Abstract
.This work explores light delivery optimization for photoacoustic-guided minimally invasive surgeries, such as the endonasal transsphenoidal approach. Monte Carlo simulations were employed to study three-dimensional light propagation in tissue, comprising one or two 4-mm diameter arteries located 3 mm below bone, an absorbing metallic drill contacting the bone surface, and a single light source placed next to the 2.4-mm diameter drill shaft with a 2.9-mm diameter spherical drill tip. The optimal fiber distance from the drill shaft was determined from the maximum normalized fluence to the underlying artery. Using this optimal fiber-to-drill shaft distance, Zemax simulations were employed to propagate Gaussian beams through one or more 600 micron-core diameter optical fibers for detection on the bone surface. When the number of equally spaced fibers surrounding the drill increased, a single merged optical profile formed with seven or more fibers, determined by thresholding the resulting light profile images at times the maximum intensity. We used these simulations to inform design requirements, build a one to seven multifiber light delivery prototype to surround a surgical drill, and demonstrate its ability to simultaneously visualize the tool tip and blood vessel targets in the absence and presence of bone. The results and methodology are generalizable to multiple interventional photoacoustic applications.
Highlights
Photoacoustic imaging has the potential to enable real-time visualization of regions of interest during surgery
The most straightforward method to integrate an optical fiber is to couple a bare fiber to a pulsed laser and detect signals with an external ultrasound probe, which was the method used in ex vivo pilot studies to discriminate nerves from tendons[1] and localize blood vessels hidden by bone.[2]
This plot and the corresponding example images indicate that much of the light is blocked by the drill when the fiber is too close to the drill shaft, but when the fiber is too far, the light does not adequately illuminate the underlying vessel
Summary
Photoacoustic imaging has the potential to enable real-time visualization of regions of interest during surgery. Ultrasound imaging provides real-time images of internal structures, it is often difficult to deliver miniature probes to the surgical site without sacrificing image quality (e.g., resolution). For these and other reasons, several researchers are investigating interventional photoacoustic systems. Microscopic applications utilize a more conventional approach by integrating the light delivery system with a single ultrasound transducer element to receive acoustic signals, enabling tasks such as the evaluation of both intraoperative breast tumor margins[5] and intravascular positions of stents
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