Scientist profiles A-F
Sunnybrook Health Sciences Centre
2075 Bayview Ave., Room S6 60
Administrative Assistant: Marcelline Ramcharan
Phone: 416-480-6100, ext. 5765
- B.Sc., 1974, mathematical physics, University of Sussex, UK
- PhD, 1983, medicine (radiodiagnosis), University of Bristol, UK
Appointments and Affiliations:
- Senior scientist, Physical Sciences, Odette Cancer Research Program, Sunnybrook Research Institute
- Chair and professor, department of medical biophysics, University of Toronto
- Noninvasive imaging of the microcirculation using ultrasound and microbubbles
Ultrasound imaging is familiar to many for the pictures it produces of the developing fetus in pregnancy. It is also one of the most widely used methods to examine the heart, the organs of the abdomen and pelvis, muscles, tendons, and other soft tissue structures. By virtue of the acoustical Doppler effect, it also provides images of human blood flow without the need to inject radioactive compounds, X-ray or other dyes into the circulation. Although in recent years the clinical use of Doppler ultrasound instruments has become widespread, its role has been confined to answering qualitative questions about flow in relatively large vessels.
Dr. Burns seeks to extend this method into a quantitative technique able to measure important hemodynamic variables in the body such as the flow rate of blood, its pressure and the resistance in large vessels. He is analyzing the interaction of ultrasound with moving blood as well as the dynamic characteristics of blood flow and the vessels themselves.
Many significant blood vessels in the body - for example, in the muscular wall of the heart, the myocardium - are so small that they lie below the resolution limit of most radiological methods. Detecting flow in this microcirculation is important, because it can reveal information about the function of tissue and is especially relevant to heart disease and cancer.
Recently, it has become possible to make real-time images of flow in the microcirculation with the help of a new class of materials that can be used as contrast agents for ultrasound. These comprise encapsulated microbubbles of gas, which are smaller than a red blood cell (a few microns across) and can pass harmlessly through the circulation. Dr. Burns and his research team has developed several new imaging methods in which these bubbles are induced to nonlinear resonance in an ultrasound field and thus made to emit harmonic frequencies. These harmonics effectively provide a 'signature' to the echo from blood and allow its separation from that of the surrounding tissue.
With this method, Doppler ultrasound offers a new tool to detect flow in the microscopic vessels of the myocardium after a heart attack. Many clinical research centres are now using methods developed in his lab for diagnosis in heart disease.
The microcirculation also plays an important role in the development of cancers. The growth of new blood vessels in a solid tumour - a process known as malignant angiogenesis - is not only of interest as a way of identifying a cancer, but also is the target of a new generation of cancer therapies. They are working to make imaging methods that can be used to guide and monitor these therapies. They are already using prototype systems in patients with breast and liver cancers with promising results.
Finally, the bubbles themselves can be disrupted remotely using carefully designed ultrasound pulses. This introduces two exciting areas for our current research: first, the interruption of the flow of agents allows perfusion rates to be mapped and flow in the microcirculation to be measured quantitatively; second, the disruption of flowing bubbles in a selected area can be used as a new way to deliver drugs, or even genetic material itself, to a specific organ targeted by the ultrasound beam.
New techniques are developed on the bench but implemented rapidly using modern programmable clinical ultrasound scanning equipment. Dr. Burns' laboratory includes state-of-the-art digital colour flow ultrasound systems with unusually extensive access to the operating software. This allows his team to create prototypes of entirely new methods in the acquisition, processing and display of ultrasonic echoes from the body. As well as laboratory testing, collaborative clinical studies with cardiologists and radiologists in Toronto hospitals are then used to help them evaluate and refine their methods.
- More than 20 years experience in research in medical ultrasound imaging and blood flow measurement.
- Holds three patents in diagnostic ultrasound imaging; has published 4 books, more than 70 refereed papers and 25 book chapters.
- Specializes in Doppler techniques for the detection of blood flow. Pioneer in the development of ultrasound contrast agents for the detection of microvascular blood flow; developer of harmonic and pulse inversion imaging. Patent holder of pulse inversion imaging and Doppler, now widely commercialized in diagnostic ultrasound instruments.
- Winner of the Ultrasound in Medicine and Biology prize (for the first reported ultrasonic detection of blood flow in cancer), Roentgen Ray Award (for the best uro-radiology paper in 1992), and the World Federation of Ultrasound in Medicine and Biology Pioneer Award.
- Fellow of the American Institute of Ultrasound in Medicine, serves on the editorial boards of Ultrasound in Medicine and Biology and the Journal of Vascular Technology, as well as review panels of the MRC, the NIH and the FDA.
- Burns PN. Contrast ultrasound technology. In: Solbiati L, Martegani A, Leen E, Correas J-M, Burns PN, Becker D. Contrast-Enhanced Ultrasound of Liver Diseases. Milan: Springer; 2002. p. 1–19.
- Becher H, Burns PN. A Handbook of Contrast Echocardiography. New York: Springer Verlag; 2000. (download from: sunnybrook.utoronto.ca/EchoHandbook).
- Burns, PN, Hope Simpson D, Averkiou, M. Nonlinear imaging. Ultrasound Med Biol. 2000 May;26 Suppl 1:S19–22.
- Burns PN, Wilson SR, Hope Simpson D. Pulse inversion imaging of liver blood flow: improved method for characterization of focal masses with microbubble contrast. Invest Radiol. 2000 Jan;35(1):58–71.
- Taylor KJW, Burns PN, Wells PNT. Clinical Applications of Doppler Ultrasound. 2nd ed. New York: Raven Press; 1996.
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