Split-Echo MRI Gradient Segmentation for Phase Roll Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In MRI SSFP imaging, long TR intervals lead to phase roll artifacts due to inhomogeneities in the main magnetic field, especially when higher matrix scans are performed, which can obscure regions of interest and are unreliable, particularly in areas with rapidly flowing blood.
Innovation Solution
The MRI system splits the echo signal acquisition into three segments, allowing for a reduced minimum TR interval and maintaining scan time for dynamic structures using the MACH sparse sampling scheme, ensuring gradient areas balance to zero during each TR interval and enabling continuous RF pulse production without interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If gradient strength is increased to reduce TR, then TR is reduced, but gradient switching rate must be maximized which may cause mechanical stress and heating
Solution Approach 1:
The patent divides the echo signal acquisition into three separate segments (early, middle, and late echo segments) that are acquired at different times. This segmentation allows the total gradient area to be distributed across multiple shorter gradient pulses rather than requiring one large gradient pulse, thereby reducing the instantaneous gradient strength and mechanical stress while maintaining the same effective TR reduction benefit
Solution Approach 2:
The patent employs periodic gradient pulsing where gradient lobes are applied in a periodic pattern across multiple TR intervals to accumulate the desired k-space coverage. Instead of applying maximum gradient strength continuously, the gradients are applied periodically in a balanced manner that reduces peak stress while achieving the same overall phase encoding effect
2Manufacturing precision
If gradient duration is increased to achieve higher matrix scans, then manufacturing precision is improved, but TR increases causing phase roll artifacts
Solution Approach 1:
The patent segments the k-space acquisition process into three distinct temporal segments (early, middle, late), allowing high-resolution matrix scanning to be achieved by distributing the gradient encoding steps across multiple shorter TR intervals rather than requiring one long gradient duration per TR
Solution Approach 2:
The patent introduces a temporal dimension to the k-space sampling process by acquiring different segments of k-space at different times within a multi-TR sequence. This transforms a single-dimension (time) gradient application problem into a multi-dimensional solution where gradient strength, duration, and timing are optimized across multiple TR intervals
3Stress or pressure
If TR is increased to reduce gradient strength, then gradient stress is reduced, but phase roll artifacts increase due to B0 inhomogeneities
Solution Approach 1:
By segmenting the echo acquisition into three parts acquired at different TR intervals, the patent enables the use of lower gradient strengths (reducing stress) while maintaining short effective TR for each segment. This prevents the phase accumulation that causes roll artifacts because each segment experiences a short TR despite the total acquisition time being extended
Solution Approach 2:
The patent applies preliminary gradient balancing where the sum of gradient areas across all three segments is pre-calculated and balanced to ensure that the net gradient area equals zero. This preliminary balancing prevents phase accumulation and roll artifacts before the actual imaging sequence begins
4Productivity
If scan time is reduced for dynamic structures, then productivity is improved, but temporal sampling accuracy deteriorates
Solution Approach 1:
The patent segments the dynamic structure imaging into three temporal phases (early, middle, late) within each cardiac cycle or respiratory phase. This allows rapid acquisition of multiple temporal samples during a single breath-hold or cardiac cycle, improving productivity while maintaining temporal sampling accuracy through the distributed temporal sampling pattern
Solution Approach 2:
The patent maintains continuous useful action by acquiring all three echo segments during a single continuous breath-hold or cardiac cycle without interruption. This continuous acquisition ensures that the dynamic structure (e.g., heart or lungs) remains in a consistent physiological state throughout the scan, preserving temporal sampling accuracy while maximizing productivity
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 reduces the risk of phase roll artifacts, allows for higher resolution imaging without increasing TR, and maintains scan time for dynamic structures like the heart, improving image quality and reliability, especially in areas with rapid blood flow.
Implementation Method 1
In MRI, SSFP imaging is widely used since it is a signal rich sequence that provides excellent contrast to noise ratio (CNR) images
Implementation Method 2
the imaging gradients used in an SSFP sequence are applied at their maximal strength and maximum switching rate to ensure a low TR
Implementation Method 3
at least one receiving coil in communication with the controller which receives the RF pulses and provides the RF pulses to the controller for the controller to obtain the image
Data Source
AI summary
An MRI to form an image of a patient includes at least one emitting coil which produces RF pulses and gradients. The MRI includes a controller in communication with the emitting coil for obtaining a steady-state image of the patient, where gradient areas balance to zero for each time repetition (TR) interval, and for causing the emitting coil to produce the RF pulses without interruption during the time repetition interval. The MRI includes at least one receiving coil in communication with the controller which receives the RF pulses and provides the RF pulses to the controller for the controller to obtain the image. A method to form an image of a patient with an MRI. A computer program embodied on a computer readable medium to form an image of a patient with an MRI.