Development and application of a non-contact, depth-resolved optical skin oximeter

氧气对生命至关重要。身体里的每个细胞都需要持续的氧气供应，否则就会死亡。将氧气从肺部输送到细胞是微循环最重要的功能。皮肤是人体最大的器官，在保护身体免受外界环境影响方面起着至关重要的作用。因此，它的健康对我们的整体福祉至关重要。皮肤由不同的层组成。最上层是角质层，由死细胞组成。其下是约0.1毫米厚的表皮，其下是真皮层。1 ~ 2mm厚。表皮的独特之处在于它包含活细胞但没有血管：它的存活完全依赖于氧气从其他地方的被动扩散。如果表皮的氧气供应因任何原因中断，那么很可能导致严重的医疗状况。皮肤疼痛，如静脉溃疡。压疮(如：“褥疮”)或糖尿病性溃疡（即所谓的“糖尿病足”）可能是由于向表皮的氧气运输受到干扰而引起的。因此，有必要测量通过微循环输送到皮肤的氧气。50多年前提出的一种方法至今仍有价值。美国科学家米利根证明，光谱学可以通过血红蛋白颜色的变化来测量血液中与血红蛋白结合的氧气量。氧合血红蛋白。它在动脉血中占主导地位，呈鲜红色，而脱氧血红蛋白。多见于静脉血。出现红褐色。密立根利用这一效应让美国轰炸机飞行员在5-6英里的高空飞行时检查自己是否吸入了足够的氧气。目前所有的仪器都与密立根的仪器具有相同的基本概念设计。因此，在研究皮肤时，它们的局限性变得非常有限。皮肤微循环在1毫米的深度范围内是高度结构化的，但目前的仪器无法提供关于含氧血红蛋白随深度分布的直接信息。这些设备与皮肤有物理接触。它很容易产生足够的机械压力来关闭最小的血管，从而扭曲测量结果。我们的项目建议是使用现代技术。在过去几年里发展起来的。为解决这些缺点，研制出更好的光学皮肤血氧仪。我们的方法将应用超声成像的光学模拟，称为光学相干断层扫描（OCT），这是在过去12年中出现的最具前景的皮肤成像新光学技术。光谱OCT可以产生关于吸收化合物分布的深度分辨信息，通过在许多不同的波长进行OCT。到目前为止，这项技术主要用于测量组织的含水量，因为水在下午1点3分到1点55分之间显示出很强的吸收带。OCT光源通常在这些波长上可用，因为它们也是用于光纤通信的波长。由于没有合适的光源，光谱OCT尚未在测量血红蛋白氧合的理想波长范围450至600 nmi范围内进行尝试。这些波长的光谱OCT可以形成下一代皮肤血氧仪的基础，有效地克服当前设备的所有限制。最近，主要的技术障碍，缺乏蓝绿色OCT光源，已经开始克服超连续光源的发明。我们的项目将探索使用这种新型光源的蓝绿光谱oct的潜力，以改善微循环中氧气输送紊乱的皮肤状况的诊断和管理。

Oxygen is vital for life. Every cell in the body requires a continuous supply of oxygen or it will die. The delivery of oxygen from the lungs to cells is the most important function of the microcirculation. The skin represents the largest organ' of the body and plays a vital role in protecting the body from the outside environment. Its health is thus of critical importance to our general well-being. The skin is comprised of distinct layers. the uppermost layer is the stratum corneum and consists of dead cells. Below this lies the epidermis, about 0.1mm thick and below this is the dermis. 1-2 mm thick. The epidermis is unique in that it contains living cells but no blood vessels: to remain alive it relies totally on the passive diffusion of oxygen from elsewhere. If the supply of oxygen to the epidermis is interrupted for any reason then a serious medical condition is likely to result. Painful skin conditions such as venous ulcers. pressure ulcers (e.g. 'bed sores') or diabetic ulcers (i.e. the condition known as 'diabetic foot ) are potentially caused by disturbed oxygen transport to the epidermis. There is thus a need to measure oxygen delivery to the skin via the microcirculation.Over 50 years ago an approach was suggested that has remained of value today. The American scientist Millikan demonstrated that optical spectroscopy can measure the amount of oxygen bound to haemoglobin in blood via changes in the colour of haemoglobin. Oxygenated haemoglobin. which predominates in arterial blood, appears bright crimson whereas deoxygenated haemoglobin. more prevalent in venous blood. appears reddish-brown. Millikan used this effect to allow American bomber pilots to check that they were breathing in sufficient oxygen whilst flying at altitudes of 5-6 miles. All current instruments are of the same basic conceptual design as Millikan's instrument. Consequently they have limitations that become very restrictive when studying the skin. The microcirculation of the skin is highly structured on a depth-scale of 1 mm. but current instruments provide no direct information about the distribution of oxygenated haemoglobin with depth. The devices make physical contact with the skin. which can easily produce mechanical pressures sufficient to close off the smallest blood vessels and thus distort the measurements. Our project proposal is to use modern technology. developed over the last few years. to address these shortcomings and build a better optical skin oximeter.Our approach will apply an optical analogue of ultrasound imaging called optical coherence tomography (OCT), which has emerged over the last 12 years as the most promising new optical technique for skin imaging. Spectroscopic OCT can yield depth-resoived information about the distribution of absorbing compounds by performing OCT at a number of different wavelengths. To date, this technique has mainly been used to measure the water content of tissues, as water shows a strong absorption band between 1.3 pm and 1.55 pm. OCT light sources are commonly available at these wavelengths because they are also the wavelengths used for optical fibre communications. Spectroscopic OCT has not been attempted over the wavelength range 450 to 600 nmi ideal for measuring haemoglobin oxygenation, due to the unavailability of suitable light sources. Spectroscopic OCT at these wavelengths can form the basis of the next generation of skin oximeters, effectively overcoming all the limitations of current devices. Recently the chief technical obstacle, the lack of blue-green OCT sources, has started to be overcome via the invention of supercontinuum' light sources.Our project will explore the potential that blue-green spectrosopic OCT. using this new type of light source, has for improving the diagnosis and management of skin conditions that involve disturbed oxygen delivery by the microcirculation.