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Quantification of fluorophore concentration in vivo using two simple fluorescence-based measurement techniques
Kevin R Diamond1, Pawel P Malysz, Joseph E Hayward
1Juravinski Cancer Centre and McMaster University, Department of Medical Physics, 699 Concession Street, Hamilton, Ontario, Canada L8V 5C2. kevin.diamond@hrcc.on.ca
Journal of Biomedical Optics
|May 25, 2005
Summary
Quantifying photosensitizer concentration is crucial for photodynamic therapy. This study found that in vivo fluorescence measurements correlate with chemical extraction in some tissues, but underestimate higher concentrations.
Area of Science:
- Biomedical Engineering
- Photochemistry
- Medical Physics
Background:
- Photodynamic therapy (PDT) efficacy relies on precise photosensitizer concentration at the target site.
- Accurate quantification of photosensitizers in vivo is essential for optimizing PDT treatment outcomes.
- Aluminum phthalocyanine tetrasulfonate (AlPcS4) is a photosensitizer used in PDT research.
Purpose of the Study:
- To compare the accuracy of two in vivo fluorescence-based techniques for quantifying AlPcS4 concentration.
- To validate in vivo measurements against post-mortem chemical extraction and fluorometric assays.
- To investigate the fluorescence properties of AlPcS4 in various tissues.
Main Methods:
- In vivo fluorescence measurements using optical fiber and reflectance-ratio instruments.
- Comparison with ex vivo chemical extraction and fluorometric assays of skin, muscle, fascia, liver, and kidney.
- Use of tissue-simulating phantoms for calibration and concentration estimation.
- Fluorescence lifetime measurements in vivo and in phantoms.
Main Results:
- Good agreement between the two in vivo fluorescence techniques in lighter tissues (skin, muscle, fascia).
- In vivo measurements correlated well with chemical extraction at low AlPcS4 concentrations (< 0.6 microg/g).
- Higher tissue concentrations were underestimated by in vivo methods.
- AlPcS4 exhibited mono-exponential fluorescence decay in skin, muscle, and fascia, similar to phantoms.
- Liver and kidney tissues showed an additional short fluorescence lifetime component.
Conclusions:
- In vivo fluorescence techniques offer a simple method for estimating AlPcS4 concentration, particularly in less pigmented tissues.
- Current in vivo methods may underestimate high photosensitizer concentrations, requiring further refinement.
- Tissue-specific differences in fluorescence decay kinetics (liver, kidney) warrant further investigation for accurate quantification.