MR fingerprinting using fast imaging with steady state precession (FISP) with spiral readout

Abstract

Purpose: This study explores the possibility of using gradient echo-based sequences other than balanced steady-state free precession (bSSFP) in the magnetic resonance fingerprinting (MRF) framework to quantify the relaxation parameters .

Methods: An MRF method based on a fast imaging with steady-state precession (FISP) sequence structure is presented. A dictionary containing possible signal evolutions with physiological range of T1 and T2 was created using the extended phase graph formalism according to the acquisition parameters. The proposed method was evaluated in a phantom and a human brain. T1 , T2 , and proton density were quantified directly from the undersampled data by the pattern recognition algorithm.

Results: T1 and T2 values from the phantom demonstrate that the results of MRF FISP are in good agreement with the traditional gold-standard methods. T1 and T2 values in brain are within the range of previously reported values.

Conclusion: MRF-FISP enables a fast and accurate quantification of the relaxation parameters. It is immune to the banding artifact of bSSFP due to B0 inhomogeneities, which could improve the ability to use MRF for applications beyond brain imaging.

Keywords: FISP; MR fingerprinting; quantitative imaging; relaxation time; spiral.

Figure 1

a: A pulse sequence diagram of the MRF-FISP sequence. An adiabatic inversion pulse is followed by a series of FISP acquisitions. b: A sinusoidal variation of flip angles, and repetition times in a Perlin noise pattern, are used in the MRF-FISP sequence. c: One interleaf of a variable density spiral trajectory is used in each repetition. The spiral trajectory is zero moment compensated. It needs 24 interleaves to fully sample the center of the k space, and 48 interleaves for 256*256. The trajectory rotates 7.5 degrees every repetition.

Figure 2

T₁ (a), T₂ (b) and proton density (c) maps of the phantom with varied concentration of gadolinium and agarose generated using MRF-FISP.

Figure 3

a-b: The comparison of T₁ (a) and T₂ (b) values of MRF-FISP with the standard spin echo methods. c-d: T₁ and T₂ values and their standard deviations measured by MRF-FISP for each tube with increasing acquisition time (the number for frames). e-f: The efficiency of MRF-FISP compared to the efficiency of MRF-bSSFP at different T₁ and T₂ values.

Figure 4

a: The field maps at different shim settings. The correlations of T₁ (b) and T₂ (c) between the results of MRF-FISP at different shim settings and the results from the spin-echo methods.

Figure 5

A set of representative dictionary entries with a) T₁ values from 700 ms to 900 ms with 50 ms gap, and T₂ of 85 ms, b) a fixed T₁ value of 795 ms and T₂ values from 60 ms to 100 ms with 10 ms gap.

Figure 6

The representative images, the signal curves of one voxel with T₁ of 795 ms and T₂ of 85 ms, their matched dictionary entries from a fully sampled data (a), and retrospectively undersampled data at rate (R) of 4 (b), 12 (c), and 48 (d). For comparison of the signal-to-noise ratio among the data with different R, the plotted signals were normalized to the maximum of the fully sampled data.

Figure 7

a: An example of the undersampled images from MRF-FISP. b: A representative time course of one pixel as indicated by the white circle in (a) and its matched dictionary entry. The estimated T₁ and T₂ values of this pixel are 750 ms and 65 ms, respectively. The longitudinal axis represents the fraction of the full magnetization that is equal to one.

Figure 8

T₁ (a), T₂ (b) and proton density maps (c) generated from an asymptomatic volunteer with the MRF-FISP acquisition. The unbalanced gradient moment along the slice selection gradient achieves 8pi dephasing per voxel.

Figure 9

a: T₁-weighted images calculated from the maps in Figure 8 with TR = 250 ms and TE = 2.5 ms; b: T₂-weighted images using TR = 10000 ms and TE = 90 ms and c: FLAIR images calculated with TI = 3600 ms, TE = 90 ms.