MRI Fold-Over Artifact Reduction via Rotated Slab Excitation
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) systems face challenges in acquiring high spatial resolution images of the abdomen or pelvis within a short breath-hold time, especially when patients' arms are positioned beside their bodies, leading to longer acquisition times due to large field-of-view requirements and undesirable artifacts from out-of-field signals.
Innovation Solution
The use of a minimum-phase RF pulse combined with a rotated slab excitation sequence and a chemical-shift technique for fat/water separation, allowing for optimal echo times and high acceleration factors to achieve homogeneous fat suppression and out-of-FOV signal suppression within a breath-hold scan, enabling high-resolution imaging without increasing echo times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large FOV is used to image the abdomen/pelvis with arms positioned beside the patient, then wrap-around artifacts are avoided, but acquisition time increases beyond breath-hold duration
Solution Approach 1:
The harmful out-of-FOV signals from the patient's arms are extracted and suppressed using a rotated slab excitation sequence. This sequence selectively excites only the desired imaging slab while suppressing signals from regions outside the FOV, thereby eliminating wrap-around artifacts without requiring a larger FOV that would increase acquisition time.
Solution Approach 2:
The excitation parameters are changed by using a rotated slab excitation sequence with specific slice selection gradients and RF pulse parameters. This allows precise control over which regions are excited, enabling suppression of out-of-FOV signals while maintaining adequate FOV coverage for breath-hold imaging.
2Object-affected harmful factors
If a Rotated Slab Excitation (ROSE) approach is used to suppress out-of-FOV signals, then foldover artifacts are reduced, but minimum echo times increase due to prolonged RF pulses
Solution Approach 1:
The RF pulse parameters are optimized by using minimum-phase RF pulses with specific duration and shape characteristics. This allows the ROSE sequence to achieve adequate out-of-FOV suppression with shorter echo times, preserving the ability to perform chemical-shift fat/water separation at optimal TE values.
3Loss of time
If high acceleration factors are used with large FOV to reduce scan time, then acquisition fits within breath-hold, but undesirable artifacts from out-of-FOV signals increase
Solution Approach 1:
The harmful out-of-FOV signals are extracted and suppressed using the rotated slab excitation sequence before parallel imaging acceleration is applied. This ensures that the accelerated imaging process works with clean data that has already had foldover artifacts suppressed, maintaining image quality while achieving breath-hold scan times.
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
This approach enables high spatial resolution MRI images with uniform fat/water separation and reduced scan times, allowing patients to be comfortably imaged with arms positioned beside their bodies, while preventing foldover artifacts and maintaining optimal echo times.
Implementation Method 1
performs volume excitation based upon minimum-phase radio-frequency (RF) pulses in a sagittal plane
Implementation Method 2
a Rotated Slab Excitation (ROSE) approach, in which a 3D volume is encoded in the coronal plane while volume excitation is switched from an anterior-posterior (AP) direction to an RL direction (e.g., a sagittal excitation)
Implementation Method 3
when this ROSE approach is combined with chemical-shift approach for fat separation
Implementation Method 4
Magnetic Resonance Imaging (MRI) to acquire images of an abdomen and/or pelvis of a patient
Data Source
Figure 1
Figure 2
Figure 3A~4C
AI summary
A magnetic resonance imaging (MRI) system (500), the system includes at least one controller (510) which performs a modified rotated slab excitation (mROSE) sequence for volume selection to exclude portions of a subject under exam which are within the scanning volume and outside of a field-of-view (FOV) so as to reduce foldover artifacts which originate from the excluded portions of the subject under exam, where the mROSE sequence performs volume excitation based upon either optimized symmetrical, minimum-phase, or stretched minimum-phase radio- frequency (RF) pulses in a sagittal plane and encodes the scanning volume in a coronal plane. The controller also performs a chemical-shift sequence including a modified DIXON (mDIXON) sequence for substantially uniform fat/water separation within a FOV which lies within the scanning volume; and/or acquires echo information for reconstructing at least a part of an image.