University of California

Toshiba America Mri, Inc.

Barry M McCarten

Mitsuaki A Arakawa

Leon Kaufman

Joseph W Carlson

John H Fehn

Stephen Krasnor

William H Harrison

David M Kramer

Kevin A Derby

William K Lu

Christine Hawryszko

A nuclear magnetic resonance imaging system is described. The nuclear magnetic resonance imaging system includes an RF transmit device formed as two rectangular coils arranged in planes orthogonal to one another and formed by two U-shaped loops. The U-shaped loops improve B.sub.1 field homogeneity in the vertical direction. The rectangular coils may be used in a four post MRI device to improve access to the body being imaged.

Spatially orthogonal rectangular coil pair suitable for vertical

An RF coil sub-assembly for a transverse magnet MRI system includes substantially co-planar serially-connected turns mounted on a common substrate. Preferably, half of the turns are directed clockwise, while the other half are directed counter clockwise to produce a plurality of equal commonly directed currents along spaced apart parallel conductors. A low-loss expanded dielectric spacer is used to mount the RF coils within a pre-existing depression formed by the annular magnetic shims of a transverse magnet structure thus substantially eliminating any obstruction to the image volume for at least the RF transmit coils.

RF coil providing reduced obstruction access to image volume in

Continuously updated real-time magnetic resonance imaging processes are used to display an MR image volume to an operator and/or patient co-located with the MRI magnet, viewing console and other elements of an MRI system within the same shielded gantry room. A CRT display may be used for lower field MRI systems while liquid crystal displays may be necessary for higher field MRI systems since the viewing console is to be co-located within the shielded gantry room near the MRI magnet assembly. Suitable RF shielding is provided to RF-isolate the viewing console and its related power and video signal cables from the MRI RF coils being used to monitor relatively weak NMR signals emanating from the image volume within the magnet assembly. When used with open access MRI magnet assemblies, such real-time viewing of the image volume within the gantry room permits performance of simultaneous patient procedures guided by real-time visual feedback to the patient and/or doctor, nurse, patient attendant and the like while located within the gantry room and having direct access to the patient anatomy within the image volume.

Real-time MR imaging inside gantry room

An array of plural magnetic resonance imaging (MRI) RF coils is provided having different and overlapping fields of view. Controllable switches are connected with each individual coil of the array and are capable of selectively conditioning any one of the coils for individual usage in an MRI procedure. Either mechanical or electrical (e.g., PIN diode) switching control may be utilized. Preferably, controllable electrical switches are located at points having approximately zero RF potential. Distributed capacitance is also preferably employed for reducing terminal inductance, preventing the establishment of spurious magnetic fields and facilitating the use of electrical switching diodes and/or varactor capacitance elements. Such distributed capacitances are also dimensioned so as to cause the terminal inductance of each coil to be within the tuning/matching range of a common tuning/matching RF circuit.

Switchable MRI RF coil array with individual coils having different and

A detuning/decoupling arrangement for a Magnetic Resonance Imaging (MRI) system quadrature RF coil arrangement (of the type using the nuclear magnetic resonance, or NMR, phenomenon) uses switching diodes to selectively connect and disconnect portions of a segmented RF coil in response to a DC control signal. The DC control signal selectively forward biases and reverse biases the switching diodes. The DC control current flows through the RF coil itself, through the diodes, and then through the center conductor of a semi-rigid transmission line disposed in proximity to the RF coil. Because the DC current flowing through the transmission line is equal and opposite to the DC current flowing through the RF coil, the net magnetic field generated by the DC current flow is approximately zero--eliminating artifacts in the MRI image that would otherwise be generated due to continuous DC current flowing whenever the coil is being used to transmit or receive RF.

MRI QD RF coil having diode switched detuning circuit producing reduced

A pair of co-located RF surface coils extend axially and part-circumferentially about a volume to be imaged. Because surface coils are employed, the RF field distribution will be non-symmetric, non-homogeneous and non-uniform within the volume. Nevertheless, if the two coils are rotationally offset by the proper amount (and possibly including capactive isolation coupling therebetween), the coils produce a pair of RF signals to/from the volume which are in quadrature phase thus providing signal-to-noise ratio improvements due to: (a) the fact that quadrature detection techniques are employed and (b) the fact that only a portion of the cross-sectional volume is effectively addressed by the surface coils (i.e., due to their non-symmetric, non-homogeneous and non-uniform field distribution).

QD MRI RE coil using non-homogeneous and non-uniform RF field

Shaped RF field distributions from separate 'surface' coils overlap to define a limited inner-volume deep within a human body or other object under examination. A spin echo MRI signal is effectively elicited only from such limited inner-volume so as to permit conventional MRI signal processing (e.g., utilizing Fourier Transformations) to derive and display magnetic resonance images of desired cross-sections of the limited inner-volume thus avoiding possible motion artifact and/or other potential noise sources located elsewhere in the object. A special receiver coil decoupling circuit is used to automatically increase its resonant frequency during RF transmit times.

Arrangement of RF coils and related method for magnetic resonance

Undesirable RF coupling via the outside of an outer coaxial cable conductor to/from RF coils in a magnetic resonance imaging apparatus is minimized by employing a parallel resonance tuned RF choke in the circuit. The choke is realized by forming a short coiled section of the coaxial cable with a lumped fixed capacitance connected in parallel thereacross and a conductive tuning rod positioned within the center of the coiled section so as to trim the parallel resonant frequency to the desired value.

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Piedmont, CA, United States of America

Barry M McCarten