Nonlinear optical image processing with bacteriorhodopsin polymer films

作者：Yelleswarapu CS; Wu PF; Kothapalli SR; Rao DVGLN^*

来源：Molecular Crystals and Liquid Crystals, 2006, 446: 273-294.

DOI：10.1080/15421400500379756

• bacteriorhodopsin film
• breast cancer
• mammography
• optical Fourier processing
• spatial filtering

Real-time medical image processing through nonlinear optical Fourier filtering and transient Fourier holography is demonstrated using bio-organic polymer films of Bacteriorhodopsin (bR). In nonlinear Fourier filtering, the photo-controlled light modulation characteristics of bR films are exploited for early detection of microcalcifications in analog (screen film) as well as digital mammograms. bR films are well known for light modulation between the two states: the initial stable B state with broad absorption band with maximum at 570 nm and the relatively long lived M state with absorption maximum at 412 nm. The spatial frequency information carried by a blue probe beam is selectively manipulated in the bR film by changing the position and intensity of a yellow control beam. In transient Fourier holography, photoisomerizative gratings are recorded and reconstructed in bR films. The laser output from an Ar-Kr ion is expanded and split into two beams. One of them, the object beam is Fourier transformed by a lens on to the bR film placed at the Fourier plane. The second beam (reference beam) overlaps the Fourier transform of the object beam on the bR film thereby recordi00000000ng a Fourier hologram. When the object beam is blocked, the reference beam performs the reconstruction of the recorded Fourier hologram. The filtered spectrum is inverse Fourier transformed on to the CCD camera. The image processing is based on the fact that the desired spatial frequency band is recorded with optimum diffraction efficiency and matching the reference beam intensity to their intensity in the Fourier spectrum. A novel feature of the technique is the ability to transient display selected spatial frequencies in the reconstructing process which enables the radiologist to study the features of interest in time scale. Both the techniques are applied to filter out low spatial frequencies corresponding to soft dense breast tissue and display only high spatial frequencies corresponding to microcalcifications in clinical screen film mammograms. The results offer useful information to radiologists for early detection of breast cancer.

• 出版日期2006