Ultraviolet induced fluorescence

In the case of the ultraviolet fluorescence technique, a source of ultraviolet radiation filtered with an ultraviolet transmission filter - or excitation filter - is aimed at the subject in a completely darkened room. The subject reflects the ultraviolet and may also emit a visible fluorescence. The ultraviolet is then prevented from entering the lens by an ultraviolet absorbing filter (or barrier filter) and fast black-and-white or colour film records any visible fluorescence emitted in the region 400 -700nm. Figure 4 shows the basic technique used. Whether one is examining a primary autofluorescence or a secondary fluorochrome fluorescence, the technique is essentially the same. It must be emphasised that this technique requires a completely darkened environment, as any daylight will wash the fluorescence. This requirement can be quite a challenge, particularly when trying to work on location. Ingenious solutions to this problem include the use of light-tight tents, or box enclosures, as for example in Callender (1977), who devised an enclosure with a bite block and retractors at one end and the recording camera at the other for photographing fluorescence of the teeth on location. Myers (1981) found that he could work in subdued room lighting when he used electronic flash synchronised to the between-the-lens shutter of a Hasselblad set to the fastest shutter speed. It should be possible to use the latest generation of focal plane shutters that synchronise flash at 1/125th sec. in the same way.

Figure 4 (above). The basic technique of ultraviolet induced fluorescence. The subject is photographed in a darkened room, illuminated by a source of ultraviolet radiation and then visible fluorescence recorded onto high-speed film (all the ultraviolet having been blocked at the lens by the use of an ultraviolet absorbing filter.

References

• Callender, R., 1977, "An ultraviolet camera system for intra-oral photography," Med. Bioi. Illus.27:113-115.
• Myers, B., 1981, "How to photograph fluorescein in a normally illuminated room," Plast. Reconstr. Surg. 67 (6):809-810.

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