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Purpose To assess the esophagogastric junction (EGJ) on real-time MRI and compare imaging parameters to EGJ morphology on high-resolution manometry (HRM). Methods A total of 105 of 117 eligible patients who underwent real-time MRI and high-resolution manometry for GERD-like symptoms between 2015 and 2018 at a single center were retrospectively evaluated (male n = 57; female n = 48; mean age 52.5 ± 15.4 years). Real-time MRI was performed at a median investigation time of 15 min (1 frame/40 ms). On HRM, EGJ morphology was assessed according to the Chicago classification of esophageal motility disorders. Real-time MRI was performed at 3 T using highly undersampled radial fast low-angle shot acquisitions with NLINV image reconstruction. A 10 mL pineapple juice bolus served as oral contrast agent at supine position. Real-time MRI films of the EGJ were acquired during swallowing events and during Valsalva maneuver. Anatomic and functional MRI parameters were compared to EGJ morphology on HRM. Results On HRM, n = 42 patients presented with EGJ type I (40.0%), n = 33 with EGJ type II (31.4%), and n = 30 with EGJ type III (28.6%). On real-time MRI, hiatal hernia was more common in patients with EGJ type III (66.7%) than in patients with EGJ type I (26.2%) and EGJ type II (30.3%; p p = 0.017). The mean esophagus–fundus angle of patients was 85 ± 31° at rest and increased to 101 ± 36° during Valsalva maneuver. Conclusion Real-time MRI is a non-invasive imaging method for assessment of the esophagogastric junction. Real-time MRI can visualize dynamic changes of the EGJ during swallowing events.

To develop a real-time radial tagging MRI for accurate measurement of rotational motion and twist of the left ventricle (LV).A FLASH-based radial tagging sequence with an undersampled radial reading scheme was developed for both single and double-slice imaging in real-time. The Polar Fourier Transform was used for reconstruction to push the undersampling artifacts out of a reduced FOV. The developed technique was used to image five normal subjects during rest, plus one during both exercise and rest conditions. LV rotational motions were estimated for five consecutive cardiac cycles in all cases. The process was validated using a numerical phantom. The real-time measurement of global rotational motion was compared with those measured from a non-real-time exam using linear regression analysis and the Bland-Altman plot.The real-time acquisition was performed successfully with a temporal resolution of 46.2 ms. Image quality was sufficient for the reproducible calculation of rotation at rest and exercise. The feasibility of double-slice acquisition on human was further studied and a real-time twist of the left ventricle was demonstrated. The difference between LV global rotations from real-time and non-real-time approaches was 0.27 degrees. A significant reverse recoiling, induced by exercise, was reproducibly measured by the technique.A real-time radial tagging MRI technique was developed based on the undersampled radial acquisition and Polar Fourier Transform reconstruction, for accurate measuring of the heart rotational motion and twist. The technique was able to extract a meaningful change of diastolic recoiling under stress test conditions during physical activities (cycling).

Background: Correction of tetralogy of Fallot (cTOF) often results in pulmonary valve pathology and right ventricular (RV) dysfunction. Reduced exercise capacity in cTOF patients cannot be explained by these findings alone. We aimed to explore why cTOF patients exhibit impaired exercise capacity with the aid of a comprehensive cardiopulmonary exercise testing (CPET) and real-time cardiovascular magnetic resonance exercise testing (CMR-ET) protocol. Methods: Thirty three cTOF patients and 35 matched healthy controls underwent CPET and CMR-ET in a prospective case-control study. Real-time steady-state free precession cine and phase-contrast sequences were obtained during incremental supine in-scanner cycling at 50, 70, and 90 W. RV and left ventricle (LV) volumes and pulmonary blood flow (Qp) were calculated. Differences of CPET and CMR-ET between cTOF versus controls and correlations between CPET and CMR-ET parameters in cTOF were evaluated statistically for all CMR exercise levels using Mann-Whitney U and Spearman rank-order correlation tests. Results: CPET capacity was significantly lower in cTOF than in controls. cTOF patients exhibited not only significantly reduced Qp and RV function but also lower LV function on CMR-ET. Higher CPET values in cTOF correlated with higher Qp (Qp 90 W versus carbon dioxide ventilatory equivalent %: R =−0.519, P R =0.452, P r =−0.463, P r =0.66, P r =0.52, P Conclusions: Impaired exercise capacity in cTOF resulted from a reduction in not only RV, but also LV function. cTOF with good exercise capacity on CPET demonstrated higher LV reserve and pulmonary blood flow during incremental CMR-ET. Apart from RV parameters, CMR-ET–derived LV function could be a valuable tool to stratify cTOF patients for pulmonary valve replacement.

To assess the diagnostic potential of real-time MRI for assessment of hiatal hernias in patients with GERD-like symptoms compared to endoscopy.One hundred eight patients with GERD-like symptoms were included in this observational cohort study between 2015 and 2017. Real-time MRI was performed at 3.0 Tesla with temporal resolution of 40 ms, dynamically visualizing the esophageal transport of a pineapple juice bolus, its passage through the gastroesophageal junction, and functional responses during Valsalva maneuver. Hernia detection on MRI and endoscopy was calculated using contingency tables with diagnosis of hernia on either modality as reference.Of 108 patients, 107 underwent successful MRI without adverse events; 1 examination was aborted to inability to swallow pineapple juice in supine position. No perforation or acute bleeding occurred during endoscopy. Median examination time was 15 min. Eighty-five patients (79.4%) were diagnosed with hiatal hernia on either real-time MRI or endoscopy. Forty-six hernias were visible on both modalities. Seventeen hernias were evident exclusively on MRI, and 22 exclusively on endoscopy. Sixteen of the 63 MRI-detected hernias (25.4%) were detectable only during Valsalva maneuver, which were smaller compared to hernias at rest (median - 13.5 vs - 33.0 mm, p 0.001). Diagnostic accuracy for hernia detection was comparable for MRI and endoscopy (sensitivity 74% vs 80%, p = 0.4223; specificity 100% vs 100%, p 0.99).Real-time MRI is a fast and safe modality for assessment of the gastroesophageal junction, without radiation exposure or administration of gadolinium-based contrast media. Although MRI and endoscopy yield comparable diagnostic accuracy, dynamic MRI sequences are able to visualize hiatal hernias that were occult on static MRI sequences or endoscopy in a relevant number of cases.• Real-time MRI is a safe and fast imaging modality for examination of the gastroesophageal junction, combining anatomical and functional information for enhanced detection of hiatal hernias. • Real-time MRI and endoscopy yield comparably high diagnostic accuracy: real-time MRI visualizes hiatal hernias that were occult on endoscopy in a relevant number of patients; however, several hiatal hernias detected on endoscopy were occult on real-time MRI. • There is clinical potential of real-time MR imaging in patients with GERD-like symptoms and equivocal findings on endoscopy or pH-metry, for anatomical visualization in patients planned for surgical intervention, or those with suspected fundoplication failures.

To assess the diagnostic potential of dynamic real-time MRI for fundoplication failure in patients with persistent or recurrent GERD-like (gastroesophageal reflux disease) complaints. Twenty-two consecutive patients (male n = 11; female n = 11; median age 59 years) with recurrent or persistent GERD-like symptom after fundoplication were enrolled between 2015 and 2017. Median duration of GERD-like symptoms was 21 months. Real-time MRI (3 Tesla) was performed at 40 ms temporal resolution using undersampled radial fast low-angle shot acquisitions with nonlinear inverse image reconstruction. MRI movies dynamically visualized bolus transit of pineapple juice through the gastroesophageal junction, position of the fundoplication wrap and recurring hernia or reflux during Valsalva maneuver. MRI results were compared to endoscopic findings. Real-time MRI was successfully completed in all patients without adverse events (average examination time 15 min). Morphological correlates for GERD-like symptoms were evident in 20 patients (90.1%) with gastric reflux in 19 cases. Nine patients (40.1%) had wrap disruption and recurrent gastric hernia. Wrap migration or telescoping hernia was detected in nine patients (40.1%). One patient presented with continued reflux despite intact fundoplication wrap. Esophageal dysmotility with delayed bolus passage was observed in one case. On endoscopy, gastric hernia or wrap disruption was diagnosed in seven cases, and esophagitis or Barret’s metaplasia in nine cases. Real-time MRI is a fast and safe modality for dynamic imaging after fundoplication, without radiation exposure or administration of gadolinium-based contrast media. In a relevant number of cases, real-time MRI reveals correlates for GERD-like symptoms. • Real-time MRI reliably visualizes the gastroesophageal junction after fundoplication surgery. • Patients with recurring GERD-like symptoms have a high rate of morphological failure patterns that can be identified by real-time MRI. • Dynamic assessment of gastroesophageal junction by real-time MRI is a perspective diagnostic tool for detection of fundoplication failure.

Background: Right heart catheterization using exercise stress is the reference standard for the diagnosis of heart failure with preserved ejection fraction (HFpEF) but carries the risk of the invasive procedure. We hypothesized that real-time cardiac magnetic resonance (RT-CMR) exercise imaging with pathophysiologic data at excellent temporal and spatial resolution may represent a contemporary noninvasive alternative for diagnosing HFpEF. Methods: The HFpEF-Stress trial (CMR Exercise Stress Testing in HFpEF; URL: https://www.clinicaltrials.gov ; Unique identifier: NCT03260621. URL: https://dzhk.de/ ; Unique identifier: DZHK-17) prospectively recruited 75 patients with echocardiographic signs of diastolic dysfunction and dyspnea on exertion (E/e′>8, New York Heart Association class ≥II) to undergo echocardiography, right heart catheterization, and RT-CMR at rest and during exercise stress. HFpEF was defined according to pulmonary capillary wedge pressure (≥15 mm Hg at rest or ≥25 mm Hg during exercise stress). RT-CMR functional assessments included time–volume curves for total and early (1/3) diastolic left ventricular filling, left atrial (LA) emptying, and left ventricular/LA long axis strain. Results: Patients with HFpEF (n=34; median pulmonary capillary wedge pressure at rest, 13 mm Hg; at stress, 27 mm Hg) had higher E/e′ (12.5 versus 9.15), NT-proBNP (N-terminal pro–B-type natriuretic peptide; 255 versus 75 ng/L), and LA volume index (43.8 versus 36.2 mL/m 2 ) compared with patients with noncardiac dyspnea (n=34; rest, 8 mm Hg; stress, 18 mm Hg; P ≤0.001 for all). Seven patients were excluded because of the presence of non-HFpEF cardiac disease causing dyspnea on imaging. There were no differences in RT-CMR left ventricular total and early diastolic filling at rest and during exercise stress ( P ≥0.164) between patients with HFpEF and noncardiac dyspnea. RT-CMR revealed significantly impaired LA total and early ( P P =0.001) after adjustment for clinical and imaging measures and emerged as the best predictor for HFpEF (area under the curve at rest 0.82 versus exercise stress 0.93; P =0.029). Conclusions: RT-CMR allows highly accurate identification of HFpEF during physiologic exercise and qualifies as a suitable noninvasive diagnostic alternative. These results will need to be confirmed in multicenter prospective research studies to establish widespread routine clinical use. Registration: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT03260621. URL: https://dzhk.de/ ; Unique identifier: DZHK-17.

Purpose To investigate imaging findings of esophageal motility disorders on dynamic real-time. Material and methods 102 patients with GERD-like symptoms were included in this retrospective study between 2015−2018. Dynamic real-time MRI visualized the transit of a 10 mL pineapple juice bolus through the esophagus and EGJ with a temporal resolution of 40 ms. Dynamic and anatomic parameters were measured by consensus reading. Imaging findings were compared to HRM utilizing the Chicago classification of esophageal motility disorders, v3.0. Results All 102 patients completed real-time MRI in a median examination time of 15 min. On HRM, 14 patients presented with disorders with EGJ outlet obstruction (EGJOO) (13.7 %), 7 patients with major disorders of peristalsis (6.9 %), and 32 patients with minor disorders of peristalsis (31.4 %). HRM was normal in 49 patients (48.0 %). Incomplete bolus clearance was significantly more frequent in patients with esophageal motility disorders on HRM than in patients with normal HRM (p = 0.0002). In patients with motility disorders with EGJOO and major disorders of peristalsis, the esophageal diameter tended to be wider (23.6 ± 8.0 vs. 21.2 ± 3.5 mm, p = 0.089) and the sphincter length longer (19.7 ± 7.3 vs. 16.7 ± 3.0 mm, p = 0.091) compared to patients with normal HRM. 3/7 patients with achalasia type II were correctly identified by real-time MRI and one further achalasia type II patient was diagnosed with a motility disorder on MRI films. The other 3/7 patients presented no specific imaging features. Conclusion Real-time MRI is an auxiliary diagnostic tool for the assessment of swallowing events. Imaging parameters may assist in the detection of esophageal motility disorders.

Purpose: The aim of this work is to shed light on the issue of reproducibility in MR image reconstruction in the context of a challenge. Participants had to recreate the results of "Advances in sensitivity encoding with arbitrary k-space trajectories" by Pruessmann et al. Methods: The task of the challenge was to reconstruct radially acquired multi-coil k-space data (brain/heart) following the method in the original paper, reproducing its key figures. Results were compared to consolidated reference implementations created after the challenge, accounting for the two most common programming languages used in the submissions (Matlab/Python). Results: Visually, differences between submissions were small. Pixel-wise differences originated from image orientation, assumed field-of-view or resolution. The reference implementations were in good agreement, both visually and in terms of image similarity metrics. Discussion and Conclusion: While the description level of the published algorithm enabled participants to reproduce CG-SENSE in general, details of the implementation varied, e.g., density compensation or Tikhonov regularization. Implicit assumptions about the data lead to further differences, emphasizing the importance of sufficient meta-data accompanying open data sets. Defining reproducibility quantitatively turned out to be non-trivial for this image reconstruction challenge, in the absence of ground-truth results. Typical similarity measures like NMSE of SSIM were misled by image intensity scaling and outlier pixels. Thus, to facilitate reproducibility, researchers are encouraged to publish code and data alongside the original paper. Future methodological papers on MR image reconstruction might benefit from the consolidated reference implementations of CG-SENSE presented here, as a benchmark for methods comparison., Submitted to Magnetic Resonance in Medicine; 29 pages with 10 figures and 1 table

Cardiac Magnetic Resonance Imaging (MRI) is time-consuming and error-prone. To ease the patient's burden and to increase the efficiency and robustness of cardiac exams, interest in methods based on continuous steady-state acquisition and self-gating has been growing in recent years. Self-gating methods extract the cardiac and respiratory signals from the measurement data and then retrospectively sort the data into cardiac and respiratory phases. Repeated breathholds and synchronization with the heart beat using some external device as required in conventional MRI are then not necessary. In this work, we introduce a novel self-gating method for radially acquired data based on a dimensionality reduction technique for time-series analysis (SSA-FARY). Building on Singular Spectrum Analysis, a zero-padded, time-delayed embedding of the auto-calibration data is analyzed using Principle Component Analysis. We demonstrate the basic functionality of SSA-FARY using numerical simulations and apply it to in-vivo cardiac radial single-slice bSSFP and Simultaneous Multi-Slice radiofrequency-spoiled gradient-echo measurements, as well as to Stack-of-Stars bSSFP measurements. SSA-FARY reliably detects the cardiac and respiratory motion and separates it from noise. We utilize the generated signals for high-dimensional image reconstruction using parallel imaging and compressed sensing with in-plane wavelet and (spatio-)temporal total-variation regularization., Comment: 6 figures, 2 tables and Supplementary Document. Parts of this work was presented at SCMR 2019, Bellevue, and ISMRM 2019, Montreal

To develop a single-shot multi-sliceSMS excitations are combined with a single-shot IR radial FLASH sequence for data acquisition. A previously developed single-slice calibrationless model-based reconstruction is extended to SMS, formulating the estimation of parameter maps and coil sensitivities from all slices as a single nonlinear inverse problem. Joint-sparsity constraints are further applied to the parameter maps to improvePhantom results confirm goodThe IR SMS radial FLASH acquisition together with a nonlinear model-based reconstruction enable rapid high-resolution multi-slice

Purpose: To develop a simple and robust tool for the estimation of gradient delays from highly undersampled radial k-space data. Theory: In radial imaging gradient delays induce parallel and orthogonal trajectory shifts, which can be described using an ellipse model. The intersection points of the radial spokes, which can be estimated by spoke-by-spoke comparison of k-space samples, distinctly determine the parameters of the ellipse. Using the proposed method (RING), these parameters can be obtained using a least-squares fit and utilized for the correction of gradient delays. Methods: The functionality and accuracy of the proposed RING method is validated and compared to correlation-based gradient-delay estimation from opposing spokes using numerical simulations, phantom and in vivo heart measurements. Results: In all experiments, RING robustly provides accurate gradient delay estimations even for as few as three radial spokes. Conclusion: The simple and straightforward to implement RING method provides accurate gradient delay estimation for highly undersampled radial imaging. Keywords: trajectory correction, radial imaging, gradient delay, artifacts, system imperfections, RING, 13 pages, 4 figures. Submitted to Magnetic Resonance in Medicine as a Note

Conventional Magnetic Resonance Imaging (MRI) is hampered by long scan times and only qualitative image contrasts that prohibit a direct comparison between different systems. To address these limitations, model-based reconstructions explicitly model the physical laws that govern the MRI signal generation. By formulating image reconstruction as an inverse problem, quantitative maps of the underlying physical parameters can then be extracted directly from efficiently acquired k-space signals without intermediate image reconstruction -- addressing both shortcomings of conventional MRI at the same time. This review will discuss basic concepts of model-based reconstructions and report about our experience in developing several model-based methods over the last decade using selected examples that are provided complete with data and code., Comment: 8 figures, review accepted to Philos. Trans. R. Soc. A

Purpose: To develop a method that adaptively generates tiny dictionaries for joint T1-T2 mapping. Theory: This work breaks the bond between dictionary size and representation accuracy (i) by approximating the Bloch-response manifold by piece-wise linear functions and (ii) by adaptively refining the sampling grid depending on the locally-linear approximation error. Methods: Data acquisition was accomplished with use of an 2D radially sampled Inversion-Recovery Hybrid-State Free Precession sequence. Adaptive dictionaries are generated with different error tolerances and compared to a heuristically designed dictionary. Based on simulation results, tiny dictionaries were used for T1-T2 mapping in phantom and in vivo studies. Reconstruction and parameter mapping were performed entirely in subspace. Results: All experiments demonstrated excellent agreement between the proposed mapping technique and template matching using heuristic dictionaries. Conclusion: Adaptive dictionaries in combination with manifold projection allow to reduce the necessary dictionary sizes by one to two orders of magnitude.

Objective The aim of this study is to evaluate a real-time magnetic resonance imaging (MRI) method that not only promises high spatiotemporal resolution but also practical robustness in a wide range of scientific and clinical applications. Materials and methods The proposed method relies on highly undersampled gradient-echo sequences with radial encoding schemes. The serial image reconstruction process solves the true mathematical task that emerges as a nonlinear inverse problem with the complex image and all coil sensitivity maps as unknowns. Extensions to model-based reconstructions for quantitative parametric mapping further increase the number of unknowns, for example, by adding parameters for phase-contrast flow or T1 relaxation. In all cases, an iterative numerical solution that minimizes a respective cost function is achieved with use of the iteratively regularized Gauss-Newton method. Convergence is supported by regularization, for example, to the preceding frame, whereas temporal fidelity is ensured by downsizing the regularization strength in comparison to the data consistency term in each iterative step. Practical implementations of highly parallelized algorithms are realized on a computer with multiple graphical processing units. It is "invisibly" integrated into a commercial 3-T MRI system to allow for conventional usage and to provide online reconstruction, display, and storage of regular DICOM image series. Results Depending on the application, the proposed method offers serial imaging, that is, the recording of MRI movies, with variable spatial resolution and up to 100 frames per second (fps)-corresponding to 10 milliseconds image acquisition times. For example, movements of the temporomandibular joint during opening and closing of the mouth are visualized with use of simultaneous dual-slice movies of both joints at 2 × 10 fps (50 milliseconds per frame). Cardiac function may be studied at 30 to 50 fps (33.3 to 20 milliseconds), whereas articulation processes typically require 50 fps (20 milliseconds) or orthogonal dual-slice acquisitions at 2 × 25 fps (20 milliseconds). Methodological extensions to model-based reconstructions achieve improved quantitative mapping of flow velocities and T1 relaxation times in a variety of clinical scenarios. Conclusions Real-time gradient-echo MRI with extreme radial undersampling and nonlinear inverse reconstruction allows for direct monitoring of arbitrary physiological processes and body functions. In many cases, pertinent applications offer hitherto impossible clinical studies (eg, of high-resolution swallowing dynamics) or bear the potential to replace existing MRI procedures (eg, electrocardiogram-gated cardiac examinations). As a consequence, many novel opportunities will require a change of paradigm in MRI-based radiology. At this stage, extended clinical trials are needed.

To achieve dynamic water/fat separation andThis work introduces an undersampled triple-echo multi-spoke radial FLASH sequence, which uses (i) complementary radial spokes per echo train for faster spatial encoding, (ii) asymmetric echoes for flexible and nonuniform echo spacing, and (iii) a golden angle increment across frames for optimal k-space coverage. Joint estimation of water, fat,Up to 18-fold undersampling is achieved in this work. Even in the presence of rapid physiological motion, largeThe combination of a triple-echo acquisition and joint reconstruction technique provides a practical solution to time-resolved and motion robust water/fat separation at high spatial and temporal resolution.

Purpose To evaluate the diagnostic potential of real-time MRI for dynamic assessment of gastroesophageal reflux in patients with GERD (gastroesophageal reflux disease)-like symptoms compared to pH-metry and impedance. Methods Patients who underwent real-time MRI and pH-metry between 2015-2018 were included in this retrospective study. Real-time MRI at 3 Tesla was achieved by undersampled radial FLASH acquisitions with iterative image reconstruction by NLINV. Real-time MRI visualized transit of pineapple juice through the gastroesophageal junction and during Valsalva maneuver. MRI results were compared to 24 -h pH-metry to assess acidic reflux (following Lyon Consensus guidelines) and to impedance to assess non-acidic reflux. A standard 2 × 2 table was chosen to calculate diagnostic performance. Results 91/93 eligible patients fulfilled inclusion criteria (male n = 49; female n = 42; median age 55 y). All MRI studies were successfully completed without adverse events at a mean examination time of 15 minutes. On real-time MRI, reflux was evident in 60 patients (66%). pH-metry revealed reflux in 41 patients (45%), and impedance in 54 patients (59%). Compared to pH-metry and impedance, real-time MRI sensitivity was 0.78 (95% CI: 0.66-0.87), specificity 0.67 (95% CI: 0.45-0.84) and PPV 0.87 (95% CI: 0.75-0.94). Conclusion Real-time MRI is an imaging method for assessment of gastroesophageal reflux in patients with GERD-like symptoms. Considering its high positive predictive value, real-time MRI can accurately identify patients in which further invasive testing with pH-metry and impedance might be considered.

Purpose: A novel subspace-based reconstruction method for frequency-modulated balanced steady-state free precession (fmSSFP) MRI is presented. In this work, suitable data acquisition schemes, subspace sizes, and efficiencies for banding removal are investigated. Theory and Methods: By combining a fmSSFP MRI sequence with a 3D stack-of-stars trajectory, scan efficiency is maximized as spectral information is obtained without intermediate preparation phases. A memory-efficient reconstruction routine is implemented by introducing the low-frequency Fourier transform as a subspace which allows for the formulation of a convex reconstruction problem. The removal of banding artifacts is investigated by comparing the proposed acquisition and reconstruction technique to phase-cycled bSSFP MRI. Aliasing properties of different undersampling schemes are analyzed and water/fat separation is demonstrated by reweighting the reconstructed subspace coefficients to generate virtual spectral responses in a post-processing step. Results: A simple root-of-sum-of-squares combination of the reconstructed subspace coefficients yields high-SNR images with the characteristic bSSFP contrast but without banding artifacts. Compared to Golden-Angle trajectories, turn-based sampling schemes were superior in minimizing aliasing across reconstructed subspace coefficients. Water/fat separated images of the human knee were obtained by reweighting subspace coefficients. Conclusion: The novel subspace-based fmSSFP MRI technique emerges as a time-efficient alternative to phase-cycled bSSFP. The method does not need intermediate preparation phases, offers high SNR and avoids banding artifacts. Reweighting of the reconstructed subspace coefficients allows for generating virtual spectral responses with applications to water/fat separation.

Purpose A new acquisition and reconstruction method called T2 Shuffling is presented for volumetric fast spin-echo (three-dimensional [3D] FSE) imaging. T2 Shuffling reduces blurring and recovers many images at multiple T2 contrasts from a single acquisition at clinically feasible scan times (6-7 min). Theory and methods The parallel imaging forward model is modified to account for temporal signal relaxation during the echo train. Scan efficiency is improved by acquiring data during the transient signal decay and by increasing echo train lengths without loss in signal-to-noise ratio (SNR). By (1) randomly shuffling the phase encode view ordering, (2) constraining the temporal signal evolution to a low-dimensional subspace, and (3) promoting spatio-temporal correlations through locally low rank regularization, a time series of virtual echo time images is recovered from a single scan. A convex formulation is presented that is robust to partial voluming and radiofrequency field inhomogeneity. Results Retrospective undersampling and in vivo scans confirm the increase in sharpness afforded by T2 Shuffling. Multiple image contrasts are recovered and used to highlight pathology in pediatric patients. A proof-of-principle method is integrated into a clinical musculoskeletal imaging workflow. Conclusion The proposed T2 Shuffling method improves the diagnostic utility of 3D FSE by reducing blurring and producing multiple image contrasts from a single scan. Magn Reson Med 77:180-195, 2017. © 2016 Wiley Periodicals, Inc.

The purpose of this study was to assess the reproducibility of functional and anatomical parameters of swallowing events as determined by real-time MRI at 40 ms temporal resolution (25 frames per second). Twenty-three consecutive patients with gastroesophageal reflux disease (GERD) underwent real-time MRI of the gastroesophageal junction at 3.0 T. Real-time MRI was based on highly undersampled radial fast low angle shot (FLASH) acquisitions with iterative image reconstruction by regularized nonlinear inversion (NLINV). MRI movies visualized the esophageal transport of a pineapple juice bolus, its passage through the gastroesophageal junction and functional responses during a Valsalva maneuver. His-angle, sphincter position, sphincter length and sphincter transit time were assessed by two radiologists. Interobserver and intraobserver intraclass correlation coefficients (ICC) were evaluated and Bland-Altman plots were constructed to assess the observer agreement. Interobserver agreement was excellent for sphincter transit time (ICC = 0.92), His-angle (ICC = 0.93), His-angle during Valsalva maneuver (ICC = 0.91) and sphincter-to-diaphragm distance (ICC = 0.98). Sphincter length and oesophageal diameter showed good interobserver agreement (ICC = 0.62 and ICC = 0.70). Intraobserver agreement was good for sphincter length (ICC = 0.80) and excellent for sphincter transit time, His-angle and His-angle during Valsalva maneuver, sphincter-to-diaphragm distance, and esophageal diameter (ICC = 0.91; ICC = 0.97; ICC = 0.97; ICC = 0.998; ICC = 0.93). All functional parameters of the gastroesophageal junction had good to excellent reproducibility. Visual assessment of Bland Altman plots did not reveal any systematic interobserver bias. In conclusion, the visualization of swallowing events by real-time MRI has a high potential for clinical application in gastroesophageal reflux disease.

Diagnostic testing often assesses the cardiovascular or respiratory systems in isolation, ignoring the major pathophysiologic interactions between the systems in many diseases. When both systems are assessed currently, multiple modalities are utilized in costly fashion with burdensome logistics and decreased accessibility. Thus, we have developed a new acquisition and reconstruction paradigm using the flexibility of MRI to enable a comprehensive exam from a single 5–15 min scan. We constructed a compressive-sensing approach to pseudo-randomly acquire highly subsampled, multi-dimensionally-encoded and time-stamped data from which we reconstruct volumetric cardiac and respiratory motion phases, contrast-agent dynamics, and blood flow velocity fields. The proposed method, named XD flow, is demonstrated for (a) evaluating congenital heart disease, where the impact of bulk motion is reduced in a non-sedated neonatal patient and (b) where the observation of the impact of respiration on flow is necessary for diagnostics; (c) cardiopulmonary imaging, where cardiovascular flow, function, and anatomy information is needed along with pulmonary perfusion quantification; and in (d) renal function imaging, where blood velocities and glomerular filtration rates are simultaneously measured, which highlights the generality of the technique. XD flow has the ability to improve quantification and to provide additional data for patient diagnosis for comprehensive evaluations.

To develop a model-based reconstruction technique for single-shot TThe proposed model-based reconstruction jointly estimates all model parameters, that is, the equilibrium magnetization, steady-state magnetization, 1/ T1*, and all coil sensitivities from the data of a single-shot IR FLASH acquisition with a small golden-angle radial trajectory. Joint sparsity constraints on the parameter maps are exploited to improve the performance of the iteratively regularized Gauss-Newton method chosen for solving the nonlinear inverse problem. Validations include both a numerical and experimental TIn comparison to previous reconstruction methods for single-shot TThe comprehensive model-based reconstruction with L1 regularization offers rapid and robust T

Purpose: The development of a calibrationless parallel imaging method for accelerated simultaneous multi-slice (SMS) MRI based on Regularized Nonlinear Inversion (NLINV), evaluated using Cartesian and radial FLASH. Theory and Methods: NLINV is a parallel imaging method that jointly estimates image content and coil sensitivities using a Newton-type method with regularization. Here, NLINV is extended to SMS-NLINV for reconstruction and separation of all simultaneously acquired slices. The performance of the extended method is evaluated for different sampling schemes using phantom and in-vivo experiments based on Cartesian and radial SMS-FLASH sequences. Results: The basic algorithm was validated in Cartesian experiments by comparison with ESPIRiT. For Cartesian and radial sampling, improved results are demonstrated compared to single-slice experiments, and it is further shown that sampling schemes using complementary samples outperform schemes with the same samples in each partition. Conclusion: The extension of the NLINV algorithm for SMS data was implemented and successfully demonstrated in combination with a Cartesian and radial SMS-FLASH sequence., Comment: Part of this work has been presented at the ISMRM Annual Conference 2016 (Singapore) and 2017 (Honolulu). 25 pages, 8+4 figures

In radial fast spin-echo MRI, a set of overlapping spokes with an inconsistent T2 weighting is acquired, which results in an averaged image contrast when employing conventional image reconstruction techniques. This work demonstrates that the problem may be overcome with the use of a dedicated reconstruction method that further allows for T2 quantification by extracting the embedded relaxation information. Thus, the proposed reconstruction method directly yields a spin-density and relaxivity map from only a single radial data set. The method is based on an inverse formulation of the problem and involves a modeling of the received MRI signal. Because the solution is found by numerical optimization, the approach exploits all data acquired. Further, it handles multi-coil data and optionally allows for the incorporation of additional prior knowledge. Simulations and experimental results for a phantom and human brain in vivo demonstrate that the method yields spin-density and relaxivity maps that are neither affected by the typical artifacts from TE mixing, nor by streaking artifacts from the incomplete k-space coverage at individual echo times., 25 pages, 6 figures, 2 tables. Copyright 2009 IEEE

Dynamic MRI studies of the upper airway during speaking, singing or swallowing are complicated by the need for high temporal resolution and the presence of air-tissue interfaces that may give rise to image artifacts such as signal void and geometric distortions. This work exploits a recently developed real-time MRI technique to address these challenges for monitoring speech production at 3 T. The method combines a short-echo time radial FLASH MRI sequence (pulse repetition time/echo time = 2.22/1.44 ms; flip angle 5°) with pronounced undersampling (15 radial spokes per image) and image reconstruction by regularized nonlinear inversion. The resulting serial images at 1.5 mm in-plane resolution and 33.3 ms acquisition time are free of motion or susceptibility artifacts. This application focuses on a dynamic visualization of the main articulators during natural speech production (Standard Modern German). Respective real-time MRI movies at 30 frames per second clearly demonstrate the spatiotemporal coordination of lips, tongue, velum, and larynx for generating vowels, consonants, and coarticulations. The quantitative results for individual phonetic events are in agreement with previous non-MRI findings. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. Since the earliest studies of human articulation in the late 18th century, methods and applications have continuously been expanded. Nowadays, articulatory processes during speaking may be analyzed by a wide range of techniques including laryngoscopy and laryngography, electropalatography, electromyography, electromagnetic articulography, or imaging based on X-ray videofluoroscopy or sonography (1). However, while former approaches require an invasive procedure, which eventually disturbs the natural articulation of vowels and consonants, videofluoroscopy involves the exposure to radiation and sonography is restricted to specific image orientations. Although MRI promises noninvasive examinations as well as more flexible and detailed insights into the vocal tract, insufficient temporal resolution, and limited image quality still emerge as two major obstacles for studying speech production. For example, because long image acquisition times require either repetitively generated (2, 3) or continuant (4) speech sounds, such strategies preclude a proper visualization of the lips and tongue for plosive consonants that are characterized by rapid movements within 50–100 ms (5). In addition, motion-induced image blurring may result from data sharing when using long acquisitions with sliding-window reconstructions to achieve high frame rates (6, 7). It has therefore been concluded that the true temporal resolution for MRI should be comparable to that of standard videofluoroscopy, ideally no longer than 40 ms per image (8). Other problems are the occurrence of focal signal losses and geometric distortions that depend on the sensitivity of a chosen MRI acquisition technique to the unavoidable susceptibility differences near air-tissue interfaces in the upper airway (9, 10). Most recently, we have described a real-time MRI technique using highly undersampled radial FLASH with image reconstruction by regularized nonlinear inversion (11–13). Preliminary applications to cardiovascular function (14), quantitative blood flow (15), and normal swallowing (16) allow for serial real-time images (i.e., movies) with 1.5 to 2.0 mm in-plane resolution and 20–30 ms acquisition time. Accordingly, the purpose of this study was to exploit this real-time MRI method to address the challenges posed by dynamic MRI of speaking and to investigate the key articulatory configurations during natural speech production including vowels, consonants, and coarticulation effects in vowels preceded by consonants.

The desire to visualize noninvasively physiological processes at high temporal resolution has been a driving force for the development of MRI since its inception in 1973. In this article, we describe a unique method for real-time MRI that reduces image acquisition times to only 20 ms. Although approaching the ultimate limit of MRI technology, the method yields high image quality in terms of spatial resolution, signal-to-noise ratio and the absence of artifacts. As proposed previously, a fast low-angle shot (FLASH) gradient-echo MRI technique (which allows for rapid and continuous image acquisitions) is combined with a radial encoding scheme (which offers motion robustness and moderate tolerance to data undersampling) and, most importantly, an iterative image reconstruction by regularized nonlinear inversion (which exploits the advantages of parallel imaging with multiple receiver coils). In this article, the extension of regularization and filtering to the temporal domain exploits consistencies in successive data acquisitions and thereby enhances the degree of radial undersampling in a hitherto unexpected manner by one order of magnitude. The results obtained for turbulent flow, human speech production and human heart function demonstrate considerable potential for real-time MRI studies of dynamic processes in a wide range of scientific and clinical settings. Copyright © 2010 John Wiley & Sons, Ltd.

To develop and assess motion correction techniques for high-resolution pediatric abdominal volumetric magnetic resonance images acquired free-breathing with high scan efficiency.First, variable-density sampling and radial-like phase-encode ordering were incorporated into the 3D Cartesian acquisition. Second, intrinsic multichannel butterfly navigators were used to measure respiratory motion. Lastly, these estimates are applied for both motion-weighted data-consistency in a compressed sensing and parallel imaging reconstruction, and for nonrigid motion correction using a localized autofocusing framework. With Institutional Review Board approval and informed consent/assent, studies were performed on 22 consecutive pediatric patients. Two radiologists independently scored the images for overall image quality, degree of motion artifacts, and sharpness of hepatic vessels and the diaphragm. The results were assessed using paired Wilcoxon test and weighted kappa coefficient for interobserver agreements.The complete procedure yielded significantly better overall image quality (mean score of 4.7 out of 5) when compared to using no correction (mean score of 3.4, P0.05) and to using motion-weighted accelerated imaging (mean score of 3.9, P0.05). With an average scan time of 28 seconds, the proposed method resulted in comparable image quality to conventional prospective respiratory-triggered acquisitions with an average scan time of 91 seconds (mean score of 4.5).With the proposed methods, diagnosable high-resolution abdominal volumetric scans can be obtained from free-breathing data acquisitions.

A model-based reconstruction technique for accelerated T2 mapping with improved accuracy is proposed using undersampled Cartesian spin-echo MRI data. The technique employs an advanced signal model for T2 relaxation that accounts for contributions from indirect echoes in a train of multiple spin echoes. An iterative solution of the nonlinear inverse reconstruction problem directly estimates spin-density and T2 maps from undersampled raw data. The algorithm is validated for simulated data as well as phantom and human brain MRI at 3 T. The performance of the advanced model is compared to conventional pixel-based fitting of echo-time images from fully sampled data. The proposed method yields more accurate T2 values than the mono-exponential model and allows for undersampling factors of at least 6. Although limitations are observed for very long T2 relaxation times, respective reconstruction problems may be overcome by a gradient dampening approach. The analytical gradient of the utilized cost function is included as Appendix., Comment: 10 pages, 7 figures

To investigate four-dimensional flow denoising using the divergence-free wavelet (DFW) transform and compare its performance with existing techniques.DFW is a vector-wavelet that provides a sparse representation of flow in a generally divergence-free field and can be used to enforce "soft" divergence-free conditions when discretization and partial voluming result in numerical nondivergence-free components. Efficient denoising is achieved by appropriate shrinkage of divergence-free wavelet and nondivergence-free coefficients. SureShrink and cycle spinning are investigated to further improve denoising performance.DFW denoising was compared with existing methods on simulated and phantom data and was shown to yield better noise reduction overall while being robust to segmentation errors. The processing was applied to in vivo data and was demonstrated to improve visualization while preserving quantifications of flow data.DFW denoising of four-dimensional flow data was shown to reduce noise levels in flow data both quantitatively and visually.

To develop a method for fast pediatric 3D free-breathing abdominal dynamic contrast enhanced (DCE) magnetic resonance imaging (MRI) and investigate its clinical feasibility.A combined locally low rank parallel imaging method with soft gating is proposed for free-breathing DCE MRI acquisition. With Institutional Review Board (IRB) approval and informed consent/assent, 23 consecutive pediatric patients were recruited for this study. Free-breathing DCE MRI with ∼1 mm(3) spatial resolution and a 6.5-sec frame rate was acquired on a 3T scanner. Undersampled data were reconstructed with a compressed sensing method without motion correction (FB-CS) and the proposed method (FB-LR). A follow-up respiratory-triggered acquisition (RT-CS) was performed as a reference standard. The reconstructed images were evaluated independently by two radiologists. Wilcoxon tests were performed to test the hypothesis that there was no significant difference between different reconstructions. Quantitative evaluation of contrast dynamics was also performed.The mean score of overall image quality of FB-LR was 4.0 on a 5-point scale, significantly better (P0.05) than FB-CS reconstruction (mean score 2.9), and similar to RT-CS (mean score 4.1). FB-LR also matched the temporal fidelity of contrast dynamics with a root mean square error less than 5%.Fast 3D free-breathing DCE MRI with high scan efficiency and image quality similar to respiratory-triggered acquisition is feasible in a pediatric clinical setting.

Purpose: To develop a model-based reconstruction technique for T2 mapping based on multi-echo spin-echo MRI sequences with highly undersampled Cartesian data encoding. Materials and Methods: The proposed technique relies on a nonlinear inverse reconstruction algorithm which directly estimates a T2 and spin-density map from a train of undersampled spin echoes. The method is applicable to acquisitions with single receiver coils but benefits from multi-element coil arrays. The algorithm is validated for trains of 16 spin echoes with a spacing of 10 to 12 ms using numerical simulations as well as human brain MRI at 3 Tesla (T). Results: When compared with a standard T2 fitting procedure using fully sampled T2-weighted images, and depending on the available signal-to-noise ratio and number of coil elements, model-based nonlinear inverse reconstructions for both simulated and in vivo MRI data yield accurate T2 estimates for undersampling factors of 5 to 10. Conclusion: This work describes a promising strategy for T2-weighted MRI that simultaneously offers accurate T2 relaxation times and properly T2-weighted images at arbitrary echo times. For a standard spin-echo MRI sequence with Cartesian encoding, the method allows for a much higher degree of undersampling than obtainable by conventional parallel imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley-Liss, Inc.

Velocity-encoded phase-contrast MRI of cardiovascular blood flow commonly relies on electrocardiogram-synchronized cine acquisitions of multiple heartbeats to quantitatively determine the flow of an averaged cardiac cycle. Here, we present a new method for real-time phase-contrast MRI that combines flow-encoding gradients with highly undersampled radial fast low-angle shot acquisitions and phase-sensitive image reconstructions by regularized nonlinear inversion. Apart from calibration studies using steady and pulsatile flow, preliminary in vivo applications focused on through-plane flow in the ascending aorta of healthy subjects. With bipolar velocity-encoding gradients of alternating polarity that overlap the slice-refocusing gradient, the method yields flow-encoded images with an in-plane resolution of 1.8 mm, section thickness of 6 mm and measuring time at 3 T of 24 ms (TR/TE = 3.44/2.76 ms; flip angle, 10º; seven radial spokes per image). Accordingly, phase-contrast maps and corresponding velocity profiles achieve a temporal resolution of 48 ms. The evaluated peak velocities, stroke volumes, flow rates and respective variances over at least 20 consecutive heartbeats are in general agreement with literature data.

This work demonstrates that the principles underlying phase-contrast MRI may be used to encode spatial rather than flow information along a perpendicular dimension, if this dimension contains an MRI-visible object at only one spatial location. In particular, the situation applies to 3D mapping of curved 2D structures which requires only two projection images with different spatial phase-encoding gradients. These phase-contrast gradients define the field of view and mean spin-density positions of the object in the perpendicular dimension by respective phase differences. When combined with highly undersampled radial fast low angle shot (FLASH) and image reconstruction by regularized nonlinear inversion, spatial phase-contrast MRI allows for dynamic 3D mapping of 2D structures in real time. First examples include 3D MRI movies of the acting human hand at a temporal resolution of 50 ms. With an even simpler technique, 3D maps of curved 1D structures may be obtained from only three acquisitions of a frequency-encoded MRI signal with two perpendicular phase encodings. Here, 3D MRI movies of a rapidly rotating banana were obtained at 5 ms resolution or 200 frames per second. In conclusion, spatial phase-contrast 3D MRI of 2D or 1D structures is respective two or four orders of magnitude faster than conventional 3D MRI.

A new approach based on nonlinear inversion for autocalibrated parallel imaging with arbitrary sampling patterns is presented. By extending the iteratively regularized Gauss–Newton method with variational penalties, the improved reconstruction quality obtained from joint estimation of image and coil sensitivities is combined with the superior noise suppression of total variation and total generalized variation regularization. In addition, the proposed approach can lead to enhanced removal of sampling artifacts arising from pseudorandom and radial sampling patterns. This is demonstrated for phantom and in-vivo measurements.

Background Functional assessments of the heart by dynamic cardiovascular magnetic resonance (CMR) commonly rely on (i) electrocardiographic (ECG) gating yielding pseudo real-time cine representations, (ii) balanced gradient-echo sequences referred to as steady-state free precession (SSFP), and (iii) breath holding or respiratory gating. Problems may therefore be due to the need for a robust ECG signal, the occurrence of arrhythmia and beat to beat variations, technical instabilities (e.g., SSFP "banding" artefacts), and limited patient compliance and comfort. Here we describe a new approach providing true real-time CMR with image acquisition times as short as 20 to 30 ms or rates of 30 to 50 frames per second. Methods The approach relies on a previously developed real-time MR method, which combines a strongly undersampled radial FLASH CMR sequence with image reconstruction by regularized nonlinear inversion. While iterative reconstructions are currently performed offline due to limited computer speed, online monitoring during scanning is accomplished using gridding reconstructions with a sliding window at the same frame rate but with lower image quality. Results Scans of healthy young subjects were performed at 3 T without ECG gating and during free breathing. The resulting images yield T1 contrast (depending on flip angle) with an opposed-phase or in-phase condition for water and fat signals (depending on echo time). They completely avoid (i) susceptibility-induced artefacts due to the very short echo times, (ii) radiofrequency power limitations due to excitations with flip angles of 10° or less, and (iii) the risk of peripheral nerve stimulation due to the use of normal gradient switching modes. For a section thickness of 8 mm, real-time images offer a spatial resolution and total acquisition time of 1.5 mm at 30 ms and 2.0 mm at 22 ms, respectively. Conclusions Though awaiting thorough clinical evaluation, this work describes a robust and flexible acquisition and reconstruction technique for real-time CMR at the ultimate limit of this technology.

A previously proposed nonlinear inverse reconstruction for autocalibrated parallel imaging simultaneously estimates coil sensitivities and image content. This work exploits this property for real-time MRI, where coil sensitivities need to be dynamically adapted to the conditions generated by moving objects. The development comprises (i) an extension of the nonlinear inverse algorithm to non-Cartesian k-space encodings, (ii) its implementation on a graphical processing unit to reduce reconstruction times, and (iii) the use of a convolution-based iteration, which considerably simplifies the graphical processing unit implementation compared to a gridding technique. The method is validated for real-time MRI of the human heart at 3 T using radio frequency-spoiled radial FLASH (pulse repetition time/echo time = 2.0/1.3 ms, flip angle 8 ◦ ). The results demonstrate artifact-free reconstructions from only 65–85 spokes, with 256 oversampled data points. Acquisition times of 130– 170 ms resulted in 29–38 frames per second for sliding window reconstructions (factor 5). While offline reconstructions required 1–2 sec, real-time applications with modified parameters and slightly lower image quality were achieved within 90 ms per graphical processing unit. Magn Reson Med 63:1456–1462, 2010. © 2010 Wiley-Liss, Inc.

Each k-space segment in multishot diffusion-weighted MRI is affected by a different spatially varying phase which is caused by unavoidable motions and amplified by the diffusion-encoding gradients. A proper image reconstruction therefore requires phase maps for each segment. Such maps are commonly derived from two-dimensional navigators at relatively low resolution but do not offer robust solutions. For example, phase variations in diffusion-weighted MRI of the brain are often characterized by high spatial frequencies. To overcome this problem, an inverse reconstruction method for segmented multishot diffusion-weighted MRI is described that takes advantage of the full k-space data acquired from multiple receiver coils. First, the individual coil sensitivities are determined from the non-diffusion-weighted acquisitions by regularized nonlinear inversion. These coil sensitivities are then used to estimate accurate motion-associated phase maps for each segment by iterative linear inversion. Finally, the coil sensitivities and phase maps serve to reconstruct artifact-free images of the object by iterative linear inversion, taking advantage of the data of all segments. The efficiency of the new method is demonstrated for segmented diffusion-weighted stimulated echo acquisition mode MRI of the human brain.

The use of parallel imaging for scan time reduction in MRI faces problems with image degradation when using GRAPPA or SENSE for high acceleration factors. Although an inherent loss of SNR in parallel MRI is inevitable due to the reduced measurement time, the sensitivity to image artifacts that result from severe undersampling can be ameliorated by alternative reconstruction methods. While the introduction of GRAPPA and SENSE extended MRI reconstructions from a simple unitary transformation (Fourier transform) to the inversion of an ill-conditioned linear system, the next logical step is the use of a nonlinear inversion. Here, a respective algorithm based on a Newton-type method with appropriate regularization terms is demonstrated to improve the performance of autocalibrating parallel MRI--mainly due to a better estimation of the coil sensitivity profiles. The approach yields images with considerably reduced artifacts for high acceleration factors and/or a low number of reference lines.

The reconstruction of artifact-free images from radially encoded MRI acquisitions poses a difficult task for undersampled data sets, that is for a much lower number of spokes in k-space than data samples per spoke. Here, we developed an iterative reconstruction method for undersampled radial MRI which (i) is based on a nonlinear optimization, (ii) allows for the incorporation of prior knowledge with use of penalty functions, and (iii) deals with data from multiple coils. The procedure arises as a twostep mechanism which first estimates the coil profiles and then renders a final image that complies with the actual observations. Prior knowledge is introduced by penalizing edges in coil profiles and by a total variation constraint for the final image. The latter condition leads to an effective suppression of undersampling (streaking) artifacts and further adds a certain degree of denoising. Apart from simulations, experimental results for a radial spin-echo MRI sequence are presented for phantoms and human brain in vivo at 2.9 T using 24, 48, and 96 spokes with 256 data samples. In comparison to conventional reconstructions (regridding) the proposed method yielded visually improved image quality in all cases. Magn Reson Med 57:1086–1098, 2007. © 2007 Wiley-Liss, Inc.