The Biomedical Optics Research Laboratory

The Biomedical Optics Research Laboratory is located within the Department of Medical Physics & Bioengineering at University College London (UCL). The research activities of the laboratory concern the development of new optical and photoacoustic monitoring instruments and techniques for medical applications. These exploit the optical properties of natural chromophores, and of haemoglobin and the cytochromes in particular, both of which have oxygenated and deoxygenated forms with different characteristic absorption spectra in the visible and near-infrared wavelength range. While haemoglobin, only present in red blood cells, provides an indicator of blood oxygenation, the cytochrome enzymes in the oxidative metabolic pathway provides an indicator of tissue oxygenation. Optical methods offer several significant advantages over other clinical spectroscopic and imaging methods, including i) non-invasiveness through the use of safe, non-ionising radiation, ii) display of contrast between soft tissues based on optical properties, iii) disclosure of functional information, such as the oxygenation state of haemoglobin, and iv) a facility for continuous bedside monitoring. The laboratory consists of four closely-linked research groups whose activities are outlined below.

Near-infrared Spectroscopy Group

Clare Elwell, Terence Leung, Murad Banaji, Anna Blasi, Ilias Tachtsidis

Near-infrared spectroscopy (NIRS) is being developed as clinical and research tool for monitoring, continuously and non-invasively, haemodynamic and metabolic variables in human organs, with negligible sensitivity to superficial tissues. Long standing collaborations have led to the timely clinical application of various diagnostic systems to both adults and newborn infants with a focus on measurements in the brain. Studies currently underway include those investigating acute brain injury, stroke, autonomic failure and sleep disorders in adult patients, as well characterising neurophysiological processes in the normal adult and developing infant brain. Experimentation involves use of a variety of spectrometic instruments. An essential aspect to this work is the well established and productive collaborations with industry, most notably a long-standing partnership with Hamamatsu Photonics (Japan). This has resulted in several major instrumentation development projects, including the design of a clinical near-infrared spectrometer which is now sold commercially.

Experimental Imaging Group

Jem Hebden, Adam Gibson, Nick Everdell, Louise Enfield, Salavat Magazov

Novel optical instruments are being developed and evaluated for diagnostic and functional imaging in the clinical environment. The principal focus of this work is the pursuit of three-dimensional optical tomography, which involves generating images of the internal structure of large thicknesses of human tissue using measurements of transmitted light. A prototype imaging system (known as MONSTIR) has been constructed which consists of 32 parallel time-correlated single photon counting (TCSPC) detectors which measure the times-of-flight of transmitted photons at two wavelengths (780 nm and 815 nm) simultaneously. Spatial maps of the tissue's intrinsic absorbing and scattering properties are generated from the measured data using non-linear image reconstruction algorithms. The primary clinical objectives are a device for imaging oxygenation and function in the newborn infant brain, and a safe and effective tool for the detection and specification of breast disease. Another instrument has also been developed to acquire rapid images of haemodynamic and oxygenation changes occurring in the human cortex, a technique known as optical topography.

An optical coherence tomography (OCT) instrument is being constructed for monitoring the distribution of biochemical species within laboratory-grown tissues at specific mid-infrared wavelengths. The instrument is intended to satisfy the urgent need of tissue engineers for real-time sensors to guide the development of tissues grown in bioreactors, and ultimately in vivo. A free-space two-beam interferometer will perform optical coherence tomography on tissues using custom-built quantum cascade lasers with short coherence lengths. The device will facilitate real-time imaging of tissue-engineered constructs during growth at a resolution of a few tens of microns. Images will highlight the characteristic absorption at mid-infrared wavelengths by collagen amide, and phosphate and carbonate compounds. This will enable both normal and pathological tissue function and development to be observed, and the growth of tissue to be controlled and directed through non-invasive measurement of the metabolism and morphology of cells during all phases of the growth cycle.

Image Reconstruction, Theory, and Modelling Group

Simon Arridge, Martin Schweiger

The theory group has developed considerable expertise in mathematical and numerical modelling of light propagation in tissue (the forward problem) and their application to optical tomography (the inverse problem). The application of sophisticated FEM modelling of photon transport in tissue has been studied, and the use of non-linear optimisation methods for image reconstruction. The group has developed a software package called TOAST (Time-resolved optical absorption and scattering tomography) which uses an iterative FEM-based model-fitting approach to derive internal maps of regions with arbitrarily complex boundaries from sets of time- or frequency-domain data.

Photoacoustics and Optical Ultrasound Sensing Group

Paul Beard, Jan Laufer, Ben Cox, Bradley Treeby, Edward Zhang

Photoacoustic techniques and instruments are being developed as both a spectroscopic modality and as a means of generating images. The approach combines the functional information available from optical measurements with the spatial localisation characteristic of diagnostic ultrasound. Our current research in this area encompasses the development of novel optoelectronic instrumentation for the generation and detection of photoacoustic signals, rapid quantitative image reconstruction methods, and spectroscopic methods for the measurement of blood oxygenation. Potential applications include the assessment of neonatal brain abnormalities, breast cancer, vascular disease, skin pathologies, and the study of tumour physiology. The extensive website of the photoacoustic imaging group is accessed by clicking here.

Medical Lasers and Endoscopy

Tim Mills, Sandy Mosse, Martin Austwick

This group is involved in the exploration of novel methods of propelling endoscopes within the body, and the development and application of surgical instruments for use with flexible endoscopes. Other recent projects include investigation of laser light delivery for photodynamic therapy (PDT) of hollow organs, and use of coherent backscatter to measure tissue optical properties. The group also provides technical support to the National Medical Laser Centre and laser safety advice to UCL, UCL Hospitals and private clinics based in London and elsewhere. Click here for more information about the activities of this group.