1. Optical Coherence Tomography
What it is and How it Works
This presentation provides a simple explanation of what intravascular Optical Coherence Tomography (OCT) is and how it works.

2. What is Intravascular OCT?
An optical imaging modality that uses near-infrared light for high-resolution imaging of vessel anatomy, tissue microstructure and stents.
Key Features:
Uses light, not sound
Does not use X-ray
Image acquisition is fast
Images acquired are sharp, detailed and easy to interpret
OCT uses near-infrared light (unlike intravascular ultrasound, which uses sound) to create images. OCT provides detailed views of the inside of coronary arteries to help assess the anatomical characteristics of the vessel and plaque. The latest technology in use is called frequency domain OCT (FD-OCT).
As a result of its high resolution and speed, OCT produces clear, easy-to-understand views of vessel anatomy and plaque composition for planning and optimizing treatment.
The use of near-infrared light permits an almost ‘histological’ resolution of the coronary artery, and overcomes many limitations of angiography and intravascular ultrasound when imaging coronary stents.
(Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010)
OCT is light-based, which means image acquisition is fast; it also means that the vessel must be cleared of blood to facilitate imaging.
Frequency domain OCT acquires pullback images at a speed of up to 25 mm/s and the vessel is cleared of blood using a rapid flush of contrast.
Key defining features of OCT include:
The technology uses light and not sound waves
It does not use ionizing radiation, so there are no X-rays used in OCT
Images can be acquired very quickly
Images are sharp, detailed and easy to interpret. Resolution is very high (micron-scale, with one micron being 1/millionth of a meter). OCT can penetrate beneath the surface of tissue and the high contrast of the images makes it possible to differentiate between different types of tissue. Unlike intravascular ultrasound, OCT can even visualize tissue behind calcium, and is able to visualize bioabsorbable stents.
Images: Drs. Grube, Buellesfeld, Guerkens and Mueller, Helios Heart Center, Siegburg, Germany
Image: Image: Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

3. OCT Technology from St. Jude Medical
Console
Rapid exchange (Rx) imaging catheter
Contrast flush; balloon occlusion not required
Fast image acquisition: 5 cm pullback in 2.5 sec
In order to perform OCT procedures, St. Jude Medical provides a console (C7-XR™) and an imaging catheter (Dragonfly™). With the current C7-XR technology, no balloon occlusion is required; rather, the vessel is cleared of blood for imaging by a rapid flush of contrast. The images themselves are acquired extremely quickly: acquiring a 5 cm pullback image takes only 2.5 seconds. 3

4. Image Display Cross-sectional View Longitudinal View
The console has two displays, one for the operator of the console, and one that faces the physician.
Shown on the OCT system display are two simultaneous views of the vessel: a cross-sectional and a longitudinal view. Terms sometimes used (coming from intravascular ultrasound terminology) are “B-mode” and “L-mode.”
These terms have been borrowed from ultrasound.
B-mode = cross-sectional view
L-mode = longitudinal view (imagine cutting a tube lengthwise and viewing it from the side)
Longitudinal View

5. Dragonfly™ Imaging Catheter
Optical fiber core
2.7 F  x 135 cm usable length
Rapid exchange
Fits 0.014" guidewire
Used with 6-7 F guide catheter
Radiopaque markers
Markers 20 mm apart
Pullback
length: 5 cm
Lens
The catheter used for performing OCT procedures is called the Dragonfly imaging catheter. It is a rapid exchange catheter that is 2.7 F in diameter with a usable length of 135 cm. At the core of the imaging catheter is an optical fiber.
The imaging catheter is compatible with a inch guidewire and is used with a 6-7 F guide catheter.
It has two radiopaque markers to help during positioning for pullback image acquisition. 5

6. How Does OCT Work?
Optical fiber inside catheter spins around to create a radar-style image
Using a guide catheter, the Dragonfly imaging catheter is back-loaded with a conventional guidewire and introduced percutaneously through the femoral (or radial) artery, then advanced into the coronary tree past the segment of interest.
During image acquisition, the optical fiber inside the catheter spins and automatically pulls back while emitting near-infrared light, to obtain a 360°continuous pullback image of an arterial segment 5 cm long. 6

7. Image Generation – Pullback
As the fiber pulls back to map a vessel segment, a 5 cm long spiral scan is created
One pullback = approximately 270 frames
A pullback image is generated by acquiring a series of frames and “stacking” them up. One pullback consists of approximately 270 frames.

8. Image Generation
Light emitted by the optical fiber is reflected back by different types of tissue
The system measures the time delay of the reflected light waves
An OCT image is generated showing vessel anatomy and tissue microstructure
catheter
optical fiber
This cross-sectional view of the vessel shows how the image is created.
The catheter can be seen in the middle of the image, with the optical fiber at its core.
OCT measures the ”echo” time delay of light reflected from different parts of tissue.
A pulse of light is sent out that bounces off the different layers of tissue and returns back to be analyzed by the system. The system measures the time delays very precisely and generates an OCT image showing vessel anatomy and tissue microstructure.
Like a photograph, the image is made up of lines and pixels. The image quality is determined by the high resolution:
Optical resolution = 15 µm axial = 20 to 40 µm lateral
One pixel = 5 x 19 µm
One axial line = 1024 pixels
One frame = 500 axial lines
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010
axial
lateral
guidewire shadow
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

9. Physics of OCT Interference of Light Waves Constructive Interference
Destructive Interference
OCT imaging is based on the measurement of “echo” time delays. Very small differences are measured in “time of flight” between “echoes” bouncing off one part of tissue versus another. With ultrasound, the ”time of flight” can be directly measured, but the speed of light is too fast to be able to do this. Something called “interference” is therefore used to indirectly measure the time of flight of the light waves.
An example of interference is raindrops on a puddle. Where waves meet, peaks and valleys are formed.
OCT interference works basically like this: One light wave is generated from a reflector at a precisely known reference position, and another is generated from the tissue being imaged.
When two light waves that are in phase meet (peaks and valleys all line up), this forms a bigger wave (constructive interference).
When two light waves are not in phase, they cancel each other out (destructive interference).
By looking at the peaks and valleys of the interference patterns, it is possible to tell how far apart the two waves are from each other in time. In the case of constructive interference, the two waves are coming in at the same time. In the case of destructive interference, there is a time delay with one wave coming in after the other. The OCT measures the time delay and based on this, generates an image.

10. Time vs. Frequency Domain Intravascular OCT
Time Domain OCT (TD-OCT):
Commercially available for cardiovascular use 2001-present
Moderate image quality
Slow imaging
Requires occlusion balloon
Frequency Domain OCT (FD-OCT):
Commercially available for cardiovascular use present
Exceptional image quality
Fast imaging: x increase in speed
Rapid contrast flush instead of balloon occlusion
M3 system: TD-OCT
20 fps, 1 mm/s pullback
C7-XR system: FD-OCT
There are two types of OCT: Time Domain OCT (TD-OCT) and Frequency Domain OCT (FD-OCT).
FD-OCT (the newest) is the type that is currently in use for intravascular imaging and is used in the C7 system.
There are great advantages to FD-OCT. The older type of OCT meant slower imaging speeds and made it necessary to totally block the blood flow in the vessel using an occlusion balloon. A full pullback took about 30 seconds using TD-OCT.
FD-OCT offers much faster image acquisition (3 seconds versus 30 seconds for a full pullback), a less cumbersome procedure and better image quality.
The images shown here (postmortem, formalin fixed artery) illustrate the improved image quality achieved using FD-OCT using the C7 system compared with TD-OCT using the M3 system.
100 fps, 20 mm/s pullback
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

11. Optical Frequency Domain Imaging
Frequency Domain OCT
Multiple terms are used to describe the same type of OCT imaging, but there is no fundamental difference between these methods.
St. Jude Medical:
Frequency Domain OCT
FD-OCT
Terumo, MGH:
Optical Frequency Domain Imaging
OFDI
Volcano:
High Definition OCT
HD-OCT
Others:
Swept Source OCT
SS-OCT
Fourier Domain OCT
There is only one type of OCT currently used for intravascular procedures, though different companies use different terminology. The St. Jude Medical OCT system uses the term ”Frequency Domain OCT” or ”FD-OCT”.
Note: FD-OCT, OFDI, HD-OCT, and SS-OCT all use a narrow-band frequency-tuned light source (“swept-source”).
Spectral domain OCT (SD-OCT) is another type of OCT. SD-OCT does not use a swept-source, but rather a broad-band continuous light source and a spectometer. SD-OCT is used extensively in ophthalmology, but currently is not the preferred technological choice for intravascular OCT.
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

12. What Determines System Performance? (1/3)
Parameter
Determines
Controlled By
C7-XR Value
Imaging Speed
Acquisition time
Required flush volume
Laser sweep rate
Catheter rotation rate
Pullback speed
50,000 axial lines/s
100 Hz
20 mm/s
Sensitivity
Minimum detectable tissue reflection
Image contrast
Electrical and optical system design
Better than 100 db
Imaging Range
Maximum vessel diameter
Laser line width
10 mm (in contrast)
Resolution
Minimum detectable tissue feature
Speckle size and image granularity
Laser tuning range (axial)
Catheter focusing optics (lateral)
15 µm (axial)
20 – 40 µm (lateral)
Tissue Penetration
Visible depth into vessel wall
Scattering and absorption of tissue
1 – 2 mm
Listed in this table are five parameters that control system performance, or what the user will be able to see when looking at the OCT images.
Imaging speed: Determines the time it takes to acquire the data, and as a consequence determines how much contrast flush is needed.
It is controlled by how fast the laser can be tuned, how fast the catheter can spin, and how fast the catheter can be pulled back.
The C7-XR system can take 50,000 image lines per second, spins at 100 Hz and pulls back at 20 mm/second.
Sensitivity:
This determines the smallest amount of light that we can see, or the smallest tissue reflection that can be observed with the system. This is what controls the image contrast. For example, if we could only see very large reflections, you might only be able to see stents; if we could see large and also small reflections, we could see both stents and also calcium. Sensitivity on the C7-XR system is better than 100 decibels, this is good and means that we can see a very broad range of tissue types.
(Continued on next slide).
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

13. What Determines System Performance? (2/3)
Parameter
Determines
Controlled By
C7-XR Value
Imaging Speed
Acquisition time
Required flush volume
Laser sweep rate
Catheter rotation rate
Pullback speed
50,000 axial lines/s
100 Hz
20 mm/s
Sensitivity
Minimum detectable tissue reflection
Image contrast
Electrical and optical system design
Better than 100 dB
Imaging Range
Maximum vessel diameter
Laser line width
10 mm (in contrast)
Resolution
Minimum detectable tissue feature
Speckle size and image granularity
Laser tuning range (axial)
Catheter focusing optics (lateral)
15 µm (axial)
20 – 40 µm (lateral)
Tissue Penetration
Visible depth into vessel wall
Scattering and absorption of tissue
1 – 2 mm
(Continued from previous slide).
Imaging range or scan diameter:
This determines the largest vessel diameter that we can image. This can also be thought of as the “field of view” of the image. It is determined by the laser properties and also by the system design. With the C7-XR system, we can see a 10 mm vessel diameter if it’s filled with contrast fluid (important to specify, because the speed of light varies in different media – air, saline, contrast – so need to calibrate the distance for the time of flight of light in that medium), and with the catheter centered in the vessel lumen.
Resolution:
This tells us what the smallest spatial feature is that we can see; e.g., a 10 μm or a 5 μm feature or a 100 μm feature. It also controls the size and number of grains in the image. The higher the resolution of the system, the smaller the speckle cells get and the more visually pleasing the images get.
(Continued on next slide).
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

14. What Determines System Performance? (3/3)
Parameter
Determines
Controlled By
C7-XR Value
Imaging Speed
Acquisition time
Required flush volume
Laser sweep rate
Catheter rotation rate
Pullback speed
50,000 axial lines/s
100 Hz
20 mm/s
Sensitivity
Minimum detectable tissue reflection
Image contrast
Electrical and optical system design
Better than 100 dB
Imaging Range
Maximum vessel diameter
Laser line width
10 mm (in contrast)
Resolution
Minimum detectable tissue feature
Speckle size and image granularity
Laser tuning range (axial)
Catheter focusing optics (lateral)
15 µm (axial)
20 – 40 µm (lateral)
Tissue Penetration
Visible depth into vessel wall
Scattering and absorption of tissue
1 – 2 mm
(Continued from previous slide)
Tissue Penetration:
The maximum depth into the blood vessel wall that can be imaged before all of the light is lost into the tissue. The tissue penetration for any intracoronary OCT system is 1 – 2 mm. NOTE: tissue penetration can sometimes be confused with scan diameter. Even though the C7-XR has a scan diameter of 10 mm, it cannot image 10 mm deep into the vessel wall. It could, however, image 1 mm deep into the wall of a vessel with a lumen diameter of 8 mm.
Scattering:
Occurs when light strikes an object and is redirected, like when one pool ball strikes another. Scattered photons (a single particle of light, can be compared to the optical version of an electron), may be redirected at any angle.
In OCT, photons that are scattered directly backward (“backscattered”) are captured by the catheter optics, guided back to the engine, and are detected by the electronics. These backscattered photons help to form the image. Photons that are scattered at other angles are not captured by the imaging system, and can also be thought of as being “lost.” Scattering is heavily dependent on the size and shape of the particles that make up the sample. Red blood cells have extremely high scattering, which is the main reason that we cannot see through blood with OCT. You can observe scattering by placing a laser pointer against your finger. The diffuse blob of light that seems to emanate from your skin is heavily scattered.
Absorption:
Occurs when light strikes an object (such as tissue) and “vanishes” into the material. The absorbed photons do not propagate beyond the object and are lost forever. Absorption is heavily dependent on the wavelength of light. Lipid is an example of a material that has very high absorption at OCT wavelengths. Calcium, on the other hand, does not heavily absorb our light. Black material becomes hot in the sunlight because the black dye absorbs visible wavelengths.
Reflection:
Occurs when light strikes a solid, “shiny” material (such as a stent strut or catheter sheath) and a portion of the light bounces off the sample. Example: if you shine light off a mirror that is perpendicular to the light beam, it will reflect directly backward. If you tilt the mirror 45 degrees, it will reflect light at 90 degrees.
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

15. Performance Comparison: FD-OCT vs. TD-OCT
C7-XR M3 M2
Axial Resolution
15 – 20 µm
Beam Width
20 – 40 mm
Frame Rate
100 frames/s
20 frames/s
15 frames/s
Pullback Speed
20 mm/s
1.5 mm/s
1 mm/s
Max. Scan Dia.
10 mm
6.8 mm
Tissue Penetration mm
Lines per Frame
500
240
200
Lateral Sampling (3 mm Artery)
19 µm
39 µm
The M3 and M2 systems are older technology from St. Jude Medical that use Time Domain OCT (TD-OCT). The latest technology from St. Jude Medical includes the C7-XR system using FD-OCT, which enables faster image acquisition and better image quality and makes it possible to image larger vessels. A major difference with the latest technology is that OCT is easier to perform. With the C7-XR system, balloon occlusion is no longer required. Instead, a rapid flush of contrast is sufficient to clear the vessel of blood and facilitate image acquisition.
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

16. Performance Comparison: FD-OCT vs. IVUS
C7-XR
IVUS
Axial Resolution
15 – 20 µm
100 – 200 µm
Beam Width
20 – 40 mm
200 – 300 mm
Frame Rate
100 frames/s
30 frames/s
Pullback Speed
20 mm/s
mm/s
Max. Scan Dia.
10 mm
15 mm
Tissue Penetration mm
Lines per Frame
500
256
Lateral Sampling (3 mm Artery)
19 µm
225 µm
Blood Clearing
Required
Not Required
Compared with IVUS, OCT images using technology from St. Jude Medical are clearer, more detailed, easier to interpret and quicker to acquire. This is due to the nature of the image acquisition (light-based) as well as the high level of technical performance that has been achieved through engineering and years of development.
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010 16

17. OCT Technical Terms
Pixel: Like a photograph, each image consists of lines and pixels. Each pixel is approximately 5x19 microns. Line: Each frame consists of 500 rotational lines. The greater the number of lines per frame, the finer the texture of the image. Frame: The optical fiber spins around to form a frame. Frame rate: Frame rate is the number of cross-sectional frames that can be acquired over a given period of time. Axial: Axial is the direction that is parallel to the optical beam in an OCT system. The axial resolution of OCT is 15 µm. Each axial line consists of 1024 pixels. Lateral: Lateral is the direction perpendicular to the optical beam in an OCT system. The lateral resolution of the C7-XR system is 20–40 µm, depending on the distance away from the catheter. Optical resolution: A measure of the smallest physical feature that can be detected with an imaging system. Measured in units of millimetres (mm) or micrometers (microns, µm). One mm is equal to one thousand µm. A piece of paper is about 90 µm thick, while a human red blood cell is about 10 µm long. The optical resolution of OCT is approximately 15 µm axial by µm lateral, depending on how far the tissue is away from the center of the catheter. Hertz: Frame rate is measured in units of Hertz (Hz). The optical fiber rotates at 20 Hz during preview mode (= 20 frames/second), and rotates at 100 Hz (= 100 frames/second) during high-speed pullback. The C7-XR system acquires 50,000 axial image lines per second. This is sometimes abbreviated by saying that it is “a 50 kHz system.”
For reference, here is a list of some of the technical terms used to describe optical coherence tomography.

18. OCT Technology: Key Concepts to Remember
OCT uses reflected light waves to image coronary arteries in microscopic detail.
The latest FD-OCT is faster, the images are better, and it does not require balloon occlusion.
The latest technology from St. Jude Medical scans a 5 cm segment of an artery in less than 3 seconds.
As a result of its resolution and speed, OCT produces clear, easy-to-understand views of vessel morphology and plaque composition for planning and optimizing treatment.
In summary, intravascular OCT is a light-based invasive imaging method that provides near-histological images to assess vessel anatomy and tissue microstructure and to visualize stents.
Using the latest technology from St. Jude Medical, OCT image acquisition is fast and easy to perform and the images that result are clear, detailed and easy to interpret.
Gonzalo N. Optical Coherence Tomography for the Assessment of Coronary Atherosclerosis and Vessel Response After Stent Implantation (Thesis) 2010

19. RX Only Please review the Instructions for Use prior to using these devices for a complete listing of indications, contraindications, warnings, precautions, potential adverse events, and directions for use. Product referenced is approved for CE Mark. Unless otherwise noted, ™ indicates a registered or unregistered trademark or service mark owned by, or licensed to, St. Jude Medical, Inc. or one of its subsidiaries. GOLDEN IMAGE, the color Gold, Dragonfly, ST. JUDE MEDICAL , the nine-squares symbol and MORE CONTROL. LESS RISK. are registered and unregistered trademarks and service marks of St. Jude Medical, Inc. and its related companies. ©2010 St. Jude Medical, Inc. All rights reserved.