Crohn?s disease (CD) produces chronic intestinal bowel damage and stenosis in the majority of patients. Accurate characterization of these strictures is critical, as acute inflammatory strictures can respond to anti- inflammatory therapy, but chronic strictures, which include both fibrosis and muscular hypertrophy, require surgical resection. Intestinal fibrosis is an important predictor of future intestinal obstruction and penetrating complications of CD. The standard diagnostic procedure for CD is endoscopic biopsy, in which small pieces of tissue are removed from the innermost layer of the intestine for histopathology. Due to limited sampling depth, endoscopic biopsy does not assess fibrosis in submucosal and muscular layers. Conventional non-invasive modalities, such as MRI, CT and ultrasound (US), have shown limited sensitivity for intestinal fibrosis. Intestinal strictures are often a mixture of chronic fibrosis and acute inflammation, which are respectively correlated with increased collagen and hemoglobin in tissues, which act as molecular markers of distinct CD pathologies. In addition, extensive previous studies of compressional US elastography have documented that increased stiffness is a mechanical marker of chronic fibrotic strictures. These molecular and mechanical markers complement each other, providing orthogonal diagnostic information. A diagnostic imaging procedure that can simultaneously assess these phenotypes of CD is highly desirable for personalized therapeutic planning and improved patient outcomes. Our preliminary studies in animals in vivo, human tissue samples ex vivo, and in human subjects have validated that the molecular and mechanical markers of CD stricture pathology can be characterized by advanced photoacoustic (PA)-US dual modality imaging approaches, including spectroscopic PA imaging, US elastography, and our recent innovation of strain-PA imaging. An imaging catheter probe compatible with standard ileocolonoscopy procedures, integrating all these imaging technologies, has been developed and validated with tissue samples and in animals in vivo. Encouraged by our exciting preliminary results, we propose to fill this long-standing prognostic gap with accurate characterization of molecular and mechanical phenotypes of CD. In the proposed project, we will first objectively assess the sensitivity and specificity of each molecular and mechanical marker quantified by the proposed imaging technology through experiments on clinically relevant rabbit models. In addition, to pave the road to clinical translation, we will examine the feasibility and identify the limitations of the proposed technique for use during clinical ileocolonoscopy via a pilot study in CD patients. The success of this project will advance these molecular and mechanical biomarkers of distinct pathologies in CD strictures to practical clinical measurement with PA-US dual modality endoscopic imaging, enabling accurate prognostic assessment and treatment monitoring in CD.
The well-established technologies of spectroscopic photoacoustic imaging and ultrasound elastography, and our novel PA-US imaging technology are promising tools for the measurement of molecular and mechanical biomarkers of intestinal inflammation and fibrosis. The proposed endoscopic photoacoustic-ultrasound dual modality imaging procedure will, for the first time, facilitate the comprehensive assessment of intestinal inflammation and fibrosis in Crohn?s disease intestinal strictures.
