A 360° Radial Electronic Echoendoscope: A New Technology in Endoscopic Ultrasound (EUS)

Abstract

Background: EUS is performed with radial imaging perpendicular to the endoscope shaft, and lateral imaging parallel to the shaft and biopsy channel. Radial imaging is preferred for some diagnostic and staging purposes because of ease of use as well as the production of a full 360° field of view. Mechanical radial imaging has been used to achieve this perpendicular 360° field. A separate image processor from linear imaging echoendoscopes is required, and radial imaging does not allow Doppler analysis of vascular flow. We tested a prototype electronic radial echoendoscope (Olympus Corp., Tokyo) that featured production of a 360° image with Doppler analysis. Methods: The electronic radial prototype was connected to an Aloka 160 XX processor used for linear electronic array imaging with the Olympus GF-UC140P. We evaluated 26 patients with the prototype. Indications were: evaluation of pancreatic mass(9); esophageal cancer staging(5); gastric MALT lymphoma staging(4); ampullary mass(3); possible choledocholithiasis(4); mediastinal mass evaluation(1). Results: There was no difficulty in passing the prototype instrument into the upper GI tract in all patients. The distal tip measured 14.2 mm which is similar in size to the electronic linear Olympus GF-UC140P, but larger than the 12.8 mm tip on the Olympus GF-UM160 mechanical radial echoendoscope. The prototype instrument was judged to be more ergonomic and comfortable to use than the GF-UM160, though the prototype weighed just 200 grams less. Maneuvering the prototype was comparable to the GF-UM160, with 55° forward oblique optics, and a bending section 130° up, 90° down, and 90° left and right. The 2.2 mm biopsy channel and 140 cm working length allowed passage of pediatric biopsy forceps. The prototype was operated at ultrasound frequencies of 5, 6, 7.5, and 10 MHz. The scanning area was perpendicular to the insertion direction, and the image was 360° at all frequencies. In addition to standard B-mode imaging, the prototype was operated using flow-mode and power-flow mode Doppler. Imaging at all frequencies and Doppler imaging was judged to be excellent. The Doppler imaging was very helpful in distinguishing blood vessels from other structures in the retroperitoneum. Conclusion: A prototype electronic radial echoendoscope has been developed which, for the first time, with electronic imaging produces a full 360° ultrasound image perpendicular to the insertion direction. It allows for ease of anatomical interpretation and excellent Doppler analysis of vascular flow.