Similar to the parking-assist sensors on modern automobiles, which alert drivers of impending impact to an object, we are developing an auditory photoacoustic-based guidance system to assist with avoidance of impending injuries to ureters during hysterectomy procedures. The contribution described in this paper considers international standards for medical alarms. The system was demonstrated during both open and laparoscopic hysterectomy procedures on two human cadavers. Using methylene blue to enhance ureter contrast, the proximity of a surgical tool tip to the ureter was measured using the visual information provided in photoacoustic images. Distance measurements were then successfully mapped to auditory signals, which increased in auditory frequency as the tool-to-ureter distance decreased to convey surgical tool proximity to the ureter. Fundamental frequencies increased from 150 Hz to 866 Hz for tool-to-ureter distances of 2.47 mm to 5 mm. These results are promising to assist with the avoidance of accidental ureteral injuries during hysterectomy and other procedures that suffer from similar challenges with regard to iatrogenic ureteral injuries.
Gynecologic surgery accounts for 75% of all intraoperative injuries to the ureters, which often occur due to the close proximity of the ureter to the uterine artery. We propose dual-wavelength photoacoustic imaging in order to distinguish the ureter from the uterine artery, identify the position of the surgical tool in proximity to these critical structures, and assist with guidance of hysterectomy procedures. Experiments were preformed in a pilot human cadaver study and a dual-wavelength approach was introduced to visualize the uterine artery and a ureter filled with urine and methylene blue. The ureter location was identified with low contrast at a wavelength of 750 nm and higher contrast at a wavelength of 690 nm, resulting in a 5.8 dB contrast difference in photoacoustic signals from the ureter at these two different wavelengths. The uterine artery was identified at laser wavelengths of both 690 nm and 750 nm, with similarly high contrasts of 17.4 dB and 16.0 dB, respectively. By using a dual-wavelength display, both the ureter and the uterine artery were identified and their position was estimated in the photoacoustic image. The proximity of a surgical tool tip to the ureter was additionally estimated based on the information provided in the dual-wavelength photoacoustic display and mapped to an auditory signal. This auditory information can be provided as either an alternative or an addition to photoacoustic images that inform surgeons of the risk of injury. Results highlight the promise of dual-wavelength photoacoustic imaging to achieve our ultimate goal of avoiding accidental ureteral injuries during hysterectomies and possibly other similar gynecologic surgeries and procedures.
Gynecologic surgery requires the clamping, cauterization, and transection of arteries that lie within mil- limeters of the ureter, posing significant potential risk for ureteral injury. By leveraging the optical absorption properties of hemoglobin and methylene blue (an FDA-approved contrast agent), we propose intraoperative pho- toacoustic imaging during hysterectomies to simultaneously visualize the uterine arteries and ureter, respectively. Three experiments were performed to test the feasibility of a spectroscopic system aimed at intraoperative visual- ization. At 690 nm, the contrast from blood and urine mixed with 200 uM methylene blue was 13.83 dB and 11.06 dB, respectively, representing a 2.77 dB contrast difference. Conversely, at 750 nm, the contrast from blood was similar (14.61 dB), and the contrast from urine mixed with 200 uM methylene blue decreased to 1.74 dB, which produced a greater contrast difference of 12.87 dB. When tissue was added, similar contrast differences were observed at these wavelengths. Finally, a laparoscopic tool was additionally visualized in real time in proximity to the ureter and uterine arteries, which supports the feasibility of a spectroscopic photoacoustic approach to differentiating the ureter from the uterine arteries in relationship to a laparoscopic tool during hysterectomies.
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