Page 32 - 00. Complete Version - Progress Report IPEN 2014-2016

32 Lasers Technology | Progress Report

used. All samples were submitted to erosive crovascular plexus are collected by a CCD or a
cycles with citric acid solution. After 10 days CMOS camera during a selected exposure time.
of acid challenges, lesions became visible and The captured image presents a granular pat-
OCT readouts were performed on day 01 (be- tern, known as speckle pattern, due to inter-
fore the first acid challenge, on day 05, day ferences of the scattered radiation. The pattern
10, day 15, day 17 and day 20 The OCT imag- changes with the movement of the red blood
es generated made it possible to measure the cells. The differences in the statistics of speck-
amount of tooth tissue loss over the 20 days le patterns from static and moving structures
of erosive cycle, before and after treatments, are explored to compute a quantity related to
and to monitor early dentin demineralization the skin blood flow (SBF). A sequence of imag-
progression. After statistical analysis, the flu- es is captured (,) and each frame is processed
oride group was observed to be the one that producing a mapping of blood flow in the in-
showed smaller loss of tissue over time. The vestigated region. A region of interest (ROI)
OCT technique is promising for diagnosing and can be selected to compute a regional (into the
monitoring erosive lesion damage; however, ROI) blood flow. The result is a time series of
further in vitro and in vivo research is need- SBF values. This spatial processing methodol-
ed to improve its use. ogy allows high sampling rate (typically in the
order of 25 frames/s), detecting rapid changes
Studies regarding the detection of flow are of flow. As a result of the non-contact feature
also being carried in the laboratory. Speckle, of the LSCI system, any body movement of the
a form of coherent noise present in OCT, was target generally interferes in the measurement.
shown to hold a time-dependent relation with This fact may restrict the use of the LSCI sys-
regions of flow in the sample being imaged (,) tem to monitor the blood flow from anesthe-
and have (has) been used to generate maps of tized mice due to breathing movements. In at-
such regions. A microfluidic volumetric flow tempt to correct the baseline of a signal with
determination using optical coherence tomog- peaks, the background signal of each register
raphy speckle was done. We propose a simple was estimated using the MATLAB function ms-
approach to the autocorrelation of OCT signal backadj. Baseline tracking and correction is a
to enable volumetric flow rate differentiation, common problem in DNA sequencing. Auto-
based on decorrelation time. Our results show mated DNA sequencing is a well stablished (es-
that this technique could distinguish flows tablished) technique. In this case, the accurate
separated by 3 ul/min, limited by the acquisi- identification of a DNA sequence depends on
tion speed of the system. We further perform the correction of the baseline of the chromato-
a B-scan of gradient flow inside a microchan- graphic signal. The raw chromatogram gen-
nel, enabling the visualization of the drag ef- erally presents a slowly varying baseline. For
fect on the walls(.) DNA sequencing, the correction of the base-
line is necessary in order to establish a trust-
Laser Speckle Contrast Imaging (LSCI) is a tech- able reference of the background signal to fur-
nique proposed to assess the microvascular ther processing. In this case, the corrected data
function. Briefly, a low power (typically 50 is the raw data minus the estimated baseline
mW), non-collimated laser radiation, frequent- signal. Here (blood flow measurement(,) the
ly in the range from 635 nm to 780 nm, illumi- estimated baseline is the useful signal. The
nates the skin. Scattered photons from static raw data are used only to estimate the back-
and moving (mainly red) blood cells in the mi- ground signal. The measured SBF signal from

Instituto de Pesquisas Energéticas e Nucleares