**8. EUS combined modalities**

There has been recent interest in mucosal imaging (as discussed below), but none has yet been accepted in the standard of care in diagnosing pancreatic cancer. Narrow band imaging technology uses light of specific blue and green wavelengths to enhance the detail of certain aspects of the surface of the mucosa. This technology has made it possible to visualize the wall of the pancreatic duct with the help of a small catheter inserted into the pancreatic duct ('pancreatoscopy') [58].

Optical endomicroscopy using a small diameter probe advanced into the pancreatic duct, at the time of ERCP or EUS, allows real time microscopic imaging of the epithelial lining of the pancreatic duct and pancreatic cyst wall. This allows direct high yield targeted tissue sampling in the region of interest. Two modalities used in this fashion include confocal laser endomi‐ croscopy (CLE) [59;60] and high resolution microendoscopy [59;61]. On the other hand, optical coherence tomography uses infrared light to scan areas beneath the mucosal lining of the duct but the field of view is limited to only a few millimeters making evaluation of the entire pancreatic duct difficult and time consuming [62].

During intraductal ultrasound (IDUS), a mini-ultrasound probe is advanced into the main pancreatic duct to evaluate the wall of the pancreatic duct in indeterminate pancreatic strictures. This allows diagnosis of early pancreatic cancers and outlines margins of IPMNs before surgical resection [63;64]. IDUS is not widely used in United States due to the risk of pancreatitis associated with the procedure and inability to obtain tissue for pathological examination [65]. Another modality using EUS, contrast enhanced EUS, utilizes intravenous contrast to highlight the echogenicity and enhancement of a lesion [66]. In a recent metaanalysis, the pooled sensitivity of contrast-enhanced EUS for the differential diagnosis of pancreatic adenocarcinomas was 94% (95% CI, 0.91-0.95), and the specificity was 89% (95% CI, 0.85-0.92) [67].

EUS elastography allows quantitative analysis of tissue stiffness and helps differentiate pancreatic cancers from benign conditions such as chronic pancreatitis. In one study, the sensitivity and specificity for detecting pancreatic malignancies was 100% and 92.9% respec‐ tively [68]. Three-dimensional reconstruction and spectrum analysis using EUS has shown promising results, and will likely be used more often in the future [69].
