APT MR Imaging with Intrinsic B0 Correction and Fat Elimination
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Solution Overview
Problem
Conventional APT and CEST MR imaging techniques face challenges with B0 inhomogeneity correction and fat signal elimination, leading to inefficient scan times and artifacts, especially in applications with significant fat content.
Innovation Solution
A method involving saturation RF pulses with varying frequency offsets and echo time shifts in a spin echo-based sequence, combined with a multi-point Dixon technique for intrinsic B0 determination and water/fat separation, allowing for efficient and precise MR imaging without additional B0 mapping scans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional APT and CEST MR imaging techniques are used, then contrast enhancement is achieved, but B0 inhomogeneity correction and fat signal elimination require additional scans and time
Solution Approach 1:
The patent combines B0 mapping, fat signal elimination, and APT/CEST contrast enhancement into a single integrated MR imaging sequence. The multi-echo spin-echo sequence simultaneously acquires data for B0 field mapping and fat suppression while maintaining APT/CEST contrast, eliminating the need for separate preliminary scans and reducing total acquisition time.
Solution Approach 2:
The MR imaging sequence is designed to perform multiple functions simultaneously: it provides B0 field mapping for inhomogeneity correction, eliminates fat signals through multi-echo Dixon techniques, and maintains APT/CEST contrast enhancement. This multi-functional approach allows a single sequence to replace multiple separate scans.
2Measurement precision
If separate B0 mapping scans are performed for APT/CEST imaging, then B0 inhomogeneity correction is improved, but the overall acquisition time increases
Solution Approach 1:
The patent merges B0 field mapping with the APT/CEST imaging sequence by incorporating multiple echo times within the same scan. The multi-echo spin-echo sequence acquires signals at different echo times (TE1, TE2, TE3) that are used to calculate B0 field maps, eliminating the need for separate B0 mapping scans and improving imaging efficiency.
Solution Approach 2:
The B0 field mapping is performed intrinsically during the APT/CEST imaging sequence itself rather than as a separate preliminary step. The multi-echo data acquisition is designed to simultaneously provide both the B0 field information needed for correction and the contrast enhancement data, optimizing the use of scan time.
3Measurement precision
If multi-echo spin-echo sequences are used with varying echo times, then intrinsic B0 determination is achieved, but sequence complexity increases
Solution Approach 1:
The patent segments the MR imaging sequence into multiple echo acquisitions (TE1, TE2, TE3) within a single scan, where each echo time provides specific information for B0 field mapping. The sequence is divided into multiple repetitions with different saturation frequency offsets and echo times, allowing systematic data collection for intrinsic B0 determination while maintaining structured organization.
Solution Approach 2:
The sequence employs periodic repetition of saturation RF pulses at different frequency offsets combined with multi-echo spin-echo acquisitions. The periodic structure with varying parameters (saturation offset, echo time) enables systematic collection of data needed for B0 mapping and fat suppression while maintaining a regular, manageable sequence pattern.
4Measurement precision
If saturation RF pulses are applied at multiple frequency offsets, then APT/CEST contrast enhancement is achieved, but the number of required scans increases
Solution Approach 1:
The patent merges multiple saturation frequency offset acquisitions into a single multi-echo spin-echo sequence. By repeating the sequence with different saturation offsets (e.g., -3.5 ppm, -2.5 ppm, -1.5 ppm, +1.5 ppm, +2.5 ppm, +3.5 ppm) and varying echo times within the same scan, it simultaneously collects data for APT/CEST contrast enhancement and B0 field mapping, reducing total acquisition time.
Solution Approach 2:
The sequence maintains continuous useful action by performing APT/CEST contrast enhancement and B0 field mapping in a single integrated acquisition rather than separate scans. The multi-echo spin-echo sequence continuously collects data at multiple frequency offsets and echo times, maximizing the utility of each scan repetition and eliminating idle time between separate scanning tasks.
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 enables high-quality, high-contrast MR imaging with reduced acquisition time and improved precision by intrinsic B0 correction and robust fat signal elimination, enhancing clinical efficiency and image accuracy.
Implementation Method 1
Image-forming MR methods which utilize the interaction between magnetic fields and nuclear spins
Implementation Method 2
subjecting the portion of the body to a saturation RF pulse at a saturation frequency offset
Implementation Method 3
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)
Implementation Method 4
the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time)
Implementation Method 5
the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Implementation Method 6
The variation of the magnetization can be detected by means of receiving RF coils which are arranged and oriented within the 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
Implementation Method 7
The dephasing can be compensated by means of a refocusing pulse (for example a 180° pulse). This produces an echo signal (spin echo) in the receiving coils
Implementation Method 8
the dephasing can be compensated by means of a magnetic gradient pulse, producing an echo signal (gradient echo) in the receiving coils
Implementation Method 9
In order to realize spatial resolution in the body, linear magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field, leading to a linear spatial dependency of the spin resonance frequency
Data Source
AI summary
The invention relates to a method of CEST or APT MR imaging of at least a portion of a body (10) placed in a main magnetic field B0 within the examination volume of a MR device. The method of the invention comprises the following steps: •a) subjecting the portion of the body (10) to a saturation RF pulse at a saturation frequency offset; •b) subjecting the portion of the body (10) to an imaging sequence comprising at least one excitation/refocusing RF pulse and switched magnetic field gradients, whereby MR signals are acquired from the portion of the body (10) as spin echo signals; •c) repeating steps a) and b) two or more times, wherein the saturation frequency offset and/or a echo time shift in the imaging sequence are varied, such that a different combination of saturation frequency offset and echo time shift is applied in two or more of the repetitions; •d) reconstructing a MR image and/or B0 field homogeneity corrected APT/CEST images from the acquired MR signals. Moreover, the invention relates to a MR device (1) for carrying out the method of the invention and to a computer program to be run on a MR device.