An Accurate Dictionary Creation Method for MR Fingerprinting Using a Fast Bloch Simulator

Abstract

This study proposes an accurate method for creating a dictionary for magnetic resonance fingerprinting (MRF) using a fast Bloch image simulator. An MRF sequence based on a fast imaging with steady precession sequence and a numerical phantom were used for dictionary generation. Cartesian and spiral readout gradients were used for the Bloch image simulation. The validity and usefulness of the method for accurate dictionary creation were demonstrated by MRF parameter maps obtained by pattern matching with the dictionaries generated by the proposed method.

Keywords: Bloch simulator; graphics processing unit; magnetic resonance fingerprinting; spiral.

Fig. 1

(a) A TR unit of the magnetic resonance fingerprinting (MRF) pulse sequence. The spiral readout gradient was used for dictionary as well as MRF image acquisition. The Cartesian readout gradients were also used for dictionary and MRF image acquisition. (b) k-trajectory for the spiral readout gradients with 0th moments. FA, flip angle.

Fig. 2

(a−c) PD, T₁, and T₂ maps of a numerical phantom with various sets of relaxation times stored in the cylindrical containers (diameter = 35 mm, length = 110 mm). The PDs of the materials were constant, and the combinations of (T₁, T₂) (in ms) were (228, 47), (368, 56), (446, 72), (486, 51), (669, 71), (794, 84), (813, 37), (977, 88), (1227, 146), and (1666, 150). The backgrounds of the bottles in the T₁ and T₂ maps were filled with their average values. (d−f) PD, T₁, and T₂ maps of a numerical phantom for an magnetic resonance fingerprinting (MRF) dictionary. The phantom was 170 mm wide, 90 mm high, and 110 mm deep. PD, proton density.

Fig. 3

(a) The 280th image of the relaxation phantom reconstructed from three successive spiral shots acquired with a one-shot magnetic resonance fingerprinting (MRF) sequence. (b) Image intensity measured at the centers of the S01, S02, and S10 samples versus the TR_index.

Fig. 4

(a) The 280th images of the MRF dictionaries acquired with the Cartesian and spiral full sampling magnetic resonance fingerprinting (MRF) sequences. Red, green, and blue (RGB) image (left) and their bird’s eyes view (right). (b) T₂ dependence of the temporal intensity change of the MRF dictionaries acquired with the Cartesian (left) and spiral full (right) sampling MRF sequences without LPF. LPF, low-pass filtering.

Fig. 5

(a−d) Matching results (T₁, T₂, and PD maps) for image datasets of the relaxation time phantom and the two dictionaries, deviation maps from the true values, and correlation plots of designed and measured values for T₁ and T₂. The Cartesian dictionary was used for the matching in (a) and (c) and the spiral dictionary was used for the matching in (b) and (d). The Cartesian sampling magnetic resonance fingerprinting (MRF) image dataset and the full spiral sampling MRF image dataset were used in (a) and (b), respectively. The one-shot spiral sampling MRF image dataset was used for (c) and (d). (e and f). Enlarged ΔT₂ map and correlations between T₂ and ΔT₂/T₂ for (c) and (d). PD, proton density.