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Biomedical Imaging and Instrumentation

Biomedical Imaging and Instrumentation - Poster Session E

Poster F9 - Ultrasound and Photoacoustic Guided Gastrostomy to Prevent Colonic Injury

Saturday, October 26, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Gastrostomy tube (G-tube) placement is a common surgical procedure, usually guided by fluoroscopy. In the United States, over 160,000 cases are reported annually, with pediatric patients accounting for 20% of these cases. The lack of non-ionizing image guidance in G-tube placement impedes the accurate identification of tissue types along the needle's path, thereby increasing the risk for pediatric patients. The blind insertions and heightened risks of complications, such as abdominal bleeding from colon perforations, have led surgeons to predominantly prefer laparoscopic-assisted percutaneous endoscopic gastrostomy (PEG) which reduced the rate of colonic injury, but it requires intra-abdominal access. Photoacoustic (PA) imaging is an emerging non-invasive imaging modality capable of obtaining optical properties for tissue characterization, giving it the potential to distinguish the stomach and transverse colon. The stomachs and transverse colon’s similar optical property, dominated by blood, limits the capability of PA to distinguish both organs. Using an externally administered bio-safe contrast agent (indocyanine green) in the transverse colon allows for PA detection and differentiation of the colon and stomach. Combined ultrasound and photoacoustic imaging limits the risk of hollow viscus injury without needing a laparoscopic procedure and/or exposing patients to ionizing X-ray radiation.

Materials and

Methods:  A feasibility study was conducted using colon- and stomach-mimicking phantoms. The colon was coated with contrast agent, IR-806 indocyanine green (ICG), while the stomach remained with natural blood contrast. Mimicking the dual-needle technique in PEG, two puncture needles were position 1 cm each from the internal surface of the stomach and the external surface of the colon. Two optical fibers were simultaneously coupled with imaging wavelengths, 532 and 800 nm (corresponding to the peak absorbances of blood and ICG). The pulse energy of approximately 150 μJ was used. Co-registered ultrasound (US) and PA images were acquired in real-time as the two fibers moved closer to the tissue boundaries. While navigating the puncture needle, the difference between acquired PA signals at two wavelengths was used to identify the tissue in front of the needle.
We also quantified the sensitivity of PA imaging for detecting a contrast agent-coated colon. The minimum concentration required for detection and the maximum detectable range were assessed by varying the ICG concentration and distance between the tube and the needle.
Furthermore, the proposed USPA-guided G-tube placement method was evaluated ex-vivo using excised rabbit transverse colon and stomach tissues. The colon was coated with food graded ICG inclusions while the stomach remained un-coated. A puncture needled with an integrated optical fiber was positioned 5mm from the tissue and PA images were acquired at two wavelengths (532nm, 780nm). Similarly to the feasibility study, the ratio of PA signals at the different wavelengths can be used to differentiate tissue types.

Results, Conclusions, and Discussions: Initial results with the phantom model demonstrated that the PA signals from the two wavelengths remained at a constant difference (ΔPA) when the needle was far away from the tissue. However, at about 1 mm from the colon mimic, a stronger PA signal was observed at 800 nm compared to 532 nm, indicating the presence of the colon. In contrast, a weaker PA signal at 800 nm compared to 532 nm was observed on the stomach side, where blood is the primary absorber.
The distance sensitivity of ICG detection (with a concentration of 0.25 mg/mL) also demonstrated that at distances beyond 8mm, the PA signal was negligible, but as the distance decreased, the PA signal became stronger. For the concentration sensitivity study, the PA signal plateaus at an ICG concentration of 0.25mg/mL, which showed that even low concentrations can be detected by the system.
The ex-vivo study showed accurate identification of the colon and stomach through the ratio calculation of PA signals from each wavelength in real-time with high resolution (0.2 x 0.2 mm). A ratio greater than one indicates the presence of the ICG inclusions, a ratio less than one indicates blood of colon tissues, and a nearly constant ratio (around one) indicates the optical fiber tip. These ratios allow for functional PA images to be color-coded, identifying the different tissues along the needle’s pathway.
The presence of the contrast agent coated colon can be detected non-invasively and distinguished from the stomach by exploiting the difference in PA signals during gastrostomy tube placement. In summary, a novel, non-invasive US and PA-guided method for gastrostomy placement has been designed, which has the potential to avoid colonic injury during G-tube placement consistently.

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