Transillumination

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Transillumination of the breast began in 1929 with the real-time viewing (diaphanoscopy) of the breast by a dark-adapted examiner (Cutler, 1929). The technique was found somewhat helpful in distinguishing cystic from solid lesions and, specifically, in suggesting the diagnosis of hematoma and retroareolar intraductal papilloma. After a period of initial interest, the technique lapsed into relative obscurity, only to be revived in France in the 1950s with the recording of hard-copy images (diaphanography) on photographic film. Subsequent modifications in technique resulted in improved diagnostic performance, but transillumination still was considered useful only as an adjunct to other breast diagnostic procedures, especially, for identifying hematomas and some benign breast cysts (Gros et al., 1972). Specifically, the technique was not able to distinguish reliably between benign and malignant breast masses. For this reason, and particularly because dramatic advances in mammography were permitting accurate and early detection of breast cancer, transillumination was not used widely.

In the 1980s, changes in diaphanoscopy and diaphanography derived from the observation that tumor visibility was improved when transillumination imaging emphasized the near infrared wavelengths (Carlsen, 1982; Isard, 1981; Ohlsson et al., 1980). Two theories have been advanced to explain these findings. One is based on the concept of preferential near infrared absorption of nitrogen-rich components [i.e., that material high in nitrogen content will absorb more (therefore appear to transilluminate less) near infrared radiation than will nitrogen-poor materials]. It, therefore, has been proposed that the breast is suitable for study with transillumination because fibroglandular tissue is thought to contain considerably less nitrogen than does cancerous tissue (Caspersson and Santesson, 1942). The second theory suggests that transillumination with near infrared radiation does not depict tumor masses per se, but rather images the increased amount of blood, specifically hemoglobin molecules that they contain. It is well-known that both reduced and oxygenated hemoglobin have strong absorption bands in the near infrared spectrum and one can speculate that breast cancers harbor relatively large quantities of hemoglobin,

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either because of tumor neovascularity or because of increased transcapillary leakage of red blood cells within areas of malignancy. To take advantage of the enhanced tumor detection that comes with use of the near infrared spectrum, some transillumination techniques record images with special infrared sensitive photographic film (Isard, 1981; Ohlsson et al., 1980). A more technically advanced application of breast transillumination involves the recording of images by a television camera sensitive to near infrared radiation coupled to a standard television monitor (Bartrum and Crow, 1984; Carlsen, 1982; Watmough, 1982). This provides both real-time viewing of near infrared-rich images and hard-copy recording of images with videotape or with a multiformat film camera. A sophisticated modification of television-based transillumination involves post acquisition image processing with false color rendition of transmitted near infrared wavelength light to maximize visibility of those findings most likely to represent malignancy (Bartrum and Crow, 1984). Pilot studies using television-enhanced transillumination systems indeed have detected some nonpalpable breast cancers (Carlsen, 1982; Marshall et al., 1984; Merritt et al., 1984). However, several more fully-documented clinical studies, in which state-of-the-art mammography was done on all patients, indicated that these transillumination techniques are far inferior to mammography in detecting nonpalpable cancer (Alveryd et al., 1990; Bosanko et al., 1990; Geslien et al., 1985; Gisvold et al., 1986; Jarlman et al., 1992a; 1992b; Monsees et al., 1987a; 1987b; 1988; Sickles, 1984b).

Currently, all transillumination techniques remain experimental procedures. The major weakness of transillumination appears to be a relative inability to image both deep lesions and most of the very small cancers now routinely detected by mammography (Bartrum and Crow, 1984; Bosanko et al., 1990; Geslien et al., 1985; Gisvold et al., 1986; Jarlman et al., 1992a; 1992b; Monsees et al., 1987a; 1987b; 1988; Sickles, 1984b).

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