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Objective:
Interventional radiologists (IR) frequently use percutaneous, image-guided procedures with minimal side-effects. However, the extent of procedures possible with current IR techniques is limited to the resolution of CT and ultrasound imaging, versus the higher resolution of optical imaging. In addition, saline hydrodissection is limited by gravity and rapid dissipation limiting thermal protection and true retraction. We propose using image-guided injection of a clear hydrogel to enhance the scope of IR procedures by allowing direct endoscopic visualization while enabling durable focal hydrodissection. This study demonstrates the initial utility of gel endoscopy (geloscopy) to generate durable operative spaces for IR procedures ranging from enteric access to tumor ablation.

Materials and Methods:
Multiple biocompatible GRAS (generally recognized as safe) polymers were iteratively tested to develop a hydrogel that is reproducible, optically clear, and viscous. The hydrogel was assessed for shear thinning, absorbance, biocompatibility, injectability, viscosity, tensile strength, and insulation. The optimal compounds were then used in four in vivo terminal porcine experiments approved by the institutional IACUC. Optical clarity was first assessed ex vivo by injecting the gel through a percutaneous sheath into the subcutaneous space and then pleural cavity. The gel was then injected in vivo into the peritoneal cavity to facilitate the placement of a G-tube under ultrasound and CT guidance. Portable CT scans were obtained before and after the procedures to confirm adequate tube placement, demonstrate a stable intraperitoneal pocket of hydrogel, and assess for immediate complications.

Results:
A hydrogel formulation was created using biocompatible GRAS (generally recognized as safe) polymers, which demonstrated optical clarity, injectability through an 18G x 20-cm Chiba needle, and optimal viscosity for holding shape under stress. The initial hydrogel and its subsequent iterations were used in four successive porcine experiments. The in vivo experiments demonstrated formation of stable, optically clear subcutaneous and pleural cavity pockets in which a portable endoscopy camera was inserted and easily manipulated through a 10 French sheath. The gel maintained position for over one hour. In the abdominal cavity, 80 mL of the gel was injected adjacent to the stomach which held its shape along the greater curvature significantly longer than saline alone. Subsequent geloscopy enabled direct visualization of enteric tube placement without the need for insufflation of the stomach or the peritoneal cavity.

Conclusion:
Geloscopy is a platform technology that can improve CT or ultrasound guided IR procedures by adding components of laparoscopy and endoscopy. This can extend the scope of IR to include optical imaging resulting in benefits ranging from controlled focal hydrodissection for ablations to direct visualization of enteric access for use in gastrostomy or jejunostomy tube placement.