7086 In-vivo real-time mr-monitoring of endoscopic laser application in the porcine colon.

Abstract

Background: Magnetic resonance (MR) imaging is uniquely sensitive to temperature changes. This preliminary study assessed the feasibility of real-time MR-monitoring of the endoscopic laser application in an interventional scanner. Methods: The procedures were performed with a MRcompatible endoscope (XGIF-MR30C, Olympus, Tokyo, Japan) in two domestic pigs in an interventional 0.5 Tesla MR-system (Signa SP, General Electric Medical, Schenectady, NY, USA) with a 56 cm gap permitting vertical access to the animal. Both the endoscopic view and the MR-images were simultaneously visible on two liquid crystal monitors within the scanner. An external circular balloon filled with gadolinium rendered the endoscope tip visible for MR-imaging. A 10 meter long 365 μm bare laser fiber connected to a Nd:YAG laser located outside the scanner room was inserted through the accessory channel of the endoscope. Laser applications were performed in the rectum (n=5) and the transverse colon (n=1) with energy outputs ranging between 1200 and 1950 Joules delivered at a power of 5 Watts during 4 to 6.5 minutes. The laser induced temperature changes were visualized using a color-coded subtraction technique based on amplitude alterations of T1-weighted gradient echo sequences enabling an image update every 3 seconds in a single axial, sagittal or coronal plane. The animals were sacrificed and the macroscopic coagulation sizes were compared with the lesion sizes seen at real-time MR.Results: The endoscope did not cause any artifacts at continuous MR-imaging. The sizes of the macroscopic coagulation zones of the laser induced lesions were correctly predicted by the color-coded MR-images in a 5 mm lesion in the transverse colon and two 10 mm and 15 mm lesions in the rectum. One lesion was underestimated (5 mm instead of 15 mm) by MR. The lack of a visible pre-treatment lesion inherent with the healthy animal model complicated the accurate MR-localization of the intended laser application sites. This resulted in the failed MR-delineation of two 10 mm laser lesions. Conclusion: Real-time MR-monitoring of endoscopic laser application in an interventional scanner is feasible. This new technique may allow future safe and predictable destruction of gastrointestinal tumors with fewer treatment sessions.