Jens Frahm PhD, Presenter: Research collaboration, Siemens AG

Martin Uecker, Abstract Co-Author: Research collaboration, Siemens AG

Dirk Voit, Abstract Co-Author: Research collaboration, Siemens AG

Klaus-Dietmar Merboldt, Abstract Co-Author: Research collaboration, Siemens AG

Shuo Zhang MS, Abstract Co-Author: Research collaboration, Siemens AG

To introduce a novel method for real-time cardiac magnetic resonance imaging (MRI) that yields high-quality images with acquisition times as short as 20 ms and movies with 50 frames per second.

The approach combines two major principles: a fast low-angle shot (FLASH) MRI acquisition technique with radial data encoding, and a regularized nonlinear inversion technique for image reconstruction. The former allows for rapid, continuous and motion-robust imaging without sensitivity to off-resonance artifacts. The latter enhances the usable degree of data undersampling (acceleration) in an hitherto unexpected manner to a factor of 20. Studies of healthy subjects were performed on a conventional 3T MRI system using a 32-element cardiac array coil comprising a 16-element anterior and posterior portion.

Preliminary applications demonstrate a surprising quality of real-time MRI movies that monitor cardiac motions during free breathing and without synchronization to the electrocardiogram. Typical images have an in-plane resolution of 1.5 to 2.0 mm and acquisition times of 20 to 30 ms, which corresponds to a true temporal resolution of 33 to 50 frames per second. T1-weighted images along anatomically defined orientations exhibit a relatively high signal of the myocardium and a good blood-tissue contrast. Furthermore, the ultra-short imaging times may be exploited for either dual-echo or multi-slice acquisitions. The former allows for simultaneous imaging of two cardiac movies with in-phase and opposed-phase contrast where water and fat signals mutually superimpose (e.g. for improved visualization of the pericardium) or cancel (e.g. for better delineation of blood vessels or flow dynamics). The latter allows for simultaneous imaging of multiple anatomical sections - even along different orientations.

The proposed real-time MRI method demonstrates unsurpassed potential for anatomical and functional studies of the heart. The high spatial and temporal fidelity promises more reliable assessments of quantitative functional parameters.

Though awaiting clinical evaluations, ultra-fast real-time MRI promises improved patient comfort, efficiency, and spatiotemporal fidelity in dynamic studies of cardiac anatomy and function.

Frahm, J, Uecker, M, Voit, D, Merboldt, K, Zhang, S, Real Time Cardiac MR Imaging at Ultra High Temporal Resolution.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9015280.html