Johns Hopkins University

Projects include:

• Designing a weighted and regularized non-convex optimization method for better recovering velocities from low-Venc data.
• Using advanced convex optimization techniques to generate time optimal gradient waveforms to reduce the scan time of 4D-Flow acquisitions.
• Using bootstrapping based methods to estimate velocity error in PC-MRI data.
• Assessing hemodynamic changes in intracranial aneurysms that may lead to rupture.

Three month collaborative exchange working on TKE VIPR implementations and divergence constrained compressed sensing reconstructions.

PhD Research:

• Creating an easy to use and effective automatic phase unwrapping algorithm for 4D datasets based on minimizing 4D Laplacian convolutions of the entire dataset.
• Improving velocity to noise ratios and streamline quality by enforcing divergence-free constraints with post-processing methods and as a constraint in compressed sensing reconstructions.
• Improving streamline quality by correcting for displacement based offsets accrued during measurement.
• Extending probabilistic streamlines and the previously described algorithms to create 'virtual injections' from 4D MR Flow data to better track the expected path of blood through the vasculature.

Preclinical MR cancer research on small animals, mainly DCE-MRI analysis to measure tumor response to chemotherapeutic agents.

ISMRM Flow and Motion Study Group

"Novel hemodynamic parameters and correction methods for PC-MRI for aid in diagnosis of brain AVMs and aneurysms"
American Heart Association, 12PRE12080073

Taught classes on compressed sensing and constrained reconstructions in 'Med Phys / Biomedical Engineering 710 - Advances in MRI'

Zimmermann, J., Loecher, M., Kolawole, F. O., Bäumler, K., Gifford, K., Dual, S. A., Levenston, M., Marsden, A. L., & Ennis, D. B. (2021). On the impact of vessel wall stiffness on quantitative flow dynamics in a synthetic model of the thoracic aorta. Scientific Reports, 11(1), 6703. https://doi.org/10.1038/s41598-021-86174-6

Maier, O., Baete, S. H., Fyrdahl, A., Hammernik, K., Harrevelt, S., Kasper, L., Karakuzu, A., Loecher, M., Patzig, F., Tian, Y., Wang, K., Gallichan, D., Uecker, M., & Knoll, F. (2021). CG‐SENSE revisited: Results from the first ISMRM reproducibility challenge. Magnetic Resonance in Medicine, 85(4), 1821–1839. https://doi.org/10.1002/mrm.28569

Perotti, L. E., Verzhbinsky, I. A., Moulin, K., Cork, T. E., Loecher, M., Balzani, D., & Ennis, D. B. (2021). Estimating cardiomyofiber strain in vivo by solving a computational model. Medical Image Analysis, 68, 101932. https://doi.org/10.1016/j.media.2020.101932

Zimmermann, J., Bäumler, K., Loecher, M., Cork, T. E., Kolawole, F. O., Gifford, K., Marsden, A. L., Fleischmann, D., & Ennis, D. B. (2021). Quantitative Hemodynamics in Aortic Dissection: Comparing in Vitro MRI with FSI Simulation in a Compliant Model. Lecture Notes in Computer Science (Including Subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 12738 LNCS, 575–586. https://doi.org/10.1007/978-3-030-78710-3_55

Loecher, M., Hannum, A. J., Perotti, L. E., & Ennis, D. B. (2021). Arbitrary Point Tracking with Machine Learning to Measure Cardiac Strains in Tagged MRI. Lecture Notes in Computer Science (Including Subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 12738 LNCS, 213–222. https://doi.org/10.1007/978-3-030-78710-3_21

Middione, M. J., Loecher, M., Moulin, K., & Ennis, D. B. (2020). Optimization methods for magnetic resonance imaging gradient waveform design. NMR in Biomedicine, 33(12). https://doi.org/10.1002/nbm.4308

Loecher, M., Middione, M. J., & Ennis, D. B. (2020). A gradient optimization toolbox for general purpose time‐optimal MRI gradient waveform design. Magnetic Resonance in Medicine, 84(6), 3234–3245. https://doi.org/10.1002/mrm.28384

Chiang, J., Loecher, M., Moulin, K., Meloni, M. F., Raman, S. S., McWilliams, J. P., Ennis, D. B., & Lee, E. W. (2020). 4D Flow MR Imaging to Improve Microwave Ablation Prediction Models: A Feasibility Study in an In Vivo Porcine Liver. Journal of Vascular and Interventional Radiology, 31(10), 1691–1696.e1. https://doi.org/10.1016/j.jvir.2019.11.034

Verzhbinsky, I. A., Perotti, L. E., Moulin, K., Cork, T. E., Loecher, M., & Ennis, D. B. (2019). Estimating Aggregate Cardiomyocyte Strain Using In Vivo Diffusion and Displacement Encoded MRI. IEEE Transactions on Medical Imaging. https://doi.org/10.1109/TMI.2019.2933813

Loecher, M., Magrath, P., Aliotta, E., & Ennis, D. B. (2019). Time‐optimized 4D phase contrast MRI with real‐time convex optimization of gradient waveforms and fast excitation methods. Magnetic Resonance in Medicine, 82(1), 213–224. https://doi.org/10.1002/mrm.27716

Cork, T. E., Perotti, L. E., Verzhbinsky, I. A., Loecher, M., & Ennis, D. B. (2019). High-Resolution Ex Vivo Microstructural MRI After Restoring Ventricular Geometry via 3D Printing. Lecture Notes in Computer Science (Including Subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 11504 LNCS, 177–186. https://doi.org/10.1007/978-3-030-21949-9_20

Loecher, M., & Ennis, D. B. (2018). Velocity reconstruction with nonconvex optimization for low-velocity-encoding phase-contrast MRI. Magnetic Resonance in Medicine, 80(1), 42–52. https://doi.org/10.1002/mrm.26997

Loecher, M., Schrauben, E., Johnson, K. M., & Wieben, O. (2016). Phase unwrapping in 4D MR flow with a 4D single-step laplacian algorithm. Journal of Magnetic Resonance Imaging, 43(4), 833–842. https://doi.org/10.1002/jmri.25045

Santelli, C., Loecher, M., Busch, J., Wieben, O., Schaeffter, T., & Kozerke, S. (2015). Accelerating 4D flow MRI by exploiting vector field divergence regularization. Magnetic Resonance in Medicine. https://doi.org/10.1002/mrm.25563

Chang, W., Wu, Y., Johnson, K., Loecher, M., Wieben, O., Edjlali, M., Oppenheim, C., Roca, P., Hald, J., Aagaard-Kienitz, B., Niemann, D., Mistretta, C., & Turski, P. (2015). Fast contrast-enhanced 4D MRA and 4D flow MRI using constrained reconstruction (HYPRFlow): Potential applications for brain arteriovenous malformations. American Journal of Neuroradiology, 36(6), 1049–1055. https://doi.org/10.3174/ajnr.A4245

Chang, W., Loecher, M., Wu, Y., Niemann, D. B., Ciske, B., Aagaard-Kienitz, B., Kecskemeti, S., Johnson, K. M., Wieben, O., Mistretta, C., & Turski, P. (2012). Hemodynamic changes in patients with arteriovenous malformations assessed using high-resolution 3D radial phase-contrast MR angiography. AJNR. American Journal of Neuroradiology, 33(8), 1565–1572. https://doi.org/10.3174/ajnr.A3010

Turowski, S. G., Seshadri, M., Loecher, M., Podniesinski, E., Spernyak, J. A., & Mazurchuk, R. V. (2008). Performance of a novel piezoelectric motor at 4.7 T: applications and initial tests. Magnetic Resonance Imaging, 26(3), 426–432. https://doi.org/10.1016/j.mri.2007.07.005

Loecher, M., Perotti, L. E., & Ennis, D. B. (2021). Voxel-wise Tracking of Grid Tagged Cardiac Images using a Neural Network Trained with Synthetic Data. ISMRM Annual Meeting, Remote.

Loecher, M., Perotti, L. E., & Ennis, D. B. (2020). Cardiac Tag Tracking with Deep Learning Trained with Comprehensive Synthetic Data Generation. ISMRM Annual Meeting, Remote.

Loecher, M., Perotti, L. E., Magrath, P., & Ennis, D. B. (2020). Measuring Cardiac Strain in Duchenne Muscular Dystrophy with a Convolutional Neural Net Tag Tracking Method. ISMRM Annual Meeting, Remote.

Loecher, M., Middione, M. J., & Ennis, D. B. (2020). Gradient Optimization (GrOpt) Toolbox: A Software Package for Fast Gradient WaveformDesign. ISMRM Annual Meeting, Remote.

Loecher, M., & Ennis, D. B. (2018). New Techniques for Imaging Cardiac Motion with MRI. Cardiac Imaging, Mechanics, and Modeling Symposium, Stanford, USA.

Loecher, M., Magrath, P., Aliotta, E., & Ennis, D. B. (2018). Accelerating 4D-Flow Acquisitions by Reducing TE and TR with Optimized RF and Gradient Waveforms. ISMRM Annual Meeting, Paris, France.

Loecher, M., Magrath, P., Aliotta, E., & Ennis, D. B. (2017). Optimizing TE and TR of 4D-Flow Acquisitions for Reduced Scan Times. SMRA Annual Meeting, Stellenbosch, South Africa.

Loecher, M., & Ennis, D. B. (2017). Pushing the Boundaries of Low-Venc PC-MRI Acquisition Strategies with a Weighted, Regularized Optimization Reconstruction. ISMRM Annual Meeting, Honolulu, USA.

Loecher, M., & Ennis, D. B. (2016). Improving Velocity Accuracy for Low-Venc Phase Contrast Acquisitions with a Constrained Optimization Reconstruction. ISMRM Flow and Motion Workshop, San Francisco, USA.

Loecher, M., & Ennis, D. B. (2016). More accurate velocimetry for high-moment phase contrast using weighted non-convex optimization. SMRA Annual Meeting, Chicago, USA.

Loecher, M., Johnson, K. M., Turski, P., & Wieben, O. (2014). Improved “virtual injections” with 4D MR flow. MR Angiography Club, Rome, Italy.

Loecher, M., Johnson, K. M., Turski, P., & Wieben, O. (2014). Robust Whole-Brain Blood Tracking from 4D Flow Using Displacement Corrected Probabilistic Streamlines. ISMRM Annual Meeting, Milan, Italy.

Loecher, M., Wieben, O., & Johnson, K. M. (2013). 4 Dimensional, Single Step Laplacian Algorithm for Phase Unwrapping in 4D MR Flow. ISMRM Annual Meeting, Salt Lake City, USA.

Loecher, M., & Ennis, D. B. (2017). Bootstrapped Estimates of Velocity Uncertainty for 4D Flow PC-MRI. ISMRM Annual Meeting, Honolulu, USA.

Loecher, M., Hu, P., & Ennis, D. B. (2016). Temporal Dynamics and Sampling Rate Effects for Background Phase Estimates in 4D Flow MRI. ISMRM Annual Meeting, Singapore.

Loecher, M., Johnson, K. M., Turski, P., & Wieben, O. (2015). Radial displacement errors and correction efficiency for streamline visualization in 4D-Flow MRI. ISMRM Annual Meeting, Toronto, Canada.

Loecher, M., Santelli, C., Wieben, O., & Kozerke, S. (2013). L1-SPIRiTPhase for Separate Magnitude and Phase Reconstruction with a Divergence Penalty for 3D Phase-Contrast Flow Measurements. ISMRM Data Sampling and Image Reconstruction Workshop, Sedona, USA.

Loecher, M., Santelli, C., Wieben, O., & Kozerke, S. (2013). Improved L1-SPIRiT Reconstruction with a Phase Divergence Penalty for 3D Phase-Contrast Flow Measurements. ISMRM Annual Meeting, Salt Lake City, USA.

Loecher, M., Kecskemeti, S., Turski, P., & Wieben, O. (2012). Comparison of divergence-free algorithms for 3D MRI with three-directional velocity encoding. ISMRM Flow and Motion Workshop, Orlando, USA.

Loecher, M., Kecskemeti, S., Johnson, K. M., Turski, P., & Wieben, O. (2012). Evaluation of divergence-free correction algorithms in high resolution 4-D flow images of cranial vasculature. ISMRM Annual Meeting, Melbourne, Australia.

Loecher, M., Johnson, K. M., Francois, C. J., & Wieben, O. (2011). 4D Gradient Based Phase Unwrapping for PC-MR Flow Data. ISMRM Annual Meeting, Montreal, Canada.

Loecher, M., Johnson, K. M., Francois, C. J., & Wieben, O. (2010). Peak Angiogram Calculations from 4D Flow Imaging. ISMRM Annual Meeting, Stockholm, Sweden.

Loecher, M., Francois, C. J., Johnson, K. M., Lum, D., & Wieben, O. (2010). Benefits and Pitfalls in the Use of Contrast Agents in 4D Flow Imaging. ISMRM Annual Meeting, Stockholm, Sweden.