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Modelling river hydrodynamics in an efficient approach remains a technical challenge which limits our ability to assess river flood hazard or to use process-based erosion laws at a high-resolution in landscape evolution models. Here we present a fast iterative method, entitled FastFlood, to compute river depth and velocity in 2D on a digital elevation model (DEM). This new method solves for the 2D shallow water equation, without the inertia terms, by iteratively building the river water depth using classical flow routing algorithms based on directed acyclic graphs, including the classical single or multi-flow, applied to the water surface. At each iteration, the water depth of each cell of the DEM increases by an increment that is a function of water discharge, computed using a flow accumulation operation, and decreases based on a flow resistance equation, in a manner similar to the Floodos model (Davy et al., 2017). In the hydrostatic mode, this operation is repeated until reaching a near constant water depth over the entire DEM, which occurs after a few tens or hundreds of iterations. FastFlood can also solve for the dynamic propagation of a flood in the hydrodynamic mode. In this case, the water depth increment is only a function of the water discharge exiting the direct upstream neighbors and the iterations are replaced by a time evolution of the water depth. Water depths obtained with the hydrostatic solution were validated against an analytical solution in the case of a rectangular channel and with the Floodos model for natural DEMs. Compared to previous hydrodynamic models, the main benefits of FastFlood are its simplicity of implementation, which mainly requires a classical flow routing algorithm, and its efficiency. Indeed, for a DEM of 106 cells, the algorithm takes about 2 minutes on a laptop to find the hydrostatic solution, about 10 times faster than using the Floodos model (Davy et al., 2017) that was already significantly faster than other hydrodynamic models. Moreover, the computational time scales a little more than linearly with the number of cells, which makes FastFlood a suitable solution even for DEMs larger than 106 – 107 cells. In the future, we expect to make progress on the numerical method by adapting graph-based solutions to the issue of flow water routing. Following Davy et al. (2017), we will also include FastFlood in a landscape evolution model to couple it to process-based laws for erosion, transport and deposition of sediments.

To develop high-spatial-resolution cardiac T 2 mapping that allows for a reduced acquisition time while maintaining its precision. We implemented and optimized a new golden-angle radial T 2 mapping technique named SKRATCH (Shared k-space Radial T 2 Characterization of the Heart) that shares k-space peripheries of T 2 -weighted images while preserving their contrasts. Six SKRATCH variants (gradient-recalled echo and balanced SSFP, free-breathing and breath-held, with and without a saturation preparation) were implemented, and their precision was compared with a navigator-gated reference technique in phantoms and 22 healthy volunteers at 3 T. The optimal breath-held SKRATCH technique was applied in a small cohort of patients with subacute myocardial infarction. The faster free-breathing SKRATCH technique reduced the acquisition time by 52.4%, while maintaining the precision and spatial resolution of the reference technique. Similarly, the most precise and robust breath-held SKRATCH technique demonstrated homogenous T 2 values that did not significantly differ from the navigator-gated reference (T 2 = 39.9 ± 3.4 ms versus 39.5 ± 3.4 ms, P > .20, respectively). All infarct patients demonstrated a large T 2 elevation in the ischemic regions of the myocardium. The optimized SKRATCH technique enabled the accelerated acquisition of high-spatial-resolution T 2 maps, was validated in healthy adult volunteers, and was successfully applied to a small initial group of patients.

PURPOSE Ultra-short echo time MRI is a promising alternative to chest CT for cystic fibrosis patients. Black-blood imaging in particular could help discern small-sized anomalies, such as mucoid plugging, which may otherwise be confused with neighboring blood vessels, particularly when contrast agent is not used. We, therefore, implemented and tested an ultra-short echo time sequence with black-blood preparation. Additionally, this sequence may also be used to generate bright-blood angiograms. METHODS Using this sequence, data was acquired during free breathing in 10 healthy volunteers to obtain respiratory-motion-resolved 3D volumes covering the entire thorax with an isotropic resolution of (1 mm)3 . The magnitude of signal suppression relative to a bright-blood reference acquisition was quantified and compared with that obtained with a turbo-spin echo (TSE) acquisition. Bright-blood angiograms were also generated by subtraction. Finally, an initial feasibility assessment was performed in 2 cystic fibrosis patients, and images were visually compared with contrast-enhanced images and with CT data. RESULTS Black-blood preparation significantly decreased the average normalized signal intensity in the vessel lumen (-66%; P < 0.001). Similarly, blood signal was significantly lowered (-60%; P = 0.001) compared with the TSE acquisition. In patients, mucoid plugging could be emphasized in the black-blood datasets. An intercostal artery could also be visualized in the subtraction angiograms. CONCLUSION Black-blood free-breathing ultra-short echo time imaging was successfully implemented and motion-resolved full volumetric coverage of the lungs with high spatial resolution was achieved, while obtaining an angiogram without contrast agent injection. Encouraging initial results in patients prompt further investigations in a larger cohort.

Purpose The goal of this study was to characterize the accuracy and precision of cardiac T2 mapping as a function of different factors including low signal-to-noise ratio (SNR), imaging in systole, and off-resonance frequencies. Methods Bloch equation and Monte Carlo simulations were used to determine the influence of SNR and the choice of T2 preparation echo time (TET2prep) increments on the accuracy and precision of high-resolution radial cardiac T2 mapping at 3.0 T. Healthy volunteers were scanned to establish the difference in precision and inter- and intraobserver variability between T2 mapping in diastole and systole, as well as the effect of SNR and off-resonance frequencies on the accuracy of T2 maps. Results The simulations demonstrated that a TET2prep increment of ∼0.75 times the T2 value of interest optimally increases the precision of the T2 fit. Systolic T2 maps were found to have a higher precision (P = 0.002), but similar inter- and intraobserver variability compared with diastolic T2 maps, whereas off-resonance frequencies beyond ± 100 Hz cause a significant decrease in both accuracy and precision (P

Purpose To test the hypothesis that both coronary anatomy and ventricular function can be assessed simultaneously using a single four-dimensional (4D) acquisition. Methods A free-running 4D whole-heart self-navigated acquisition incorporating a golden angle radial trajectory was implemented and tested in vivo in nine healthy adult human subjects. Coronary magnetic resonance angiography (MRA) datasets with retrospective selection of acquisition window width and position were extracted and quantitatively compared with baseline self-navigated electrocardiography (ECG) -triggered coronary MRA. From the 4D datasets, the left-ventricular end-systolic, end-diastolic volumes (ESV & EDV) and ejection fraction (EF) were computed and compared with values obtained from conventional 2D cine images. Results The 4D datasets enabled dynamic assessment of the whole heart with isotropic spatial resolution of 1.15 mm3. Coronary artery image quality was very similar to that of the ECG-triggered baseline scan despite some SNR penalty. A good agreement between 4D and 2D cine imaging was found for EDV, ESV, and EF. Conclusion The hypothesis that both coronary anatomy and ventricular function can be assessed simultaneously in vivo has been tested positive. Retrospective and flexible acquisition window selection allows to best visualize each coronary segment at its individual time point of quiescence. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.

Purpose To implement and characterize an isotropic three-dimensional cardiac T2 mapping technique. Methods A self-navigated three-dimensional radial segmented balanced steady-state free precession pulse sequence with an isotropic 1.7-mm spatial resolution was implemented at 3T with a variable T2 preparation module. Bloch equation and Monte Carlo simulations were performed to determine the influence of the heart rate, B1 inhomogeneity and noise on the T2 fitting accuracy. In a phantom study, the accuracy of the pulse sequence was studied through comparison with a gold-standard spin-echo T2 mapping method. The robustness and homogeneity of the technique were ascertained in a study of 10 healthy adult human volunteers, while first results obtained in patients are reported. Results The numerical simulations demonstrated that the heart rate and B1 inhomogeneity cause only minor deviations in the T2 fitting, whereas the phantom study showed good agreement of the technique with the gold standard. The volunteer study demonstrated an average myocardial T2 of 40.5 ± 3.3 ms and a

ObjectivesThis study sought to establish an accurate and reproducible T2-mapping cardiac magnetic resonance (CMR) methodology at 3 T and to evaluate it in healthy volunteers and patients with myocardial infarct.BackgroundMyocardial edema affects the T2 relaxation time on CMR. Therefore, T2-mapping has been established to characterize edema at 1.5 T. A 3 T implementation designed for longitudinal studies and aimed at guiding and monitoring therapy remains to be implemented, thoroughly characterized, and evaluated in vivo.MethodsA free-breathing navigator-gated radial CMR pulse sequence with an adiabatic T2 preparation module and an empirical fitting equation for T2 quantification was optimized using numerical simulations and was validated at 3 T in a phantom study. Its reproducibility for myocardial T2 quantification was then ascertained in healthy volunteers and improved using an external reference phantom with known T2. In a small cohort of patients with established myocardial infarction, the local T2 value and extent of the edematous region were determined and compared with conventional T2-weighted CMR and x-ray coronary angiography, where available.ResultsThe numerical simulations and phantom study demonstrated that the empirical fitting equation is significantly more accurate for T2 quantification than that for the more conventional exponential decay. The volunteer study consistently demonstrated a reproducibility error as low as 2 ± 1% using the external reference phantom and an average myocardial T2 of 38.5 ± 4.5 ms. Intraobserver and interobserver variability in the volunteers were –0.04 ± 0.89 ms (p = 0.86) and –0.23 ± 0.91 ms (p = 0.87), respectively. In the infarction patients, the T2 in edema was 62.4 ± 9.2 ms and was consistent with the x-ray angiographic findings. Simultaneously, the extent of the edematous region by T2-mapping correlated well with that from the T2-weighted images (r = 0.91).ConclusionsThe new, well-characterized 3 T methodology enables robust and accurate cardiac T2-mapping at 3 T with high spatial resolution, while the addition of a reference phantom improves reproducibility. This technique may be well suited for longitudinal studies in patients with suspected or established heart disease.

The goal of this study was to characterize the accuracy and precision of cardiac TBloch equation and Monte Carlo simulations were used to determine the influence of SNR and the choice of TThe simulations demonstrated that a TEThis evaluation of the accuracy and precision of cardiac T

Background In recent years, several successful variations of T2-prepared cardiac T2 mapping techniques have been described for the quantification of cardiac edema [1,2,3]. Radial imaging for high-resolution T2 mapping [3] has the advantage of reduced motion sensitivity, but suffers from a lower signal-to-noise ratio (SNR) due to the undersampling of the periphery of k-space and the density compensation function (DCF) that increases the weight of the relatively noisy and less densely sampled k-space periphery (Fig.1a). Since the contrast of an image is defined by the center of k-space, a KWIC (kspace weighted image contrast [4]) filter can be used to share only the periphery among radial images that have the same geometry and different contrast, such as those used to generate a T2 map (Fig.1b). Furthermore, when undersampling is used to acquire more images per T2 map (resulting in more k-space peripheries that can be shared), KWIC filtering further reduces the noise-like undersampling artifacts (Fig.1c). The goal of this study was therefore to test whether the use of the KWIC filter leads to a higher precision in radial T2 maps for a given acquisition time.

PURPOSE: To implement and characterize an isotropic three-dimensional cardiac T2 mapping technique. METHODS: A self-navigated three-dimensional radial segmented balanced steady-state free precession pulse sequence with an isotropic 1.7-mm spatial resolution was implemented at 3T with a variable T2 preparation module. Bloch equation and Monte Carlo simulations were performed to determine the influence of the heart rate, B1 inhomogeneity and noise on the T2 fitting accuracy. In a phantom study, the accuracy of the pulse sequence was studied through comparison with a gold-standard spin-echo T2 mapping method. The robustness and homogeneity of the technique were ascertained in a study of 10 healthy adult human volunteers, while first results obtained in patients are reported. RESULTS: The numerical simulations demonstrated that the heart rate and B1 inhomogeneity cause only minor deviations in the T2 fitting, whereas the phantom study showed good agreement of the technique with the gold standard. The volunteer study demonstrated an average myocardial T2 of 40.5 ± 3.3 ms and a

Background Recently, T2-weighted MRI for the characterization of edema after myocardial infarction has attracted considerable attention (Friedrich, NatRevCardiol2010). Furthermore, the recently proposed combination of bSSFP imaging and T2Prep for T2-mapping at 1.5T has enabled a rapid quantitative cardiac T2 estimation (Huang et al., MRM2007). However, the accuracy of this method may still be limited due to the complex T2/T1 signal weighting. Especially for longitudinal studies designed for monitoring and/or guiding therapy, accurate and reproducible T2 measurements will be critical. A novel quantitative 3T T2-mapping protocol was therefore developed and tested in both healthy volunteers and patients.

Background Cardiac T2 mapping using a variable T2 preparation module (T2Prep) has recently gained attention for its ability to quantify the extent of edema (Giri, JCMR 2009). Due to time constraints, the T2 maps are commonly acquired as one or several two-dimensional slices, while the underlying pathology has a three-dimensional (3D) structure. The next logical step would therefore be to exploit recent hardware and software advances to directly acquire 3D T2 maps. To this end, we tested the feasibility of using a self-navigated 3D radial acquisition with a variable T2Prep for 3D T2 mapping at 3T.

Background T2 mapping through variation of the T2 preparation (T2Prep) duration has been increasingly used to robustly detect and quantify cardiac edema (Giri et al., JCardiovMagnReson2009). However, if images with incremental T2Prep duration are acquired in a sequential fashion, irregular breathing patterns and heart rates may adversely affect the quality of the T2 maps due to misalignment of the source images. A logical alternative is then to acquire all images in an alternating manner (Figure 1ab), where the T2Prep duration changes cyclically from one heartbeat to the next. Combined with a radial signal readout, this may minimize the vulnerability to respiratory or RR variability. We therefore simulated, implemented and tested the utility of an alternating magnetization preparation approach to T2 mapping.