Читать книгу Interventional Cardiology - Группа авторов - Страница 233

Intravascular optical coherence tomography (OCT), originally described in the early 1990s by David Huang, was firstly applied in the field of ophthalmology [1] and named OCT by James Fujimoto. In 1996, the Massachussets General Cardiology group [2] applied a catheter‐based modification of this technology to image coronary arteries. Subsequent advances in OCT technology enabled faster image acquisition rates, sufficient for its in vivo application in humans.

OCT is a high‐resolution imaging technology that employs advanced fiber optics to create images with a bandwidth in the near‐infrared spectrum with wavelengths ranging from 1250 to 1350 nm. The light that illuminates the vessel is absorbed, backscattered or reflected, by tissue structures at different degrees. Like for intravascular ultrasound (IVUS) images are formed by measuring magnitude and time delay of the reflected backscattered light signal [3]. The speed of light (3×10⁸ m/s), however, is several orders of magnitude faster than the speed of sound (1.5×10³ m/s). Compared with IVUS, OCT offers a 10 times higher image resolution, with an axial resolution of 10–20 μm. The price to pay for this high resolution is a reduced penetration depth into tissue and the need to create a transient blood‐free field of view during imaging acquisition. The tissue penetration is limited to 1–3 mm compared to 4–8 mm achieved by IVUS [4]. Early versions of the technology used time domain (TD) detection, while the second‐generation systems using Fourier domain (FD) significantly improved the signal‐to‐noise ratio and allowed high speed pullbacks with faster acquisition [5]. All commercially available systems (Ilumien Optis^TM Abbott/LightLab Imaging Inc., USA, Fastview Lunawave® Terumo, Japan) now employ frequency‐domain OCT, which enables rapid imaging of long segments during short injections for blood clearance maintaining good longitudinal resolution.

FD, Fourier domain; IVUS, intravenous ultrasound; OCT, optical coherence tomography; OFDI, optical frequency domain imaging.

The optical probe is integrated into a short monorail catheter that can be advanced in the coronary artery over any conventional 0.014‐inch guide wire. The catheter profile varies from 2.4 to 3.2 Fr and is compatible with 5 Fr guiding catheters. Six Fr guiding catheters are preferable for a more efficient contrast flushing during aquisition. During imaging, the optical fiber probe is pulled along the catheter sheath with the length of pullback anticipated by the position of the radiopaque markers and the fluoroscopically visible rotating sensor. A summary of the characteristics of the OCT systems is shown in Table 9.1. The Dragonfly OpStar imaging catheter has recently been redesigned with enhanced features. The catheter has a restructured lens for improved brightness and visibility of the EEM and plaque. The lens marker is now immediately proximal to the imaging lens. The newly designed shaft improves pushability through tortuous anatomy and a tapered three‐layer guide wire rail tip assists with lesion crossability. The reinforced guidewire port and straightened guidewire exit improve trackability.

Table 9.1 Comparison of optical coherence tomography systems.

	IVUS	HD ‐ IVUS	Ilumien Optis	Lunawave Terumo
Energy wave	Ultrasound	Ultrasound	Near‐infrared	Near‐infrared
Wavelegth (μm)	35–80	35–80	1.3	1.3
Axial resolution (μm)	100–150	100–150	10–15	10–20
Lateral resolution (μm)	150–300	150–300	20–30	20
Tissue penetration (mm)	4–8	4–8	1.5–2	1–2
Frame rate (frames/s)	30	30	180	158
Pullback speed (mm/s)	0.5–2	0.5–1	18 or 36	Up to 40
Maximal length pullback(mm)/duration (sec)	10/200	100	54/3 or 75/2.1	Up to 150 mm