Pulsed RF Sequences for Arterial Spin Labeling MRI
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Solution Overview
Problem
Conventional MRI techniques for imaging fluid flow and perfusion face challenges such as image artifacts due to magnetization transfer effects and excessive RF power deposition, which are difficult to manage with existing commercially available equipment.
Innovation Solution
The use of pulsed RF sequences and amplitude modulated magnetic gradient sequences that alternate between nonzero and zero amplitude periods, allowing for safer and more efficient imaging by reducing RF power deposition and enabling standard MRI equipment to generate the necessary signals without overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional continuous RF sequences are used for spin labeling, then adequate labeling of flowing fluid can be achieved, but excessive RF power deposition occurs causing equipment overheating and safety issues
Solution Approach 1:
The patent applies periodic pulsed RF sequences instead of continuous RF waves for spin labeling. The RF pulses are delivered in periodic trains with specific timing intervals, allowing the system to achieve adequate spin labeling of flowing fluid while reducing average RF power deposition. This periodic action enables standard MRI equipment to operate within safety limits while maintaining imaging capability.
2Illumination intensity
If higher RF power is used to improve signal strength, then better imaging quality is achieved, but magnetization transfer artifacts increase
Solution Approach 1:
The patent changes the temporal parameters of RF delivery by using pulsed sequences with specific pulse widths, repetition times, and duty cycles. This parameter modification allows achieving adequate signal strength for fluid flow imaging while reducing the continuous exposure that causes magnetization transfer artifacts. The pulsed nature of the RF sequence modulates the interaction between RF energy and tissue magnetization.
3Ease of manufacture
If standard MRI equipment is used, then accessibility and cost-effectiveness are improved, but the equipment cannot generate sufficient RF power for adequate spin labeling
Solution Approach 1:
The patent enables standard MRI equipment to perform spin labeling by using periodic pul RF sequences that operate within the equipment's existing power capabilities. The pulsed delivery method allows accumulation of labeling effect over multiple pulses while keeping instantaneous and average power within safe limits for commercial equipment, thus making the technique accessible without requiring specialized high-power systems.
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 accurate imaging of fluid flow and perfusion while minimizing artifacts and RF power deposition, making it feasible with commercially available MRI equipment and ensuring safer imaging procedures.
Implementation Method 1
MRI is based on detecting nuclear magnetic resonance (NMR) signals emitted by molecules under the influence of electro-magnetic fields. In particular, magnetic resonance (MR) techniques involve detecting electro-magnetic changes resulting from re-alignment of atomic spin of molecules in the tissue of the human body.
Implementation Method 2
The NMR phenomenon is invoked by the RF signals, applied at the Larmor frequency, exciting the hydrogen nuclei and causing the spin to briefly precess about an axis in the direction of the applied RF signal, rather than in the direction of the applied magnetic field. The Larmor frequency is related to the rate at which a nucleus precesses about an axis, which is, in turn, proportional to the strength of the applied magnetic field.
Implementation Method 3
By applying a gradient magnetic field to align the spins, the spin inversion effect may be localized to a particular region of interest. In particular, to achieve spin inversion, the RF field is applied at an appropriate frequency (i.e., the Larmor frequency), which depends, at least in part, on the strength of the magnetic field.
Implementation Method 4
The NMR signals may be detected using one or more RF coils sensitive to electromagnetic changes caused by the NMR signals.
Data Source
AI summary
In one aspect, a method for imaging fluid flow and/or perfusion using spin labeling is provided. The method comprises applying a first magnetic gradient sequence at least to a labeling region, applying a first pulsed radio frequency (RF) sequence to the labeling region to label the fluid, the first pulsed RF sequence comprising a first plurality of pulses wherein an amplitude envelope is non-zero, the first plurality of pulses each separated by a respective first plurality of intervals wherein the amplitude envelope is substantially zero, and acquiring at least one first signal emitted from an imaging region a predetermined delay after applying the first pulsed RF sequence.