Faculty Bibliography

In this article we present an up-to-date overview of the potential biomedical applications of sodium magnetic resonance imaging (MRI) in vivo. Sodium MRI is a subject of increasing interest in translational imaging research as it can give some direct and quantitative biochemical information on the tissue viability, cell integrity and function, and therefore not only help the diagnosis but also the prognosis of diseases and treatment outcomes. It has already been applied in vivo in most human tissues, such as brain for stroke or tumor detection and therapeutic response, in breast cancer, in articular cartilage, in muscle, and in kidney, and it was shown in some studies that it could provide very useful new information not available through standard proton MRI. However, this technique is still very challenging due to the low detectable sodium signal in biological tissue with MRI and hardware/software limitations of the clinical scanners. The article is divided in three parts: 1) the role of sodium in biological tissues, 2) a short review on sodium magnetic resonance, and 3) a review of some studies on sodium MRI on different organs/diseases to date.J. Magn. Reson. Imaging 2013;38:511-529. (c) 2013 Wiley Periodicals, Inc.

Purpose:To assess the potential use of sodium magnetic resonance (MR) imaging of cartilage, with and without fluid suppression by using an adiabatic pulse, for classifying subjects with versus subjects without osteoarthritis at 7.0 T.Materials and Methods:The study was approved by the institutional review board and was compliant with HIPAA. The knee cartilage of 19 asymptomatic (control subjects) and 28 symptomatic (osteoarthritis patients) subjects underwent 7.0-T sodium MR imaging with use of two different sequences: one without fluid suppression (radial three-dimensional sequence) and one with fluid suppression (inversion recovery [IR] wideband uniform rate and smooth truncation [WURST]). Fluid suppression was obtained by using IR with an adiabatic inversion pulse (WURST pulse). Mean sodium concentrations and their standard deviations were measured in the patellar, femorotibial medial, and lateral cartilage regions over four consecutive sections for each subject. The minimum, maximum, median, and average means and standard deviations were calculated over all measurements for each subject. The utility of these measures in the detection of osteoarthritis was evaluated by using logistic regression and the area under the receiver operating characteristic curve (AUC). Bonferroni correction was applied to the P values obtained with logistic regression.Results:Measurements from IR WURST were found to be significant predicators of all osteoarthritis (Kellgren-Lawrence score of 1-4) and early osteoarthritis (Kellgren-Lawrence score of 1 or 2). The minimum standard deviation provided the highest AUC (0.83) with the highest accuracy (>78%), sensitivity (>82%), and specificity (>74%) for both all osteoarthritis and early osteoarthritis groups.Conclusion:Quantitative sodium MR imaging at 7.0 T with fluid suppression by using adiabatic IR is a potential biomarker for osteoarthritis.(c) RSNA, 2013.

The critical design aim for a sodium/proton coil is to maximize sodium sensitivity and transmit field homogeneity while simultaneously providing adequate proton sensitivity and homogeneity. While most dual-frequency coils use lossy high-impedance trap circuits or PIN diodes to allow dual-resonance, we explored a nested-coil design for sodium/proton knee imaging at 7 T. A stand-alone eight-channel sodium receive array was implemented without standard dual-resonance circuitry to provide improved sodium signal-to-noise ratio. A detunable sodium birdcage was added for homogeneous sodium excitation and a four-channel proton transmit-receive array was added to provide anatomical reference imaging and B(0) shimming capabilities. Both additional modules were implemented with minimal disturbance to the eight-channel sodium array by managing their respective resonances and geometrical arrangement. In vivo sodium signal-to-noise ratio was 1.2-1.7 times greater in the developed eight-channel array than in a mononuclear sodium birdcage coil, whereas the developed four-channel proton array provided signal-to-noise ratio similar to that of a commercial mononuclear proton birdcage coil. Magn Reson Med, 2012. (c) 2012 Wiley Periodicals, Inc.

Osteoarthritis is a degenerative disease of articular cartilage that may be associated with a loss of glycosaminoglycans. Quantitative sodium magnetic resonance imaging is highly specific to glycosaminoglycan content and could be used to assess the biochemical degradation of cartilage in early osteoarthritis. However, the reproducibility and repeatability of this technique are not well documented. The aim of this study is to test the reproducibility and repeatability of sodium quantification in cartilage in vivo using intraday and interday acquisitions at 3 T and 7 T, with a radial 3D sequence, with and without fluid suppression. Fluid suppression was obtained by adiabatic inversion recovery (IR WURST) and is expected to improve the sensitivity of the method to glycosaminoglycan content. The root mean square of coefficients of variation are all in the range of 7.5-13.6%. No significant intermagnet, intersequence, intraday, and interday differences in the coefficients of variation were observed. Sodium quantification using IR WURST gave values closer to those reported in the literature for healthy cartilage (220-310 mM) than radial 3D. In conclusion, IR WURST was more accurate in context of sodium measurement, with a reproducibility and repeatability comparable to other compositional magnetic resonance imaging techniques of cartilage. Magn Reson Med, 2011. (c) 2011 Wiley Periodicals, Inc.

OBJECTIVES: To evaluate cartilage repair and native tissue using a three-dimensional (3D), radial, ultra-short echo time (UTE) (23)Na MR sequence without and with an inversion recovery (IR) preparation pulse for fluid suppression at 7 Tesla (T). METHODS: This study had institutional review board approval. We recruited 11 consecutive patients (41.5 +/- 11.8 years) from an orthopaedic surgery practice who had undergone a knee cartilage restoration procedure. The subjects were examined postoperatively (median = 26 weeks) with 7-T MRI using: proton-T2 (TR/TE = 3,000 ms/60 ms); sodium UTE (TR/TE = 100 ms/0.4 ms); fluid-suppressed, sodium UTE adiabatic IR. Cartilage sodium concentrations in repair tissue ([Na(+)](R)), adjacent native cartilage ([Na(+)](N)), and native cartilage within the opposite, non-surgical compartment ([Na(+)](N2)) were calculated using external NaCl phantoms. RESULTS: For conventional sodium imaging, mean [Na(+)](R), [Na(+)](N), [Na(+)](N2) were 177.8 +/- 54.1 mM, 170.1 +/- 40.7 mM, 172.2 +/- 30 mM respectively. Differences in [Na(+)](R) versus [Na(+)](N) (P = 0.59) and [Na(+)](N) versus [Na(+)](N2) (P = 0.89) were not significant. For sodium IR imaging, mean [Na(+)](R), [Na(+)](N), [Na(+)](N2) were 108.9 +/- 29.8 mM, 204.6 +/- 34.7 mM, 249.9 +/- 44.6 mM respectively. Decreases in [Na(+)](R) versus [Na(+)](N) (P = 0.0.0000035) and [Na(+)](N) versus [Na(+)](N2) (P = 0.015) were significant. CONCLUSIONS: Sodium IR imaging at 7 T can suppress the signal from free sodium within synovial fluid. This may allow improved assessment of [Na(+)] within cartilage repair and native tissue. KEY POINTS : * NaIR magnetic resonance imaging can suppress signal from sodium within synovial fluid. * NaIR MRI thus allows assessment of sodium concentration within cartilage tissue alone. * This may facilitate more accurate assessment of repair tissue composition and quality.

The sodium concentration correlates directly with the concentration of proteoglycans (PG) in cartilage, the loss of which is an early signature of osteoarthritis (OA). As a result, quantitative sodium MRI is a promising technique for assessing the degradation of articular cartilage in patients with OA. Sodium relaxation times can also provide information on the degradation of cartilage: it has already been shown on bovine cartilage that T(1) and T(2long) are longer and T(2short) shorter when the PG concentration decreases. In this study, sodium T(1) , T2short * and T2long * relaxation maps were measured in vivo at 7 T on 8 healthy volunteers and in 4 different regions of the cartilage in the knee joint. The patellar, femoro-tibial medial, lateral, and femoral condyle cartilage have an average T(1) approximately 20 ms, but different T2short * (from 0.5 ms to 1.4 ms) and T2long * (from 11.4 ms to 14.8 ms). Statistically significant differences in T(1) , T2short * and T2long * were observed between the different regions in cartilage (p << 10(- 5) ). Statistical differences in T(1) were also observed between male and female data (p << 10(- 5) ). These relaxation times measurements can further be applied as correction factors for sodium concentration maps in vivo and can also be useful as complementary information to quantitative sodium MRI in the quest for detecting early OA. These measurements were done on low resolution sodium images in order to acquire sufficient quality data for fitting (5 images for T(1) and 9 images for T2 *) while keeping the total time of acquisition of the data reasonable for the volunteer's comfort (1 h 15 min)

PURPOSE: To compare a new birdcage-transmit, 28-channel receive array (28-Ch) coil and a quadrature volume coil for 7T morphologic MRI and T2 mapping of knee cartilage. MATERIALS AND METHODS: The right knees of 10 healthy subjects were imaged on a 7T whole body magnetic resonance (MR) scanner using both coils. 3D fast low-angle shot (3D-FLASH) and multiecho spin-echo (MESE) sequences were implemented. Cartilage signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), thickness, and T2 values were assessed. RESULTS: SNR/CNR was 17%-400% greater for the 28-Ch compared to the quadrature coil (P </= 0.005). Bland-Altman plots show mean differences between measurements of tibial/femoral cartilage thickness and T2 values obtained with each coil to be small (-0.002 +/- 0.009 cm / 0.003 +/- 0.011 cm) and large (-6.8 +/- 6.7 msec/-8.2 +/- 9.7 msec), respectively. For the 28-Ch coil, when parallel imaging with acceleration factors (AF) 2, 3, and 4 was performed SNR retained was: 62%-69%, 51%-55%, and 39%-45%. CONCLUSION: A 28-Ch knee coil provides increased SNR/CNR for 7T cartilage morphologic imaging and T2 mapping. Coils should be switched with caution during clinical studies because T2 values may differ. The greater SNR of the 28-Ch coil could be used to perform parallel imaging with AF2 and obtain similar SNR as the quadrature coil. J. Magn. Reson. Imaging 2012;441-448. (c) 2011 Wiley Periodicals, Inc

Sodium MRI has been shown to be highly specific for glycosaminoglycan (GAG) content in articular cartilage, the loss of which is an early sign of osteoarthritis (OA). Quantitative sodium MRI techniques are therefore under development in order to detect and assess early biochemical degradation of cartilage, but due to low sodium NMR sensitivity and its low concentration, sodium images need long acquisition times (15-25min) even at high magnetic fields and are typically of low resolution. In this preliminary study, we show that compressed sensing can be applied to reduce the acquisition time by a factor of 2 at 7T without losing sodium quantification accuracy. Alternatively, the nonlinear reconstruction technique can be used to denoise fully-sampled images. We expect to even further reduce this acquisition time by using parallel imaging techniques combined with SNR-improved 3D sequences at 3T and 7T