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Home > Articles > Infrared Photography > >Biomedical applications of infrared photography
INFRARED PHOTOGRAPHYAuthors: Prof. Robin Williams and Gigi Williams Biomedical applications of infrared photographyInfrared photography has literally hundreds of applications, and for a comprehensive review the reader is referred to Gibson (1978). A gallery of some of the more important applications on the next page. Certain "key" applications stand out. The property of differential reflection and transmission of infrared by leaves provides many applications for both terrestrial and aerial photography in botany, agriculture, ecology, forestry and land management (Colwell, 1967). Colwell (1968) and Graham & Read (1986) offer general review of the aerial applications, while Spurr (1960) discussed in detail the applications in forestry. Different types of trees of crops can be readily identified by their infrared signature (Haack, 1962; Stellingwerf, 1966 and Northrop, 1970) and diseased crops can be identified (Norman 1965, Heller 1966, Ciesla et al. 1967, Jackson 1964 & 1971, and Graham 1992). Infrared photography is especially useful in distinguishing polluted from clean water in aerial photography (Strandberg, 1967a) for drainage analysis (Parry, 1971) and for assessing the damage by oil pollution (Wobber, 1971). Infrared is often used in studies of animal populations because their natural camouflage is of no use in the longer wavelengths (Cott, 1956; Colwell et al, 1966). Mathews (1968), Strandberg (1967b), and Wilson (1960), describe many useful applications in archaeology, where changes in vegetation covering sites can be better delineated. Reflected infrared has found many applications in document examination, as it is able to reveal different types of inks, uncover erased or overwritten material, and recover writing on blackened, aged or burned documents (see, for example, Bendikson, 1932; Tholl, 1951; O'Hara, 1949). Similarly much extra information can be revealed about paintings by using the reflected infrared technique: old varnish can be penetrated (Nickel, 1960), chronology and development may be established (Bridgman, 1963) or false attribution discovered (Hours-Miedan, 1957). It is perhaps in medical photography that infrared radiation has found more applications than in any other area. There are two useful properties: firstly, its ability to penetrate the superficial layers of the epidermis and to reveal structures beneath them, and secondly the reflection and absorption characteristics differ from that in respect of the visible spectrum. These two properties form the basis of all reported medical applications. Venous blood absorbs infrared heavily, whereas oxygenated blood reflects infrared well; thus vascular disorders such as varicose veins or venous obstruction are clearly delineated . Only the superficial veins can be recorded due to the limited depth of penetration. The sinuous curved stems of varicose veins are clearly seen, and the changing pattern of superficial vessels in the breasts and abdomen due to pregnancy have been mapped. When one of the main venous trunks of the body is obstructed a "collateral" circulation develops to circumvent the problem. These engorged and distended cutaneous veins stand out more vividly in an infrared photograph, and obstruction of the femoral, subclavian and portal veins, the vena cava, and mediastinal tumours are classic examples of applications for infrared photography. Others have reported the usefulness of the technique for studying venous patterns in congenital heart disease and pericardial effusion, in thrombotic conditions and in venous stasis, and for hypertension. A great deal of work has been done on the vascular patterns of the female breast during pregnancy, or in neoplastic disease. The vascular changes in diabetic patients have been mapped by infrared as have postprandial engorgement of veins. The clarity of the venous record obtained depends on various factors such as the thickness of subcutaneous fat, the thickness of the vessel walls and the depth of the vessel from the skin surface. In cases where an opaque cornea is obscuring the pupil, its size, shape and position can be revealed by infrared photography. Dark brown pigmented irises often record lighter in tone than blue ones, the deeply pigmented trabeculae often registering the lightest . Infrared colour film has been used to penetrate a vitreous humor clouded with blood to provide a record of the fundus. Similarly, cataracts have been penetrated to record retinal changes in retinitis pigmentosa, and melanotic lesions become strongly emphasized in the false colour record. Scleral melanosis can be distinguished from associated vascularities and vascular lesions of the choroid have been recorded through the retina. Infrared radiation has been used to record the diameter of the pupil in numerous studies of physical and physiological effects in both human and animal subjects (since the eye does not see infrared, the pupil does not respond to this radiation). In pathological applications, there is increased detail and differentiation between silicotic and pneumocotic lesions from the surrounding lung tissue. Injection techniques using mercuric sulphide (red cinnabar) into arteries and suspended carbon (India ink) into veins can be used to record these vessels as white (reflecting infrared) or black (absorbing infrared) respectively. The translucent amniotic membrane is penetrated to reveal details of the feotus. It is also possible to distinguish between otherwise visually similar substances, for example, silver sulphide deposits and melanin granules in localized argyria. In dental photography, enamel photographs darker than dentine, although there is some evidence to show that this situation is reversed with precarious chalky degeneration. In the healthy living tooth, the condition of the incisal edge can be clearly seen. Uneven areas of thin enamel appear light in tone. Infrared records are able to show clearly a variety of clinical conditions such as the healing process under deep seated lesions such as lupus vulgaris and eczema, hair stubble in shaved areas, tattoo patterns obliterated to visual examination. Xanthomata also record very clearly. Infrared photography has been much used in the study of tumours, especially for delineating the increased blood supply to breast tumours, and for differentiating between benign and malignant pigmented lesions of skin. Much work has been done on the relationship between cirrhosis of the liver and collateral circulation, and infrared photography is useful in early detection. There are conflicting reports on the value of infrared photography for transilluminating the breast, while others reported much enhanced recording particularly with infant skulls. For the sake of both clarity and brevity, the major biomedical applications are presented below in tabular form.
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