Protoporphyrin IX delayed fluorescence imaging: a modality for hypoxia-based surgical guidance

Abstract

. Significance Hypoxia imaging for surgical guidance has never been possible, yet it is well known that most tumors have microregional chronic and/or cycling hypoxia present as well as chaotic blood flow. The ability to image oxygen partial pressure ( ) is therefore a unique control of tissue metabolism and can be used in a range of disease applications to understand the complex biochemistry of oxygen supply and consumption. Aim Delayed fluorescence (DF) from the endogenous molecule protoporphyrin IX (PpIX) has been shown to be a truly unique reporter of the local oxygen partial pressure in tissue. PpIX is endogenously synthesized by mitochondria in most tissues, and the particular property of DF emission is directly related to low microenvironmental oxygen concentration. Here, it is shown that PpIX has a unique emission in hypoxic tumor tissue regions, which is measured as a DF signal in the red to near-infrared spectrum. Approach A time-gated imaging system was used for PpIX DF for wide field direct mapping of changes. Acquiring both prompt and DF in a rapid sequential cycle allowed for imaging oxygenation in a way that was insensitive to the PpIX concentration. By choosing adequate parameters, the video rate acquisition of images could be achieved, providing real-time tissue metabolic information. Results In this report, we show the first demonstration of imaging hypoxia signals from PpIX in a pancreatic cancer model, exhibiting contrast relative to surrounding normal oxygenated tissues. Additionally, tissue palpation amplifies the signal and provides intuitive temporal contrast based upon neoangiogenic blood flow differences. Conclusions PpIX DF provides a mechanism for tumor contrast that could easily be translated to human use as an intrinsic contrast mechanism for oncologic surgical guidance.

Fluorescence lifetime of injected indocyanine green as a universal marker of solid tumours in patients

“…The past two decades have seen a dramatic growth in the development of molecularly targeted fluorescent tracers and imaging systems for intraoperative tumor identification [1][2][3] . Besides probes targeting tumor-specific molecular expression [4][5][6][7][8][9][10][11] , fluorescent probes have been developed to target the aberrant tumor microenvironment, such as enzyme activity [12][13][14] , hypoxia 15 , increased lysosomal viscosity [16][17][18] , and acidic pH 19,20 . The FDA approved near infrared (NIR) dye, indocyanine green (ICG), has also been extensively evaluated for cancer image guided surgery [21][22][23][24][25][26][27][28][29][30] .…”

Subsurface fluorescence time-of-flight imaging using a large-format single-photon avalanche diode sensor for tumor depth assessment

“…The coefficient c fluo from Eqs. (10) and (11) is in theory constant and only depends on the setup geometry.…”

“…Depth calibration can be achieved by quantifying changes induced by varied optical properties, as described by Eqs. ( 10) and (11). Two methods were investigated for this purpose: first, reflectance-based calibration using direct time-resolved measurements from the SPAD camera; and second, using an established external modality (i.e., SFDI).…”

“…Intraoperative visualization of tumors using FGS has the potential not only to achieve complete resections but also to improve patient safety by reducing unnecessary damage to normal tissue, 5 – 8 leading to shorter operative times and a decreased likelihood of needing additional surgery. Recent developments in FGS have led to the introduction of several new imaging probes, 9 – 12 each with unique spectral characteristics, tissue and/or biomarker targets, and pharmacokinetic properties, complementing existing probes and providing a growing repertoire of useful tools for FGS. Although conventional FGS techniques are useful, they have certain limitations; these methods typically involve continuous fluorescence excitation and imaging, which only provides two-dimensional information about imaged features (e.g., the location of disease).…”

Prototype dual-channel fluorescence/transmission optical tomography system for quantification of capillary permeability and porphyrin production

“…In this work, a single-channel prototype was developed for an optical fiber-based tomography system to sample fluorescence in a manner that passively removes the influence of tissue optical properties. The potential for high optical contrast with centimeter-level penetration into tissue motivates sampling: (i) Capillary leakage with a temporal sampling of indocyanine green (ICG) [16] and (ii) Mitochondrial activity with protoporphyrin IX (PpIX) intensity [17]. The proposed system comprised two sources of laser diodes at 633 nm and 780 nm wavelengths, two avalanche photodiode (APD) detectors, and an NI DAQ 6002 module as a controlling medium with real-time data acquisition, executed via LabVIEW.…”