US 5,545,993 AGranted

Method of motion tracking measurement in MR imaging system

AssigneeHitachi Medical Corporation

InventorsJun'ichi Taguchi, Kunihiko Kido, Koichi Sano

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Abstract

Physical quantities representing six kinds of freedom relating to parallel movement and rotation of an inspection object are detected during repetition of a measurement sequence of magnetic resonance imaging, and a direction and a position of a desired slice moved with parallel movement and rotation of the inspection object are calculated in accordance with the detection result. An intensity ratio of gradient magnetic fields in x-, y- and z-axes directions for synthesizing a slice direction gradient magnetic field, an intensity of a phase encoder gradient magnetic field and a read direction gradient magnetic field are determined so that a direction of an excitation slice coincides with the direction of the desired slice after movement. Similarly, a center frequency of excitation pulses is determined so that a position of the excitation slice coincides with the position of the desired slice after movement. Magnetic resonance signals are measured by imaging parameters so updated, and an image is reconstructed.

Claims20

Dependent claims

In a magnetic resonance (MR) imaging system including means for generating a static magnetic field in an inspection space, means for generating gradient magnetic fields in three directions, respectively, means for generating a radio frequency (RF) magnetic field for exciting an inspection object, measurement means for measuring magnetic resonance signals from said inspection object, arithmetic means for executing various arithmetic operations inclusive of image reconstruction from detection signals for said detection signals, and control means for controlling execution of each of said means, a method of motion tracking measurement in MR imaging system comprising obtaining a plurality of sets of magnetic resonance signal data from a desired slice of said inspection object by repeating a plurality of times the following steps (a) to (c):

(a) a step of detecting physical quantities determining six kinds of freedom relating to parallel movement and rotation of a position/direction detection coordinate system defined on, and fixed to, said inspection object;
(b) a step of changing an intensity ratio of said gradient magnetic fields in said three directions with respect to intensity ratio of a prior step (b) for synthesizing a slice selection gradient magnetic field, and calculating a center frequency of an RF magnetic field to be simultaneously generated with a slice selection gradient magnetic field so that the position and the direction of an excitation slice follow the changes of the direction and the position of a desired slice to be imaged, said changes being caused by the movement of said inspection object;
and
(c) a step of selectively exciting magnetization of said excitation slice by generating said gradient magnetic fields having the changed intensity ratio in said three directions and said RF magnetic field having the calculated center frequency, and measuring the resulting magnetic resonance signals.

1 more element

(a) a step of setting a direction and a position of a desired slice to be imaged on said inspection object set in a reference position of said inspection space;
(b) a step of fixedly defining a coordinate system on said inspection object for detecting a position and direction of said inspection object, and determining a direction and an origin position of said coordinate system and determining a correlation between said coordinate system and said desired slice, and preserving data representing said correlation;
(c) a step of detecting physical quantities determining six kinds of freedom relating to parallel movement and rotation of said coordinate system;
(d) a step of calculating the direction and the position of said desired slice moved by the movement of said inspection object by using said preserved data representing said correlation, and the result of said detection, setting an intensity ratio of said gradient magnetic fields in said three directions which intensity ratio changes from a prior step (d) and the frequency of said RF magnetic field so that the position and the direction of an excitation slice are in conformity with the position and the direction of said desired slice moved, and executing an imaging operation;
and
(e) a step of repeating said steps (c) and (d) until the number of times of repetition of a predetermined imaging operation reaches a predetermined number of times.

3 more elements

(a) a step of determining a direction and a position of a desired slice to be imaged and a center position of an image to be imaged on said inspection object set in a reference position of said inspection space;
(b) a step of fixedly defining a coordinate system on said inspection object for detecting position and direction of said inspection object, and determining a direction and an origin position of said coordinate system defined, and obtaining a correlation between said coordinate system and said desired slice, and preserving data representing said correlation;
(c) a step of detecting physical quantities determining six kinds of freedom relating to parallel movement and rotation of said coordinate system of said inspection object;
(d) a step of calculating a direction and a position of said desired slice moved with the movement of said inspection object, by using said preserved data representing said correlation and said detected physical quantities, and obtaining an intensity ratio of said gradient magnetic fields in said three directions which intensity ratio changes from a prior step (d) for synthesizing a slice selection gradient magnetic field necessary for making the direction of said moved desired slice coincident with the direction of said excitation slice, obtaining a center frequency of an RF magnetic field necessary for making the position of said moved desired slice coincident with the position of said excitation slice, and a positional difference between said center position of said desired image and a center position of an image predicted by reconstructing a predicted measurement signal obtained by assuming that said moved desired slice is excited by using said slice selection gradient magnetic field and said RF magnetic field;
(e) a step of generating said gradient magnetic fields having the obtained intensity ratio of said three directions and said RF magnetic field having the obtained center frequency so as to selectively excite magnetization of said excitation slice, and measuring the resulting magnetic resonance signals;
(f) a step of correcting the phases of the magnetic resonance signals measured, on the basis of said position error;
(g) a step of repeating said steps (c) to (f) until the number of times of repetition of predetermined imaging operation reaches a predetermined number of times, and obtaining a plurality of phase-corrected magnetic resonance signal data;
and
(h) a step of reconstructing an image of said desired slice of said inspection object from a plurality of sets of said phase-corrected magnetic resonance signal data.

6 more elements

(a) a step of detecting physical quantities determining no more than five kinds of freedom relating to parallel movement and rotation of a position/direction detection coordinate system defined on, and fixed to, said inspection object, if at least one type of freedom is fixed;
(b) a step of changing an intensity ratio of said gradient magnetic fields in said three directions with respect to a prior step (b) for synthesizing a slice selection gradient magnetic field, and calculating a center frequency of an Rf magnetic field to be simultaneously generated with a slice selection gradient magnetic field so that the position and the direction of an excitation slice follow the changes of the direction and the position of a desired slice to be imaged, said changes being caused by the movement of said inspection object;
and
(c) a step of selectively exciting magnetization of said excitation slice by generating said gradient magnetic fields having the changed intensity ratio in said three directions and said RF magnetic field having the calculated center frequency, and measuring the resulting magnetic resonance signals.

1 more element

Dependencies are inferred from the claim text.