Gerhard Gaida

Frequency-domain optical mammography: Edge effect corrections

We have investigated the problem of edge effects in laser-beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency-domain measurements by employing a two-step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge-corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency-domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two-step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images.

Frequency-domain optical mammography: the correction of tissue thickness variations within the scanned region

A possible approach to optical mammography consists of a planar tandem scan of a light source and an optical detector in a transmission geometry. The main difficulty with interpreting the data collected in this sampling geometry arises from edge effects, which are due to variable breast thickness within the scanned region and to photon losses through the sides of the breast. We have developed an algorithm for frequency-domain data analysis that corrects for edge effects, thus providing significantly enhanced image contrast with respect to raw data images. The application of our algorithm to data collected in vivo strongly improves the detectability of optical inhomogeneities in the breast.