Category: Biophotonic techniques, Type: Diagnosing
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NameInfrared backscattering for metabolic detection (NIRS – Diffuse Reflectance Spectroscopy)
From an optical point of view, biological tissue can be considered as an absorbing matrix in which a high number of inhomogeneities, which act as light scatterers, are present. When near-infrared (NIR) light is injected into the tissue, scattering provides a way to recover part of the injected light as “diffuse reflectance” from the injection surface.
In the NIR region, the optical absorption is strongly dominated by haemoglobin, the blood constituent that carries oxygen. Smaller contributions to absorption are given by other chromophores, whose absorption spectrum may give information on tissue oxygen consumption. Oxygen metabolism is most certainly a crucial problem in many fields of medical activity. Sport medicine, rehabilitative cardiology, intensive care, anaesthesia, tumour detection, rely on some form of metabolic oxygen analysis. Using a spectral analysis of the backscattered light (in the medical literature, referred to as “NIRS” or “Diffuse Reflectance Spectroscopy”), the key issue of real-time non-invasive evaluation of blood content and oxygenation in a non-stationary condition, such as upon exercise or during respiratory manoeuvres, can be approached by non-invasive optical measurements.
Schemes and typical results
A first line of research relates to the implementation of a line of backscattering instruments optimised for direct clinical use. In the recent past, for example, one of the St Andrews experts has developed a high-performance wearable backscattering spectrometer, on the size scale of a cigarette packet, dedicated to sports, high-altitude medicine and to rehabilitative cardiology. A simplified block diagram is reported in Fig. 1, and a sports medicine example is reported in Figure 2.
On the opposite side of complexity and sensitivity, the tiny variation in near-infrared backscattering deriving from oxygen consumption by a few brain cortex cells, during their normal signalling activity, has recently been detected. In particular, highly sensitive apparatus connected to a miniaturised in-vivo probe has been built, and used during surgery to detect optical backscattering directly from the brain cortex. correlated to external peripheral stimulation. For the first time, signals deriving from individual stimuli have been detected. A representative signal is reported in Figure 3.
In the microfabrication facilities available in St Andrews, microphotonic devices specifically dedicated to in-vivo backscattering measurements are under development.
Finally, as a side activity, we perform steady-state simulation of optical transmission and backscattering in complex biological structures, to the level of complexity of a full human head as derived from MRI scanning.
Special features and limitations
The advantages of the technique are
The limitation of the technique is
What equipment do you use?
Custom equipment, built in-house.
What analytes do you measure?
Mainly, oxy- and deoxyhaemoglobin, and cytochrome aa3 oxydase.
What physical or chemical substances do you use?
As implemented in St Andrews, the technique is label-free, though in the literature indocyanine green has been used to enhance contrast
|2||Stevenson David||2010-01-28 20:40||View|
|1||Stevenson David||2010-01-28 20:39|
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