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

氧气对生命至关重要。人体内的每一个细胞都需要持续的氧气供应，否则就会死亡。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，在保护人体免受外界环境影响方面起着至关重要的作用。因此，它的健康对我们的总体福祉至关重要。皮肤由不同的层组成。最上层是角质层，由死细胞组成。在此之下是表皮，约0.1毫米厚，下面是真皮。1-2 mm厚。表皮的独特之处在于它含有活细胞，但没有血管：为了保持活力，它完全依赖于来自其他地方的氧气的被动扩散。如果由于任何原因而中断了对表皮的氧气供应，则可能导致严重的医疗状况。疼痛性皮肤病，如静脉溃疡。压力性溃疡（例如“褥疮”）或糖尿病性溃疡（即，称为“糖尿病足”的病症）可能是由到表皮的氧输送受到干扰而引起的。因此，需要测量通过微循环输送到皮肤的氧气。50多年前，提出了一种方法，至今仍有价值。美国科学家密立根证明，光谱学可以通过血红蛋白颜色的变化来测量血液中血红蛋白结合的氧气量。氧合血红蛋白。其主要存在于动脉血中，呈现明亮的深红色，而脱氧血红蛋白。在静脉血中更常见。呈红棕色。密立根利用这种效应，让美国轰炸机飞行员检查他们在5-6英里的高度飞行时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，他们有局限性，成为非常严格的研究皮肤时。皮肤的微循环在1 mm的深度尺度上是高度结构化的，但目前的仪器不能提供关于氧合血红蛋白随深度分布的直接信息。器械与皮肤发生物理接触。其可以容易地产生足以关闭最小血管的机械压力，从而使测量失真。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。为了解决这些缺点，并建立一个更好的光学皮肤血氧计。我们的方法将应用一个光学模拟超声成像称为光学相干断层扫描（OCT），这已经出现在过去12年来最有前途的新的光学技术的皮肤成像。光谱OCT可以通过在多个不同波长处执行OCT来产生关于吸收化合物的分布的深度分辨信息。迄今为止，该技术主要用于测量组织的含水量，因为水在1.3 pm和1.55 pm之间显示出强吸收带。OCT光源通常在这些波长下可用，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还没有尝试在450至600 nm的波长范围内测量血红蛋白氧合的理想。在这些波长下的光谱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，已经开始通过发明超连续谱光源来克服。我们的项目将探索使用这种新型光源的蓝绿色光谱OCT，对于改善涉及微循环氧输送紊乱的皮肤状况的诊断和管理的潜力。

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.