Triple-tuned birdcage and single-tuned dipole array for quadri-nuclear head MRI at 7 T.

PURPOSE: The purpose of this work was to design and build a coil for quadri-nuclear MRI of the human brain at 7 T. METHODS: We built a transmit/receive triple-tuned (45.6 MHz for 2 $$ {}^2 $$ H, 78.6 MHz for 23 $$ {}^{23} $$ Na, and 120.3 MHz for 31 $$ {}^{31} $$ P) quadrature four-rod birdcage that was geometrically interleaved with a transmit/receive four-channel dipole array (297.2 MHz for 1 $$ {}^1 $$ H). The birdcage rods contained passive, two-pole resonant circuits that emulated capacitors required for single-tuning at three frequencies. The birdcage assembly also included triple-tuned matching networks, baluns, and transmit/receive switches. We assessed the performance of the coil with quality factor (Q) and signal-to-noise ratio (SNR) measurements, and performed in vivo multinuclear MRI and MR spectroscopic imaging (MRSI). RESULTS: Q measurements showed that the triple-tuned birdcage efficiency was within 33% of that of single-tuned baseline birdcages at all three frequencies. The quadri-tuned coil SNR was 78%, 59%, 44%, and 48% lower than that of single or dual-tuned reference coils for 1 $$ {}^1 $$ H, 2 $$ {}^2 $$ H, 23 $$ {}^{23} $$ Na, and 31 $$ {}^{31} $$ P, respectively. Quadri-nuclear MRI and MRSI was demonstrated in brain in vivo in about 30 min. CONCLUSION: While the SNR of the quadruple tuned coil was significantly lower than dual- and single-tuned reference coils, it represents a step toward truly simultaneous quadri-nuclear measurements.

Super-resolution of sodium images from simultaneous 1 H MRF/23 Na MRI acquisition.

In this work, we introduce a super-resolution method that generates a high-resolution (HR) sodium (23 Na) image from simultaneously acquired low-resolution (LR) 23 Na density-weighted MRI and HR proton density, T1 , and T2 maps from proton (1 H) MR fingerprinting in the brain at 7 T. The core of our method is a partial least squares regression between the HR (1 H) images and the LR (23 Na) image. An iterative loop and deconvolution with the point spread function of each acquired image were included in the algorithm to generate a final HR 23 Na image without losing features from the LR 23 Na image. The method was applied to simultaneously acquired HR proton and LR sodium data with in-plane resolution ratios between sodium and proton data of 3.8 and 1.9 and the same slice thickness. Four volunteers were scanned to evaluate the method's performance. For the data with a resolution ratio of 3.8, the mean absolute difference between the generated and ground truth HR 23 Na images was in the range of 1.5%-7.2% of the ground truth with a multiscale structural similarity index (M-SSIM) of 0.93 ± 0.03. For the data with a resolution ratio of 1.9, the mean absolute difference was in the range of 4.8%-6.3% with an M-SSIM of 0.95 ± 0.01.

Simultaneous 3D acquisition of 1 H MRF and 23 Na MRI.

PURPOSE: To develop a 3D MR technique to simultaneously acquire proton multiparametric maps (T1 , T2 , and proton density) and sodium density weighted images over the whole brain. METHODS: We implemented a 3D stack-of-stars MR pulse sequence which consists of interleaved proton (1 H) and sodium (23 Na) excitations, tailored slice encoding gradients that can encode the same slice for both nuclei, and simultaneous readout with different radial trajectories (1 H, full-radial; 23 Na, center-out radial). The receive chain of our 7T scanner was modified to enable simultaneous acquisition of 1 H and 23 Na signal. A heuristically optimized flip angle train was implemented for proton MR fingerprinting (MRF). The SNR and the accuracy of proton T1 and T2 were evaluated in phantoms. Finally, in vivo application of the method was demonstrated in five healthy subjects. RESULTS: The SNR for the simultaneous measurement was almost identical to that for the single-nucleus measurements (<2% change). The proton T1 and T2 maps remained similar to the results from a reference 2D MRF technique (normalized RMS error in T1 ≈ 4.2% and T2 ≈ 11.3%). Measurements in healthy subjects corroborated these results and demonstrated the feasibility of our method for in vivo application. The in vivo T1 values measured using our method were lower than the results measured by other conventional techniques. CONCLUSIONS: With the 3D simultaneous implementation, we were able to acquire sodium and proton density weighted images in addition to proton T1 , T2 , and B1+ from 1 H MRF that covers the whole brain volume within 21 min.

T1 and T2 quantification using magnetic resonance fingerprinting in mild traumatic brain injury.

OBJECTIVES: To assess whether MR fingerprinting (MRF)-based relaxation properties exhibit cross-sectional and prospective correlations with patient outcome and compare the results with those from DTI. METHODS: Clinical imaging, MRF, and DTI were acquired in patients (24 ± 10 days after injury (timepoint 1) and 90 ± 17 days after injury (timepoint 2)) and once in controls. Patient outcome was assessed with global functioning, symptom profile, and neuropsychological testing. ADC and fractional anisotropy (FA) from DTI and T1 and T2 from MRF were compared in 12 gray and white matter regions with Mann-Whitney tests. Bivariate associations between MR measures and outcome were assessed using the Spearman correlation and logistic regression. RESULTS: Data from 22 patients (38 ± 12 years; 17 women) and 18 controls (32 ± 8 years; 12 women) were analyzed. Fourteen patients (37 ± 12 years; 11 women) returned for timepoint 2, while two patients provided only timepoint 2 clinical outcome data. At timepoint 1, there were no differences between patients and controls in T1, T2, and ADC, while FA was lower in mTBI frontal white matter. T1 at timepoint 1 and the change in T1 exhibited more (n = 18) moderate to strong correlations (|r|= 0.6-0.85) with clinical outcome at timepoint 2 than T2 (n = 3), FA (n = 7), and ADC (n = 2). High T1 at timepoint 1, and serially increasing T1, accounted for five of the six MR measures with the highest utility for identification of non-recovered patients at timepoint 2 (AUC > 0.80). CONCLUSION: T1 derived from MRF was found to have higher utility than T2, FA, and ADC for predicting 3-month outcome after mTBI. KEY POINTS: • In a region-of-interest approach, FA, ADC, and T1 and T2 all showed limited utility in differentiating patients from controls at an average of 24 and 90 days post-mild traumatic brain injury. • T1 at 24 days, and the serial change in T1, revealed more and stronger predictive correlations with clinical outcome at 90 days than did T2, ADC, or FA. • T1 showed better prospective identification of non-recovered patients at 90 days than ADC, T2, and FA.

A radially interleaved sodium and proton coil array for brain MRI at 7 T.

The objective of the current study was to design and build a dual-tuned coil array for simultaneous 23 Na/1 H MRI of the human brain at 7 T. Quality factor, experimental B1+ measurements, and electromagnetic simulations in prototypes showed that setups consisting of geometrically interleaved 1 H and 23 Na loops performed better than or similar to 1 H or 23 Na loops in isolation. Based on these preliminary findings, we built a transmit/receive eight-channel 23 Na loop array that was geometrically interleaved with a transmit/receive eight-channel 1 H loop array. We assessed the performance of the manufactured array with mononuclear signal-to-noise ratio (SNR) and B1+ measurements, along with multinuclear magnetic resonance fingerprinting maps and images. The 23 Na array within the developed dual-tuned device provided more than 50% gain in peripheral SNR and similar B1+ uniformity and coverage as a reference birdcage coil of similar size. The 1 H array provided good B1+ uniformity in the brain, excluding the cerebellum and brain stem. The integrated 23 Na and 1 H arrays were used to demonstrate truly simultaneous quantitative 1 H mapping and 23 Na imaging.

Hippocampal single-voxel MR spectroscopy with a long echo time at 3 T using semi-LASER sequence.

The hippocampus is one of the most challenging brain regions for proton MR spectroscopy (MRS) applications. Moreover, quantification of J-coupled species such as myo-inositol (m-Ins) and glutamate + glutamine (Glx) is affected by the presence of macromolecular background. While long echo time (TE) MRS eliminates the macromolecules, it also decreases the m-Ins and Glx signal and, as a result, these metabolites are studied mainly with short TE. Here, we investigate the feasibility of reproducibly measuring their concentrations at a long TE of 120 ms, using a semi-adiabatic localization by adiabatic selective refocusing (sLASER) sequence, as this sequence was recently recommended as a standard for clinical MRS. Gradient offset-independent adiabatic refocusing pulses were implemented, and an optimal long TE for the detection of m-Ins and Glx was determined using the T2 relaxation times of macromolecules. Metabolite concentrations and their coefficients of variation (CVs) were obtained for a 3.4-mL voxel centered on the left hippocampus on 3-T MR systems at two different sites with three healthy subjects (aged 32.5 ± 10.2 years [mean ± standard deviation]) per site, with each subject scanned over two sessions, and with each session comprising three scans. Concentrations of m-Ins, choline, creatine, Glx and N-acetyl-aspartate were 5.4 ± 1.5, 1.7 ± 0.2, 5.8 ± 0.3, 11.6 ± 1.2 and 5.9 ± 0.4 mM (mean ± standard deviation), respectively. Their respective mean within-session CVs were 14.5% ± 5.9%, 6.5% ± 5.3%, 6.0% ± 3.4%, 10.6% ± 6.2% and 3.5% ± 1.4%, and their mean within-subject CVs were 17.8% ± 18.2%, 7.5% ± 6.3%, 7.4% ± 6.4%, 12.4% ± 5.3% and 4.8% ± 3.0%. The between-subject CVs were 25.0%, 12.3%, 5.3%, 10.7% and 6.4%, respectively. Hippocampal long-TE sLASER single voxel spectroscopy can provide macromolecule-independent assessment of all major metabolites including Glx and m-Ins.

Functional connectivity of the default mode, dorsal attention and fronto-parietal executive control networks in glial tumor patients.

PURPOSE: Resting state functional magnetic resonance imaging (rsfMRI) is an emerging tool to explore the functional connectivity of different brain regions. We aimed to assess the disruption of functional connectivity of the Default Mode Network (DMN), Dorsal Attention Network(DAN) and Fronto-Parietal Network (FPN) in patients with glial tumors. METHODS: rsfMRI data acquired on 3T-MR of treatment-naive glioma patients prospectively recruited (2015-2019) and matched controls from the 1000 functional-connectomes-project were analyzed using the CONN functional toolbox. Seed-Based Connectivity Analysis (SBCA) and Independent Component Analysis (ICA, with 10 to 100 components) were performed to study reliably the three networks of interest. RESULTS: 35 patients with gliomas (17 WHO grade I-II, 18 grade III-IV) and 70 controls were included. Global increased DMN connectivity was consistently found with SBCA and ICA in patients compared to controls (Cluster1: Precuneus, height: p < 10-6; Cluster2: subcallosum; height: p < 10-5). However, an area of decreased connectivity was found in the posterior corpus callosum, particularly in high-grade gliomas (height: p < 10-5). The DAN demonstrated small areas of increased connectivity in frontal and occipital regions (height: p < 10-6). For the FPN, increased connectivity was noted in the precuneus, posterior cingulate gyrus, and frontal cortex. No difference in the connectivity of the networks of interest was demonstrated between low- and high-grade gliomas, as well as when stratified by their IDH1-R132H (isocitrate dehydrogenase) mutation status. CONCLUSION: Altered functional connectivity is reliably found with SBCA and ICA in the DMN, DAN, and FPN in glioma patients, possibly explained by decreased connectivity between the cerebral hemispheres across the corpus callosum due to disruption of the connections.

Simultaneous proton magnetic resonance fingerprinting and sodium MRI.

PURPOSE: The goal of this work is to demonstrate a method for the simultaneous acquisition of proton multiparametric maps (T1 , T2 , and proton density) and sodium density images in 1 single scan. We hope that the development of such capabilities will help to ease the implementation of sodium MRI in clinical trials and provide more opportunities for researchers to investigate metabolism through sodium MRI. METHODS: We developed a sequence based on magnetic resonance fingerprinting (MRF), which contains interleaved proton (1 H) and sodium (23 Na) excitations followed by a simultaneous center-out radial readout for both nuclei. The receive chain of a 7T scanner was modified to enable simultaneous acquisition of 1 H and 23 Na signal. The obtained signal-to-noise ratio (SNR) was evaluated, and the accuracy of both proton T1 , T2 , and B1+ and sodium density maps were verified in phantoms. Finally, the method was demonstrated in 2 healthy subjects. RESULTS: The SNR obtained using the simultaneous measurement was almost identical to single-nucleus measurements (<1% change). Similarly, the proton T1 and T2 maps remained stable (normalized root mean square error in T1 ≈ 2.2%, in T2 ≈ 1.4%, and B1+ ≈ 5.4%), which indicates that the proposed sequence and hardware have no significant effects on the signal from either nucleus. In vivo measurements corroborated these results and demonstrated the feasibility of our method for in vivo application. CONCLUSIONS: With the proposed approach, we were able to simultaneously acquire sodium density images in addition to proton T1 , T2 , and B1+ maps as well as proton density images.

A dual-tuned 17 O/1 H head array for direct brain oximetry at 3 Tesla.

PURPOSE: To design and build a dual-tuned 17 O/1 H coil for direct brain oximetry at 3T. METHODS: A dual-tuned 17 O/1 H coil comprising 2 degenerate mode birdcage coils was constructed to facilitate high-sensitivity 17 O and 1 H imaging. In vivo 17 O brain images were acquired in a healthy volunteer using a fermat looped orthogonally encoded trajectories sequence, together with high-resolution structural brain 1 H images. RESULTS: Natural abundance 17 O images with a nominal resolution of 8 mm3 were acquired in under 20 minutes exhibiting clear delineation of the physiological 17 O distribution. One-millimeter isotropic 1 H structural brain images demonstrated excellent quality and anatomical detail using routine clinical imaging sequence parameters and parallel acceleration. CONCLUSION: A dual-tuned 17 O/1 H array was constructed to enable high-sensitivity 17 O and 1 H imaging under standard clinical 3 T scanning conditions.

Diagnostic test accuracy of ADC values for identification of clear cell renal cell carcinoma: systematic review and meta-analysis.

OBJECTIVES: To perform a systematic review on apparent diffusion coefficient (ADC) values of renal tumor subtypes and meta-analysis on the diagnostic performance of ADC for differentiation of localized clear cell renal cell carcinoma (ccRCC) from other renal tumor types. METHODS: Medline, Embase, and the Cochrane Library databases were searched for studies published until May 1, 2019, that reported ADC values of renal tumors. Methodological quality was evaluated. For the meta-analysis on diagnostic test accuracy of ADC for differentiation of ccRCC from other renal lesions, we applied a bivariate random-effects model and compared two subgroups of ADC measurement with vs. without cystic and necrotic areas. RESULTS: We included 48 studies (2588 lesions) in the systematic review and 13 studies (1126 lesions) in the meta-analysis. There was no significant difference in ADC of renal parenchyma using b values of 0-800 vs. 0-1000 (p = 0.08). ADC measured on selected portions (sADC) excluding cystic and necrotic areas differed significantly from whole-lesion ADC (wADC) (p = 0.002). Compared to ccRCC, minimal-fat angiomyolipoma, papillary RCC, and chromophobe RCC showed significantly lower sADC while oncocytoma exhibited higher sADC. Summary estimates of sensitivity and specificity to differentiate ccRCC from other tumors were 80% (95% CI, 0.76-0.88) and 78% (95% CI, 0.64-0.89), respectively, for sADC and 77% (95% CI, 0.59-0.90) and 77% (95% CI, 0.69-0.86) for wADC. sADC offered a higher area under the receiver operating characteristic curve than wADC (0.852 vs. 0.785, p = 0.02). CONCLUSIONS: ADC values of kidney tumors that exclude cystic or necrotic areas more accurately differentiate ccRCC from other renal tumor types than whole-lesion ADC values. KEY POINTS: • Selective ADC of renal tumors, excluding cystic and necrotic areas, provides better discriminatory ability than whole-lesion ADC to differentiate clear cell RCC from other renal lesions, with area under the receiver operating characteristic curve (AUC) of 0.852 vs. 0.785, respectively (p = 0.02). • Selective ADC of renal masses provides moderate sensitivity and specificity of 80% and 78%, respectively, for differentiation of clear cell renal cell carcinoma (RCC) from papillary RCC, chromophobe RCC, oncocytoma, and minimal-fat angiomyolipoma. • Selective ADC excluding cystic and necrotic areas are preferable to whole-lesion ADC as an additional tool to multiphasic MRI to differentiate clear cell RCC from other renal lesions whether the highest b value is 800 or 1000.

CT-guided radiofrequency ablation for osteoid osteomas: a systematic review.

OBJECTIVES: CT-guided radiofrequency ablation (CT-RFA) is considered to be the gold standard for treatment of osteoid osteoma (OO) yet treatment failures (TFs) continue to be reported. This systematic review was conducted to evaluate factors associated with TF, such as ablation time, lesion location, and patient age as well as evaluating how TF has trended over time. METHODS: Original studies reporting on patients undergoing CT-RFA of OO published between 2002 and 2019 were identified. TF was defined as patients with (1) recurrent or persistent pain +/- (2) imaging evidence of persistent OO. TFs were subdivided into those occurring after the index procedure (primary TF) or those occurring after repeat RFA (secondary TF). Subgroup analysis was performed for TF based on the study date (2002-2010 or 2010-2019), time duration of ablation at 90 °C (6 min or > 6 min), patient age, and tumor location (spinal vs. appendicular). RESULTS: Sixty-nine studies were included for a total of 3023 patients. The global primary TF rate was 8.3% whereas the secondary TF rate was 3.1%. The TF rate reported in studies published after 2011(7%) was about half that during the earlier time period 2002-2010 (14%). There was no statistical difference in TF corrected for age, OO location, or duration of ablation (respectively p = 0.39, 0.13, and 0.23). The global complication rate was 3%, the most frequent being skin burns (n = 24; 0.7%). CONCLUSIONS: A decrease in TF observed between 2011-2019 compared to 2002-2010 may reflect improvements in operator technique or advancements in equipment. Duration of ablation, patient age, or location of OO failed to significantly correlate with TF. KEY POINTS: • CT-guided radiofrequency ablation of osteoid osteomas is a safe technique with a low rate of treatment failure (8.3% failure rate after the primary radiofrequency reducing to 3.1% following a secondary treatment). • The treatment failure rate has decreased over time, possibly due to an improved understanding of the disease process, better technique, and advances in equipment. • Duration of ablation, patient age, or lesion location did not significantly correlate with treatment failure.

A dual-tuned multichannel bilateral RF coil for 1 H/23 Na breast MRI at 7 T.

PURPOSE: Sodium MRI has shown promise for monitoring neoadjuvant chemotherapy response in breast cancer. The purpose of this work was to build a dual-tuned bilateral proton/sodium breast coil for 7T MRI that provides sufficient SNR to enable sodium breast imaging in less than 10 minutes. METHODS: The proton/sodium coil consists of 2 shielded unilateral units: 1 for each breast. Each unit consists of 3 nested layers: (1) a 3-loop solenoid for sodium excitation, (2) a 3-loop solenoid for proton excitation and signal reception, and (3) a 4-channel receive array for sodium signal reception. Benchmark measurements were performed in phantoms with and without the sodium receive array insert. In vivo images were acquired on a healthy volunteer. RESULTS: The sodium receive array boosted 1.5 to 3 times the SNR compared with the solenoid. Proton SNR loss due to residual interaction with the sodium array was less than 10%. The coil enabled sodium imaging in vivo with 2.8-mm isotropic nominal resolution (~5-mm real resolution) in 9:36 minutes. CONCLUSION: The coil design that we propose addresses challenges associated with sodium's low SNR from a hardware perspective and offers the opportunity to investigate noninvasively breast tumor metabolism as a function of sodium concentration in patients undergoing neoadjuvant chemotherapy.

Dynamic phosphocreatine imaging with unlocalized pH assessment of the human lower leg muscle following exercise at 3T.

PURPOSE: To develop a high temporal resolution imaging method that measures muscle-specific phosphocreatine (PCr) resynthesis time constant (τPCr ) and pH changes in muscles of the lower leg following exercise on a clinical 3T MRI scanner. METHODS: We developed a frequency-selective 3D non-Cartesian FLORET sequence to measure PCr with 17-mm nominal isotropic resolution (28 mm actual resolution) and 6-s temporal resolution to capture dynamic metabolic muscle activity. The sequence was designed to additionally collect inorganic phosphate spectra for pH quantification, which were localized using sensitivity profiles of individual coil elements. Nineteen healthy volunteers were scanned while performing a plantar flexion exercise on an in-house developed ergometer. Data were acquired with a dual-tuned multichannel coil array that enabled phosphorus imaging and proton localization for muscle segmentation. RESULTS: After a 90-s plantar flexion exercise at 0.66 Hz with resistance set to 40% of the maximum voluntary contraction, τPCr was estimated at 22.9 ± 8.8 s (mean ± standard deviation) with statistical coefficient of determination r2 = 0.89 ± 0.05. The corresponding pH values after exercise were in the range of 6.9-7.1 in the gastrocnemius muscle. CONCLUSION: The developed technique allows measurement of muscle-specific PCr resynthesis kinetics and pH changes following exercise, with a temporal resolution and accuracy comparable to that of single voxel 31 P-MRS sequences. Magn Reson Med 79:974-980, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

An eight-channel sodium/proton coil for brain MRI at 3 T.

The purpose of this work is to illustrate a new coil decoupling strategy and its application to a transmit/receive sodium/proton phased array for magnetic resonance imaging (MRI) of the human brain. We implemented an array of eight triangular coils that encircled the head. The ensemble of coils was arranged to form a modified degenerate mode birdcage whose eight shared rungs were offset from the z-axis at interleaved angles of ±30°. This key geometric modification resulted in triangular elements whose vertices were shared between next-nearest neighbors, which provided a convenient location for counter-wound decoupling inductors, whilst nearest-neighbor decoupling was addressed with shared capacitors along the rungs. This decoupling strategy alleviated the strong interaction that is characteristic of array coils at low frequency (32.6 MHz in this case) and allowed the coil to operate efficiently in transceive mode. The sodium array provided a 1.6-fold signal-to-noise ratio advantage over a dual-nuclei birdcage coil in the center of the head and up to 2.3-fold gain in the periphery. The array enabled sodium MRI of the brain with 5-mm isotropic resolution in approximately 13 min, thus helping to overcome low sodium MR sensitivity and improving quantification in neurological studies. An eight-channel proton array was integrated into the sodium array to enable anatomical imaging.

Longitudinal study of sodium MRI of articular cartilage in patients with knee osteoarthritis: initial experience with 16-month follow-up.

OBJECTIVES: To evaluate the potential of sodium MRI to detect changes over time of apparent sodium concentration (ASC) in articular cartilage in patients with knee osteoarthritis (OA). METHODS: The cartilage of 12 patients with knee OA were scanned twice over a period of approximately 16 months with two sodium MRI sequences at 7 T: without fluid suppression (radial 3D) and with fluid suppression by adiabatic inversion recovery (IR). Changes between baseline and follow-up of mean and standard deviation of ASC (in mM), and their rate of change (in mM/day), were measured in the patellar, femorotibial medial and lateral cartilage regions for each subject. A matched-pair Wilcoxon signed rank test was used to assess significance of the changes. RESULTS: Changes in mean and in standard deviation of ASC, and in their respective rate of change over time, were only statistically different when data was acquired with the fluid-suppressed sequence. A significant decrease (p = 0.001) of approximately 70 mM in mean ASC was measured between the two IR scans. CONCLUSION: Quantitative sodium MRI with fluid suppression by adiabatic IR at 7 T has the potential to detect a decrease of ASC over time in articular cartilage of patients with knee osteoarthritis. KEY POINTS: • Sodium MRI can detect apparent sodium concentration (ASC) in cartilage • Longitudinal study: sodium MRI can detect changes in ASC over time • Potential for follow-up studies of cartilage degradation in knee osteoarthritis.

Quantitative sodium imaging and gliomas: a feasibility study.

PURPOSE: Recent advances in sodium brain MRI have allowed for increased signal-to-noise ratio, faster imaging, and the ability of differentiating intracellular from extracellular sodium concentration, opening a new window of opportunity for clinical application. In gliomas, there are significant alterations in sodium metabolism, including increase in the total sodium concentration and extracellular volume fraction. The purpose of this study is to assess the feasibility of using sodium MRI quantitative measurements to evaluate gliomas. METHODS: Eight patients with treatment-naïve gliomas were scanned at 3 T with a homemade 1H/23Na head coil, generating maps of pseudo-intracellular sodium concentration (C1), pseudo-extracellular volume fraction (α2), apparent intracellular sodium concentration (aISC), and apparent total sodium concentration (aTSC). Measurements were made within the contralateral normal-appearing putamen, contralateral normal-appearing white matter (NAWM), and solid tumor regions (area of T2-FLAIR abnormality, excluding highly likely areas of edema, cysts, or necrosis). Paired samples t test were performed comparing NAWM and putamen and between NAWM and solid tumor. RESULTS: The normal-appearing putamen demonstrated significantly higher values for aTSC, aISC, C1 (p < 0.001), and α2 (p = 0.002) when compared to those of NAWM. The mean average of all solid tumors, when compared to that of NAWM, demonstrated significantly higher values of aTSC and α2 (p < 0.001), and significantly lower values of aISC (p = 0.02) for each patient. There was no significant difference between the values of C1 (p = 0.19). CONCLUSION: Quantitative sodium measurements can be done in glioma patients and also has provided further evidence that total sodium and extracellular volume fraction are increased in gliomas.

A nested phosphorus and proton coil array for brain magnetic resonance imaging and spectroscopy.

A dual-nuclei radiofrequency coil array was constructed for phosphorus and proton magnetic resonance imaging and spectroscopy of the human brain at 7T. An eight-channel transceive degenerate birdcage phosphorus module was implemented to provide whole-brain coverage and significant sensitivity improvement over a standard dual-tuned loop coil. A nested eight-channel proton module provided adequate sensitivity for anatomical localization without substantially sacrificing performance on the phosphorus module. The developed array enabled phosphorus spectroscopy, a saturation transfer technique to calculate the global creatine kinase forward reaction rate, and single-metabolite whole-brain imaging with 1.4cm nominal isotropic resolution in 15min (2.3cm actual resolution), while additionally enabling 1mm isotropic proton imaging. This study demonstrates that a multi-channel array can be utilized for phosphorus and proton applications with improved coverage and/or sensitivity over traditional single-channel coils. The efficient multi-channel coil array, time-efficient pulse sequences, and the enhanced signal strength available at ultra-high fields can be combined to allow volumetric assessment of the brain and could provide new insights into the underlying energy metabolism impairment in several neurodegenerative conditions, such as Alzheimer's and Parkinson's diseases, as well as mental disorders such as schizophrenia.

A flexible nested sodium and proton coil array with wideband matching for knee cartilage MRI at 3T.

PURPOSE: We describe a 2 × 6 channel sodium/proton array for knee MRI at 3T. Multielement coil arrays are desirable because of well-known signal-to-noise ratio advantages over volume and single-element coils. However, low tissue-coil coupling that is characteristic of coils operating at low frequency can make the potential gains from a phased array difficult to realize. METHODS: The issue of low tissue-coil coupling in the developed six-channel sodium receive array was addressed by implementing 1) a mechanically flexible former to minimize the coil-to-tissue distance and reduce the overall diameter of the array and 2) a wideband matching scheme that counteracts preamplifier noise degradation caused by coil coupling and a high-quality factor. The sodium array was complemented with a nested proton array to enable standard MRI. RESULTS: The wideband matching scheme and tight-fitting mechanical design contributed to >30% central signal-to-noise ratio gain on the sodium module over a mononuclear sodium birdcage coil, and the performance of the proton module was sufficient for clinical imaging. CONCLUSION: We expect the strategies presented in this study to be generally relevant in high-density receive arrays, particularly in x-nuclei or small animal applications. Magn Reson Med 76:1325-1334, 2016. © 2015 Wiley Periodicals, Inc.

Classification of sodium MRI data of cartilage using machine learning.

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: Machine learning is a promising technique for classifying osteoarthritis patients and controls from sodium magnetic resonance imaging data.

7T MRI detects deterioration in subchondral bone microarchitecture in subjects with mild knee osteoarthritis as compared with healthy controls.

PURPOSE: To determine how subchondral bone microarchitecture is altered in patients with mild knee osteoarthritis. MATERIALS AND METHODS: This study had Institutional Review Board approval. We recruited 24 subjects with mild radiographic knee osteoarthritis and 16 healthy controls. The distal femur was scanned at 7T using a high-resolution 3D FLASH sequence. We applied digital topological analysis to assess bone volume fraction, markers of trabecular number (skeleton density), trabecular network osteoclastic resorption (erosion index), plate-like structure (surface), rod-like structure (curve), and plate-to-rod ratio (surface-curve ratio). We used two-tailed t-tests to compare differences between osteoarthritis subjects and controls. RESULTS: 7T magnetic resonance imaging (MRI) detected deterioration in subchondral bone microarchitecture in both medial and lateral femoral condyles in osteoarthritis subjects as compared with controls. This was manifested by lower bone volume fraction (-1.03% to -5.43%, P < 0.04), higher erosion index (+8.49 to +22.76%, P < 0.04), lower surface number (-2.31% to -9.63%, P < 0.007), higher curve number (+6.85% to +16.93%, P < 0.03), and lower plate-to-rod ratio (-7.92% to -21.71%, P < 0.05). CONCLUSION: The results provide further support for the concept that poor subchondral bone quality is associated with osteoarthritis and may serve as a potential therapeutic target for osteoarthritis interventions. J. Magn. Reson. Imaging 2015;41:1311-1317. © 2014 Wiley Periodicals, Inc.