With the commercial success of portable devices as smartphones, smartwatches, tablets, etc., simple spectral imaging devices (e.g. color cameras and optical sensors) now have a potential global reach. This has led to a tremendous growth in implementing emerging and advanced optical methods through clever adaptations of these portable devices and sensors. Yet with all this progress and promise, only a few optical devices have reached clinical acceptance and significant challenges and barriers remain.
One issue stems from the standard and expected methods used to demonstrate the efficacy, utility and accuracy of these novel optical devices and techniques. Traditionally, these techniques require animal studies to illustrate its potential and impact in addressing specific unmet clinical needs. Use of animal studies in this context, however, is problematic for multiple reasons:
- Costs – these studies require highly trained personnel as well as specialized facilities and equipment to house the animals and ethically conduct the studies.
- Inefficiency – Feasibility and efficacy studies often require large numbers of animals in order to account and isolate normal biological variances from that of the intended effect (disease, affliction, etc.) these devices are designed to detect or monitor.
- Lack of a Gold Standard – Without an independent, quantitative reference or benchmark, there is little opportunity to learn or adapt from these studies.
This project proposes a fundamental shift in early medical device development that replaces animal studies with physical proxies that are constructed specifically to mimic human tissue over a range of pathological states while also covering normal biological variances (such as skin pigmentation, diet, age, etc.). Here, not only can these proxies, otherwise known as “tissue simulating phantoms,” remove the need for animal experiments and all of its associated costs and oversight, but it can also evaluate the optical device’s sensitivity to other known sources of biological variance and thereby provide constructive feedback on the device design and performance. Lastly, these proposed phantoms are inert, stable over time and independently traceable, so these can also provide a Gold Standard to evaluate the device performance not just in its developmental stage, but again when it is seeking clearance for medical use.
Examples of simple phantom constructs: Melanoma proxy (Left), Blood flow at different depths (Right)
Custom fabrication and characterization services are available to both internal and external parties (in either academia or industry). Contact Rolf Saager, rolf.saager@liu.se, to discuss your specific needs and see whether a custom solution can address these needs, timeframe, and budget.
What (general) resources we offer:
Phantom Fabrication Media:
- Silicone (PDMS)
- Advantages: Solid, stackable/interchangeable, Stable over long periods of time (years)
- Disadvantages: Hydrophobic, so non-aqueous dyes must be used to approximate tissue chromophores (e.g. freeze-dried coffee for melanin, yellow food dyes for carotenoids, etc.)
- Common uses: calibration standards, layered tissue structures
- Gelatin
- Advantages: semi-solid, variable mechanical properties (ultrasound), hydrophillic, so aqueous dyes and chromophores can be used, water fraction can be controlled.
- Disadvantages: Stable only for 1-3 days, complex structures are additive, but not interchangeable.
- Common uses: simple structured constructs that require variable water concentrations, aqueous chromophores, water diffusion dynamics
- Liquid
- Advantageous: hydrophillic and allows for dynamic changes (e.g. oxygenation changes)
- Disadvantages: Stable only over hours, emulates only homogeneous media
- Common uses: validation and accuracy of blood oxygenation measurements, dynamics
Quantitative Characterization Systems:
- Spatial Frequency Domain Spectroscopy
- Spectral range: 450-1000nm, at ~1nm spectral resolution
- Measurements on “thick” samples: ~1-3cm
- Quantified properties: absorption and reduced scattering coefficients
- Integrating Sphere measurements using Inverse Adding Doubling
- Spectral range: 450-1000nm, at ~4nm spectral resolution
- Measurements on “thin” samples: ~.5-4mm
- Quantified properties: absorption and reduced scattering coefficients, and potentially scattering anisotropy, g.
