Contrast Enhanced Ultrasound for Improved Prostate Cancer Diagnosis
Computed Tomography (better known as CT scanning), Magnetic Resonance Imaging (MRI) and Ultrasound Imaging are three mainstay technologies for clinical imaging across the globe. Of these options, ultrasound is often used in a wide variety of medical imaging applications because it is widely recognised to be non-ionizing and is also relatively affordable. A standard ultrasound works by sending ultrasound waves from a transmitter into the body and then by analysing the time that the waves take to be returned to a receiver and the strength or amplitude at which they return, the location and certain properties of different types of tissue can be determined. Imaging technologies are often enhanced in modern medicine through the introduction of agents that act as a contrast medium to highlight certain parts of the anatomy or tissue into which they have been introduced, however, agents can often have side effects or the possibility of long-term risks if the body is unable to adequately process and excrete the agents.
With traditional ultrasound the response of blood and blood cells is very weak and hence is not very useful for visualising small vessels in the cardiovascular system. In contrast enhanced ultrasound imaging (CEUS), a minute amount of tiny micro-bubbles only several micrometres across (roughly 5% of the diameter of human hair) are used as the contrasting agent. These bubbles are made of an inert gas, typically air or perfluorocarbon and have an organic shell often made of lipids (naturally occurring compounds found in the body) which prevents that gas from being absorbed too quickly and therefore prolonging the time that imaging can be carried out. The micro-bubbles as they circulate in the blood, provide a target for the ultrasound to reflect from offering significantly improved image quality of the circulating blood flow throughout the body, including the detail in the much smaller microcirculation structures as well as veins and arteries. Due to their composites these agents are easy to process and excrete by human body.
Prostate cancer is one of the most common male cancers, most people with prostate cancer do not end up dying directly from the disease, however, the cancer can spread to other parts of the body leading to potentially fatal cancers occurring there. Current diagnosis involves imaging or examination and if the presence of a tumour is suspected a biopsy is carried out. At present imaging through ultrasound does not present clear enough pictures to accurately carry out diagnosis and although MRI is slightly better, neither offers sufficient support for clinicians carrying out biopsies and as a result several samples are needed in order to provide an accurate diagnosis, detection rates are typically around 50%. Such “random” biopsies lead to significant cancers being missed or under-sampled, or conversely, many small, clinically insignificant tumours are subjected to unnecessary treatment. The current biopsy process is also highly invasive, can have severe complications and carries a relatively high cost.
For Dr Mengxing Tang, improvements in medical imaging techniques, especially ultrasound imaging has been a key research interest for over a decade. Through his work in the laboratory and in collaboration and discussion with clinicians working at the various hospitals linked to the College, Mengxing identified a clear opportunity to improve imaging techniques and processing to assist in the early stage diagnosis of prostate cancers. By developing improved techniques for analysing and processing the outputs from CEUS, Mengxing and his researchers have been working on improved signal processing techniques which they hope will provide clinicians with a tool to identify tumours through ultrasound imaging which will show up the different patterns that exist in the microcirculation structures of tumours as opposed to those found in healthy tissue. Support from the EPSRC IAA, ex-vivo work on tissue samples has provided very encouraging early results and Mengxing hopes to further the work and get the set-up approved for clinical testing.