PHOTOACOUSTIC IMAGING TO DETECT TUMOR

HAIFENG WANGSUBHASHINI PAKALAPATIVU TRAN

Department of Electrical and Computer EngineeringUniversity of Massachusetts Lowell

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OUTLINE

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

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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.

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3D photoacoustic imaging of melanoma in vivo.

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The picture is from Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis

Infrasound Acoustic Ultrasound

20Hz 20KHz 2MHz 200MHz

Low bass notes Medical and DestructiveDiagnostic and

Nondestructive Testing (NDT)

Ultrasound applications:

Ultrasound in optical fibers

Introduction of Ultrasound

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.

Principle of photoacoustic by gold nanoparticle

Optical fiber

Energy absorption layer

GoldnanoparticleLaser pulse Sound pulse

Laser excitation

Acoustic signals

Experimental set up of photoacoustic molecular imaging

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

A typical PAT/TAT system

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The picture is from OptoSonics, Inc and Fairway Medical Technologies, Inc.

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

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

PAImaging Using Gold Nano Particles

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Qizhi Zhang et.al,2010

14Qizhi Zhang et.al.,2010

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

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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

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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

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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

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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

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ADVANTAGES1. Ability to detect deeply situated

tumor and its vasculature2. Monitors angiogenesis3. High resolution4. Compatible to Ultra Sound5. High penetration depth6. Non-ionizing/Non-radioactivity7. Small size8. Easy to clean and maintenance9. No acoustic noise

1. Limited path length2. Temperature dependence3. Weak absorption at short

wavelengths

DISADVANTAGES

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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.

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THANK YOU

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