Alexeeva Natalia V, Arnold Mark A
Department of Chemistry and Optical Science & Technology Center, University of Iowa, Iowa City, Iowa, USA.
J Diabetes Sci Technol. 2009 Mar 1;3(2):219-32. doi: 10.1177/193229680900300202.
Noninvasive glucose measurements are possible by analysis of transmitted near-infrared light over the 4000- to 5000-cm(-1) spectral range. Such measurements are highly sensitive to the exact position of the fiber-optic interface on the surface of the skin sample. A critical question is the degree of heterogeneity of the major chemical components of the skin matrix in relation to the size of the fiber-optic probed used to collect noninvasive spectra. Microscopic spectral mapping is used to map the chemical distribution for a set of excised sections of rat skin.
A Fourier transform near-infrared microspectrometer was used to collect transmission spectra from 16 tissue samples harvested from a set of four healthy Harlan-Sprague male rats. A reference point in the center of the tissue sample was probed regularly to track dehydration, changes in tissue composition, and changes in instrument performance. Amounts of the major skin constituents were determined by fitting microspectra to a set of six pure component absorbance spectra corresponding to water, type I collagen protein, keratin protein, fat, an offset term, and a slope term.
Microspectroscopy provides spectra with root mean square noise levels on 100% lines between 418 and 1475 microabsorbance units, which is sufficient for measuring the main chemical components of skin. The estimated spatial resolution of the microscope is 220 microm. The amounts of each tissue matrix component were determined for each 480 x 360-microm(2) location of a 4.8 x 3.6-mm(2) rectangular block of skin tissue. These spectra were used to generate two-dimensional distribution maps for each of the principal skin components.
Distribution of the chemical components of rat skin is significant relative to the dimensions of noninvasive glucose sensing. Chemical distribution maps reveal that variations in the chemical composition of the skin samples are on the same length scale as the fiber-optic probe used to collect noninvasive near-infrared spectra. Analysis of variance between tissue slices collected for one animal and analysis of variations between animals indicate that animal-to-animal variation for all four chemical components is significantly higher than variations between samples for a given animal. These findings justify the collection and interpretation of near-infrared microspectroscopic maps of human skin to establish chemical heterogeneity and its impact on noninvasive glucose sensing for the management of diabetes.
通过分析4000至5000厘米（-1）光谱范围内的透射近红外光，可以进行无创血糖测量。此类测量对皮肤样本表面光纤接口的确切位置高度敏感。一个关键问题是皮肤基质主要化学成分的异质性程度与用于收集无创光谱的光纤探头大小之间的关系。微观光谱映射用于绘制一组大鼠皮肤切除切片的化学分布图。
使用傅里叶变换近红外显微光谱仪从一组四只健康的哈兰-斯普拉格雄性大鼠身上采集的16个组织样本中收集透射光谱。定期探测组织样本中心的一个参考点，以跟踪脱水、组织成分变化和仪器性能变化。通过将显微光谱与一组对应于水、I型胶原蛋白、角蛋白、脂肪、一个偏移项和一个斜率项的六个纯组分吸收光谱进行拟合，确定主要皮肤成分的含量。
显微光谱提供的光谱在100%谱线上的均方根噪声水平在418至1475微吸光度单位之间，足以测量皮肤的主要化学成分。显微镜的估计空间分辨率为220微米。对于一块4.8×3.6平方毫米的皮肤组织矩形块，在每个480×360微米（2）的位置确定每种组织基质成分的含量。这些光谱用于生成每种主要皮肤成分的二维分布图。
大鼠皮肤化学成分的分布相对于无创血糖传感的尺寸具有重要意义。化学分布图显示，皮肤样本化学成分的变化与用于收集无创近红外光谱的光纤探头处于相同的长度尺度。对一只动物采集的组织切片之间的方差分析以及动物之间的变化分析表明，所有四种化学成分的动物间差异显著高于给定动物样本之间的差异。这些发现证明了收集和解释人体皮肤近红外显微光谱图以确定化学异质性及其对糖尿病管理中无创血糖传感的影响是合理的。
