Repeatability assessment of sodium (23Na) MRI at 7.0 T in healthy human calf muscle and preliminary results on tissue sodium concentrations in subjects with Addison's disease.

OBJECTIVES: To determine the relaxation times of the sodium nucleus, and to investigate the repeatability of quantitative, in vivo TSC measurements using sodium magnetic resonance imaging (23Na-MRI) in human skeletal muscle and explore the discriminatory value of the method by comparing TSCs between healthy subjects and patients with Addison's disease. MATERIALS AND METHODS: In this prospective study, ten healthy subjects and five patients with Addison's disease were involved. 23Na-MRI data sets were acquired using a density-adapted, three-dimensional radial projection reconstruction pulse sequence (DA-3DPR) with a modification for the relaxation times measurements. Differences in TSC between muscle groups and between healthy participants were analysed using a nonparametric Friedman ANOVA test. An interclass correlation coefficient (ICC) was used as the repeatability index. Wilcoxon rank sum test was used for evaluation of differences in TSC between study participants. RESULTS: The mean T1 in the gastrocnemius medialis (GM), the tibialis anterior (TA), and the soleus (S) was 25.9 ± 2.0 ms, 27.6 ± 2.0 ms, and 28.2 ± 2.0 ms, respectively. The mean short component of T2*, T2*short were GM: 3.6 ± 2.0 ms; TA: 3.2 ± 0.5 ms; and S: 3.0 ± 1.0 ms, and the mean long component of T2*, T2*long, were GM: 12.9 ± 0.9 ms; TA: 12.8 ± 0.7 ms; and S: 12.9 ± 2.0 ms, respectively. In healthy volunteers, TSC values in the GM were 19.9 ±0.1  mmol/L, 13.8 ±0.2 mmol/L in TA, and 12.6 ± 0.2 mmol/L in S, and were significantly different (p = 0.0005). The ICCs for GM, TA and S were 0.784, 0.818, 0.807, respectively. In patients with Addison's disease, TSC in GC, TA, and S were 10.2 ± 1.0 mmol/L, 8.4 ± 0.6 mmol/L, and 7.2 ± 0.1 mmol/L, respectively. CONCLUSIONS: TSC quantification in a healthy subject's calf at 7.0 T is reliable; the technique is able to distinguish sodium level differences between muscles and between healthy subjects and Addison's disease patients.

Tissue Sodium Concentration Quantification at 7.0-T MRI as an Early Marker for Chemotherapy Response in Breast Cancer: A Feasibility Study.

Background Tissue sodium concentration (TSC) is elevated in breast cancer and can determine chemotherapy response. Purpose To test the feasibility of using a sodium 23 (23Na) MRI protocol at 7.0 T for TSC quantification to predict early treatment outcomes of neoadjuvant chemotherapy in breast cancer and to determine whether those quantitative values provide additional information about efficacy. Materials and Methods Women with primary breast cancer were included in this prospective study. From July 2017 to June 2018, participants underwent 7.0-T 23Na MRI. Multichannel data sets were acquired with a density-adapted, three-dimensional radial projection reconstruction pulse sequence. Two-dimensional tumor size and TSC were evaluated before and after the first and second chemotherapy cycle, and statistical tests were performed based on the presence or absence of a pathologic complete response (pCR). Results Fifteen women with breast cancer and six healthy women were enrolled. The mean baseline tumor size in women with a pCR was 7.0 cm2 ± 5.0 (standard deviation), and the mean baseline tumor size in women without a pCR was 19.0 cm2 ± 12.0. After the first chemotherapy cycle, women with a pCR showed a reduced tumor size of 32.9% (2.3 cm2/7.0 cm2), compared with 15.3% (2.9 cm2/19.0 cm2) in those without a pCR. The areas under the receiver operating characteristic curve for tumor size reduction after the first and second chemotherapy cycle were 0.73 (95% CI: 0.09, 0.50; P = .12) and 0.93 (95% CI: 0.04, 0.60; P < .001), respectively. Women with a pCR had a mean baseline TSC of 69.4 mmol/L ± 6.1, with a reduction of 12.0% (8.3 mmol/L), whereas those without a pCR had a mean baseline TSC of 71.7 mmol/L ± 5.7, with a reduction of 4.7% (3.4 mmol/L) after the first cycle. The areas under the receiver operating characteristic curve for TSC after the first and second cycles were 0.96 (95% CI: 0.86, 1.00; P < .001) and 1.000 (95% CI: 1.00, P < .001), respectively. Conclusion Using 7.0-T MRI for tissue sodium concentration quantification to predict early treatment outcomes of neoadjuvant chemotherapy in breast cancer is feasible, with reduced tissue sodium concentration indicative of cancer response. © RSNA, 2021 Online supplemental material is available for this article.

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

Sodium magnetic resonance imaging (23 Na-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 (1 H) imaging, 23 Na-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 23 Na-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 23 Na-MRI to become a standard imaging tool. The future role of sodium imaging is not to be considered as an alternative to 1 H MRI, but to provide early, diagnostically valuable information about altered metabolism or tissue function associated with disease genesis and progression. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1.

Combining phase images from array coils using a short echo time reference scan (COMPOSER).

PURPOSE: To develop a simple method for combining phase images from multichannel coils that does not require a reference coil and does not entail phase unwrapping, fitting or iterative procedures. THEORY AND METHODS: At very short echo time, the phase measured with each coil of an array approximates to the phase offset to which the image from that coil is subject. Subtracting this information from the phase of the scan of interest matches the phases from the coils, allowing them to be combined. The effectiveness of this approach is quantified in the brain, calf and breast with coils of diverse designs. RESULTS: The quality of phase matching between coil elements was close to 100% with all coils assessed even in regions of low signal. This method of phase combination was similar in effectiveness to the Roemer method (which needs a reference coil) and was superior to the rival reference-coil-free approaches tested. CONCLUSION: The proposed approach-COMbining Phase data using a Short Echo-time Reference scan (COMPOSER)-is a simple and effective approach to reconstructing phase images from multichannel coils. It requires little additional scan time, is compatible with parallel imaging and is applicable to all coils, independent of configuration. Magn Reson Med 77:318-327, 2017. © 2015 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Investigating the prediction value of multiparametric magnetic resonance imaging at 3 T in response to neoadjuvant chemotherapy in breast cancer.

OBJECTIVE: To explore the predictive value of parameters derived from diffusion-weighted imaging (DWI) and contrast-enhanced (CE)-MRI at different time-points during neoadjuvant chemotherapy (NACT) in breast cancer. METHODS: Institutional review board approval and written, informed consent from 42 breast cancer patients were obtained. The patients were investigated before and at three different time-points during neoadjuvant chemotherapy (NACT) using tumour diameter and volume from CE-MRI and ADC values obtained from drawn 2D and segmented 3D regions of interest. Prediction of pathologic complete response (pCR) was evaluated using the area under the curve (AUC) of receiver operating characteristic analysis. RESULTS: There was no significant difference between pathologic complete response and non-pCR in baseline size measures (p > 0.39). Diameter change was significantly different in pCR (p < 0.02) before the mid-therapy point. The best predictor was lesion diameter change observed before mid-therapy (AUC = 0.93). Segmented volume was not able to differentiate between pCR and non-pCR at any time-point. The ADC values from 3D-ROI were not significantly different from 2D data (p = 0.06). The best AUC (0.79) for pCR prediction using DWI was median ADC measured before mid-therapy of NACT. CONCLUSIONS: The results of this study should be considered in NACT monitoring planning, especially in MRI protocol designing and time point selection. KEY POINTS: • Mid-therapy diameter changes are the best predictors of pCR in neoadjuvant chemotherapy. • Volumetric measures are not strictly superior in therapy monitoring to lesion diameter. • Size measures perform as a better predictor than ADC values.

Quantitative Sodium MR Imaging at 7 T: Initial Results and Comparison with Diffusion-weighted Imaging in Patients with Breast Tumors.

Purpose To investigate the clinical feasibility of a quantitative sodium 23 ((23)Na) magnetic resonance (MR) imaging protocol developed for breast tumor assessment and to compare it with 7-T diffusion-weighted imaging (DWI). Materials and Methods Written informed consent in this institutional review board-approved study was obtained from eight healthy volunteers and 17 patients with 20 breast tumors (five benign, 15 malignant). To achieve the best image quality and reproducibility, the (23)Na sequence was optimized and tested on phantoms and healthy volunteers. For in vivo quantification of absolute tissue sodium concentration (TSC), an external phantom was used. Static magnetic field, or B0, and combined transmit and receive radiofrequency field, or B1, maps were acquired, and image quality, measurement reproducibility, and accuracy testing were performed. Bilateral (23)Na and DWI sequences were performed before contrast material-enhanced MR imaging in patients with breast tumors. TSC and apparent diffusion coefficient (ADC) were calculated and correlated for healthy glandular tissue and benign and malignant lesions. Results The (23)Na MR imaging protocol is feasible, with 1.5-mm in-plane resolution and 16-minute imaging time. Good image quality was achieved, with high reproducibility (mean TSC values ± standard deviation for the test, 36 mmol per kilogram of wet weight ± 2 [range, 34-37 mmol/kg]; for the retest, 37 mmol/kg ± 1 [range, 35-39 mmol/kg]; P = .610) and accuracy (r = 0.998, P < .001). TSC values in normal glandular and adipose breast tissue were 35 mmol/kg ± 3 and 18 mmol/kg ± 3, respectively. In malignant lesions (mean size, 31 mm ± 24; range, 6-92 mm), the TSC of 69 mmol/kg ± 10 was, on average, 49% higher than that in benign lesions (mean size, 14 mm ± 12; range, 6-35 mm), with a TSC of 47 mmol/kg ± 8 (P = .002). There were similar ADC differences between benign ([1.78 ± 0.23] × 10(-3) mm(2)/sec) and malignant ([1.03 ± 0.23] × 10(-3) mm(2)/sec) tumors (P = .002). ADC and TSC were inversely correlated (r = -0.881, P < .001). Conclusion Quantitative (23)Na MR imaging is clinically feasible, may provide good differentiation between malignant and benign breast lesions, and demonstrates an inverse correlation with ADC. (©) RSNA, 2016 Online supplemental material is available for this article.

Bilateral diffusion-weighted MR imaging of breast tumors with submillimeter resolution using readout-segmented echo-planar imaging at 7 T.

PURPOSE: To evaluate the image quality, robustness, and diagnostic performance of submillimeter in-plane resolution diffusion-weighted ( DW diffusion-weighted ) magnetic resonance (MR) imaging at 7 T in the assessment of breast tumors. MATERIALS AND METHODS: Institutional review board approval and written informed consent of five volunteers and 33 patients with 33 breast lesions (31 with histopathologic confirmation, two with confirmation at follow-up) were obtained. Image quality optimization and comparisons of readout-segmented echo-planar imaging ( rs-EPI readout-segmented echo-planar imaging ) and single-shot echo-planar imaging ( ss-EPI single-shot echo-planar imaging ) with or without parallel imaging were performed in volunteers. In all patients, bilateral DW diffusion-weighted imaging was performed in 3 minutes 35 seconds by using combined rs-EPI readout-segmented echo-planar imaging and parallel imaging with 0.9 × 0.9 mm in-plane resolution with a 7-T whole-body MR imager. Image quality, lesion conspicuity, and image properties (ie, signal-to-noise ratio, contrast-to-noise ratio) were assessed. Regions of interest were drawn in the largest lesion in each patient (23 malignant lesions, 10 benign lesions) by two independent readers. Apparent diffusion coefficient ( ADC apparent diffusion coefficient ) values were used to differentiate between benign and malignant breast tumors. RESULTS: DW diffusion-weighted imaging with combined parallel imaging and rs-EPI readout-segmented echo-planar imaging reduced artifacts (ie, blurring and geometric distortions) by a calculated factor of seven when compared with DW diffusion-weighted imaging with ss-EPI single-shot echo-planar imaging , and it improved image quality from a score of 1 of 10 to a score of 8 of 10. The rs-EPI readout-segmented echo-planar imaging sequence with a b value of 0 sec/mm(2) yielded high-spatial-resolution T2-weighted MR images. An ADC apparent diffusion coefficient threshold of 1.275 × 10(-3) mm(2)/sec enabled differentiation between benign and malignant breast lesions, with sensitivity and specificity of 96% and 100%, respectively, for both independent readers. CONCLUSION: At 7 T, one DW diffusion-weighted imaging examination of less than 4 minutes yielded high-quality ADC apparent diffusion coefficient maps and high-spatial-resolution T2-weighted MR images that were used to assess tumor and breast morphology. ADC apparent diffusion coefficient quantification alone enabled excellent differentiation of benign and malignant breast lesions.

Multiparametric MR Imaging with High-Resolution Dynamic Contrast-enhanced and Diffusion-weighted Imaging at 7 T Improves the Assessment of Breast Tumors: A Feasibility Study.

PURPOSE: To ascertain whether multiparametric magnetic resonance (MR) imaging of the breast in combination with dynamic contrast material-enhanced (DCE) imaging and diffusion-weighted imaging (DWI) at 7 T is feasible and improves diagnostic accuracy. MATERIALS AND METHODS: From December 2011 to December 2013, 40 patients with suspicious breast lesions were included in this institutional review board-approved prospective study. Before bilateral multiparametric MR imaging of the breast at 7 T, all patients gave written informed consent. Lesions were classified according to Breast Imaging Reporting and Data System (BI-RADS) and assessed for apparent diffusion coefficient (ADC) values by two readers independently. For combined analysis of DCE MR imaging and DWI, the BI-RADS-adapted reading algorithm, which adapted ADC thresholds to the BI-RADS assessment category, was used. Diagnostic values of multiparametric, DCE MR imaging, and DWI were calculated. Receiver operating characteristic curve analysis was performed. Image quality and interreader agreement were assessed. Histopathologic results were used as the highest standard. RESULTS: There were 29 malignant and 17 benign lesions (range, 6-95 mm; mean, 23.3 mm). Multiparametric MR imaging yielded a sensitivity of 100% (29 of 29 lesions), a specificity of 88.2% (16 of 18 lesions), and an area under the curve of 0.941, which was greater than for DCE MR imaging (P = .003), which had a sensitivity of 100% (29 of 29 lesions), a specificity of 53.2% (nine of 17 lesions), and an area under the curve of 0.765. DWI had a sensitivity of 93.1% (27 of 29 lesions), a specificity of 88.2% (15 of 17 lesions), and an area under the curve of 0.907. Multiparametric MR imaging at 7 T of the breast eliminated all false-negative findings and reduced false-positive findings, from eight false-positive findings with DCE MR imaging to two false-positive findings. Thus, if used clinically, 7-T multiparametric MR imaging may have potentially obviated unnecessary breast biopsies in six of eight lesions (P = .031). Multiparametric MR imaging demonstrated either excellent or good image quality and interreader agreement (κ = 0.89-1.00). CONCLUSION: The clinical use of 7-T multiparametric MR imaging is feasible, provides good or excellent image quality, and has the potential to improve diagnostic accuracy.

Compressed sensing and the use of phased array coils in 23Na MRI: a comparison of a SENSE-based and an individually combined multi-channel reconstruction.

PURPOSE: To implement and to evaluate a compressed sensing (CS) reconstruction algorithm based on the sensitivity encoding (SENSE) combination scheme (CS-SENSE), used to reconstruct sodium magnetic resonance imaging (23Na MRI) multi-channel breast data sets. METHODS: In a simulation study, the CS-SENSE algorithm was tested and optimized by evaluating the structural similarity (SSIM) and the normalized root-mean-square error (NRMSE) for different regularizations and different undersampling factors (USF=1.8/3.6/7.2/14.4). Subsequently, the algorithm was applied to data from in vivo measurements of the healthy female breast (n=3) acquired at 7T. Moreover, the proposed CS-SENSE algorithm was compared to a previously published CS algorithm (CS-IND). RESULTS: The CS-SENSE reconstruction leads to an increased image quality for all undersampling factors and employed regularizations. Especially if a simple 2nd order total variation is chosen as sparsity transformation, the CS-SENSE reconstruction increases the image quality of highly undersampled data sets (CS-SENSE: SSIMUSF=7.2=0.234, NRMSEUSF=7.2=0.491 vs. CS-IND: SSIMUSF=7.2=0.201, NRMSEUSF=7.2=0.506). CONCLUSION: The CS-SENSE reconstruction supersedes the need of CS weighting factors for each channel as well as a method to combine single channel data. The CS-SENSE algorithm can be used to reconstruct undersampled data sets with increased image quality. This can be exploited to reduce total acquisition times in 23Na MRI.

7T CEST MRI: A potential imaging tool for the assessment of tumor grade and cell proliferation in breast cancer.

OBJECTIVES: To investigate the feasibility of chemical exchange saturation transfer (CEST) MRI in patients with breast carcinomas and possible correlations between magnetization transfer asymmetry (MTRasym) values and histological features, such as tumor grade and the Ki-67 proliferation index. MATERIALS AND METHODS: Nine healthy subjects and 18 female patients were enrolled for this study. The imaging protocol for the patients consisted of diffusion-weighted imaging (DWI), CEST imaging, and T1-weighted, contrast-enhanced (CE)-MRI. CEST was performed using a 3D gradient echo (GRE) sequence, employing eight pre-saturation pulses of a duration of 50 ms and a duty cycle (DC) of 80%, with a mean amplitude of the saturation pulse train of 1 µT. The Z-spectrum was plotted and MTRasym values calculated for the frequency of the maximum of MTRasym curve, were correlated with the Ki-67 proliferation index and apparent diffusion coefficient (ADC). Patient data were statistically assessed using the Games-Howell post-hoc and Pearson's correlation test. RESULTS: Different tumor types had asymmetry peaks at different positions of Z-spectrum. MTRasym (mean ±â€¯SD) (%) calculated for G1 (3.0 ±â€¯0.3; range: 2.70-3.50) was not significantly lower than for G2 (4.50 ±â€¯1.30; range: 3.20-6.50; p = 0.066). In contrast, the increase in MTRasym between G1 and G3 (6.40 ±â€¯1.70; range: 4.80-9.80) lesions was significant (p = 0.007). No significant difference was observed between G2 and G3 with regard to MTRasym (p = 0.089). There was a strong positive correlation between the MTRasym, and Ki-67 proliferation index (r = 0.890; p = 0.001), while there was a moderate negative correlation between MTRasym and ADC values (r = -0.506; p = 0.027). CONCLUSIONS: Calculated MTRasym demonstrates a strong positive correlation with tumor proliferation and has the potential to become a valuable biomarker for breast tumor characterization.

Compressed sensing reconstruction of 7 Tesla 23Na multi-channel breast data using 1H MRI constraint.

PURPOSE: To reduce acquisition time and to improve image quality in sodium magnetic resonance imaging (23Na MRI) using an iterative reconstruction algorithm for multi-channel data sets based on compressed sensing (CS) with anatomical 1H prior knowledge. METHODS: An iterative reconstruction for 23Na MRI with multi-channel receiver coils is presented. Based on CS it utilizes a second order total variation (TV(2)), adopted by anatomical weighting factors (AnaWeTV(2)) obtained from a high-resolution 1H image. A support region is included as additional regularization. Simulated and measured 23Na multi-channel data sets (n = 3) of the female breast acquired at 7 T with different undersampling factors (USF = 1.8/3.6/7.2/14.4) were reconstructed and compared to a conventional gridding reconstruction. The structural similarity was used to assess image quality of the reconstructed simulated data sets and to optimize the weighting factors for the CS reconstruction. RESULTS: Compared with a conventional TV(2), the AnaWeTV(2) reconstruction leads to an improved image quality due to preserving of known structure and reduced partial volume effects. An additional incorporated support region shows further improvements for high USFs. Since the decrease in image quality with higher USFs is less pronounced compared to a conventional gridding reconstruction, proposed algorithm is beneficial especially for higher USFs. Acquisition time can be reduced by a factor of 4 (USF = 7.2), while image quality is still similar to a nearly fully sampled (USF = 1.8) gridding reconstructed data set. CONCLUSION: Especially for high USFs, the proposed algorithm allows improved image quality for multi-channel 23Na MRI data sets.

Dynamic contrast-enhanced magnetic resonance imaging of breast tumors at 3 and 7 T: a comparison.

OBJECTIVES: The objective of this study was to compare the image quality, contrast enhancement behavior, and diagnostic value of bilateral 3-dimensional dynamic contrast-enhanced breast magnetic resonance imaging (MRI), with high spatial and temporal resolution, at 3 and 7 T, in the same patient group. MATERIALS AND METHODS: Twenty-four consecutive patients (mean [SD] age, 57 [17] years) were included in this prospective institutional review board-approved study. Written informed consent was obtained from all patients. T1-weighted 3-dimensional sequences (time-resolved angiography with stochastic trajectories) were optimized at 3 and 7 T, with high temporal (both 14 seconds) and spatial resolution (1.1 × 1.1 × 1.1 mm [3 T], 0.7 × 0.7 × 0.7 mm [7 T]): echo time/repetition time, 2.84/6.01 milliseconds (3 T) and 2.5/4.75 milliseconds (7 T); acquisition time, 9 minutes (3 T/7 T). Dotarem (gadoterate meglumine, Guerbet, Roissy CdG, France) contrast agent was injected intravenously as a bolus (0.2 mL/kg of body weight) after 3 baseline images. The images were rated according to breast imaging-reporting and data system by 2 radiologists in consensus. Signal-to-noise ratio and average enhancement ratios were measured quantitatively by means of region of interest analysis. In addition, B1 mapping was done in the same 5 healthy subjects at both field strengths. RESULTS: Twenty-eight enhancing lesions were detected in the 24 patients at both field strengths (16 malignant, 12 benign). At 7 T, higher contrast than that at 3 T and good image quality were achieved. With the high spatial isotropic resolution of 0.7 mm at 7 T, images with more detailed information could be acquired when compared with those acquired at 3 T. Sensitivity was 93.75% and 100%, at 3 and 7 T, respectively. Specificity was 91.67% at both field strengths. The signal-to-noise ratio at both field strengths was comparable, but at 7 T, the spatial resolution was 3.2-times higher than that at 3 T. A signal-to-noise ratio decrease toward prepectoral breast regions due to B1 inhomogeneities was observed at both field strengths but was stronger at 7 T (51%) than at 3 T (19%)(P = 0.0002). At 7 T, B1+ dropped by 20.7% and 32.8% in the prepectoral and lateral region of the breast in healthy subjects. CONCLUSIONS: Our comparison study shows that 7-T DCE-MRI provides simultaneous high temporal and spatial resolution that is significantly improved compared with lower field strengths, but further technical improvements are necessary to overcome B1 inhomogeneity problems at 7 T to fully unfold the potential of breast MRI at 7 T.