Precision depth control of bone resection is necessary for safe surgical procedures in the spine. In this paper, we compare the control and quality of cutting bovine tail bone, as an ex vivo model of laminectomy and bony resection simulating spinal surgery, planned with micro-CT data and executed using two approaches: (a) mechanical milling guided by optical topographical imaging (OTI) and (b) optical milling using closed-loop inline coherent imaging (ICI) to monitor and control the incision depth of a high-power 1070 nm fiber laser in situ. OTI provides the in situ topology of the 2-dimensional surface of the bone orientation in the mechanical mill which is registered with the treatment plan derived from the micro-CT data. The coregistration allows the plan to be programmed into the mill which is then used as a benchmark of current surgical techniques. For laser cutting, 3D optical land marking with coaxial camera vision and the ICI system is used to coregister the treatment plan. The unstable, carbonization-mediated ablation behaviour of 1070 nm light and the unknown initial geometry of bone leads to unpredictable ablation which substantially limits the depth accuracy of open-loop cutting. However, even with such a non-ideal cutting laser, we demonstrate that ICI provides in situ high-speed feedback that automatically and accurately limits the laser’s cut depth to effectively create an all-optical analogue to the mechanical mill.
Multichannel optical coherence tomography (MOCT) imaging is demonstrated using a high-power wavelength-swept
laser source. The main benefit of MOCT is faster image acquisition rates without a corresponding increase in the laser
tuning speed. The wavelength-swept laser was constructed using a compact telescope-less polygon-based filter in
Littman arrangement. High output power, necessary for MOCT, was achieved by incorporating two serial
semiconductor optical amplifiers in a ring laser cavity in Fourier domain mode-locked configuration. The laser has a
measured wavelength tuning range of 111 nm centered at 1329 nm, coherence length of 5.5 mm, and total average
output power of 131 mW at 43 kHz sweeping rate. Using this laser, a six-channel imaging system was constructed. The
imaging arm consisted of a multi-fiber push-on connector mounted on a galvanometer-based scanner. All channels,
spaced 250 μm apart, were focused at the same depth. Six-channel OCT imaging to achieve 258 kHz scan rate is
demonstrated. The increase in effective frame rate using multichannel acquisition may be beneficial for 3-dimensional
in-vivo imaging where bulk tissue motion can adversely affect the image quality.
We demonstrate the potential of a forward-looking Doppler optical coherence tomography (OCT) probe for color flow imaging in several commonly seen narrowed artery morphologies. As a proof of concept, we present imaging results of a surgically exposed thrombotic occlusion model that was imaged superficially to demonstrate that Doppler OCT can identify flow within the recanalization channels of a blocked artery. We present Doppler OCT images in which the flow is nearly antiparallel to the imaging direction. These images are acquired using a flexible 2.2-mm-diam catheter that used electrostatic actuation to scan up to 30 deg ahead of the distal end. Doppler OCT images of physiologically relevant flow phantoms consisting of small channels and tapered entrance geometries are demonstrated.
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