Researchers in China have created a miniature microprobe that can produce high-resolution, 360-degree images inside blood vessels far smaller than those accessible to current clinical imaging tools. The device, described in the journal Biomedical Optics Express, is designed to improve the diagnosis and treatment planning of atherosclerotic disease, which is responsible for roughly three-quarters of global cardiovascular deaths.
Intravascular optical coherence tomography (IV-OCT) uses near-infrared light emitted and received at the tip of a catheter to map the walls and texture of blood vessels. Traditional IV-OCT catheters are about 2 mm in diameter and perform best in vessels around 10 mm across — the medium and large arteries of the body. Their size is limited by the electromagnetic motors needed to rotate the sensor and the wiring that powers them. Proximal designs, which generate rotational force outside the body, suffer from friction-induced distortion in smaller vessels, while distal designs, with a motor inside the catheter, are blocked from a full 360-degree view by wire artefacts.
Led by Dawei Wu at Nanjing University of Aeronautics and Astronautics and Rui Liu at Nanjing University Medical School, the team developed a piezoelectric micro-optical probe just 0.55 mm in diameter, optimal for imaging vessels around 2 mm across. Instead of an electromagnetic motor, the probe uses a single-phase AC circuit and a piezoelectric crystal to vibrate a glass tube. A 10-degree groove in the glass converts longitudinal vibration into torsional vibration, generating elliptical motion of the lens in a manner similar to a crank and slider. When AC voltage is applied, the crystal expands and contracts, rotating the lens to produce the required optical scan.
First author Boquan Wang and colleagues tested the probe by imaging metal tubes arranged around a small, curved vessel. The device scanned at 50 revolutions per second while maintaining an angular deviation of just 1 degree, compared with 9 degrees for traditional proximal IV-OCT catheters. The test also confirmed a full 360-degree field of view, and the single-phase voltage meant wiring could be kept to a minimum.
The researchers then verified the probe's ability to navigate and image small vessels using leaf microveins, a vascular stent, and ex vivo pig vessels. In a key milestone for assessing its suitability for the cerebrovascular system, the probe successfully traversed a full-scale human vascular model to reach the middle cerebral artery. To confirm its effectiveness at identifying pathological lesions, the team compared images of human plaques acquired by the probe with histological analyses. The OCT and histology findings agreed well in identifying plaque rupture sites and regions rich in collagen fibres.
By placing a novel miniature rotational motor directly inside the probe and powering it with a single-phase AC circuit, the team produced a device smaller than traditional IV-OCT probes that eliminates rotational torsion artefacts while achieving full 360-degree imaging. The improved catheter navigation could allow access to high-resolution images of arterial wall structure in smaller, more curved vessels than is currently possible clinically, opening the door to assessment of plaque pathology and planning of stent positions in the heart-brain system.
«Although the probe would need more development and testing to be used clinically, intravascular OCT could one day give physicians a much closer look at what is happening inside the small arteries of the brain,» Wu said in a press statement.
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