Optical Molecular Imaging

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Optical (Molecular) Imaging

• Dr Jeffrey Carson
• jcarson_at_lawsonimaging.ca

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Outline

• Properties of light
• Using light to analyze molecular composition
• Interaction of light with molecules
• Imaging approaches
• Applications
• Caveats

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Why Optical Methods?

• Light is non-ionizing and safe (Vis-NIR)
• Very sensitive - single molecule detection)
• Quantitative e.g. haemoglobin, oxygenation
• Particle sizing, e.g. cell nucleus
• Identify and track molecules of interest -
  targeted contrast agents
• Genetic activity bioluminescence and GFP
• Simultaneous detection of multiple contrast
  agents MCA and spectral un-mixing

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Electromagnetic Spectrum
http//www.britannica.com/ebi/art/print?id70892a
rticleTypeId0
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Beta-Carotene
www.ch.ic.ac.uk/wiki/index.php/ItBeta_Carotene
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Haemoglobin
omlc.ogi.edu/spectra/hemoglobin/index.html
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Beer-Lambert Law
dx
- dI I a c dx
It
I0
I I-dI
It I0 exp(-a c L)
A - log(It / I0) E c L
x
L
E a / 2.303
A - log(T)
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Multicomponent Analysis A EC
(ET E)-1 ET
C
A
c1
e11
e12
e13
e1m
a1
c2
e11
e21
a2
c3
e31
a3

cn
en1
enm
am
n x 1
n x m
m x 1
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Jablonski Diagram
http//web.uvic.ca/ail/techniques/Jablonski.jpg
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Absorbance/Fluorescence SpectraCy7
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Time scales of fluorescence
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Optical Imaging Approaches

• Microscopy
• Mesoscopic
• Macroscopic
• Multispectral-hyperspectral

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Fluorescence Reflectance Imaging

• High sensitivity
• Low cost
• Safe
• Simple to operate

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Fluorescence Reflectance Imaging (FRI)
CCD camera
Laser output gated to image capture
I
f/1
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Example of FRI

• Gated ICCD images (/- 50 ns diffuse laser
  illumination)
• nu/nu mouse SCCVII tumour
• Cy7-2Deoxyglucose - EX 680 nm, EM 780 nm
• Hepatic Metabolism/Excretion
• Tumor targeting

Benaron D.A., Parachikov I.H., Maxim P.G., Carson
J.J.L, Bornhop D. Real-Time, Noninvasive Optical
Imaging and Spectroscopic Monitoring of
Pharmacokinetics and Biodistribution In
Vivo. Second Annual Meeting of the Society for
Molecular Imaging, Aug. 10-15, 2003 in San
Francisco.
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Tracking Cell Lineage
Image courtesy of A. Chamson and D. Hill
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Quantum Dots (QD)s
www.greenspine.ca/en/quantum_dots.html
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Benefits of QDs for FRI

• Fabricated from semiconductor materials
• Highest extinction coefficients
• Brightest fluorescence
• Tunable emission properties (NIR)
• Immune to photobleaching
• Biocompatible (capping and conjugation)
• Can be conjugated to targeting molecules

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Cell tracking with QDs and FRI
Carson, JJL, PG Maxim, N Le, MS Kovacs N
Jones. High sensitivity tumor cell tracking in
vivo using quantum dots. Proceedings of the
International Union of Radio Science (2005).
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FRI and Stray Light
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Optical Scatter and FRI
CCD images Capillary tube (1mm ID) 1 µM ICG EX
780nm EM 830nm 1 Intralipid
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Bioluminescence
www.inspirationline.com/Brainteaser/firefly.htm
earthguide.ucsd.edu/.../acct/lzace/jellyfish.htm
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Figure 1 Normalized bioluminescence spectra
obtained at pH 7.8 with ATP (solid line) and
2-dATP (dashed line)
Biochemical Journal www.biochemj.org
Biochem. J. (1998) 336, 109-113
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Bioluminescence Imaging (BLI)

• Firefly luciferase
• substrate D-luciferin, oxygen and adenosine
  triphosphate (ATP) must be present for reaction
  to occur
• Peak wavelength of glow for naturally occurring
  firefly luciferase is at 560 nm
• No excitation necessary

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Bioluminescence Imaging
Deeply cooled CCD camera
f/1
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Cell homing monitored with BLI
Molecular Imaging of Bone Marrow Mononuclear Cell
Homing and Engraftment in Ischemic
Myocardium. Ahmad Y. Sheikh, Shu-An Lin, Feng
Cao, Yuan Cao, Koen E.A. van der Bogt, Pauline
Chu, Ching-Pin Chang, Christopher H. Contag,
Robert C. Robbins and Joseph C. Wu. Stem Cells
2007252677-2684
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BLI
From European Journal of Nuclear Medicine and
Molecular Imaging Vol. 32, No. 14, December 2005
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BLI Depth Penetration
From European Journal of Nuclear Medicine and
Molecular Imaging Vol. 32, No. 14, December 2005
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BLI Resolution
From European Journal of Nuclear Medicine and
Molecular Imaging Vol. 32, No. 14, December 2005
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From European Journal of Nuclear Medicine and
Molecular Imaging Vol. 32, No. 14, December 2005
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Can Optical Scatter Be Beat?

• Correction algorithms
• Angular domain
• Time domain (Alfano Benaron Wang)
• Limited to small objects, e.g. mice
• 1 cm for ballistic photons
• 4 cm for snake
• Photoacoustic (Oraevsky Kruger Wang)
• Larger objects, e.g. breast
• Suitable for small animal imaging