Medical Applications of Laser Spectroscopy

Another example is the femtosecond-transient absorption and fluorescence after two-photon excitation of carotenoids. The excited -carotene decays with a time constant of 9 0.2ps. The energy transfer process from the excited Si state in light-harvesting proteins can be monitored by the observed chlorophyl fluorescence [15.146]. 

An important piece of information is the change in molecular structure during these fast processes. Here time-resolved Raman spectroscopy and X-ray diffraction with femtosecond laser-produced brilliant X-ray sources are powerful tools that are more and more applied to molecular biology. 

There are, however, also very promising direct applications of laser spectroscopy for the solution of problems in medicine. They are based on new diagnostic techniques and are discussed in this section. 

Numerous books have been published on laser applications in medical research and in hospital practice [1538-1540, 1542], Most of these applications rely on the high laser-output power, which can be focused into a small volume. The strong dependence of the absorption coefficient of living tissue on the wavelength allows selection of the penetration depth of the laser beam by choosing the proper laser wavelength [1540], 

The penetration depth of radiation into tissue is determined by absorption, scattering and reflection [1544], Attenuation of light in deep biological tissue depends on the effective attenuation coefficient which is defined as 

Since water is a major component in living tissue the absorption of water gives a first hint to the wavelength-dependence of the penetration depth. In Fig. 10.46 the wavelength dependence of the absorption coefficient a(k) of water is shown on a logarithmic scale together with lasers that are used for medical applications. 

For a special medical treatment the laser wavelength should be chosen such that the penetration depth dp = l/a into the tissue reaches the tissue-layer that should be treated. 

The different components of the human body have different absorption coefficients. As example the molar extinction curves of oxy-hemoglobin in the arteries and of desoxy-hemoglobin in the veins are shown in Fig. 10.47. 

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The last chapter illustrates by some examples the broad field of applications of laser spectroscopy to the solution of scientific, technical, and medical problems. 

Albrecht, H., MUller, G., Schaldach, M., Application of Laser Raman Spectroscops to Medical Diagnosis II in Proceedings of the Sixth International Corference on Raman Spectroscopy, Bangalore, India, September 4-9, 1978, Vol. 2, pp. 526-527. 

More information on application of lasers and particular laser spectroscopy in medicine can be found in the Journal Medical Laser Applications [1574] and in reviews and books [1577]. 

In the previous chapter we have seen how tunable lasers can be used in a multitude of ways to gain basic information on atomic and molecular systems. Thus, the laser has had a considerable impact on basic research, and its utility within the applied spectroscopic field is not smaller. We shall here discuss some applications of considerable interest. Previously, we have mainly chosen atomic spectroscopic examples rather than molecular ones, but in this chapter we shall mainly discuss applied molecular spectroscopy. First we will describe diagnostics of combustion processes and then discuss atmospheric monitoring by laser techniques. Different aspects of laser-induced fluorescence in liquids and solids will be considered with examples from the environmental, industrial and medical fields. We will also describe laser-induced chemical processes and isotope separation with lasers. Finally, spectroscopic aspects of lasers in medicine will be discussed. Applied aspects of laser spectroscopy have been covered in [10.1,2]. 

Excimer lasers are of great importance for UV and vacuum UV (VUV) spectroscopy and photochemistry. They are also found in a wide range of applications. For example, they are used in micromachine medical devices, including refractive surgery, in photo-lithography for the microelectronics industry, for material processing, as optical pump sources for other type of lasers (dyes), and so on. More details about excimer lasers can be found in Rodhes (1979). 

Raman spectroscopy failed to live up to its original expectation when the technique was discovered. This was due to instrumental problems, high cost of the instrument, and the fluorescence problem. However, with improvement in instrumentation, the use of a near infrared laser with FT-Raman, the introduction of fiber optics, the number of applications (some of which were discussed in Chapter 3) has escalated. The applications are expanded in this chapter, which deals with materials applications involving structural chemistry, solid state, and surfaces. Additional applications are presented in Chapter 5 (analytical applications), Chapter 6 (biochemical and medical applications) and Chapter 7 (industrial applications). 

Another advantage of the SERS spectroscopy is to obtain vibrational spectroscopic informations in electrolyte solution under conditions close to the real biological situation. The continuous development of laser sources with new excitation wavelength lines renders it possible to expand the study of adsorbed biomolecules on different metal surfaces which can also be chemically or electrically modified to adjust specific adsorption properties. Such a crucial event in medical applications as the behaviour of implants in contact with blood can be thus envisaged by the study of the adsorption of blood proteins and its physiological consequences. The possibility to monitor the interfacial electric field of the electrode surface can also be used to... 

Fundamental quantities, such as wavelengths and transition probabilities, determined using spectroscopy, for atoms and molecules are of direct importance in several disciplines such as astro-physics, plasma and laser physics. Here, as in many fields of applied spectroscopy, the spectroscopic information can be used in various kinds of analysis. For instance, optical atomic absorption or emission spectroscopy is used for both qualitative and quantitative chemical analysis. Other types of spectroscopy, e.g. electron spectroscopy methods or nuclear magnetic resonance, also provide information on the chemical environment in which a studied atom is situated. Tunable lasers have had a major impact on both fundamental and applied spectroscopy. New fields of applied laser spectroscopy include remote sensing of the environment, medical applications, combustion diagnostics, laser-induced chemistry and isotope separation. 

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