Characterization and standardization of tissue-simulating protoporphyrin IX optical phantoms

Abstract

Abstract. Optical devices for measuring protoporphryin IX (PpIX) fluorescence in tissue are routinely validated by measurements in optical phantoms. Yet there exists limited data to form a consensus on the recipe for phantoms that both mimic the optical properties found in tissue and yield a reliable and stable relationship between PpIX concentration and the fluorescence remission intensity. This study characterizes the influence of multiple phantom components on PpIX fluorescence emission intensity, using Intralipid as the scattering source, bovine whole blood as the background absorber, and Tween as a surfactant to prevent PpIX aggregation. Optical measurements showed a linear proportionality (r > 0.99) between fluorescence intensity and PpIX concentration (0.1 to 10 μg∕mL) over a range of Intralipid (1 to 2%) and whole blood (0.5 to 3%) for phantoms containing low surfactant (≤0.1%), with fluorescence intensities and scattering and absorption properties stable for 5 h after mixing. The role of surfactant in PpIX phantoms was found to be complex, as aggregation was evident in aqueous nonturbid phantoms with no surfactant (0% Tween), and avoided in phantoms containing Intralipid as the scattering source with no additional or low amounts of added surfactant (≤0.1% Tween). Conversely, phantoms containing higher surfactant content (>0.1% Tween) and whole blood showed interactions that distorted the fluorescence emissions.

Nonlinear relation between concentration and fluorescence emission of protoporphyrin IX in calibrated phantoms

“…1 by addition of HCl into S 0 to reach a pH of 5 and then addition of 1 mL of Tween 20 and 1 mL of Intralipid, as proposed in Ref. 15. This fit yields the two parameters α 634 and α 620 .…”

“…PpIX concentration was set around 10 −5 mol∕L to be close to in vivo concentrations. 7,13 Additional components were sequentially added as proposed by Marois et al 15 to get various microenvironments of PpIX. Solutions were prepared by dissolving 6.1 mg of PpIX (Sigma Aldrich, Saint Louis) into 10 mL of DMSO to get a stock solution at 1.2 × 10 −3 mol∕L.…”

“…Recent works proposed a standardization of PpIX optical phantoms. 15 They proposed a standardized PpIX phantom recipe to respect the proportionality between fluorescence intensity and PpIX concentration of the phantom. However, this phantom recipe does not consider a variation of the peak position in the fluorescence spectrum, whereas other studies have introduced it.…”

Spectral complexity of 5-ALA induced PpIX fluorescence in guided surgery: a clinical study towards the discrimination of healthy tissue and margin boundaries in high and low grade gliomas

“…[37]. We u by [44] cleaved so that excited tissue area and emitting tissue area are the same. Light goes through a low pass filter with a rejection band between 450 nm and 700 nm.…”

Optimization and characterization of the endogenous production of protoporphyrin IX in a yeast model

“…22,23 The objective of this study was to develop a model producing endogenous levels of PpIX comparable to those observed in the abovementioned clinical applications. Such a model is of high interest to optimize or study basic mechanisms involved in PDT and PDD, such as the influence of agents or environmental factors on the modulation of the PpIX biosynthetic pathway; 23,24 the study of steady-state and time-resolved spectroscopy of PpIX produced endogenously, in particular, its dependence on environmental factors [temperature and oxygen partial pressure (pO 2 )]; 12,13,25 the development of optical phantoms mimicking the PpIX fluorescence spectroscopy and intensity observed in tumors, 26,27 the study of agents modulating the production of ROS, including singlet oxygen, to optimize and/or monitor PDT. 28 Thus, the determination of the conditions reproducibly leading to the maximal PpIX fluorescence intensity produced by Saccharomyces cerevisiae was studied and is reported in this paper.…”