Lecture 2 - Center for Biomedical Optics and New Laser Systems

Consider a cup of coffee with cream.Shine a laser onto liquid.The reflectance is R.Now, add some water to the coffee/cream.Does the R increase, decrease, or remain the same?

LLT = e −µ a L

R ≈ e −µ a Ladd a drop ofabsorberΔµ a R 2≈ e −(µ a +Δµ a )L€€LL =⎛−ln⎜R 2⎝ RΔµ a⎞⎟⎠

LRR ≈ 0.3 to 0.8R = e −µ a L≈ e −µ a Aδµ s ’/µ a= e−A⎛3 µ s ' ⎞⎜ +1⎝ µ⎟a ⎠Aµ s ’/µ aA ≈ 7 to 8

Measurement vs properties gridCollectionfibers1.51Collection fiberzzz [cm]0.5r 2r 2= 1.0 cmxSource fiber0Source fiberr 1= 0.3 cmCollection fiber-0.5-1 -0.5 0 0.5 1x [cm]xr 1

diffusion lengthoptical penetrationdepthtransmissioncollected byfiber #1transmissioncollected byfiber #2

lack x = µ s ’ < 10µ ablue = const µ s', red = const µ a10 1 r 1= 0.1 cmr 2= 1.0 cm0.01µ s '1010010 01000T 2[1/cm 2 ]10 -11.0µ a 0.11.010 -210 0 10 2 10 4T 1[1/cm 2 ]

lack x = µ s ’ < 10µ ablue = const µ s', red = const µ a10 1 0.01r 1= 0.3 cmr 2= 1.0 cmµ s '1010010 01000T 2[1/cm 2 ]10 -1µ a 0.11.01.0As r 1 r 2 T 1 ≈ T 2 , so only one measurement,and the grid collapses. One no longer can specifyµ a and µ s ’, just the ratio µ s ’/µ a .10 -210 0 10 2 10 4T 1[1/cm 2 ]

lack x = µ s ’ < 10µ ablue = const µ s', red = const µ a10 110 00.01r 1= 0.6 cmr 2= 1.0 cmµ s '101001000T 2[1/cm 2 ]µ a0.110 -11.01.0As r 1 r 2 T 1 ≈ T 2 , so only one measurement,and the grid collapses. One no longer can specifyµ a and µ s ’, just the ratio µ s ’/µ a .10 -210 0 10 2 10 4T 1[1/cm 2 ]

lue = const µ s', red = const µ a1000r 1= 0.9 cmr 2= 1.0 cmµ s '10010T 2[1/cm 2 ]1.010 110 00.01µ a0.110 -11.0As r 1 r 2 T 1 ≈ T 2 , so only one measurement,and the grid collapses. One no longer can specifyµ a and µ s ’, just the ratio µ s ’/µ a .10 -210 0 10 2 10 4T 1[1/cm 2 ]

µ a = 0.1 cm -1

µ a = 0.1 cm -1

µ a = 0.1 cm -1

µ a = 0.1 cm -1

µ a = 0.1 cm -1

lack x = µ s ’ < 10µ ablue = const µ s', red = const µ a10 1 r 1= 0.1 cmr 2= 1.0 cm0.01µ s '1010010 01000T 2[1/cm 2 ]10 -11.0µ a 0.11.010 -210 0 10 2 10 4T 1[1/cm 2 ]

Oblique R(r)Light is delivered at an angle by a optical fiber (or laser beam). The light is launched a distance of one mfp’ =1/µ s ’ into the tissue at an angle θ. The center of the diffusion process is offset from the point of point of photonentry by Δx. Hence, two measurements (Δx, δ) ----> µ a , µ s ’.row0.0CCD camera with tilted sourceopticalfiberCCDcameraδ ≈ abs(1/slope)slopeΔx1000.00.0col1000.0 2000.0 3000.0 4000.0ag_labvδ =mfp' =1( )3 µ aµ a+ µ s'1µ a+ µ s'µ a= δ 2 mfp'3' 1µ s= − µ amfp'

Oblique R(r)Light is delivered at an angle by a optical fiber (or laser beam). The light is launched a distance of one mfp’ =1/µ s ’ into the tissue at an angle θ. The center of the diffusion process is offset from the point of point of photonentry by Δx. Hence, two measurements (Δx, δ) ----> µ a , µ s ’.0.0CCD camera with tilted sourceopticalfiberCCDcameraδ ≈ abs(1/slope)sloperow1000.00.0col1000.0 2000.0 3000.0 4000.0ag_labvδ =mfp' =1( )3 µ aµ a+ µ s'1µ a+ µ s'µ a= δ 2 mfp'3' 1µ s= − µ amfp'

lack x = µ s ’ < 10µ ablue = const µ s', red = const µ a10 1 0.001Oblique R(r)µ a10 01.00.10.011.0mfp' [cm]10 -110 µ s '10 -210010 -3100010 -2 10 -1 10 0 10 1 10 2delta [cm]

R(r)Reflectance as a function ofsource-detector separation

CameraBeam of lightM total.std example: R std = 0.97Standard reflectance:SpectralonTeflonthick stack of white paper

R std M total M total.std RCameraBeam of lightM total M(r)δM(r)rTest material:Intralipid phantomBiological tissue

mua = 0.1mua = 0

mua = 0.5mua = 0

mua = 0.5mua = 0

δ ≈ -1/slope

R std M total M total.std RM total M(r)δM(r)rM total.std

lack x = µ s ’ < 10µ ablue = const µ s', red = const µ a10 1 0.011.0µ s 'µ a0.11010 0100δdelta1.0100010 -110 -20.2 0.4 0.6 0.8 1RtotalR

Added absorber methodDetector senses total RBeam of lightM stdReflectanceStandardR std

Added absorber methodDetector senses total RBeam of lightM

Added absorber methodBeam of lightDetector senses total RM

Added absorber methodDetector senses total RAdd an absorberBeam of light

Added absorber methodDetector senses total RBeam of lightAdd an absorber

Added absorber methodDetector senses total RBeam of light+ Add an absorber

Added absorber methodDetector senses total RBeam of lightAdd more an absorber

Added absorber methodDetector senses total RBeam of light+ more added an absorber

10.90.8blue = const µ s', red = const µ a∆µ a= 0.00 cm -1101001000R total + added absorber0.70.60.50.40.30.2µ a0.11.00.010.11.000 0.2 0.4 0.6 0.8 1R total

10.90.8blue = const µ s', red = const µ a∆µ a= 0.10 cm -11000100R total + added absorber0.70.60.50.40.30.2µ a0.11.00.010.11.000 0.2 0.4 0.6R total0.8 110

R total + added absorber10.90.80.70.60.50.40.30.2blue = const µ s', red = const µ a∆µ a= 1.00 cm -1µ s ' 1001010000.1µ 0.010.11.01.0 a00 0.2 0.4 0.6 0.8 1R total

10.9blue = const µ s', red = const µ a∆µ a= 10.00 cm -10.8R total + added absorber0.70.60.50.40.310001000.2µ s '0.1101.0 µ 0.0100.11.0a0 0.2 0.4 0.6 0.8 1R total

M = M tissueM std= S T tissueG tissueDS T stdG stdD€

M = M tissueM std= S T tissueG tissueDS T stdG stdD€

M = M tissueM std= S T tissueG tissueDS T stdG stdD€= T tissueG tissueT stdG std= T tissuecalib€

M = M tissueM std= S T tissueG tissueDS R stdG stdDlight beam delivered,detector distant from surface€= R tissueG tissueR stdG std= R tissuecalib€know R std , but don’t knowoptical properties of standard

M = M tissueM std= S T tissueG tissueDS T stdG stdD€delivery and collectionfibers contact surface...= T tissueG tissueT stdG std= T tissuecalib€cannot know T stdwithout knowing optical properties of standard

Non-diffusive light transportexamples:Confocal microscopy (CM)Optical coherence microscopy (OCT)

Reflectance-mode ConfocalMicroscopy

ρe −µz€CM

Coherence gate of OCT provides a 45-fstime slice that rejects ~99.9% of the noise.45 fstimesliceArea undercurve is totaldiffusereflectance R.

ρe −µz€CM

ρe −µz€~1/1000 thCMOCT

R(z)ρ = local reflectivity [-]µ = attenuation [cm -1 ]ρe −µz€

R(z)€ρ = local reflectivity [-]µ = attenuation [cm -1 ]ρe −µz?µ s = scattering coefficient [cm -1 ]g = anisotropy of scattering [-]

a T in= e −a(g)µ s z f Gg

T inT out= e −a(g)µ s z f 2Gag

iso ρ = µ s L f b(g)g

R = T inρT out= ρe −µz f= µ sΔzb(g)e −a(g )µ s 2Gz f

l = 488 nmgmouse tissuesµµ s0.1 µm dia, 2.5% vol. fractionpolystyreneρ

Mietheory

…so why bother with this pedanticpile of purposeless preoccupationwith optical properties?…glad you asked.

Consider a rCLSM or OCT image…

Consider a rCLSM or OCT image…

Consider a rCLSM or OCT image…R(z) @x=1mm

ρ 1e −µ 1 z€E 1ρ 2e −µ 2 z€z1− ∫0E 1= e€µ 1 dzE 2= E€ 1e−z 2∫z1µ 2 dzE 2ρ 1e −µ 1 z€

perturbationnormal

example… characterizing perturbations incardiovascular vessel wallµρ

Osteogenesis Mouse imperfecta skinoim = Mouse Osteogenesis model imperfecta mutationRaviSamathamscanningdown intoskinwith Paul Campagnola, Univ. of Conn. Medical Center

wildtypemutant

RickyWangIn vivo optical properties ofretinal layer and choroidRetina800-nm OCT imagez [mm]ρ [-]

Optical characterization of smooth muscle cellremodeling of collagen gelsDavidLevitzDay 1Day 5

Smooth muscles cells cause the scattering of collagengels to shift to lower anisotropy (g), …as if smaller structures develop that scatterisotropically.

Breast cancer lymph nodeRobertMcLaughlinUniv. ofWesternAustralia

ρ [dimensionless]RobertMcLaughlinUniv. ofWesternAustralia

µ [cm -1 ]RobertMcLaughlinUniv. ofWesternAustralia

Tissue OpticsSteven L. Jacquesjacquess@ohsu.eduhttp://omlc.ogi.eduDepts. of Biomedical Engineeringand DermatologyOregon Health & Science University,Portland OR, USA1. Optical properties2. How to measure opticalproperties3. Light transport4. Complex tissues