US 5,779,636 AGranted

Method of echo volume imaging and MRI system using the same

AssigneeKabushiki Kaisha Toshiba

InventorHitoshi Kanazawa

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Abstract

A method of acquiring MR echo data and MRI system to reconstruct a three or more dimensional image of an object use a "hybrid echo volume imaging (EVI)" technique. In the hybrid EVI, applied to the object at predetermined timings are one RF excitation pulse concurrently with a slice-selective pulse, a readout gradient pulse, and a plurality of RF refocusing pulses. After each of the plurality of RF refocusing pulses, applied to the object is a slice-encoding gradient pulse having a first encoding value changed at every application of each of the RF refocusing pulses. After the slice-encoding gradient pulse, applied are a plurality of further readout magnetic gradient pulses whose polarities are alternately inverted, thereby a plurality of echoes are generated from the object in response to inversion of the polarities. Concurrently with applying the slice-encoding pulse and the plurality of further readout gradient pulses, applied are phase-encoding gradient pulses having a second encoding value changed at every inversion of the polarities. GRASE-specific ringing artifacts are preferably eliminated without degrading an imaging matrix size or spatial resolution and without prolonging imaging time.

Claims29

Dependent claims

A method of acquiring echo data in magnetic resonance imaging, said echo data being reconstructed into a more than two dimensional MR image and said magnetic resonance imaging being carried out based on a pulse sequence applied to an object to which a coordinate system having mutually-orthogonal first, second and third directions is set, said method comprising the steps of:

applying to the object a magnetic RF excitation pulse and a magnetic slice-selective pulse set in the first direction;
after applying the magnetic RF excitation pulse and the magnetic slice-selective pulse, applying a magnetic RF refocusing pulse to the object;
after applying the magnetic RF refocusing pulse, applying to the object:
in the first direction, one of two phase-encoding magnetic gradient pulses being incorporated in the pulse sequence and providing a first encoding value changed according to every application of the magnetic RF excitation pulse,
in the second direction, a plurality of readout magnetic gradient pulses whose polarities are alternately inverted at every application, thereby a plurality of echoes are generated consecutively from the object in response to inversion of the polarities of the readout magnetic gradient pulses, and
in the third direction, the remaining one of the two phase-encoding magnetic gradient pulses being incorporated in the pulse sequence and providing a second encoding value changed according to every application of the magnetic RF excitation pulse and to every inversion of the polarities of the readout-magnetic gradient pulses;
and
repeating plural times the applying of the magnetic RF refocusing pulse, the applying of the two phase-encoding magnetic gradient pulses, and the applying of the plurality of readout magnetic gradient pulses, said first encoding value being changed at every application of the magnetic RF excitation pulse and the magnetic RF refocusing pulse.

5 more elements

An MRI system in which echo data to reconstruct a more than two dimensional image of an object are acquired based on a pulse sequence applied to the object to which a coordinate system having mutually-orthogonal first , second and third directions is set, said system comprising:

means for applying to the object a magnetic RF excitation pulse and a magnetic slice-selective pulse set in the first direction;
means for applying a plurality of magnetic RF refocusing pulses to the object after applying the magnetic RF excitation pulse and the magnetic slice-selective pulse, a predetermined interval being set after each magnetic RF-refocusing pulse;
means for applying to the object, in the first direction and in each predetermined interval, a first of two phase-encoding magnetic gradient pulses incorporated in the pulse sequence and providing a first encoding value changed according to every application of the magnetic RF excitation pulse and each of the plurality of magnetic RF refocusing pulses;
means for applying to the object in the second direction a plurality of readout magnetic gradient pulses whose polarities are alternately inverted at every application, the readout magnetic gradient pulses being applied after application of the first of the two phase-encoding magnetic gradient pulses in each predetermined interval, thereby generating a plurality of echoes consecutively from the object in response to inversion of the polarities of the readout magnetic gradient pulses;
and
means for applying to the object in the third direction a second of the two phase-encoding magnetic gradient pulses incorporated in the pulse sequence and providing a second encoding value changed according to every application of the magnetic RF excitation pulse and according to every inversion of the polarities of the readout magnetic gradient pulses.

3 more elements

An MRI system in which echo data to reconstruct a more than two dimensional image of an object are acquired based on a pulse sequence applied to the object to which a coordinate system having mutually-orthogonal first, second and third directions is set, said system comprising:

a magnet for generating a static magnetic field in which the object is placed;
a gradient coil for generating magnetic gradient fields applied to the object, said magnetic gradient fields being incorporated in the pulse sequence and including a magnetic slice-selective pulse set in the first direction, two phase-encoding magnetic gradient pulses, and a readout magnetic gradient pulse set in the second direction, one of the two phase-encoding magnetic gradient pulses being set in the first direction and the remaining one of the two phase-encoding magnetic gradient pulses being set in the third direction;
an RF coil for generating RF fields transmitted to the object and for receiving an echo signal from the object, said echo signal being processed into echo data and said RF fields including a magnetic RF excitation pulse and a plurality of magnetic RF refocusing pulses;
and
a sequencer controlling the gradient coil and the RF coil for producing the functions of:
generating the magnetic RF excitation pulse and the magnetic slice-selective pulse,
generating the plurality of magnetic RF refocusing pulses after generation of the magnetic RF excitation and magnetic slice-selective pulses, a predetermined interval being set after each magnetic RF refocusing pulse,
generating in each interval a first of the two phase-encoding magnetic gradient pulses, the first pulse providing a first encoding value changed according to every application of the magnetic RF excitation pulse and each of the plurality of magnetic RF refocusing pulses,
generating plural times the readout magnetic gradient pulse to form a series of adjacent readout gradients whose polarities are alternately inverted, said series of adjacent readout gradients being formed after application of the first of the two phase-encoding magnetic gradient pulses in each interval, the echo signals being thereby generated consecutively from the object in response to inversion of the polarities of the series of adjacent readout gradients, and
generating a second of the two phase-encoding magnetic gradient pulses, the second pulse providing a second encoding value changed according to every application of the magnetic RF excitation pulse and according to every inversion of the polarities of the series of adjacent readout gradients.

7 more elements

Dependencies are inferred from the claim text.