This is a revolutionary IR-camera-based dynamic imaging technique recently pioneered in the CADIPT [1,2]. The high axial resolution due to thermal-wave localization, the dynamic range and depth resolution result in “crisp” images (unprecedented in diffusive fields), generating depth-selective time-evolving, rather than depth-integrated, imaging (figure below, left). Early results demonstrated depth-profiling performance (~3.2 – 4 mm) superior to optical coherence tomography (<1 mm) [1-4] and the absence of image artifacts due to unwanted coherent reflections. Compiling a series of subsurface time/depth resolved image slices (figure, left) results in Photothermal Coherence Tomography (figure, right), the thermal-wave counterpart of Optical Coherence Tomography (OCT). Two distinct applications of TC-PCT have been reported:
Depth scaled planar images for a goat rib bone showing gradual penetration from cortical surface to trabecular interior
Volumes of thermal-wave occupation and its rectangular envelope for a goat rib sample.
1) Resolving the trabecular network of a goat rib bone in three dimensions through the cortical region with and without a soft-tissue overlayer [3], resulted in quantitative early demineralization-detection capability using a marker we labeled “thermal wave occupation index” (figure above, right). Cortical and trabecular regions were analyzed independently and together using the computational slicing advantage of TC-PCT. The results were verified using micro-computed tomography imaging as the gold standard [4].
2) Images of subsurface structures and discontinuities in opaque solids, such as holes in steel, were obtained. They showed strong potential in industrial materials high-resolution NDI [1].
References
[1] Kaiplavil S, Mandelis A. Truncated-correlation photothermal coherence tomography for deep subsurface analysis, Nature Photonics 2014, 8, 653-642 / DOI: 10.10.1038/NPHOTON.2014.111.
[2] “Systems and Methods for Performing Truncated-Correlation Photothermal Coherence Tomography”, Inventors: A. Mandelis and S. Kaiplavil (submitted to US patent office, October, 2014; patent application # 14/518984).
[3] Kaiplavil S, Mandelis A, Wang XD, Feng T. Photothermal tomography for the functional and structural evaluation and early mineral loss monitoring in bones, Biomed. Opt. Express 2014; 5(8), 2488.
[4] Kaiplavil S, Mandelis A, Amaechi BA. Truncated-correlation photothermal coherence tomography (TC-PCT) of artificially demineralized animal bones: 2- and 3-dimensional markers for mineral-loss monitoring, J. Biomed. Opt. 2014; 19(2), 026015.