Biomedical Engineering Seminar: Molecular/Cellular Photoacoustic Imaging and High Sensitivity Non-Contact Optical Detection to Laser

Biomedical Engineering seminar Tuesday January 27, 2015, MEEM 111; 
Jinjun Xia, Ph.D.,
Title: Molecular/Cellular Photoacoustic Imaging and High Sensitivity

Non-Contact Optical Detection to Laser Photoacoustic (PA) imaging is based on the detection of acoustic signals induced by the distribution of specific optical heterogeneities in targeted objects when irradiated by short laser pulses. Contrast in PA images is primarily determined by optical absorption, while spatial resolution is the same as in ultrasound. The advantages of PA imaging including low cost, non-ionizing operation, and sub-mm spatial resolution at centimeters depth, make it a promising modality to probe nanoparticle-targeted abnormalities in real time at cellular and molecular levels. However, detecting rare cell types in a heterogeneous background with strong optical scattering and absorption remains a big challenge. For example, differentiating circulating tumor cells in vivo (typically fewer than 10 cells/mL for an active tumor) among billions of erythrocytes in the blood is nearly impossible. In this presentation, I will present two newly developed techniques, magneto-motive photoacoustic (mmPA) imaging and laser induced nonlinear ultrasonic/photoacoustic imaging, which can significantly increase the sensitivity and specificity of sensing targeted cells or molecular interactions. The primary advantage of these methods is suppression of background signals through magnetic enrichment/manipulation and laser induced bubbles with gold nanospheres coated emulsion beads with simultaneous PA detection of contrast agent targeted objects. The extension of these techniques and their applications in my future research will be presented. In the instrumentation aspect, the current integrated photoacoustic (PA)/Ultrasonic(US) imaging systems use bulky, low repetition rate lasers to provide sufficient pulse energies to image at depth within the body. However, integrating these lasers with real-time clinical ultrasound scanners is problematic due to their size and cost. In this presentation, I will present an integrated PA/US imaging system that can operate at frame rates >30Hz by employing a portable, low-cost, low-pulse energy, high repetition rate, 1053nm laser and a rotating galvo-mirror system enabling rapid laser beam scanning over the imaging area. This approach is demonstrated for potential applications requiring a few centimeters of penetration. The future improvement of this system will also be presented. Non-contact optical detection for laser generated ultrasound is very attractive for its flexibility.

Current non-contact systems have relatively low sensitivity compared to contact piezoelectric detection. They are difficult to adjust, very expensive, and strongly influenced by environmental noise. Here I will present a new type of a balanced fiber-optic Sagnac interferometer as part of an all-optical laser ultrasonics (LU) pump-probe system for non-destructive testing and evaluation of aircraft composites. This new system eliminates the most of current LU drawbacks by combining a new generation of compact, inexpensive fiber lasers with new developments on fiber telecommunication optics and an optimally designed balanced probe scheme. The performance of this LU system is demonstrated on a composite sample with known defects. A system noise figure of 12.3dB above the Nyquist thermal noise limit is achieved at a rough composite surface. Biomedical applications of this system and its modifications will be presented.