Surgical microscope integrated MHz SS-OCT with live volumetric visualization

Abstract

Intraoperative optical coherence tomography is still not overly pervasive in routine ophthalmic surgery, despite evident clinical benefits. That is because today's spectral-domain optical coherence tomography systems lack flexibility, acquisition speed, and imaging depth. We present to the best of our knowledge the most flexible swept-source optical coherence tomography (SS-OCT) engine coupled to an ophthalmic surgical microscope that operates at MHz A-scan rates. We use a MEMS tunable VCSEL to implement application-specific imaging modes, enabling diagnostic and documentary capture scans, live B-scan visualizations, and real-time 4D-OCT renderings. The technical design and implementation of the SS-OCT engine, as well as the reconstruction and rendering platform, are presented. All imaging modes are evaluated in surgical mock maneuvers using ex vivo bovine and porcine eye models. The applicability and limitations of MHz SS-OCT as a visualization tool for ophthalmic surgery are discussed.

Fig. 1.

Optics schematic of the 4D-OCT engine highlighting the allocation of components in the integrated module and the add-on module.

Fig. 2.

Add-on module for connecting the sample arm of the OCT engine to the surgical microscope. (a) Interface between microscope and add-on module. (b) RESIGHT 700 attached to the add-on module.

Fig. 3.

Scan patterns used in microscope integrated OCT. (a) B-scan line. (b) B-scan cross. (c) Raster capture. (d) 4D Spiral.

Fig. 4.

Schematic of the processing pipeline. (a) Raw buffers are treated according to the spectral splitting demands, via different strides of the pointer through the data buffer. Raw buffers are acquired by the DAQ and then directly copied onto the GPU for processing. (b) SS-OCT signal processing step: we perform as many operations as possible inplace, utilizing three different data buffers during an entire signal reconstruction run-through. (c) Remapping of every A-scan in a buffer onto the Cartesian volume grid. (d) Volume buffer, containing the entire reconstructed volume, ready to be processed by CAMPVis.

Fig. 5.

Layout of live 4D-OCT display rendering canvas. (a) 3D-rendered entire OCT volume. The widget is interactive and allows the user to rotate, move, zoom in and out, or change the origin in space of the rendered volume via mouse and keyboard commands. (b) cross-sectional B-scan (optical x-direction) and (c) the orthogonal direction cross-sectional B-scan (optical y-direction). (d) enface projection of the entire volume. The dynamic display ranges of the 3D-rendered volume (a), the cross-sectional B-scans ((b) and (c)) and of the enface (d) can be fine-tuned individually via the respective transfer functions to optimize the visual impression of every image. The screen capture video of this figure can be viewed in the supplementary materials (Visualization 1).

Fig. 6.

Screenshots of the Nvidia Nsight Systems Profiler, displaying the compute times of a full OCT buffer reconstruction cycle for five different selected imaging modes. All displayed timelines ((i)-(v)) were each taken at arbitrary points in time during reconstruction. The green continuous bars display memcopy processes, and the blue continuous ones display compute times of the kernels. The two lines below display the individual kernel execution times and individual memcopy processes. (i) Raster Scan, Cross Scan (ii), Spiral Scan with an effective A-scan rate of 600kHz (iii), Spiral Scan with an effective A-scan rate of 1.2MHz, utilizing spectral splitting on the 600kHz mode (iv), Spiral Scan with an effective A-scan rate of 1.2MHz (v). For a better comparison, we display all time scales identically, even though the selected modes are not meant to be directly compared to each other. However, with an offset from mode to mode.

Fig. 7.

B-scan of cow's retina covering an area of 8.7mmx11.8 mm (in z-, x-direction). One can clearly see a detached membrane (indicated by blue arrows) towards the anterior side of the scan and a large retinal vessel (indicated by yellow arrows).

Fig. 8.

B-scan of a phantom eye mimicking the length of an eye. The blue dashed horizontal lines indicate the positions of cornea and retina and the blue solid line the A-scan that was taken for analyzing the eye length. The intensity profile of that A-scan along the depth is shown on the right. The other white horizontal lines in the B-scan are imaging artifacts, originating from the DAQ and optical system.

Fig. 9.

23G surgical forceps moving above the retina of a cow’s eye. Looking at the images from (a) to (d), the surgeon gets closer to the retina. The video can be viewed in the supplementary materials (Visualization 3).

Fig. 10.

Microscopic enface view (left) aside 4D-OCT volumes (right) of membrane peeling procedure in ex vivo cow's eyes (see supplementary materials Visualization 1).

Fig. 11.

4D-OCT volume series of surgical tool moving above the retina of a cow’s eye. (d) Rendering is 180° rotated compared to (a) – (c).