摘要:
The invention relates to a system comprising an array of two or more receiving antennas (11, 12, 13) for receiving RF signals, each receiving antenna being connected, via a matching network (19, 20, 21), to a low-noise amplifier (22, 23, 24) presenting an input impedance to the matching network (19, 20, 21), each chain consisting of a receiving antenna (11, 12, 13), a matching network (19, 20, 21) and a low-noise amplifier (22, 23, 24) constituting a part of a receiving channel of the system, the matching networks (19, 20, 21) transforming optimum impedances of the low-noise amplifiers (22, 23, 24), the optimum impedances providing optimum noise performance of the low-noise amplifiers (22, 23, 24), wherein each receiving channel comprises at least one switchable impedance (28, 29, 30) at the input of each low-noise amplifier (22, 23, 24) for switching the input impedance as presented to each matching network (19, 20, 21) to a value being the complex conjugate of the optimum impedance of the respective low-noise amplifier (22, 23, 24). The system is arranged to perform an optimization procedure comprising the following steps: a) switching the input impedance presented to the matching network (19, 20, 21) in each receiving channel to the complex conjugate of the optimum impedance of the respective low-noise amplifier (22, 23, 24); b) receiving RF signals via the receiving antennas (11, 12, 13); c) forming a weighted sum of the signal power of the received RF signals; d) modifying the matching networks (19, 20, 21) of all receiving channels so as to find an optimum matching condition by maximizing the weighted power sum; c) switching the input impedance in each receiving channel back to a value for regular operation of the system.
摘要:
For detuning of radio-frequency coils (in magnetic resonance imaging and spectroscopy, for example), a conducting element (102) of a transmission cable is configured to form a primary resonant circuit tunable to at least one first resonance frequency. A second conducting element (104) of the transmission cable is configured to form a switching circuit that is electrically insulated from and reactively coupled via inductive coupling and/or capacitive coupling to the primary resonant circuit, and is adapted to tune the primary resonant circuit to at least one second resonance frequency, thereby detuning the primary resonant circuit.
摘要:
A radio frequency receive coil for receiving a magnetic resonance signal includes a radio frequency antenna. The radio frequency antenna includes one or more electrical conductors (72, 74, 76, 78, 172, 173, 176, 180, 252, 254), at least one of which is a substantially hollow conductor (72, 78, 172, 252, 254). At least one electrical component (100, 110, 110′, 110″, 140, 160, 200) is mounted to be shielded from interfering with the MR signal by disposing it inside the substantially hollow conductor. The at least one electrical component can be, for example, a battery (100, 160, 200), a storage capacitor (140), or coil electronics (110, 110′,110″).
摘要:
The invention relates to an MR apparatus that is provided with an open magnet system and a quadrature coil system that includes a resonator that is tuned by tuning capacitors on at least one of the two sides of the steady magnetic field, said resonator including two large-area electrical conductors that are situated at a distance from one another and are connected to one another in a number of connection points that are distributed along the circumference, and are also provided with at least two terminals that are distributed along the circumference in order to receive or generate RF magnetic fields that are mutually offset in phase. The invention also relates to a corresponding quadrature coil system.
摘要:
A magnetic resonance method of electric properties tomography imaging of an object includes applying an excitation RF field to the object via a coil at a first spatial coil position (402), acquiring resulting magnetic resonance signals via a receiving channel from the object, determining from the acquired magnetic resonance signals a first phase distribution and a first amplitude of a given magnetic field component of the excitation RF field of the coil at the first coil position (402), repeating these steps with a coil at a second different spatial coil position (404), to obtain a second phase distribution, determining a phase difference between the first and second phase distribution, determining a first and a second complex permittivity of the object, the first complex permittivity comprising the first amplitude of the given magnetic field component and the second complex permittivity comprising the second amplitude of the given magnetic field component and the phase difference, equating the first complex permittivity and the second complex permittivity for receiving a final equation and determining from the final equation a phase of the given magnetic field component for the first coil position (402).
摘要:
A radio-frequency coil assembly (18), for use in a magnetic resonance imaging system (10), includes a plurality of coil elements (18n). The coil elements (18n) are connected to a decoupling network (40) which includes a plurality of decoupling elements (40n,x) connected (via transmission lines) to pairs of coil elements (18n, 18x) at corresponding ports (64n,64x) from which the coil can be fed. The decoupling elements (40n,x) compensate for mutual coupling between pairs of corresponding coil elements. An inductive coupling loop (51n), with a constant or adjustable mutual inductance, inductively couples the associated coil element (18n) to the corresponding decoupling network port (64n). Transmission lines (52n) electrically connect each inductive coupling loop (51n) to the decoupling network (40) at the corresponding port (64x). Each transmission line (52n) has an electrical length of kλ/2 where k=0,1,2,3 . . . and λ is a wavelength of the excited and/or received resonance signals inside the transmission line.
摘要:
The present invention relates to a magnetic resonance imaging system (1) comprising a plurality of RF coils (4) forming a multi-coil array and furthermore to a magnetic resonance imaging method for such a system. In order to provide an MR imaging system and method in which a desired excitation pattern is achieved in a simple way, it is suggested to utilize an analytical procedure how to combine the single coil elements to obtain the most homogeneous B1 excitation possible with a given coil array. In other words, the homogeneity of the B1 field is improved in a very simple way. The sensitivity of each RF coil (4) of the coil array is scaled or weighted by a complex factor, i.e. phase and amplitude of each coil drive signal is adjusted accordingly. These complex factors are determined analytically utilizing the sensitivities S(8) of the coil elements (4) and the desired excitation pattern P (IO, 11). The invention allows an optimized control of the field distribution (RF shimming) for arbitrary RF coil arrays. With the invention a fast and easy independent phase and amplitude control of the coil elements (4) is provided for reducing body-induced RF non-uniformities, which appear in high field MR systems.
摘要:
The present invention relates to a magnetic resonance imaging system (1) comprising a plurality of RF coils (4) forming a multi-coil array and furthermore to a magnetic resonance imaging method for such a system. In order to provide an MR imaging system and method in which a desired excitation pattern is achieved in a simple way, it is suggested to utilize an analytical procedure how to combine the single coil elements to obtain the most homogeneous B1 excitation possible with a given coil array. In other words, the homogeneity of the B1 field is improved in a very simple way. The sensitivity of each RF coil (4) of the coil array is scaled or weighted by a complex factor, i.e. phase and amplitude of each coil drive signal is adjusted accordingly. These complex factors are determined analytically utilizing the sensitivities S(8) of the coil elements (4) and the desired excitation pattern P (IO, 11). The invention allows an optimized control of the field distribution (RF shimming) for arbitrary RF coil arrays. With the invention a fast and easy independent phase and amplitude control of the coil elements (4) is provided for reducing body-induced RF non-uniformities, which appear in high field MR systems.
摘要:
A radio frequency receive coil for receiving a magnetic resonance signal includes a radio frequency antenna. The radio frequency antenna includes one or more electrical conductors (72, 74, 76, 78, 172, 173, 176, 180, 252, 254), at least one of which is a substantially hollow conductor (72, 78, 172, 252, 254). At least one electrical component (100, 110, 110′, 110″, 140, 160, 200) is mounted to be shielded from interfering with the MR signal by disposing it inside the substantially hollow conductor. The at least one electrical component can be, for example, a battery (100, 160, 200), a storage capacitor (140), or coil electronics (110, 110′,110″).
摘要:
The Magnetic Resonance Imaging (MRI) system includes a radio-frequency transmitter with multiple transmit channels. The MRI system includes an impedance matching network (320, 1402, 1502, 1602) for matching the radio-frequency transmitter to a remotely adjustable radio-frequency antenna (310, 1504, 1602) with multiple antenna elements (312, 314, 316, 318, 1404). The MRI system includes a processor (336) for controlling the MRI system. The execution of the instructions by the processor causes it to: measure (100, 200) a set of radio-frequency properties (352) of the radio-frequency antenna, calculate (102, 202) a matching network command (354) using the set of radio-frequency properties and a radio frequency model (366), and adjust (104, 204) the impedance matching network by sending the matching network command to the impedance matching network, thereby enabling automatic remote impedance matching.