PHOTO-MEDICINE LAB UNIVERSITY OF WATERLOO
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PARS PLATFORM IMAGING
pHOTOACOUSTIC iMAGING
sURGICAL oNCOLOGY

hISTOLOGY
DERMATOLOGY
eYE DISEASE & bLINDNESS

INTELLIGENT ALGORITHM DEVELOPMENT
ENDOSCOPY
sPECTROSCOPY

DUAL-MODALITY iMAGING
PHARMACEUTICAL DEVELOPMENT
Chromophore Selectivity & Multiwavelength Source Research & Development

PARS® Imaging 

Photon Absorption Remote Sensing (PARS®) microscopy
​

Similar to ultrasound imaging, traditional photon absorption imaging systems require a coupling media, such as water or ultrasound gel, in between the ultrasound detector and the sample. This limits the use of these imaging systems in several clinical applications including wound healing, burn diagnostics, surgery, brain imaging, and many other endoscopic procedures where physical contact is impractical or undesirable as it may cause further damage or infection. There are also significant depth limitations to cellular-resolution, optically-focused, bio-microscopy which are hampering our ability to unravel cellular information at depths beyond ~1mm in living subjects.  Development of a non-contact deep cellular-resolution PA is essential for many clinical and pre-clinical applications.

Dr. Haji Reza recently discovered and pioneered a new technique (P
hoton Absorption Remote Sensing - PARS®) that allows photon absorption imaging without the need for any coupling media. This technique uses all-optical detection to remotely detect the photon absorption signals through air and is capable of providing real-time imaging with cellular resolution. To achieve this, we use two laser beams at different wavelengths. One is visible light used to generate the signal, while the other is near-infrared invisible light used to detect the signal. The energy of these beams are very low and not harmful to tissue. PARS® can provide breath-taking images of blood vessels down to the capillary level and can even visualize individual red blood cells in real-time. PARS® is also capable of visualizing physiologically important parameters such as the oxygen saturation of blood vessels and can be used to distinguish arteries and veins. This is important for various disease including cancer, diabetes, and ischemia. We believe that this technology will have significant impact in visualizing and understanding cancer biology, as well, impacting dermatological application and even enabling functional brain imaging. 
​
Our team has developed several interesting future research pathways for investigating novel PARS
®-based devices.  Some of these include combining concepts from PARS® and OCT, facilitating full depth-resolved optical absorption acquisitions and vastly improving volumetric imaging rates. We are likewise interested in PARS®-based approaches which utilize similar wavelengths for excitation and detection to reduce or even avoid chromatic effects.

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In vivo images of the CAM from a chicken embryo. (a) En-face C-scan PARS® images (b) A snapshot of real-time imaging of capillaries at 30 FPS. (Media 1) (c) PARS® images of a melanoma tumor and surrounding vasculature. Scale bar: 100 μm. Ref: Parsin Hajireza et. al, Non-interferometric photoacoustic remote sensing microscopy. [Nature's Light: Science & Applications 6, e16278  (2017)  https://www.nature.com/articles/lsa2016278]
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Structural and Blood oxygenation mapping within a mouse ear and mouse microvasculature structure. [Optica 5.7 (2018): 814-820.]
Read More:
  1. P. Hajireza, Wei Shi, Kevan Bell, Robert J. Paproski and Roger Zemp, “Non-Interferometric Photoacoustic Remote Sensing Microscopy” Nature’s Light: Science & Applications (2017) 6, e16278; doi: 10.1038/lsa.2016.278 
  2. P. Hajireza, Kevan Bell, Wei Shi, James Shapiro​ and Roger Zemp, Deep Non-Contact Photoacoustic Initial Pressure Imaging, Optica 2018. 
  3. Saad Abbasi*, Martin Le*, Bazil Sonier*, Deepak Dinakaran, Gilbert Bigras, Kevan Bell*, John R. Mackey, Parsin Haji Reza, “All-optical Reflection-mode Microscopic Histology of Unstained Human Tissues”, Scientific Reports (Sept 2019), SREP-19-21757 DOI 10.1038/s41598-019-49849-9
  4. Junjie Yao, “When pressure meets light: detecting the photoacoustic effect at the origin”, News and Views, Nature’s Light: Science & Applications (2017) 6, e17062; doi:10.1038/lsa.2017.62
  5. Kevan L. Bell, Parsin Hajireza, Wei Shi, and Roger J. Zemp, "Temporal evolution of low-coherence reflectrometry signals in photoacoustic remote sensing microscopy," Appl. Opt. 56, 5172-5181 (2017).
  6. Kevan Bell, Parsin Hajireza, and Roger Zemp, "Scattering cross-sectional modulation in photoacoustic remote sensing microscopy," Opt. Lett. 43, 146-149 (2018)
  7. Kevan L. Bell, Parsin Hajireza, and Roger J. Zemp, "Coherence-gated photoacoustic remote sensing microscopy," Opt. Express 26, 23689-23704 (2018)​
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