Three-dimensional surface profile intensity correction for spatially modulated imaging

Abstract

We describe a non-contact profile correction technique for quantitative, wide-field optical measurement of tissue absorption (µ a ) and reduced scattering (µ s ') coefficients, based on geometric correction of the sample's Lambertian (diffuse) reflectance intensity. Since the projection of structured light onto an object is the basis for both phase-shifting profilometry and modulated imaging, we were able to develop a single instrument capable of performing both techniques. In so doing, the surface of the 3-dimensional object could be acquired and used to extract the object's optical properties. The optical properties of flat polydimethylsiloxane (silicone) phantoms with homogenous tissue-like optical properties were extracted, with and without profilometry correction, after vertical translation and tilting of the phantoms at various angles. Objects having a complex shape, including a hemispheric silicone phantom and human fingers, were acquired and similarly processed, with vascular constriction of a finger being readily detectable through changes in its optical properties. Using profilometry correction, the accuracy of extracted absorption and reduced scattering coefficients improved from 2-to 10-fold for surfaces having height variations as much as 3 cm and tilt angles as high as 40°. These data lay the foundation for employing structured light for quantitative imaging during surgery.

Quantitative assessment of graded burn wounds in a porcine model using spatial frequency domain imaging (SFDI) and laser speckle imaging (LSI)

“…Using an analysis approach similar to what we have employed in previously reported SFDI based research [30], a single white Monte Carlo simulation was generated and then scaled to determine lookup table values for different optical properties [33]. A surface profilometry calibration measurement of a sample with known optical properties was used to correct the effects of surface curvature and day to day instrument variations [34]. The absorption maps at each wavelength were used to estimate chromophore concentration maps of oxygenated and deoxygenated hemoglobin that could be converted to tissue oxygen saturation (stO 2 ) by dividing oxygenated hemoglobin by the sum of oxygenated and deoxygenated hemoglobin.…”

Real-time endoscopic optical properties imaging

“…It is often difficult to control the surface height and profile of a sample, and so a profilecorrection method was developed by utilizing the distance-dependent phase-shifting behavior of angled sinusoidal projections [16]. Profile corrections are absolutely crucial for both SFDI [16,17] and SSOP [20] as varying sample height causes uncorrected measurements of absorption and reduced scattering properties.…”

“…Profile corrections are absolutely crucial for both SFDI [16,17] and SSOP [20] as varying sample height causes uncorrected measurements of absorption and reduced scattering properties. Hence, this work also implements and demonstrates the need for a height-based correction.…”

“…projected spatial frequency and the radiance of source intensity. However, each of these parameters can be calibrated and accounted for over a range of distances by using the same principles demonstrated previously [16,20]. For any given parameter, calibration measurements on a reference phantom are made at several known distances from the endoscope and the parameter is fit to a regression as a function of distance.…”

“…SFDI offers a widefield, noncontact approach for acquiring optical property maps that can be analyzed over several wavelengths to produce chromophore concentrations of endogenous tissue constituents [13][14][15]. Several steps have been made to improve the technique's robustness and processing schemes, including a fast 2-D look-up Table [15], a 3-D height correction method [16,17], and an optimization of wavelengths for spectroscopic fitting of tissue constituent concentrations [18]. These developments led to a first-in-human pilot study that measured skin flap oxygenation during reconstructive breast surgery [19].…”