Imaging Speed Demons
Charles A. Mistretta, Ph.D.
Breaking Angiographic Speed Limits: Accelerated 4D MRA and 4D DSA Using Undersampled Acquisition and Constrained Reconstruction
Accelerated angiographic methods in MRA, using novel non-Cartesian k-space sampling schemes combined with constrained reconstruction, have led to acceleration factors up to 1000 relative to Nyquist requirements. Related approaches have permitted the extension of X-ray DSA to a full 4D modality, according to Dr. Mistretta, providing 3D vascular volumes 200 times faster than conventional rotational DSA.
Fast 4D angiographic techniques are useful for evaluation of dynamic phenomena such as arteriovenous malformations—in the X-ray case, the availability of all view angles at all times eliminates the need for the X-ray exposure and contrast dose associated with repeat injections. Undersampled acquisition and constrained reconstruction will play a major role in a wide variety of medical imaging applications leading to improved diagnosis, greater interventional flexibility and dose reduction, Dr. Mistretta said.
Dr. Mistretta, the 2010 RSNA Outstanding Researcher, is the director of the International Center for Accelerated Medical Imaging at the University of Wisconsin, where he also serves as John R. Cameron Professor of Medical Physics and vice-chairman of the Department of Medical Physics.
Mickael Tanter, Ph.D.
Ultrasound Goes Supersonic: Very-High-Speed Plane Wave Transmission Imaging for New Morphological and Functional Imaging Modes
Advances in ultra-high-speed ultrasound imaging employ the concept of plane wave transmissions rather than line-by-line scanning beams. The frame rate reaches the theoretical limit of physics dictated by the ultrasound speed and an ultrasonic map can typically be provided in tens of micro-seconds. This leap in frame rate, Dr. Tanter says, makes it possible to track in real time the transient vibrations—known as shear waves—propagating through organs.
Such "human body seismology" provides quantitative maps of local tissue stiffness, of which the added diagnostic value has been recently demonstrated. For blood flow imaging, ultrafast Doppler permits high-precision characterization of complex vascular and cardiac flows and enables detection of subtle blood flow in very small vessels. In the brain, such ultrasensitive Doppler paves the way for fUltrasound (functional ultrasound), offering unprecedented spatial and temporal resolution compared to fMRI.
Dr. Tanter is a research professor at the French National Institute for Health and Medical Research and heads the Physics Methods for Biomedical Imaging and Therapy unit at Institut Langevin in Paris.