CEST MRI Signal Acquisition Using Dual-Sequence K-Space Merging
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Solution Overview
Problem
Traditional CEST imaging methods require a lengthy imaging time to generate a Z-spectrum, as they necessitate the acquisition of 161 MR images by applying saturation pulses across a range of frequencies, leading to elongated imaging times and potential failures in data acquisition.
Innovation Solution
The implementation of a magnetic resonance imaging apparatus with sequence control circuitry that performs two sequences under different saturation pulse conditions, where the first sequence acquires MR signals for a low frequency region and the second sequence acquires signals for a high frequency region, with the latter's signals being assigned to the low frequency region to shorten the overall imaging time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple saturation pulses are applied at frequencies from -8 ppm to 8 ppm by increments of 0.1 ppm to accurately obtain CEST effects, then measurement precision of Z-spectrum is improved, but imaging time is significantly elongated
Solution Approach 1:
The patent segments the frequency range into multiple bands and processes them in separate sequences. The first sequence handles frequencies from -8 ppm to 8 ppm, while the second sequence handles frequencies from 0 ppm to 8 ppm. By segmenting the acquisition process and reusing k-space data across sequences, the patent reduces redundant measurements while maintaining measurement precision for CEST effects.
2Reliability
If all k-space data pieces are not obtained by one acquisition, then data completeness is compromised, but re-excitation and re-acquisition of MR signals further elongates imaging time
Solution Approach 1:
The patent performs preliminary acquisition of k-space data in the first sequence that can be reused in the second sequence. By acquiring low-frequency k-space data first and then reusing it in the second sequence while only acquiring high-frequency data, the patent prevents the need for re-excitation and re-acquisition, thereby maintaining data completeness while reducing imaging time.
3Measurement precision
If 161 MR images are generated to create a single Z-spectrum, then measurement precision is improved, but productivity is significantly reduced
Solution Approach 1:
The patent merges the acquisition processes of two sequences by reusing k-space data from the first sequence in the second sequence. Instead of independently acquiring 161 MR images for each sequence, the patent combines the data acquisition strategies, reducing the total number of images that need to be processed while maintaining the accuracy required for Z-spectrum generation.
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 significantly reduces the imaging time for CEST imaging while maintaining the accuracy of the Z-spectrum generation by strategically assigning MR signals from the second sequence to the low frequency region, thereby addressing the inefficiencies of traditional methods.
Implementation Method 1
transmission of a radiofrequency (RF) saturation pulse at a frequency particular to the solute protons causes a phenomenon that saturation is transferred from the solute protons to the water protons, which are supposed to be unsaturated. Such a phenomenon is referred to as chemical exchange saturation transfer (CEST).
Implementation Method 2
a single CEST-based image (hereinafter, CEST image) is obtained by repeatedly applying saturation pulses and acquiring magnetic resonance signals (hereinafter, MR signals) responsive to the applied saturation pulses
Data Source
AI summary
A magnetic resonance imaging apparatus includes sequence control circuitry and processing circuitry. In CEST imaging the sequence control circuitry performs a first sequence and a second sequence under different saturation pulse conditions. The first sequence is for acquiring first magnetic resonance signals corresponding to a first frequency region of a k-space and second magnetic resonance signals corresponding to a second frequency region of the k-space. The second sequence is for acquiring third magnetic resonance signals corresponding to at least the first frequency region. The processing circuitry assigns the third magnetic resonance signals and the second magnetic resonance signals to a single k-space generated for the second sequence. Frequency including the first frequency region is lower than frequency including the second frequency region.