Medical Physics Seminar - Monday, November 16, 2009

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Making Waves in Biomedical Research with Micro-Ultrasound

F. Stuart Foster, Ph.D.

Professor, University of Toronto

Sunnybrook Health Sciences Centre (SHSC) and Department of Medical Biophysics

University of Toronto Canada

The recent development of array based micro-ultrasound in the 15 - 50 MHz range is now transforming preclinical ultrasound imaging.  These instruments provide a quantum leap in imaging performance with resolution in the 50 – 150 micron range and are now used in many biomedical research applications in cancer, cardiovascular disease and many other areas.  At the heart of the array scanner is a laser machined high frequency transducer array capable of forming dynamic diffraction limited beams.   This new imaging system offers dramatically increased (> ten fold) depth of field and greatly expanded scope for realtime functional imaging.  Frame rates in excess of 200 frames per second enable rapid evaluation of the dynamic morphology and hemodynamics of the mouse heart and contribute to a wide range of biomedical studies of the cardiovascular system.  Of particular relevance to cancer researchers is the ability to provide rapid accurate measures of tumor burden in orthotopic mouse models and the ability to monitor microvascular flow in realtime using color flow and power Doppler.  Non-contrast and contrast applications of 15 - 50 MHz micro-ultrasound will be described.  Imaging of cardiovascular, prostate, hepatocellular carcinoma, and melanoma models will be used to demonstrate vessel detectability down to 50 microns using the native contrast of blood and down to the capillary microcirculation using microbubble contrast agents.  By labeling the microbubbles with appropriate ligands it is possible to perform molecular imaging of endothelial cell surface markers.  Examples of molecular imaging of VEGFR-2 expression in a variety of tumor models will be demonstrated with the new array imager.  One of the limitations of the current contrast modes available for micro-ultrasound is their reliance on linear subtraction methods.  This talk will include discussion the implementation of a real-time nonlinear contrast mode on the array based system, and the challenges faced in high-frequency contrast imaging, namely nonlinear propagation in tissue. In vitro and in vivo results for high frequency nonlinear contrast will be presented.

Location: 1345 Health Sciences Learning Center (HSLC)

Time:  4:00pm-5:00pm

Refreshments will be provided prior to the talk

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