Fig. 1. 3D-printed needle-beam endoscopic probe design. (a) Sketch of the optical design of the 3D-printed needle-beam probe. Here, we omit the mechanical parts, which are irrelevant from the optical standpoint. (b) Close-up schematic to highlight the distal end of the needle-beam probe. The laser beam at 1310 nm comes from SMF28 fiber and gets expanded in a spliced piece of no-core fiber. The lens is 3D-printed directly onto the cleaved facet of the no-core fiber in one step. The 3D-printed biconic TIR surface reflects the beam under an 80-deg angle to the optical axis of the fiber and precompensates the astigmatism arising from the protection tube and the catheter. After reflection at the TIR surface, the Gaussian laser beam is shaped to the needle beam by an axicon exit surface. (c) Optical microscope image of the fully assembled needle-beam probe at its distal end. (d) Zoom in to the 3D-printed micro-axicon micro-optics.

Fig. 2. Resolution characterization. (a) Sketch of the resolution measurement. A resolution target (APL-OP01, Arden Photonics, Solihull, United Kingdom) was pulled back relative to the 3D-printed needle-beam probe along the x axis and later along the y axis, resulting in two OCT scans—xz and yz, respectively. The lateral resolution pattern on the APL-OP01 target contains eight layers. The separation among each subsequent layer is 75μm (physical distance), so the bottom layer is 525μm from the top layer (physical distance). The purpose of the lateral resolution pattern is to measure the line spacing. Each line (n) is separated from the next line (n+1) laterally by a distance of 11(m−1)+n, where m is the group number. (b) OCT image of the lateral resolution target obtained by the 3D-printed needle-beam probe along the x axis in Fig. 1(b). (c) OCT image of the lateral resolution target obtained by a conventional GRIN fiber probe along the x axis. (d) OCT image of the lateral resolution target obtained by the 3D-printed needle-beam probe along the y axis. (e) OCT image of the lateral resolution target obtained by a conventional GRIN fiber probe along the y axis. All images are obtained with the endoscopic probe placed inside the same inner tube, intracoronary catheter sheath and in water. The 3D-printed lens has a significantly more extended DOF than that of a GRIN fiber probe. Scale bars indicate optical distances, and the refractive index of the resolution validation phantom is 1.45. Scale bar: 250μm.

Fig. 3. Ex vivo comparison of 3D-printed needle-beam probe with conventional OCT probe imaging in a human carotid artery with advanced plaque. (a) and (b) 3D rendering of the artery created by 210 frames of OCT images obtained with a 3D-printed needle-beam endoscopic probe. (c) Representative OCT image obtained at the black box in (b) the 3D-printed needle-beam endoscopic probe. (d) Representative OCT image obtained at the same location by a GRIN fiber probe. (e) Corresponding H&E histology image. (f)–(h) Magnified views of the dashed line regions in panels (c)–(e). Blue arrows denote the landmark features used for matching needle-beam, GRIN, and histology images. CC, cholesterol clefts; S, sheaths. Scale bar: 250μm (Video 1, MP4, 4.02 MB [URL: https://doi.org/10.1117/1.AP.7.2.026003.s1]).

Fig. 4. In vivo imaging capability of 3D-printed needle-beam probe in comparison with a conventional GRIN fiber OCT probe. Images of a porcine circumflex coronary artery with early neointimal hyperplasia, highlighted by the orange arrows. (a) Image obtained with a 3D-printed needle-beam endoscopic probe. (b) Image obtained with a conventional GRIN fiber OCT probe. (c) Matching H&E histology image confirming the presence of neointimal hyperplasia (orange arrow). S, sheaths. Scale bar: 0.5 mm.

Fig. 5. Serial intracoronary imaging in a live swine with our 3D-printed needle-beam endoscopic probe. (a) Cardiac catheterization laboratory setup for the intracoronary imaging procedure, where an interventional cardiologist inserts the 3D-printed needle-beam endoscopic probe into the coronary artery of the anesthetized swine via right femoral artery access. (b) X-ray angiography image showing the placement of the 3D-printed endoscopic probe in the anterior interventricular artery. Inset: magnified version with an arrow denotes the radiopaque marker at the tip of the 3D-printed needle-beam endoscopic probe. (c) Representative OCT image obtained in the anterior interventricular artery at the 3-month time point. (d) Representative OCT image obtained in the anterior interventricular artery at the 9-month time point. (e) Matching ionized calcium-binding adapter molecule 1 (Iba1)-stained histology image of panel (d). Blue arrows pointing to the necrotic region of this plaque. I, intima; IEL, internal elastic lamina; A, adventitia; G, guidewire. Scale bar: 0.5 mm.