Parallel Multi-Slice MR Imaging With Dynamic Phase Encoding
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Solution Overview
Problem
Current MR imaging techniques using fixed phase-modulation schemes in CAIPIRINHA do not adequately consider a-priori information, leading to sub-optimal phase-modulation and reconstruction performance, particularly in multi-slice imaging.
Innovation Solution
A method employing a multi-shot multi-echo imaging sequence with varying phase offsets in the slice direction, combined with parallel reconstruction algorithms that incorporate spatial sensitivity profiles and phase information of RF coils, to enhance image resolution, reduce geometrical distortions, and increase signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed phase-modulation schemes are used in CAIPIRINHA for multi-slice imaging, then the imaging process is simplified, but reconstruction performance and image quality deteriorate due to sub-optimal phase-modulation
Solution Approach 1:
The patent applies dynamics by transitioning from fixed phase-modulation schemes to variable phase-modulation schemes where the phase offset is varied from shot to shot. This dynamic approach allows the system to adapt phase encoding parameters during the imaging process, optimizing reconstruction performance while maintaining operational feasibility through systematic variation patterns.
Solution Approach 2:
The patent implements parameter changes by varying the phase offset parameter across different shots in the multi-shot sequence. This parameter variation enables optimal conditioning of the reconstruction problem by distributing aliasing artifacts differently in each shot, thereby improving overall reconstruction quality without complicating the basic imaging protocol.
2Productivity
If multiple slices are simultaneously excited using fixed phase offsets, then scan efficiency is improved, but image resolution and geometrical accuracy deteriorate due to sub-optimal slice separation
Solution Approach 1:
The patent applies dynamics by varying the phase offset dynamically across different shots when multiple slices are simultaneously excited. This dynamic phase modulation ensures that aliasing patterns change between shots, enabling optimal separation of slice signals during reconstruction while maintaining the efficiency benefits of simultaneous multi-slice excitation.
Solution Approach 2:
The patent implements periodic action by systematically varying the phase offset in a periodic manner across shots. This periodic variation ensures consistent and predictable aliasing patterns that can be effectively exploited by parallel reconstruction algorithms, improving slice separation and image resolution while maintaining scan efficiency.
3Loss of time
If under-sampled k-space data is acquired from multiple RF coils in parallel, then acquisition time is reduced, but image quality deteriorates due to aliasing artifacts
Solution Approach 1:
The patent applies dynamics by varying the phase offset across different shots during under-sampled parallel acquisition. This dynamic phase modulation creates diverse aliasing patterns in each shot, which when combined with parallel coil data and appropriate reconstruction algorithms, enables effective suppression of aliasing artifacts while maintaining reduced acquisition time.
Solution Approach 2:
The patent implements feedback by using the known phase offset variations and coil sensitivity profiles to guide the reconstruction process. The reconstruction algorithm incorporates this phase information to iteratively separate and reconstruct images from under-sampled data, effectively suppressing aliasing artifacts while maintaining the speed benefits of under-sampling.
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 improves image resolution, reduces geometrical distortions, and increases signal-to-noise ratio by applying flexible phase encoding in the slice direction, optimizing the separation of slice images and reconstruction performance.
Implementation Method 1
The magnetic field 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
Implementation Method 2
The magnetic field 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)
Implementation Method 3
The variation of the magnetization can be detected by means of receiving RF coils which are arranged and oriented within an examination volume of the MR device in such a manner that the variation of the magnetization is measured in the direction perpendicular to the z-axis
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method of MR imaging of an object (10) placed in an examination volume of a MR device (1). The method comprises the steps of: - generating MR signals by subjecting the object (10) to a number N of shots of a multi-echo imaging sequence comprising multi-slice RF pulses (21) for simultaneously exciting two or more spatially separate image slices, with a phase offset in the slice direction being imparted to the MR signals, wherein the phase offset is varied from shot to shot, - acquiring the MR signals, wherein the MR signals are received in parallel via a set of at least two RF coils (11, 12, 13) having different spatial sensitivity profiles within the examination volume, and - reconstructing a MR image for each image slice from the acquired MR signals using a parallel reconstruction algorithm, wherein the MR signal contributions from the different image slices are separated on the basis of the spatial encodings of the MR signals according to the spatial sensitivity profiles of the RF coils (11, 12, 13) and on the basis of the phase offsets attributed to the respective image slices and shots. Moreover, the invention relates to a MR device for carrying out this method as well as to a computer program to be run on a MR device.