The hybrid imaging technique called photoacoustic computed tomography (PACT) combines the advantages of optical and ultrasonic imaging while circumventing their primary limitations, according to Mark Anastasio, PhD, and Kun Wang, PhD, of the Department of Biomedical Engineering at Washington University in St. Louis (WUSTL). Also known as optoacoustic tomography, PACT is an emerging soft-tissue imaging modality that uses a reconstruction algorithm.

Conventional PACT reconstruction methods assume the object and surrounding medium are described by a constant speed-of-sound (SOS) value. To accurately recover fine structures, it is necessary to quantify and compensate for SOS heterogeneities during PACT image reconstruction.

In a study article published online in the February 23, 2015 edition of the journal SPIE, authors Anastasio and Wang explain how they are developing advanced image reconstruction methods for PACT and USCT with leading instrument builders.

“In collaboration with Lihong Wang, we are developing transcranial PACT brain imaging and ultrasound-informed methods for small animal PACT imaging applications,” said the authors. “An important goal of this research is to improve PACT image quality by compensating for acoustic aberrations that result from bones and/or gas pockets.”

The team’s current work proposes a shift in how images are reconstructed in the hybrid PACT-USCT approach, seeking to jointly reconstruct the absorbed optical energy density and SOS distributions from a combined set of USCT and PACT measurements, thereby reducing the two reconstruction problems into one. The authors report that this approach has several advantages over conventional approaches, in which PACT and USCT images are reconstructed independently.

Anastasio and Wang are also reportedly developing ultrasound-informed reconstruction methods for imaging both the breast and small animals. More information about their research can be found on the WUSTL Computational Bioimaging Laboratory Web page.

Photo credit: Courtesy of SPIE.orgFigure 1. Left: Photoacoustic computed tomography (PACT) image of a section through a mouse abdomen. Right: Speed-of-sound image of the same slice. (Data acquired by TomoWave Laboratories Inc.)