Dixon Water Fat Separation MR Imaging Sequence
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Solution Overview
Problem
Conventional dual-acquisition Dixon gradient-echo MR imaging sequences suffer from reduced scan efficiency due to dead time introduced by shifting the readout magnetic field gradient, which increases scan time and decreases the ratio of acquisition time to repetition time.
Innovation Solution
Implementing a dual-acquisition gradient-echo imaging sequence with partial echo acquisition, where the duration and strength of the readout magnetic field gradient are adjusted to eliminate dead time, allowing for longer acquisition time without compromising image resolution, and optimizing scan efficiency by varying the partial echo factor in accordance with phase-encoding constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the readout magnetic field gradient is shifted in conventional dual-acquisition Dixon gradient-echo imaging, then water/fat separation is achieved, but dead time is introduced which reduces scan efficiency
Solution Approach 1:
The patent applies partial echo acquisition where only a portion of the echo signal is sampled instead of the complete echo. By acquiring partial echoes at two different echo times with alternating patterns, the method achieves water/fat separation through Dixon-type processing while reducing the gradient shifting requirements, thereby eliminating dead time and improving scan efficiency
Solution Approach 2:
The patent implements alternating echo time patterns where the echo time alternates between a first value and a second value in successive repetitions of the gradient-echo imaging sequence. This periodic alternation enables Dixon water/fat separation while maintaining continuous gradient operation without dead time intervals
2Measurement precision
If the readout magnetic field gradient is shifted to achieve Dixon water/fat separation, then chemical shift encoding is enabled, but the acquisition time to repetition time ratio decreases
Solution Approach 1:
By sampling only partial echoes rather than complete echoes, the method reduces the time required for gradient shifting and repositioning between acquisitions. This partial sampling approach maintains sufficient data for Dixon water/fat separation and chemical shift encoding while increasing the effective acquisition time to repetition time ratio
Solution Approach 2:
The alternating partial echo acquisition pattern ensures continuous useful data collection throughout the repetition cycle. By eliminating dead time through continuous gradient operation and strategic partial sampling, the method maximizes the proportion of repetition time dedicated to actual signal acquisition and water/fat separation
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 eliminates dead time in conventional dual-acquisition Dixon gradient-echo imaging, enhancing scan efficiency by increasing acquisition time for partially sampled echoes while maintaining image resolution, and allowing for superior water/fat separation in MR imaging.
Implementation Method 1
at least one main magnet coil for generating an essentially uniform, static magnetic field B0 within an examination volume
Implementation Method 2
a number of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume
Implementation Method 3
at least one body RF coil for generating RF pulses within the examination volume and/or for receiving MR signals from a body of a patient positioned in the examination volume
Implementation Method 4
The magnetic field B0 produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency)
Data Source
AI summary
The invention relates to a method of Dixon-type MR imaging of an object (10) placed in an examination volume of a MR device (1). It is an object of the invention to provide a method that enables an improved Dixon water/fat separation in combination with a dual-acquisition gradient-echo imaging sequence. The method comprises the steps of: —subjecting the object (10) to a dual-acquisition gradient-echo imaging sequence comprising a series of temporally equidistant RF excitations, wherein one gradient echo is generated in each repetition time between successive RF excitations with the echo time alternating between a first and a second value (TE1, TE2), and wherein phase-encoding magnetic field gradients (P, S) are switched in each repetition time to sample a pre-defined region of k-space; —acquiring echo signals from the object (10), wherein each gradient echo associated with either the first or the second echo time value (TE1, TE2) is sampled as a partial echo, and —reconstructing an MR image from the acquired echo signals, whereby signal contributions from water and fat are separated. Moreover the invention relates to an MR device (1) and to a computer program to be run on an MR device (1).