摘要:
An RF coil array arrangement for enhanced magnetic resonance imaging of the breast or spine regions of prone and supine patients within a vertically oriented B0 field is disclosed. Several RF coil array embodiments are disclosed that provide for both generating a nuclei nutation field pulse and acquiring nuclear magnetic resonance signals when functioning in an MRI apparatus environment that employs a vertical main magnetic field. A coil array may include one or more RF coils that are intended to be oriented such that their primary B field direction(s) are perpendicular to the vertical magnetic field of the MRI apparatus. Each coil array may further include one or more single loop or solenoidal coil(s) that are oriented having their central or longitudinal axis aligned parallel to the vertical main magnetic field so as to make advantageous use of non-axial field components associated with the coil(s) to further generate and receive desired NMR signal components.
摘要:
An inherently de-coupled sandwiched solenoidal array coil (SSAC) is disclosed for use in receiving nuclear magnetic resonance (NMR) radio frequency (RF) signals in both horizontal and vertical-field magnetic resonance imaging (MRI) systems. In its most basic configuration, the SSAC comprises two coaxial RF receive coils. The first coil of the array has two solenoidal (or loop) sections that are separated from one another along a common axis. The two sections are electrically connected in series but the conductors in each section are wound in opposite directions so that a current through the coil sets up a magnetic field of opposite polarity in each section. The second coil of the SSAC is disposed (“sandwiched”) between the two separated solenoidal sections of the first coil in a region where the combined opposing magnetic fields cancel to become a null. Due to the winding arrangement and geometrical symmetry, the receive coils of the array become electromagnetically “de-coupled” from one another while still maintaining their sensitivity toward receiving NMR signals. The multiple coil array arrangement also allows for selecting between a larger or smaller field-of-view (FOV) to avoid image fold-over problems without time penalty in image data acquisition. Alternative embodiments are disclosed which include unequal constituent coil diameters, unequal constituent coil windings, non-coaxial coil configurations, a three-coil quadrature detection (QD) SSAC arrangement, multiple SSAC arrangements, and optimized SSAC configurations for breast imaging in both horizontal and vertical-field MRI systems.
摘要:
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.
摘要:
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.
摘要:
An RF coil tuning circuit is disclosed in which two banks of parallel capacitive branches are provided. Each capacitive branch includes a fixed value capacitor, a relay and a PIN diode connected in series. An impedance of the tuning circuit is adjusted to the optimum VSWR=1 condition by first switching the eight PIN diodes to learn which open/closed condition applies the fixed value capacitors in the optimum combination. Then, the PIN diodes are all closed and the optimum combination is applied using the open/closed states of the relays.
摘要:
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.
摘要:
Methods and devices for improving the machine-to-machine and temporal (e.g., inter and intra-machine) and database consistency of coronary calcium scoring by applying a filtering algorithm that sharpens and/or smoothes the image so as to return a filtered image having a spatial resolution of a certain reference value.
摘要:
Switched magnetic fields (in addition to the usual pulsed magnetic gradient fields) aiding and/or opposing the usual constant static magnetic field B.sub.o are utilized so as to increase the signal-to-noise ratio for given available imaging sequence times and/or to provide special imaging effects.
摘要:
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.c superconductive electromagnet coil is utilized, an asymmetric electromagnet shim winding may also be employed so as to further increase the magnetic field homogeneity within what is now an asymmetrically located patient imaging volume within the air gap of the magnet structure.
摘要:
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.