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Modulation frequency selection and efficient look-up table inversion for frequency domain diffuse optical

Matthew Applegate1, Carlos Gómez1, Darren Roblyer1

  • 1Boston Univ., United States.

Journal of Biomedical Optics
|March 26, 2021
PubMed
Summary
This summary is machine-generated.

Single low-frequency measurements in frequency domain diffuse optical spectroscopy (FD-DOS) provide similar accuracy to broadband sweeps for extracting optical properties. Simpler single-frequency systems are sufficient for many FD-DOS applications.

Keywords:
diffuse opticsfrequency domainhigh speedmodulation frequencynoise model

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Area of Science:

  • Biomedical Optics
  • Spectroscopy
  • Photonics

Background:

  • Frequency domain diffuse optical spectroscopy (FD-DOS) measures tissue optical properties using intensity-modulated light.
  • Current FD-DOS instruments vary in modulation frequency usage, from single to hundreds of frequencies.
  • The impact of modulation frequency choice and bandwidth on optical property (OP) extraction accuracy remains incompletely understood.

Purpose of the Study:

  • To evaluate how modulation frequency selection affects OP extraction error in FD-DOS.
  • To develop a high-speed look-up table (LUT) approach for efficient OP estimation.

Main Methods:

  • Noise-free simulations of light transport in homogeneous media were used to optimize iterative inversion parameters.
  • A novel multi-frequency LUT method was developed to accelerate inversion processes.
  • Experimentally derived noise models from two FD-DOS instruments were applied to simulated data across various OPs and modulation frequencies to assess accuracy.

Main Results:

  • Single low-frequency (110 MHz) measurements showed comparable OP errors to broadband frequency sweeps (50–253 MHz) under realistic noise models.
  • Including modulation frequencies above 300 MHz degraded performance for one instrument.
  • A LUT inversion algorithm achieved up to 6x speed increase (1000 inversions/s) with ~1% error using a single modulation frequency.

Conclusions:

  • Simpler single-frequency FD-DOS systems are adequate for numerous applications.
  • The findings support the development of next-generation digital FD-DOS systems for rapid, large-volume measurements with real-time feedback.