Parallel Multi-Slice MR Imaging Side-Band Artefact Suppression
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Solution Overview
Problem
Conventional parallel multi-slice MR imaging techniques suffer from side-band artefacts due to unintentional excitation of MR signals by higher order harmonics of the fundamental frequency of multi-slice RF pulses, which are not effectively suppressed, limiting image quality.
Innovation Solution
A method that uses a parallel image reconstruction algorithm, such as SENSE, to separate and suppress side-band artefacts by employing a signal model that distinguishes between main-band and side-band signal contributions based on the spatial sensitivity profiles of RF coils, without requiring prior information about the excitation spectra, and iteratively adjusts the ratio of these contributions to achieve convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If parallel multi-slice MR imaging is performed using multi-slice RF pulses, then imaging efficiency is improved, but side-band artefacts occur due to unintentional excitation by higher order harmonics
Solution Approach 1:
The patent extracts and separates the harmful side-band artefact signals from the desired main-band MR signals during the image reconstruction process. By modeling the signal as a combination of main-band and side-band components and using the spatial sensitivity profiles of multiple RF coils, the reconstruction algorithm isolates and removes the side-band contributions, leaving only the clean main-band image data.
Solution Approach 2:
The patent converts the harmful side-band artefacts into useful information by utilizing their distinct spatial distribution patterns across multiple RF coils. The side-band signals, while unwanted in the final image, provide additional spatial encoding information that helps the reconstruction algorithm differentiate and separate them from the main-band signals through the use of coil sensitivity profiles.
2Ease of operation
If conventional parallel imaging reconstruction is used, then image reconstruction is achieved, but side-band artefacts are not suppressed
Solution Approach 1:
The patent segments the total MR signal into distinct components: main-band signal contributions from the desired slices and side-band signal contributions from unintentionally excited regions. This segmentation is achieved by creating separate signal models for each component and using the spatial sensitivity profiles of multiple RF coils to differentiate them, allowing independent processing and suppression of the side-band portion.
Solution Approach 2:
The patent introduces an intermediary signal model that acts as a mediator between the raw acquired signals and the final reconstructed image. This signal model explicitly accounts for both main-band and side-band contributions and uses the spatial sensitivity profiles of RF coils as intermediary information to separate and suppress the side-band artefacts during reconstruction.
3Productivity
If multi-slice RF pulses with higher order harmonics are used, then simultaneous excitation of multiple slices is achieved, but unintentional excitation of regions outside target slices occurs
Solution Approach 1:
The patent extracts the harmful signals from regions unintentionally excited by higher order harmonics of the multi-slice RF pulses. By modeling the signal contributions from both target and non-target regions and using the spatial sensitivity profiles of multiple RF coils, the reconstruction algorithm identifies and removes the unwanted signal components, retaining only the desired slice information.
Data Source
AI summary
An object (10) placed in an examination volume of a MR device (1) is subject to an imaging sequence including multi-slice RF pulses for simultaneously exciting two or more spatially separate image slices. MR signals are received in parallel via a set of RF coils (11, 12, 13) having different spatial sensitivity profiles within the examination volume. An MR image is reconstructed for each image slice from the acquired MR signals. MR signal contributions from the different image slices are separated on the basis of the spatial sensitivity profiles of the RF coils (11, 12, 13). Side-band artifacts, namely MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, are suppressed in the reconstructed MR images on the basis of the spatial sensitivity profiles of the RF coils (11, 12, 13).