1. PHOTOACOUSTIC IMAGING TO DETECT TUMOR
HAIFENG WANG
SUBHASHINI PAKALAPATI
VU TRAN
Department of Electrical and Computer Engineering
University of Massachusetts Lowell

2. OUTLINE Introduction Brief Principle of Photoacoustic (PA)
Different Techniques of PAI
Comparison of Various Imaging Techniques
Advantages and Disadvantages
Conclusion
Reference

3. Brief
Conversion of photons to acoustic waves due to absorption and localized thermal excitation.
Pulses of light is absorbed, energy will be radiated as heat.
Heat causes detectable sound waves due to pressure variation.

4. 3D photoacoustic imaging of melanoma in vivo.
The picture is from Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis

5. Introduction of Ultrasound
Ultrasound applications:
Ultrasound in optical fibers
Advantages of the all optical fiber ultrasonic generator-receiver: compact size. Can be used in a limited space such as artery.

6. Principle of photoacoustic
Optical fiber
Energy absorption layer
Laser excitation
Acoustic signals
The light energy is converted into thermal energy via energy absorption layer;
The thermal energy converts into mechanical wave because of thermal expansion;
An acoustic wave is generated.

7. Principle of photoacoustic by gold nanoparticle
Energy absorption layer
Laser excitation
Acoustic signals
Optical fiber
Laser pulse
Sound pulse
Gold
nanoparticle

8. Experimental set up of photoacoustic molecular imaging
Seunghan Ha, Andrew Carson, Ashish Agarwal, Nicholas A. Kotov, and Kang Kim; Detection and monitoring of the multiple inflammatory responses by photoacoustic molecular imaging using selectively targeted gold nanorods , Optical Society of America , 1 March 2011 / Vol. 2, No. 3 / BIOMEDICAL OPTICS EXPRESS 645
The pictureSeunghan Ha, Andrew Carson, Ashish Agarwal, Nicholas A. Kotov, and Kang Kim; Detection and monitoring of the multiple inflammatory responses by photoacoustic molecular imaging using selectively targeted gold nanorods

9. A typical PAT/TAT system
Photoacoustic waves are generated proportional to the distribution of optical absorption in the target, and are detected by an ultrasonic transducer
The picture is from OptoSonics, Inc and Fairway Medical Technologies, Inc.

10. Tumor Detection Using Endogenous Contrast
Xueding Wang, William W. Roberts, Paul L. Carson, David P. Wood and J. Brian Fowlkes, Photoacoustic tomography: a potential new tool for prostate cancer, 2010 :Vol. 1, No. 4 : Biomedical Optics Express 1117

12. Using Exogenous Contrast
3-D photoacoustic imaging
Evans Blue acted as a contrast agent.
Deep lying blood vessels in real tissue samples were imaged at depths of 5 mm and at 9 mm from the plane of detection.
The sensitivity of the technique was proven by photoacoustic detection of single red blood cells upon a glass plate.
C.G.A Hoelen et.al,1998

13. PAImaging Using Gold Nano Particles
Qizhi Zhang et.al,2010

14. Qizhi Zhang et.al.,2010

15. COMPARISON OF DIFFERENT IMAGING TECHNIQUES: ULTRASOUND
Transducer emit ultrasound wave and get signals back from object. D= t.v
Scan volume to get image
Pros & cons: No side effects but low resolution

16. COMPUTED TOMOGRAPHY Use X-ray to collect data
Detector collects the sum of absorption factors in one direction
Using the computing algorithms, the absorption factor of each voxel will be calculated.
3D image will be constructed based on these factors.
Pros & cons: 3D, high resolution but increase the risk of cancer in those exposed

17. MRI
A powerful magnetic field is used to align the magnetization of Hydrogen atoms in the body
Radio frequency fields are used to alter the alignment of this magnetization
Nuclei to produce a rotating magnetic field detectable by the scanner
Pros and Cons: 3D, good contrast but make acoustic noise and may effect on some implants in patients

18. POSITRON EMISSION TOMOGRAPHY
Positron-emitting radionuclide (tracer) is introduced into the body on a biologically active molecule
System detects pairs of gamma rays emitted indirectly by a tracer
Three-dimensional images of tracer concentration within the body are then constructed by computer analysis

19. Photoacoustic Imaging
PAI: Combine advantages of optical (high contrast) and ultrasound (great imaging depth and high resolution):
high optical contrast images
microscale resolution
reasonable penetration depth

20. ADVANTAGES DISADVANTAGES
Ability to detect deeply situated tumor and its vasculature
Monitors angiogenesis
High resolution
Compatible to Ultra Sound
High penetration depth
Non-ionizing/Non-radioactivity
Small size
Easy to clean and maintenance
No acoustic noise
1. Limited path length
2. Temperature dependence
3. Weak absorption at short wavelengths

21. Conclusion PAI has an edge over other imaging modalities.
Though it is in its infancy and there have as yet been no large clinical trials,many initial studies have demonstrated the possibilities for its application in the biomedical field.
Clearly, we should expect to see many exciting clinical applications of PA technologies in the near future.

22. References
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23. THANK YOU