Intracoronary OCT catheter is connected to a rotary junction, which uses a motor to rotate the optical fiber in the catheter and couples light from this rotating fiber to light from the reference arm [6]. The rotary junction mounted to an automated pullback device (Fig. 11.2). There are two types of OCT system: time domain and frequency domain . The first-generation OCT is time domain (TD-OCT ) which requires balloon occlusion in the proximal vessel, which provides blood clearing during image generation. The problem of TD-OCT was prolonged examination time, shorter lengths of imaging segment, and intermediate imaging quality [7]. The first commercial second-generation FD-OCT was introduced in 2007, which overcomes the limitation of the TD-OCT system (Tables 11.2 and 11.3) [8].

Using the FD-OCT system, the OCT probe is first positioned over a regular guidewire, distal to the region of interest. Identification of the pullback starting point is a simple task as a dedicated marker identifies the exact position of the OCT beam, located at 20 mm proximal to the marker itself. When the OCT catheter is positioned and blood clearance is visually obtained distally through the contrast injection, the acquisition of a rapid OCT image sequence with fast pullback can be automatically commenced by injecting a bolus of solution through the guiding catheter , with the pullback speed of 20 mm/s (Fig. 11.3). The infusion rate of contrast is usually set to 3–4 ml/s for the left coronary artery and 2–3 ml/s for the right coronary, but can be modified based on the vessel runoff and size. This contrast agent is recommended for low arrhythmogenic potential and high viscosity, which help to prolong imaging time [9]. Most expert users advocate the use of automated contrast injection to optimize image quality. The pullback can start automatically when blood clearance is distally recognized or can be manually activated. An acquisition speed of 20 mm/s enables the acquisition of 200 cross-sectional image frames over a 5 cm length of artery in 2.5 s with a total infused volume of 14 ml of contrast [4]. This may represent a concrete advantage of FD-OCT for use in percutaneous coronary interventions (PCI), allowing quick evaluation of the stent and of the landing zones and avoiding geographical miss. The FD-OCT pullback speed is too fast to interpret the run during the acquisition, but the recorded images are stored digitally and can be reviewed in a slow playback loop [10].