Systems and methods for acceleration magnetic resonance fingerprinting
Systems and methods for accelerating magnetic resonance fingerprinting (“MRF”} acquisitions are described. Acquisition parameters can be optimized to reduce the number of acquisitions necessary while maximizing the discrimination between the physical parameters to be estimated. The systems and methods may also include implementing pulse sequences that rapidly acquire large volumes of k-space data, including echo-planar imaging (“EPI”} and segmented EPI sequences.
1. A method for estimating quantitative parameters of a subject using a magnetic resonance imaging (MRI) system, the steps of the method comprising:
(a) estimating acquisition parameters that are optimized to direct an MRI system to generate a plurality of different signal evolutions that maximize discrimination between different quantitative parameters in a minimized number of repetition time (TR) periods; wherein estimating the acquisition parameters includes minimizing an objective function that simulates the acquisition parameters and computing a matrix that is based on estimated values of the acquisition parameters and the quantitative parameters to be estimated;
(b) acquiring data with the MRI system by directing the MRI system with a gradient system and a radio frequency (RF) system to perform a plurality of pulse sequences using the optimized acquisition parameters, the acquired data representing the plurality of different signal evolutions that maximize discrimination between different quantitative parameters; and
(c) estimating quantitative parameters of the subject by comparing the acquired data with a dictionary database comprising a plurality of different signal templates.
2. The method as recited in claim 1 , wherein step (a) includes selecting initial estimates of the acquisition parameters and forming the matrix based on the initial estimates.
3. The method as recited in claim 2 , wherein the initial estimates of the acquisition parameters are selected by randomly generating values for the acquisition parameters.
4. The method as recited in claim 1 , wherein the matrix comprises a first matrix that defines a dot product between a second matrix and a transpose of the second matrix, wherein the second matrix includes estimates of the acquisition parameters and simulated values for the quantitative parameters.
5. The method as recited in claim 1 , wherein the objective function is minimized by searching for the acquisition parameters that minimize a difference between a sum of off-diagonal elements of the matrix and a sum of on-diagonal elements of the matrix.
6. The method as recited in claim 5 , wherein the sum of on diagonal elements of the matrix is weighted by a penalty term to avoid minimizing the on-diagonal elements.
7. The method as recited in claim 1 , wherein the plurality of pulse sequences performed in step (b) are echo-planar imaging (EPI) pulse sequences.
8. The method as recited in claim 7 , wherein each EPI pulse sequence samples k-space in satisfaction of a Nyquist criterion.
9. The method as recited in claim 8 , wherein each EPI pulse sequence sampling k-space along a Cartesian trajectory.
10. The method as recited in claim 7 , wherein the EPI pulse sequences are segmented EPI pulse sequences that each sample less than a full extent of k-space.
11. The method as recited in claim 7 , wherein each EPI pulse sequence is a spin-echo EPI pulse sequence.
12. The method as recited in claim 1 , wherein step (c) includes reconstructing images from the acquired data and comparing the reconstructed images to the dictionary database.
13. A method for estimating quantitative parameters of a subject using a magnetic resonance imaging (MRI) system, the steps of the method comprising:
(a) acquiring data with the MRI system by directing the MRI system with a gradient system and a radio frequency (RF) system to perform an echo-planar imaging (EPI) pulse sequence that samples k-space in during each of a plurality of different repetition time (TR) periods, the acquired data representing a plurality of different signal evolutions acquired using different acquisition parameter settings in each TR period; and
(b) estimating quantitative parameters of the subject by minimizing an objective function that simulates the acquisition parameter, computing a matrix that is based on estimated values of the acquisition parameters and the quantitative parameters to be estimated and comparing the acquired data with a dictionary database comprising a plurality of different signal templates.
14. The method as recited in claim 13 , wherein the EPI pulse sequence samples k-space along a Cartesian trajectory.
15. The method as recited in claim 13 , wherein the EPI pulse sequence is a spin-echo EPI pulse sequence.
16. The method as recited in claim 13 , further comprising estimating acquisition parameter settings that are optimized to direct the MRI system to generate different signal evolutions that maximize discrimination between different quantitative parameters in the plurality of different TR periods.
17. A magnetic resonance imaging (MRI) system, comprising:
a magnet system configured to generate a polarizing magnetic field about at least a portion of a subject arranged in the MRI system;
a magnetic gradient system including a plurality of magnetic gradient coils configured to apply at least one magnetic gradient field to the polarizing magnetic field;
a radio frequency (RF) system configured to apply an RF field to the subject and to receive magnetic resonance signals from the subject using a coil array;
a computer system programmed to:
estimate acquisition parameters to generate a plurality of different signal evolutions that achieve a desired discrimination between different quantitative parameters in a desired number of repetition time (TR) periods; wherein estimating the acquisition parameters includes minimizing an objective function that simulates the acquisition parameters and computing a matrix that is based on estimated values of the acquisition parameters and the quantitative parameters to be estimated;
control the magnetic gradient system and the RF system to acquire data using the estimated acquisition parameters, the data representing the plurality of different signal evolutions that achieve a desired discrimination between different quantitative parameters; and
estimate quantitative parameters of the subject by comparing the acquired data with a dictionary database comprising a plurality of different signal templates.
18. The system as recited in claim 17 , wherein the computer system is configured to control the magnetic gradient system and the RF system to acquire the data by performing an echo-planar imaging (EPI) pulse sequence that samples k-space in satisfaction of a Nyquist criterion during each of a plurality of different repetition time (TR) periods.
19. The system of claim 17 , wherein the computer system is configured to determine optimized acquisition parameters such that the data representing the plurality of different signal evolutions maximizes discrimination between different quantitative parameters.