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Laser applications in medicine and biology
BOOK REVIEW LASER
APPLICATIONS
IN MEDICINE
AND
BIOLOGY
M. L. WOLBARSrn"(Editor) (Vol. 5, 371 pp., Plenum Press, New York and London. D-306-43753-8, 1991) This book sets out to provide the reader with a thorough understanding of the theoretical background supporting the use of lasers in medicine and biology. It is to the credit of the various contributors and the editor that this laudable objective has been achieved. The trade-off is the narrow range of topics covered. There are six chapters. The first, on "Stimulation of Metabolic Processes by Low-Intensity Visible Light", is subtitled "A Scientific Basis for Biostimulation" to which some may wish to add a question mark. However, there is no question about the fact that light does interact with tissue, and exploring this at the cellular level provides a fascinating subject for study. Effects of different wavelengths, dose and irradiation regimes on DNA and RNA synthesis are described, along with other phenomena. Experiments with cell components of the immune sysem are also discussed. The final concluding remarks are rather speculative and many readers would have preferred a concluding section which drew together the various studies described earlier in the chapter. The second chapter describes the "Present Status of Research on Haematoporphyrin Derivatives and their Photophysical Properties". This begins with a brief historical review of the diagnostic and therapeutic use of haematoporphyrin (Hp) and haematoporphyrin derivative (HpD). HpD tends to localise preferentially in malignant tissues. Excitation with blue-violet light induces a strong red fluorescence which allows localisation of cancer. However, HpD is more widely used for therapy, called photodynamic therapy (PDT), in which red light is used to initiate the formation of cytotoxic products. Most of the chapter is taken up with the photophysics of HpD. Materials and experimental techniques are described and this is invaluable to those who are unfamiliar with the techniques employed. Following this, experimental results are presented. These describe the behaviour of HpD in solution, in model systems, in vitro, and briefly, in vivo. Present limitations and future prospects are also discussed. The Q-switched NdYAG laser is widely used in ophthalmic microsurgery and this is studied in the next chapter. After a brief outline of clinical applications, the characteristics of laser-induced breakdown in liquids are described. There then follows the major section of the chapter dealing with temporal and spatial dynamics of laser-induced plasmas in liquids. This describes models for plasma breakdown and compares theoretical predictions with experimental findings. Surgical lasers often suffer from significant power loss within the optical fibre delivery system. This can lead to unpredictable treatment outcomes. The chapter on High-Power Laser Transmission through Optical Fibres is, therefore, well worth reading. It gives a clear account of the basic elements of an optical fibre, including coupling of the laser beam into the fibre, as well as examining specific problems related to high-power laser beam transmission. The section on optical beam shaping, including sapphire tips, is most instructive. Some practical examples, comparing ray diagrams with measured values, would have been helpful. "Can Physical Modelling Lead to an Optimal Laser Treatment Strategy for Port-Wine Stains?" is the somewhat provocative title of the next chapter. It adopts a highly logical 249
250
Book review
approach to the problem of treating port-wine stain (PWS), the familiar congenital vascular malformation occurring commonly in the head and neck. Models are described, taking account of anatomy, light distribution and optical properties, leading to a predicted temperature distribution and damage distribution, following which biological healing takes place. Predictions are compared with experimental and clinical results for a number of laser types and treatment parameters. It is no surprise to read the authors' conclusion that "physical modelling has substantially contributed to optimising the early treatment strategies for port wine stain". It may also be noted that subtle changes in treatment strategy will require a more sophisticated model. The last chapter deals with Choroidal Circulation and Heat Convection at the Fundus of the Eye. Although photocoagulation of the retina has been around for a long time, the role of the choroidal circulation in heat dissipation is still a subject of controversy. The choroid is highly vascularised and is in close proximity to the retina, separated by the retinal pigment epithelium. Temperature measurement studies using a probe of 20 #m diameter are described and results are compared with a mathematical model. This is a very elegant study which shows that heat loss by way of the choroidal circulation has practically no effect on the thermal lesions produced by light coagulation at the fundus of the eye. The book contains six well-written chapters on selected subjects, which are connected only by the overall title of the work. Each chapter is well-supported by references, and there is a good index at the end of the book. It is not a book for beginners. On the other hand it is to be recommended for anyone who has an active interest in any of the selected topics. Dr Harry Moseley West of Scotland Health Boards Department of Clinical Physics and Bio-Engineering 11 West Graham Street Glasgow G4 9LF Scotland 4 August 1992
APPLICATIONS
IN MEDICINE
AND
BIOLOGY
M. L. WOLBARSrn"(Editor) (Vol. 5, 371 pp., Plenum Press, New York and London. D-306-43753-8, 1991) This book sets out to provide the reader with a thorough understanding of the theoretical background supporting the use of lasers in medicine and biology. It is to the credit of the various contributors and the editor that this laudable objective has been achieved. The trade-off is the narrow range of topics covered. There are six chapters. The first, on "Stimulation of Metabolic Processes by Low-Intensity Visible Light", is subtitled "A Scientific Basis for Biostimulation" to which some may wish to add a question mark. However, there is no question about the fact that light does interact with tissue, and exploring this at the cellular level provides a fascinating subject for study. Effects of different wavelengths, dose and irradiation regimes on DNA and RNA synthesis are described, along with other phenomena. Experiments with cell components of the immune sysem are also discussed. The final concluding remarks are rather speculative and many readers would have preferred a concluding section which drew together the various studies described earlier in the chapter. The second chapter describes the "Present Status of Research on Haematoporphyrin Derivatives and their Photophysical Properties". This begins with a brief historical review of the diagnostic and therapeutic use of haematoporphyrin (Hp) and haematoporphyrin derivative (HpD). HpD tends to localise preferentially in malignant tissues. Excitation with blue-violet light induces a strong red fluorescence which allows localisation of cancer. However, HpD is more widely used for therapy, called photodynamic therapy (PDT), in which red light is used to initiate the formation of cytotoxic products. Most of the chapter is taken up with the photophysics of HpD. Materials and experimental techniques are described and this is invaluable to those who are unfamiliar with the techniques employed. Following this, experimental results are presented. These describe the behaviour of HpD in solution, in model systems, in vitro, and briefly, in vivo. Present limitations and future prospects are also discussed. The Q-switched NdYAG laser is widely used in ophthalmic microsurgery and this is studied in the next chapter. After a brief outline of clinical applications, the characteristics of laser-induced breakdown in liquids are described. There then follows the major section of the chapter dealing with temporal and spatial dynamics of laser-induced plasmas in liquids. This describes models for plasma breakdown and compares theoretical predictions with experimental findings. Surgical lasers often suffer from significant power loss within the optical fibre delivery system. This can lead to unpredictable treatment outcomes. The chapter on High-Power Laser Transmission through Optical Fibres is, therefore, well worth reading. It gives a clear account of the basic elements of an optical fibre, including coupling of the laser beam into the fibre, as well as examining specific problems related to high-power laser beam transmission. The section on optical beam shaping, including sapphire tips, is most instructive. Some practical examples, comparing ray diagrams with measured values, would have been helpful. "Can Physical Modelling Lead to an Optimal Laser Treatment Strategy for Port-Wine Stains?" is the somewhat provocative title of the next chapter. It adopts a highly logical 249
250
Book review
approach to the problem of treating port-wine stain (PWS), the familiar congenital vascular malformation occurring commonly in the head and neck. Models are described, taking account of anatomy, light distribution and optical properties, leading to a predicted temperature distribution and damage distribution, following which biological healing takes place. Predictions are compared with experimental and clinical results for a number of laser types and treatment parameters. It is no surprise to read the authors' conclusion that "physical modelling has substantially contributed to optimising the early treatment strategies for port wine stain". It may also be noted that subtle changes in treatment strategy will require a more sophisticated model. The last chapter deals with Choroidal Circulation and Heat Convection at the Fundus of the Eye. Although photocoagulation of the retina has been around for a long time, the role of the choroidal circulation in heat dissipation is still a subject of controversy. The choroid is highly vascularised and is in close proximity to the retina, separated by the retinal pigment epithelium. Temperature measurement studies using a probe of 20 #m diameter are described and results are compared with a mathematical model. This is a very elegant study which shows that heat loss by way of the choroidal circulation has practically no effect on the thermal lesions produced by light coagulation at the fundus of the eye. The book contains six well-written chapters on selected subjects, which are connected only by the overall title of the work. Each chapter is well-supported by references, and there is a good index at the end of the book. It is not a book for beginners. On the other hand it is to be recommended for anyone who has an active interest in any of the selected topics. Dr Harry Moseley West of Scotland Health Boards Department of Clinical Physics and Bio-Engineering 11 West Graham Street Glasgow G4 9LF Scotland 4 August 1992