Elasticity imaging techniques aim at the detection of tissue abnormalities following an external, internal or inherent mechanical stimulation. By taking advantage of the additional depth information provided by ultrasound imaging, the local tissue response (i.e., displacement, strain and/or vibration amplitude) that depends on its mechanical properties can be imaged. After introducing methods for 2D and 3D strain estimation, examples will be shown on imaging of normal and pathological myocardium in finite-element models and in vivo murine, canine and human subjects. Additional elasticity imaging techniques, such as Pulse Wave Imaging for the characterization of abdominal aortic aneurysms in vivo and Electromechanical Wave Imaging for the assessment of the conduction properties of the myocardium, will also be discussed.
In the second part of this lecture, therapeutic ultrasound techniques will be introduced together with application of elasticity imaging for simultaneous monitoring of the treatment procedures. Most precisely, Focused Ultrasound (FUS) for ablation of tumors substantially modifies the stiffness of the tissue being treated in order to annihilate the function of the latter. By monitoring this stiffness change, the radiation-force-based Harmonic Motion Imaging (HMI) technique can successfully detect the temperature rise and coagulation onset during treatment. As a result, an all ultrasound-based system providing simultaneous tumor detection and treatment application as well as monitoring can be developed. Applications of such a system in both in vivo breast tumor ablation and opening of the blood-brain barrier (BBB) for brain drug delivery in mice will be shown. In conclusion, elasticity imaging techniques, whether applied using an external or internal mechanical stimulus, can provide important complementary information to ultrasonic imaging in applications ranging from cancer and cardiovascular disease detection to thermal therapy monitoring; reinforcing, thus, the role of ultrasonic imaging in medical diagnosis and treatment.
Elisa E. Konofagou is the Robert and Margaret Hariri Professor of Biomedical Engineering and Professor Radiology as well as Director of the Ultrasound and Elasticity Imaging Laboratory at Columbia University in New York City. Her main interests are in the development of novel elasticity imaging techniques and therapeutic ultrasound methods and more notably focused ultrasound in the brain for drug delivery and stimulation, myocardial elastography, electromechanical and pulse wave imaging, harmonic motion imaging with several clinical collaborations in the Columbia Presbyterian Medical Center and elsewhere. Elisa is an Elected Fellow of the American Institute of Biological and Medical Engineering, a member of the IEEE in Engineering in Medicine and Biology, IEEE in Ultrasonics, Ferroelectrics and Frequency Control Society, the Acoustical Society of America and the American Institute of Ultrasound in Medicine. She has co-authored over 170 published articles in the aforementioned fields. Prof. Konofagou is also a technical committee member of the Acoustical Society of America, the International Society of Therapeutic Ultrasound, the IEEE Engineering in Medicine and Biology conference (EMBC), the IEEE International Ultrasonics Symposium and the American Association of Physicists in Medicine (AAPM). Elisa serves as Associate Editor in the journals of IEEE Transactions in Ultrasonics, Ferroelectrics and Frequency Control, Ultrasonic Imaging and Medical Physics, and is recipient of awards such as the CAREER award by the National Science Foundation (NSF) and the Nagy award by the National Institutes of Health (NIH) as well as others by the American Heart Association, the Acoustical Society of America, the American Institute of Ultrasound in Medicine, the Wallace H. Coulter foundation, the Bodossaki foundation, the Society of Photo-optical Instrumentation Engineers (SPIE) and the Radiological Society of North America (RSNA).