Flow MR fingerprinting

Abstract

Purpose To investigate the feasibility to quantify blood velocities within the magnetic resonance fingerprinting framework, while providing relaxometric maps of static tissue. Methods Bipolar gradients are inserted into an SSFP‐based MRF sequence to achieve velocity‐dependent signal phases, allowing tri‐directional time‐resolved velocity component quantification. The accuracy of both relaxometric mapping and velocity quantification was validated in vivo and in phantom studies. Results Simulations determined that even for strong cardiac cycle length variations (700–1400 ms) Flow‐MRF determines accurate velocity maps deviating <0.1% from the ground truth on average. The cardiac cycle length variability only results in reduced velocity‐to‐noise ratios. Good agreement in the velocity quantification between a standard phase–contrast cine and the Flow‐MRF sequence was reached in phantom experiments. Relaxometric phantom experiments determined mean deviations between Flow‐MRF and spin‐echo‐based reference measurements of 89 ± 25 ms / 0.8 ± 2.5 ms over the range of 630–2630 ms / 49–145 ms for T1 / T2, respectively. The in vivo study of a human knee determined mean T1 / T2 values of 1383 ± 75 ms / 26 ± 4 ms for the gastrocnemius muscle that agree with literature values. Conclusion Flow‐MRF presents a novel way of quantifying velocities while simultaneously providing relaxometric maps of static tissue and it can potentially be a viable method to accelerate the inherently long acquisition times of time‐resolved velocity quantification.

Magnetic resonance fingerprinting Part 1: Potential uses, current challenges, and recommendations

“…To accomplish this, Flassbeck et al incorporated motion encoding gradients into an SSFP‐MRF sequence, varying the FA and strength of the x, y, and z gradients each TR. Unlike the conventional MRF methods, TR was kept constant.…”

3D free‐breathing cardiac magnetic resonance fingerprinting

“…Magnetic resonance fingerprinting (MRF) 22 is an established research technique for simultaneous and multi-parametric quantitative MR where system parameters (such as flip angle and repetition time) vary in time to sensitize the sequence to tissue parameters of interest (such as T 1 and T 2 ). MRF attempts to capture the parametric encoding within the transient state using directly the Bloch equations and can be extended to include not only additional parameters of interest (eg flow, 23 chemical exchange saturation transfer (CEST) 24 ), but also additional model corrections (eg B 1 , 25 slice profile 26 ). Initially proposed for brain acquisitions, MRF has since been extended to 2D cardiac imaging (cMRF) 27 for simultaneous, co-registered T 1 and T 2 myocardial mapping in a single breath-hold.…”

Sodium relaxometry using 23Na MR fingerprinting: A proof of concept

“…In MRF, non‐steady‐state conditions can be generated by temporal variations of excitations, sequence timings, and gradients, resulting in a unique signal evolution that depends on relaxometric as well as other parameters. MRF has successfully been used for the simultaneous quantification of several different parameters in various applications, such as relaxometry, 20 diffusion, 21 velocity, 22 and chemical exchange 23 . In X‐nuclei MR, MRF principles were exploited for determination of the signal contribution of different compartments 24 .…”