Advantages and disadvantages
The advantages of optoacoustic imaging are:
- Spectral information
The excitation of pressure is by light, so the absorption spectrum of the object can be probed by changing the wavelength of the laser. For example, one could probe with two near-infrared wavelengths and image the oxygenation of blood vessels. Of course one must have some understanding of the light propagation to the object to accurately conduct such absorption spectroscopy, but this is quite achievable.
- Spatial resolution
Despite the diffuse nature of how light propagates to the object, the speed of light is fast so the energy deposition is instantaneous. Once the pressure is generated, the pressure waves are only modestly scattered and attenuated by the tissue and the pressure signals faithfully encode the spatial information about how laser energy was deposited in the tissue.
The disadvantages of optoacoustic imaging are:
- Shielding by strongly absorbing objects
A strongly absorbing object will attenuate the light as it penetrates the object. Only the front edge of the object will generate strong signals, and the remainder of the object will be optically shielded.
- Requires a laser
Currently, a pulsed laser is required and can be costly, but the cost of solid-state lasers is dropping. Other light sources such as a sub-us flash lamp would also work. It is likely that the future will provide inexpensive options for implementing optoacoustics.
Standard optical imaging using diffuse light and optoacoustic imaging are complimentary. Optical imaging provides good information about the conservation of optical energy. Optoacoustic imaging provides good information about edges of objects. Combining these strengths, the assignment of absorbed optical energy specifed by optical imaging to the spatially defined object specified by optoacoustic imaging should allow accurate spectroscopic imaging of an object.
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