodiments, an optimization process can be performed on a computer system such as operator workstation 102 shown in FIG. 1 or computer system 1000 shown in FIG. 10.

[0042] FIGs. 6A an 6B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using a radiation control array in accordance with an embodiment. In FIG. 6A, a magnet assembly can include a magnet 602 and an RF shield 606 disposed within an inner radius of the magnet 602. In some embodiments, the magnet 602 can be a cylindrical superconducting magnet and the RF shield 606 can be a cylindrical RF shield. The magnet assembly also include an RF birdcage body coil 604 disposed within an inner radius of the RF shield 606. In FIG. 6A, a subject 608 is illustrated positioned within a bore of the magnet assembly. To control or mitigate EM radiation (or RF radiation) emitted by the RF birdcage body coil 604 during operation (e.g., transmission of EF excitation pulses), a plurality of radiation control arrays (RCAs) can advantageously be included in the magnet assembly. In the embodiment illustrated in FIG. 6A, aa dual RCA configuration includes a first RCA (or anterior RCA) 614 and a second (or posterior) RCA 616 are positioned symmetrically inside the bore on each side of the RF birdcage body coil 604. In some embodiments, the first and second RCA 614, 616 can include, for example, 8 channels. In some embodiments, the RF birdcage body coil 604 can be a circularly polarized (CP) driven high-pass body birdcage coil. FIG. 6B illustrates the first RCA 614, the second RCA 416 and the RF birdcage body coil 604. Also illustrated in FIG. 6B are two input ports 620 of the first RCA 614, input ports 622 of the second RCA 616, and inputs ports 624 of the RF birdcage body coil 604. In some embodiments, the first RCA 514MGH 2024-162-02 Q&B 125141.04905 and the second RCA 616 can consist of 8 evenly spaced loops. The first RCA 614 and the second RCA 616 can be located at a predetermined distance from the RF birdcage body coil 604, for example, a predetermined distance that minimizes coupling. In some embodiments, adjacent RCA channels can be capacitively decoupled.

[0043] In some embodiments, an electromagnetic (EM) absorber (not shown) can be placed at a service end 612 of the magnet assembly bore. The EM absorber can, for example, include 5 layers of high-dielectric materials optimized for graded interference impedance matching. Accordingly, the EM absorber can be configured to provide passive mitigation of EM radiation from the RF birdcage body coil 604.

[0044] Advantageously, in some embodiments, the first RCA 614 and the second RCA 616 can be used to minimize the EM radiation produced by the RF birdcage body coil 604 during operation of the RF birdcage body coil 604. For example, the first RCA 614 and the second RCA 616 can be used to actively suppress EM radiation from the RF birdcage body coil 604. In another example, in some embodiments, the first RCA 614 and the second RCA 616 can be used to control (or minimize or reduce) the EM radiation emitted by the RF birdcage body coil 604 so that it is below a predetermined threshold. For example, in some embodiments the predetermined threshold can be a safety standard or limit, for example, the IEC 60601-1-2 and CISPR-11 limits on the peak E-field (peak-Eiom) or H-field (peak-Hiom) radiated at a 10-meter radius.Advantageously, the first RCA 614 and the second RCA 616 can generate minimal Bi+and SAR within the imaging volume which can preserve the RF birdcage body coil’s efficiency. In some embodiments, the RCA drive amplitudes and phases can be optimized to destructively cancel the far-field EM radiation and reduce the EM radiation below the predetermined threshold.Accordingly, the first RCA 614 and the second RCA 1616 can provide spatial and phase control to cancel the RF birdcage body coil generated EM radiation. In some embodiments, known optimization techniques can be used to optimize RCA drive amplitudes and phases. In some embodiments, a virtual observation (VOP) technique, which was developed for control of SAR in the body of a subject (e.g., E-fields in the body), can be used for the control of the E-fields and B-fields on a 10m surface outside of the magnet and the body of the subject (i.e., the regular metric for emitted radiation). The VOP technique for control of SAR is described in Eichfelder, Gabriele, and Matthias Gebhardt. "Local specific absorption rate control for parallel transmission by virtual observation points." Magnetic Resonance in Medicine 66.5 (2011): 1468-1476, hereinMGH 2024-162-02 Q&B 125141.04905 incorporated by reference in its entirety. In some embodiments, the VOP technique can be used to determine the excitations in the first RCA 614 and the second RCA 616 to optimally reduce the radiated emission. In some embodiments, an optimization process can be performed on a computer system such as operator workstation 102 shown in FIG. 1 or computer system 1000 shown in FIG. 10.

[0045] As mentioned, in some embodiments, a parallel transmit (pTx) array can be used as an alternative to an RF body transmit coil and configured, for example, for EM radiation, flip angle, and Specific Absorption Rate (SAR) control. FIG. 7 is perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using parallel transmission (pTx) in accordance with an embodiment. In FIG. 7, a magnet assembly can include a magnet 702 and an RF shield disposed within an inner radius of the magnet 702. In some embodiments, the magnet 702 can be a cylindrical superconducting magnet and the RF shield can be a cylindrical RF shield. The magnet assembly also include a parallel transmit array coil 712 disposed within an inner radius of the RF shield. In FIG. 7, a subject 706 is illustrated positioned within a bore of the magnet assembly. To control or mitigate EM radiation (or RF radiation) emitted by the magnet assembly during operation (e.g., transmission of RF excitation pulses), the parallel transmit array coil 712 can advantageously be configured for EM radiation mitigation as well as RF imaging excitation. Accordingly, the embodiment illustrated in FIG. 7 does not include an RF birdcage body coil. In some embodiments, the parallel transmit array 712 is a head / neck parallel transmit array. In one example, parallel transmit array 712 can be a 16- channel parallel transmit array. As shown in FIG. 7, the parallel transmit array 712 can be positioned around the subject’s head and neck. FIG. 7 also illustrates a perspective view 720 showing the parallel transmit array 712 positioned over the subject’s had and neck and a side view 730 of the parallel transmit array 712 positioned over the subject’s head and neck.

[0046] In some embodiments, an electromagnetic (EM) absorber 704 can be placed at a service end 710 of the magnet assembly bore. The EM absorber 704 can, for example, include 5 layer of high-dielectric materials optimized for graded interference impedance matching. Accordingly, the EM absorber 704 can be configured to provide passive mitigation of EM radiation from the RF birdcage body coil.

[0047] In some embodiments, the parallel transmit array 712 can advantageously be used to minimize the EM radiation generated during operation of the parallel transmit array 712 during aMGH 2024-162-02 Q&B 125141.04905 scan of the subject 706. In some embodiments, the parallel transmit array 712 can be used to control (or minimize or reduce) the EM radiation emitted by the parallel transmit array 712 so that it is below a predetermined threshold. For example, in some embodiments the predetermined threshold can be a safety standard of limit, for example, the IEC 60601-1-2 and CISPR-11 limits on the peak E-field (peak-Eiom) or H-field (peak-Hiom) radiated at a 10-meter radius. In some embodiments, the RF pulses (e.g., RF shimming pulses, RF excitation pulses) applied by the parallel transmit array 712 can be optimized to both reduce the EM radiation (e.g., below the predetermined threshold such as a regulatory limit) generated during a scan as well as provide sufficient imaging characteristic (e.g., sufficient flip angle excitations within the subject 308). In some embodiments, the RF pulses applied by the parallel transmit array 712 can be designed to optimize the transmit field (or field patterns) both inside and outside the subject 706. For example, the RF pulses applied by the parallel transmit array 712 can be jointly optimized to produce both uniform and efficient fields inside the subject 706 (for imaging purposes) and low peak E-field on the regulatory 10-meter radius surface (for EM radiation mitigation). In some embodiments, known optimization techniques for parallel transmission can be used to optimize the RF pulses applied by the parallel transmit array 712. In one example, the RF pulses can be designed using a least squares optimization with a target phase profile of a birdcage mode of the parallel transmit array 712 while constraining the peak-Eiom. In some embodiments, a pulse optimization process can be performed on a computer system such as operator workstation 102 shown in FIG. 1 or computer system 1000 shown in FIG. 10.

[0048] FIGs. 8A and 8B are perspective views of an apparatus for controlling electromagnetic (EM) radiation emitted by an MRI system using parallel transmission (pTx) in accordance with an embodiment. In FIG. 8A, a magnet assembly can include a magnet 802 and an RF shield 804 disposed within an inner radius of the magnet 802. In some embodiments, the magnet 802 can be a cylindrical superconducting magnet and the RF shield 804 can be a cylindrical RF shield. The magnet assembly also include a parallel transmit array coil 810 disposed within an inner radius of the RF shield 804. In FIG. 8, a subject 806 is illustrated positioned within a bore of the magnet assembly. To control or mitigate EM radiation (or RF radiation) emitted by the magnet assembly during operation (e.g., transmission of RF excitation pulses), the parallel transmit array coil 810 can advantageously be configured for EM radiation mitigation as well as RF imaging excitation. Accordingly, the embodiment illustrated in FIG. 8 does not include an RF birdcage body coil. InMGH 2024-162-02 Q&B 125141.04905 some embodiments, the parallel transmit array 810 is a parallel transmit body array, for example, a 2x8 channel loop array. As shown in FIG. 8A, the parallel transmit array 810 can be positioned around the subject 806. FIG. 8B illustrates the parallel transmit array 810 positioned around the subject. The parallel transmit array 810 can include ports 822. Decoupling resonant loops 820 can be positioned between neighboring channels to enhance decoupling efficiency.

[0049] In some embodiments, an electromagnetic (EM) absorber (not shown) can be placed at a service end of the magnet assembly bore. The EM absorber can, for example, include 5 layer of high-dielectric materials optimized for graded interference impedance matching. Accordingly, the EM absorber can be configured to provide passive mitigation of EM radiation from the RF birdcage body coil.

[0050] In some embodiments, the parallel transmit array 810 can advantageously be used to minimize the EM radiation generated during operation of the parallel transmit array 810 during a scan of the subject 806. In some embodiments, the parallel transmit array 810 can be used to control (or minimize or reduce) the EM radiation emitted by the parallel transmit array 810 so that it is below a predetermined threshold. For example, in some embodiments the predetermined threshold can be a safety standard of limit, for example, the IEC 60601-1-2 and CISPR-11 limits on the peak E-field (peak-Eiom) or H-field (peak-Hiom) radiated at a 10-meter radius. In some embodiments, the RF pulses (e.g., RF shimming pulses, RF excitation pulses) applied by the parallel transmit array 810 can be optimized to both reduce the EM radiation (e.g., below the predetermined threshold such as a regulatory limit) generated during a scan as well as provide sufficient imaging characteristic (e.g., sufficient flip angle excitations within the subject 308). In some embodiments, the RF pulses applied by the parallel transmit array 810 can be designed to optimize the transmit field (or field patterns) both inside and outside the subject 806. For example, the RF pulses applied by the parallel transmit array 810 can be jointly optimized to produce both uniform and efficient fields inside the subject 806 (for imaging purposes) and low peak E-field on the regulatory 10-meter radius surface (for EM radiation mitigation). In some embodiments, the parallel transmit body array 810 can leverage additional degrees of freedom in arbitrary trajectory pTx pulse design to constrain the radiated field. For example, parallel transmit techniques can introduce additional control over the spatial and temporal characteristics of the RF fields. The additional degree of freedom of parallel transmit pulse design can allow the constraint of the RF fields while maintaining excitation quality. In some embodiments, knownMGH 2024-162-02 Q&B 125141.04905 optimization techniques for parallel transmission can be used to optimize the RF pulses applied by the parallel transmit array 810. In some embodiments, a pulse optimization process can be performed on a computer system such as operator workstation 102 shown in FIG. 1 or computer system 1000 shown in FIG. 10.

[0051] FIG. 9 illustrates a method for generating a magnetic resonance (MR) image of a subject using a magnetic resonance imaging (MRI) system without Faraday shielding and using parallel transmission (pTx) electromagnetic (EM) radiation control in accordance with an embodiment. The process illustrated in FIG. 9 is described as being carried out by the systems in FIGs. 7, 8A and 8B, however, in some examples, the process of FIG. 9 may be implemented by a different system. Although the blocks of the process in FIG. 9 are illustrated in a particular order, in some embodiments, one or more blocks may be executed in a different order than illustrated in FIG. 9, or may be bypassed.

[0052] At block 902, a set of parameters for parallel transmission excitation can be received or retrieved. In some embodiments, the set of parameters are optimized to control (e.g., minimize, reduce) electromagnetic (EM) radiation generated by an MRI system (e.g., by parallel transmit array) during an imaging scan. For example, the parameter of one or more RF pulses applied by a parallel transmit array 712, 810 can be optimized to control the EM radiation, as discussed above with respect to FIGs. 7, 8 A and 8B. In some embodiments, known optimization methods can be used to optimized the set of parameters of the parallel transmission excitation. In some embodiments, the set of parameters may be provided by a user (or operator), for example, using a user interface or input devices of an MRI system (e.g., MRI system 100 shown in FIG. 1). In some embodiments, the one or more parameters may be retrieved from data storage of an MRI system (e.g., MRI system 100 shown in FIG. 1) or data storage of other computer systems (e.g., computer system 1000 shown in FIG. 10. For example, parameters determined using an optimization method may be stored in data storage and retrieved from data storage for performing the parallel transmission excitation as part of an MR scan of a subject.

[0053] At block 904, an MRI system (e.g., MRI system 100 shown in FIG. 1) may be used to perform a pulse sequence with a parallel transmission to acquire magnetic resonance (MR) data from a subject. The parallel transmission excitation may be utilized during the excitation phase of known pulse sequences for acquired MR data from a subject. As discussed above, the parallel transmission excitation advantageously is configured to control EM radiation emitted by the MRIMGH 2024-162-02 Q&B 125141.04905 system (e.g., a parallel transmit array 712, 810 of the MRI system) as discussed above with respect to FIGs. 7, 8A and 8B. At block 906, an image of the subject may be generated using the MR data acquired at block 904. The image of the subject may be reconstructed using known reconstruction methods. At block 908, the generated image of the subject may be displayed, for example, on a display (e.g., display 104 of an operator workstation of MRI system 1000 shown in FIG. 1 or display 1018 of computer system 1000 shown in FIG. 10). The generated image of the subject may be stored in, for example, data storage of an MRI system (e.g., MRI system 100 shown in FIG. 1) or data storage of other computer systems (e.g., computer system 1000 shown in FIG. 10).

[0054] FIG. 10 is a block diagram of an example computer system in accordance with an embodiment. Computer system 1000 may be used to implement the methods described herein. In some embodiments, the computer system 1000 may be a workstation, a notebook computer, a tablet device, a mobile device, a multimedia device, a network server, a mainframe, one or more controllers, one or more microcontrollers, or any other general-purpose or application-specific computing device. The computer system 1000 may operate autonomously or semi- autonomously, or may read executable software instructions from the memory or storage device 1016 or a computer-readable medium (e.g., a hard drive, a CD-ROM, flash memory, etc.), or may receive instructions via the input device 1020 from a user, or any other source logically connected to a computer or device, such as another networked computer or server. Thus, in some embodiments, the computer system 1000 can also include any suitable device for reading computer-readable storage media.

[0055] Data, such as data acquired with an imaging system (e.g., a computer tomography (CT) system) may be provided to the computer system 1000 from a data storage device 1016, and these data are received in a processing unit 1002. In some embodiment, the processing unit 1002 includes one or more processors. For example, the processing unit 1002 may include one or more of a digital signal processor (DSP) 1004, a microprocessor unit (MPU) 1006, and a graphics processing unit (GPU) 1008. The processing unit 1002 also includes a data acquisition unit 1010 that is configured to electronically receive data to be processed. The DSP 1004, MPU 1006, GPU 1008, and data acquisition unit 1010 are all coupled to a communication bus 1012. The communication bus 1012 may be, for example, a group of wires, or a hardware used for switching data between the peripherals or between any components in the processing unit 1002.MGH 2024-162-02 Q&B 125141.04905

[0056] The processing unit 1002 may also include a communication port 1014 in electronic communication with other devices, which may include a storage device 1016, a display 1018, and one or more input devices 1020. Examples of an input device 1020 include, but are not limited to, a keyboard, a mouse, and a touch screen through which a user can provide an input. The storage device 1016 may be configured to store data, which may include data such as, for example, optimized parallel transmission pulses; parameters of a parallel transmission excitation, etc. whether these data are provided to, or processed by, the processing unit 1002. The display 1018 may be used to display images and other information, such as magnetic resonance images, patient health data, and so on.

[0057] The processing unit 1002 can also be in electronic communication with a network 1022 to transmit and receive data and other information. The communication port 1014 can also be coupled to the processing unit 1002 through a switched central resource, for example the communication bus 1012. The processing unit can also include temporary storage 1024 and a display controller 1026. The temporary storage 1024 is configured to store temporary information. For example, the temporary storage 1024 can be a random access memory.

[0058] The following example sets forth, in detail, ways in which the present disclosure was developed and evaluated and ways in which the present disclosure may be used or implemented, and will enable one of ordinary skill in the art to more readily understand the principles thereof. The following example is presented by way of illustration and are not meant to be limiting in any way.

[0059] Computer-executable instructions for mitigation of EM emissions of an MRI system according to the above-described methods may be stored on a form of computer readable media. Computer readable media includes volatile and nonvolatile, removable, and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer readable media includes, but is not limited to, random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), flash memory or other memory technology, compact disk ROM (CD-ROM), digital volatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired instructions and which mayMGH 2024-162-02 Q&B 125141.04905 be accessed by a system (e.g., a computer), including by internet or other computer network form of access.

[0060] The present technology has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.

Claims

MGH 2024-162-02 Q&B 125141.04905CLAIMS1. An apparatus for controlling electromagnetic (EM) radiation emitted from a magnetic resonance imaging (MRI) system having a magnet assembly having a superconducting magnet and a radio frequency (RF) shield, the apparatus comprising: an RF birdcage body coil positioned in the magnet assembly proximate to an inner radius of the RF shield and configured to apply one or more RF excitation pulses; at least one radiation control array positioned in the magnet assembly and configured to control EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses; and a processor device coupled to the RF birdcage coil and the at least one radiation control array and configured to control current waveforms provided to the RF birdcage body coil and to the at least one radiation control array.

2. The apparatus according to claim 1, wherein the at least one radiation control array is a parallel transmit array coil positioned proximate to a patient end of the magnet assembly and disposed around the subject and configured to apply one or more RF pulses optimized to control the EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses.

3. The apparatus according to claim 1, wherein the at least one radiation control array is a second RF birdcage body coil positioned in the magnet assembly proximate to an outside surface of the RF shield and configured to cancel at least a portion of the EM radiation generated by the first RF birdcage body coil positioned in the magnet assembly proximate to an inner radius of the RF shield.

4. The apparatus according to claim 1, wherein the at least one radiation control array is a second RF birdcage body coil positioned in the magnet assembly proximate to an inside surface of the RF shield and overlapping with a portion of the first RF birdcage body coil, wherein the second RF birdcage body coil is configured to minimize the EM radiation generated by the first RF birdcage body coil.MGH 2024-162-02 Q&B 125141.049055. The apparatus according to claim 1, wherein the at least one radiation control array comprises a first radiation control array positioned on a first side of the RF birdcage body coil and proximate to a service end of the magnet assembly and a second radiation control array positioned on a second side of the RF birdcage body coil and proximate to a patient end of the magnet assembly.

6. The apparatus according to claim 1, further comprising an electromagnetic (EM) absorber positioned on a service end of the magnet assembly.

7. The apparatus according to claim 1, wherein the at least one radiation control array positioned in the magnet assembly is configured to reduce an amount of EM radiation generated by the RF birdcage body coil below a predetermine threshold.

8. A magnetic resonance imaging (MRI) system comprising: a magnet system configured to generate a polarizing magnetic field about at least a portion of a subject; a gradient system including a plurality of gradient coils configured to apply at least one magnetic gradient field to the polarizing magnetic field; a radio frequency (RF) system including an RF shield and an RF birdcage body coil positioned proximate to an inner surface of the RF shield and configured to apply one or more RF excitation pulses to the subject; at least one radiation control array configured to control EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses; and a computer system programmed to: direct the plurality of magnetic gradient coils, the RF birdcage body coil, to perform a pulse sequence; and direct the at least one radiation control array to apply one or more RF pulses.

9. The MRI system according to claim 8, wherein the at least one radiation control array is a parallel transmit array coil positioned proximate to a patient end of the magnet assembly and disposed around the subject and configured to apply one or more RF pulses optimized to controlMGH 2024-162-02 Q&B 125141.04905 the EM radiation generated by the RF birdcage body coil during application of the one or more RF excitation pulses.

10. The MRI system according to claim 8, wherein the at least one radiation control array is a second RF birdcage body coil positioned proximate to an outside surface of the RF shield and configured to cancel at least a portion of the EM radiation generated by the first RF birdcage body coil positioned proximate to an inner radius of the RF shield.

11. The MRI system according to claim 8, wherein the at least one radiation control array is a second RF birdcage body coil positioned proximate to an inside surface of the RF shield and overlapping with a portion of the first RF birdcage body coil, wherein the second RF birdcage body coil is configured to minimize the EM radiation generated by the first RF birdcage body coil.

12. The MRI system according to claim 8, wherein the at least one radiation control array comprises a first radiation control array positioned on a first side of the RF birdcage body coil and proximate to a service end of the magnet assembly and a second radiation control array positioned on a second side of the RF birdcage body coil and proximate to a patient end of the magnet assembly.

13. The MRI system according to claim 8, further comprising an electromagnetic (EM) absorber positioned on a service end of the magnet assembly.

14. The MRI system according to claim 8, wherein the at least one radiation control array is configured to reduce an amount of EM radiation generated by the RF birdcage body coil below a predetermine threshold.

15. A method for generating a magnetic resonance (MR) image of a subject using a magnetic resonance imaging (MRI) system without Faraday shielding and having a parallel transmit (pTx) array, the method comprising:MGH 2024-162-02Q&B 125141.04905 receiving, using the MRI system, a set of parameters for a parallel transmit excitation configured to control EM radiation generated by the MRI system during transmission of one or more RF excitation pulses; performing, using the MRI system including the parallel transmit array, a pulse sequence comprising the parallel transmit excitation to acquire magnetic resonance (MR) data from the subject; and generating, using a processor device, an image of the subject using the acquired MR data.

16. The method according to claim 15, wherein the parallel transmit excitation is configured to reduce an amount of EM radiation generated by the MRI system below a predetermine threshold.

17. The method according to claim 15, wherein the parallel transmit array is a head and neck parallel transmit array.

18. The method according to claim 15, wherein the parallel transmit array is a body array.

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