Optical Coherent Tomography for eyes

1. A brief history of OCT
Nawat Watanachai
Sir Charles Gairdner Hospital
October 2007

3. OCT : Optical Coherence Tomography
1st OCT image of the retina
Resolution: 17 μm
depth ~1.5 mm into the
tissue
• Huang, Hee, Fujimoto, Puliafito 1991
• 1st in vivo retinal images at the MIT in 1993
• Commercially available in 1996
• Optical B-scans (Cross-sections)
• Resolution ~ 10 microns

4. BASIC OCT

5. Clinical Applications
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Visualization of vitreoretinal interface
Cross-sectional visualization retinal pathology
Nerve fiber layer analysis for glaucoma
Optic nerve head analysis for glaucoma
Other jobs eg. Anterior segment

6. Does OCT make a difference?
 Clinical Diagnosis/
Decision Making
 Medical Record/
Documentation
 Patient Education/
Satisfaction

7. Medical Proof
 OCT provides objective evidence for treatment
decisions, both to treat or not to treat, and of
response to treatment
 Examples:
CNV and AMD
 cystoid macular oedema
Macular hole
 retinal vein occlusion
PMF
 diabetic maculopathy
 Others eg fleck diseases

8. Time domain OCT
 Current clinical OCT devices utilize time domain
technology ---> limit in signal acquisition time
 700-900 nm*
Samples tissue with 1024 data points
over 2mm depth
 Z Dimension:

Takes a sample every 5-60 microns
apart, 128-512 scans
X-Y Dimension:

9. Time domain OCT : problems
 1 detector, Each A-scan requires the movement of
several mechanical parts
 Excellent image quality…if device and patient are
not moving

10. Time domain OCT : problems
 ~400 A-scan per sec
 take time to catch the image
 Can give poor image resolution
 No image registration --> not easily reproduce
 Error in both quantitative and qualitative
measurement in some situations

11. So, what are we looking for in the newer OCTs?
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Higher resolution
Higher imaging speed
Image registration
Quantitative information
extraction

12. Newer OCTs
1. Spectral domain OCT -- available
2. Other OCTs
2.1 Ultrahigh resolution OCT
2.2 Adaptive optic OCT
2.3 Hybrid machines eg OCT/SLO, HRA/OCT
3. OCT for anterior segment

13. 1. Spectral domain OCT

14. 1. Spectral domain OCT
 High speed high resolution OCT
 Frequency swept light source at around 850-1040 nm
 Improved axial image resolutions (<6 microns axial
resolution appears possible)

15. 1. Spectral domain OCT
 The output is measured with
the use of a spectrometer
(may be > 2,000 detector
elements), doesn’t need
moving part during scanning
16,000-75,000 scan/sec
(TD-OCT ~400)

16. 1. Spectral domain OCT
 Real time display and data streaming capabilities
enable video-rate imaging at more than 30fps
QuickTime™ and a
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17. 1. Spectral domain OCT
 Can produce 3-D projection image which can be aligned
with the actual fundus image to provide pixel-to-pixel
registration
 3-D imaging produces layers of information
 Isolation of retinal layers makes image analysis possible
in a broad fashion
 3-D thickness map
QuickTime™ and a
Microsoft Video 1 decompressor
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18. 1. Spectral domain OCT
 Pixel-to-pixel registration
 Precise scan location
 Image reproducibility
 Some machines can
generate fundus imaging
and register the spatial
location of each OCT
section image
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19. 1. Spectral domain OCT
 Pros
 Higher resolution/ 3D imaging
 Enhanced imaging speed
 Pinpoint registration
 Cons
 Signal strength and depth resolution is dependent on the
path difference between the retina and the reference mirror
--> the greater the distance (myopic eye), the weaker the
signal and the lower the resolution
 Yes………it’s price!

20. 2. Other OCTs
2.1 Ultrahigh resolution OCT
2.2 Adaptive optic OCT
2.3 Hybrid machines eg OCT/SLO,
HRA/OCT

21. 2.1 Ultra-high Resolution OCT
 First described by Drexler and Fujimoto in 2001
 Broad bandwidth, 150nm femtosecond Ti-sapphire
laser source (TD-OCT 10-25 nm)
 1-3 microns axial resolution
QuickTime™ and a
decompressor
are needed to see this picture.

22. 2.1 Ultra-high Resolution OCT
 Video-rate with up to 25-50 B-scans/sec
3,000 axial pixels and 600 transverse pixels (OCT-3
1,024 and 512 pixels)
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.

23. 2.1 Ultra-high Resolution OCT

24. 2.1 Ultra-high Resolution OCT
 Pros
 Enhanced anatomic
detail
 Enhanced
visualization of the
subretinal CNV
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25. 2.1 Ultra-high Resolution OCT
 Cons
 Slow acquisition time of 4-5 sec (OCT-3 can do
the job in 1.3 sec)
 Require significant technical support for day-today operation
 Limited ability to localize scans in relation to
precise fundus landmarks
 Alignment of serial scans dependent on fixation is
inaccurate

26. 2.2 Adaptive optic OCT
 Use electromagnetic deformable mirror (adaptive
optic) to improve the spatial resolution
 Correct chromatic aberration of the eye to get
better light pathway

27. 2.2 Adaptive Optic OCT
 Pixel resolution of 3µm x 3µm
 Very fine image : able to Imaging the retinal cells

28. 2.2 Adaptive optic OCT
 3D video
 Voxel resolution of 3µm x 3µm x 3 µm
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.

29. 2.3 OCT/SLO : multimodal imaging
 Introduced by
Podoleanu and Jackson
in 1998
 Employs OCT scan
simultaneous with
confocal SLO images
 SLO = surface detail
 OCT = internal detail

30. 2.3 OCT/SLO : multimodal imaging
 Single illumination source with parallel detector
systems ensures pixel-to-pixel correlation between
views
 Overlay capability permits view of internal anatomy
beneath surface landmarks
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.

31. 2.3 OCT/SLO : multimodal imaging
 Coronal OCT scans capture details often lost in
fixation-driven B scanning
 SLO channel facilitates integration of functional
testing such as angiography, microperimetry, and
mfERG

32. 2.3 OCT/SLO
TD-OCT
OCT/SLO

33. Matching C-Scan Images
Provide Linear Reference

34. 2.3 OCT/HRA
 OCT + laser angiography
 Image registration --> precisely define the scan
location -->good for repeat measurement
 Record fundus image in the same time

35. 2.3 other multimodaling machines
 Ultra-high Resolution OCT/SLO
 Combined Spectral Domain/ Time Domain HighResolution OCT/SLO

36. Will you own this machine?
 Keeps in mind
 OCT has become gold standard for some diseases
eg. PMF, MH
 Non invasive
 limitation
 OCT does NOT provide dynamic information (FA
does)
 Depend on operator techniques
 Degraded in the presence of media opacity
 Computer can do wrong things

37. Which OCT is ‘the one’ for you?
devices
B-scan/ 3D
Axial
resolution
Scanning
speed
Non-OCT
imaging
(TD-OCT)
Yes/no
10
400
Near IR
Heidelberg
Spectralis
HRA/OCT
Yes/yes
7
40,000
SLO, ICG, autoF
Optopol Copernicus
2
Yes/yes
6
25,000
Near IR
Optovue RTVue1001
Yes/yes
5
26,000
Near IR
OTI OCT/SLO1
Yes/yes
5
28,000
SLO, ICG,
microperimetry
Topcon 3D-OCT10002
Yes/yes
6
18,000
Near IR/ color
Carl Zeiss Meditec
Cirrus1
Yes/yes
5
27,000
LSLO

38. Which OCT is ‘the one’ for you?
 Time domain OCT (~60,000+ AUD)
 Spectral domain OCT (>100,000 AUD)
 Researchers
 Retinal specialists who can use this
images to help with decision making in
selected difficult cases

39. Thank you