UC San Diego

Photoacoustic imaging is an emerging modality which the combination of ultrasound and optical imaging. The combination of these two techniques has many advantages including no use of ionizing radiation compared to radiography, high-resolution deep tissue imaging versus optical coherence tomography (OCT), and higher contrast and faster scanning compared to MRI. Most current equipment uses sophisticated and complicated OPO lasers with tuning and stability features inconsistent with broad clinical deployment. Low fluence illumination sources can facilitate clinical transition of photoacoustic imaging because they are rugged, portable, affordable, and safe. In this dissertation, I will present characterization of the commercial available light emitting diode (LED) based photoacoustic imaging in terms of system specifications, light source characterizations, photoacoustic spatial/temporal resolution, and penetration. Since low fluence light source based photoacoustic imaging devices generate low image quality, I will propose a denoising method using a multi-level wavelet-convolutional neural network to map low fluence illumination source images to its corresponding high fluence excitation map. This part of dissertation will show qualitative and quantitative improvements up to 2.20, 2.25, and 4.3-fold for peak signal-to-noise ratio (PSNR), similarity structural index measurement (SSIM), and contrast-to-noise ratio (CNR) metrics. Next, after improving and enhancing the low fluence light source photoacoustic imaging systems, we report molecular and functional imaging application for LED-based photoacoustic imaging . We demonstrate detection of reactive oxygen and nitrogen species (RONS) with a near-infrared (NIR) absorbing small molecule (CyBA) and LED-based photoacoustic imaging equipment. CyBA produces increasing photoacoustic signal in response to peroxynitrite (ONOO−) and hydrogen peroxide (H2O2) with photoacoustic signal increases of 3.54 and 4.23-fold at 50 μM of RONS at 700 nm, respectively. We also introduced photoacoustic imaging as a non-invasive method for detecting early tissue damage that cannot be visually observed while also staging the disease using quantitative image analysis. Finally, Here we introduce polyacrylamide (PAA) hydrogel as a candidate material for fabricating stable phantoms with well-characterized optical and acoustic properties that are biologically relevant over a broad range of system design parameters. These phantoms may also facilitate future standardization of performance test methodology.