Abstract: A system and method for decoupling coils in a medical imaging system are provided. The coil system includes a first coil of a medical imaging system, a second coil of the medical imaging system, and a balun device connected to the first and second coils. The balun device is configured to decouple the first and second coils of the medical imaging system.

Abstract: A detuning circuit for an MRI coil having a series tuning capacitor includes: a detuning inductor and a PIN diode in parallel communication with the tuning capacitor, where the tuning capacitor has a tuning inductor node and a PIN diode node; a first diode and a second diode in parallel communication with the PIN diode, where the first, second and PIN diodes are arranged with the same serial polarity and the first and second diodes have a common node; and a reactance in communication between the common node and the tuning inductor node. The circuit detunes the MRI coil in response to an MRI transmit pulse. A detuning circuit for an MRI coil having a series tuning capacitor includes a detuning inductor; and a detuning switch in parallel combination with a secondary tuning capacitor, the detuning inductor and the parallel combination being in parallel communication with the series tuning capacitor. The secondary tuning capacitor acts to reduce current during detuning of the MRI coil.

Abstract: A system and method for decoupling coils in a medical imaging system are provided. The coil system includes a first coil of a medical imaging system, a second coil of the medical imaging system, and a balun device connected to the first and second coils. The balun device is configured to decouple the first and second coils of the medical imaging system.

Abstract: A multi-channel RF cable trap (70) blocks stray RF current from flowing on shield conductors (114) of coaxial RF cables (60) of a magnetic resonance apparatus. An inductor (116) is formed by a curved semi-rigid trough (80) constructed of an insulating material coated with an electrically conducting layer. Preferably, the inductor (116) and the cable follow an “S”-shaped path to facilitate good electromagnetic coupling therebetween. The RF cables (60) are laid in the trough (80) and the shield conductors inductively couple with the inductor (116). A capacitor (82) and optional trim capacitor (83) are connected across the the trough of the inductor (116) to form a resonant LC circuit tuned to the resonance frequency. The LC circuit inductively couples with the shield conductors (114) to present a high, signal attenuating impedance at the resonance frequency. The resonant circuit is preferably contained in an RF-shielding box (84) with removable lid.

Abstract: An RF coil construction (40, 40′) includes removable, relocatable, and/or detachable sections (42, 44) that are inherently decoupled. The sections can be relocated, removed, or exchanged with sections having different coil sizes or coil configurations, allowing the coil configuration to be tailored to a desired imaging procedure and region of the brain. The coil construction provides space for stimulation devices and adjusting patient access and comfort. Since the operator can select coil removal or placement to reduce the amount of data outside the region of interest, the coil construction can also reduce scanning and reconstruction time, reduce artifacts, and provide increased temporal resolution and image throughput.

Abstract: A multi-channel RF cable trap (70) blocks stray RF current from flowing on shield conductors (114) of coaxial RF cables (60) of a magnetic resonance apparatus. An inductor (116) is formed by a curved semi-rigid trough (80) constructed of an insulating material coated with an electrically conducting layer. Preferably, the inductor (116) and the cable follow an “S”-shaped path to facilitate good electromagnetic coupling therebetween. The RF cables (60) are laid in the trough (80) and the shield conductors inductively couple with the inductor (116). A capacitor (82) and optional trim capacitor (83) are connected across the the trough of the inductor (116) to form a resonant LC circuit tuned to the resonance frequency. The LC circuit inductively couples with the shield conductors (114) to present a high, signal attenuating impedance at the resonance frequency. The resonant circuit is preferably contained in an RF-shielding box (84) with removable lid.

Abstract: A pair of quadrature radio frequency coils (32, 34) disposed adjacent an imaging region (10) are typically loaded differently due to factors such as subject geometry, subject mass, and a relative distance from the subject. A tip angle adjustment circuit (50) monitors a combined tip angle adjacent a mid-plane of the examination region, such as by analyzing delivered and reflected power to each of the coils. An adjustment circuit (54) adjusts relative RF power or amplitude to produce a selected, combined tip angle in the examination region.

Abstract: A pair of quadrature radio frequency coils (32, 34) disposed adjacent an imaging region (10) are typically loaded differently due to factors such as subject geometry, subject mass, and a relative distance from the subject. A tip angle adjustment circuit (50) monitors a combined tip angle adjacent a mid-plane of the examination region, such as by analyzing delivered and reflected power to each of the coils. An adjustment circuit (54) adjusts relative RF power or amplitude to produce a selected, combined tip angle in the examination region.

Abstract: A method of magnetic resonance imaging includes supporting a subject in an examination region of an MRI scanner(A). An MRI pulse sequence is applied to produce a detectable magnetic resonance signal (100) in a selected region of the subject. The magnetic resonance signal (100) includes a plurality of echos (102a-h) which are received. The plurality of received echos (102a-h) are subjected to a controllable gain factor such that at least two echos are subjected to different gain factors. In this manner, for example, a multi-contrast acquisition and imaging experiment may be achieved with each set of acquired echos and/or each image having a separately optimized (e.g., optimized for SNR considerations) gain factor individually selected and/or set therefor.

Abstract: A tunable radio frequency birdcage coil (26, 34) has an improved tuning range for use with a magnetic resonance apparatus. The coil includes a pair of end ring conductors (60, 62) which are connected by a plurality of spaced leg conductors (L2, L4, . . ., L26) to form a generally cylindrical volume. Both the end rings and the leg conductors contain reactive elements, preferably capacitors (C2, C4, . . ., C124). The radio frequency coil also includes a pair of tuning rings (100, 120) for tuning the reactive elements (C2, C4, . . ., C124), which each include a non-conductive support cylinder (110, 130) and a plurality of tuning bands (120, 122, . . ., 142 and 150, 152, . . ., 172) which extend axially along the outer surface of the support cylinder (110, 130). The tuning rings (100, 120) are rotated or translated with respect to the leg conductors (L2, L4, . . ., L26) in order to vary capacitance and inductance of the coil (26, 34) to tune the (26, 34) coil to the desired resonant frequency.

Abstract: A magnetic resonance apparatus includes a multi-mode receiver assembly which facilitates operation in both a quadrature combination mode and phased array mode. The multi-mode receiver assembly includes a receiver coil assembly (30) comprising a first RF coil assembly (32) and a second RF coil assembly (34). A signal combining circuit, which includes a switch means, performs at least one of combining and splitting magnetic resonance signals received by the first and second RF coil assemblies (30, 32). The application of a DC bias potential to the switch means switches the multi-mode receiver assembly into the quadrature combination mode in which the received magnetic resonance signals are phase shifted and combined into a quadrature signal and an anti-quadrature signal. The absence of a DC bias potential to the switch means switches the multi-mode receiver assembly into the phased array mode in which the received magnetic resonance signals are phase shifted and passed individually to corresponding receivers.

Abstract: A magnetic resonance imaging system includes a patient couch (10) which selectively positions a patient relative to an examination region (14). An imaging coil (B) is disposed adjacent to a region of interest for receiving magnetic resonance signals emanating from the patient. A processor (48) both controls the imaging event and processes received signals from the imaging coil. A plug and socket assembly (24, 26) having a proximal component and a distal component relative to the imaging coil provides selective electrical connectivity between the imaging coil (B) and the processor (48). A non-volatile memory device (86), such as a 1-WIRE™ EEPROM, is affixed to the proximal component of the plug and socket assembly (24, 26) for storing a variety attributes associated with the imaging coil. The memory device is most conveniently mounted to a coaxial connector (110).

Abstract: A gradient amplifier (20), for driving a gradient coil (22) of an MRI scanner, includes a plurality of first modules (60). The first modules (60) provide unipolar PWM control of an input supplied thereto to generate a unipolar waveform. A high voltage DC power supply (64) electrically connected to the first modules (60) supplies the input to the first modules (60). At least one second module (140a, b) is electrically connected to the first modules (60). The second module (140a, b) selectively provides polarity switching of the unipolar waveform output from the first modules (60) to generate a bipolar waveform which drives the gradient coil (22).

Abstract: A multi-channel balun (70, 72) blocks stray RF current from flowing on shield conductors of coaxial RF cables of a magnetic resonance apparatus. The balun comprises a parallel combination of an even number of helical coils of shielded transmission cable (L10, L12; L14, L16, L18, L20) wound in alternate directions such that voltages iduced by their external RF fields cancel. One capacitor (C10; C16, C18) is connected in parallel symmetrically with each pair of helical coils, with trim capacitors (C12; C22) fixed in the coil plug (86, 90) to retune the balun as required. The multi-channel balun (70, 72) accommodates magnetic resonance systems with an odd or even number of channels without requiring shielding. Preferably, the balun (70, 72) is constructed on a single circuit board in a close-packed relationship that is compact and space efficient, yet provides better decoupling from the transmit field.

Abstract: Magnetic resonance imaging apparatus uses magnetic field gradients X, Y, Z to spatially encode the magnetic signals arising from a patient on a couch 2 in bore 1 of a main magnet. Thermal stresses arising from aggressive gradients during multiple acquisitions result in imperfectly repeated gradients and resulting image artefacts. The invention uses a probe 4 provided with a gradient coil set similar to that for imaging, and fed by currents derived from the imaging gradient coils, connected so as to produce an opposing gradient surrounding an MR active substance in the probe. This enables a probe with a sufficiently large amount of MR active substance to produce a useful signal to be used to monitor the gradient, while overcoming the de-phasing problem. which would otherwise occur. Closed loop control of gradients thereby becomes possible.

Abstract: In a magnetic resonance imaging apparatus, a whole-body RF coil (42) disposed circumferentially around an examination region (14) is tuned to a first Larmor frequency, e.g., that of hydrogen. A first transmitter (44) transmits RF signals at the first Larmor frequency. A first T/R switch (40) electronically switches the whole-body RF coil (42) between a transmit mode in which it is electronically connected to the first transmitter (44) for exciting resonance in hydrogen nuclei, and a receive mode in which it is electronically connected to a first receiver channel for demodulating magnetic resonance signals received from resonating hydrogen nuclei. An insertable lung coil (70) is positioned inside the whole-body RF coil (42) around the examination region.

Abstract: A magnetic imaging apparatus includes an RF coil (F) in electrical communication with an RF signal generator (C) and a receiver (G) through an interface circuit (E). The signal generator transmits resonance excitation signals at one of at least two resonance frequencies, e.g. the resonance frequencies of hydrogen helium 3, fluorine, phosphorous, carbon, or xenon. During the transmit cycle, PIN diode (30) is forward biased forming a filter at a first resonance frequency, electrically isolating the receiver from first frequency excitation signals. Simultaneously during the transmit cycle, PIN diode (32) is forward biased forming a filter at a second resonance frequency electrically isolating the receiver from second frequency excitation signals. During a receive cycle, the diodes are reverse biased turning both filters into low impedance circuits around the first and second resonance frequencies allowing a received magnetic resonance signal to pass unimpeded from the RF coil to the receiver.

Abstract: A radio frequency coil (12, 19) adapted for use in interventional magnetic resonance imaging consists of a loop of an elongated electric conductor arranged to form a twisted wire pair (12, 19) and means associated with it for operating the coil both in transmit and receive mode, in order that the coil does not image anything but tracks its own path on an MR image, without affecting the magnetization in the main bulk of the body being imaged.

Abstract: A magnetic imaging apparatus generates a main magnetic field longitudinally through an image region and excites magnetic resonance in selected nuclei in a patient or subject disposed in the image area. The resonating nuclei generate radio frequency magnetic resonance signals which are received by a quadrature highpass ladder surface coil (D). The highpass ladder coil includes a central leg 34 having a capacitive element Cv disposed symmetrically about a midpoint 44. A like number of additional legs 30, 32, 36, 38 are disposed parallel to and symmetrically on opposite side of the central leg. Side elements 40, 42 include capacitive elements CA which interconnect adjacent ends of each of the legs. The capacitive elements are disposed symmetrically about the midpoint 44 and are selected such that the coil supports at least two intrinsic resonant modes including an odd mode 50 and an even mode 52.

Abstract: A method of generating motion vectors from a video signal, for use in motion compensation, is applicable to interlaced video signals. In the method alternate video fields are shifted vertically so as to align the picture lines of interlaced fields, by moving the lines of one field up by half a picture line and the lines of the next field down by half a picture line. The fields of each resultant pair are compared to produce a set of motion vectors which can be used to motion compensate the video signal. The accuracy may be improved using temporal filters operative on correlation surfaces derived over tow or more field intervals.