--- /dev/null
+\chapter*{Preface}
+
+Approximately 17 million people in the USA (6{\%} of the
+population) and 140 million people worldwide (this number is
+expected to rise to almost 300 million by the year 2025) suffer
+from \textit{diabetes mellitus}. Currently, there a few dozens of
+commercialised devices for detecting blood glucose levels [1].
+However, most of them are invasive. The development of a
+noninvasive method would considerably improve the quality of life
+for diabetic patients, facilitate their compliance for glucose
+monitoring, and reduce complications and mortality associated with
+this disease. Noninvasive and continuous monitoring of glucose
+concentration in blood and tissues is one of the most challenging
+and exciting applications of optics in medicine. The major
+difficulty in development and clinical application of optical
+noninvasive blood glucose sensors is associated with very low
+signal produced by glucose molecules. This results in low
+sensitivity and specificity of glucose monitoring by optical
+methods and needs a lot of efforts to overcome this difficulty.
+
+A wide range of optical technologies have been designed in
+attempts to develop robust noninvasive methods for glucose
+sensing. The methods include infrared absorption, near-infrared
+scattering, Raman, fluorescent, and thermal gradient
+spectroscopies, as well as polarimetric, polarization
+heterodyning, photonic crystal, optoacoustic, optothermal, and
+optical coherence tomography (OCT) techniques [1-31].
+
+For example, the polarimetric quantification of glucose is based
+on the phenomenon of optical rotatory dispersion, whereby a chiral
+molecule in an aqueous solution rotates the plane of linearly
+polarized light passing through the solution. The angle of
+rotation depends linearly on the concentration of the chiral
+species, the pathlength through the sample, and the molecule
+specific rotation. However, polarization sensitive optical
+technique makes it difficult to measure \textit{in vivo} glucose
+concentration in blood through the skin because of the strong
+light scattering which causes light depolarization. For this
+reason, the anterior chamber of the eye has been suggested as a
+sight well suited for polarimetric measurements, since scattering
+in the eye is generally very low compared to that in other
+tissues, and a high correlation exists between the glucose in the
+blood and in the aqueous humor. The high accuracy of anterior eye
+chamber measurements is also due to the low concentration of
+optically active aqueous proteins within the aqueous humor.
+
+On the other hand, the concept of noninvasive blood glucose
+sensing using the scattering properties of blood and tissues as an
+alternative to spectral absorption and polarization methods for
+monitoring of physiological glucose concentrations in diabetic
+patients has been under intensive discussion for the last decade.
+Many of the considered effects, such as changing of the size,
+refractive index, packing, and aggregation of RBC under glucose
+variation, are important for glucose monitoring in diabetic
+patients. Indeed, at physiological concentrations of glucose,
+ranging from 40 to 400 mg/dl, the role of some of the effects may
+be modified, and some other effects, such as glucose penetration
+inside the RBC and the followed hemoglobin glycation, may be
+important [30-32].
+
+Noninvasive determination of glucose was attempted using light
+scattering of skin tissue components measured by a
+spatially-resolved diffuse reflectance or NIR fre\-quen\-cy-domain
+reflectance techniques. Both approaches are based on change in
+glucose concentration, which affects the refractive index mismatch
+between the interstitial fluid and tissue fibers, and hence
+reduces scattering coefficient. A glucose clamp experiment showed
+that reduced scattering coefficient measured in the visible range
+qualitatively tracked changes in blood glucose concentration for
+the volunteer with diabetes studied.
+
+
+