Image Compression in Optical Coherence Tomography Biomedical Engineering, Tambov State Technical University, Russia K.E.S.Ghaleb, A.Yu.Potlov, S.N.Abdulkareem, S.A.Leonova, S.G.Proskurin

Abstract Conventional OCT-systems provide structural images of tissue from synthesis of a series of one-dimensional reflectivity scans (A-scans.) Application of raster averaging of adjacent A-scans increases coherence probing depth and reduces size of the image file.

What wavelengths? 805 нм

(low-coherence interferometery) principles of scanning LCI ± V detector white light CW laser, Δλ ≈ 1 nm pulsed laser, fs SLD Δλ ≈ nm light source sample modulation is necessary to tune the carrier off 1/f noise AOM, EO lateral scan OCT scanning mirror gives depth discrimination and modulation of the signal, carrier (Doppler ) frequency: f o =2V/λ

carrier of OCT system

Δf=f o (Δ λ/ λ o ) broadening of the carrier Moscow State University, 1989 Doppler spectra 2 АОМs

Doppler spectra of a flow 2 % 7 % upper part of the Doppler spectra is Gaussian in both cases Doppler spectra 4 times wider, Doppler spectra 4 times wider, ΔV/V ~ 7 %

raster averaging blood vessel diameter ~1 мм В-scan before Quantum Electronics (2004) p.1157 blood В-scan after

А-scans before averaging after averaging

Image of Blood OCT images of skin and blood vessel of human finger in vivo before averaging (a, d) and after averaging over three (b, e) and ten (c, f) adjacent A-scans. Arrows point at the location, where the structural image of blood is seen with contrast only after averaging. The image size is 2x2 mm. 180 A-scans 900 A-scans Quantum Electronics (2012) p.495

Size of the image in jpg

Size of the image in bmp_zip

Size of the image in jpg_zip

The use of the remote small-angle raster scanning with subsequent averaging shows that with the number up to 60 of averaged scans, corresponding to different angles, no asymptotic saturation of the dependence of the signal-to- noise ratio on the number of averaged scans is observed. In addition it is possible to detect the photons in the intermediate regime between the back reflection and multiple diffusion scattering. Averaging over 5 – 10 A-scans allows elimination of speckles and provides maximal contrast of the image and the minimal size of the file. Conclusion

References Proskurin S.G., Raster scan and averaging for speckle reduction in optical coherence tomography // Quantum Electronics, Vol. 42 (6), p , Proskurin S.G., Frolov S.V., Visualization of blood vessels by means of optical coherence tomography // Biomedical Engineering, No.3, p.9-14, 2012 Bonesi M., Proskurin S.G., Meglinski I.V., Imaging of subcutaneous blood vessels and flow velocity profiles by Optical Coherence Tomography // Laser Physics, Vol. 20, No. 4, p , 2010.