287 results about "Rf excitation" patented technology

A method and device for inducing anaesthesia in mammals by the application of RF energy to create hyperthermia derived neural anaesthesia. An RF generator drives a plurality of electrodes placed in tissue surrounding the target nerve fiber to desiccate the desired length of nerve fiber to be desiccated in a single deployment. The device allows high-speed selection / de-selection of bipolar electrode pairs or sets under continuous RF excitation. Activation of electrode pairs is adapted in response to sensed current density and temperature (by electrodes not in the current discharge activation phase) in order to create lesions of complex and well defined shape necessary for the production of hyperthermia derived neural anaesthesia.

A method and device for inducing anaesthesia in mammals by the application of RF energy to create hyperthermia derived neural anaesthesia. An RF generator drives a plurality of electrodes placed in tissue surrounding the target nerve fibre to desiccate the desired length of nerve fibre to be desiccated in a single deployment. The device allows high-speed selection / de-selection of bipolar electrode pairs or sets under continuous RF excitation. Activation of electrode pairs is adapted in response to sensed current density and temperature (by electrodes not in the current discharge activation phase) in order to create lesions of complex and well defined shape necessary for the production of hyperthermia derived neural anaesthesia.

A chip scale atomic clock is disclosed that provides a low power atomic time / frequency reference that employs direct RF-interrogation on an end-state transition. The atomic time / frequency reference includes an alkali vapor cell containing alkali atoms, preferably cesium atoms, flex circuits for physically supporting, heating, and thermally isolating the alkali vapor cell, a laser source for pumping alkali atoms within the alkali vapor cell into an end resonance state by applying an optical signal along a first axis, a photodetector for detecting a second optical signal emanating from the alkali vapor cell along the first axis, a pair of RF excitation coils for applying an RF-interrogation signal to the alkali atoms along a second axis perpendicular to the first axis, a pair of bias coils for applying a uniform DC magnetic field along the first axis, and a pair of Zeeman coils for applying a Zeeman interrogation signal to the alkali atoms and oriented and configured to apply a time-varying magnetic field along the second axis through the alkali vapor cell. Another flex circuit is used for physically supporting the laser source, for heating the laser source, and for providing thermal isolation of the laser source. The laser source can be a vertical cavity surface emitting laser (VSCEL). The bias coils can be Helmholtz coils.

In a method for implementation of a magnetic resonance examination, and a magnetic resonance apparatus, and an array for acquisition of magnetic resonance signals, and a magnetic resonance signal at a magnetic resonance frequency are acquired from an examination region with an array of frequency conversion units after an RF excitation and are radiated as frequency-converted signals. The resulting signal field is acquired by a number of reception antennas of a second antenna array, which are arranged at different spatial positions and thus allow a spatial resolution of the frequency-converted signals. The acquired acquisition signals are used for image reconstruction.

A parallel magnetic resonance imaging (MRI) apparatus configurable to image a physical entity comprises:a main magnetic flux source for providing a uniform fixed magnetic field, B0;an RF array system comprising a plurality of RF coils and receivers, said RF system configured for:generating rotating RF excitation magnetic fields B1; andreceiving RF signals due to precessing nuclear magnetization on multiple spatially distinct radio frequency coils and associated receiver channels, said RF system being configured to operate in accordance with a B1 sensitivity encoding technique;a control processor for controlling imaging functionality, collecting image data and effecting data processing of the captured image data the control processor being configured with post processing capability for the B1 sensitivity encoding technique;an image display means for displaying processed image data as resultant images; andan auxiliary magnetic field means capable of producing at least one auxiliary uniform B0 step magnetic field imaging region within the main B0 magnetic field;wherein:the auxiliary magnetic field, means is configured to operate in combination with the RF coil system and the B1 sensitivity encoding technique, the imaging apparatus thereby providing faster image acquisition than that attributed to the speed up factor provided solely by the B1 sensitivity encoding technique.The invention also includes a method of imaging using this apparatus.Furthermore, the invention also includes a method and apparatus for three-dimensional MR imaging using a 1D Multiple Acquisition Micro B0 array coupled with a 2D Multiple Acquisition Micro B0 array.

A system composed of multiple transmit coils with corresponding RF pulse synthesizers and amplifiers is disclosed. A method of designing RF pulses specific to each transmit coil to induce spatiotemporal variations in a composite B1 field is also disclosed. The present invention supports faithful production of desired excitation profiles and accommodates the use of any coil array geometry. The present invention also supports reduction in excitation pulse length. Through effective B1 field maps for each transmit coil, mutual coupling and other inter-coil correlations are accounted for in the RF pulse design.

In a method and magnetic resonance (MR) imaging apparatus for reducing artifacts due to resonance frequency offsets in a diagnostic MR image, a number of MR scout images of a portion of a subject containing a region of interest (ROI) are generated respectively using different radio frequency (RF) excitation frequencies. Each of the MR scout images has an identifiable image quality in the ROI. The MR scout images are analyzed as to the image quality in the ROI to identify one of the MR scout images having the best image quality in the ROI. An MR diagnostic image is then generated of the portion of the subject containing the ROI, using the RF excitation frequency that was used to generate the MR scout image having the best image quality in the ROI.

A cylindrical neutron generator is formed with a coaxial RF-driven plasma ion source and target. A deuterium (or deuterium and tritium) plasma is produced by RF excitation in a cylindrical plasma ion generator using an RF antenna. A cylindrical neutron generating target is coaxial with the ion generator, separated by plasma and extraction electrodes which contain many slots. The plasma generator emanates ions radially over 360° and the cylindrical target is thus irradiated by ions over its entire circumference. The plasma generator and target may be as long as desired. The plasma generator may be in the center and the neutron target on the outside, or the plasma generator may be on the outside and the target on the inside. In a nested configuration, several concentric targets and plasma generating regions are nested to increase the neutron flux.

In addition to the known MT (magnetization transfer) effect, an RMT (reverse MT) is newly found, which increases a detected MR signal strength. Both the MT and RMT effects can be explained with mutual interaction, such as phenomena of chemical exchange and / or cross relaxation, acted between a pool of water proton spins and another pool of macromolecule proton spins, for example, within an object. In order to enhance the MT or RMT effect, the frequency bandwidths of RF pulses, such as a 90° RF exciting pulse in a SE or FSE method, an inversion pulse in a FLAIR or fast FLAIR method, and others, are controlled. To enhance the MT effect, the bandwidth is controlled into a wider value (approx. more than 1250 Hz) than the normally (conventionally) used bandwidth, while to obtain the RMT effect, the bandwidth is controlled into a narrower value (approx. less than 1000 Hz) than the normally used bandwidth. Actively controlling the MT or RMT effect permits changed image contrast in MR imaging.

Disclosed are methods and systems for carrying out super-multiplexed magnetic resonance imaging that entwines techniques previously used individually and independently of each other in Simultaneous Echo (of Imaging) Refocusing (SER or SIR) and Multi-Band (MB) excitation, in a single pulse sequence that provides a multiplication rather than summation of desirable effects while suppressing undesirable effects of each of the techniques that previously were used independently.

A method of operating an optically pumped magnetometer (OPM) includes directing a light beam through a vapor cell of the OPM including a vapor of atoms; applying RF excitation to cause spins of the atoms to precess; measuring a frequency of the precession; for each of a plurality of different axes relative to the vapor cell, directing a light beam through the vapor cell, applying a magnetic field through the vapor cell along the axis, applying RF excitation to cause spins of the atoms to precess, and measuring a frequency of the precession in the applied magnetic field; determining magnitude and components of an ambient background magnetic field along the axes using the measured frequencies; and applying a magnetic field based on the components around the vapor cell to counteract the ambient background magnetic field to facilitate operation of the OPM in a spin exchange relaxation free (SERF) mode.

An inspection system including a radio frequency (RF) subsystem and a quadrupole resonance (QR) tube array coil. The RF subsystem may include a variable frequency RF source to provide RF excitation signals at a frequency generally corresponding to predetermined, characteristic QR frequencies of a specimen. The QR tube array coil may be implemented using a plurality of conductive tubes defining a cavity of predetermined volume. Typically, the plurality of conductive tubes are spaced at a distance relative to one another to form at least two non-conductive gaps between tubes in the array. After RF excitation signals are applied to the specimen within the cavity, the QR tube array coil may generate a QR output signal responsive to QR signals generated by the specimen.

A chip scale atomic clock is disclosed that provides a low power atomic time / frequency reference that employs direct RF-interrogation on an end-state transition. The atomic time / frequency reference includes an alkali vapor cell containing alkali atoms, preferably cesium atoms, flex circuits for physically supporting, heating, and thermally isolating the alkali vapor cell, a laser source for pumping alkali atoms within the alkali vapor cell into an end resonance state by applying an optical signal along a first axis, a photodetector for detecting a second optical signal emanating from the alkali vapor cell along the first axis, a pair of RF excitation coils for applying an RF-interrogation signal to the alkali atoms along a second axis perpendicular to the first axis, a pair of bias coils for applying a uniform DC magnetic field along the first axis, and a pair of Zeeman coils for applying a Zeeman interrogation signal to the alkali atoms and oriented and configured to apply a time-varying magnetic field along the second axis through the alkali vapor cell. Another flex circuit is used for physically supporting the laser source, for heating the laser source, and for providing thermal isolation of the laser source. The laser source can be a vertical cavity surface emitting laser (VSCEL). The bias coils can be Helmholtz coils.

A system for respiratory motion compensated MR imaging or spectroscopy, comprises an MR imaging system. The MR imaging system performs a single imaging scan including, acquiring a first imaging data set representing a spatially localized first imaging region located on a patient diaphragm, using a first RF excitation pulse sequence and by transmitting a nuclei excitation first resonant frequency and receiving data substantially at the first resonant frequency. The MR imaging system derives data representing diaphragm position over a respiratory cycle using the first imaging data set, in the single imaging scan. The MR imaging system in response to determining the diaphragm position is within a predetermined window, acquires a second anatomical imaging data set representing a spatially localized second imaging region using a second RF excitation pulse sequence and by transmitting a nuclei excitation second resonant frequency different to the first resonant frequency and receiving data substantially at the second resonant frequency in the single imaging scan.

A method and an RF transmit system for generating RF transmit signals for feeding an RF transmitter (14) in the form of, or comprising, one or more antenna device(s), coil(s), coil elements, or coil array(s) is disclosed. Furthermore, a multi-channel RF transmit system for feeding a plurality of such RF transmitters, especially for use as an RF excitation system in a magnetic resonance imaging (MRI) system for exciting nuclear magnetic resonances (NMR) is disclosed. A demand RF transmit signal is compared in the digital domain with an RF transmit signal and digitally corrected with respect to differences or errors between both by means of a complex predistorter (11), an adaption unit (17) and a look-up table unit (18).

Magnetic resonance imaging uses a pulse sequence formed to include a pre-pulse, an RF excitation pulse, an encoding gradient pulse, and a reading gradient pulse. The encoding gradient pulse has an encoding amount determined to allow a data acquisition position in a k-space to be directed outward from a center of the k-space. A train of pulses including the RF excitation pulse, the encoding gradient pulse, and the reading gradient pulse is repeated to allow the number of times of data acquisition in the k-space to become larger as approaching to a central region of the k-space. The pre-pulse is formed to be reduced in an application rate to the RF excitation pulse as approaching to an outward position in the k-space. By way of example, this pulse sequence is used for contrast enhanced MRA carried out under a dynamic scan.

A system composed of multiple transmit coils with corresponding RF pulse synthesizers and amplifiers is disclosed. A method of designing RF pulses specific to each transmit coil to induce spatiotemporal variations in a composite B1 field is also disclosed. The present invention supports faithful production of desired excitation profiles and accommodates the use of any coil array geometry. The present invention also supports reduction in excitation pulse length. Through effective B1 field maps for each transmit coil, mutual coupling and other inter-coil correlations are accounted for in the RF pulse design.

Waveforms for radio-frequency (RF) excitations pulses used in magnetic resonance imaging are designed according to a Least Squares QR (LSQR) algorithm or a Conjugate Gradient Least Squares (CGLS) algorithm, to solve the linear system of equations that arises in a multi-channel RF transmit arrangement. Better management of SAR and other factors is achieved with RF pulses designed according to these algorithms, compared to the conventionally employed singular value decomposition (SVD) algorithm.

A method for magnetic resonance spectroscopy (=MRS) or magnetic resonance imaging (=MRI) in which an NMR time-domain signal is created by an RF excitation pulse applied to an object in the presence of an applied magnetic field that may depend on spatial position and / or time, the time-domain signal being generated by an excited transverse nuclear magnetisation precessing about the applied magnetic field, whereby the RF excitation pulse is adapted to cover a whole range of NMR frequencies of interest present in the object, and time-domain signal acquisition takes place during, or during and after the application of the RF excitation pulse, is characterized in that spectral or image data are reconstructed by a matrix product of a reconstruction matrix and a vector of time-domain signal points, the reconstruction matrix being an inversion of an encoding matrix Anα whose elements are calculated using the formula:Anα=∑m=0n-1PmΦ(n,m,α),wherein n is the running number of a time-domain signal point, α is the running number of a discrete image or spectral element, Pm is the m-th discrete element of the RF excitation pulse in the time-domain, and Φ(n,m,α) is the phase accrued by the transverse nuclear magnetisation related to the discrete image or spectral element a in the time between the discrete RF excitation pulse element Pm and the time-domain signal point n under the influence of the applied magnetic field. An improved method for reconstructing spectral or image data from time-domain signal acquired as describe above is thereby provided which can be used more versatilely than conventional Fourier transform.

A parallel magnetic resonance imaging (MRI) apparatus configurable to image a physical entity comprises: a main magnetic flux source for providing a uniform fixed magnetic field, Balpha; an RF array system comprising a plurality of RF coils and receivers, said RF system configured for: generating rotating RF excitation magnetic fields B1; and receiving RF signals due to precessing nuclear magnetization on multiple spatially distinct radio frequency coils and associated receiver channels, said RF system being configured to operate in accordance with a B1 sensitivity encoding technique; a control processor for controlling imaging functionality, collecting image data and effecting data processing of the captured image data the control processor being configured with post processing capability for the B1 sensitivity encoding technique; an image display means for displaying processed image data as resultant images; and an auxiliary magnetic field means capable of producing at least one auxiliary uniform Bo step magnetic field imaging region within the main B0 magnetic field; wherein: the auxiliary magnetic field, means is configured to operate in combination with the RF coil system and the B1 sensitivity encoding technique, the imaging apparatus thereby providing faster image acquisition than that attributed to the speed up factor provided solely by the B1 sensitivity encoding technique. The invention also includes a method of imaging using this apparatus. Furthermore, the invention also includes a method and apparatus for three-dimensional MR imaging using a 1D Multiple Acquisition Micro Bo array coupled with a 2D Multiple Acquisition Micro Bo array.

A system for accelerated segmented magnetic resonance (MR) image data acquisition includes an RF (Radio Frequency) signal generator and a magnetic field gradient generator. The RF signal generator generates RF excitation pulses in anatomy and enabling subsequent acquisition of associated RF echo data. The magnetic field gradient generator generates magnetic field gradients for anatomical volume selection, phase encoding, and readout RF data acquisition in a three dimensional (3D) anatomical volume. The RF signal generator and the magnetic field gradient generator acquire consecutive segments of k-space line data representative of an individual image slice in a gradient echo method by adaptively varying RF excitation pulse flip angle between acquisition of the consecutive segments.

A dynamic MRA study of a subject is performed using a 3D fast gradient-recalled echo pulse sequence after the subject is injected with a contrast agent. The flip angle of an rf excitation pulse in the pulse sequence is modulated during the acquisition as a function of contrast agent concentration in the region of interest. In one embodiment the flip angle is updated by interleaving measurement pulse sequences which measure in real-time contrast agent concentration. In another embodiment the contrast concentration profile is determined in advance and a corresponding table of optimal flip angles are calculated and played out during the image acquisition.

Embodiments of the subject invention can utilize a single coil structure for dual-mode operation. In a specific embodiment, a single coil structure can be used as a volume coil in the transmitting phase and as a phase array in the receiving phase. In an embodiment, a transmit coil array in accordance with the subject invention can be utilized for one or more of the following: 1) parallel RF excitation on an MRI scanner equipped with a multiple-channel transmitter; 2) serial RF excitation with the use of a switch system with a single channel transmitter; and 3) generation of a homogeneous B1 field for regular MRI with the use of a power splitter on a standard scanner. In a specific embodiment, the use of a concentric double loop coil with different tunings of inner and outer loops can be implemented. In an embodiment, the coil elements can be decoupled using the CRC mode of a concentric double loop coil. In an embodiment, a surface coil transmit array can provide better compatibility with a receive array. In a specific embodiment, an over-coupled technique can be used to improve the phase control of the transmitting pulse.

Magnetic resonance imaging of a body uses steady state free precession with material separation for the selective imaging of two species, such as blood or fat. The refocusing property of SSFP is used with signal phase detection to suppress either water or lipid. Phase and / or frequency of the RF excitation pulse and repetition time are selected so that resonant frequencies of water, fw, and lipid, fl, are on opposite sides of the signal null frequency.

In a magnetic resonance tomography apparatus and method for determination of T2-weighted images of tissue with short T2 time, in the framework of a steady-state free precession sequence with non-slice-selective RF excitation pulses and projection-reconstruction methods, in each sequence repetition a first steady-state is read out in the form of a half echo and a second steady-state signal is read out in the form of a further half echo with very short echo times TE1 and TE2=2TR−TE1, and are combined by weighted addition such that an MRT image of tissue with very short T2 time is obtained with the sequence.

In diffusion weighted imaging, motion monitoring navigation echoes are measured at every measurement of data after applying an RF excitation pulse, and one of them is set as a reference navigation echo. The reference navigation echo and other navigation echoes are one-dimensionally Fourier-transformed, a linear phase gradient thereof is calculated from those data, a linear phase gradient of the reference navigation echo is compared with those of other navigation echoes, and it is judged whether a difference therebetween is within an acceptable value or not. An echo signal corresponding to a navigation echo having the above difference being larger than the acceptable value is judged that correction based on the navigated motion correction is not applicable therein, and the image is produced by using an echo signal measured along with a navigation echo having the difference being the acceptable value or less. In this manner, a motion component included in the echo signal used for producing the image is made uniform and motion artifacts are eliminated.

A low-cost single-sided NMR sensor to produce depth profiles with microscopic spatial resolution is presented. The open geometry of the NMR sensor provides a non-invasive and non-destructive testing method to characterize the depth structure of objects of arbitrary size. The permanent magnet geometry generates one plane of constant magnetic field intensity parallel to the scanner surface. By combining the highly uniform static gradient with selective RF excitation, a thin flat sensitive slice can be defined. By moving the relative position between the slice and the object, one-dimensional profiles of the near surface of large samples are produced with high spatial resolution.

In a method in the form of a turbo spin echo imaging sequence with long echo trains and optimized T1 contrast for generation of T1-weighted images of an examination subject by magnetic resonance, magnetization in the examination subject is excited with an RF excitation pulse, a number N of RF refocusing pulses with variable flip angle are radiated to generate multiple spin echoes for an excitation pulse, a restoration pulse chain is activated after switching of the N refocusing pulses and before the next RF excitation pulse. The restoration pulse chain influences the magnetization such that the magnetization is aligned opposite to the direction of the basic magnetic field by the restoration pulse chain before the next RF excitation pulse.