High-Quality 3-D Imaging with
Wolfgang Wieser, Benjamin R. Biedermann, Thomas Klein,
Christoph M. Eigenwillig and Robert Huber
Optical coherence tomography (OCT) 1 is an imaging modality
that can provide three-dimensional (3-D)
information on the scattering properties
of biological samples. However, the slow
scanning speed of early-time-domain
OCT systems in the range of 1,000
depth scans per second usually limited
OCT imaging to single 2-D frame
acquisition protocols rather than full
3-D volume acquisition. Between 2003
and 2006, the introduction of Fourier-domain-detection techniques2 for OCT
has led to an increase in imaging speed.
Depth scan rates of ~50-400 kHz are
now possible, 3-4 making it feasible to
acquire entire 3-D volumetric data sets.
However, even higher OCT imaging
speed is desired, because it would help to
reduce motion artifacts, enable volumetric real-time imaging at video rates and
allow for dense and isotropic sampling of
large volumes. Such comprehensive large
volume data sets may be used for absolute
registration of the individual 2-D OCT
frames, for large-area survey scans or for
guiding and aiming subsequent medical procedures. Up until now, scientists
debated whether it is possible to achieve
high image quality at multimegahertz
line rates due to limitations by shot noise,
laser noise and reduced bit depth of available analog-to-digital converters.
We demonstrate the most recent
increase in imaging speed, 5 pushing
the OCT line rate record of previously 370 kHz3 by a factor of more
than 50: With a sustained rate of up to
20. 8 million depth scans per second,
14,600 frames per second and one full
volume in 25 ms (see figure), our system
represents a breakthrough in high-speed
OCT imaging. Despite being fast, it is
still able to deliver high-quality OCT
images due to a nearly shot noise-limited
sensitivity of at least 98 dB and an axial
resolution of roughly 10 µm in tissue.
The high speed also opens the door to
completely new volumetric averaging
protocols for speckle reduction as well
as future volumetric OCT at video rate.
Our achievement is the result of
systematically pushing swept-source
OCT technology toward the limit: A
specially developed high speed filter
enabled us to build the fastest Fourier
domain mode-locked (FDML) laser so
far, running at a 5.2-MHz sweep repetition rate over an 80-nm tuning range at
1,300 nm. The OCT imaging speed is
further quadrupled for 3-D acquisition
to view the video that accompanies
8 m m, 640 px
by using four distinct imaging spots on
the sample in parallel.
A new design for a multispot interferometer uses both outputs of the buffered
FDML laser and thus makes better use
of the available laser power. Special low-noise, high-speed detectors, together with
8-bit sampling at 4 3 2. 5 GS/s, are used
for data acquisition. Bidirectional scanning reduces scanner-related dead times
during acquisition to merely 10 percent.
A dedicated post-processing alignment
and interpolation scheme removes bidirectional scanning artifacts and seamlessly
merges data from four spots into one 3-D
volume. This work demonstrates the feasibility of a transition from today’s kilohertz to megahertz line rates in OCT. t
The publication was chosen to be highlighted in
OSA’s Spotlight on Optics in July 2010.
Wolfgang Wieser, Benjamin R. Biedermann,
Thomas Klein, Christoph M. Eigenwillig and Robert
Huber ( email@example.com) are
with Lehrstuhl für BioMolekulare Optik, Fakultät für
Physik, Ludwig-Maximilians-Universität München,
1. D. Huang et al. Science 254, 1178-81 (1991).
2. A.F. Fercher et al. Opt. Commun. 117, 43-8 (1995).
3. R. Huber et al. Opt. Lett. 31, 2975-7 (2006).
4. B. Potsaid et al. Opt. Express 16, 15149-69 (2008).
5. W. Wieser et al. Opt. Express 18, 14685-704 (2010).
28 | OPN Optics & Photonics News