Nanoparticles as Contrast Agents for Optoacoustic Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 107

5

NaNoparticles as coNtrast
ageNts for optoacoustic
imagiNg

Anton V. Liopo and Alexander A. Oraevsky
TomoWave Laboratories, Inc., Houston, TX, USA

5.1 iNtroductioN

Optoacoustic (OA) imaging is a noninvasive biomedical imaging modality that
combines spectral selectivity and high optical contrast based on strong absorption of
laser pulses by specific molecules and nanoparticles with the high resolution of ultra-
sound imaging [1-3]. OA imaging is in vivo imaging technology [4, 5], where short
light energy pulses are absorbed by tissue and converted to thermal energy. The
thermal energy is subsequently converted to ultrasound signals that allow high-reso-
lution whole-body imaging. The term “OA imaging” used in this chapter may be
replaced with the broader terms of either photoacoustic (PA) or thermoacoustic
imaging, meaning that optical photons can be replaced, in principle, with photons
having any electromagnetic energy. Only in the optical spectral range from red to
near infrared (NIR), also known as the window of relative tissue transparency [6, 7],
can one achieve a useful compromise between strong resonance absorption and deep
penetration of electromagnetic radiation into tissues. Hence, lasers emitting in the
spectral range from approximately 650 to approximately 1700 nm are normally used
for generation of OA signals (and images) due to the relatively weak absorption of
biological tissues in this spectral range.