Thermal Endsoscope for Laparoscopic Surgery: A useful tool for intraoperative cholangiography

Jonathan P Pearl, MD1, Gilmer Blankenship, PhD2. 1University of Maryland School of Medicine, 2University of Maryland

Objective: Bile duct injury occurs in 0.4% of laparoscopic cholecystectomy cases. One method of reducing injury is liberal use of intraoperative cholangiography. Cholangiography is performed in only 10-40% of cases due to a number of factors: the procedure is cumbersome; it is time-consuming; and it is poorly-reimbursed. The objective of our technology is to provide a simpler means of performing intraoperative cholangiography using a thermal endoscope for laparoscopic surgery.

Thermography is widely used in the military and engineering. Image acquisition in thermography relies on detection of temperature differentials. New technology has miniaturized thermal images to make them compatible with laparoscopic techniques.

Description: A Lepton thermal imager measuring 8.5 mm was customized with image acquisition and processing units. The device has two microelectronics components – a PIC32 processor which allows for low level access to the thermal camera and an ARM component which interfaces with the PIC32 and can perform data integration functions. Custom circuit boards were designed for this configuration. The sensor board contains the socket for the Lepton sensor while the control board contains the PIC32 and supporting circuitry. The unit is housed in a custom enclosure created from laser-cut plastic. It is secured to the distal end of the 10 mm laparoscope.

Method of use: Explanted porcine gallbladders were brought to room temperature. Thermal images were obtained by injecting saline at 50 degrees F into the infundibulum of the gallbladder. This created a temperature differential in the biliary tree and permitted acquisition of thermal images.

Simulated gallstones were placed in the infundibulum of the gallbladder and the common bile duct. A bile duct injury was created with a scalpel. Thermal cholangiograms of normal biliary anatomy and pathologic biliary anatomy were obtained.

Results: The gallbladder and common bile were visualized in 4 different specimens. A filling defect representing a 4 mm stone was visible in the neck of the gallbladder. As the cool saline surrounded the stone, the stone retained its thermal signature and was clearly evident. As the stone reached thermal equilibrium with the saline, it became obscured.

A 2 mm lateral bile duct injury was able to be identified using thermal cholangiography. Contrast (saline) was visualized extravasating from the duct. Pinhole injuries in the biliary tree were also evident be visualizing a stream of cool saline emanating from the biliary tree.

Conclusions: This novel thermal endoscope facilitates performance of thermal cholangiograms using a hand-held device and cool liquid as contrast. These images are capable of defining biliary anatomy, detecting filling defects, and identify injuries to the biliary tract.

Future directions: The thermal endoscope will be modified to combine white light and thermal images allowing for overlay of the images. This device will then be tested in a live porcine model. Larger scale animal studies will compare fluoroscopy and thermography for biliary imaging prior to pursuing FDA approval for human use.

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