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Phantoms

The use of optical tissue simulating phantoms is a necessary part of the continued development and adoption of optically based techniques. While liquid phantoms may be the easiest to produce and characterize, there are number of phantom applications where a solid, permanent option would be better suited. These include system reference phantoms to improve signal to noise, intersystem and inter-site performance testing phantoms, and technique validating phantoms involving more complex structures.

We have the capacity to produce tissue simulating phantoms that vary in thickness from ~ 90 microns up to several centimeters which can be used alone or combined to produce multilayered structures to mimic optical properties of physiologic tissues such as skin. The optical properties of these phantoms can be characterized using a variety of methods which are outlined below.

Phantom Manufacture Capabilities

Materials

PDMS based phantoms (Note - PDMS is hydrophobic: Water based dyes and scattering agents are not easily incorporated into these phantoms. Spatial homogeneity and stability of optical properties cannot be guaranteed when water based agents are used.)

Scattering agents currently available:
  • Titanium Dioxide
Absorbing agents currently available (Absorption Spectra):
  • Nigrosin
  • Methylene Blue
  • Coffee
  • Naphthol Green
Additional dyes:
  • Hemoglobin (not fully characterized for stability over time)

Types of Phantoms

  • Homogeneous phantoms
    • Dimensions ~10x10cm or 7.5x7.5cm, *thickness: 1-3cm (though can be varied across larger range if needed)
    • Effort: 1.5-3 hr
  • Thin Layer (stackable phantoms)
    • Sets with 4-5 thicknesses of the same optical properties (single batch preparation)
    • Dimensions ~8x8cm, *thicknesses varying ~100, ~150, ~250, ~270, ~350 micron (or ~2mm+/-1mm)
    • Effort: 1.5-3 hr
  • Custom (multi-component phantoms)
    • Effort: TBD

Phantom Characterization Methods

Reference Independent Methods

  • Multi-distance Frequency Domain Measurements
    • For Homogeneous (Semi-infinite) Phantoms only
    • Determines absorption and reduced scattering coefficients at 4-6 discrete wavelengths in NIR
    • Uses Broadband reflectance spectroscopy in NIR to interpolate optical properties across entire NIR range (650-1000nm) @nm resolution
    • Probe Based measurement (non-imaging)
    • Effort: 1.5-2hr (Acquisition + Data processing: active time only)
  • Inverse Adding Doubling Method
    • For Thin Layer Samples only
    • Determines absorption and reduced scattering coefficients up to ~1nm resolution across visible and NIR Range (450-1000nm)
    • Effort: 1.5-3hr (for set of phantoms at multiple thicknesses)

Reference Based Methods

  • Spatial Frequency Domain Imaging (Instrument used: MI2)
    • For Homogeneous (Semi-infinite) Phantoms only
    • Determines absorption and reduced scattering coefficients in NIR (650-980nm) up to 10 nm resolution
    • Imaging based system: can also determine/verify the extent of any spatially dependent variance present
    • Effort: 1-1.5hr
  • Spatially Modulated Spectroscopy (SMoQS)
    • For Homogeneous (Semi-infinite) Phantoms only
    • Determines absorption and reduced scattering coefficients in visible and NIR (450-1000nm) up to ~1nm resolution
    • Point Spectroscopy Measurement (non-imaging)
    • Effort: 0.5-1hr

Absorption measurements (for non-scattering media)

  • Spectrophotometer (Shimadzu UV-3600)
    • For thin, non-scattering media
    • Characterize spectral properties of dyes in PDMS (in the event silicone polymerization process alters chemical properties of dye, though not typical)
    • Spectral range 300-1100nm, variable resolution
    • Effort: 0.5hr
  • Integrating sphere with spectrometer set up
    • For thin, non or weakly scattering media (eg coffee phantoms)
    • Characterize spectral properties of dyes in PDMS (in the event silicone polymerization process alters chemical properties of dye, though not typical)
    • Spectral range 450-1000nm, up to ~1nm resolution Effort: 0.5hr

Suggested Work for homogeneous phantoms:

Production:

  • 1 Semi-infinite Phantom per desired set of optical properties
  • 1 non-scattering sample for independent absorption verification (at phantom concentration) (Note: there would be no significant effort added to produce the non-scattering sample)

Characterization:

  • Multi-distance Frequency Domain Measurement (Determine NIR optical properties without reference/calibration phantom)
  • Spatial Frequency Domain Imaging (Verify spatial homogeneity, determine/validate NIR optical properties with Frequency Domain)
  • Spatially Modulated Spectroscopy (SMoQS) (visible domain optical properties, validate agreement with Frequency Domain and Spatial Frequency Domain determinations of Optical properties in NIR)
  • Spectrophotometer or Integrating sphere setup (for non-scattering sample)
  • Estimated Total Effort: ~5-hrs
  • By Limiting the number of resources/instruments used in phantom characterization and validation, costs can be reduced. (eg using only 1-3 methods of the ones available could potentially reduce the total effort to ~2.5-5 hrs)

Deliverables:

  • All phantoms (including any non-scattering samples)
  • Individual characterization methods results
  • Single Merged file of Absorption and Reduced Scattering coefficients
  • Spatial and Spectral variance (accuracy) associated with the Single Merged File

Conference Proceedings

Diffuse optical spectroscopy of melanoma simulating silicone phantoms

Fabrication and characterization of silicone-based tissue phantoms with tunable optical properties in the visible and near infrared domain

Multilayer silicone phantoms for the evaluation of quantitative optical techniques in skin imaging

Education & Dissemination

Contact Us

  • Hanna Kim
    Resource Coordinator
    Phone:949.824.2251
    Email: hhkim3@uci.edu

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