MRI systems, particularly methods and systems for setting their RF operating frequencies.

Abstract

A method for setting the RF operating frequency of an MRI system (1) uses a first reference frequency signal obtained from a geostationary satellite system as a stable long-term frequency reference. The first frequency reference signal is used to calibrate a second frequency source (24), which is then used as the master clock of the MRI system (1) for setting the RF operating frequency.

Description

Technical Field

[0001] This invention relates to magnetic resonance imaging (MRI) systems, and more particularly to the measurement and setting of RF resonant frequencies. Background Technology

[0002] Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to create images of the body's anatomical structures and physiological processes. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of organs inside the body.

[0003] MRI is widely used in hospitals and clinics for medical diagnosis, disease staging, and follow-up without exposing the body to radiation.

[0004] MRI is based on the ability of specific atomic nuclei to absorb radio frequency energy when placed in an external magnetic field. The resulting evolving spin polarization can induce an RF signal in a radio frequency coil, which can then be detected.

[0005] Hydrogen atoms are most commonly used to generate macroscopic polarizations, which can be detected by antennas near the object being examined. Hydrogen atoms are naturally present in humans and other biological organisms, particularly in water and fat. For this reason, most MRI scans essentially map the location of water and fat within the body.

[0006] Pulses of radio waves excite nuclear spin energy transitions, and magnetic field gradients localize polarization in space. By changing the parameters of the pulse sequence, different contrasts can be generated between tissues based on the relaxation properties of hydrogen atoms in the tissue.

[0007] Accurate knowledge of the water resonance frequency is essential for performing high-quality MR imaging, particularly for controlling the frequency of radio wave pulses to ensure they are at the correct Larmor frequency. However, the frequency settings required for the RF coil are affected by many factors, such as temperature drift, aging of electronic equipment, current loss in the magnet, and patient-induced changes in the magnetic field.

[0008] The interaction between these factors remains unclear. Several candidate mechanisms have been proposed and investigated as sources of this frequency contrast. A leading candidate is a change in the volumetric magnetic susceptibility of the tissue being imaged.

[0009] During MRI, the resonant frequency (F0) used (for RF field synthesis and detection) is used in a dedicated preparation phase (the so-called "F0 preparation phase") to determine the subvolume of the patient within the imaging chamber by analyzing free induction attenuation (FID).

[0010] During MRI examinations, the F0 preparation phase is frequently repeated even if the patient's position remains unchanged. This makes F0 determination the most time-consuming of all preparation phases.

[0011] To reduce the frequency of F0 measurements, modeling F0 variations is difficult because current methods for measuring F0 do not allow for the differentiation of potential sources of F0 variation, such as electronic devices, magnets, patients, and temperature.

[0012] Therefore, it is necessary to improve the accurate determination / prediction of the F0 frequency and / or determine the reasons for its value variation.

[0013] The article "PulseblasterDDS: Programmable TTL and DDS RF pulse generator" (XP002361616) discloses a system for setting the RF operating frequency using a reference clock oscillator. This system can use a GPS-locked reference clock oscillator.

[0014] The article "Gaseous 3He nuclear magnetic resonance probe for cryogenic environments" (XP012240173) by Fan X et al. discloses a 3He NMR probe.

[0015] The article "Multichannel magnetic resonance sounding with wirelessly operated coils - A design study" (XP055761296) by Klaus Bahner et al. discloses a wireless magnetic resonance receiving coil.

[0016] The paper "A reconfigurable platform for magnetic resonance data acquisition and processing" (XP011781004) by Marjanovic Josip et al. discloses a platform capable of simultaneous imaging and field sensing. Summary of the Invention

[0017] This invention is defined by the claims.

[0018] According to one aspect of the present invention, a method for setting the RF operating frequency of an MRI system is provided, comprising:

[0019] The first reference frequency signal obtained from the Earth Satellite Positioning System is used as a stable (long-term) frequency reference;

[0020] The first frequency reference signal is used to obtain calibration information for the second frequency source; and

[0021] The second frequency source is used as the master clock for the MRI system, and the RF operating frequency is set using the calibration information.

[0022] This method calibrates a master clock (e.g., a 10MHz clock) used to set the RF operating frequency corresponding to the Larmor frequency F0 (e.g., 63.87MHz for a 1.5T field or 127.74MHz for a 3T field). The obtained calibration information essentially involves determining the true frequency. In other words, a 10MHz signal source (the second frequency source) has the expected 10MHz clock signal output. However, for example, due to electronic drift, the actual clock signal output may differ from this. By determining the true frequency through comparison with a stable first frequency source, the RF operating frequency generated using the master clock signal can be adjusted to have a known desired frequency, regardless of the actual frequency of the clock signal.

[0023] There are several possible causes for variations in the Larmor frequency, primarily due to (i) the electronics generating the 10 MHz clock frequency used by the MRI scanner's internal RF system and thus for measuring F0, (ii) changes (reductions) in the field B0 over time, and (iii) patient characteristics. Master clock calibration based on an externally stable geosatellite clock signal eliminates fluctuations based on electronics drift. This helps maintain an accurate F0 frequency for proper application. In turn, this may result in fewer or no F0 measurements at midpoints during the scan. It also helps to more accurately determine the actual cause of the F0 frequency shift by eliminating one of the possible causes. This, in turn, can improve the workflow for application during the scan.

[0024] The first reference frequency signal is obtained, for example, from a GPS system. This is a readily available source of a long-term stable clock signal with readily available receiving circuitry. However, other Earth satellite systems can be used (e.g., Galileo, DORIS, GLONASS, Baidou).

[0025] The second frequency source includes, for example, a temperature-controlled crystal oscillator. This provides a stable short-term (e.g., at least for the entire duration of the scan) clock signal source. Therefore, calibration allows the actual frequency of the second frequency source to be known, and it can remain constant for the desired duration. Long-term drift in the second frequency source can thus be compensated for by an external, more stable source over a longer period.

[0026] The method also includes measuring the operating frequency of the MRI system, including:

[0027] The magnetic resonance signal probe is placed into the imaging chamber of the MRI system; and

[0028] A magnetic resonance signal probe is used to measure free induction decay.

[0029] This provides for the measurement of Larmor frequencies using a source that is not controlled by the electronics of the MRI imaging system. Therefore, it can be used to independently detect drift in the MR borehole main field (B0 field).

[0030] The magnetic resonance signal probe also includes a frequency reference, which is calibrated using a signal obtained from the Earth's GPS system. This provides an accurate measurement of the Larmor frequency.

[0031] This method can include measuring free induction attenuation, where the object is both inside and outside the imaging chamber of the MRI system. In this way, the object's influence on the field can also be determined. This allows for the separation of the three possible sources of drift in F0, and a better understanding of how the frequency is affected by different factors, which can then be better incorporated into the imaging workflow.

[0032] This method may include placing an array of magnetic resonance signal probes into the imaging chamber of an MRI system and using each probe to measure free induction attenuation. This allows for the acquisition of a distribution in 3D space. This can be compared with characteristics of objects (e.g., their size and density distribution) to simulate the effect of the object's presence on field strength and frequency.

[0033] This method may include monitoring the temporal characteristics of a field detected by a probe, thereby detecting changes caused by an object.

[0034] The method may also include performing resonance frequency calibration using an MRI system and determining the master clock frequency based on the resonance frequency calibration and measurements of free induction attenuation using a magnetic resonance signal probe. In this way, the master clock frequency can be determined based on measurements from both the internal system and the external probe. The desired resonance frequency (e.g., as a multiple of the actual frequency generated by the second frequency source) can then be predicted and set very accurately.

[0035] This probe can be used to measure the operating frequency of an MRI system, as follows:

[0036] The first reference frequency signal obtained from the Earth Satellite Positioning System is used as a stable (long-term) frequency reference;

[0037] The calibration information of the second frequency source is obtained using the first frequency reference signal, the second frequency source forming part of the magnetic resonance signal probe;

[0038] The magnetic resonance signal probe is placed into the imaging chamber of the MRI system; and

[0039] Free-sensing attenuation is measured using a magnetic resonance signal probe.

[0040] Therefore, the frequency calibration described above can be used to provide a signal probe for accurately measuring the operating frequency of an MRI.

[0041] The present invention also provides a system for setting the operating frequency of an MRI system, comprising:

[0042] An antenna used to receive a first reference frequency signal from a geostationary satellite system as a stable (long-term) frequency reference;

[0043] A second frequency source, which serves as the master clock for the MRI system, is used to set the RF operating frequency; and

[0044] A calibration system for obtaining calibration information for the second frequency source using the first frequency reference signal.

[0045] The antenna may include a GPS antenna.

[0046] The second frequency source may include a temperature-controlled crystal oscillator.

[0047] The system also includes a magnetic resonance signal probe for insertion into the imaging chamber of an MRI system to measure free induction decay. The probe may include, for example, an MR active material and an RF coil for excitation magnetization and detection of the magnetic resonance signal.

[0048] An array of magnetic resonance signal probes can exist for insertion into the imaging chamber of an MRI system.

[0049] Magnetic resonance signal probes can be used to measure the operating frequency of an MRI system by measuring free induction attenuation, including:

[0050] An antenna used to receive a first reference frequency signal from a geostationary satellite system as a long-term frequency reference.

[0051] A second frequency source is used as the master clock for the magnetic resonance signal probe.

[0052] A calibration system for obtaining calibration information for the second frequency source using the first frequency reference signal.

[0053] These and other aspects of the invention will become apparent and will be explained with reference to the embodiments described below. Attached Figure Description

[0054] To better understand the invention and to more clearly illustrate how it can be practiced, reference will now be made to the accompanying drawings by way of example only, wherein,

[0055] Figure 1The traditional MRI system and the additional MR sensor are shown;

[0056] Figure 2 An example of an RF transmitter is shown; and

[0057] Figure 3 A method for setting the RF operating frequency of an MRI system is shown. Detailed Implementation

[0058] The invention will be described with reference to the accompanying drawings.

[0059] It should be understood that while the detailed description and specific examples indicate exemplary embodiments of the devices, systems, and methods, they are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will be better understood from the following description, the appended claims, and the accompanying drawings. It should be understood that the drawings are schematic only and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0060] This invention provides a method for setting the RF operating frequency of an MRI system, which uses a first reference frequency signal obtained from a geostationary satellite system as a long-term frequency reference. The first frequency reference signal is used to calibrate a second frequency source, which is then used as the master clock of the MRI system for setting the RF operating frequency.

[0061] Figure 1 A conventional MRI system 1 and an additional MR sensor 30 are shown. The MRI system 1 is used to perform an MRI examination of a patient 2 within an examination region 18 inside the bore of a superconducting magnet 3, which generates a high static magnetic field. To position the patient 2 within the examination region 18, the patient 2 is positioned on a patient support 7, which can be driven in and out of the examination region 18 inside the bore of the superconducting magnet 3.

[0062] The MRI system 1 shows only its most basic components, namely those relevant to the present invention. In this respect, the MRI system 1 includes a gradient coil 4, an RF transmitting coil 5, and an RF receiving coil 6 within the bore of the superconducting magnet 3. The RF transmitting coil 5 transmits RF pulses provided by the RF transmitter 8 and generates a radio frequency magnetic field within the bore of the superconducting magnet 3.

[0063] As is well known to those skilled in the art, by emitting RF pulses that have orthogonal polarization with the magnetic field generated by the superconducting magnet 3 and match the Larmor frequency of the nuclei of interest, the spins of the nuclei can be excited and made in phase, and their net magnetization is deflected according to the direction of the magnetic field of the superconducting magnet 3, thereby generating a transverse component with respect to the longitudinal component of the net magnetization.

[0064] After the RF pulse terminates, the relaxation process of the longitudinal and reverse components of the net magnetization begins until the net magnetization returns to its equilibrium state. The magnetic resonance signal generated by the precession magnetization is detected by the RF receiving coil 6.

[0065] The received magnetic resonance signal is a time-based amplitude signal, which is further Fourier transformed into a frequency-based magnetic resonance spectrum signal and further processed to generate a magnetic resonance image of the nuclei of interest.

[0066] The RF transmitter 8 includes an RF amplifier for generating RF pulses and relaying these RF pulses to the RF transmitting coil 5 of the MRI system 1. Furthermore, the RF transmitter 8 typically includes a capacitor bank coupled to the RF amplifier for storing electrical energy and for providing current to the RF amplifier for generating the RF pulses. A mains power supply is coupled to the capacitor bank 10 to generate a charging current to charge the capacitor bank with electrical energy.

[0067] Figure 2 An example of an RF transmitter 8 is shown, including an RF amplifier 9 and a capacitor bank 10 coupled to a main power supply 11.

[0068] The RF amplifier 9 includes, for example, a temperature-controlled crystal oscillator (OCXO) 24. Suitable temperature-controlled oscillators are available as integrated devices, such as Farnell (trademark) model LFOCXO067293BULK. This provides a single component that offers a 10MHz reference with a relative stability of approximately 10 to 12.

[0069] This level of stability is sufficient to rule out electronic device drift as a source of any observed variation in F0 over long periods (e.g., weeks).

[0070] This invention utilizes an Earth satellite receiver 20, such as a GPS receiver, and its associated antenna 21. The antenna 21 is incorporated, for example, into a quench tube. The GPS signal is used to extract a first reference frequency signal CLK1 obtained from the Earth Satellite Positioning System as a long-term frequency reference.

[0071] The ranging codes and navigation messages transmitted from the satellite to the receiver are modulated onto a carrier wave. In the initial GPS design, two frequencies were used; one at 1575.42 MHz (10.23 MHz × 154), called L1; and a second at 1227.60 MHz (10.23 MHz × 120), called L2. Either of these carrier frequencies can be used as a long-term frequency reference. Of course, other Earth satellite systems may use different frequencies.

[0072] The RF amplifier includes an oscillator 24 for generating a master clock signal F_MC and a conversion unit 26 for generating the desired Larmor frequency from the master clock signal. The oscillator 24 serves as a second frequency source.

[0073] The master clock signal is, for example, a (desired / nominal) 10MHz clock signal. This master clock signal F_MC is the external clock reference for the digital phase-locked loop transmitter. It allows the master output reference frequency F0 to have almost any value and any phase between 42MHz and 300MHz (1T–7T).

[0074] Controller 22 is provided for calibrating the second frequency source using a first frequency reference signal. This calibration involves determining the actual frequency of the master clock signal F_MC by using a reference signal of known frequency CLK1 as a reference (thus taking into account any effects of electronic device drift). This provides calibration information, which is then used to determine how to process the output signal F_MC to derive the RF frequency F0.

[0075] The second frequency reference source serves as the master clock for the MRI system, which is used to set the RF operating frequency F0, i.e., for RF synthesis and reception. Therefore, the control signal “control” for the conversion unit 26 is determined by the controller, causing the correct operating frequency, i.e., the Larmor frequency, to be generated from the master clock signal based on the known master field B0.

[0076] In this manner, conversion unit 26 receives a 10MHz reference clock frequency (frequency, time, and phase) for the MRI re-emission pulse F0. The phase, time, and frequency of signal F0 are obtained using a signal generation circuit with applied digital and / or analog amplification. Controller 22 provides timing signals, digital timecodes, and digital and / or analog signals as input control for conversion unit 26 to process F_MC. The calculation of the control signals is performed in the digital domain using software.

[0077] Frequency F0 is generated in conversion unit 26 using a low-jitter, high-quality reference clock (typically quartz) locked to a GPS signal. Frequency F0 is generated by a state-of-the-art high-precision digital synthesizer.

[0078] Clock synchronization and calibration methods, as well as oscillator circuits for generating signals with desired output frequencies from reference clocks, are well known to those skilled in the art.

[0079] This method can calibrate a master clock (e.g., a 10MHz clock) to set the RF operating frequency corresponding to the Larmor frequency F0 (e.g., 63.87MHz for a 1.5T field or 127.74MHz for a 3T field).

[0080] Geostationary satellite systems provide a highly stable oscillator that can be used as a frequency reference over long periods. This is combined with the short-term stability of, for example, a cryogenic crystal oscillator (OCXO). This improves the long-term stability of measurements and also enhances the modeling and prediction of F0 by eliminating highly probable sources of frequency variation, namely electronic device drift and aging. It is currently unclear how much the electronic frequency reference has drifted over longer periods. This drift may not cause image quality issues because MR frequency calibration is performed very frequently, even during a single scan. However, it is suspected to be a significant source of the observed long-term drift in the measured resonant frequency.

[0081] The above frequency calibration measures can be used with a dedicated MR signal probe 30 placed inside the MRI system chamber. Figure 1 The combination of these methods (as shown) allows for the measurement of the FID signal from the probe independently of the MRI system. It enables the measurement of the F0 value without using examination time. It can also be used to differentiate between magnet drift and patient-induced changes.

[0082] Specialized probes can also use Earth satellite clock signals to calibrate their frequency sources in the exact same way as described above. Therefore, specialized detectors can include a frequency reference calibrated from a signal obtained from the Earth Satellite Positioning System.

[0083] A method for measuring the operating frequency of an MRI system using a dedicated signal probe includes:

[0084] The first reference frequency signal obtained from the Earth Satellite Positioning System is used as the long-term frequency reference.

[0085] The calibration information of the second frequency source, which forms part of the magnetic resonance signal probe, is obtained using a first frequency reference signal; and

[0086] Free-sensing attenuation is measured using a magnetic resonance signal probe.

[0087] The combination of these two elements allows for a better understanding of the root causes of F0 variations, which can be used in predictive models or to influence future system designs. The MR signal probe 30 primarily consists of a small volume containing MR active material and an RF coil for excitation magnetization and detection of the MR signal. Control of the RF coil utilizes the frequency source constituting the probe portion. Many known methods exist for constructing such detectors, for example, as discussed by Simon Gross et al. in “Dynamic nuclear magnetic resonancefield sensing with part-per-trillion resolution,” Nat Commun 7, 13702 (2016) doi:10.1038 / ncomms13702. Such a design can be enhanced through frequency calibration as explained above.

[0088] Using fluorine compounds as the active material is particularly advantageous because its frequency is close to that of water, but the difference is sufficient to allow simultaneous operation with the MRI system without interference.

[0089] The probe can be placed behind the borehole cover or under the patient table. By comparing measurements taken within a short period of time with and without a patient inside the borehole, the changes in the field sensed by the patient can be distinguished from magnetic drift.

[0090] Placing multiple probes around the imaging volume can be used to generate a spatial model of patient-induced field variations. Furthermore, the dynamic changes in the field can be used to determine the patient's physiological signals (respiration and heartbeat).

[0091] The first approach used to account for dynamic changes includes:

[0092] (i) The field B0 is measured at a reference position using a calibration probe;

[0093] (ii) Calculate the deviation from the ideal resonant frequency; and

[0094] (iii) Apply biases when performing image generation and reconstruction.

[0095] The second approach to considering spatial variation includes:

[0096] (i) Measuring field B0 by a calibration probe spatially resolved at multiple reference locations;

[0097] (ii) Calculate the deviation from the ideal resonant frequency;

[0098] (iii) Calculate the higher-order shimming coefficients (used for distortion correction of the field B0 of the active coil); and

[0099] (iv) Apply the calculated shimming coefficient during scanning to obtain a more uniform B1 field for the RF coil.

[0100] The third method for deriving patient physiological information includes:

[0101] (i) The field B0 is measured at a reference position using a calibration probe;

[0102] (ii) Calculate the deviation from the ideal resonant frequency and perform time resolution in the order of kHz.

[0103] (iii) Derive the time deviation and filter for cardiac (kHz) or respiratory effects (Hz);

[0104] (iv) Extract physiological signals, for example, for triggering purposes. Using multiple sensors can increase sensitivity and spatial resolution.

[0105] Using a satellite-based system ensures its global applicability, so all MRI scanners are synchronized with the same reference clock.

[0106] As a further step, the variation results of the measurement frequency of the independent probe 30, along with the frequencies determined by routine calibration within the same patient "inside," can be used to model the expected resonant frequencies of the measurements. In this way, the independent probe can be combined with a trained model to predict the resonant frequencies required for potentially very accurate imaging.

[0107] The purpose of this model is to determine the resonant frequency F0 without requiring time-consuming measurements. The model could be, for example, a trained neural network or decision tree algorithm that predicts the expected F0. Training data for the model includes the resonant frequency, the patient's detailed B0 map, and other patient data typically available during the examination (such as weight, gender, etc.). Other scanning parameters and their settings are also known and usable, such as table position and field of view.

[0108] It can acquire low-resolution MR images that are less sensitive to F0, for example, for coil selection, and provide spatial and temporal resolution data for the field probe.

[0109] Additional training data can include RF-based measurements, such as coil loading and coil coupling, which are typically acquired much faster than resonant frequency measurements. The model can be trained using known datasets.

[0110] The resonant frequency F0 has spatial resolution because the underlying B0 field varies with location. Typically, the resonant frequency is determined within a slice passing through the patient and is derived by averaging the volumes of all slices within the patient. Spatial resolution allows the resonant frequency to be measured at the location or region most representative of the scan to be performed, such as the scan slice location.

[0111] Figure 3 A method for setting the radio frequency operating frequency of an MRI system is shown, comprising:

[0112] In step 40, the first reference frequency signal obtained from the Earth Satellite Positioning System is used as a long-term frequency reference;

[0113] In step 42, the first frequency reference signal is used to obtain calibration information for the second frequency source; and

[0114] In step 44, the second reference frequency source is used as the master clock for the MRI system, and the RF operating frequency is set using the calibration information.

[0115] Those skilled in the art, through studying the accompanying drawings, the disclosure, and the claims, will be able to understand and implement variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality.

[0116] Although specific measures are described in different dependent claims, this does not imply that combinations of these measures cannot be used advantageously.

[0117] If the term “suitable” is used in the claims or description, it should be noted that the term “suitable” is intended to be equivalent to the term “configured as”.

[0118] Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A method of setting an RF operating frequency of an MRI system for RF synthesis and reception, comprising: (40) using a first reference frequency signal obtained from an earth satellite positioning system as a stable frequency reference; (42) using the first reference frequency signal to obtain calibration information for a second frequency source used to determine a true frequency; (44) using the second frequency source as a master clock for the MRI system, and using the calibration information, setting the RF operating frequency; and measuring the RF operating frequency by: placing a magnetic resonance signal probe into an imaging bore of the MRI system; and using the magnetic resonance signal probe to measure a free induction decay, wherein the magnetic resonance signal probe includes a frequency reference calibrated by a signal obtained from an earth satellite positioning system.

2. The method of claim 1, wherein, The first reference frequency signal is obtained from a GPS system.

3. The method of claim 1 or 2, wherein, The second frequency source includes an ovenized crystal oscillator.

4. The method of claim 1 or 2, comprising measuring the free induction decay with an object present in the imaging bore of the MRI system and with no object present in the imaging bore of the MRI system.

5. The method of claim 4, comprising placing an array of magnetic resonance signal probes into the imaging bore of the MRI system and using each magnetic resonance signal probe to measure a free induction decay.

6. The method of claim 4, comprising monitoring a time characteristic of a field detected by the probe, thereby detecting a change caused by an object.

7. The method of claim 1 or 2, further comprising performing a resonance frequency calibration using the MRI system, and determining the master clock frequency based on the resonance frequency calibration and the measurement of the free induction decay using the magnetic resonance signal probe.

8. The method of claim 7, comprising using a trained model to model an expected resonance frequency to determine a required resonance frequency for imaging.

9. The method of claim 8, wherein, Training data for the model includes the resonance frequency, a main field map of a patient, and additional patient data available during an examination.

10. A system for setting an RF operating frequency of an MRI system for RF synthesis and reception, comprising: an antenna (21) for receiving a first reference frequency signal (CLK1) from an earth satellite positioning system as a stable frequency reference; a second frequency source (24) used as a master clock for the MRI system for setting the RF operating frequency (F0); and a calibration system (22) for using the first reference frequency signal to obtain calibration information for the second frequency source; a magnetic resonance signal probe for insertion into an imaging bore of the MRI system for measuring a free induction decay, wherein the magnetic resonance signal probe includes a frequency reference calibrated by a signal obtained from an earth satellite positioning system. The antenna includes a GPS antenna.

11. The system of claim 10, wherein, The second frequency source includes an ovenized crystal oscillator.

12. The system of claim 10 or 11, wherein, The probe includes an MR active substance and an RF coil for exciting magnetization and detecting the magnetic resonance signal.

13. The system of claim 10 or 11, wherein, ​ 14. The system of claim 10 or 11, comprising an array of magnetic resonance signal probes for insertion into the imaging bore of the MRI system.

Images