Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Medical Biophysics

Supervisor

Dr. Jeffrey Carson

Abstract

Photoacoustic imaging is a hybrid imaging technique that combines many of the merits of both optical and ultrasound imaging. Photoacoustic imaging (PAI) has been hypothesized as a technique for imaging neonatal brain. However, PAI of the brain is more challenging than traditional methods (e.g. near infrared spectroscopy) due to the presence of the skull layer. To evaluate the potential limits the skull places on 3D PAI of the neonatal brain, we constructed a neonatal skull phantom (~1.52-mm thick) with a mixture of epoxy and titanium dioxide powder that provided acoustic insertion loss (1-5MHz) similar to human infant skull bone. The phantom was molded into a realistic infant skull shape by means of a CNC-machined mold that was based upon a 3D CAD model. Then, propagation of photoacoustic (PA) signals through the skull phantom was examined. A photoacoustic point source was raster-scanned within the imaging cavity of a 128-channel PAI system to capture the imaging operator with and without the intervening skull phantom layer. Then, effects of the skull phantom on PA signals and consequently on PA images was evaluated in detail. We captured 3D photoacoustic images of tubes filled with indocyanine green (ICG). The system was capable of reconstructing an image of a tube filled with 50 μM ICG in presence of the skull. Image processing method was developed to correct photoacoustic images from the effects of the skull. The method was tested on an image of an object captured through the skull, which demonstrated that the effects of the skull on PA images are predictable and modifiable.

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