Showing papers by "Matthias Stuber published in 2018"

5D whole-heart sparse MRI.

Abstract: Purpose A 5D whole-heart sparse imaging framework is proposed for simultaneous assessment of myocardial function and high-resolution cardiac and respiratory motion-resolved whole-heart anatomy in a single continuous noncontrast MR scan. Methods A non–electrocardiograph (ECG)-triggered 3D golden-angle radial balanced steady-state free precession sequence was used for data acquisition. The acquired 3D k-space data were sorted into a 5D dataset containing separated cardiac and respiratory dimensions using a self-extracted respiratory motion signal and a recorded ECG signal. Images were then reconstructed using XD-GRASP, a multidimensional compressed sensing technique exploiting correlations/sparsity along cardiac and respiratory dimensions. 5D whole-heart imaging was compared with respiratory motion-corrected 3D and 4D whole-heart imaging in nine volunteers for evaluation of the myocardium, great vessels, and coronary arteries. It was also compared with breath-held, ECG-gated 2D cardiac cine imaging for validation of cardiac function quantification. Results 5D whole-heart images received systematic higher quality scores in the myocardium, great vessels and coronary arteries. Quantitative coronary sharpness and length were always better for the 5D images. Good agreement was obtained for quantification of cardiac function compared with 2D cine imaging. Conclusion 5D whole-heart sparse imaging represents a robust and promising framework for simplified comprehensive cardiac MRI without the need for breath-hold and motion correction. Magn Reson Med 79:826–838, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A double echo ultra short echo time (UTE) acquisition for respiratory motion-suppressed high resolution imaging of the lung.

Abstract: PURPOSE Magnetic resonance imaging is a promising alternative to computed tomography for lung imaging. However, organ motion and poor signal-to-noise ratio, arising from short T2*, impair image quality. To alleviate these issues, a new retrospective gating method was implemented and tested with an ultra-short echo time sequence. METHODS A 3D double-echo ultra-short echo time sequence was used to acquire data during free breathing in ten healthy adult subjects. A self-gating method was used to reconstruct respiratory motion suppressed expiratory and inspiratory images. These images were objectively compared to uncorrected data sets using quantitative end-points (pulmonary vessel sharpness, lung-liver interface definition, signal-to-noise ratio). The method was preliminarily tested in two cystic fibrosis patients who underwent computed tomography. RESULTS Vessel sharpness in expiratory ultra-short echo time data sets with second echo motion detection was significantly higher (13% relative increase) than in uncorrected images while the opposite was observed in inspiratory images. The method was successfully applied in patients and some findings (e.g., hypointense areas) were similar to those from computed tomography. CONCLUSION Free breathing ultra-short echo time was successfully implemented, allowing flexible image reconstruction of two different respiratory states. Objective improvements in image quality were obtained with the new method and initial feasibility in a clinical setting was demonstrated. Magn Reson Med 79:2297-2305, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Flexible water excitation for fat-free MRI at 3T using lipid insensitive binomial off-resonant RF excitation (LIBRE) pulses

Abstract: PURPOSE To develop a robust and flexible low power water excitation pulse that enables effective fat suppression at high magnetic field strength. METHODS A water excitation method that uses spatially non-selective pulses was optimized in numerical simulations, and implemented and tested in phantoms and healthy volunteers at 3T. The lipid insensitive binomial off-resonant excitation (LIBRE) pulse comprises two low power rectangular subpulses that have a variable frequency offset, phase offset and duration. The capability and extent of LIBRE fat suppression was quantitatively compared with conventional fat saturation (FS) and water excitation (WE) techniques. RESULTS LIBRE enables simultaneous water excitation and near complete fat suppression in large volumes at 3T as demonstrated by numerical simulations, and experiments. In phantoms and in human subjects, the frequency responses matched well with those from the numerical simulation. Comparing FS and WE, LIBRE demonstrated an improved robustness to magnetic field inhomogeneities, and a much more effectively suppressed fat signal. This applied for a range of pulse durations and pulses as short as 1.4 ms. CONCLUSION A flexible water excitation method was developed that shows robust, near complete fat suppression at 3T. Magn Reson Med 79:3007-3017, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Coronary artery assessment using self-navigated free-breathing radial whole-heart magnetic resonance angiography in patients with congenital heart disease.

Abstract: To evaluate a self-navigated free-breathing three-dimensional (SNFB3D) radial whole-heart MRA technique for assessment of main coronary arteries (CAs) and side branches in patients with congenital heart disease (CHD). SNFB3D-MRA datasets of 109 patients (20.1±11.8 years) were included. Three readers assessed the depiction of CA segments, diagnostic confidence in determining CA dominance, overall image quality and the ability to freeze cardiac and respiratory motion. Vessel sharpness was quantitatively measured. The percentages of cases with excellent CA depiction were as follows (mean score): left main, 92.6 % (1.92); left anterior descending (LAD), 88.3 % (1.88); right (RCA), 87.8 % (1.85); left circumflex, 82.8 % (1.82); posterior descending, 50.2 % (1.50) and first diagonal, 39.8 % (1.39). High diagnostic confidence for the assessment of CA dominance was achieved in 56.2 % of MRA examinations (mean score, 1.56). Cardiac motion freezing (mean score, 2.18; Pearson’s r=0.73, P<0.029) affected image quality more than respiratory motion freezing (mean score, 2.20; r=0.58, P<0.029). Mean quantitative vessel sharpness of the internal thoracic artery, RCA and LAD were 53.1, 52.5 and 48.7 %, respectively. Most SNFB3D-MRA examinations allow for excellent depiction of the main CAs in young CHD patients; visualisation of side branches remains limited. • Self-navigated free-breathing three-dimensional magnetic resonance angiography (SNFB3D-MRA) sufficiently visualises coronary arteries (CAs). • Depiction of main CAs in patients with congenital heart disease is excellent. • Visualisation of CA side branches using SNFB3D-MRA is limited. • SNFB3D-MRA image quality is especially correlated to cardiac motion freezing ability.

A phantom study to determine the theoretical accuracy and precision of radial MRI to measure cross‐sectional area differences for the application of coronary endothelial function assessment

Abstract: PURPOSE MRI has been used to noninvasively assess coronary endothelial function by measuring the vasoreactivity in response to handgrip exercise. However, the spatial resolution of MRI is limited relative to the expected vasodilation response of healthy coronary arteries (10%-20%), and the sensitivity of MRI to detect such small cross-sectional area differences has yet to be quantitatively examined. METHODS Holes of different diameters were drilled in a phantom to simulate a range of physiological responses of coronary arteries to stress. Radial cine MR images with different spatial resolutions were acquired under moving conditions, and different noise levels were simulated. Cross-sectional areas were automatically measured and statistically analyzed to quantify the smallest detectable area difference. RESULTS Statistical analyses suggest that radial MRI is capable of distinguishing area differences of 0.2 to 0.3 mm2 for high signal-to-noise ratio images, which correspond to a percentage coronary area difference of 3% to 4% for a 3-mm baseline diameter. Furthermore, the smallest detectable area difference was largely independent of the pixel size for the sequence and range of diameters investigated in this study. CONCLUSION Radial MRI is capable of reliably detecting small differences in cross-sectional areas that are well within the expected physiological range of stress-induced area changes in of healthy coronary arteries. Magn Reson Med 79:108-120, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Improved respiratory self‐navigation for 3D radial acquisitions through the use of a pencil‐beam 2D‐T2‐prep for free‐breathing, whole‐heart coronary MRA

Abstract: Purpose In respiratory self-navigation (SN), signal from static structures, such as the chest wall, may complicate motion detection or introduce post-correction artefacts Suppressing signal from superfluous tissues may therefore improve image quality We thus test the hypothesis that SN whole-heart coronary magnetic resonance angiography (MRA) will benefit from an outer-volume suppressing 2D-T2-Prep and present both phantom and in vivo results Methods A 2D-T2-Prep and a conventional T2-Prep were used prior to a free-breathing 3D-radial SN sequence Both techniques were compared by imaging a home-built moving cardiac phantom and by performing coronary MRA in nine healthy volunteers Reconstructions were performed using both a reference-based and a reference-independent approach to motion tracking, along with several coil combinations Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were compared, along with vessel sharpness (VS) Results In phantoms, using the 2D-T2-Prep increased SNR by 16% to 53% and mean VS by 8%; improved motion tracking precision was also achieved In volunteers, SNR increased by an average of 29% to 33% in the blood pool and by 15% to 25% in the myocardium, depending on the choice of reconstruction coils and algorithm, and VS increased by 34% Conclusion A 2D-T2-Prep significantly improves image quality in both phantoms and volunteers when performing SN coronary MRA Magn Reson Med, 2017 © 2017 International Society for Magnetic Resonance in Medicine

Author Correction: Fetal cardiac cine magnetic resonance imaging in utero.

Abstract: A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.