This is the 1st of a 4-part series introducing Scintica’s newly formed relationship with PhotoSound and introducing the TriTom family of Photoacoustic Fluorescence Tomography (PAFT) systems. In this session, we introduced the fundamentals of both photoacoustic and fluorescence tomography. This session introduced to those who are less familiar with the individual imaging modalities and then review some example images and focus on these imaging techniques’ specific applications. This webinar’s focus was on formulating a basic understanding of the modalities to further understand the TriTom system capabilities throughout the rest of the webinar series.

1. The Basics of Photoacoustic and
Fluorescence Tomography
Aparajita Verma, Ph.D.
Scintica
averma@scintica.com

2. The Basics of Photoacoustic and
Fluorescence Tomography
Aparajita Verma, Ph.D.
Scintica
averma@scintica.com

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Outline
• Motivation and Challenges in Imaging
• Background
• Photoacoustic Tomography
• Fluorescence Tomography
• Photoacoustic and Fluorescence Tomography
• Applications & Current Research
• Take Home
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4. Motivation and Challenges in Imaging

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Various Imaging Modalities
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Weissleder & Pittet. Nature 2008
PAT

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• Safety - Non invasive imaging, non-ionizing
• Optics - High intrinsic contrast
• Lipid
• Water
• Hemoglobin
• Physiology - Endogenous contrast for
functional imaging
• Physics - Molecular structure and composition
• In vivo molecular imaging of disease markers
Motivation for Imaging with Light

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Motivation for Imaging with Light
• In vivo functional imaging analogous to
functional MRI
• In vivo metabolic imaging analogous to PET
• In vivo label-free histologic imaging of cancer
without excision
• In vivo molecular imaging of disease markers
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Current Technologies in Optical Imaging
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Confocal Microscopy Two-Photon Microscopy Optical Coherence
Tomography

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Challenges in Optical Imaging
Challenges
1. Shallow light penetration
2. Low Resolution
Photoacoustic imaging has high
depth penetration up to 7cm
Wang and Yao. Nature Methods 2016
From shallow to deep

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Challenges in Optical Imaging
Challenges of Optical Imaging
• Lack of depth penetration
• Approximation
• Data can be misinterpreted
Advantages of 3D Tomography
• Signal Reconstructed and repositioned into the 3D
representation of the mouse
• Clear details on signal size and localization
LV wang et al., Nature Methods 2016
2D 3D

11. Background –
Photoacoustic Tomography

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The Photoacoustic Effect
Light
Sound
In 1881, Alexander Graham Bell discovered that when light was focused on a selenium cell
within a metal receiver (A in this figure), the cell produced sound
Adapted from A.G. Bell, Am. J. Sci 20 (1880)

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Pulsed Laser
Illumination
Optical Absorption
Thermo-elastic
Expansion
Pressure Waves
Acoustic Detection
Optical Path Sound
Path
Laser Ultrasound
Tissue
Optical Absorber
Photoacoustic Tomography
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Light in Sound out
Probe

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Dean-Ben Chem Soc Rev 2018
Zackrisson and Gambhir, Cancer Res 2014
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Contrast Agents
Endogenous Contrast Exogenous Contrast

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Dean-Ben Chem Soc Rev 2018 15
Spatial Resolution using PAT

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Comparison among Imaging Modalities
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Photoacoustic is a high-performing imaging system compared to other modalities
Karlas et al., Photoacoustics 2019

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Optical Absorption and Oxygenation
• Chromophore: Hemoglobin
• Oxygen Saturation (%sO2) Ratio of
Oxygenated Hbt to Deoxygenated Hbt
• Total Hbt
Oxygenated Hbt + Deoxygenated Hbt
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Advantages
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• Deep tissue imaging
• Ideal for 3D imaging (~300 µm
resolution)
• Anatomical reference (skin, vasculature)

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Clinical Applications of PAT
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Huda et al., Photoacoustics 2020
Zackrisson and Gambhir, Cancer Res 2014

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Growth of Photoacoustic Tomography
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21. Background –
Fluorescence Tomography

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Fluorescent Tomography
• 3D optical non-invasive imaging modality
• Allows to determine the position and
quantity of a fluorescent source in vivo
• Ability to detect deeper fluorescent source
• Obtain functional and biological
information
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Huda et al., Photoacoustics 2020

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Fluorescent Tomography
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Huda et al., Photoacoustics 2020
Fluorescence occur at low energies or longer wavelength

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Steps of Imaging
• Excitation of an injected fluorophore (dye)
• Emission of fluorescent light upon
spontaneous emission of a photon
• Detection of emitted light by a CCD camera
using appropriate filter
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Ghesysens & Mottaghy., Methods, 2009
v

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Fluorescent Imaging and Tags
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Kevin Francis-Perkin Elmer

26. PAFT - Applications & Current Research

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Photoacoustic Fluorescence Tomography
• Innovative and compact
• Simultaneous co-registration of
orthogonal photoacoustic and optical
projection
• High resolution
• Molecular sensitivity
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Huda et al., Photoacoustics 2020

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Schematic Overview of PAFT- Imaging Module
1. Ultrasound Detector Array
2. Animal Holder with Nose Cone
3. Water Tank
4. Heating Pad
5. Orthogonal Excitation Terminal
6. Epi Excitation Terminal
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Huda et al., Photoacoustics 2020

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PAFT Workflow
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Huda et al., Photoacoustics 2020

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Laser Settings
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Huda et al., Photoacoustics 2020
• Laser
Wavelength
• Laser Power

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Camera Settings
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Huda et al., Photoacoustics 2020
•Wait for
trigger
•Exposure time
•Frame rate

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3D reconstructed volumes of PAFT data
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Huda et al., Photoacoustics 2020

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3D reconstructed images of PAFT
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Huda et al., Photoacoustics 2020
A linear relationship
between photoacoustic
signal and optical density
was observed, suggesting
high sensitivity of PAFT

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3D reconstructed images of PAFT
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Huda et al., Photoacoustics 2020
1. Lower Abdomen
2. Skin Vasculature
3. Overlay of 1 & 2
4. Spine with aorta
5. Spiral arteries with
placenta
6. Uterine vasculature
of a pregnant
mouse

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3D reconstructed images of PAFT
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Hemoglobin oxygenation measured using PA data at 100% oxygen supply
Scale bar is 3 mm
Huda et al., Photoacoustics 2020

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3D reconstructed images of PAFT data
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Longitudinal monitoring
of folate uptake in
placental tissue using
FA-PEG-ICG
Scale bar is 3 mm.
Huda et al., Photoacoustics 2020

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3D reconstructed volumes of PAFT data
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0 minute 5 minute 90 minute
Longitudinal monitoring of folate uptake in placental tissue using FA-PEG-ICG
Huda et al., Photoacoustics 2020

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Applications
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Huda et al., Photoacoustics 2020
Neuroscience
Cancer
Metabolism Pregnancy
• Cancer
• Neuroscience
• Metabolism
• Pregnancy
• Reporter Gene Expression
• Cardiovascular
• Tissue Regeneration

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Advantages
• Deep Tissue Imaging
• Ideal for 3D Imaging
• Anatomical Reference
• Reduction in background noise
• Increased sensitivity
• Perfect co-registration of imaging modality
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Take Home
• PAFT- Simultaneous co-registration of
orthogonal photoacoustic and fluorescent
images
• High spatial resolution
• Superior molecular sensitivity
• 3D localization of anatomical, functional and
molecular data
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42. Audience Poll

43. Q&A
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questions that are not addressed during
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following the event.
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