MEDICAL INFRARED PHOTOGRAPHY
In 1933 Professor Haxthausen,41 of the State Hospital of the University of Copenhagen, described the results of a study he had made of the application of infrared photography to dermatology. He argued very reasonably that, since infrared penetrated atmospheric haze and permitted photographs to be taken through it, it might allow photographs to be taken through the skin, which is also a medium that scatters light. His results unexpectedly showed that the veins underlying the skin could, in fact, be seen in an infrared photograph when they were not visible to the eye. Since that time a large number of such pictures have been made, and infrared photography has been applied to the study of other medical subjects.
That infrared rays could penetrate the skin was known before Haxthausen took his pictures, for they had been used in the practice of deep therapy, in which lamps of various kinds are used to warm up the tissues beneath the skin. Much study has been devoted to the selection of lamps most suited to this purpose.58-60 In a consideration of the principles involved in photography through the skin, therefore, much assistance can be obtained from an examination of the researches in the field of deep therapy. There are three main problems involved: the reflection, scattering, and transmission of radiation by the skin and the sub- cutaneous tissues; the spectral distribution of the radiation from sources which can be used to provide penetrating rays; and the spectral response of photographic plates and films which can be used for recording the reflected radiation.
The reflection and transmission of radiation by the skin varies considerably in different parts of the spectrum and with different