Optical coherence tomography and Doppler optical coherence tomography in the gastrointestinal tract

Optical coherence tomography(OCT) is a noninvasive,high-resolution,high-potential imaging method that has recently been introduced into medical investigations.A growing number of studies have used this technique in the field of gastroenterology in order to assist classical analyses.Lately,3D-imaging and Doppler capabilities have been developed in different configurations,which make this type of investigation more attractive.This paper reviews the principles and characteristics of OCT and Doppler-OCT in connection with analyses of the detection of normal and pathological structures,and with the possibility to investigate angiogenesis in the gastrointestinal tract.

Contrast-enhanced endoscopic ultrasonography

Contrast agents are increasingly being used to characterize the vasculature in an organ of interest,to better delineate benign from malignant pathology and to aid in staging and directing therapeutic procedures.We review the mechanisms of action of first,second and third generation contrast agents and their use in various endoscopic procedures in the gastrointestinal tract.Various applications of contrast-enhanced endoscopic ultrasonography include differentiating benign from malignant mediastinal lymphadenopathy,assessment of depth of invasion of esophageal,gastric and gall bladder cancers and visualization of the portal venous system and esophageal varices.In addition,contrast agents can be used to differentiate pancreatic lesions.The use of color Doppler further increases the ability to diagnose and differentiate various pancreatic malignancies.The sensitivity of power Doppler sonography to depict tumor neovascularization can be increased by contrast agents.Contrast-enhanced harmonic imaging is a useful aid in identifying the tumor vasculature and studying pancreatic microperfusion.In the future,these techniques could potentially be used to quantify tumor perfusion,to assess and monitor the efficacy of antiangiogenic agents,to assist targeted drug delivery and allow molecular imaging.

Confocal laser endomicroscopy and immunoendoscopy for real-time assessment of vascularization in gastrointestinal malignancies

Gastrointestinal cancers represent a major cause of morbidity and mortality,with incomplete response to chemotherapy in the advanced stages and poor prognosis.Angiogenesis plays a crucial part in tumor growth and metastasis,with most gastrointestinal cancers depending strictly on the development of a new and devoted capillary network.Confocal laser endomicroscopy is a new technology which allows in vivo microscopic analysis of the gastrointestinal mucosa and its microvascularization during ongoing endoscopy by using topically or systemically administered contrast agents.Targeting markers of angiogenesis in association with confocal laser endomicroscopic examination(immunoendoscopy),as a future challenge,will add functional analysis to the morphological aspect of the neoplastic process.This review describes previous experience in endomicroscopic examination of the upper and lower digestive tract with emphasis on vascularization,resulting in a broad spectrum of potential clinical applications,and also preclinical research that could be translated to human studies.

Autofluorescence imaging and magnification endoscopy

It is well known that angiogenesis is critical in the transition from premalignant to malignant lesions.Consequently,early detection and diagnosis based on morphological changes to the microvessels are crucial.In the last few years,new imaging techniques which utilize the properties of light-tissue interaction have been developed to increase early diagnosis of gastrointestinal(GI) tract neoplasia.We analyzed several "red-flag" endoscopic techniques used to enhance visualization of the vascular pattern of preneoplastic and neoplastic lesions(e.g.trimodal imaging including autofluorescence imaging,magnifying endoscopy and narrow band imaging).These new endoscopic techniques provide better visualization of mucosal microsurface structure and microvascular architecture and may enhance the diagnosis and characterization of mucosal lesions in the GI tract.In the near future,it is expected that trimodal imaging endoscopy will be practiced as a standard endoscopy technique as it is quick,safe and accurate for making a precise diagnosis of gastrointestinal pathology,with an emphasis on the diagnosis of early GI tract cancers.Further large-scale randomized controlled trials comparing these modalities in different patient subpopulations are warranted before their endorsement in the routine practice of GI endoscopy.

Imaging techniques used for the real-time assessment of angiogenesis in digestive cancers

Angiogenesis has a critical role in primary tumor growth and the development of metastases.Several angiogenesis inhibitors were recently developed,being a very attractive target for digestive tumor therapy.However,individualized therapy should not only be based on the pre-treatment imaging evaluation,but also on sensitive monitoring of microvascular changes during treatment.State-of-theart imaging techniques have the potential to visualize and characterize angiogenesis,although the technology and methodologies employed are recent and need further validation.The aim of this series of reviews was to analyze and enhance current knowledge and future perspectives about the real-time assessment of angiogenesis in digestive cancers,used for the longitudinal monitoring of the effects of chemo-radiotherapy(including anti-angiogenic therapies),as well as for the precise targeting of drugs through molecular-based drug-delivery systems.