New Patents XL1

Continuously updated real-time magnetic resonance imaging processes are used to display an MR image volume to an operator and/or pat- ient co-located with i:he MRI magnet, viewing console and other elements of an MRI system within the same shiel’ded 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 con- sole is to be co-located within the shielded gantry room near the MRI magnet assembly. Suitable RF shielding is pra’vided to RF-isolate the viewing console and il:s related power and video signal cables from the MRI RF coils being used to monitor relatively weak NMR signals em- anating from the irnage 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 per- mits performance of simultaneous patient pro- cedures guided by real-time visual feedback to the patient and/or doctor, nurse, patient atten- dant and the like while located within the gantry room and having direct access to the patient anatomy within the image volume.

5184075

METHOD AND APPARATUS FOR COMPENSATING FOR

NONUNIFORMITY OF STATIC MAGNETIC FIELD IN MRI

SYSTEM

Hiroshi Nishimura, Kashiwa, Japan assigned to Hitachi Medical Corporation

A method and apparatus for compensating for nonuniformity of a static magnetic field in a MRI system wherein one of X-, Y- and Z-axes of a Cartesian coordinate system is selected as a phase encoding direction, a region of a field of view is selectively excited by applying a high fre- quency pulse of a predetermined angle to an ob- ject under inspection, and an NMR signal is measured by applying a phase encoding gradient magnetic field and a frequency encoding grad- ient magnetic field after application of the high frequency pulse for a plurality of times while changing the phase encoding gradient magnetic field. A peak value is detected of the measure- ment data obtained for determining a phase encoding quantity at which the peak value can be obtained, an intensity and a polarity of a linear component of nonuniformity components of the static magnetic field in the direction selected is determined by obtaining an intensity and a

polarity of the phase encoding gradient magnetic field corresponding to the peak value, and a pulse sequence for measuring the NMR signal is executed by applying a gradient magnetic field added with a compensating gradient magnetic field having the same intensity as the linear com- ponent and a polarity opposite to the linear com- ponent to a gradient magnetic field applied in the selected direction.

5184076

MAGNETIC RESONANCE IMAGING COIL FOR APPLYING

NMR AND ESR PULSES

Gosta J Ehnholm, Helsinki, Finland assigned to Instrumentarium Corporation

A magnetic resonance imaging apparatus com- prising device for applying a magnetic field to a sample to be imaged, device for applying pulses of MR transition-exciting electromagnetic radiation to the sample, an NMR signal coil for detecting the resulting radiation from the sam- ple, and device for appling pulses of elec- tromagnetic radiation to the sample for stimulating coupled ESR transitions, in which a pulse generating device is coupled to the NMR signal coil and antennas are coupled to the coil and disposed at plural positions along the coil, whereby pulses for stimulating coupled ESR transitions may be transmitted from the pulse generating device through the coil to the ante- nnas and thence into the sample, the antennas being arranged to give a predominantly magnetic coupling to the sample.

5185573

METHOD FOR FOCUSING OF MAGNETIC RESONANCE

IMAGES

John Larson assigned to Hewlett-Packard Com-

pany

Apparati and methods for magnetic resonance imaging a selected interrogation volume in a tis- sue of a human or animal body, to provide in- creased signal-to-noise ratios for fixed data acquisition times. The method involves excita- tion of magnetic resonance in a selected inter- rogation volume that may be as small as 500- 3,000 cm3, through controllable focusing or

XL11 New Patents

steering of a rotating magnetic field signal used to induce magnetic resonance. The response signals issued by the excited volume element are then collected by focusing of these response signals, using a phased array of antennae for this purpose. Use of the invention with well known nuclear magnetic resonance excitation pro- cedures, such as spin echo, echo planar, gradient recalled and backprojection, are discussed.

5185574

NMR MEASUREMENTS USING RECURSIVE RF EXCITATION

Richard L Ehman, James Greenleaf assigned to Mayo Foundation for Medical Education and Research

An NMR echo signal is produced in a recursive process in which one or more pulse sequences are executed and the NMR echo signal produced by each pulse sequence is employed to shape the RF excitation pulse employed in the subsequent pulse sequence. The series of NMR echo signals produced by this recursive process are progres- sively modified to enhance the signals produced by prominent features in the subject.

5185575

MAGNETIC RESONANCE IMAGING APPARATUS WITH

ARTEFACT REDUCTION

Johannes Overweg, Eindhoven, Netherlands as- signed to U S Philips Corp

A high order multipole gradient field generating system in a magnetic resonant imaging ap- paratus comprises spaced quadrants of win- dings, the windings of each quadrant generating adjacent fields in each quadrant in opposing relation. The multipole system is located adja- cent to a lower order conventional gradient field coil system to shield the region of interest from field aberrations, the multipole system gene- rating a relatively strong local magnetic field ad- jacent to the coils of the gradient field coil system and a negligible change in field in the region of interest. The multipole system causes a fre- quency shift of the aberrations in the region of interest which are outside the detection fre- quency range such that the conventional grad-

ient field system signal is substantially unaffected by the multipole system in the region of interest.

5185576

LOCAL GRADIENT COIL

Robert M Vavrek, Daniel Schaefer, Christopher C Myers, Thomas G McFarland, Robert Turner assigned to General Electric Company; The United States of America as represented by the Secretary of the Department of Health and Human Servic

A compact local gradient coil is combined with a local RF coil to provide lower powered, higher strength gradient fields and faster gradient response as is useful in magnetic resonance im- aging. Interference between the RF coil and gradient coil is minimized by placement of the gradient coil external to the RF coil and by grad- ient coils that are axially symmetric and/or have conductors substantially orthogonal to the RF coil conductors. Acoustic noise in these smaller, stronger coils is reduced with ports cut into the coil forms.

5185577

RECEIVER COIL FOR NUCLEAR MAGNETIC RESONANCE

IMAGING APPARATUS

Takashi Minemura, Ootawara, Japan assigned to Kabushiki Kaisha Toshiba

A receiver coil for a nuclear magnetic resonance imaging apparatus, capable of fulfilling the con- dition for a satisfactory signal reception com- pletely for the imaging of a region of interest that cannot be placed symmetrically with respect to the central axis of the receiver coil. The receiver coil includes coil element for defining an opening section into which a region of interest is to be in- serted, and for receiving a nuclear magnetic resonance signal from the region of interest; and a coil support member for supporting the coil elements in a configuration in which a sensitivity central axis of a region of uniform signal recep- tion sensitivity for the coil elements is located away from a central axis of the opening section. The coil elements are preferably supported in a configuration corresponding to a shape of the re- gion of interest.