Real-Time, Nondestructive Optical Feedback Systems for Infrared Laser Sealing of Blood Vessels

Abstract

High-power infrared (IR) diode lasers are capable of sealing blood vessels during surgery. This study characterizes an optical feedback system for real-time, nondestructive identification of vessel seals. A low power, red aiming beam (635 nm) was used for diagnostics, co-aligned with a therapeutic high-power IR beam (1470 nm). The IR laser delivered either 30 W for 5 s for successful seals or 5 W for 5 s for unsuccessful seals (control). All studies used a linear beam measuring 8.4 × 2.0 mm. Optical signals for successful and failed seals were correlated with vessel burst pressures (BP) using destructive testing via a standard BP setup. Light scattering increased significantly as vessels were coagulated. Successful seals correlated with a percent decrease in optical transmission signal of 59 ± 11 % and seal failures to a transmission decrease of 23 ± 8% (p < 0.01). With further development, the real-time optical feedback system may be integrated into a laparoscopic device to de-activate the laser upon successful vessel sealing.

Keywords: artery; blood vessel; coagulation; feedback; fusion; infrared; laser; seal; transmission.

Figure 1.

Real-time optical transmission setup, with 1470 nm therapeutic and 635 nm diagnostic beams coupled into a multimode (MM) fiber with beam shaping via a collimating lens (L1) and cylindrical lens (L2) to form a linear beam profile of 8.4 × 2.0 mm. The blood vessel sample was clamped with a custom mount, allowing diffuse scattered light to be collected by a MM fiber. The diagnostic beam was collimated (L3), filtered (ND & IR filters), and focused (L4) into a detector.

Figure 2.

(a) Scatter plot showing BP data for 24 vessels tested. Colored data points separate data as a function of laser irradiation time (30 W for 5 s and 5 W for 5 s), while horizontal colored lines represent criteria for success (360 mmHg), hypertensive blood pressure (180 mmHg), and systolic blood pressure (120 mmHg). (b) Representation of real-time power data acquired during sealing. Green line represents 5 W, 5 s seal of 3.1 mm diameter vessel with BP = 10 mmHg (failed seal) and decrease in signal of 34%. Red line represents 30 W, 5 s seal of 3.1 mm vessel with BP = 540 mmHg (successful seal) and decrease in signal of 50%.

Figure 3.

Representative real-time, diffuse optical transmission data during the sealing procedure, using high-power therapeutic 1470 nm wavelength as the diagnostic beam. At t = 0 s, laser is activated, leading to instantaneous rise in signal. The erratic signal between t = 0 and t = 5 s can be attributed in part to different contributions and time scales of competing changes in the dynamic tissue optical properties: increased transmission due to tissue dehydration (lower absorption coefficient) and decreased transmission due to tissue coagulation (increased scattering coefficient). Loss of signal from t = 1.5 – 2.5 s is due to saturation at detector setting.