Magnetic resonance projection imaging of dynamic subjects
AssigneeGeneral Electric Company
InventorsYudong Zhu, Christopher Judson Hardy
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Abstract
An MRI system performs a cardiac gated scan of a moving coronary artery using preparatory pulse sequences and two-dimensional EPI (echo planar imaging) pulse sequences. The preparatory pulse sequence saturates spin magnetization in regions surrounding a slice which contains the coronary artery at one point in time during each cardiac cycle. The EPI imaging pulse sequence is performed later in the cardiac cycle after the coronary artery has moved and a two-dimensional image is reconstructed by projecting NMR signals from a volume within which the coronary artery moves during the cardiac cycle.
Claims24
A method for producing an image of a moving object with an MRI system, comprising the steps of:
- a) altering longitudinal magnetization of spins located outside a selected region of spins that includes the moving object, the step of altering longitudinal magnetization of spins comprising:
- i) applying a selective RF excitation pulse to produce a flip angle of (90+α) degrees in the selected region through the moving object;
- and,
- ii) applying a non-selective RF excitation pulse to alter spins throughout a volume by a flip angle of negative (90+α) degrees;
- b) performing a two-dimensional imaging pulse sequence to acquire NMR signals from spins located in the volume which includes the selected region;
- c) repeating steps a) and b) until sufficient NMR signals are acquired to form an image data set with which an image can be reconstructed;
- and
- d) reconstructing a two-dimensional image in which the NMR signals produced by spins located in the volume are projected onto the two-dimensional image.
An MRI system for producing a two-dimensional image of a moving object comprising:
- a magnet assembly for producing a polarizing magnetic field in a volume that contains the moving object;
- a physiological acquisition controller for detecting presence of the moving object in a selected region of said volume;
- an RF coil for producing transverse magnetization in spins located in said volume but outside of said selected region such that longitudinal magnetization of said spins is substantially altered when the moving object is in said selected region, said RF coil being adapted to receive an imaging pulse sequence which includes:
- a) selective RF excitation pulse for producing transverse magnetization in spins located throughout said volume;
- b) a negative, z-axis gradient pulse for rephasing the transverse magnetization throughout the volume;
- c) a transceiver for acquiring NMR signalsproduced by the transverse magnetization;
- and
- d) a system control for reconstructing a two-dimensional image from the acquired NMR signals which is a projection from said volume along a projection axis.
A method for producing an image of an object that moves within a volume, comprising the steps of:
- a) producing a polarizing magnetic field in the volume;
- b) performing a preparation pulse sequence to produce an RF excitation field and a magnetic field gradient for altering longitudinal magnetization of spins in the volume differently than longitudinal magnetization of spins that form a selected part of the object, the preparation pulse sequence including:
- i) generating a non-selective RF excitation pulse to produce transverse magnetization in spins located throughout the volume, said non-selective RF excitation pulse having a flip angle of plus (90+α) degrees;
- ii) generating a selective RF excitation pulse in the presence of a slice select magnetic field gradient pulse to re-establish longitudinal magnetization in the spins forming the selected part of the object, said selective RF excitation pulse having a flip angle of minus (90+α) degrees;
- and
- iii) at a subsequent time, applying a selective RF excitation pulse to produce transverse magnetization in said spins located throughout the volume;
- c) producing transverse magnetization in spins that form the selected part of the object
- d) acquiring NMR signals produced by spins undergoing said transverse magnetization in the presence of a readout magnetic field gradient;
- and
- e) reconstructing a projection image of the object using the acquired NMR signals.
Dependencies are inferred from the claim text.