Abstract: A RF shield for an MRI system with a cylindrical geometry is disclosed. The RF shield is a plurality of panels with polyester on one side and copper cladding on the other side. The shingles include an adhesive so the shingles can be overlapped onto each other such that half of each shingle adheres to an adjacent shingle and the other half of the shingle adheres to the inside surface of the gradient coil assembly.

Abstract: Convenient side access to an image volume located within a two-pole, two-column main magnet of an MRI system is provided by rotating the symmetry axis of the magnet to be non-perpendicular with respect to the longitudinal axis of the patient transport and/or otherwise displacing the two column structures of the magnetic circuit so as to permit open and unobstructed access to the image volume along a direction perpendicular to the longitudinal axis of the patient transport.

Abstract: An electromagnet shim coil is utilized for temporarily altering the shape of a volume in which there is provided a substantially homogeneous NMR polarizing field. By temporarily energizing the electromagnet shim coil and thus altering the shape of the volume, magnetic resonance imaging can take place in other than a substantially spherical volume (e.g., in an elongated ellipsoidal-like volume extending axially along a patient so as to encompass a longer section of the spinal column). In the exemplary embodiment, the electromagnet shim coil takes the form of a pancake-like coil with windings positioned so as to create fourth power spherical harmonic in a transverse magnet-type of MRI system.

Abstract: 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.

Abstract: An MRI magnet member (e.g., a pole piece or tip) is laminated using relatively large bar-shaped laminations instead of the usual thin sheet material. One or more layers of such bar-shaped laminations are arrayed with small insulating gaps into which a low loss insulating liquid filler material is flowed and then cured to a hardened solid state. This simultaneously produces insulated pole tip laminations which have been robustly integrated together into a unitary structure. The resulting robust laminated pole tip is relatively easy to manufacture and is also capable of withstanding rather large magnetic forces and maintaining relatively uniform magnetic field distribution within an MRI imaging region while yet providing providing sufficient eddy current reduction so as to efficiently permit rapidly changing magnetic gradient coil currents to be established.

Abstract: MRI T1 relaxometry is performed using a single fixed strength magnetic background field for RF signal transmission and reception thus greatly simplifying RF circuitry design and/or adjustment Switched differing strength background magnetic fields are employed at other times in the relaxometry cycle so as to predominate the NMR T1 relaxation parameter value and thus permit relaxometry determinations of T1 values versus magnetic field strength (or the equivalent corresponding NMR RF frequency) at N data points using as few as N+1 measurement cycles. In one embodiment, the booster field is switched on for fixed time intervals .tau. while variable initial NMR nutation pulses .alpha. are utilized as the controlled relaxometry variable parameter. Process and apparatus are disclosed for thus efficiently achieving in vivo NMR relaxometry (including magnetic resonance imaging if desired).

Abstract: An MRI RF coil is shielded from extraneous noise sources using an extremely thin conductive shield interposed between the RF coil and the static magnetic structure of an MRI system. To control eddy currents induced in such conductor by the changing magnetic flux of MRI gradient coils, the RF shield conductor thickness is less than three skin depths at the MRI RF operating frequencies of the RF coil. Preferably, the RF shield conductor thickness is on the order of only one skin depth or less.

Abstract: MRI T1 relaxometry is performed using a single fixed strength magnetic background field for RF signal transmission and reception thus greatly simplifying RF circuitry design and/or adjustment. Switched differing strength background magnetic fields are employed at other times in the relaxometry cycle so as to predominate the NMR T1 relaxation parameter value and thus permit relaxometry determinations of T1 values versus magnetic field strength (or the equivalent corresponding NMR RF frequency) at N data points using as few as N+1 measurement cycles. Process and apparatus are disclosed for thus efficiently achieving in vivo NMR relaxometry (including magnetic resonance imaging if desired).

Abstract: A high T.sub.c superconductive electromagnet winding is advantageously employed as part of an MRI magnet structure having a pair of magnetically permeable poles opposingly disposed about the patient imaging volume. The magnetic circuit is otherwise completed by a magnetically permeable yoke structure having plural open apertures for easy access to the patient imaging volume. Still further advantage can be had by asymmetrically disposing a single superconductive electromagnet winding with respect to the patient image volume thereby eliminating the need for more than one cryostat. When high T.sub.c superconductive electromagnetic windings are utilized, a non-conductive composite cryostat may also be used to further reduce spurious eddy current fields. When an asymmetric single high T.sub.

Abstract: A pair of serially-connected coils detect noise variations in an MRI background magnetic field. Although the coils are closely coupled to the primary background magnetic field generator of the MRI system, they are disposed so as to be substantially de-coupled from rapidly changing MRI gradient magnetic fields. The noise detecting loops drive a negative feedback loop including a low pass filter, amplifier and controlled current source driving a large correcting loop. The device attenuates background magnetic field noise during MRI data acquisition over a frequency band extending from a few millihertz to more than 100 Hz. It is preferably used with existing field stabilization software that otherwise compensates for fluctuations in an overlapping frequency band which starts at d.c. Thus, when used together, background magnetic field noise may be attenuated (or compensated for in subsequent MRI data processing) over a frequency band that extends from d.c. to more than 100 Hz.

Abstract: An auxiliary insert MRI gradient coil is used to produce intense auxiliary magnetic gradient pulses during MRI sequences to improve MRI system performance. Although the auxiliary gradient coil may be of considerably reduced dimensions, thus, having considerably reduced uniformity, linearity and/or reproducibility than standard MRI gradient coils, coordinated use of both the regular MRI gradient coils and the auxiliary gradient coil can produce considerably enhanced MRI system performance in certain applications. Such auxiliary magnetic gradient coil may be used, for example, to provide spoiler pulses between MRI spin echo subsequences, as diffusion gradient pulses in diffusion MRI studies or as the oscillating gradient used to form successive gradient echoes in echo planar imaging.

Abstract: Electromagnet coil driving circuitry in a magnetic resonance imaging system is modified to include a flux-driven closed-loop real-time feedback control. The result is more accurate and efficient control of the net actual gradient flux generated by the coil even in the presence of magnetic circuit materials exhibiting hysteresis effects and/or electrical conductors giving rise to eddy current effects. Such driver control can be used to simultaneously correct the magnetic flux changes induced by environmental, ambient or other outside disturbances affecting the net magnetic field within a patient imaging volume of a magnetic resonance imaging system.

Abstract: A measure of magnetic field inhomogeneity along a phase-encoded (e.g. y-axis) dimension is derived in k-space from previously acquired MRI phase-encoded projection data. From this, a measure of MRI data skewing caused by such inhomogeneity is obtained and used to compensate therefor. Since the MRI data is to be multi-dimensionally Fourier Transformed in most instances anyway, a transform in the relevant phase encoded dimension (e.g., y-axis) is taken followed with phase shifting each digitized data point by an amount proportional to the measured magnitude of inhomogeneity and to the datum coordinate in the read-out dimension (e.g., x-axis) and to the datum coordinate in each phase-encode dimension (e.g., y-axis) before the data is further Fourier Transformed with respect to the read-out dimension (e.g., x-axis). If two-dimensional phase encoding is employed (e.g., as in 3DFT), then a second level of similar inhomogeneity compensation can be had in the third dimension (e.g., z-axis) as well.

Abstract: Techniques for rapidly and accurately calibrating RF transmitter parameters in a Nuclear Magnetic Resonance (NMR) magnetic resonance imaging (MRI) system obtain an estimate of flip (nutation) angle by determining a ratio of plural echo responses to a plural (e.g., three) RF pulse sequence. The ratio may be selected to be independent of relaxation times T.sub.1 and T.sub.2 so no relaxation waiting time between successive iterations is required. Accurate RF transmitter level calibration can be performed within on the order of three to five seconds. The techniques are robust and can discriminate flip angles over a wide range.

Abstract: A bridge conductors for the turns of an MRI RF coil may be connected serially within a connector joint area of an inductive coil so as to selectively increase its physical size (e.g., so as to accommodate larger patient volumes to imaged therewithin). Serial capacitance may be included in at least one of the bridging conductors so as to substantially reduce the net inductive impedance of the added bridge conductors such that the standard coil RF tuning and impedance matching circuits may still operate within their normal predetermined adjustable ranges.

Abstract: The signal-to-noise ratio achievable for received nuclear magnetic resonance RF signals in a magnetic resonance imaging system is increased by (a) using relatively wider strips of conductor so as to reduce coil loading by the sample and (b) the use of curved edges on a coil conductor so as to reduce "hot spots" located near the conductor surfaces.

Abstract: Method and apparatus for more rapidly capturing MRI data by receiving and recording NMR RF responses in plural substantially independent RF signal receiving and processing channels during the occurrence of an NMR RF response. The resulting plural data sets respectively provided by the plural RF channels are then used to produce multiply phase-encoded MRI data from the single NMR RF response. Practical examples are disclosed for reducing required MRI data capturing time by factors of at least about one-half.

Abstract: In a gradient coil set for a magnetic resonance system, the y gradient coils are located substantially closer to the patient than are the x and z gradient coils. As a result, one may design the y gradient coils to produce a stronger y gradient, to have reduced inductance or otherwise better tailor the magnetic/electrical properties of the gradient coil set for MRI imaging sequences. In the exemplary embodiment, at least portions of the y gradient coils have a first spacing from the z-axis while the x and z gradient coils have a second substantially larger spacing from the z-axis. Furthermore, while the x and z gradient coils are centered about the z-axis in the patient access space, alternate sides of the y gradient coil set are centered about respectively off-set centers vertically displaced from the z-axis center of the patient access area.

Abstract: The axial dimensions of the usual "saddle" coils used to create transverse magnetic gradients in the static magnetic field of a magnetic resonance imaging system are substantially foreshortened. The outer arc of the saddle coil is moved axially inward while still leaving it at a position which produces negligible net transverse gradient contribution. While this new position of the outer arc can be expected to produce a significant second (third) derivative of the transverse gradient with respect to Z (the orientation of the static magnetic field) at the predetermined observation point, the inner arc of the saddle coil may be moved slightly away from the observation point so as to produce a second (third) derivative which substantially cancels that of the relocated outer arc. In this manner, the desired condition of having a net zero second (third) derivative may still be maintained even though the axial dimension of the saddle coil has been substantially reduced (e.g.

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.