Purpose: The purpose of the study is to develop a quantitative method for the relaxation properties with a reduced radio frequency (RF) power deposition by combining magnetic resonance fingerprinting (MRF) technique with quick echo splitting NMR imaging technique (QUEST).Methods: A QUEST‐based MRF sequence was implemented to acquire high‐order echoes by increasing the gaps between RF pulses. Bloch simulations were used to calculate a dictionary containing the range of physically plausible signal evolutions using a range of T₁ and T₂ values based on the pulse sequence. MRF‐QUEST was evaluated by comparing to the results of spin‐echo methods. The specific absorption rate (SAR) of MRF‐QUEST was compared with the clinically available methods.Results: MRF‐QUEST quantifies the relaxation properties with good accuracy at the estimated head SAR of 0.03 W/kg. T₁ and T₂ values estimated by MRF‐QUEST are in good agreement with the traditional methods.Conclusions: The combination of the MRF and the QUEST provides an accurate quantification of T₁ and T₂ simultaneously with reduced RF power deposition. The resulting lower SAR may provide a new acquisition strategy for MRF when RF energy deposition is problematic. Magn Reson Med 77:979–988, 2017. © 2016 International Society for Magnetic Resonance in Medicine

Purpose: Develop a general radiofrequency (RF) pulse design algorithm for the design of three‐dimensional (3D) spatially selective refocusing pulses and explore their potential applications in reduced field‐of‐view imaging.Methods: Spin‐domain representation was used to describe the effect of RF pulses and to formulate the optimization problem. The implementation was based on an auto‐differentiable simulator. Spatially selective excitation and refocusing pulses for a small regions of interest were designed with consideration of hardware limits and B₀ and B₁⁺ inhomogeneities. The designed RF pulses were validated in simulation as well as in vivo experiments in brain and prostate on a 3T scanner.Results: Pulses of short duration (4.15 ms) were designed for 3D tailored excitation and refocusing accounting for B₀ and B₁⁺ inhomogeneities. The computation time for each design was approximately 7 min. Improved outer‐volume signal suppression in phantom and in vivo spin‐echo imaging experiments was achieved by combining 3D excitation and refocusing pulses compared with using only one 3D pulse. The potential of using tailored 3D pulses to obtain images with higher spatial resolution (1 1 3 mm³) and less distortion with the same scan time was demonstrated by acquiring reduced field‐of‐view 3D images of brain and prostate.Conclusion: The proposed algorithm jointly optimizes the RF and gradient waveforms given an initial pulse and a desired spin‐domain target pattern. Our approach is broadly applicable to the design of excitation and refocusing pulses and complements existing methods based on describing individual spin isochromatic behavior. Combining 3D excitation and 3D refocusing pulses produced better spatial selectivity than using a combination of one‐dimensional and 3D pulses.

Purpose: To develop and validate a vendor‐agnostic, motion‐insensitive proton‐density fat‐fraction (PDFF) quantification method. Methods: Flip‐angle‐modulated (FAM) 2D chemical‐shift‐encoded (CSE) MRI for PDFF quantification was implemented in both the vendor‐agnostic platform Pulseq (“Pulseq‐FAM”) and one vendor‐specific platform (“GE‐specific FAM”). These implementations were distributed to four sites with twelve MR systems of three vendors (Siemens/GE/Philips) and field strengths (0.55T/1.5T/3T). A sequentially‐shipped 16‐vial phantom (PDFF = 0%–30%/T1 _water = 200–1400 ms) underwent confounder‐corrected PDFF mapping with commercial 3D‐CSE methods and GE‐specific FAM as available on each system, and Pulseq‐FAM on every system. To assess bias, phantom PDFF measurements were compared to reference. Between‐system variance was evaluated with linear mixed‐effects modeling. Different volunteers were also imaged at each site to assess free‐breathing PDFF mapping feasibility. A prospective single‐site volunteer study was also conducted. Adult patients and children were imaged with breath‐held 3D‐CSE and free‐breathing GE‐specific and Pulseq‐FAM. Radiologists evaluated images for overall quality and motion artifacts. To assess bias, Pulseq‐FAM PDFF measurements were compared to 3D‐CSE and GE‐specific FAM. Test–retest repeatability was assessed by re‐imaging after repositioning. Between‐field‐strength reproducibility was assessed at 1.5T and 3.0T. Results: In the multi‐center study, Pulseq‐FAM showed reduced T1‐bias and between‐system variability versus 3D‐CSE in phantom PDFF measurements, and free‐breathing feasibility in volunteers. In the single‐site volunteer study ( N = 57), Pulseq‐FAM improved image quality and motion artifacts versus 3D‐CSE ( p < 0.01). Pulseq‐FAM showed excellent agreement with 3D‐CSE (95% limits‐of‐agreement (LoA) = 3.4% PDFF) and GE‐specific FAM (LoA = 2.0%). Pulseq‐FAM showed excellent repeatability (repeatability coefficient (RC) = 1.6% PDFF) and between‐field‐strength reproducibility (reproducibility coefficient (RDC) = 2.4%) versus 3D‐CSE (RC = 2.7%/RDC = 3.4%; differences p < 0.05). Conclusion: Pulseq‐FAM enables accurate, reproducible, vendor‐agnostic, and motion‐insensitive PDFF quantification in adults and children.

The creatine kinase (CK) is a key enzyme involved in brain bioenergetics, playing an important role in brain function and the pathogenesis of neurological and psychiatric diseases and cancers. However, imaging its activity noninvasively in the human brain remains a significant challenge. This study aims to advance ³¹ P magnetic resonance fingerprinting for Creatine Kinase Imaging (CKI). The method was implemented and validated on a clinical 7 Tesla MRI scanner. CKI enables whole-brain mapping of CK forward rate constant, revealing regional differences. Furthermore, a functional CKI (fCKI) study demonstrated a CK activation map in response to visual stimulation, revealing an increase in CK forward rate constant in the visual cortex. The novel imaging modalities, CKI and fCKI, have the potential to offer insights into brain bioenergetics both at rest and during activity, in both healthy and pathological conditions.