SPACE MRI Flow Artifact Reduction via Gradient Timing

Solution Overview

Problem

Conventional single slab SPACE imaging is prone to flow-related artifacts in the readout direction due to the long time duration between the dephasing gradient and the first application of the readout gradient, making the sequence overly sensitive to flow, resulting in signal voids and increased acquisition time.

Innovation Solution

Shifting the dephasing gradient to be activated immediately before the second refocusing RF pulse and incorporating spoiler gradients around the first refocusing pulse to reduce sensitivity to flow and magnetic field inhomogeneities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the dephasing gradient is applied after the excitation RF pulse in conventional SPACE imaging, then the sequence can acquire magnetic resonance data, but the long time duration between dephasing gradient and first readout gradient causes flow-related artifacts in the readout direction

Engineering Contradiction:

Improveflow-related artifactsVSAvoidacquisition time

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

The dephasing gradient is applied preliminarily immediately before the second refocusing RF pulse rather than after the excitation RF pulse. This preliminary positioning of the dephasing gradient reduces the time duration during which moving spins can accumulate phase differences, thereby reducing flow-related artifacts while maintaining acceptable acquisition time

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The timing parameter of the dephasing gradient application is changed from post-excitation to pre-second-refocusing position. This parameter change in the pulse sequence timing alters the echo spacing and reduces sensitivity to flow in the readout direction without significantly increasing acquisition time

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the phase-encoding direction is aligned with the cranio-caudal axis to address flow artifacts, then flow sensitivity is reduced, but a large number of phase-encoding steps are needed resulting in very long acquisition time

Engineering Contradiction:

Improveflow artifactsVSAvoidacquisition speed

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The dephasing gradient is applied preliminarily immediately before the second refocusing RF pulse rather than after the excitation RF pulse. This preliminary positioning of the dephasing gradient reduces the time duration during which moving spins can accumulate phase differences, thereby reducing flow-related artifacts while maintaining acceptable acquisition time

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The timing parameter of the dephasing gradient application is changed from post-excitation to pre-second-refocusing position. This parameter change in the pulse sequence timing alters the echo spacing and reduces sensitivity to flow in the readout direction without significantly increasing acquisition time

Inventive Principle:

Principle #35Parameter changes

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

Significantly reduces flow-related artifacts and acquisition time by minimizing the impact of motion on detected magnetic resonance signals and improving image quality by eliminating signal voids and infolding artifacts.

Implementation Method 1

magnetic resonance data are acquired according to a SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) or equivalent pulse sequence

Methodology Applied

Scientific EffectMagnetic resonance:

Implementation Method 2

the net effect of the dephasing gradient and first application of a readout gradient on the excited (transverse) magnetization of moving nuclear spins may be, depending on the degree of motion, substantially different than that corresponding to stationary nuclear spins, which leads to a motion-induced phase difference in the detected magnetic resonance signal

Methodology Applied

Scientific EffectGradient-induced phase encoding:

Implementation Method 3

Highly sophisticated spin-echo pulse sequences include a single-slab 3D turbo or fast spin-echo pulse sequence known, for example, as SPACE

Methodology Applied

Scientific EffectSpin echo:

Implementation Method 4

The curve that represents the variation of the flip angles is designed to achieve desired signal strengths for different types of tissue (nuclear spins), and is referred to as the flip angle evolution

Methodology Applied

Scientific EffectFlip angle evolution:

Implementation Method 5

this direction is more sensitive to flow

Methodology Applied

Scientific EffectFrequency encoding:

Data Source

PatentUS9360545B2Magnetic resonance system and operating method for flow artifact reduction in slab selective space imaging

Publication Date: 2016.06.07 SIEMENS HEALTHINEERS AG

AI summary

In a SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) or equivalent magnetic resonance imaging pulse sequence, the dephasing gradient is generated (activated) so as to occur immediately in front of the second refocusing pulse, thereby eliminating the long time duration that occurs in conventional SPACE or equivalent sequences between excitation and readout. This long time duration has been identified as a source for flow-related artifacts that occur in images reconstructed from data acquired according to conventional SPACE or equivalent sequences. By eliminating this long time duration, such flow-related artifacts are substantially reduced, if not eliminated.