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PHOTOACOUSTIC TOMOGRAPHY: Ultrasonically Breaking through the Optical Diffusion Limit Lihong V. Wang Gene K. Beare Distinguished Professor Optical Imaging Laboratory Departments of Biomedical Engineering, Radiology, and Electrical & Systems Engineering Washington University, St. Louis Email: Photoacoustics@gmail.com OILAB.SEAS.WUSTL.EDU -- 1

Financial Interest Disclosure and Funding Sources FINANCIAL INTEREST Microphotoacoustics, Inc. Endra, Inc. ACTIVE GRANTS NIH/NCI U54 CA136398/NTR Ctr: SLN PA R01 CA134539: Chemo TAT/PAT R01 CA157277: PA endoscopy NIH/NIBIB R01 EB000712: PAM R01 EB008085: DOT/PAT R01 EB010049: Brain TAT COMPLETED GRANTS NIH R21 CA83760: SLT R01 CA71980: UOT R29 CA68562/FIRST: UOT R21 EB000319: MOCT R01 EB000712: PAM R33 CA094267: UOT R01 CA092415: OCT R01 NS46214/BRP: PACT R01 CA106728: OIR NSF BES-9734491/CAREER: UOT DOD Breast Program DAMD17-00-1-0455: TAT Whitaker Foundation RG-96-0221: OIR OILAB.SEAS.WUSTL.EDU -- 2

Outline Motivations and challenges Photoacoustic computed tomography Circular geometry Linear geometry Photoacoustic microscopy Acoustic resolution Optical resolution Discussion and summary OILAB.SEAS.WUSTL.EDU -- 3

Motivations for Biomedical Optics Safety Non-ionizing, non-carcinogenic (hν ~ 2 ev) Physics Molecular interaction Optics Light probes essentially all molecules Nucleic acids: DNA & RNA Carbohydrates: Glucose, cellulose Lipids: Fat Proteins: Oxy- & deoxy-hemoglobin, cytochrome c Others: Melanin, water, dye, nanoparticles Imaging Functional, metabolic, and molecular contrasts Concentration of hemoglobin (angiogenesis) Oxygen saturation of hemoglobin (hyperoxia, normoxia, or hypoxia) Cell nuclei (label-free in vivo histology) Blood flow (Doppler) Metabolic rate of oxygen (hyper-metabolism) Biomarkers: Integrin, VEGF, HER2, etc. Reporter genes Manipulation Controlled activation Optogenetics Nerve stimulation Therapeutics Low systemic toxicity Photodynamic therapy (PDT) Photothermal therapy OILAB.SEAS.WUSTL.EDU -- 4

Fundamental Challenges in in High-resolution Optical Imaging: Diffraction and Diffusion Diffraction (wave phenomenon) Limits the spatial resolution of ballistic imaging (planar, confocal, & two-photon microscopy, optical-coherence tomography). Has been overcome for super-resolution imaging (PALM/STORM). Diffusion (scattering phenomenon) Limits the penetration of ballistic imaging to ~1 mm in skin. Has been overcome for super-depth imaging (PAT). Laser Diffusion limit ~ 1 mm (Transport mean free path) Ballistic decay constant ~ 0.1 mm Diffuse decay constant ~ 10 mm OILAB.SEAS.WUSTL.EDU -- 5

Short-pulsed Laser-induced Initial Photoacoustic Pressure p T 0 a [Initial [Temperature rise] Optical photoacoustic pressure] absorption coefficient in /m OILAB.SEAS.WUSTL.EDU -- 6

Photoacoustic Computed Tomography in in Circular Geometry (1) ns laser pulse (<ANSI limit: e.g., 20 mj/cm 2 ) (2) Light absorption & heating (~ mk) Object 1 mk 8 mbar = 800 Pa! (4) Ultrasonic detection (optical scatter/1000) X Wang et al, Nature Biotech 21, 803, 2003 (3) Ultrasonic emission (~ mbar) OILAB.SEAS.WUSTL.EDU -- 8

(cm) 2.0 Non-invasive Functional Photoacoustic Imaging of of Rat Whisker Stimulation In In Vivo: Hemodynamic Response Left-whisker stimulation Right-whisker stimulation 0.5 0.5 1.0 (cm) 2.0 0 1.0 1.5 1.5 0 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 2.0 (cm) (cm) Min Differential absorption Max 0 Through intact scalp and skull In-plane resolution: 0.2 mm X Wang et al, Nature Biotech 21, 803, 2003 OILAB.SEAS.WUSTL.EDU -- 9

Growth of of Photoacoustic Tomography: Data from Conference on on Photons plus Ultrasound Chaired by by Oraevsky and Wang * * Largest in 20,000-attendee Photonics West OILAB.SEAS.WUSTL.EDU -- 10

Penetration in tissue (mm) Multiscale Photoacoustic Tomography In In Vivo with with Consistent Contrast 10 2 10 1 10 0 10-1 Lateral resolution Axial resolution Depth-resolution ratio = 200! LA-PACT AR- PAMac OR-PAM SM-PAM SW-PAM AR-PAM LA: Linear array PA: Photoacoustic CT: Computed tomography AR: Acoustic resolution Mac: Macroscopy PAM: PA microscopy OR: Optical resolution SM: Sub-micron SW: Sub-wavelength 10-2 Organelle Cell Tissue Organ 10-1 10 0 10 1 10 2 10 3 Resolution ( m) 1. Enable systems biology research at multiple length scales 2. Accelerate translation of microscopic lab discoveries to macroscopic clinical practice W, Nature Phot 3, 503, 2009 W, S Hu, Science 335, 1458, 2012 OILAB.SEAS.WUSTL.EDU -- 11

512-Element Ring Ultrasonic Array J Xia, unpublished. Collaboration: Q Zhu@UConn OILAB.SEAS.WUSTL.EDU -- 12

In In Vivo Whole body Photoacoustic Computed Tomography of of a Mouse Bar: 5 mm Bar: 3 mm In-plane resolution: 100 microns J Xia et al, unpublished. Intestine Colon Spleen Kidney Backbone muscle Intestine Portal vein Vena cave Kidney Spinal cord OILAB.SEAS.WUSTL.EDU -- 13

Hand-held Photoacoustic/Ultrasonic Imaging Probe using Modified Clinical Ultrasound Scanner US probe US image US system US Scan ner DAQ PA image Hand-held PA/US probe Fiber bundles Patient bed C Kim, T Erpelding et al, Biomed Opt Exp 1, 278, 2010 Collaboration: Philips Research OILAB.SEAS.WUSTL.EDU -- 15

Penetration in tissue (mm) 10 2 10 1 10 0 10-1 10-2 Multiscale Photoacoustic Tomography In In Vivo with Consistent Contrast Lateral resolution Axial resolution Depth-resolution ratio = 200 LA-PACT AR- PAMac OR-PAM SM-PAM SW-PAM AR-PAM Organelle Cell Tissue Organ 10-1 10 0 10 1 10 2 10 3 Resolution ( m) W, Nature Phot 3, 503, 2009 W, S Hu, Science 335, 1458, 2012 LA: Linear array PA: Photoacoustic CT: Computed tomography AR: Acoustic resolution Mac: Macroscopy PAM: PA microscopy OR: Optical resolution SM: Sub-micron SW: Sub-wavelength OILAB.SEAS.WUSTL.EDU -- 16

0 In In Vivo Photoacoustic Image of of Human Breast: Pre-Injection of of Methylene Blue 20 Depth (cm) 1 2 3 4 5 15 10 5 Tumor 6 0-1 0 1 Azimuth (cm) Erpelding, Garcia-Uribe, Jiang, Appleton, Margenthaler et al, unpublished. Collaboration: Philips Research Wavelength: 650 nm Laser fluence: 10 mj/cm 2 (1/2 ANSI safety limit) OILAB.SEAS.WUSTL.EDU -- 17

In In Vivo Photoacoustic Tomography of of Sentinel Lymph Node (SLN) in in Human Breast: Post Injection of of Methylene Blue Photoacoustic (PA) Ultrasonic (US) Radiographic US PA Clip Erpelding, Garcia-Uribe, Appleton, Margenthaler et al, unpublished. Collaboration: Philips Research OILAB.SEAS.WUSTL.EDU -- 18

Dark-field Confocal Photoacoustic Microscopy: 3 mm Penetration at at 50-MHz Ultrasonic Frequency z y x Motor driver Translation stages Conical lens Amplifier Tunable laser Photodiode Nd:YAG pump laser Optical illumination Ultrasonic transducer Sample holder Base AD Computer Mirror Heater & temperature controller K Maslov et al, Optics Letters 30, 625, 2005 H Zhang, K Maslov et al, Nature Biotech 24, 848, 2006 H Zhang, K Maslov, W, Nature Protocols 2, 797, 2007 Dual foci Sample Annular illumination with a dark center OILAB.SEAS.WUSTL.EDU -- 20

In In Vivo Photoacoustic Microscopy of of Human Skin and and Melanoma Photo En face PAM 5 PAM of 4 melanoma B-scan PAM @ 584 nm 3 2 1 1 mm Epiderm.-derm. junction 1 Dermis 2 Stratum corneum Subpapillary plexus Epidermis 3 4 5 1 mm C Favazza et al, J Biomed Opt 16, 016015, 2011 W Xing, unpublished. Collaboration: L. Cornelius OILAB.SEAS.WUSTL.EDU -- 22

In InVivo VivoMolecular MolecularPhotoacoustic PhotoacousticImaging Imagingof ofb16 B16Melanoma Melanoma in inaarat RatUsing UsingTargeted TargetedGold GoldNanocages Nanocages(AuNCs) (AuNCs) 0h 3h 6h 50 40 30 2mm Tumor PEG-AuNCs 13 ± 1 (%) at 6 hr 3 h Tumor 0h Tumor 20 10 6h Tumor 0 Increase in PA signal [%] [Nle4,D-Phe7]-α-MSH-AuNCs 38 ± 3 (%) at 6 hr (3X control) Sensitivity : ~ 5000 AuNCs / voxel C Kim et al, ACS Nano 4, 4559, 2010. Nature Mat 8, 935, 2009. Collaboration: Y Xia MSH: melanocytestimulating hormone OILAB.SEAS.WUSTL.EDU -- 23

Photoacoustic Endoscopy of of Rabbit Esophagus In In Vivo Ultrasonic transducer Scanning mirror Magnets N S S N Optical fiber Micromotor Lung Trachea Photoacoustic Ultrasonic J Yang, Nature Med, accepted J Yang et al, Optics Letters 34, 1591, 2009 Collaboration: Zhou & Shung @ USC Axial resolution: 55 microns Lateral resolution: 80 microns Diameter of probe: 3.8 mm or 2.5 mm Ultrasonic frequency: 36 MHz OILAB.SEAS.WUSTL.EDU -- 24

CL PH OL DL IP AL Optical Resolution Photoacoustic Microscopy: 1.2 mm Penetration UT Light Sound Light transmitting & sound reflecting interface K Maslov et al, Optics Letters 33, 929, 2008 CL: Condenser lens PH: Pinhole OL: Objective lens UT: Ultrasonic transducer DL: De-aberrating lens IP: Isosceles prism AL: Acoustic lens Optic NA = 0.1 Lateral resolution = 2.6 µm Acoustic NA = 0.45 Center f ~ 85 MHz Axial resolution < 15 µm OILAB.SEAS.WUSTL.EDU -- 26

Penetration in tissue (mm) 10 2 10 1 10 0 10-1 10-2 Multiscale Photoacoustic Tomography In In Vivo with Consistent Contrast Lateral resolution Axial resolution Depth-resolution ratio = 200 LA-PACT AR- PAMac OR-PAM SM-PAM SW-PAM AR-PAM Organelle Cell Tissue Organ 10-1 10 0 10 1 10 2 10 3 Resolution ( m) LA: Linear array PA: Photoacoustic CT: Computed tomography AR: Acoustic resolution Mac: Macroscopy PAM: PA microscopy OR: Optical resolution SM: Sub-micron SW: Sub-wavelength W, Nature Phot 3, 503, 2009 W, S Hu, Science 335, 1458, 2012 OILAB.SEAS.WUSTL.EDU -- 27

In In Vivo Optical-Resolution Photoacoustic Microscopy of of Mouse Ear: 2.6 Micron Lateral Resolution 500 µm Capillary bed 50 µm 5 mm x 5 mm x 0.45 mm 1 Oxygen saturation of hemoglobin 0 RBCs S Hu et al, Optics Lett 36, 1134, 2011 OILAB.SEAS.WUSTL.EDU -- 28

In In Vivo Photoacoustic Microscopy of of Human Finger Cuticle 1.0 Eponychium 0.5 mm so 2 Capillary loop 0.3 Cross section 1 mm S Hu et al, unpublished OILAB.SEAS.WUSTL.EDU -- 29

Photoacoustic Microscopy of of Single Red Blood Cells and Oxygen Release In In Vivo 1 Hz B-scan 20 Hz B-scan Hemoglobin (20 volumetric images/second) Oxygen saturation of hemoglobin (so 2 ) LD Wang & K Maslov et al, unpublished. OILAB.SEAS.WUSTL.EDU -- 30

Time-reversed Ultrasound-encoded (TRUE) Optical Focusing 1. Virtual guide star 2. Arbitrary focal position 3. Label free 4. Applications in Imaging (fluorescence) Sensing (oxygenation) Manipulation (opto-genetics) Therapy (photodynamic therapy) PCM: phase conjugate mirror DC: un-modulated light TR: time-reversed UE: ultrasonic encoding X Xu et al, Nature Photonics 5, 154, 2011 OILAB.SEAS.WUSTL.EDU -- 32

Conclusions 1. Optical excitation and ultrasonic detection integrated 2. Diffusion limit (~1 mm) broken: depths up to 7 cm reached 3. Single capillaries, cells, and organelles resolved in vivo (220 nm res) 4. Multiscale imaging achieved by scaling depth and resolution 5. Background-free detection built-in (no absorption, no signal) 6. Sensitivity to optical absorption maximized to 100% 7. Either non-fluorescent or fluorescent pigments detected 8. Multiple chromophores resolved spectrally 9. Functional imaging derived from endogenous chromophores 10. Molecular imaging enabled by targeted contrast agents 11. Reporter genes imaged 12. Doppler imaging of flow demonstrated 13. Data acquired fast: 1 s for 1.5 mm depth; 100 s for 15 cm depth 14. Speckle artifacts avoided 15. Non-ionizing radiation used 16. Costs kept relatively low OILAB.SEAS.WUSTL.EDU -- 33

Challenges Ultrasound reflection by gas cavities and bones Ultrasound attenuation by lung parenchyma Ultrasound attenuation and aberration by adult skulls Insensitivity to optical scattering contrast Light delivery at even greater depths Scattering does not destroy photons Ballistic decay constant (1/e) ~ 0.1 mm Diffuse decay constant (1/e) ~ 1 cm Absorption decay constant (1/e) ~ 10 cm OILAB.SEAS.WUSTL.EDU -- 34

Credit to to Lab Members CURRENT Alejandro Garcia-Uribe Amos Danielli Amy Winkler Arie Krumholz Bin Huang Bin Rao Chi Zhang Chris Favazza Da Kang Yao Guo Li Haixin Ke Honglin Liu Joon Mo Yang Jun Xia Junjie Yao Konstantin Maslov CURRENT Lidai Wang Liming Nie Puxiang Lai Rameez Chatni Robert Berry Song Hu Wenxin Xing Xiao Xu Xin Cai Yan Liu Yu Wang Yuchen Yuan Yuta Suzuki Zhen Jiang Zhun Xu Zijian Guo RECENT ALUMNI Changhui Li Chul-Hong Kim Hao Zhang Hui Fang Kwanghyun Song Liang Song Manojit Pramanik Minghua Xu Roger Zemp Xueding Wang Yuan Xu BME Dept Washington U OILAB.SEAS.WUSTL.EDU -- 35

Source codes 2007 Chapters 1. Introduction to biomedical optics 2. Single scattering: Rayleigh theory and Mie theory 3. Monte Carlo modeling of photon transport 4. Convolution for broad-beam responses 5. Radiative transfer equation and diffusion theory 6. Hybrid model of Monte Carlo method and diffusion theory 7. Sensing of optical properties and spectroscopy 8. Ballistic imaging and microscopy 9. Optical coherence tomography 10. Mueller optical coherence tomography 11. Diffuse optical tomography 12. Photoacoustic tomography 13. Ultrasound-modulated optical tomography Homework solutions provided for instructors Joseph W. Goodman Book Writing Award OILAB.SEAS.WUSTL.EDU -- 36

JOB OPENINGS: Postdoctoral Predoctoral Recorded presentations available on our web Please visit our web at http://oilab.seas.wustl.edu OILAB.SEAS.WUSTL.EDU -- 37

Scan the QR Codes with a Smart Phone Web: http://oilab.seas.wustl.edu vcard: LHWANG@WUSTL.EDU OILAB.SEAS.WUSTL.EDU -- 38