DEVELOPMENT AND APPLICATION OF PHOTOACOUSTIC IMAGING FOR THE CLINICAL AND LIFE SCIENCES

The purpose of this research is to develop a promising new biomedical imaging technique called photoacoustic (PA) imaging. This involves firing very short (nanosecond) pulses of laser light into tissue. The light is absorbed by structures such as blood vessels producing a small heating effect. This leads to rapid thermoelastic expansion which generates high frequency (~tens of MHz) acoustic waves which travel though the tissue back to the surface. By measuring the time of arrival of these acoustic waves at a number of detectors positioned over the tissue surface, and with knowledge of the speed of sound, the acoustic signals can be backprojected to produce a 3D image of the internal absorbing structures within the tissue. The key advantage of the technique is that it combines the strong contrast of optical methods with the high spatial resolution available to ultrasound. This may make the technique a powerful diagnostic tool for identifying abnormalities such as certain types of cancer tumours that would be difficult to see using conventional medical imaging techniques such as X-ray or ultrasound imaging. This technique has many potential clinical applications, including detecting tumours in the breast, assessing skin abnormalities such as malignant melanomas or soft tissue damage such as burns or wounds. It can also be used to image small animals such as mice which are used extensively to model a wide range of human diseases. One of the most exciting features of photoacoustic imaging is its potential to characterise specific molecular processes, so called molecular imaging. This is achieved using probe molecules that strongly absorb certain wavelengths of light and have a high affinity for a specific cellular or molecular receptor that is characteristic of a particular disease such as cancer. In order to advance the technique to practical application, a substantial research program will be undertaken. A novel high resolution instrument, designed for non invasive imaging to depths of several mm, will be developed both for clinical use, for example to study skin pathologies and for the pre-clinical study of disease processes in small animal models. Endoscopic probes that are capable of being inserted into the body and guided deep within to image, for example, the inside of coronary arteries to assess the plaques that can build up and cause heart attacks will be developed. In addition, a dedicated instrument will be designed for the early detection and diagnosis of breast cancers and monitoring their treatment. Novel methods for recovering physiological information such as blood oxygenation and flow will also be explored and clinically tested. A programme of in vivo imaging both in humans and small animals to apply and validate these methods is planned, with specific emphasis on demonstrating the utility of the technique for the diagnosis and treatment of cancer, cardiovascular disease and neurological conditions. Overall this research offers the prospect of developing a powerful new diagnostic imaging tool that can be used to advance our understanding of disease mechanisms at an anatomical, physiological and molecular level and improving the clinical diagnosis and treatment of cancer and other major diseases.