Biomedical research seminar
Nicol Hall 222, Beirut campus; Science Building 607, Byblos campus
The seminar, titled “Techniques for Phase Aberration Correction in in vivo Ultrasonic Imaging of the Human Calcaneus Bone,” will be given by Dr. Mohamad Nasreddine.
Abstract
Trabecular bone is a complex medium which induces phase aberration when an ultrasonic wave propagates inside. Even when a pulse propagates in homogeneous tissue, the frequency, phase, and even the pulse length are changed compared to the original signal. The reflection from point scatterers corresponds to a double derivation of the pressure, which fortifies the higher frequencies. In many biomedical applications related to bone diagnosis (osteoporosis assessment, bone imaging, etc.) , the transmitted ultrasonic pulse is aberrated due to the propagation in a typical heterogeneous medium: the pulse is changed both in time and frequency, in addition to amplitude modulation and wave front destruction due to the focusing and defocusing effects of the body wall. As a consequence, the diameter of PSF (Point Spread Function) is increased and a loss in axial resolution is observed: Many techniques for phase aberration correction exist in the literature. In the “central element correction technique” the echo-signal at each array element is aligned with the signal at the central array element. In the “variable speckle look-back” correction technique the signal at each array element is aligned with the sum of signals from all previously corrected elements. In the “variable central speckle look-back” correction technique the signal at each array element is aligned with the sum of signals from the central group of all previously corrected elements. The aim of this seminar is to present a new technique for phase aberration in the calcaneus. The tool for the study is a 2D arrays ultrasonic imaging system, the Beam scanner, developed at Tours University (France), which provided elementary transfer functions and allowed testing of a first simple method of correction based on time shifting. The limits of this method have motivated the development of a medium assumption-free technique of correction, called “propagation inverse filtering” (adapted from Mathias Fink’s work in LOA, Paris). This method decomposes the propagation between the focal plane and the reception aperture on a basis of singular wave planes. This method has been tested on a phantom and on in vivo bone images, and promising results have been obtained, with a clear effect on enhancing the optimal focusing of the instrument.
Biography of presenter
Dr. Nasreddine is a consultant in biomedical engineering, quality control and accreditation of health care institutions. For the past three years, he has been working for the Lebanese Social Security, Lebanese army, and more than 10 hospitals in Lebanon and the Middle East. He has also been teaching materials and biomedical engineering courses at the Mechanical Engineering Department of the American University of Beirut and biomedical quality control (master’s level) at the Lebanese University.
Dr. Nasreddine obtained his Ph.D. in Biomedical Engineering from Tours University, France. His graduate work focused on the development of ultrasonic machines in transmission mode, in the correction of phase aberration on bone ultrasonic images and he was selected during his Ph.D. to participate in a European research project in biomechanics and medical imaging (Berlin Bed Rest) supervised by the European Space Agency.
Event organizer: LAU’s School of Arts and Sciences