Am I Blue?
30 January 2011 (v. 2.0)
Brian C. Madden, Ph.D.
Department of Dermatology
University of Rochester
Interaction of Light and Tissue
• Physics of light
• Optics of skin
• Models of light transport in skin
• Perceptual influences
Example: The appearance of veins in vivo
Physics of Light
• Particle nature
• Wave nature
The Particle Nature of Light
The Wave Nature of Light
Optical Effects
• Transmission
• Reflection
• Absorption
• Scattering
Transmission (Refraction)
Reflection
Bidirectional Reflectance
Distribution Function
Surface Effects on the BRDF
• Geometry of normals
• Multiple reflections
• Total internal reflection
Polarization
Linear Circular
Fresnel Reflection
Absorption
I0
A log 10 lc
I
Beer’s Law
Chromophores of the Skin
Measured Hemoglobin Spectra
Scattering
• Tyndall
• Rayleigh
• Mie
• Thomson
Structural Blue
Other Sources of Blue
Mammalian Blue
Blue Lesions
3D Models of the Skin
• Uniform slab
Wellman Lab (Anderson & Parrish, 1981)
• Serial reconstruction
Yale (Braverman et al, 1986)
UC Irvine (Smithies et al, 1997)
Hokkaido (Matsumura et al 1999)
The Neapolitan Model of Skin
Models of Light Transport
• Kubelka-Munk diffusion
• Monte Carlo simulation
Every model is the embodiment of a trade between
computational convenience and reality
Kubelka - Munk Diffusion
dJ1
S KM J1 AKM J1 S KM J 2
dz
dJ 2
S KM J 2 AKM J 2 S KM J1
dz
J1 z c11exp- z c12 exp z
J 2 z c21exp- z c22 exp z
AKM 2 AKM S KM
2
Monte Carlo Simulation
3D Models of the Skin
• Uniform slab
Wellman Lab (Parrish & Anderson, 1981)
• Serial reconstruction
Yale (Braverman et al, 1986)
UC Irvine (Smithies et al, 1997)
Hokkaido (Matsumura et al 1999)
Cherry Angioma Model
3D Models of the Skin
• Uniform slab
Wellman Lab (Parrish & Anderson, 1981)
• Serial reconstruction
Yale (Braverman et al, 1986)
UC Irvine (Smithies et al, 1997)
Hokkaido (Matsumura et al 1999)
Port Wine Stain Model
(0.8 MB)
3D Models of the Skin
• Uniform slab
Wellman Lab (Parrish & Anderson, 1981)
• Serial reconstruction
Yale (Braverman et al, 1986)
UC Irvine (Smithies et al, 1997)
Hokkaido (Matsumura et al 1999)
(0,6MB) (0.4MB) (1.4MB)
Optical/Biological/Psychological
Influences
• Absorption
• Scattering
• Anatomy
• Physiology
• Perception
What is physically different
about blue veins?
• Vein depth in dermis diffuses borders
• Vein depth in dermis supports
accumulation of superimposed scatter
• Vein diameters are sufficiently large
to concentrate hemoglobin
• Hemoglobin absorption in veins is
sufficient to visibly reduce total
backscatter at the surface
Perceptual Influences
• Chromatic sensitivity
• Spatial Contrast sensitivity
• HVS nonlinearities
• Simultaneous brightness contrast
• Simultaneous color contrast
Perceptual Examples
Skin Tones
Skin and Edges
Sample image
Do you trust what you see?
Macro view
Should you?
p
Skin Reflectance Samples
H S B
1 1
2 area 22 37 84
3
2 1 24 38 86
2 21 33 79
3 3 21 38 85
Reflectance Differences
B
S S B
Simultaneous Contrast Distribution
Unresolved Issues
• Contributions of hematocrit and oxygenation
• Pressure and flow related sedimentation and clustering
• Erythrocyte scattering model
• Dermatoglyphic patterns and surface hydration
• Fresnel reflection and backscatter contribution
• Diffuse vein segmentation
• Structure of dermal vasculature
Sample image
Is this the same image you viewed 11 slides ago?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Sample image redux
Do you still trust what you see?
Summary and Conclusions
Differential absorption leads to simultaneous contrast
Differential scatter leads to desaturation
Vein depth leads to a diffuse surface profile
Taken together they promote a color contrast effect
Expectation transforms a collection of weak effects
into a substantial perceptual change
Interpreting a diagnostic image
How much should you trust your vision when you need to be right?
So …
am I blue?