Photoacoustic Imaging in Gastroenterology: Advances and Needs

Abstract

Gastroenterologists routinely use optical imaging and ultrasound for the minimally invasive diagnosis and treatment of chronic inflammatory diseases and cancerous tumors in gastrointestinal tract and related organs. Recent advances in gastroenterological photoacoustics represent combination of multispectral and multiscale photoacoustic (PA), ultrasound (US), and near-infrared (NIR) fluorescent imaging. The novel PA endoscopic methods have been evaluated in preclinical models using catheter-based miniature probes either noncontact, all-optical, forward-viewing probe or contact, side-viewing probe combined with ultrasound (esophagus and colon). The deep-tissue PA tomography has been applied to preclinical research on targeted contrast agents (pancreatic cancer) using benchtop experimental setups. The clinical studies engaging human tissue ex vivo have been performed on endoscopic mucosal resection tissue with PA-US tomography system and intraoperative imaging of pancreatic tissue with PA and NIR fluorescence multimodality. These emerging PA methods are very promising for early cancer detection and prospective theranostics. The noninvasive transabdominal examination with PA-US handheld probe has been implemented into clinical trials for the assessment of inflammatory bowel disease. To facilitate translational and clinical research in PA imaging in gastroenterology, we discuss potential clinical impact and limitations of the proposed solutions and future needs.

3D Ultrasound-Guided Photoacoustic Imaging to Monitor the Effects of Suboptimal Tyrosine Kinase Inhibitor Therapy in Pancreatic Tumors

“…We believe that these changes may become even more pronounced through intravenous delivery of the therapies, as oral delivery may not produce as drastic volumetric reductions as anticipated and seen in previous studies ( 76 ). Furthermore, recent developments in clinical translation of PAI ( 77 – 79 ) including portable real-time LED-based PAI systems for cancer applications ( 80 ) and endoscopic PAI systems ( 81 – 83 ) show promise toward employing photoacoustic monitoring of tumor response to treatment not only for pancreatic tumors but also for other solid tumors undergoing neoadjuvant treatment. Overall, given the exponential rise in the technical advances and biological applications of PAI over the past decade, the results presented in this study further support its utility as a useful tool to monitor cancer treatment response, especially in imaging response of suboptimal therapies.…”

Peptide-Based Nanoassemblies in Gene Therapy and Diagnosis: Paving the Way for Clinical Application

“…The choice of diagnostic modality depends on many factors, such as the underlying pathological condition, the tissue/organ, and the intended application. For example, optical and photoacoustic imaging are suitable for studying superficial structures, endoscopy is a powerful tool for examining the walls and internal organs of the gastrointestinal tract and digestive diseases [181], non-invasive MRI, PET, and CT can be applied for whole-body imaging [182], while ultrasound is a rapid and low-cost method of examining the body's internal organs [183].…”

“…Superfibril formation through co-assembly of racemic mixtures (Mito-Rac) was observed inside mitochondria, resulting in disrupted mitochondria both in vitro and in tumor xenografts [192]. In Another NIR dye-labeled peptide (P18-PLGVRGRGD) forming nanofibers at tumor sites was used in photoacoustic imaging (PA) [181,[189][190][191]. This peptide comprised an RGD for tumor targeting and a sequence (PLGVRG) that was cleaved by gelatinase overexpressed in the tumor microenvironment.…”

“…Another NIR dye-labeled peptide (P18-PLGVRGRGD) forming nanofibers at tumor sites was used in photoacoustic imaging (PA) [ 181 , 189 , 190 , 191 ]. This peptide comprised an RGD for tumor targeting and a sequence (PLGVRG) that was cleaved by gelatinase overexpressed in the tumor microenvironment.…”

Deep-learning-based image super-resolution of an end-expandable optical fiber probe for application in esophageal cancer diagnostics

“…In recent years, in-vivo optical microscopy techniques, such as confocal laser endomicroscopy (CLE) and high-resolution microendoscopy (HRME), have been applied to visualize the nuclear morphology of the esophageal epithelium and assist in differentiating neoplasia from benign tissue. 3 , 5 – 7 In contrast to conventional tissue biopsies and histopathologic analysis, these optical techniques are non-invasive and able to provide real-time results. However, microendoscopy is currently limited by its small FOV (the average diameter of a probe is 0.3 mm) that hinders it from imaging larger tissue areas.…”