Multiple-Fiber Probe Design for Fluorescence Spectroscopy in Tissue

Harvard University, Cambridge, Massachusetts, United States
Applied Optics (Impact Factor: 1.78). 09/2002; 41(22):4712-21. DOI: 10.1364/AO.41.004712
Source: PubMed

ABSTRACT The fiber-optic probe is an essential component of many quantitative fluorescence spectroscopy systems, enabling delivery of excitation light and collection of remitted fluorescence in a wide variety of clinical and laboratory situations. However, there is little information available on the role of illumination--collection geometry to guide the design of these components. Therefore we used a Monte Carlo model to investigate the effect of multifiber probe design parameters--numerical aperture, fiber diameter, source--collection fiber separation distance, and fiber-tissue spacer thickness--on light propagation and the origin of detected fluorescence. An excitation wavelength of 400 nm and an emission wavelength of 630 nm were simulated. Noteworthy effects included an increase in axial selectivity with decreasing fiber size and a transition with increasing fiber-tissue spacer size from a subsurface peak in fluorophore sensitivity to a nearly monotonic decrease typical of single-fiber probes. We provide theoretical evidence that probe design strongly affects tissue interrogation. Therefore application-specific customization of probe design may lead to improvements in the efficacy of fluorescence-based diagnostic devices.

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    • "Fluorescence measurements are non-destructive, fast, and less expensive in instrumentation. Recently the fluorescence technique was used to investigate biological materials (Kim et al., 2003; Pfefer et al., 2002), detect environmental, chemical, and biological stresses in plants (Gavel and Marsalek, 2004; Kim et al., 2001) and monitor food quality and safety (Kong et al., 2004; Vargas et al., 2004). Chlorophyll fluorescence has been researched for measuring fruit postharvest quality and condition such as defects and ripeness (Bodria et al., 2002; Mir et al., 2001). "
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    ABSTRACT: Chlorophyll fluorescence has been researched for assessing fruit post-harvest quality and condition. The objective of this preliminary research was to investigate the potential of fluorescence spectroscopy for measuring apple fruit quality. Ultraviolet (UV) and blue light was used as an excitation source for inducing fluorescence in apples. Fluorescence spectra were measured from 'Golden Delicious' (GD) and 'Red Delicious' (RD) apples by using a visible/near-infrared spectrometer after one, three, and five minutes of continuous UV/blue light illumination. Standard destructive tests were performed to measure fruit firmness, skin and flesh color, soluble solids and acid content from the apples. Calibration models for each of the three illumination time periods were developed to predict fruit quality indexes. The results showed that fluorescence emission decreased steadily during the first three minutes of UV/blue light illumination and was stable within five minutes. The differences were minimal in the model prediction results based on fluorescence data at one, three or five minutes of illumination. Overall, better predictions were obtained for apple skin chroma and hue and flesh hue with values for the correlation coefficient of validation between 0.80 and 0.90 for both GD and RD. Relatively poor predictions were obtained for fruit firmness, soluble solids content, titrational acid, and flesh chroma. This research demonstrated that fluorescence spectroscopy is potentially useful for assessing selected quality attributes of apple fruit and further research is needed to improve fluorescence measurements so that better predictions of fruit quality can be achieved.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2005; 35(2). DOI:10.1117/12.629901 · 0.20 Impact Factor
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    ABSTRACT: The design of fiber-optic probes plays an important role in optical spectroscopic studies, including fluorescence spectroscopy of biological tissues. It can affect the light delivery and propagation into the tissue, the collection efficiency (total number of photons collected vs. total number of photons launched) and the origin of collected light. This in turn affects the signal to noise ratio (SNR) and the extend of tissue interrogation, thus influencing the diagnostic value of such techniques. Three specific fiber-optic probe designs were tested both experimentally and computationally via Monte Carlo simulations. In particular, the effects of probe architecture (single-fiber vs. two bifurcated multifiber probes), probe-to-target distance (PTD), and source-to-detector separation (SDS) were investigated on the collected diffuse reflectance of a Lambertian target and an agar-based tissue phantom. This study demonstrated that probe architecture, PTD, and SDS are closely intertwined and considerably affect the light collection efficiency, the extend of target illumination, and the origin of the collected reflected light. Our findings can be applied towards optimization of fiber-optic probe designs for quantitative fluorescence spectroscopy of diseased tissues.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2003; 4958. DOI:10.1117/12.476141 · 0.20 Impact Factor
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