Tiny Imaging Scope with 3D Printed Lens Can Scan Inside Blood Vessels

According to Dr. Jiawen Li, Heart Foundation Postdoctoral Fellow at the Institute for Photonics and Advanced Sensing (IPAS) with the University of Adelaide, one person every 19 minutes in the country is killed by cardiovascular disease. The statistics aren’t much better in the US, and in fact, the World Heart Federation states that it is the “world’s most common cause of death.”

That’s why a multidisciplinary team of clinicians, engineers, and researchers led by Australia’s University of Adelaide and Germany’s University of Stuttgart, aided by researchers from The South Australian Health and Medical Research Institute (SAHMRI), The Royal Adelaide Hospital (RAH), and Monash University, worked together to create what they’re calling the smallest flexible imaging scope in the world, made with 3D microprinting, that can actually be inserted into, and scan inside of, the blood vessels of mice.

“It’s exciting to work on a project where we take these innovations and build them into something so useful,” Dr. Li said. “It’s amazing what we can do when we put engineers and medical clinicians together.”

The thickness of a human hair, this optical probe has a tiny lens 3D printed into its side, allowing unprecedented 3D scanning access through blood vessels and other hard-to-reach places in the body.

The team recently published a study on their work, “Ultrathin monolithic 3D printed optical coherence tomography endoscopy for preclinical and clinical use,” in the journal Light: Science & Applications.

The abstract states, “Miniaturized endoscopic probes are necessary for imaging small luminal or delicate organs without causing trauma to tissue. However, current fabrication methods limit the imaging performance of highly miniaturized probes, restricting their widespread application. To overcome this limitation, we developed a novel ultrathin probe fabrication technique that utilizes 3D microprinting to reliably create side-facing freeform micro-optics (<130 µm diameter) on single-mode fibers.”

3D printing continues to be a very useful tool in the fight against cardiovascular disease, and this research is no exception. The team’s tiny, camera-like imaging device features a 3D printed lens on the end of an optical fiber, and is only as thick as a single strand of human hair. But as small as it is, the device is still able to capture high-quality 3D images at microscopic resolutions, which will give scientists a much better understanding into what causes heart diseases to progress, and could even help prevent and treat them.

Dr. Li, a co-author of the study, explained, “A major factor in heart disease is the plaques, made up of fats, cholesterol and other substances that build up in the vessel walls. Preclinical and clinical diagnostics increasingly rely on visualising the structure of the blood vessels to better understand the disease. Miniaturised endoscopes, which act like tiny cameras, allow doctors to see how these plaques form and explore new ways to treat them.”

a) Schematic of the 3D-printed OCT endoscope inside an artery. b) Microscope image of the 3D-printed off-axis freeform total internal reflection (TIR) mirror on the tip of the no-core fiber that is fusion spliced onto the light-guiding single-mode fiber. c) Optical design of the system with light exiting the single-mode fiber, expanding in the no-core fiber, being reflected and phase-shaped at the freeform mirror, passing the catheter sheath and focusing into the artery tissue. d) Photo of the 3D printed OCT endoscope, which rotates and is pulled back to accomplish full 3D OCT scanning.

A fine optical fiber, with a diameter of less than 0.02 inches, or less than half a millimetre, was used to fabricate the minuscule endoscope. Dr. Simon Thiele, Group Leader of Optical Design and Simulation at the University of Stuttgart, used Nanoscribe‘s 3D microprinting technology to print a side-facing lens, with a diameter of less than 0.13 mm, into the fiber.

Dr. Thiele said, “Until now, we couldn’t make high quality endoscopes this small. Using 3D micro-printing, we are able to print complicated lenses that are too small to see with the naked eye. The entire endoscope, with a protective plastic casing, is less than half a millimetre across.”

To fashion a flexible probe, the researchers connected the optical fiber to an optical coherence tomography (OCT) scanner, which is often used by ophthalmologists and optometrists to map the retina. This 3D depth-sensitive scanning penetrates tissue using near-infrared light, and measures wave interference between a probe beam and a reference beam. These measurements are used to build up live 3D images capable of looking through body surfaces, at microscopic resolutions, into the underlying structures to get a clearer picture of what’s going on.

a) Microscope image of the probe with flat front surface highlighted. b) Microscope image of the probe with curved TIR surface highlighted. c) Confocal surface measurement result of flat interface from a. d) Confocal surface measurement result of curved TIR mirror surface b. e) Deviation from ideal shape in the case of the flat surface. The RMS deviation for a beam footprint corresponding to an NA of 0.14 is 43 nm. f) Deviation from ideal shape in the case of the TIR surface. The RMS deviation for a beam footprint corresponding to an NA of 0.14 is 19 nm. Visible elliptical ring patterns are caused by the 3D printer’s rasterization within each layer and had no  discernible impact on the optical performance.

The ultra-thin probe on the team’s OCT scanning device can be rotated, pushed through, and pulled backwards through blood vessels in order to build a detailed 3D map of the vascular system, and see how much of that plaque Dr. Li mentioned has built up in the blood vessel walls.

“We are now able to reveal details of the tissue microarchitecture at depths not previously achieved with such small imaging probes. To the best of our knowledge, this is the smallest aberration-corrected intravascular probe to have been developed,” the researchers state in their paper.

OCT imaging of a severely diseased human carotid artery, using this ultra-thin probe.

They successfully tested their device in the blood vessels of mice, and of humans, to prove that it was flexible enough to provide high-quality OCT images—in fact, the 3D printed lens makes it possible for the scanner to capture 3D images at depths that are five times deeper than other devices have managed. The multidisciplinary researchers think that their probe can be used for even more tiny medical scanning applications, such as in the nervous system or the cochlea of the ear.

(Sources: University of Adelaide, New Atlas / Images courtesy of University of Adelaide)