Magnetic Resonance Apparatus CEST Imaging Phase Cycling
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Solution Overview
Problem
The CEST method struggles to effectively detect the magnetization transfer of protons due to the appearance of multiple signal reduction peaks near the center frequency, making it difficult to correct shifts in the center frequency and recognize the CEST effect.
Innovation Solution
The magnetic resonance apparatus cycles the phases of RF pulses to create a phase difference between consecutive pulses, allowing for the use of rectangular wave-shaped RF pulses, which shortens the time interval between pulses and enables a larger flip angle per unit time even with small individual flip angles, thereby enhancing the detection of the CEST effect while reducing side lobes in the z-spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the flip angle of RF pulses is increased to enhance CEST effect detection, then the CEST effect becomes more recognizable, but side lobes of the z-spectrum become conspicuous making it difficult to correct center frequency shifts
Solution Approach 1:
The patent segments the RF pulse sequence into multiple pulses with different phase differences. By dividing the saturation process into multiple phase-staggered pulses, the method achieves effective CEST saturation while distributing the energy in a way that reduces side lobe formation in the z-spectrum, thus resolving the contradiction between CEST detection and center frequency correction.
Solution Approach 2:
The patent changes the phase parameter of RF pulses systematically across multiple pulses. By varying the phase difference between consecutive RF pulses, the method modifies the saturation pattern to enhance CEST effect visibility while suppressing side lobe artifacts, thereby enabling both accurate CEST detection and center frequency correction.
2Manufacturing precision
If Gaussian or Blackman filter shaped RF pulses are used to reduce side lobes, then side lobes are sufficiently reduced, but the time interval between pulses increases reducing flip angle efficiency
Solution Approach 1:
The patent employs periodic RF pulses with systematically varying phase differences. This periodic structure allows the use of rectangular wave-shaped pulses with short durations, maintaining high flip angle efficiency while the phase modulation controls side lobe formation, thus resolving the trade-off between pulse efficiency and side lobe suppression.
Solution Approach 2:
The patent introduces dynamic phase variation across the RF pulse sequence. By making the phase parameter dynamic rather than static, the method enables the use of short rectangular pulses that maintain high efficiency while the time-varying phase pattern suppresses side lobes, overcoming the limitation of static pulse shaping methods.
3Productivity
If rectangular wave-shaped RF pulses are used to shorten time interval and increase flip angle per unit time, then productivity increases, but side lobes may become more prominent
Solution Approach 1:
The patent applies systematic phase parameter changes across multiple rectangular RF pulses. This phase modulation transforms the spectral characteristics of the rectangular pulses, suppressing side lobes while maintaining the short pulse duration and high flip angle efficiency inherent to rectangular wave shapes, thus resolving the contradiction between productivity and side lobe suppression.
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 allows for the clear detection of the CEST effect with reduced side lobes, facilitating the identification of the center frequency and improving the accuracy of CEST imaging by using small flip angles for each RF pulse.
Implementation Method 1
pulse sequences each including a plurality of RF pulses for generating magnetization transfer of protons
Implementation Method 2
magnetic resonance apparatus that acquires data of a region at which magnetization transfer of protons occurs
Data Source
AI summary
A magnetic resonance apparatus is provided. The magnetic resonance apparatus includes a scanner configured to execute a plurality of pulse sequences each including a plurality of RF pulses for generating magnetization transfer of protons and a data acquisition sequence for acquiring data from a region in which proton magnetization transfer occurs, wherein the phases of the plurality of RF pulses are cycled so as to make a phase difference between the phase of a pth RF pulse of the plurality of RF pulses and the phase of a p+1th RF pulse of the plurality of RF pulses different for each pulse sequence, and a controller configured to control operations that include processing for determining a spectrum indicative of a relationship between a signal intensity of each signal obtained from the region and the associated phase differences based on data obtained by executing the plurality of pulse sequences.