Abstract
Recently, multimodal imaging has gained an increasing interest in medical applications thanks to the inherent combination of strengths of the different techniques. For example, diffuse optics is used to probe both the composition and the microstructure of highly diffusive media down to a depth of few centimeters, but its spatial resolution is intrinsically low. On the other hand, ultrasound imaging exhibits the higher spatial resolution of morphological imaging, but without providing solid constitutional information. Thus, the combination of diffuse optical imaging and ultrasound may improve the effectiveness of medical examinations, e.g. for screening or diagnosis of tumors. However, the presence of an ultrasound coupling gel between probe and tissue can impair diffuse optical measurements like diffuse optical spectroscopy and diffuse correlation spectroscopy, since it may provide a direct path for photons between source and detector. A systematic study on the effect of different ultrasound coupling fluids was performed on tissue-mimicking phantoms, confirming that a water-clear gel can produce detrimental effects on optical measurements when recovering absorption/reduced scattering coefficients from time-domain spectroscopy acquisitions as well as particle Brownian diffusion coefficient from diffuse correlation spectroscopy ones. On the other hand, we show the suitability for optical measurements of other types of diffusive fluids, also compatible with ultrasound imaging.
Highlights
The worldwide growing research efforts and funding for multimodal imaging diagnostic devices highlight their importance as they permit to overcome limitations of the different single measurement techniques by combining their strengths, enabling in particular the acquisition of complementary morphological, compositional and/or functional information to maximize the diagnostic potential of a single examination [1]
Another complementary optical technique is diffuse correlation spectroscopy (DCS), which allows the estimation of the microvascular blood flow by measuring the speckle fluctuations of coherent light backscattered by biological tissues [10]
2.2 Diffuse optical spectroscopy (DOS) measurements Setup The DOS measurements were carried on using a state-of-the-art time domain broadband diffuse optical spectroscopy system [30]
Summary
The worldwide growing research efforts and funding for multimodal imaging diagnostic devices highlight their importance as they permit to overcome limitations of the different single measurement techniques by combining their strengths, enabling in particular the acquisition of complementary morphological, compositional and/or functional information to maximize the diagnostic potential of a single examination [1]. When performed at different wavelengths, functional parameters related to blood and tissue composition can be estimated from the absorption spectrum, while the scattering spectrum provides information about the microstructure like the density and size of biological cells and subcellular components [9] Another complementary optical technique is diffuse correlation spectroscopy (DCS), which allows the estimation of the microvascular blood flow by measuring the speckle fluctuations of coherent light backscattered by biological tissues [10]. This can be useful in many clinical contexts related to neurology (e.g. to assess the cerebral blood flow) and oncology (e.g. to characterize microvascular blood flow in tumors). The combination of optical techniques with any other technique capable of providing morphological information, like ultrasound (US) [12,13,14,15,16,17,18] or magnetic resonance [19,20,21,22,23,24,25] imaging, is considered a promising solution to improve the effectiveness of medical examinations
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