ASL-MRF Combined MRI Sequence for Simultaneous Perfusion and Tissue Mapping
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Solution Overview
Problem
Conventional Arterial Spin Labeling (ASL) magnetic resonance imaging techniques face limitations in simultaneously acquiring accurate perfusion information and tissue parameters like T1 and T2 due to inefficiencies in encoding relaxation parameters and patient-dependent arterial flow velocities, leading to suboptimal diagnostic information.
Innovation Solution
Integrating Magnetic Resonance Fingerprinting (MRF) into the ASL protocol by using low flip-angle RF pulses during background suppression, allowing for simultaneous acquisition of ASL and MRF data without increasing scan time, and utilizing cerebral blood flow maps to customize the MRF dictionary for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional ASL protocol is used to acquire perfusion information, then accurate cerebral blood flow measurement is achieved, but tissue parameters like T1 and T2 cannot be simultaneously acquired
Solution Approach 1:
The patent combines ASL and MRF protocols into a unified imaging sequence, merging perfusion information acquisition with tissue parameter mapping. The low flip-angle RF pulses used during the ASL post-labeling delay period simultaneously encode both ASL and MRF signals, enabling concurrent acquisition of cerebral blood flow and tissue parameters without separate scanning sessions.
Solution Approach 2:
The imaging sequence is designed to serve multiple functions: it acquires ASL perfusion data through the standard post-labeling delay mechanism while simultaneously capturing MRF signals for T1 and T2 parameter estimation. The same RF pulse train and gradient scheme fulfill both diagnostic needs, making the protocol multi-functional rather than requiring specialized sequences for each parameter type.
2Loss of information
If MRF protocol is added to ASL to acquire tissue parameters, then diagnostic information is improved, but scan time increases
Solution Approach 1:
The patent maintains continuous useful action by utilizing the ASL post-labeling delay period—which would otherwise be idle time for tissue signal recovery—as an opportunity to acquire MRF data. The low flip-angle RF pulses are applied continuously during this delay period, transforming previously wasted time into productive data acquisition time for tissue parameter mapping without extending the overall scan duration.
Solution Approach 2:
The MRF encoding is performed preliminarily during the ASL delay period before the actual ASL image acquisition. By preparing and encoding the MRF signals in advance during the post-labeling delay, the patent ensures that both ASL and MRF data are ready simultaneously, eliminating the need for additional post-processing time or extended scanning.
3Measurement precision
If background suppression is performed during ASL delay, then tagged blood imaging quality is improved, but encoding of relaxation parameters becomes inefficient
Solution Approach 1:
The patent applies different RF pulse characteristics to different spatial and temporal regions: high flip-angle pulses are used for background suppression in static tissues, while low flip-angle pulses are applied during the same period to encode MRF signals in flowing blood. This local differentiation of pulse properties allows simultaneous achievement of background suppression quality and relaxation parameter encoding accuracy without mutual interference.
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 enhances the quality of ASL imaging by providing additional tissue parameter maps, improving diagnostic information and reducing noise artifacts, while maintaining the efficiency of the ASL protocol.
Implementation Method 1
During an MRI scan, Radio Frequency (RF) pulses generated by one or more transmitter coils cause a called B1 field. Additionally applied gradient fields and the B1 field cause perturbations to the effective local magnetic field. RF signals are then emitted by the nuclear spins
Implementation Method 2
A large static magnetic field is used by Magnetic Resonance Imaging (MRI) scanners to align the nuclear spins of atoms as part of the procedure for producing images within the body of a patient
Data Source
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AI summary
The invention provides for a method of operating a magnetic resonance imaging system for imaging a subject. The method comprises acquiring (700) tagged magnetic resonance data (642) and a first portion (644) of fingerprinting magnetic resonance data by controlling the magnetic resonance imaging system with tagging pulse sequence commands (100). The tagging pulse sequence commands comprise a tagging inversion pulse portion (102) for spin labeling a tagging location within the subject. The tagging pulse sequence commands comprise a background suppression portion (104). The background suppression portion comprises MRF pulse sequence commands for acquiring fingerprinting magnetic resonance data according to a magnetic resonance fingerprinting protocol. The tagging pulse sequence commands comprise an image acquisition portion (106). The method comprises acquiring (702) control magnetic resonance data (646) and a second portion (648) of the fingerprinting magnetic resonance data by controlling the magnetic resonance imaging system with control pulse sequence commands. The control pulse sequence commands comprise a control inversion pulse portion (202). The control pulse sequence commands comprise the background suppression portion (104'). The control pulse sequence commands comprise the image acquisition portion (106). The method comprises reconstructing (704) tagged magnitude images (650) using the tagged magnetic resonance data. The method comprises reconstructing (706) a control magnitude images (652) using the control magnetic resonance data. The method comprises constructing (708) an ASL image by subtracting the control magnitude images and the tagged magnitude images from each other. The method comprises reconstructing (710) a series of magnetic resonance fingerprinting images (656) using the first portion of the fingerprinting magnetic resonance data and/or the second portion of the fingerprinting magnetic resonance data. The method comprises generating (712) at least one magnetic resonance parametric map (658) by comparing the series of magnetic resonance fingerprinting images with a magnetic resonance fingerprinting dictionary.