Sodium Magnetic Resonance Imaging Research Articles

Quantitative sodium MR imaging: A review of its evolving role in medicine

Sodium magnetic resonance (MR) imaging in humans has promised metabolic information that can improve medical management in important diseases. This technology has yet to find a role in clinical practice, lagging proton MR imaging by decades. This review covers the literature that demonstrates that this delay is explained by initial challenges of low sensitivity at low magnetic fields and the limited performance of gradients and electronics available in the 1980s. These constraints were removed by the introduction of 3T and now ultrahigh (≥7T) magnetic field scanners with superior gradients and electronics for proton MR imaging. New projection pulse sequence designs have greatly improved sodium acquisition efficiency. The increased field strength has provided the expected increased sensitivity to achieve resolutions acceptable for metabolic interpretation even in small target tissues. Consistency of quantification of the sodium MR image to provide metabolic parametric maps has been demonstrated by several different pulse sequences and calibration procedures. The vital roles of sodium ion in membrane transport and the extracellular matrix will be reviewed to indicate the broad opportunities that now exist for clinical sodium MR imaging. The final challenge is for the technology to be supplied on clinical ≥3T scanners.

Changes in Cartilage and Tendon Composition of Patients With Type I Diabetes Mellitus: Identification by Quantitative Sodium Magnetic Resonance Imaging at 7 T.

The aim of this study was to investigate possible biochemical alterations in tendons and cartilage caused by type 1 diabetes mellitus (DM1), using quantitative in vivo 7 T sodium magnetic resonance (MR) imaging. The institutional review board approved this prospective study, and written informed consent was obtained. Eight DM1 patients with no history of knee trauma and 9 healthy age- and weight-matched volunteers were examined at 7 T using dedicated knee coils.All participants underwent morphological and sodium MR imaging. Region-of-interest analysis was performed manually for the non-weight-bearing area of the femoral condyle cartilage and for the patella tendon. Two readers read the image data sets independently, twice, for intrareader and interreader agreement. Normalized mean sodium signal intensity (NMSI) values were compared between patients and volunteers for each reader using analysis of variance. On morphological images, cartilage in the non-weight-bearing area and the patellar tendon was intact in all patients. On sodium MR imaging, bivariate analysis of variance showed significantly lower mean NMSI values in the cartilage (P = 0.008) and significantly higher values in the tendons (P = 0.025) of patients compared with those of volunteers. Our study showed significantly different NMSI values between DM1 patients and matched volunteers. Differences observed in the cartilage and tendon might be associated with a DM1-related alteration of biochemical composition that occurs before it can be visualized on morphological MR sequences.

Brain intra- and extracellular sodium concentration in multiple sclerosis: a 7 T MRI study.

Intra-axonal accumulation of sodium ions is one of the key mechanisms of delayed neuro-axonal degeneration that contributes to disability accrual in multiple sclerosis. In vivo sodium magnetic resonance imaging studies have demonstrated an increase of brain total sodium concentration in patients with multiple sclerosis, especially in patients with greater disability. However, total sodium concentration is a weighted average of intra- and extra-cellular sodium concentration whose changes reflect different tissue pathophysiological processes. The in vivo, non-invasive measurement of intracellular sodium concentration is quite challenging and the few applications in patients with neurological diseases are limited to case reports and qualitative assessments. In the present study we provide first evidence of the feasibility of triple quantum filtered (23)Na magnetic resonance imaging at 7 T, and provide in vivo quantification of global and regional brain intra- and extra-cellular sodium concentration in 19 relapsing-remitting multiple sclerosis patients and 17 heathy controls. Global grey matter and white matter total sodium concentration (respectively P < 0.05 and P < 0.01), and intracellular sodium concentration (both P < 0.001) were higher while grey matter and white matter intracellular sodium volume fraction (indirect measure of extracellular sodium concentration) were lower (respectively P = 0.62 and P < 0.001) in patients compared with healthy controls. At a brain regional level, clusters of increased total sodium concentration and intracellular sodium concentration and decreased intracellular sodium volume fraction were found in several cortical, subcortical and white matter regions when patients were compared with healthy controls (P < 0.05 family-wise error corrected for total sodium concentration, P < 0.05 uncorrected for multiple comparisons for intracellular sodium concentration and intracellular sodium volume fraction). Measures of total sodium concentration and intracellular sodium volume fraction, but not measures of intracellular sodium concentration were correlated with T2-weighted and T1-weighted lesion volumes (0.05 < P < 0.01) and with Expanded Disability Status Scale (P < 0.05). Thus, suggesting that while intracellular sodium volume fraction decrease could reflect expansion of extracellular space due to tissue loss, intracellular sodium concentration increase could reflect neuro-axonal metabolic dysfunction.

Optimization and comparison of two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging.

In this study, two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging (MRI) were designed and compared. Two 1.5 T dual-tuned birdcages, a four-ring birdcage (FRB) and an alternating rungs birdcage (ARB), were built and then characterized by bench and MRI measurements. The relative uniformity (RU) and the efficiency of the coils were compared using (23)Na and (1)H B1 maps. In vivo images of a volunteer were acquired. Bench measurements showed matching and decoupling coefficients of the quadrature channels lower than -20 dB. The RUs and 180° pulse amplitudes of the FRB/ARB were determined as: (1)H RU =94.4/74.4%, (23)Na RU =95.2/93.6%, (1)H 180° pulse amplitude =69.2/75.4 V and (23)Na 180° pulse amplitude =45.1/45.9 V. The in vivo (23)Na images acquired with the FRB show a signal-to-noise ratio (SNR) of 6 to 14 in the cartilage. Due to its superior (1)H homogeneity and efficiency and its slightly better (23)Na homogeneity, the FRB is the overall preferred coil for the given requirements of this study. The achieved in vivo SNR is adequate for quantitative (23)Na and high resolution (1)H imaging.

Comparison of multiple quantitative MRI parameters for characterization of the goat cartilage in an ongoing osteoarthritis: dGEMRIC, T1ρ and sodium

Rationale and ObjectivesOsteoarthritis (OA) is a degenerative joint disease leading to cartilage deterioration by loss of matrix, fibrillation, formation of fissures, and ultimately complete loss of the cartilage surface. Here, three magnetic resonance imaging (MRI) techniques, dGEMRIC (delayed Gadolinium enhanced MRI of cartilage; dG1=T1,post; dG2=1/T1,post-1/T1,pre), T1ρ,and sodium MRI, are compared in a preclinical in vivo study to evaluate the differences in their potential for cartilage characterization and to establish an examination protocol for a following clinical study. Materials and MethodsOA was induced in 12 caprine knees (6 control, 6 therapy). Adipose derived stem cells were injected afterwards as a treatment. The animals were examined healthy, 3 and 16 weeks postoperatively with all three MRI methods.Using statistical analysis, the OA development and the degree of correlation between the different MRI methods were determined. ResultsA strong correlation was observed between the dGEMRIC indices dG1 and dG2 (r=–0.87) which differ only in considering or not considering the T1 baseline. Moderate correlations were found between T1ρ and dG1 (r=0.55), T1ρ and dG2 (r=0.47) and at last, sodium and dG1 (r=0.45).The correlations found in this study match to the biomarkers which the methods are sensitive to. ConclusionEven though the goat cartilage is significantly thinner than the human cartilage and even more in a degenerated cartilage, all three methods were able to characterize the cartilage over the whole period of time during an ongoing OA.Due to measurement and post processing optimizations, as well as the correlations detected in this work, the overall measurement time in future goat studies can be minimized. Moreover, an examination protocol for characterizing the cartilage in a clinical study was established.

Sodium inversion recovery MRI on the knee joint at 7 T with an optimal control pulse

In the field of sodium magnetic resonance imaging (MRI), inversion recovery (IR) is a convenient and popular method to select sodium in different environments. For the knee joint, IR has been used to suppress the signal from synovial fluids, which improves the correlation between the sodium signal and the concentration of glycosaminoglycans (GAGs) in cartilage tissues. For the better inversion of the magnetization vector under the spatial variations of the B0 and B1 fields, the IR sequence usually employ adiabatic pulses as the inversion pulse. On the other hand, it has been shown that RF shapes robust against the variations of the B0 and B1 fields can be generated by numerical optimization based on optimal control theory. In this work, we compare the performance of fluid-suppressed sodium MRI on the knee joint in vivo, between one implemented with an adiabatic pulse in the IR sequence and the other with the adiabatic pulse replaced by an optimal-control shaped pulse. While the optimal-control pulse reduces the RF power deposited to the body by 58%, the quality of fluid suppression and the signal level of sodium within cartilage are similar between two implementations.

Heterogeneity of acute multiple sclerosis lesions on sodium (23Na) MRI

Background: Advanced magnetic resonance imaging (MRI) techniques provide a window into pathological processes in multiple sclerosis (MS). Nevertheless, to date only few studies have performed sodium MRI in MS. Objectives: We analysed total sodium concentration (TSC) in hyperacute, acute and chronic lesions in MS with 23Na MRI. Methods: 23Na MRI and 1H MRI were performed in 65 MS patients and 10 healthy controls (HC). Mean TSC was quantified in all MS lesions with a diameter of >5 mm and in the normal appearing white and grey matter (NAWM, NAGM). Results: TSC in the NAWM and the NAGM of MS patients was significantly higher compared to HC (WM: 37.51 ± 2.65 mM versus 35.17 ± 3.40 mM; GM: 43.64 ± 2.75 mM versus 40.09 ± 4.64 mM). Acute and chronic MS lesions showed elevated TSC levels of different extent (contrast-enhancing lesions (49.07 ± 6.99 mM), T1 hypointense lesions (45.06 ± 6.26 mM) and remaining T1 isointense lesions (39.88 ± 5.54 mM)). However, non-enhancing hyperacute lesions with a reduced apparent diffusion coefficient showed a TSC comparable to the NAWM (37.22 ± 4.62 mM). Conclusions: TSC is not only a sensitive marker of the severity of chronic tissue abnormalities in MS but is also highly sensitive to opening of the blood–brain barrier and vasogenic tissue oedema in contrast-enhancing lesions.

In Vivo Sodium MRI for Mouse Model of Ischemic Stroke at 7 T: Preliminary Results

Previous studies have used sodium magnetic resonance imaging (MRI) to investigate the increase in tissue sodium concentration that occurs during a stroke by using various animal models of brain ischemia. However, most of these studies have involved rats, cats, or nonhuman primates. Although studies involving mice are relatively scant, mice have become the principal animal model for studying many human diseases, particularly in the field of genetics. Accordingly, this study employed sodium MRI to monitor changes in the intensity of sodium signals in a mouse model of ischemic stroke. The experiments were conducted using a 7-T MRI system, and a commercial double-tuned sodium/proton transmit-receive surface coil was used to capture the sodium and proton signal images. Sodium MRI was performed using a fast low-angle shot pulse sequence. The mice underwent middle cerebral artery occlusion to induce focal brain ischemia 48 h before the MRI scans were performed. The signal intensity of the sodium image was determined for a region of interest (ROI) in the ischemic area, and an ROI contralateral to this area. The average signal intensity in the sodium images of the mouse brains exhibited a 2.51-fold increase and a standard deviation was 0.93. The results of this study demonstrate the feasibility of using a 7-T MRI system to perform sodium MRI of a mouse model of ischemic stroke. The sodium signal intensity of the mouse brain revealed a substantial increase in sodium levels in the ischemic area compared with that in the contralateral brain hemisphere.

Balancing wobbles in the body sodium.

Sodium balance is achieved within a matter of days and everything that enters should come out; sodium stores are of questionable relevance and sodium accumulation is accompanied by weight gain. Careful balance studies oftentimes conflicted with this view, and long-term studies suggested that total body sodium (TBNa) fluctuates independent of intake or body weight. We recently performed the opposite experiment in that we fixed sodium intake for weeks at three levels of sodium intake and collected all urine made. We found weekly (circaseptan) patterns in sodium excretion that were inversely related to aldosterone and directly related to cortisol. TBNa was not dependent on sodium intake, but instead exhibited far longer (greater than or equal to monthly) infradian rhythms independent of extracellular water, body weight or blood pressure. To discern the mechanisms further, we delved into sodium magnetic resonance imaging (Na-MRI) to identify sodium storage clinically. We found that sodium stores are greater in men than in women, increase with age and are higher in hypertensive than normotensive persons. We have suggestive evidence that these sodium stores can be mobilized, also in dialysis patients. The observations are in accordance with our findings that immune cells regulate a hypertonic interface in the skin interstitium that could serve as a protective barrier. Returning to our balance studies, we found that due to biological variability in 24-h sodium excretion, collecting urine for a day could not separate 12, 9 or 6 g/day sodium intakes with the precision of tossing a coin. Every other daily urine sampling correctly classified a 3-g difference in salt intake less than half the time, making the gold standard 24-h urine collection of little value in predicting salt intake. We suggest that wobbles in expected outcomes can lead to novel clinical insights even with respect to banal salt questions.

High Field Sodium MRI Assessment of Stem Cell Chondrogenesis in a Tissue-Engineered Matrix.

The development of non-invasive assessment techniques in vitro and in vivo is essential for monitoring and evaluating the growth of engineered cartilage tissues. Magnetic resonance imaging (MRI) is the leading non-invasive imaging modality used for assessing engineered cartilage. Typical MRI uses water proton relaxation times (T1 and T2) and apparent diffusion coefficient (ADC) to assess tissue growth. These techniques, while excellent in providing the first assurance of tissue growth, are unspecific to monitor the progress of engineered cartilage extracellular matrix components. In the current article, we present high field (11.7 T, (1)H freq. = 500 MHz) sodium MRI assessment of tissue-engineered cartilage at the early stage of tissue growth in vitro. We observed the chondrogenesis of human bone marrow derived stromal cells seeded in a gradient polymer-hydrogel matrix made out of poly(85 lactide-co-15 glycolide)--PuraMatrix™ for 4 weeks. We calculated the sodium concentration in the engineered constructs using a model of sodium MRI voxels that takes into account scaffold volume, cell density and amount of glycosaminoglycan (GAG). The sodium concentration was then converted to the fixed charge density (FCD) and compared with FCD derived from biochemical GAG analysis. Despite the small amount of GAG present in the engineered constructs, the sodium MRI derived FCD is found to be correlated (Pearson correlation coefficient R = 0.79) with the FCD derived from biochemical analysis. We conclude that sodium MRI could prove to be an invaluable tool in assessing engineered cartilage quantitatively during the repair or regeneration of cartilage defects.

3 Tesla 23Na Magnetic Resonance Imaging During Aerobic and Anaerobic Exercise

The aim of the work described here was to determine the feasibility of monitoring Na(+) concentration and distribution in muscle/skin during aerobic/anaerobic exercise with (23)Na magnetic resonance imaging (MRI). The Na(+) concentration and water content of muscle/skin of the left lower leg of six healthy subjects (mean age, 26 years; range, 22-30 years; three men and three women) were assessed before and after aerobic/anaerobic cycle ergometry and during recovery with 3-T (23)Na/(1)H MRI. (23)Na MRI was performed with a custom-made knee coil. A gradient echo sequence with an acquisition time of 3.25 minutes, echo time of 2.07 ms, repetition time of 100 ms, and spatial resolution of 3 × 3 × 30 mm(3) was applied. Phantoms with increasing sodium concentration served for quantification via linear extrapolation. Blood values were determined by blood gas analysis. The concentration of Na(+) significantly increased during anaerobic exercise in all muscle compartments except the medial gastrocnemius muscle, whereas no significant change was observed in most muscle compartments during aerobic exercise (only the soleus muscle exhibited a significant increase in Na(+) concentration during aerobic exercise: 1.6 ± 1.5 mmol/kg, 4.5%, P = .046). During anaerobic exercise, the mean Na(+) concentration of the triceps surae and the whole leg increased by 9.0% (3.1 ± 2.1 mmol/kg, P = .016) and 6.5% (2.2 ± 1.3 mmol/kg, P < .01). MRI revealed a water-independent increase in Na(+) concentration in most muscle compartments during anaerobic exercise. Na(+) concentration significantly decreased during recovery after anaerobic and aerobic exercise in all muscle compartments except the soleus. The Na(+) concentration of the skin did not significantly change during anaerobic/aerobic exercise. Sodium(23) MRI allows reliable and noninvasive visualization and quantification of Na(+) concentration and distribution in muscle and skin during exercise. (23)Na MRI can be used to gain new insights into Na(+) homeostasis, presumably leading to better comprehension of pathophysiology.

Retrospectively-gated CINE 23Na imaging of the heart at 7.0 Tesla using density-adapted 3D projection reconstruction

PurposeImplementation, evaluation and application of a pulse sequence for retrospectively-gated sodium magnetic resonance imaging of the human heart. MethodsMeasurements were conducted at a magnetic field strength of 7.0Tesla. A 3D projection reconstruction technique using a standard (ST) and a golden angle (GA) acquisition scheme for short echo time 23Na MR was applied. Data were acquired continuously without cardiac triggering using a free breathing regime. Arbitrary phases of the cardiac cycle were reconstructed using synchronization with a physiological trigger signal and different temporal resolutions. Phantom measurements and examinations of healthy subjects were performed to evaluate the performance of the ST and GA acquisition schemes. A signal-to-background ratio (SBR) — that compromises both the signal-to-noise ratio and artifacts — was calculated for benchmarking the GA and ST scheme. ResultsIn phantom measurements, the measured SBR of the GA acquisition scheme was up to 88% higher versus ST. Undersampling artifacts were reduced in GA compared to the ST sampling scheme. Whole heart coverage sodium images could be reconstructed with a nominal spatial resolution of (6mm)3 and a temporal resolution of Δt=0.1s for covering the entire cardiac cycle. Changes in overall heart volume and myocardial wall thickness throughout the cardiac cycle were clearly visible in the reconstructed images. For the in vivo data and the imaging protocol used, GA provided a mean SBR of 38.0±5.5 while ST provided a mean SBR of 37.2±2.2. ConclusionRetrospectively-gated CINE 23Na imaging of the heart at 7.0T using density-adapted 3D projection reconstruction is feasible. The GA acquisition scheme is superior to the ST acquisition.

Sodium-23 MRI of whole spine at 3 Tesla using a 5-channel receive-only phased-array and a whole-body transmit resonator

Sodium magnetic resonance imaging (23Na MRI) is a unique and non-invasive imaging technique which provides important information on cellular level about the tissue of the human body. Several applications for 23Na MRI were investigated with regard to the examination of the tissue viability and functionality for example in the brain, the heart or the breast. The 23Na MRI technique can also be integrated as a potential monitoring instrument after radiotherapy or chemotherapy. The main contribution in this work was the adaptation of 23Na MRI for spine imaging, which can provide essential information on the integrity of the intervertebral disks with respect to the early detection of disk degeneration.In this work, a transmit-only receive-only dual resonator system was designed and developed to cover the whole human spine using 23Na MRI and increase the receive sensitivity. The resonator system consisted of an already presented 23Na whole-body resonator and a newly developed 5-channel receive-only phased-array. The resonator system was first validated using bench top and phantom measurements. A threefold SNR improvement at the depth of the spine (∼7cm) over the whole-body resonator was achieved using the spine array. 23Na MR measurements of the human spine using the transmit-only receive-only resonator system were performed on a healthy volunteer within an acquisition time of 10minutes. A density adapted 3D radial sequence was chosen with 6mm isotropic resolution, 49ms repetition time and a short echo time of 540μs. Furthermore, it was possible to quantify the tissue sodium concentration in the intervertebral discs in the lumbar region (120ms repetition time) using this setup.

Sodium magnetic resonance imaging of ankle joint in cadaver specimens, volunteers, and patients after different cartilage repair techniques at 7 T: initial results.

The goal of cartilage repair techniques such as microfracture (MFX) or matrix-associated autologous chondrocyte transplantation (MACT) is to produce repair tissue (RT) with sufficient glycosaminoglycan (GAG) content. Sodium magnetic resonance imaging (MRI) offers a direct and noninvasive evaluation of the GAG content in native cartilage and RT. In the femoral cartilage, this method was able to distinguish between RTs produced by MFX and MACT having different GAG contents. However, it needs to be clarified whether sodium MRI can be useful for evaluating RT in thin ankle cartilage. Thus, the aims of this 7-T study were (1) to validate our sodium MRI protocol in cadaver ankle samples, (2) to evaluate the sodium corrected signal intensities (cSI) in cartilage of volunteers, (3) and to compare sodium values in RT between patients after MFX and MACT treatment. Five human cadaver ankle samples as well as ankles of 9 asymptomatic volunteers, 6 MFX patients and 6 MACT patients were measured in this 7-T study. Sodium values from the ankle samples were compared with histochemically evaluated GAG content. In the volunteers, sodium cSI values were calculated in the cartilages of ankle and subtalar joint. In the patients, sodium cSI in RT and reference cartilage were measured, morphological appearance of RT was evaluated using the magnetic resonance observation of cartilage repair tissue (MOCART) scoring system, and clinical outcome before and after surgery was assessed using the American Orthopaedic Foot and Ankle Society score and Modified Cincinnati Knee Scale. All regions of interest were defined on morphological images and subsequently transferred to the corresponding sodium images. Analysis of variance, t tests, and Pearson correlation coefficients were evaluated. In the patients, significantly lower sodium cSI values were found in RT than in reference cartilage for the MFX (P = 0.007) and MACT patients (P = 0.008). Sodium cSI and MOCART scores in RT did not differ between the MFX and MACT patients (P = 0.185). No significant difference in sodium cSI was found between reference cartilage of the volunteers and the patients (P = 0.355). The patients showed significantly higher American Orthopaedic Foot and Ankle Society and Modified Cincinnati scores after treatment than they did before treatment. In the volunteers, sodium cSI was significantly higher in the tibial cartilage than in the talar cartilage of ankle joint (P = 0.002) and in the talar cartilage than in the calcaneal cartilage of subtalar joint (P < 0.001). Data from the cadaver ankle samples showed a strong linear relationship between the sodium values and the histochemically determined GAG content (r = 0.800; P < 0.001; R = 0.639). This study demonstrates the feasibility of in vivo quantification of sodium cSI, which can be used for GAG content evaluation in thin cartilages of ankle and subtalar joints at 7 T. A strong correlation observed between the histochemically evaluated GAG content and the sodium values proved the sufficient sensitivity of sodium MRI to changes in the GAG content of cartilages in the ankle. Both MFX and MACT produced RT with lower sodium cSI and, thus, of lower quality compared with reference cartilage in the patients or in the volunteers. Our results suggest that MFX and MACT produce RT with similar GAG content and similar morphological appearance in patients with similar surgery outcome. Sodium MRI at 7 T allows a quantitative evaluation of RT quality in the ankle and may thus be useful in the noninvasive assessment of new cartilage repair procedures.

Partial volume correction for in vivo 23Na-MRI data of the human brain

The concentration of sodium is a functional cell parameter and absolute quantification can be interesting for diagnostical purposes. The accuracy of sodium magnetic resonance imaging (23Na-MRI) is strongly biased by partial volume effects (PVEs). Hence our purpose was to establish a partial volume correction (PVC) method for 23Na-MRI.The existing geometric transfer matrix (GTM) correction method was transferred from positron emission tomography (PET) to 23Na-MRI and tested in a phantom study. Different parameters, as well as accuracy of registration and segmentation were evaluated prior to first in vivo measurements. In vivo sodium data-sets of the human brain were obtained at B0=7T with a nominal spatial resolution of (3mm)3 using a density adapted radial pulse sequence. A volunteer study with four healthy subjects was performed to measure partial volume (PV) corrected tissue sodium concentration (TSC) which was verified by means of an intrinsic correction control.In the phantom study the PVC algorithm yielded a good correction performance and reduced the discrepancy between the measured sodium concentration value and the expected value in the smallest compartments of the phantom by 11% to a mean PVE induced discrepancy of 5.7% after correction. The corrected in vivo data showed a reduction of PVE bias for the investigated compartments for all volunteers, resulting in a mean reduction of discrepancy between two separate CSF compartments from 36% to 7.6%. The absolute TSC for two separate CSF compartments (sulci, lateral ventricles), gray and white brain matter after correction were 129±8mmol/L, 138±4mmol/L, 48±1mmol/L and 43±3mmol/L, respectively.The applied PVC algorithm reduces the PV-bias in quantitative 23Na-MRI. Accurate, high-resolution anatomical data is required to enable appropriate PVC. The algorithm and segmentation approach is robust and leads to reproducible results.

Repeatability of quantitative sodium magnetic resonance imaging for estimating pseudo-intracellular sodium concentration and pseudo-extracellular volume fraction in brain at 3 T.

The purpose of this study is to assess the repeatability of the quantification of pseudo-intracellular sodium concentration (C1) and pseudo-extracellular volume fraction (α) estimated in brain in vivo using sodium magnetic resonance (MRI) at 3 T. Eleven healthy subjects were scanned twice, with two sodium MRI acquisitions (with and without fluid suppression by inversion recovery), and two double inversion recovery (DIR) proton MRI. DIR MRIs were used to create masks of gray and white matter (GM, WM), that were subsequently applied to the C1 and α maps calculated from sodium MRI and a tissue three-compartment model, in order to measure the distributions of these two parameters in GM, WM or full brain (GM+WM) separately. The mean, median, mode, standard deviation (std), skewness and kurtosis of the C1 and α distributions in whole GM, WM and full brain were calculated for each subject, averaged over all data, and used as parameters for the repeatability assessment. The coefficient of variation (CV) was calculated as a measure of reliability for the detection of intra-subject changes in C1 and αfor each parameter, while intraclass correlation (ICC) was used as a measure of repeatability. It was found that the CV of most of the parameters was around 10–20% (except for C1 kurtosis which is about 40%) for C1 and α measurements, and that ICC was moderate to very good (0.4 to 0.9) for C1 parameters and for some of the α parameters (mainly skewness and kurtosis). In conclusion, the proposed method could allow to reliably detect changes of 50% and above of the different measurement parameters of C1 and αin neuropathologies (multiple sclerosis, tumor, stroke, Alzheimer’s disease) compared to healthy subjects, and that skewness and kurtosis of the distributions of C1 and αseem to be the more sensitive parameters to these changes.

Multiparametric MR Imaging Depicts Glycosaminoglycan Change in the Achilles Tendon during Ciprofloxacin Administration in Healthy Men: Initial Observation.

To determine if quantitative magnetic resonance (MR) imaging techniques (sodium MR imaging, glycosaminoglycan [GAG] chemical exchange saturation transfer [CEST], and T2* mapping) could be used as potential markers for biochemical changes in the Achilles tendon induced by ciprofloxacin intake. The ethics committee of the Medical University of Vienna approved the protocol (number 1225/2012), and all patients gave written informed consent. Fourteen ankles from seven men (mean age, 32 years ± 12 [standard deviation]) were included in the study. All patients underwent 7-T MR imaging examinations of the Achilles tendon at baseline and 10 days and 5 months after ciprofloxacin intake. Sodium signal and T2* maps were acquired with the variable echo-time sequence and the GAG CEST values were acquired with a three-dimensional radiofrequency spoiled gradient-recalled-echo sequence. The mean sodium signal was significantly decreased by 25% in the whole tendon (from baseline to 10 days after ciprofloxacin intake, 130 arbitrary units [au] ± 8 to 98 au ± 5, respectively; P = .023) and returned to baseline after 5 months (116 au ± 10), as observed also at the tendon insertion (baseline, 10 days after ciprofloxacin intake, and 5 months after ciprofloxacin intake, 134 au ± 8, 105 au ± 5, and 119 au ± 9, respectively; P = .034). The mean GAG CEST value in the whole tendon was parallel to the sodium signal with a decrease from baseline to 10 days after ciprofloxacin intake, 4.74% ± 0.75 to 4.50% ± 0.23, respectively (P = .028) and an increase at 5 months after ciprofloxacin intake to 4.88% ± 1.02. In conclusion, this study demonstrates a ciprofloxacin-induced reversible reduction of the normalized sodium MR imaging signal and the GAG CEST effect in the Achilles tendon of healthy volunteers. Changes in sodium MR imaging and GAG CEST in men may reflect a decrease of GAG content in the Achilles tendon after ciprofloxacin intake.

Tissue sodium storage: evidence for kidney-like extrarenal countercurrent systems?

Recent evidence from chemical analysis of tissue electrolyte and water composition has shown that body Na(+) content in experimental animals is not constant, does not always readily equilibrate with water, and cannot be exclusively controlled by the renal blood purification process. Instead, large amounts of Na(+) are stored in the skin and in skeletal muscle. Quantitative non-invasive detection of Na(+) reservoirs with sodium magnetic resonance imaging ((23)NaMRI) suggests that this mysterious Na(+) storage is not only an animal research curiosity but also exists in humans. In clinical studies, tissue Na(+) storage is closely associated with essential hypertension. In animal experiments, modulation of reservoir tissue Na(+) content leads to predictable blood pressure changes. The available evidence thus suggests that the patho(?)-physiological process of Na(+) storage might be of relevance for human health and disease.

Sodium magnetic resonance imaging using ultra-short echo time sequences with anisotropic resolution and uniform k-space sampling

A method for uniform k-space sampling of 3D ultra-short echo time (UTE) techniques with anisotropic resolution in one direction is introduced to increase signal-to-noise ratio (SNR). State-of-the-art acquisition schemes for sodium MRI with radial (projection reconstruction) and twisting (twisted projection imaging (TPI)) trajectories are investigated regarding SNR efficiency, blurring behavior under T2⁎ decay, and measurement time in case of anisotropic field-of-view and resolution. 3D radial and twisting trajectories are redistributed in k-space for UTE sodium MRI with homogeneous noise distribution and optimal SNR efficiency, if T2⁎ decay can be neglected. Simulations based on Voronoi tessellations and phantom simulations/measurements were performed to calculate SNR efficiency. Point-spread functions were simulated to demonstrate the influence of T2⁎ decay on SNR and resolution. Phantom simulations/measurements and in vivo measurements confirm the SNR gain obtained by simulations based on Voronoi cells. An increase in SNR of up to 21% at an anisotropy factor of 10 could be theoretically achieved by TPI with projection adaption compared to the same sequence but without redistribution of projections in k-space. Sodium MRI with anisotropic resolution and uniform k-space sampling is demonstrated by in vivo measurements of human intervertebral disks and heart at 3 T. The SNR gain can be invested in a measurement time reduction of up to 32%, which is important especially for sodium MRI.

Classification of sodium MRI data of cartilage using machine learning.

To assess the possible utility of machine learning for classifying subjects with and subjects without osteoarthritis using sodium magnetic resonance imaging data. Theory: Support vector machine, k-nearest neighbors, naïve Bayes, discriminant analysis, linear regression, logistic regression, neural networks, decision tree, and tree bagging were tested. Sodium magnetic resonance imaging with and without fluid suppression by inversion recovery was acquired on the knee cartilage of 19 controls and 28 osteoarthritis patients. Sodium concentrations were measured in regions of interests in the knee for both acquisitions. Mean (MEAN) and standard deviation (STD) of these concentrations were measured in each regions of interest, and the minimum, maximum, and mean of these two measurements were calculated over all regions of interests for each subject. The resulting 12 variables per subject were used as predictors for classification. Either Min [STD] alone, or in combination with Mean [MEAN] or Min [MEAN], all from fluid suppressed data, were the best predictors with an accuracy >74%, mainly with linear logistic regression and linear support vector machine. Other good classifiers include discriminant analysis, linear regression, and naïve Bayes. Machine learning is a promising technique for classifying osteoarthritis patients and controls from sodium magnetic resonance imaging data.