Tissue Sodium Concentration Research Articles

Combined imaging of potassium and sodium in human skeletal muscle tissue at 7 T.

To validate the feasibility of quantitative combined potassium (39 K) and sodium (23 Na) MRI in human calf muscle tissue, as well as to evaluate the reproducibility of the apparent tissue potassium concentration (aTPC) and apparent tissue sodium concentration (aTSC) determination in healthy muscle tissue. Quantitative 23 Na and 39 K MRI acquisition protocols were implemented on a 7 T MR system. A double-resonant 23 Na/39 K birdcage RF coil was used. Measurements of human lower leg were performed in a total acquisition time of TANa = 10:54 min/TAK = 8:06 min and using a nominal spatial resolution of 2.5 × 2.5 × 15 mm3 /7.5 × 7.5 × 30 mm3 for 23 Na/39 K MRI. Two aTSC and aTPC examinations in muscle tissue were performed during the same day on 10 healthy subjects. The proposed acquisition and postprocessing workflow for 23 Na and 39 K MRI data sets provided reproducible aTSC and aTPC measurements. In human calf muscle tissue, the coefficient of variation between scan and re-scan was 5.7% for both aTSC and aTPC determination. Overall, mean values of aTSC = (17 ± 1) mM and aTPC = (85 ± 5) mM were measured. Moreover, for 39 K in calf muscle tissue, components of = (1.2 ± 0.2) ms and = (7.9 ± 0.9) ms, as well as a residual quadrupolar interaction of = (143 ± 17) Hz, were determined. The fraction of the fast component was f = (58 ± 4)%. Using the presented measurement and postprocessing approach, a reproducible aTSC and aTPC determination using 23 Na and 39 K MRI at 7 T in human skeletal muscle tissue is feasible in clinically acceptable acquisition durations.

Frontiers of Sodium MRI Revisited: From Cartilage to Brain Imaging.

Sodium magnetic resonance imaging (23Na‐MRI) is a highly promising imaging modality that offers the possibility to noninvasively quantify sodium content in the tissue, one of the most relevant parameters for biochemical investigations. Despite its great potential, due to the intrinsically low signal‐to‐noise ratio (SNR) of sodium imaging generated by low in vivo sodium concentrations, low gyromagnetic ratio, and substantially shorter relaxation times than for proton (1H) imaging, 23Na‐MRI is extremely challenging. In this article, we aim to provide a comprehensive overview of the literature that has been published in the last 10–15 years and which has demonstrated different technical designs for a range of 23Na‐MRI methods applicable for disease diagnoses and treatment efficacy evaluations. Currently, a wider use of 3.0T and 7.0T systems provide imaging with the expected increase in SNR and, consequently, an increased image resolution and a reduced scanning time. A great interest in translational research has enlarged the field of sodium MRI applications to almost all parts of the body: articular cartilage tendons, spine, heart, breast, muscle, kidney, and brain, etc., and several pathological conditions, such as tumors, neurological and degenerative diseases, and others. The quantitative parameter, tissue sodium concentration, which reflects changes in intracellular sodium concentration, extracellular sodium concentration, and intra–/extracellular volume fractions is becoming acknowledged as a reliable biomarker. Although the great potential of this technique is evident, there must be steady technical development for 23Na‐MRI to become a standard imaging tool. The future role of sodium imaging is not to be considered as an alternative to 1H MRI, but to provide early, diagnostically valuable information about altered metabolism or tissue function associated with disease genesis and progression.Level of Evidence1Technical Efficacy Stage1

Tissue sodium content in hypertension and related organ damage.

: Most textbooks state that sodium (Na) accumulation goes hand in hand with fluid retention to maintain the environmental isotonicity. In the last century, several studies found, however, that Na is stored in the extravascular space leading to an activation of the monocyte phagocytic system cells that work as a regulator of the interstitial electrolyte homeostasis. Na-MRI was developed to quantify noninvasively, accurately and reliably tissue Na content. In this review, we give an up-to-date overview of clinical studies utilizing this Na-MRI technique to elucidate the importance of tissue Na content in patients with cardiovascular risk factors leading to microvascular and macrovascular complications. Na storage leads ultimately to organ damage such as left ventricular hypertrophy or hypertrophic vascular remodeling of resistance vessels. Elevated Na content in muscle and skin has been detected in patients with treatment resistant hypertension, type 2 diabetes mellitus, acute and chronic heart failure, chronic kidney disease and end-stage renal failure. Pharmacological interventions have shown that a mobilization of extracellular accumulated Na is possible and may emerge as a new therapeutic approach in some diseases.

Arbuscular mycorrhizal fungi as mitigating agents of salt stress in Formosa papaya seedlings

The objective of the present study was to evaluate the effect of mycorrhization on the nutritional, hydric and biochemical components of papaya seedlings, Carica papaia L., from the Formosa Group, Hybrid Tainung Nº 1, submitted to irrigation with saline water. The research was conducted at the Federal Institute of Paraíba, Sousa Campus, from March to December 2018. The experimental design used completely randomized blocks, with treatments arranged in a 4 x 5 factorial scheme, referring to the fungi species: Gigaspora candida, Acaulospora scrobiculata, Dentiscutata heterogama and without mycorrhizae, and the five salt concentrations in irrigation water: 0.0; 10.0; 20.0; 30.0 and 40.0 mmolc L-1 in four repetitions. The characteristics evaluated were: relative water content, water saturation deficit, membrane damage, photosynthetic pigments, concentration and accumulation of nitrogen, phosphorus, potassium, sodium and the relationship between potassium and sodium concentrations in leaf tissue. The species D. heterogama and G. candida presented the highest rates of leaf hydration and the lowest damage to biomembranes at all saline levels. Mycorrhizae increased the absorption of N and P, especially from 30 mmolc L-1 of salt. A greater relationship between potassium and sodium concentrations was evidenced in seedlings mycorrhized with D. heterogama.

Neuroimaging of Cerebral Blood Flow and Sodium in Women with Lipedema.

Lipedema is characterized by pain, fatigue, and excessive adipose tissue and sodium accumulation of the lower extremities. This case-control study aims to determine whether sodium or vascular dysfunction is present in the central nervous system. Brain magnetic resonance imaging was performed at 3 T in patients with lipedema (n = 15) and control (n = 18) participants matched for sex, age, race, and BMI. Standard anatomical imaging and intracranial angiography were applied to evaluate brain volume and vasculopathy, respectively; arterial spin labeling and sodium magnetic resonance imaging were applied to quantify cerebral blood flow (CBF) (milliliters per 100 grams oftissue/minute) and brain tissue sodium content (millimoles per liter), respectively. A Mann-Whitney U test (significance criteria P < 0.05) was applied to evaluate group differences. No differences in tissue volume, white matter hyperintensities, intracranial vasculopathy, or tissue sodium content were observed between groups. Gray matter CBF was elevated (P = 0.03) in patients with lipedema (57.2 ± 9.6 mL per 100 g/min) versus controlparticipants (49.8 ± 9.1 mL per 100 g/min). Findings provide evidence that brain sodium and tissue fractions are similar between patients with lipedema and control participants and that patients with lipedema do not exhibit abnormal radiological indicators of intracranial vasculopathy or ischemic injury. Potential explanations for elevated CBF are discussed in the context of the growing literature on lipedema symptomatology and vascular dysfunction.

Upper and Lower Extremity Measurement of Tissue Sodium and Fat Content in Patients with Lipedema.

The aim of this study is to compare tissue sodium and fat content in the upper and lower extremities of participants with lipedema versus controls using magnetic resonance imaging (MRI). MRI was performed at 3.0T in females with lipedema (n = 15, age = 43.2 ± 10.0 years, BMI = 30.3 ± 4.4 kg/m2 ) and controls without lipedema (n = 14, age = 42.8 ± 13.2 years, BMI = 28.8 ± 4.4 kg/m2 ). Participants were assessed for pain and disease stage. Sodium MRI was performed in the forearm and calf to quantify regional tissue sodium content (TSC, mmol/L). Chemical-shift-encoded water-fat MRI was performed in identical regions for measurement of fat/water (ratio). In the calf, skin TSC (16.3 ± 2.6 vs. 14.4 ± 2.2 mmol/L, P = 0.04), muscle TSC (20.3 ± 3.0 vs. 18.3 ± 1.7 mmol/L, P = 0.03), and fat/water (1.03 ± 0.37 vs. 0.56 ± 0.21 ratio, P < 0.001) were significantly higher in participants with lipedema versus control participants. In the forearm, skin TSC (13.4 ± 3.3 vs. 12.0 ± 2.3 mmol/L, P = 0.2, Cohen's d = 0.50) and fat/water (0.65 ± 0.24 vs. 0.48 ± 0.24 ratio, P = 0.07, Cohen's d = 0.68) demonstrated moderate effect sizes in participants with lipedema versus control participants. Calf skin TSC was significantly correlated with pain (Spearman's rho = 0.55, P = 0.03) and disease stage (Spearman's rho = 0.82, P < 0.001) among participants with lipedema. MRI-measured tissue sodium and fat content are significantly higher in the lower extremities, but not upper extremities, of patients with lipedema compared with BMI-matched controls.

Tissue sodium concentrations in chronic kidney disease and dialysis patients by lower leg sodium-23 magnetic resonance imaging.

Sodium-23 magnetic resonance imaging (23Na MRI) allows direct measurement of tissue sodium concentrations. Current knowledge of skin, muscle and bone sodium concentrations in chronic kidney disease (CKD) and renal replacement therapy patients is limited. In this study we measured the tissue sodium concentrations in CKD, hemodialysis (HD) and peritoneal dialysis (PD) patients with 23Na MRI of the lower leg and explored their correlations with established clinical biomarkers. Ten healthy controls, 12 CKD Stages 3-5, 13 HD and 10 PD patients underwent proton and 23Na MRI of the leg. The skin, soleus and tibia were segmented manually and tissue sodium concentrations were measured. Plasma and serum samples were collected from each subject and analyzed for routine clinical biomarkers. Tissue sodium concentrations were compared between groups and correlations with blood-based biomarkers were explored. Tissue sodium concentrations in the skin, soleus and tibia were higher in HD and PD patients compared with controls. Serum albumin showed a strong, negative correlation with soleus sodium concentrations in HD patients (r = -0.81, P < 0.01). Estimated glomerular filtration rate showed a negative correlation with tissue sodium concentrations (soleus: r = -0.58, P < 0.01; tibia: r = -0.53, P = 0.01) in merged control-CKD patients. Hemoglobin was negatively correlated with tissue sodium concentrations in CKD (soleus: r = -0.65, P = 0.02; tibia: r = -0.73, P < 0.01) and HD (skin: r = -0.60, P = 0.04; tibia: r = -0.76, P < 0.01). Tissue sodium concentrations, measured by 23Na MRI, increase in HD and PD patients and may be associated with adverse metabolic effects in CKD and dialysis.

Assessing the variability of 23 Na MRI in skeletal muscle tissue: Reproducibility and repeatability of tissue sodium concentration measurements in the lower leg at 3 T.

The goal of this study was to evaluate the reproducibility and repeatability of tissue sodium concentration (TSC) measurements using 23 Na MRI in skeletal muscle tissue. 23 Na MRI was performed at 3 T on the right lower leg of eight healthy volunteers (aged 28 ± 4 years). The examinations were repeated at the same site after ~ 22 weeks to assess the variability over a medium-term period. Additionally, they were scanned at a second site shortly before or shortly after the first visit (within 3 weeks) to evaluate the inter-site reproducibility. Moreover, we analysed the effect of B0 correction on the variability. Coefficients of variations (CVs) from mean TSC values as well as Bland-Altman plots were used to assess intra-site repeatability and inter-site reproducibility. In phantom measurements, the B0 correction improved the quantitative accuracy. We observed differences of up to 4.9 mmol/L between the first and second visit and a difference of up to 3.7 mmol/L between the two different sites. The CV for the medium-term repeatability was 15% and the reproducibility CV was 9%. The Bland-Altman plots indicated high agreement between the visits in all muscle regions. The systematic bias of -0.68 mmol/L between site X and Y (P = 0.03) was slightly reduced to -0.64 mmol/L after B0 correction (P = 0.04). This work shows that TSC measurements in healthy skeletal muscle tissue can be performed with good repeatability and reproducibility, which is of importance for future longitudinal or multicentre studies.

Tissue sodium content in patients with systemic lupus erythematosus: association with disease activity and markers of inflammation.

Sodium (Na+) is stored in the skin and muscle and plays an important role in immune regulation. In animal models, increased tissue Na+ is associated with activation of the immune system, and high salt intake exacerbates autoimmune disease and worsens hypertension. However, there is no information about tissue Na+ and human autoimmune disease. We hypothesized that muscle and skin Na+ content is (a) higher in patients with systemic lupus erythematosus (SLE) than in control subjects, and (b) associated with blood pressure, disease activity, and inflammation markers (interleukin (IL)-6, IL-10 and IL-17 A) in SLE. Lower-leg skin and muscle Na+ content was measured in 23 patients with SLE and in 28 control subjects using 23Na+ magnetic resonance imaging. Demographic and clinical information was collected from interviews and chart review, and blood pressure was measured. Disease activity was assessed using the SLE Disease Activity Index (SLEDAI). Plasma inflammation markers were measured by multiplex immunoassay. Muscle Na+ content was higher in patients with SLE (18.8 (16.7-18.3) mmol/L) than in control subjects (15.8 (14.7-18.3) mmol/L; p < 0.001). Skin Na+ content was also higher in SLE patients than in controls, but this difference was not statistically significant. Among patients with SLE, muscle Na+ was associated with SLEDAI and higher concentrations of IL-10 after adjusting for age, race, and sex. Skin Na+ was significantly associated with systolic blood pressure, but this was attenuated after covariate adjustment. Patients with SLE had higher muscle Na+ content than control subjects. In patients with SLE, higher muscle Na+ content was associated with higher disease activity and IL-10 concentrations.

Correction to: Accelerated quantification of tissue sodium concentration in skeletal muscle tissue: quantitative capability of dictionary learning compressed sensing

The original version of this article unfortunately contained a mistake. Title was incorrect.

Regulation of CSF and Brain Tissue Sodium Levels by the Blood-CSF and Blood-Brain Barriers During Migraine

Cerebrospinal fluid (CSF) and brain tissue sodium levels increase during migraine. However, little is known regarding the underlying mechanisms of sodium homeostasis disturbance in the brain during the onset and propagation of migraine. Exploring the cause of sodium dysregulation in the brain is important, since correction of the altered sodium homeostasis could potentially treat migraine. Under the hypothesis that disturbances in sodium transport mechanisms at the blood-CSF barrier (BCSFB) and/or the blood-brain barrier (BBB) are the underlying cause of the elevated CSF and brain tissue sodium levels during migraines, we developed a mechanistic, differential equation model of a rat's brain to compare the significance of the BCSFB and the BBB in controlling CSF and brain tissue sodium levels. The model includes the ventricular system, subarachnoid space, brain tissue and blood. Sodium transport from blood to CSF across the BCSFB, and from blood to brain tissue across the BBB were modeled by influx permeability coefficients PBCSFB and PBBB, respectively, while sodium movement from CSF into blood across the BCSFB, and from brain tissue to blood across the BBB were modeled by efflux permeability coefficients and , respectively. We then performed a global sensitivity analysis to investigate the sensitivity of the ventricular CSF, subarachnoid CSF and brain tissue sodium concentrations to pathophysiological variations in PBCSFB, PBBB, and . Our results show that the ventricular CSF sodium concentration is highly influenced by perturbations of PBCSFB, and to a much lesser extent by perturbations of . Brain tissue and subarachnoid CSF sodium concentrations are more sensitive to pathophysiological variations of PBBB and than variations of PBCSFB and within 30 min of the onset of the perturbations. However, PBCSFB is the most sensitive model parameter, followed by PBBB and , in controlling brain tissue and subarachnoid CSF sodium levels within 3 h of the perturbation onset.

Accelerated quantification of tissue sodium concentration in skeletal muscle tissue: quantitative capability of dictionary learning compressed sensing.

To accelerate tissue sodium concentration (TSC) quantification of skeletal muscle using 23Na MRI and 3D dictionary-learning compressed sensing (3D-DLCS). Simulations and in vivo 23Na MRI examinations of calf muscle were performed with a nominal spatial resolution of [Formula: see text]. Fully sampled and three undersampled 23Na MRI data sets (undersampling factors (USF) = 3, 4.4, 6.7) were evaluated. Ten healthy subjects were examined on a 3 Tesla MRI system. Results of the simulation study and the in vivo measurements were compared to the ground truth (GT) and the fully sampled fast Fourier transform (NUFFT) reconstruction, respectively. Reconstruction results of simulated data with optimized 3D-DLCS yielded a lower deviation (< 4%) from the GT than results of the NUFFT reconstruction (> 5%) and a lower standard deviation (SD). For in vivo measurements, a TSC of [Formula: see text] was observed. The mean deviation from the reference is lower for the undersampled 3D-DLCS reconstructions (3.4%) than for NUFFT reconstructions (4.6%). SD is reduced using 3D-DLCS. Compared to a fully sampled NUFFT reconstruction, acquisition time could be reduced by a factor of 4.4 while maintaining similar quantitative accuracy. The optimized 3D-DLCS reconstruction enables accelerated TSC measurements with high quantification accuracy.

Tissue sodium and chloride concentrations in relation to needle injury in boreal conifer seedlings subjected to salt stress

Tissue Na and Cl concentrations can be used for estimation of salt injury for white spruce, black spruce, and jack pine growing at salt affected areas. Elevated soil salinity is among the most challenging environmental factors affecting plant growth and survival. Due to the widespread salinity concerns in agricultural soils, most of the salinity research has been carried out with agricultural crop plants. However, salinity is also frequently a factor affecting the sites reclaimed following surface mining including the oil sands mining areas located in the boreal forest of the northeastern Alberta, Canada. The present study examined the relationship between NaCl uptake, tissue Na and Cl concentrations, and plant injury in seedlings of three conifer species, which are commonly used for oil sands reclamation including black spruce (Picea mariana), white spruce (Picea glauca), and jack pine (Pinus banksiana). The seedlings were grown under controlled-environment conditions in sand culture and were subjected to 0 (control), 30, 60, and 90 mM NaCl treatments. Compared with control, stem diameters and shoot heights of black spruce, white spruce, and jack pine seedlings were significantly reduced by all NaCl treatments. White spruce and jack pine also exhibited reduced total dry weights. Needle chlorophyll concentrations decreased under NaCl treatments in all species. Visible symptoms of salt injury were observed in young and old needles of seedlings treated with NaCl. Significant needle necrosis was present in all species subjected to the 90 mM NaCl treatment. We found significant correlation between needle Na and Cl concentrations and necrosis extent. Therefore, we propose using the tissue Na and Cl concentration as an effective monitoring tool to estimate salt injury of conifers grown in NaCl-affected areas.

Tissue Sodium Content and Arterial Hypertension in Obese Adolescents.

Early-onset obesity is known to culminate in type 2 diabetes, arterial hypertension and subsequent cardiovascular disease. The role of sodium (Na+) homeostasis in this process is incompletely understood, yet correlations between Na+ accumulation and hypertension have been observed in adults. We aimed to investigate these associations in adolescents. A cohort of 32 adolescents (13–17 years), comprising 20 obese patients, of whom 11 were hypertensive, as well as 12 age-matched controls, underwent 23Na-MRI of the left lower leg with a standard clinical 3T scanner. Median triceps surae muscle Na+ content in hypertensive obese (11.95 mmol/L [interquartile range 11.62–13.66]) was significantly lower than in normotensive obese (13.63 mmol/L [12.97–17.64]; p = 0.043) or controls (15.37 mmol/L [14.12–16.08]; p = 0.012). No significant differences were found between normotensive obese and controls. Skin Na+ content in hypertensive obese (13.33 mmol/L [11.53–14.22] did not differ to normotensive obese (14.12 mmol/L [13.15–15.83]) or controls (11.48 mmol/L [10.48–12.80]), whereas normotensive obese had higher values compared to controls (p = 0.004). Arterial hypertension in obese adolescents is associated with low muscle Na+ content. These findings suggest an early dysregulation of Na+ homeostasis in cardiometabolic disease. Further research is needed to determine whether this association is causal and how it evolves in the transition to adulthood.

P4993Tissue sodium concentration emerged as a determinant of hypertrophic vascular remodeling in type 2 diabetes

Abstract Background Studies describe a linkage between greater sodium intake and higher incidence of organ damage and cardiovascular end points. Sodium intake is usually assessed by measuring 24-hour urinary sodium excretion, which is prone to high fluctuation. For the assessment of tissue sodium a new technique (23Na-MRI) has been developed. We analyzed whether tissue sodium is linked to vascular remodeling of small resistance vessels in patients with type-2 diabetes. Methods In patients with type 2 diabetes we assessed tissue sodium content and vascular structural parameters of the retinal arterioles, since structural changes of resistance vessels (150–300 μm) can be non-invasively and reliably assessed in the retinal circulation by Scanning Laser Doppler Flowmetry (SLDF). Patients with antidiabetic medication were off the therapy (antihypertensives were kept constant) for 4 weeks. The structural parameters of retinal arterioles assessed were outer- and inner diameter (OD &amp; ID), wall thickness (WT), wall-to-lumen ratio (WLR) and wall cross sectional area (WCSA). Tissue sodium content was assessed non-invasively with a 3.0 T clinical MRI system in each patient. Subject placed their lower legs in the center of a 23Na knee coil and sodium content in skin and muscle (musculus triceps surae) were measured. Results In patients with type 2 diabetes (N=52) we observed a significant correlation between tissue sodium content (muscle and skin) and OD, WT and WCSA and a trend has been noticed between muscle sodium content and ID and WLR. Multiple linear regression analysis demonstrated that tissue sodium content is a significant determinant of hypertrophic vascular remodeling as indicated by increased WT and WCSA, independent of age, gender and 24-hour ambulatory diastolic blood pressure. Correlation coefficients Muscle sodium content (mmol/l) Skin sodium content (mmol/l) OD (μmol) r=0.402, p=0.003 r=0.299, p=0.033 ID (μmol) r=0.265, p=0.058 r=0.202, p=0.154 WT (μm) r=0.402, p=0.003 r=0.313, p=0.026 WLR r=0.247, p=0.078 r=0.171, p=0.230 WCSA (μm2) r=0.417, p=0.002 r=0.322, p=0.021 Conclusion With the novel 23Na-MRI technology, we could demonstrate that high tissue sodium concentration is linked to with hypertrophic vascular remodeling of retinal arterioles. Thus, the reduction of tissue sodium content may emerge as a therapeutic target.

Salt and Water Retention Is Associated with Microinflammation and Endothelial Injury in Chronic Kidney Disease

Background: Progressive chronic kidney disease (CKD) inevitably leads to salt and water retention and disturbances in the macro-and microcirculation. Objectives: We hypothesize that salt and water dysregulation in advanced CKD may be linked to inflammation and microvascular injury pathways. Methods: We studied 23 CKD stage 5 patients and 11 healthy controls (HC). Tissue sodium concentration was assessed using ²³Sodium magnetic resonance (MR) imaging. Hydration status was evaluated using bioimpedance spectroscopy. A panel of inflammatory and endothelial biomarkers was also measured. Results: CKD patients had fluid overload (FO) when compared to HC (overhydration index: CKD = 0.5 ± 1.9 L vs. HC = –0.5 ± 1.0 L; p = 0.03). MR-derived tissue sodium concentrations were predominantly higher in the subcutaneous (SC) compartment (median [interquartile range] CKD = 22.4 mmol/L [19.4–31.3] vs. HC = 18.4 mmol/L [16.6–21.3]; p = 0.03), but not the muscle (CKD = 24.9 ± 5.5 mmol/L vs. HC = 22.8 ± 2.5 mmol/L; p = 0.26). Tissue sodium in both compartments correlated to FO (muscle: r = 0.63, p < 0.01; SC: r_s = 0.63, p < 0.01). CKD subjects had elevated levels of vascular cell adhesion molecule (p < 0.05), tumor necrosis factor-alpha (p < 0.01), and interleukin (IL)-6 (p = 0.01) and lower levels of vascular endothelial growth factor-C (p = 0.04). FO in CKD was linked to higher IL-8 (r = 0.51, p < 0.05) and inversely associated to E-selectin (r = –0.52, p = 0.01). Higher SC sodium was linked to higher intracellular adhesion molecule (ICAM; r_s = 0.54, p = 0.02). Conclusion: Salt and water accumulation in CKD appears to be linked with inflammation and endothelial activation pathways. Specifically IL-8, E-Selectin (in FO), and ICAM (in salt accumulation) may be implicated in the pathophysiology of FO and merit further investigation.

Compressed sensing effects on quantitative analysis of undersampled human brain sodium MRI.

The clinical application of sodium MRI is hampered due to relatively low image quality and associated long acquisition times. Compressed sensing (CS) aims at a reduction of measurement time, but has been found to encompass quantitative estimation bias when used in low SNR x-Nuclei imaging. This work analyses CS in quantitative human brain sodium MRI from undersampled acquisitions and provides recommendations for tissue sodium concentration (TSC) estimation. CS reconstructions from 3D radial acquisitions of 5 healthy volunteers were investigated over varying undersampling factors (USFs) and CS penalty weights on different sparsity domains, Wavelet, Discrete Cosine Transform (DCT), and Identity. Resulting images were compared with highly sampled and undersampled NUFFT-based images and evaluated for image quality (i.e. structural similarity), image intensity bias, and its effect on TSC estimates in gray and white matter. Wavelet-based CS reconstructions show highest image quality with stable TSC estimates for most USFs. Up to an USF of 4, images showed good structural detail. DCT and Identity-based CS enable good image quality, however show a bias in TSC with a reduction in estimates across USFs. The image intensity bias is lowest in Wavelet-based reconstructions and enables an up to fourfold acquisition speed up while maintaining good structural detail. The associated acquisition time reduction can facilitate a translation of sodium MRI into clinical routine.

Motion reduction for quantitative brain sodium MR imaging with a navigated flexible twisted projection imaging sequence at 9.4 T.

Quantitative measurement of the tissue sodium concentration (TSC) provides a metric for tissue cell volume fraction for monitoring tumor responses to therapy and neurodegeneration in the brain as well as applications outside the central nervous system such as the fixed charge density in cartilage. Despite the low detection sensitivity of the sodium MR signal compared to the proton signal and the requirement for a long repetition time to minimize longitudinal magnetization saturation, acquisition time has been reduced to less than 10 min for a nominal isotropic voxel size of 3.3 mm with the improved acquisition efficiency of twisted projection imaging (TPI) at 9.4 T. However, patient motion can degrade the accuracy of the quantification even within these acquisition times. Our goal has been to improve the robustness of quantitative sodium MR imaging by minimizing the impact of motion that may occur even in cooperative patients. We present a method to spatially encode a lower resolution navigator echo after encoding the free induction decay signal for the quantitative image at no time penalty. Both the imaging and navigator data are sampled with flexTPI readout trajectories. Navigator images are generated at a higher temporal resolution (∼1 min) albeit at lower spatial resolution (8 mm) than the quantitative high-resolution images. The multiple volumes of navigator echo images are then aligned to extract the translational and rotational motion parameters assuming rigid-body motion. These parameters are used to align the k-space data during the acquisition of each volume of the quantitative images. Our results show significantly reduced image blurring with this method when the subject's head moved randomly by up to 7° between the navigator acquisitions.

Exploring a new method for quantitative sodium MRI in the human upper leg with a surface coil and symmetrically arranged reference phantoms.

The aim of this study is to validate and evaluate the reproducibility of a new setup for the quantification of the tissue sodium concentration (TSC) in the human upper leg muscles with sodium MRI at 3 Tesla. This setup is making use of an emit and receive single loop surface coil together with a set of square, symmetrically arranged reference phantoms. As a second aim, the performances of two MRI protocols for the TSC quantification in the upper leg muscles are compared: one using an ultra-short echo time (UTE) 3-dimensional radial sequence (UTE-protocol), and the other one using standard gradient echo sequence (GRE-protocol). A validation test of the quantification of sodium concentration is performed in phantoms. The bias of the method is estimated and compared between both protocols. The reproducibility of TSC quantification is assessed in phantoms by the coefficient of variation (CV) and compared between both protocols. The reproducibility is also assessed in 11 health volunteers. Signal to noise ratio (SNR) maps are acquired in phantoms with both protocols in order to compare the resulting SNR. The apparatus and post processing were successfully implemented. The bias of the method was smaller than 10% in phantoms (excepted for Na concentration of 10 mmol/L when using the GRE protocol). The reproducibility of the method using symmetrically arranged phantoms was high in phantoms and humans (CV <5%). The GRE-protocol leads to a better SNR than the UTE-protocol in 2D images. The use of symmetrically arranged reference phantoms lead to reproducible results in phantoms and humans. Sodium imaging in the human upper leg with a single loop surface coil should be performed with a standard 2-dimensional GRE protocol if an optimal SNR is needed. However, the quantification of the fast and slow decay time constants of the sodium signal, which plays a role in the TSC quantification, still has to be done with a UTE sequence. Moreover, the quantification of sodium concentration is more accurate with the UTE protocol for small sodium concentrations (<20 mmol).

Correlation of quantitative conductivity mapping and total tissue sodium concentration at 3T/4T.

To investigate the correlation between electrical conductivity and sodium concentration, both measured in vivo, in the human brain. Conductivity measurements were performed on samples with different sodium (Na+ ) and agarose concentrations using a dielectric probe, and the correlation between conductivity and Na+ content was evaluated. Subsequently, brain conductivity and total Na+ content maps were measured in 8 healthy subjects using phase-based MREPT and sodium MRI, respectively. After co-registration and spatial normalization to the 1 mm 152 MNI brain atlas, the relationship between conductivity and tissue sodium concentration (TSC) was examined within different brain regions. The conductivities of agarose gels increased linearly with NaCl concentration, while remaining almost independent of agarose content. When measured in healthy subjects, conductivities showed positive correlation with total tissue sodium concentration (R = 0.39, P < 0.005). The same trend was found in gray matter (R = 0.36, P < 0.005) and in white matter (R = 0.28, P < 0.05). Tissue conductivity shows a positive correlation with total sodium concentration. Conductivity might serve as a novel technique to visualize the total tissue electrolyte concentration, although refinements in the consideration of e.g., tissue water content, would be necessary to improve the quantitative value.