Abstract: 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.

Abstract: The effective Q of a capacitively coupled RF coil in a magnetic resonance imaging (or magnetic resonance spectroscopic imaging) system is controllably lowered from its intrinsic maximum value by controlling the impedance reflected across the coil via a tuning/matching network associated and located with the coil. The Q may be advantageously lowered during transmit time as compared with receive times (during which the Q may be relatively increased) by effecting controlled impedance mismatches within the RF feed network used to supply RF signals to/from the RF coil.

Abstract: 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.

Abstract: Frequency tuning and coupling capacitances in MRI RF receive coils are typically realized, at least in part, as reverse biased varactor diodes. During RF tuning of the transmit coil (i.e., so as to achieve resonance and matched impedance conditions), at least some if not all of the varactors associated with the receive coil are forward biased so as to simultaneously maximize detuning of the receive coil to resonant frequencies removed as far as possible from that of the transmitter coil being tuned while also then substantially reducing the Q of the receive coil.

Abstract: An RF coil for a magnetic resonance imaging device using nuclear magnetic resonance phenomena includes self-tracking ganged coupling capacitors which provide impedance matching and also tune out coil inductance to establish resonance at the RF operating frequency. At least one variable capacitor connected in parallel with the RF coil is mechanically ganged to at least one variable capacitor connected in series to the RF coil. The parallel and series capacitances are initially set to achieve resonance at a desired operating frequency. As the shaft of one variable capacitor is rotated in a first direction through a given angle, the shaft of the other variable capacitor rotates in the opposite direction through the same angle, thereby varying the ratio (but not the sum) of parallel and series capacitances. A servo controller connected to a standing wave ratio detector automatically adjusts the ratio of parallel to series capacitances to optimize impedance matching between the source and the RF coil.

Abstract: 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.

Abstract: A detuning/decoupling arrangement for a Magnetic Resonance Imaging (MRI) system RF coil arrangement (of the typing using the nuclear magnetic resonance, or NMR, phenomenon) uses switching diodes to selectively connect and disconnect portions of an RF resonant circuit in response to a DC control signal. The DC control signal selectively forward biases and reverse biases the switching diodes. The DC control current is fed to the resonant circuit along the same RF transmission line used to feed RF signals to/from the circuit. An in-line coaxial shielded RF choke connected to the RF transmission line isolates the DC control signals from the RF signals flowing on the same transmission line--reducing the number and complexity of isolation devices required on the ends of the transmission line to separate the RF and DC signals.

Abstract: A quadrature detection MRI radio frequency coil includes plural axially-extending conductive legs. At least two of the legs include breaks in conductivity at their mid-point with circumferentially extending inner-bridge conductors connected thereacross to which RF input/output feed connections are conveniently made so as to achieve a center fed coil structure, open at both ends. Other axially-extending legs may also include conductive breaks with capacitive coupling thereacross and circumferentially extending outer-bridges between the outer or distal ends of the legs may also include breaks in conductivity with capacitive coupling thereacross.

Abstract: A quadrature detection magnetic resonance imaging (MRI) RF coil is constructed from non-overlapping axially-extending conductors arrayed about the circumference of a cylinder in four circumferentially spaced-apart groupings. Axially-extending annular gaps in the fingers (e.g, at their mid-points) are bridged across by RF coupling capacitors. The outer ends of the fingers are also coupled by annular conductors having one or more conductive gaps bridged by coupling capacitance. First and second quadrature detection RF input/output ports are coupled to at least one respective finger element in each of two adjacent groups of elements.

Abstract: 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).

Abstract: In an MRI system, a passive conductive RF decoupling structure is disposed about a portion of the volume to be imaged but at a location which is proximate a sub-volume from which MRI RF responses are to suppressed. The passive decoupling structure may be a sheet of conductive material or a shorted loop of conductive material (preferably having a gap in conductivity bridged by RF bypass capacitance so as to suppress lower frequency eddy currents otherwise caused by changing magnetic gradient fields in the MRI system).

Abstract: 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.

Abstract: First and second co-located axially extending RF coils are displaced spatially with respect to one another by 90 degrees so as to produce a pair of RF signals from the enclosed volume which are in phase quadrature. The same coils or one of them may also be utilized for transmitting NMR RF signals into the same volume. The coils have a common open-end through which objects to be imaged may be inserted and a common "closed" end for convenient location of RF coupling and feeding structures. Each of the coils has an RF feedline structure which extends across a diameter of common closed end and the two feedline structures are disposed substantially perpendicular with respect to one another so as to minimize cross coupling. The feedlines are also spatially configured to facilitate mounting of associated tuning and coupling capacitors.

Abstract: 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.

Abstract: An imaging NMR scanner generates multi-dimensional NMR spin echo responses from selected sub-volumes of an object. 90.degree. and 180.degree. r.f. nutation pulses are used together with a variable amplitude gradient between these nutation pulses to phase encode a second dimension in the spin echo response which is already phase-encoded in a first dimension by use of a magnetic gradient during signal readout. Two-dimensional Fourier transforms or multiple angle projection reconstruction processes are then used to generate an array of pixel value data signals representing a visual image of the point-by-point spatial distribution of nutated nuclei within the object. Image artifacts potentially caused by relatively moving elements of the object are avoided by selecting the spin echo generating sub-volumes to avoid the moving elements. High resolution images of sub-volumes of interest can be obtained by selection of a sub-volume of interest in conjunction with these reconstruction techniques.

Abstract: An imaging NMR scanner obtains plural spin echo signals during each of successive measurement cycles permitting determination of the T2 parameter for each display pixel after but a single measurement sequence. The amplitude of the NMR spin echo responses is dependent on an "a" machine parameter (the elapsed time between initiation of a given measurement cycle and the occurrence of the NMR response) and upon a "b" machine parameter (the elapsed time between initiation of successive measurement cycles). These a and b machine time parameters are selectively controlled to enhance resultant image contrast between different types of tissue or other internal structures of an object under examination. Special phase control circuits ensure the repeatability of relative phasing between successive NMR responses from the same measured volume and/or of reference RF signals utilized to frequency translate and synchronously demodulate the NMR responses in the successive measurement cycles of a complete measurement sequence.

Abstract: Densities of resonant nuclei within elemental volumes along a line are measured using the nuclear magnetic resonance phenomenon called "spin echo". A first planar volume of nuclei is selectively excited to nutate spins by approximately 90.degree.. Thereafter a second planar volume of nuclei, transverse to the first planar volume, is selectively excited to nutate spins by approximately 180.degree.. The nuclei in the line volume common to both of the planar volumes thereafter generate characteristic spin echo signals. A magnetic gradient is established along this line volume during the spin echo read out so that the resultant spin echo signals can be processed to determine the respective densities of resonant nuclei along the line volume. Appropriate phasing of the excitations enables interference with the spin echo signals by the free induction decay to be eliminated. To enable rapid development, successive line volumes are read out which do not lie in previously excited planes.

Abstract: Densities of resonant nuclei within elemental volumes along a line are measured using the nuclear magnetic resonance phenomenon called "spin echo." A first planar volume of nuclei is selectively excited to nutate spins by approximately 90.degree.. Thereafter a second planar volume of nuclei, transverse to the first planar volume, is selectively excited to nutate spins by approximately 180.degree.. The nuclei in the line volume common to both of the planar volumes thereafter generate characteristic spin echo signals. A magnetic gradient is established along this line volume during the spin echo read out so that the resultant spin echo signals can be processed to determine the respective densities of resonant nuclei along the line volume. Special pulsing sequences for rapidly effecting measurement of successive multiple line volumes and suitable apparatus for effecting such sequences are also described.

Abstract: An imaging NMR scanner obtains plural spin echo signals during each of successive measurement cycles permitting determination of the T2 parameter for each display pixel after but a single measurement sequence. The amplitude of the NMR spin echo responses is dependent on an "a" machine parameter (the elapsed time between initiation of a given measurement cycle and the occurrence of the NMR response) and upon a "b" machine parameter (the elapsed time between initiation of successive measurement cycles). These a and b machine time parameters are selectively controlled to enhance resultant image contrast between different types of tissue or other internal structures of an object under examination. Special phase control circuits ensure the repeatability of relative phasing between successive NMR responses from the same measured volume and/or of reference RF signals utilized to frequency translate and synchronously demodulate the NMR responses in the successive measurement cycles of a complete measurement sequence.