MRI SSFP Sequence Bipolar Gradient Control
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Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face challenges in reducing image acquisition time and minimizing distortions caused by patient movements, such as heartbeat and breathing, which can lead to low-quality images.
Innovation Solution
An MRI apparatus and method utilizing a steady-state free precession (SSFP) sequence with bipolar gradient magnetic fields and RF pulses to control spatial encoding gradients, ensuring opposite polarities and magnitudes to reduce interference and distortions, while acquiring and processing MR signals to generate high-quality images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a long scanning time is used for MR image acquisition, then the signal quality may be improved, but image distortions occur due to movements caused by heartbeat, breathing, and other peristaltic movements
Solution Approach 1:
The patent applies periodic RF pulses in an SSFP sequence to maintain steady-state magnetization, enabling rapid image acquisition while preserving signal quality. The periodic application of RF pulses and gradient magnetic fields allows for shortened scanning time without sacrificing measurement precision, thereby resolving the contradiction between signal quality and image distortion.
2Manufacturing precision
If the scanning time is shortened to reduce motion artifacts, then image distortion is reduced, but the signal quality and image resolution deteriorate
Solution Approach 1:
The SSFP sequence maintains continuous steady-state magnetization through repeated RF pulses, allowing for rapid sequential imaging without signal decay. This continuity enables shortened scanning time while maintaining both signal quality and image resolution, resolving the contradiction between fast acquisition and image quality.
Solution Approach 2:
The patent optimizes parameters including RF pulse flip angles, gradient magnetic field strengths, and repetition times to achieve steady-state conditions that maximize signal intensity while enabling rapid acquisition. These parameter adjustments allow short scanning time without compromising signal quality or image resolution.
3Manufacturing precision
If bipolar gradient magnetic fields with opposite polarities are applied to reduce interference, then image distortion is reduced, but the complexity of gradient control increases
Solution Approach 1:
The patent employs asymmetric bipolar gradient lobes where the area under the positive lobe differs from the negative lobe, creating a net gradient moment that refocuses spins while compensating for field inhomogeneities. This asymmetric design reduces image distortion and interference artifacts while maintaining manageable gradient control complexity through systematic pulse sequencing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach significantly shortens image acquisition time and reduces distortions, resulting in improved image quality by effectively managing gradient magnetic fields and RF pulses to stabilize MR signal acquisition and processing.
Implementation Method 1
controlling a first gradient magnetic field in a first direction in correspondence with a first RF pulse and a second gradient magnetic field in the first direction in correspondence with a second RF pulse, from among spatial encoding gradients, to have opposite polarities with respect to each other
Implementation Method 2
an MRI apparatus for generating an MR image based on a steady state free precession (SSFP) sequence
Implementation Method 3
A magnetic resonance imaging (MRI) apparatus uses a magnetic field to capture an image of a target object
Data Source
AI summary
Provided is a magnetic resonance imaging (MRI) apparatus for generating an MR image based on a steady state free procession (SSFP) sequence. The MRI apparatus includes: a radio frequency (RF) controller configured to apply to an object a first RF pulse corresponding to a first slice and a second RF pulse corresponding to a second slice; a gradient magnetic field controller configured to control respective gradient magnetic fields in a first direction corresponding to the first and second RF pulses, from among spatial encoding gradients, to have opposite polarities with respect to each other; a data acquisition unit configured to acquire first and second MR signals corresponding to the first and second slices; and an image processor configured to generate first and second MR images corresponding to the first and second slices, respectively, based on the acquired first and second MR signals.