Near Infrared Confocal Imaging of the Human Liver During Ongoing Mini-Laparoscopy: A Newly Developed Rigid Endomicroscope with Increased Imaging Plane Depth

Abstract

Introduction: Histopathology is the gold standard in the diagnosis of liver diseases. However, it can be complicated by sampling error and bleeding and does not allow dynamic tissue monitoring. Confocal laser endomicroscopy (CLE) is a novel imaging modality providing in vivo histology at subcellular resolution during ongoing endoscopy. Previous studies using rigid CLE (Optiscan, Australia) for in vivo liver microscopy have suffered from limited imaging depth (<250 μm) using blue laser light and fluorescein as a contrast agent. Aim of the current study was to evaluate in vivo confocal imaging of the human liver by mini-laparoscopy using a newly developed near infrared (NIR) light probe (Optiscan) in conjunction with indocyanine green (ICG) contrast injection. Methods and Patients: The rigid laparoscopy probe (diameter 6.3 mm) used a 780 nm diode laser for fluorophore excitation. Light emission was detected at >795 nm. Subsurface images at different depths with 0.7 μm lateral resolution at 2-3 sites were generated in real time at 1024×512 pixels (approximating a 1000fold magnification) by gently placing the sterile probe onto the human liver. Targeted liver biopsy of one examined area was performed for histopathological correlation. Results: 22 patients were examined under conscious sedation (44.3yrs (26-67), f: m=6: 16; toxic liver damage n=6, viral n=12, suspected steatosis n=4). Maximum imaging depth was over 350 μm. Typical aspects of normal liver architecture and liver diseases, such as nuclei, sinusoids, fibrous tissue, fatty inclusions and bile ducts could be visualized at high resolution in 21/22 pts. The presence of steatosis and fibrosis was predicted correctly in 81% and 90% of patients, resp., and semiquantitative assessment was possible from images generated in vivo. In accordance with the macroscopic liver aspect, confocal microscopy even detected 2 cases of fibrosis that were not seen in histopathology (suspected biopsy sampling error). ICG fluorescence intensity was dependent on liver function, adding functional information to morphology. No liver damage or severe adverse events were noted upon confocal microscopy. Discussion: The newly developed near infrared confocal probe allowed for the first time in vivo imaging of the human liver with deeper imaging plane depths compared to the so far available blue laser systems. Such an increase of imaging depth could potentially also be used for submucosal imaging of the GI tract. ICG augmented confocal imaging of the human liver is a safe method and allowed in vivo imaging with subcellular resolution of typical aspects of human liver diseases during ongoing mini-laparoscopy.