Content

  • About Me
  • Real-time MRI
  • Image Reconstruction
  • Software
  • Publications
  • Real-time Magnetic Resonance Imaging

    Introduction

    Continuous advances in hardware and software have made it possible to image dynamic processes in the human body in real-time with good quality using MRI. This page gives some information and references about a new reconstruction algorithm for dynamic MRI, which I have developed and implemented while working with Jens Frahm at the Biomedizinische NMR Forschungs GmbH at the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany. When combined with a real-time acquisition method developed by Shuo Zhang et al. [2], the method yields MRI movies at high spatial and temporal resolution. The method is fast enough to observe turbulence after stirring in a water beaker, visualize swallowing and speaking, and to acquire images of the human heart without synchronization to an ECG [1].

    Figure: Real-time MRI of a human heart at a resolution of 50 ms during free breathing and without synchronization to an ECG. More movies can be found on wikimedia.

    Data Acquisition

    Data acquisition is based on a radial FLASH sequence (based on work by Tobias Block with later contributions by Dirk Voit) with an interleaved acquisition scheme [2]. Most experiments have been performed on a Siemens Tim Trio at 3 Tesla with 32 receive channels.

    Image Reconstruction

    The reconstruction algorithm uses the iteratively regularized Gauss-Newton method to jointly estimate the image and receiver sensitivities [5] (similar to ideas from Leslie Ying and Jinhua Sheng [4]) from data acquired on a non-Cartesian (radial) trajectory [3] and makes use of temporal regularization and non-linear filtering to exploit the temporal redundancy in a time series of images [1]. To achieve reasonable reconstruction times, it has been implemented on a graphical processing unit (GPU) [3]. Reconstruction is performed on a dedicated computer system which is connected to the MRI scanner via ethernet. Real-time export of the data during the measurement and (real-time) re-import of the reconstructed images into the MRI scanner is automatic [6]. The newer multi-GPU implementation which is developed by Sebastian Schätz currently achieves 25 Hz frame-rate without compromising image quality [7]. Because acquisition rates can be 50 Hz or more, reconstruction can - so far - not always be performed in real-time.

    Applications

    Applications developed at the BiomedNMR research institute range from cardiac imaging [1, 6, 8], phase-contrast MRI of cardiovascular flow [9, 10], to dynamic imaging of speaking [1, 11] and swallowing [1, 12, 13], tablet disintegration [14] and more [15]. Another method derived from this work is a technique for dynamic MRI called Temporal Resolution Acceleration with Constrained Evolution Reconstruction (TRACER) developed by Xu et al. at Cornell University [16].

    Figure: A single frame from a real-time movie of the human heart (2 mm x 2 mm in-plane resolution, 8 mm slice thickness, 15 radial spokes, 30 ms acquisition time) a. conventional gridding reconstruction b. nonlinear inverse reconstruction with temporal regularization and filtering

    References

    [1] Martin Uecker, Shuo Zhang, Dirk Voit, Alexander Karaus, Klaus-Dietmar Merboldt, and Jens Frahm, Real-time magnetic resonance imaging at a resolution of 20 ms, NMR in Biomedicine 23: 986–994 (2010)

    [2] Shuo Zhang, Kai Tobias Block, and Jens Frahm, Magnetic resonance imaging in real time: Advances using radial FLASH, J Magn Reson Imaging 31:101–109 (2010)

    [3] Martin Uecker, Shuo Zhang, and Jens Frahm, Nonlinear Inverse Reconstruction for Real-time MRI of the Human Heart Using Undersampled Radial FLASH, Magnetic Resonance in Medicine 63 (6): 1456–1462 (2010)

    [4] Leslie Ying and Jinhua Sheng, Joint image reconstruction and sensitivity estimation in SENSE (JSENSE), Magn Reson Med, 57: 1196–1202 (2007).

    [5] Martin Uecker, Thorsten Hohage, Kai Tobias Block, and Jens Frahm, Image Reconstruction by Regularized Nonlinear Inversion - Joint Estimation of Coil Sensitivities and Image Content, Magnetic Resonance in Medicine 60:674-682 (2008)

    [6] Shuo Zhang, Martin Uecker, Dirk Voit, Klaus-Dietmar Merboldt, and Jens Frahm, Real-time cardiac MRI at high temporal resolution: radial FLASH with nonlinear inverse reconstruction, Journal of Cardiovascular Magnetic Resonance 12:39 (2010)

    [7] Sebastian Schätz and Martin Uecker, A Multi-GPU Programming Library for Real-Time Applications, 12th International Conference on Algorithms and Architectures for Parallel Processing (ICA3PP-2012), Fukuoka 2012, In Lecture Notes in Computer Science, 7439:114-128 (2012) arXiv:1301.1215 [cs.DC]

    [8] Dirk Voit, Shuo Zhang, Christina Unterberg-Buchwald, Jan M Sohns, Joachim Lotzm and Jens Frahm, Real-time cardiovascular magnetic resonance at 1.5 T using balanced SSFP and 40 ms resolution Journal of Cardiovascular Magnetic Resonance, 15:79 (2013)

    [9] Arun A Joseph, Klaus-Dietmar Merboldt, Dirk Voit, Shuo Zhang, Martin Uecker, Joachim Lotz, and Jens Frahm. Real-time phase-contrast MRI of cardiovascular blood flow using undersampled radial fast low-angle shot and nonlinear inverse reconstruction. NMR in Biomedicine 25:917-924 (2012)

    [10] Arun Joseph, Johannes T Kowallick, Klaus-Dietmar Merboldt, Dirk Voit, Sebastian Schaetz, Shuo Zhang, Jan M Sohns, Joachim Lotz, and Jens Frahm, Real-time flow MRI of the aorta at a resolution of 40 msec. Journal of Magnetic Resonance Imaging. EPub (2013)

    [11] Aaron Niebergall, Shuo Zhang, Esther Kunay, Götz Keydana, Michael Job, Martin Uecker, and Jens Frahm. Real-time MRI of Speaking at a Resolution of 33 ms: Undersampled Radial FLASH with Nonlinear Inverse Reconstruction, Magnetic Resonance in Medicine, 69:477-485 (2013)

    [12] Shuo Zhang, Arno Olthoff, and Jens Frahm. Real-time magnetic resonance imaging of normal swallowing. Journal of Magnetic Resonance Imaging, 35: 1372-1379 (2012)

    [13] Arno Olthoff, Shuo Zhang, Renate Schweizer, and Jens Frahm. On the Physiology of Normal Swallowing as Revealed by Magnetic Resonance Imaging in Real Time. Gastroenterology Research and Practice, 2014:493174 (2014)

    [14] Julian Quodbach, Amir Moussavi, Roland Tammer, Jens Frahm, and Peter Kleinebudde, Tablet Disintegration Studied by High-Resolution Real-Time Magnetic Resonance Imaging. Journal of Pharmaceutical Sciences, 103: 249-255 (2014).

    [15] Martin Uecker, Shuo Zhang, Dirk Voit, Klaus-Dietmar Merboldt, and Jens Frahm. Real Time MRI: recent advances using radial FLASH. Imaging in Medicine 4:461-476 (2012)

    [16] B Xu, P Spincemaille, G Chen, M Agrawal, T. D. Nguyen, M. R. Prince, and Y. Wang, Fast 3D contrast enhanced MRI of the liver using temporal resolution acceleration with constrained evolution reconstruction,. Magnetic Resonance in Medicine 69: 370–381 (2013).