Phantoms for diffuse optical imaging based on totally absorbing objects, part 1: basic concepts

Abstract

Abstract. The design of inhomogeneous phantoms for diffuse optical imaging purposes using totally absorbing objects embedded in a diffusive medium is proposed and validated. From time-resolved and continuous-wave Monte Carlo simulations, it is shown that a given or desired perturbation strength caused by a realistic absorbing inhomogeneity of a certain absorption and volume can be approximately mimicked by a small totally absorbing object of a so-called equivalent black volume (equivalence relation). This concept can be useful in two ways. First, it can be exploited to design realistic inhomogeneous phantoms with different perturbation strengths simply using a set of black objects with different volumes. Further, it permits one to grade physiological or pathological changes on a reproducible scale of perturbation strengths given as equivalent black volumes, thus facilitating the performance assessment of clinical instruments. A set of plots and interpolating functions to derive the equivalent black volume corresponding to a given absorption change is provided. The application of the equivalent black volume concept for grading different optical perturbations is demonstrated for some examples.

Multi-channel medical device for time domain functional near infrared spectroscopy based on wavelength space multiplexing

“…The nEUROPt protocol instead aims at assessing the capability of a TD fNIRS system to measure optical quantities also on heterogeneous phantoms mimicking a real in vivo activation [4,31,38]. The whole data analyses were performed dividing the reflectance curve in time gates with fixed width (500 ps) and variable delay (from 500 ps to 4000 ps, in 500 ps steps).…”

Chromophore decomposition in multispectral time-resolved diffuse optical tomography

“…Nevertheless, optical phantoms containing heterogeneities are difficult to obtain and each lab has its own protocol [21,23]. For purely absorbing inclusions assessed at a single wavelength we preferred the Equivalent Black Volume (EBV) approach, which can mimic a wide Equivalence Class of realistic perturbations with different combination of volume, shape and absorption changes [24,25]. However, to cope with multichromophore problems we had to implement a different approach.…”

Large area silicon photomultipliers allow extreme depth penetration in time-domain diffuse optics

“…According to the nEUROPt protocol [14], we characterized the system capability of detecting the contrast produced by a totally absorbing inclusion made by a black cylinder with 100 mm 3 volume, corresponding to a ∆μ= 0.15 cm -1 over a volume of 1 cm 3 [15] . The cylinder is aligned to the middle point of  and it is moved along an increasing depth z (ranging from 2.5 mm up to 50 mm) inside an homogeneus liquid phantom, which optical properties were: (i) absorption coefficient µ a = 0.1 cm .…”