Translational photoacoustic and ultrasound imaging catheter for characterizing gastrointestinal inflammation and fibrosis: a study with a pig model <i>in vivo</i>

Our previous studies demonstrated that a prototype photoacoustic (PA) and ultrasound (US) imaging catheter can differentiate intestinal inflammation and fibrosis. However, its compatibility with clinical endoscopic procedures has not been validated. Here, we present a translational PA-US dual-modality imaging catheter with a reduced diameter to fit the biopsy channel of standard adult colonoscopes and therapeutic upper endoscopes (∼3.7 mm). The catheter integrates an angle-tipped optical fiber (600-µm core) for PA illumination and a miniaturized 48-element ultrasound array operating at a center frequency of ∼9 MHz for signal reception. These components are enclosed in a hydrostatic balloon (12 mm diameter, 15 mm length when fully inflated) to ensure acoustic coupling with the intestinal lumen. The system was upgraded from our previous setup by incorporating a more portable optical parametric oscillator (OPO) laser and a Verasonics imaging platform. The imaging catheter was positioned at the disease locations in a pig model of esophageal fibrosis induced by argon plasma coagulation (APC). Multi-wavelength PA imaging and US imaging were performed to resolve the tissue components. The results demonstrate the catheter's ability to assess inflammation and fibrosis in the gastrointestinal tract during a standard clinical endoscopy procedure.