摘要:
In a transmit apparatus, a multi-channel radio frequency transmitter (30, 46) includes a plurality of transmit elements (32) defining at least two independently operable transmit channels. A transmit configuration selector (54) determines a selected transmit configuration (60) specifying amplitude and phase applied to each transmit channel to generate a B1 field in a corresponding selected region (90) of a subject (38) coupled with the radio frequency transmitter. The transmit configuration selector determines the selected transmit configuration based on B1 mapping (58) of the subject and a B1 field quality assessment employing at least two different B1 field quality measures.
摘要:
An MRI apparatus is provided. The apparatus includes a main magnet for generating a main magnetic field in an examination region, a plurality of gradient coils for generating gradient fields within the main field, an RF transmit coil for transmitting RF signals into the examination region and exciting magnetic resonance in a subject disposed therein in accordance with a plurality of imaging parameters, the transmitted RF signals having a SAR associated therewith, and a SAR processor for maintaining the transmitted RF signals below a prescribed SAR level.
摘要:
A gradient coil assembly generates magnetic field gradients across the main magnetic field of a magnetic resonance imaging apparatus and includes a primary gradient coil (22p) switchable between a first configuration which generates magnetic field gradients which are substantially linear over a first useful imaging volume, and a second configuration which generates magnetic field gradients which are substantially linear over a second useful imaging volume. A first shield coil set (22s1) is complimentary to the primary gradient coil in one of the first and second configurations, and a second shield coil set (22s2), when either used alone or in combination with the first shield coil, is complimentary to the other of the first and second configurations.
摘要:
When correcting for attenuation in a positron emission tomography (PET) image, a magnetic resonance (MR) image (24) of a subject is generated with spectroscopic data (38) describing the chemical composition of one or more of the voxels in the MR image. A table lookup is performed to identify a tissue type for each voxel based on the MR image data and spectral composition data, and an attenuation value is assigned to each voxel based on its tissue type to generate an MR attenuation correction (MRAC) map (30). The MRAC map (30) is used during reconstruction of the nuclear image (37) to correct for attenuation therein. Additionally, attenuation due to MR coils and other accessories that remain in a nuclear imager field of view during a combined MR/nuclear scan is corrected using pre-generated attenuation correction maps that are applied to a nuclear image after executing an MR scan to identify anatomical landmarks, which are used to align the pre- generated attenuation correction maps to the patient.
摘要:
In a method for aligning a magnetic field modifying structure (74) in a magnet bore (12) of a magnetic resonance imaging scanner (8), a reference magnetic field map of the magnet bore (12) is measured without the magnetic field modifying structure (74) inserted. The magnetic field modifying structure (74) is inserted into the magnet bore (12). A second magnetic field map of the magnetic bore (12) is measured with the magnetic field modifying structure (74) inserted. At least one odd harmonic component of the first and second magnetic field maps is extracted. The magnetic field modifying structure (74) is aligned in the magnet bore (12) based on a comparison of the odd harmonic component of the first and second magnetic field maps.
摘要:
In preparation for acquiring PET image data, subject motion models are built based on physiologic signal monitoring and MR data is collected and used for improved PET imaging. The physiologic signal monitoring is also used during PET imaging, and the acquired MR data is used for prospective or retrospective gating of the PET image acquisition, or in the PET reconstruction for improved correction/imaging.
摘要:
An imaging method comprises: acquiring magnetic resonance data of a subject using a magnetic resonance component (30, 30′) disposed with the subject; acquiring nuclear imaging data of the subject with the magnetic resonance component disposed with the subject; determining a position of the magnetic resonance component respective to a frame of reference of the nuclear imaging data; and reconstructing the nuclear imaging data (60) to generate a nuclear image (62) of at least a portion of the subject. The reconstructing includes adjusting at least one of the nuclear imaging data and the nuclear image based on a density map (46) of the magnetic resonance component and the determined position of the magnetic resonance component respective to the frame of reference of the nuclear imaging data to correct the nuclear image for radiation absorption by the magnetic resonance component.
摘要:
A radio frequency coil assembly includes an annular conductor (20, 22) configured to support a sinusoidal electrical current distribution at a magnetic resonance frequency, and a radio frequency shield (30, 32, 34) shielding the annular conductor in at least one direction, the radio frequency shield including at least one oi (i) a cylindrical shield portion (30) surrounding a perimeter of the annular conductor, and (ii) a planar shield portion (32, 34) arranged generally parallel with the annular conductor. In a magnetic resonance scanner embodiment, a magnet generates a static magnetic field (B0), a magnetic field gradient system is configured to superimpose selected magnetic field gradients on the static magnetic field, and said radio frequency coil assembly is arranged with the annular conductor generally transverse to the static magnetic field (B0).
摘要:
A radio frequency coil for magnetic resonance imaging includes an active coil member (70, 701, 170, 270) that defines an imaging volume. The active coil member has a first open end (74) with a first cross-sectional dimension (dactive). A shield coil member (72, 721, 722, 723, 724, 725, 172, 1722, 272) substantially surrounds the active coil member. The shield coil member has a constricted open end (88) arranged proximate to the first open end of the active coil member with a constricted cross-sectional dimension (dconst) that is less than the cross-sectional dimension (dShieid) of the shield coil member. In some embodiments, the radio frequency coil further includes an outer shield coil member (100) that is substantially larger than the shield coil member (72, 721, 722, 723, 724, 725, 172, 1722, 272), and surrounds both the active coil member and the shield coil member.