Purpose To develop a framework for 3D sodium (23Na) MR fingerprinting (MRF), based on irreducible spherical tensor operators with tailored flip angle (FA) pattern and time‐efficient data acquisition for simultaneous quantification of T1, T2normall∗, T2normals∗, and T2∗ in addition to ΔB0. Methods 23Na‐MRF was implemented in a 3D sequence and irreducible spherical tensor operators were exploited in the simulations. Furthermore, the Cramér Rao lower bound was used to optimize the flip angle pattern. A combination of single and double echo readouts was implemented to increase the readout efficiency. A study was conducted to compare results in a multicompartment phantom acquired with MRF and reference methods. Finally, the relaxation times in the human brain were measured in four healthy volunteers. Results Phantom experiments revealed a mean difference of 1.0% between relaxation times acquired with MRF and results determined with the reference methods. Simultaneous quantification of the longitudinal and transverse relaxation times in the human brain was possible within 32 min using 3D 23Na‐MRF with a nominal resolution of (5 mm)3. In vivo measurements in four volunteers yielded average relaxation times of: T1,brain = (35.0 ± 3.2) ms, T2normall,brain∗ = (29.3 ± 3.8) ms and T2normals,brain∗ = (5.5 ± 1.3) ms in brain tissue, whereas T1,CSF = (61.9 ± 2.8) ms and T2,CSF∗ = (46.3 ± 4.5) ms was found in cerebrospinal fluid. Conclusion The feasibility of in vivo 3D relaxometric sodium mapping within roughly ½ h is demonstrated using MRF in the human brain, moving sodium relaxometric mapping toward clinically relevant measurement times.

The presented body coil enables full body width Na MRI with long z-axis coverage at 7 T for the first time. Additionally, the retrospective respiratory self-gating performance is demonstrated for free-breathing lung and abdominal Na MRI in 3 subjects.

C ancer cells predominantly gain energy through a high rate of glycolysis followed by lactic acid fermentation even in the presence of abundant oxygen (known as the Warburg effect). Consequently, both the higher glucose uptake rate and the reduced cerebral metabolic rate of oxygen (CMRO 2 ) consumption pose possible targets for imaging metabolic tumor activity.Conventional MRI sequences do not provide information on tissue metabolic activity. MR spectroscopy allows for the detection of metabolic products in vivo (eg, lactate) (1), but has limited routine applicability because of technical complexity, low spatial resolution, and clinical time constraints (2). Further, chemical exchange saturation transfer MRI has recently gained considerable attention as an imaging technique sensitive to tissue pH by amide proton transfer (3). However, recent studies (4) suggest that the endogenous amide contrast in tumors is dominated by histologic and genetic features through altered protein concentrations.Blood oxygen level2dependent imaging, most commonly applied to functional MRI, can be used to quantitatively measure CMRO 2 (5-7). However, these techniques provide only indirect measures and rely on complex physiologic assumptions in data interpretation and calibration processes (8), which impair robustness and specificity. Alternative approaches to assess tumor hypoxia are on the basis of PET or single photon emission CT, available with fluorine 18 fluoromisonidazole or other radioligands (9). Direct CMRO 2 assessment is possible by using the short-lived (~122 seconds) radioisotope oxygen 15 ( 15 O)

Highlights MRI derived total 23 Na concentration differs significantly in glioma subregions. Total 23 Na concentration could reflect IDH mutation status and tumor grade. 23 Na MRI yields potential non-invasive biomarkers for the treatment of gliomas.

Purpose: To quantify the tissue sodium concentration (TSC) in cardiac 23 Na MRI.To evaluate the influence of different correction methods on the measured myocardial TSC. Methods: 23 Na MRI of four healthy subjects was conducted at a whole-body 7T MRI system using an oval-shaped 23 Na birdcage coil. Data acquisition was performed with a density-adapted 3D radial pulse sequence using a golden angle projection scheme. 1 H MRI data were acquired at a 3T MRI system to generate a myocardial mask. Retrospective cardiac and respiratory gating were used to reconstruct 23 Na MRI data in the diastolic phase and exhaled state. B 0 and B 1 inhomogeneity and partial volume (PV) effects were corrected. Relaxation times and TSC of ex vivo blood samples and calf muscle were determined. These values were used in the PV correction to estimate myocardial TSC, which was compared with the measured TSC of calf muscle. Results: Without any correction the measured myocardial TSC was (54 ± 5) mM.The applied correction methods reduced these values by (48 ± 5)% to (29 ± 3) mM, where PV correction had the largest effect (reduction of (34 ± 1)%). Respiratory and cardiac motion gating decreased the concentrations by (11 ± 1)%. With the applied setup, the corrections of B 0 and B 1 inhomogeneity (reduction of (3 ± 2)%) had negligible influences on TSC values. The resulting myocardial TSC was approximately 1.4-fold higher than the measured TSC of calf muscle tissue of the same healthy subjects ((20 ± 3) mM). |LOTT eT aL. |LOTT eT aL. F I G U R E 1Schematic outline of the measurements and the post-processing workflow. The process can be divided into a main path and a side path. The main part contains the cardiac 23 Na and 1 H MR measurements, all applied corrections and the determination of the myocardial TSC. In the side path, parameters, that are required for the corrections, such as relaxation times and sodium concentration of whole blood were determined for each volunteer individually F I G U R E 2 Retrospectively gated cardiac 23 Na in vivo data in a diastolic cardiac phase for one volunteer as an example. The not sorted 23 Na data (A) were reconstructed with the full set of projections. 49% of the projections were used to conduct the diastolic 23 Na image reconstruction (B). The measured sodium concentration in the diastolic image (C, red) is slightly reduced compared with the not sorted data (C, blue). Cardiac 23 Na data and line plots for the other three volunteers are shown in the Supporting Information Figure S3

Ultrahigh magnetic fields offer significantly higher signal-to-noise ratio, and several magnetic resonance applications additionally benefit from a higher contrast-to-noise ratio, with static magnetic field strengths of B 0 ≥ 7 T currently being referred to as ultrahigh fields (UHFs). The advantages of UHF can be used to resolve structures more precisely or to visualize physiological/pathophysiological effects that would be difficult or even impossible to detect at lower field strengths. However, with these advantages also come challenges, such as inhomogeneities applying standard radiofrequency excitation techniques, higher energy deposition in the human body, and enhanced B 0 field inhomogeneities. The advantages but also the challenges of UHF as well as promising advanced methodological developments and clinical applications that particularly benefit from UHF are discussed in this review article.

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