STONE Pulse Sequence for Free-Breathing T1 Mapping
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Solution Overview
Problem
Current T1 mapping techniques in MRI, such as MOLLI, suffer from inaccurate T1 estimates due to heart rate variability, sensitivity to T2 times, and magnetization transfer dependencies, and require lengthy scan times and multiple breath-holds for full left ventricular coverage, which is inconvenient for patients.
Innovation Solution
The slice-interleaved T1 (STONE) pulse sequence allows for free-breathing multi-slice T1 mapping with volumetric LV coverage by interleaving data acquisition from different slices during the recovery time of adjacent slices, using a method that includes a first acquisition block for fully recovered longitudinal magnetization and a second block with a single inversion of longitudinal magnetization followed by a recovery period, repeated multiple times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If MOLLI pulse sequence samples longitudinal magnetization recovery curve multiple times after a single magnetization preparation pulse, then scan time is reduced, but T1 measurement accuracy deteriorates due to heart rate variability, sensitivity to T2 times, and magnetization transfer dependencies
Solution Approach 1:
The patent divides the imaging process into multiple separate 2D scans for different slices, each requiring its own breath-hold and magnetization preparation. This segmentation allows each slice to be independently optimized for accurate T1 measurement while reducing the overall scan time by eliminating the need for multiple sampling points per slice.
Solution Approach 2:
The patent performs full longitudinal magnetization recovery before each acquisition block, ensuring that the magnetization is fully reset prior to measurement. This preliminary action eliminates the need for multiple sampling points during recovery, as each slice is measured from a known starting state, improving accuracy while reducing total scan time.
2Area of stationary object
If multiple separate 2D scans are performed for different slices to obtain complete LV coverage, then full ventricular coverage is achieved, but scan time increases and patient convenience deteriorates due to numerous breath-holds
Solution Approach 1:
The patent performs multiple acquisition blocks sequentially, with each block acquiring data from all slices during their respective recovery periods. This continuous approach maintains full LV coverage while minimizing idle time between acquisitions, reducing total scan time compared to traditional methods that require repeated breath-holds.
Solution Approach 2:
The patent uses periodic inversion pulses applied at regular intervals between acquisition blocks, allowing longitudinal magnetization to recover fully before each measurement series. This periodic resetting enables efficient multi-slice coverage with reduced breath-hold requirements.
3Measurement precision
If extensive rest periods are inserted between inversion pulses in traditional T1 mapping, then T1 measurement accuracy is improved, but scan time increases significantly
Solution Approach 1:
The patent performs full longitudinal magnetization recovery before each acquisition block, ensuring that the magnetization is fully reset prior to measurement. This preliminary recovery action eliminates the need for extensive rest periods between inversion pulses, as each slice is measured from a known fully-recovered state, thereby reducing scan time while maintaining accuracy.
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 provides more accurate and precise T1 mapping with reduced scan time, eliminating the need for extensive rest periods and breath-holds, resulting in improved patient convenience and clinical applicability.
Implementation Method 1
When a substance such as human tissue is subjected to a uniform magnetic field, i.e., a static magnetic field B0, the individual magnetic moments of the nuclear spins in the tissue attempt to align with the static magnetic field B0
Implementation Method 2
If, however, the substance is subjected to a magnetic excitation field B1 which is in the x-y plane and which is near the Larmor frequency, the net magnetization aligned moment Mz may be rotated, i.e., tipped, into the x-y plane to generate a net transverse magnetic moment Mt
Implementation Method 3
An MR signal is emitted by the excited nuclei, i.e., spins, after the excitation magnetic field B1 is terminated, and the MR signal may be received by a radio-frequency (RF) coil
Implementation Method 4
the amplitude of the MR signal is dependent on the spin-lattice relaxation process that is characterized by the time constant T1, i.e., a spin-lattice relaxation time. It describes the recovery of the net magnetic moment M to its equilibrium value along the axis of magnetic polarization, i.e., z-magnetization
Data Source
AI summary
An MRI method includes: performing a first data acquisition block of a pulse sequence to acquire a first MR data from a plurality of slices of a subject during a period of fully recovered longitudinal magnetization within the plurality of slices disposed at different locations in the subject; performing a second data acquisition block of the pulse sequence including a magnetization preparation module followed by a recovery period and an imaging sequence executed during the recovery period, to acquire a second MR data from the plurality of slices during the recovery period; and generating a T1 map of the subject based on the first MR data and the second MR data, of the plurality of slices.