Keywords: Muscle, Rare disease, Potassium, Sodium

Motivation: Recent advances have enabled the application of ³⁹K-MRI in skeletal muscle in vivo. Moreover, information on disease progression/pathogenesis from non-invasive ¹H-MRI is still limited.

Goal(s): Determination of apparent tissue potassium and tissue sodium concentrations (aTPC/aTSC) in myofibrillar myopathies.

Approach: Less severe effected lower legs of 10 patients with filaminopathy-, desminopathy- and zaspopathy-causing mutations measured by ³⁹K/²³Na-MRI at 7T and Dixon-type-sequence at 3T.

Results: Fat-corrected ion concentrations were significantly altered in calf muscles of all patients with myofibrillar myopathies in comparison to healthy control subjects. Despite incoherencies with respect to disease progression and etiology fat-corrected aTSC were in- and aTPC were decreased.

Impact: Combined ³⁹K/²³Na-MRI detects changes in ionic balance beyond fatty replacement of muscle in a diverse cohort of myofibrillar myopathies. Further studies are needed to investigate whether different genotypes or whether disease progression can be detected in early stages by ³⁹K/²³Na-MRI.      

Keywords: Non-Proton, Non-Proton

Motivation: With advancing hardware, scan durations of ²³Na-MRI have decreased, enabling novel applications that probe dynamic  or functional processes; existing sequences, though, may not fully exploit the possible acceleration.

Goal(s): Implement and demonstrate a highly efficient ultrashort echo time non-Cartesian sequence based on 3D Seiffert spirals, for temporally-resolved applications of ²³Na-MRI.

Approach: A possible acquisition protocol for functional brain ²³Na-MRI at a temporal resolution of 47s was tested on a healthy volunteer at rest, at 3T.

Results: Image quality and SNR are high considering the temporal resolution, with compressed sensing successfully reducing noise. Further work will optimise the sequence analytically, ensuring homogeneous k-space sampling.

Impact: Dynamic ²³Na-MRI at 3T is possible at sub-minute temporal resolution with a 3D Seiffert spiral k-space trajectory. Unlike for other sequences, efficient k-space coverage is achieved without downsides of unpleasant acoustic noise, or exciting mechanical resonances of scanner hardware.  

Keywords: Non-Proton, Non-Proton, Dynamic Mode Decomposition, Signal separation

Motivation: Sodium (²³Na) Multi-Quantum Coherences (MQC) MRI potentially provides richer tissue information. However, separation of the single (SQ) and triple (TQ) quantum coherences is challenging and is done by computing the Fourier transform (FT). Unfortunately, the FT is susceptible to noise and phase-cycle imperfections.

Goal(s): To enable reliable frequency separation of the superimposed ²³Na MQC signal even with undersampling phase-cycling. 

Approach: Dynamic Mode Decomposition (DMD) was used to separate the signal components and was tested on numerical simulations, phantom and in vivo brain data acquired at 3T. 

Results: DMD reliably separated SQ and TQ signal components from ²³Na MQC MRI despite missing phase-cycling steps.

Impact: DMD reliably separates SQ and TQ signal components and has the potential to enable phase-cycle undersampling below the TQ Nyquist limit to accelerate ²³Na MQC MRI. Despite ²³Na MQC MRI, every MRI experiment involving phase-cycling could benefit from this approach.

Keywords: Non-Proton, Non-Proton, low-rank matrix completion, sequence optimization

Motivation: Sodium (²³Na) Multi-Quantum Coherences (MQC) MRI potentially provides richer tissue information. However, 3D ²³Na multi-quantum coherences imaging lacks conventional ²³Na MRI resolution and requires multiple radiofrequency phase-cycling limiting spatial resolution.

Goal(s): We propose an efficient sequence to simultaneously acquire Cartesian double-half echo (DHE) ²³Na and accelerated ²³Na MQC MRI.

Approach: Leveraging advanced low-rank matrix completion frameworks to enable simultaneous DHE ²³Na and ²³Na MQC MRI were tested on numerical simulations, retro- and prospectively undersampled phantom and in vivo brain data acquired at 7T.

Results: Simultaneous Cartesian ²³Na and higher resolution 3-fold prospectively undersampled ²³Na MQC brain MRI of 4 volunteers were obtained. 

Impact: The new sequence, in combination with the low-rank reconstruction frameworks, enables efficient ²³Na and higher resolution ²³Na MQC MRI while supporting conventional ¹H-based acceleration techniques and offers, therefore, a convenient sequence for the sodium MRI community.

Keywords: Non-Proton, Non-Proton, Sodium MRI, 23Na MRI, interleaved 23Na/1H MRI, High-Field MRI

Motivation: Interleaved dual-nuclear acquisition enables time-efficient ²³Na and ¹H cardiac MRI within one measurement. However, at 7T the reduced excitation wavelengths can lead to flip angle (FA) inhomogeneities in ²³Na MRI and even to signal dropouts in ¹H MRI. Both effects impair a reproducible quantitative evaluation of the myocardial ²³Na signal.

Goal(s): To reduce FA inhomogeneities for interleaved ²³Na/¹H MRI.

Approach: We included three different pTx pulses in ¹H MRI of the interleaved sequence and introduced a fast ²³Na FA mapping. 

Results: All three pTx pulses improved the ¹H FA homogeneity and ²³Na images showed better signal homogeneity after FA correction.

Impact: Interleaved ²³Na/¹H (pTx) MRI in combination with additional fast ²³Na FA mapping is less prone to FA inhomogeneities and by that should enable reliable quantification of myocardial ²³Na signal within clinically feasible acquisition times.

Keywords: Non-Proton, Non-Proton

Motivation: Sodium MRI can provide tissue sodium concentration (TSC) and enable assessment of knee cartilage degradation.

Goal(s): We aim to quantify TSC, proton density (PD) and ¹H T1 and T2 in the knee from multinuclear simultaneous acquisition.

Approach: We acquired ²³Na-only FLORET and simultaneous ¹H MRF/²³Na MRI data in the knee of four healthy volunteers. We calculated TSC maps from both ²³Na acquisitions for comparison, and PD, T1 and T2 maps from ¹H MRF.

Results: Mean TSC in patellar and femorotibial cartilage, and gastrocnemius muscle showed no significant differences between both sodium acquisitions. Mean TSC, PD, T1 and T2 values were within previously-reported range.

Impact: We showed that a 3D simultaneous ¹H MRF/²³Na MRI acquisition at 7 T can provide reliable quantitative maps of TSC, PD, and ¹H T1 and T2 relaxation times in cartilage.

Keywords: Non-Proton, Non-Proton

Motivation: To perform ²³Na MRI to study dynamic studies of changes in tissue sodium concentration in-vivo.

Goal(s): To demonstrate the application of NOise Reduction with DIstribution Corrected (NORDIC) PCA denoising to ²³Na MRI data.

Approach: Dynamic timeseries of ²³Na GRE data and NORDIC denoising to validate measurement of a known change in sodium concentration in a phantom, and dynamic changes in calf muscle in response to exercise.

Results: NORDIC PCA denoising allows detection of the temporal change in sodium in a phantom with good spatial resolution. This is applied to study the dynamics of sodium changes in muscle in response to exercise.

Impact: NOise Reduction with DIstribution Corrected (NORDIC) PCA denoising provides the potential to improve low SNR ²³Na MRI measures to study dynamic changes in sodium on a spatially resolved level. Here, applied to study ²³Na changes in calf muscle on exercise.

Keywords: Non-Proton, Non-Proton, skin

Motivation: The storage of sodium in the skin is thought to be a physiologically important regulatory mechanism for blood pressure, volume regulation, and to change with age, hypertension and disease such as renal and cardiovascular disease.

Goal(s): To image the skin at higher spatial resolution for improved estimation of skin sodium quantification.

Approach: To develop a dual-tuned ²³Na/¹H skin coil to image a skin ‘phantom’ and the skin in-vivo. To apply a B₁-mapping correction and use the skin ‘phantom’ to validate methods, and study the effects of spatial resolution on skin sodium measures.  

Results: High resolution skin sodium imaging was achieved, improving ²³Na quantification.

Impact: Improved spatial resolution of sodium imaging measures of the skin will provide improved assessment of quantification of skin sodium to study the effects of age, ethnicity and disease.

Keywords: MR Fingerprinting, MR Fingerprinting, 31P, MRF, creatine kinase rate, kCK, MRSI, 7T

Motivation: Using ³¹P MRS combined with magnetization transfer (MT) experiments including saturation transfer or inversion transfer to assess chemical exchange rate of creatine kinase (k_CK) in the human brain are time-consuming and limited to 1D-acquisitions.

Goal(s): Acquiring a 3D whole brain k_CK map.

Approach: In this abstract, we introduce an advanced, fast 3D-³¹P-MRF sequence for the human brain at 7T.

Results: The novel 3D-³¹P-MRF approach is feasible for whole brain mapping of k_CK, enabling the investigation of region-specific energy metabolism under various pathological conditions.

Impact: Using the novel 3D-³¹P-MR Fingerprinting approach for whole brain mapping of k_CK enables us to investigate region-specific energy metabolism under various pathological conditions and may enhance our understanding of the underlying molecular and metabolic processes.

Keywords: Non-Proton, Non-Proton

Motivation: Measuring brain intracellular NAD levels has long been of interest, but the current ³¹P-MRSI methods would take prohibitively long scan times for mapping NAD.

Goal(s): To present a method for fast volumetric NAD mapping of the entire human brain. 

Approach: In vivo ³¹P-MRSI scans were performed at 7T with a nominal resolution of 1.0 cc within 20 minutes. A probabilistic subspace-based method integrating spectral prior, spatial constraint, and statistical distributions was applied for denoising. 

Results: The proposed method successfully provided high-resolution brain NAD mapping within 20-minute scans. The results also showed promises in revealing metabolic tissue heterogeneity and age correlation of NAD. 

Impact: This work demonstrates the feasibility of volumetric brain NAD mapping with a nominal resolution of 1.0 cc within 20 minutes. It may provide a powerful metabolic imaging tool for many applications.