A Novel Ultrasound Modulated Optical Tomography System

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Optical imaging of biological tissue is able to provide structural and functional information, which potentially enables early detection of abnormalities such as tumours and detection of tissue oxygenation. However, one disadvantage of such technique is the difficulty to image objects at depth. By comparison, ultrasound imaging is able to provide good image resolution at depth and is an established clinical imaging modality. However, ultrasound imaging is based on the detection of the mechanical properties in tissues which is not as sensitive as optical techniques in e.g. detecting tumours.Ultrasound-modulated optical tomography (UOT) is a new technique to take advantage of the combined strengths of the two imaging modalities. In UOT, light is transmitted into the target tissue and at the same time an ultrasonic wave is focused into the tissue to modulate the light. The scattered light from the tissue can be measured and images of tissue optical properties can be reconstructed, with a spatial resolution primarily defined by ultrasound. Studies of UOT as a medical imaging tool only began in the 90s. Although promising images have been produced with laboratory phantoms and excised tissues, a significant challenge of the current UOT technique is the weak optical modulation signal to be measured. A direct way to tackle the problem of weak optical signal is to maximise the ultrasonic modulation of all light passing through the ultrasound focus. Past studies show that simply increasing the ultrasound amplitude may not be sufficient and also has some adverse effects. In this project, we propose to develop a novel UOT system with dual-frequency ultrasound excitation to maximise the modulated light signal. In this pilot study both a computer simulation system and an experimental system will be developed and results compared with the conventional UOT system. This new system has the potential to significantly improve UOT image quality.