53 results about "B1 field" patented technology

In a method and magnetic resonance tomography apparatus for spatially resolved measurement of the magnetic high frequency field distribution in the apparatus, a double echo high frequency pulse sequence with a first excitation pulse following by at least two refocusing pulses are emitted for generation of a first echo and a following second echo. At least the excitation pulse is slice selective. In an excitation layer defined by the slice selective excitation pulse a first echo image and second echo image are spatially resolved by using suitable gradient pulses for phase or frequency encoding Using the relationships of the amplitudes of the first and second echo image in the various locations the flip angles representing the field strength at the relevant locations in the relevant slice are determined.

An apparatus, system, and method including a magnetic resonance imaging (MRI) apparatus includes a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet, and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images, and a computer. The computer is programmed to apply a first off-resonant radio frequency (RF) pulse at a first frequency different than the resonant frequency to a plurality of nuclei excited at a resonant frequency, acquire a first signal from the plurality of nuclei after application of the first off-resonant RF pulse, determine a phase shift from the first signal based on the first off-resonant RF pulse, determine a B1 field based on the phase shift, and store the B1 field on a computer readable storage medium.

A local coil unit for a magnetic resonance apparatus, which radiates a radio-frequency field into an examination subject, has a housing and at least a part of the housing is formed of an insulating dielectric material that passively compensates for an inhomogeneity in the high-frequency field in the subject. The material has a relative dielectric value εr of greater than 50, preferably greater than 100, and a dielectric loss factor tan δ of less than 2.5×10−2, preferably less than 1×10−3. In the dielectric material displacement currents are generated which create an additional magnetic field that compensates for the minima in the B1 field as a result of the eddy currents arising in the patient due to the radio-frequency radiation.

In a method and magnetic resonance system for homogenization of the B1 field for a magnetic resonance data acquisition with a number of iteration steps. An iteration step includes the following sub-steps: Measurement data are acquired that represent a B1 field distribution in at least one part of the examination volume of the magnetic resonance system. A B1 homogeneity analysis based on the acquired measurement data is automatically implemented. A specific homogenization action is automatically selected from among a number of possible homogenization actions based on the B1 homogeneity analysis, or the iterative homogenization method is ended if the diagnosed homogeneity is sufficient for an intended magnetic resonance measurement. The selected homogenization action is implemented.

In magnetic resonance tomography apparatus and method for determining the field strength of high-frequency pulses which are emitted during a magnetic resonance measurement by the antenna, a magnetic resonance signal excited by a radio-frequency pulse or a radio-frequency pulse sequence is measured, and a phase of the magnetic resonance signal is determined. Based on this phase, the field strength is then determined.

A RF coil compression system for use with an MRI system configured to image a patient's breast is disclosed. In one embodiment, the compression system comprises a first compression plate comprising a first plurality of RF coil elements, which is positioned in a plane oriented orthogonal to a direction of the main magnetic field and the first RF coil elements having a reception sensitivity to a B1 field and is orthogonal to a main magnetic field of the MRI system. The compresses system may further comprise a second compression plate, configured to be positioned opposing the first compression plate and orthogonal to the superior-inferior direction, the second compression plate comprising a second plurality of RF coil elements, the second RF coil elements having a reception sensitivity to a B1 field oriented in a direction substantially orthogonal to the first direction and to the main magnetic field of the MRI system.

The invention discloses a magnetic resonance system imaging method, which comprises the following steps: under a multichannel emission mode, according to spin echo signal intensity SSE and stimulated echo signal intensity SSTE, carrying out optimization on amplitude and phase parameters of a plurality of radio frequency emission channels to generate a target B1 field, wherein the target B1 field meets B1 field uniformity and radio frequency emission power optimization simultaneously; loading the optimized amplitude and phase parameters to a radio frequency pulse controller, and driving the plurality of radio frequency emission channels to generate the target B1 field; under the target B1 field, exciting a part to be scanned of a subject to obtain a magnetic resonance signal of the part to be scanned; and carrying out Fourier transform on the magnetic resonance signal to obtain a magnetic resonance image of the part to be scanned. The spin echo signal intensity and the stimulated echo signal intensity are collected to reflect distribution of the B1 field; and fast correction can be carried out to obtain a uniform B1 field, and radio frequency emission power can be corrected. The invention also provides a magnetic resonance system.

A method for determining the spatial distribution of the magnitude of the radio frequency transmission field B1 in a magnetic resonance imaging apparatus, wherein the method comprises performing an MRI experiment in which a B1-sensitive complex image (SI) of a sample is obtained, wherein the phase distribution within the B1-sensitive complex image (SI) depends on the spatial distribution of the magnitude of the field B1. For establishing the dependency of the phase distribution within the B1-sensitive complex image (SI) on the spatial distribution of the field B1, one or more adiabatic RF pulses are applied. The method provides a simple procedure for mapping the B1 field of a magnetic resonance imaging apparatus with an improved accuracy and a wider measurement range.

The invention discloses a magnetic resonance imaging method and system, wherein the method comprises: before imaging scanning, determining a preset deflection angle of a radio frequency pulse to excite specific tissues; analyzing a corresponding dual-saturated pulse deflection angle according to the preset deflection angle; combining a dual-saturated pulse and a gradient pulse to form a dual-saturated pulse saturation module, wherein the gradient pulse includes a layer-selecting gradient pulse that is used for exciting a corresponding layer of the specific tissues; executing an imaging scanning process, to be specific, applying the dual-saturated pulse saturation module and an imaging pulse sequence sequentially to a scanning area to perform magnetic resonance imaging. By carrying out magnetic resonance imaging through the dual-saturated pulse saturation module and the imaging pulse sequence, saturated band signal inhibition non-uniformity due to non-uniformity of B1 field can be overcome, and motion artifacts due to organ motion, tissue motion and other motions can be inhibited.

A magnetic resonance imaging apparatus produces calculations of local specific energy absorption rates (SAR) by calculating an electrical permittivity map of a subject. The electric permittivity is calculated by measuring the components of the B1 field induced by a radio frequency (RF) coil (16). The Hx and Hy components of the B1 field can be directly measured. The Hz component is measured by encoding it into the phase of the resonance signals. Alternately, Hz can be calculated by solving Gauss's law for magnetism. Hz can also be estimated by finding the z component of the electric field. In the specific case of a birdcage RF coil, Hz can be estimated by using a model of the RF coil and a subject, a model of the RF coil alone, or setting Hz to a constant.

A local radio frequency (RF) transmitting coil (26) of a magnetic resonance imaging system (5) has a plurality of coil elements (100). Each coil element (100) has an adjustable load (62) which is adjusted by a control unit (60) to adjust a transmitted B1field distribution. The load can be adjusted to shim for a uniform B1 field distribution. Non-uniform B1 field distributions can be selected to perform magnetic resonance sequences that use such B1 field distributions, such as parallel imaging. The B1 field distribution can be changed during the magnetic resonance sequence to track a moving region of interest, time division multiplex parallel imaging, and the like.

An arrangement for radiation of a radio-frequency field into an examination subject has a local coil unit with a housing. An insulating dielectric material is embodied at least at one part of the housing in order to passively compensate an inhomogeneity of the B1 field that occurs in the examination subject. An adjustment arrangement allows for fixed but detachable provision of the insulating dielectric material at the housing part.

A local coil unit for a magnetic resonance apparatus, which radiates a radio-frequency field into an examination subject, has a housing and at least a part of the housing is formed of an insulating dielectric material that passively compensates for an inhomogeneity in the high-frequency field in the subject. The material has a relative dielectric value εr of greater than 50, preferably greater than 100, and a dielectric loss factor tan δ of less than 2.5×10−2, preferably less than 1×10−3. In the dielectric material displacement currents are generated which create an additional magnetic field that compensates for the minima in the B1 field as a result of the eddy currents arising in the patient due to the radio-frequency radiation.

A dielectric element for positioning on an examination subject for locally influencing the B1 field distribution during magnetic resonance data acquisition contains a relaxation agent bound to mutually separated particles. The relaxation agent incorporates a paramagnetic substance. In a corresponding method for acquiring magnetic resonance data from an examination subject, such a dielectric element is positioned on the examination subject for locally influencing the B1 field distribution, by homogenizing the B1 field of a magnetic resonance apparatus.

A method for determining the spatial distribution of the magnitude of the radio frequency transmission field B1 in a magnetic resonance imaging apparatus, wherein the method comprises performing an MRI experiment in which a B1-sensitive complex image (SI) of a sample is obtained, wherein the phase distribution within the B1-sensitive complex image (SI) depends on the spatial distribution of the magnitude of the field B1. For establishing the dependency of the phase distribution within the B1-sensitive complex image (SI) on the spatial distribution of the field B1, one or more adiabatic RF pulses are applied. The method provides a simple procedure for mapping the B1 field of a magnetic resonance imaging apparatus with an improved accuracy and a wider measurement range.

In a method and arrangement for local manipulation of a B1 field in a first region of an examination subject in an examination volume of a magnetic resonance system, a B1 measurement value that represents the B1 field in the sub-volume during an adjustment measurement is integrally determined, and in desired radio-frequency signal parameters for a subsequent magnetic resonance measurement are predetermined on the basis of the determined B1 measurement value. At least during the adjustment measurement, the B1 field is influenced within a second region counter to the manipulation intended in the first region by means of an auxiliary coil element which is arranged in or at the second region of the sub-volume remote from the first region.

A dielectric element for positioning on an examination subject for locally influencing the B1 field distribution during magnetic resonance data acquisition contains a relaxation agent bound to mutually separated particles. The relaxation agent incorporates a paramagnetic substance. In a corresponding method for acquiring magnetic resonance data from an examination subject, such a dielectric element is positioned on the examination subject for locally influencing the B1 field distribution, by homogenizing the B1 field of a magnetic resonance apparatus.

In a method and arrangement for local manipulation of a B1 field in a first region of an examination subject in an examination volume of a magnetic resonance system, a B1 measurement value that represents the B1 field in the sub-volume during an adjustment measurement is integrally determined, and in desired radio-frequency signal parameters for a subsequent magnetic resonance measurement are predetermined on the basis of the determined B1 measurement value. At least during the adjustment measurement, the B1 field is influenced within a second region counter to the manipulation intended in the first region by means of an auxiliary coil element which is arranged in or at the second region of the sub-volume remote from the first region.

Coil elements (18) generate a B1 excitation field in an examination region (14), which B1 excitation field is distorted by patient loading (e.g., wavelength effects). Passive shimming elements (22, 24) are disposed between the coil elements and the subject in order to improve the B1 field uniformity. In one embodiment, passive shimming elements include one or more dielectric rods (55) disposed below the subject which generate no substantial MR proton signal and which have a permittivity of at least 100 and preferably greater than 500. In another embodiment, tubes (24) adjacent each coil element are supplied with a dielectric liquid, a thickness of the dielectric liquid between the coil element and the subject adjusting a phase of the B1 field generated by the coil element. Active B1 shimming may be combined with passive shimming elements (22, 24) to effect an improved RF field homogeneity result.

A radio-frequency transmission arrangement for an MR system for generation of a total B1 field which has a first antenna device that generates a first portion of the total B1 field and at least one antenna insert that generates a second portion of the total B1 field, such that the resulting B1 field is generated by the first antenna device and the at least one antenna insert.

The present invention provides a radio frequency (RF) coil (140) for applying an RF field to an examination space (116) of a magnetic resonance (MR) imaging system (110) and / or for receiving MR signals from the examination space (116), whereby the RF coil (140) is provided having a tubular body (142), the RF coil (140) is segmented in a longitudinal direction (154) of the tubular body (142) into two coil segments (146), and the two coil segments (146) are spaced apart from each other in the longitudinal direction (144) of the tubular body (142), whereby a gap (148) is formed between the two coil segments (146). The present invention further provides a magnetic resonance (MR) imaging system (110) comprising at least one radio frequency (RF) coil (140) as specified above. The present invention still further provides a medical system (200) comprising the above magnetic resonance (MR) imaging system (110) and a medical device (202), which is arranged to access to the examination space (116) of the magnetic resonance (MR) imaging system (110) through the gap (148) of the RF coil (140). Even further, the present invention provides a method for applying a radio frequency (RF) field to an examination space (116) of a magnetic resonance (MR) imaging system (110), comprising the steps of providing at least one above radio frequency antenna device (140), and commonly controlling the two RF coil segments (146) to provide a homogenous B1 field within the examination space (116), in particular within the gap (148).

In a method and magnetic resonance apparatus for determining a B1 field map in a scanner of the apparatus, the B1 field map describing a local field distribution of a B1 field resulting from excitation pulses radiated in a measurement sequence, first and second measured values are acquired from a region in which nuclear spins are excited by an excitation pulse having an assigned flip angle, and a provisional flip angle is determined from the first and second measured values. A correction factor, dependent on the pulse shape of a selected excitation pulse, is then determined, and the provisional flip angle is multiplied thereby to obtain a corrected value for entry into said B1 field map.

The invention provides an MR local coil system, mr system and method of operation. The MR local coil system has a plurality of local MR-transmitting coils which can be coupled inductively to at least one feeder coil of an MR apparatus, wherein by means of local MR-transmitting coils local B1-exciting field which is differently structured to each other can be generated. The MR system has an MR device with a supply reel and a local MR local coil system, wherein the local MR-transmitting coils and the supply reel are inductively coupled, the MR-device is used for selectively producing a differently structured global B1 field component of a global B1-exciting field produced by the supply reels, and the differently structured global B1 field component and MR-transmitting coils of the local MR local coils system are coupled. One method is used to operate the MR system in which differently structured B1 field of the global B1-exciting field component is generated by the supply reel of the MR system.

The invention provides a prediction method and a prediction device for temperature rise used for predicting the temperature rise of an electrode under a magnetic resonance imaging examination i.e., MRI examination. The prediction method for the temperature rise comprises the following steps: acquiring a B1 image of a particular range around the electrode under the MRI examination; comparing the B1image to a B1 image of a background radio frequency field under the MRI examination to calculate a received coefficient of the electrode; determining a to-be-scanned sequence under the MRI examination and a magnitude of a radio frequency field of the sequence, i.e., B1+rms; determining a B1 field within the particular range according to the received coefficient and the B1+rms of the sequence; andpredicting a temperature rise of the electrode according to the B1 field within the particular range. According to the prediction method and the prediction device for the temperature rise, an RF induction heating can be more accurately characterized under the consideration of the shape, the angle, and the placement position of the electrode, and the like, thereby determining the RF induction heating of the electrode based medical device under the MRI examination.

The invention relates to a high-dielectric-constant ultrahigh-field animal magnetic resonance radio frequency probe which comprises a coil unit, the coil unit comprises a cylindrical coil circuit substrate and a cylindrical inner wall substrate, and the inner wall substrate is arranged in the coil circuit substrate. The two ends of a high-dielectric-constant ceramic unit are fixed between the coilcircuit substrate and the coil inner wall substrate through a ceramic unit support. All the units are independent of one another, assembling is flexible, and the sensitivity of the radio frequency probe can be effectively improved. The plurality of high-dielectric-constant ceramic blocks can greatly improve the B1 field emission efficiency in the central region, and avoids the adverse effects ofcoil mode increase and disorder caused by complete cylindrical barium titanate ceramic.

A method comprises: performing a number of B i field mapping sequences (24) using a set of radio frequency transmit coils (11) to acquire a B1 field mapping data set wherein said number is less than a number of radio frequency transmit coils in the set of radio frequency transmit coils; and determining coil sensitivities (30) for the set of radio frequency transmit coils based on the acquired B1 field mapping data set. In some embodiments, the performed B1 field mapping sequences are defined by (i) performing a linear transform (40) on the set of radio frequency transmit coils to generate a set of orthogonal virtual radio frequency transmit coils (42) and (ii) selecting (44) a sub- set (46) of the set of orthogonal virtual radio frequency transmit coils that define the performed B1 field mapping sequences.