Standardization of intralipid for light scattering in clinical photodynamic therapy

Dual Layered Models of Light Scattering in the Near Infrared A: Optical Measurements and Simulation

Intralipid emulsion is often used as optical model substance to mimick living tissue's strong scattering properties. As such it is of considerable importance to utilize realistic parameters for any type of simulation or calculation in context of Near Infrared Spectroscopy. We determined optical properties of diluted Intralipid solutions at often used, realistic volume concentrations ρ_il and at two NIRS wavelengths (780nm and 850nm) in a double integrating Ulbricht-sphere setup. The results were used in Monte Carlo (MC) simulations of an experiment, described in our companion paper. Both, phantom experiments and MC simulation showed qualitatively similar results and demonstrated the effects of changing the three major NIRS factors, namely the penetrated layer depth (d), the Intralipid concentration ρ_il and the source-detector separation (SDS). The results demonstrated that light reaching the detectors was inversely proportional to ρ_il and d. It also showed that very low Intralipid concentrations do not follow the optical properties documented for Intralipid 20%.

Dual Layered Models of Light Scattering in the Near Infrared B: Experimental Results with a Phantom

Intralipid emulsion is often used as optical model substance to mimic living tissue's strong scattering properties. As such it is of considerable importance to utilize realistic parameters for any type of simulation or calculation in context of Near Infrared Spectroscopy. We determined optical characteristics of diluted Intralipid solutions at often used, realistic volume concentrations ρil and at two wavelengths (780nm and 850nm) in a simple phantom setup featuring multiple sensors with different source-detector-separation (SDS) and penetration depths d. Both, phantom experiments and MC simulation showed qualitatively similar results and demonstrated the influence of the three major NIRS factors, namely the penetrated layer depth (d), the Intralipid concentration ρ_il and the source-detector separation (SDS). The results demonstrated that light reaching the detectors is inversely proportional to ρ_il and d. It corroborates the need for differential measurements with at least two SDS to account for superficial large angle scattering.

31 P NMR Evidence for Peroxide Intermediates in Lipid Emulsion Photooxidations: Phosphine Substituent Effects in Trapping

Intralipid is a lipid emulsion used in photodynamic therapy (PDT) for its light scattering and tissue-simulating properties. The purpose of this study is to determine whether or not Intralipid undergoes photooxidation, and we have carried out an Intralipid peroxide trapping study using a series of phosphines [2'-dicyclohexylphosphino-2,6-dimethoxy-1,1'-biphenyl-3-sulfonate, 3-(diphenylphosphino)benzenesulfonate, triphenylphosphine-3,3',3''-trisulfonate and triphenylphosphine]. Our new findings are as follows: (1) An oxygen atom is transferred from Intralipid peroxide to the phosphine traps in the dark, after the photooxidation of Intralipid. 3-(Diphenylphosphino)benzenesulfonate is the most suitable trap in the series owing to a balance of nucleophilicity and water solubility. (2) Phosphine trapping and monitoring by 31 P NMR are effective in quantifying the peroxides in H2 O. An advantage of the technique is that peroxides are detected in H2 O; deuterated NMR solvents are not required. (3) The percent yield of the peroxides increased linearly with the increase in fluence from 45 to 180 J cm-2 based on our trapping experiments. (4) The photooxidation yields quantitated by the phosphines and 31 P NMR are supported by the direct 1 H NMR detection using deuterated NMR solvents. These data provide the first steps in the development of Intralipid peroxide quantitation after PDT using phosphine trapping and 31 P NMR spectroscopy.

Dependence of optical scattering from Intralipid in gelatin-gel based tissue-mimicking phantoms on mixing temperature and time

Intralipid is widely used as an optical scattering agent in tissue-mimicking phantoms. Accurate control when using Intralipid is critical to match the optical diffusivity of phantoms to the prescribed value. Currently, most protocols of Intralipid-based hydrogel phantom fabrication focus on factors such as Intralipid brand and concentration. In this note, for the first time to our knowledge, we explore the dependence of the optical reduced scattering coefficient (at 532 nm optical wavelength) on the temperature and the time of mixing Intralipid with gelatin-water solution. The studied samples contained 1% Intralipid and were measured with oblique-incidence reflectometry. It was found that the reduced scattering coefficient increased when the Intralipid-gelatin-water mixture began to solidify at room temperature. For phantoms that had already solidified completely, the diffusivity was shown to be significantly influenced by the temperature and the duration of the mixing course. The dependence of the measured diffusivity on the mixing conditions was confirmed by experimental observations. Moreover, the mechanism behind the dependence behavior is discussed.

The Application of Fluorescence Lifetime Readouts in High-Throughput Screening

Measurement of fluorescence lifetime is a well-established technique, which has recently been introduced into the portfolio of assay formats used in high-throughput screening (HTS). This investigation establishes appropriate conditions for using lifetime measurements to reduce the impact of compound interference effects during large-scale HTS of corporate screening files. Experimental data on mixtures of standard fluorophores and interfering compounds (from 5 HTS campaigns) have been combined with a theoretical model to identify the minimum data quality required, defined by the photon count in the peak channel, for discrimination of biological activity. Single-component fluorophore lifetimes can be recovered with an error of 1%, with a peak photon count of 102, but the same accuracy with a 2-component decay requires a peak photon count of 103. When a 3rd component is introduced, the minimum peak count increases to 104. The influence of scattered light on lifetime determination was investigated using an emulsion (diameters 25-675 nm). The measured decays of interfering compounds, identified as autofluorescent, show that the vast majority have a very short lifetime that can readily be resolved from the reporter fluorophore, using appropriate data-fitting methods.

In vivo measurements of the wavelength dependence of tissue-scattering coefficients between 760 and 900 nm measured with time-resolved spectroscopy

We present in vivo values for the optical transport coefficients (mu(a), mu(s)?) of the adult human forearm, calf, and head from 760 to 900 nm measured with time-resolved spectroscopy. The accuracy of the method is tested with tissue-simulating phantoms. We obtain mu(s)?(lambda) approximately 1.1 - (5.1 x 10(-4) lambda) mm(-1) (forearm), 1.6 - (8.9 x 10(-4) lambda) mm(-1) (calf), and 1.45 - (6.5 x 10(-4) lambda) mm(-1) (head), where lambda is measured in nanometers. At 800 nm we obtain mu(a) = 0.023 +/- 0.004 mm(-1) (forearm), 0.017 +/- 0.005 mm(-1) (calf), and 0.016 +/- 0.001 mm(-1) (head). Our values differ substantially from published in vitro data. In particular, our transport coefficients for the adult head are substantially lower than previously reported values for adult human cerebral matter and pig skull cortical bone measured in vitro.

Adjuvant intraoperative photodynamic therapy for colorectal carcinoma: a clinical study

The local recurrence rate of colorectal carcinoma after surgery is unacceptable in most series, and adjuvant therapies have made only a small impact on this. There is experimental evidence that adjuvant intraoperative photodynamic therapy (AIOPDT) may be effective. AIOPDT involves systematically photosensitizing the patient preoperatively with a drug (HpD) which relatively localizes to tumour and is activated using visible light. At operation the resected tumour bed is illuminated with a predetermined uniform light energy density to eradicate microscopic tumour deposits left at the lateral resection margin. We have previously investigated technical and biological factors leading to this clinical trial. Seventeen patients have received AIOPDT in a potentially effective dose, and safety and technical matters have been investigated. Cutaneous phototoxicity occurred in 3 patients. Three patients had anastomotic breakdown, none considered attributable to PDT. The intraoperative technique was a practical option. AIOPDT carried a low patient morbidity and should be investigated in prospective clinical trials to determine if local recurrence rates can be decreased.