Acoustic fingerprints of dye-labeled protein submicrosphere photoacoustic contrast agents

Molecular Photoacoustic Contrast Agents: Design Principles & Applications

Photoacoustic imaging (PAI) is a rapidly growing field which offers high spatial resolution and high contrast for deep-tissue imaging in vivo. PAI is nonionizing and noninvasive and combines the optical resolution of fluorescence imaging with the spatial resolution of ultrasound imaging. In particular, the development of exogenous PA contrast agents has gained significant momentum of late with a vastly expanding complexity of dye materials under investigation ranging from small molecules to macromolecular proteins, polymeric and inorganic nanoparticles. The goal of this review is to survey the current state of the art in molecular photoacoustic contrast agents (MPACs) for applications in biomedical imaging. The fundamental design principles of MPACs are presented and a review of prior reports spanning from early-to-current literature is put forth.

Protein Nanospheres: Synergistic Nanoplatform-Based Probes for Multimodality Imaging

No single clinical imaging modality has the ability to provide both high resolution and high sensitivity at the anatomical, functional and molecular level. Synergistically integrated detection techniques overcome these barriers by combining the advantages of different imaging modalities while reducing their disadvantages. We report the development of protein nanospheres optimized for enhancing MRI, CT and US contrast while also providing high sensitivity optical detection. Transferrin protein nanospheres (TfpNS), silicon coated, doped rare earth oxide and rhodamine B isothiocyanate nanoparticles, Si⊂Gd(2)O(3):Eu,RBITC, (NP) and transferrin protein nanospheres encapsulating Si⊂Gd(2)O(3):Eu,RBITC nanoparticles (TfpNS-NP) were prepared in tissue-mimicking phantoms and imaged utilizing multiple cross-sectional imaging modalities. Preliminary results indicate a 1:1 NP to TfpNS ratio in TfpNS-NP and improved sensitivity of detection for MRI, CT, US and fluorescence imaging relative to its component parts and/or many commercially available contrast agents.

Advances in Clinical and Biomedical Applications of Photoacoustic Imaging

IMPORTANCE OF THE FIELD: Photoacoustic imaging is an imaging modality that derives image contrast from the optical absorption coefficient of the tissue being imaged. The imaging technique is able to differentiate between healthy and diseased tissue with either deeper penetration or higher resolution than other functional imaging modalities currently available. From a clinical standpoint, photoacoustic imaging has demonstrated safety and effectiveness in diagnosing diseased tissue regions using either endogenous tissue contrast or exogenous contrast agents. Furthermore, the potential of photoacoustic imaging has been demonstrated in various therapeutic interventions ranging from drug delivery and release to image-guided therapy and monitoring. AREAS COVERED IN THIS REVIEW: This article reviews the current state of photoacoustic imaging in biomedicine from a technological perspective, highlights various biomedical and clinical applications of photoacoustic imaging, and gives insights on future directions. WHAT THE READER WILL GAIN: Readers will learn about the various applications of photoacoustic imaging, as well as the various contrast agents that can be used to assist photoacoustic imaging. This review will highlight both pre-clinical and clinical uses for photoacoustic imaging, as well as discuss some of the challenges that must be addressed to move photoacoustic imaging into the clinical realm. TAKE HOME MESSAGE: Photoacoustic imaging offers unique advantages over existing imaging modalities. The imaging field is broad with many exciting applications for detecting and diagnosing diseased tissue or processes. Photoacoustics is also used in therapeutic applications to identify and characterize the pathology and then to monitor the treatment. Although the technology is still in its infancy, much work has been done in the pre-clinical arena, and photoacoustic imaging is fast approaching the clinical setting.

Photoacoustic generation by multiple picosecond pulse excitation

PURPOSE

The purpose of this work is to demonstrate that higher amplitude of ultrashort laser induced photoacoustic signal can be achieved by multiple-pulse excitation when the temporal duration of the pulse train is less than the minimum of the medium's thermal relaxation time and stress relaxation time. Thus, improved signal-to-noise ratio can thus be attained through multiple-pulse excitation while minimizing the energy of each pulse.

METHODS

The authors used a Michelson interferometer together with a picoseconds laser system to introduce two 6 ps pulses separated by a controllable delay by introducing a path length difference between the two arms of the interferometer. The authors then employed a series of three interferometers to create a pulse train consisting of eight pulses. The average pulse energy was 11 nJ and the temporal span of the pulse train was less than 1 ns.

RESULTS

The detected peak-to-peak amplitude of the multiple-pulse induced photoacoustic waves were linearly dependent on the number of pulses in the pulse train and such a linearity held for different optical absorption coefficients. The signal-to-noise ratio improved when the number of pulses increased. Moreover, nonlinear effects were not detected and no photoacoustic saturation effect was observed.

CONCLUSIONS

The authors have shown that multiple-pulse excitation improves the signal-to-noise ratio through an accumulated energy deposition effect. This method is invaluable for photoacoustic measurements that require ultrashort laser pulses with minimized pulse energy to avoid laser damage.