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RESEARCH ARTICLE
MEMS-Based Handheld Fourier Domain
Doppler Optical Coherence Tomography
for Intraoperative Microvascular
Anastomosis Imaging
Yong Huang
1
*, Georg J. Furtmu¨ ller
2
, Dedi Tong
2,3
, Shan Zhu
2,4
,
W. P. Andrew Lee
2
, Gerald Brandacher
2
*, Jin U. Kang
1
1. Department of Electrical and Computer Engineering, Johns Hopkins University, 3400 N. Charles Street,
Baltimore, Maryland, 21218, United States of America, 2. Department of Plastic and Reconstructive Surgery,
Vascularized Composite Allotransplantation (VCA) Laboratory, Johns Hopkins University School of Medicine,
720 Rutland Avenue, Ross 749D, Baltimore, Maryland, 21205, United States of America, 3. Department of
Hand Surgery, Beijing Jishuitan Hospital, 31 Xinjiekou East Street, Xicheng District, Beijing, 10035, China, 4.
Peking Union Medical College and Chinese Academy of Medical Sciences, Department of Plastic and
Reconstructive Surgery, Plastic Surgery Hospital, 3 Ba-Da-Chu Road, Shijingshan District, Beijing, 10044,
China
*yhuang60@jhu.edu (YH);brandacher@jhmi.edu (GB)
Abstract
Purpose: To demonstrate the feasibility of a miniature handheld optical coherence
tomography (OCT) imager for real time intraoperative vascular patency evaluation
in the setting of super-microsurgical vessel anastomosis.
Methods: A novel handheld imager Fourier domain Doppler optical coherence
tomography based on a 1.3-mm central wavelength swept source for extravascular
imaging was developed. The imager was minimized through the adoption of a 2.4-
mm diameter microelectromechanical systems (MEMS) scanning mirror,
additionally a 12.7-mm diameter lens system was designed and combined with the
MEMS mirror to achieve a small form factor that optimize functionality as a
handheld extravascular OCT imager. To evaluate in-vivo applicability, super-
microsurgical vessel anastomosis was performed in a mouse femoral vessel cut
and repair model employing conventional interrupted suture technique as well as a
novel non-suture cuff technique. Vascular anastomosis patency after clinically
successful repair was evaluated using the novel handheld OCT imager.
Results: With an adjustable lateral image field of view up to 1.5 mm by 1.5 mm,
high-resolution simultaneous structural and flow imaging of the blood vessels were
successfully acquired for BALB/C mouse after orthotopic hind limb transplantation
using a non-suture cuff technique and BALB/C mouse after femoral artery
anastomosis using a suture technique. We experimentally quantify the axial and
OPEN ACCESS
Citation: Huang Y, Furtmu¨ller GJ, Tong D, Zhu S,
Lee WPA, et al. (2014) MEMS-Based Handheld
Fourier Domain Doppler Optical Coherence
Tomography for Intraoperative Microvascular
Anastomosis Imaging. PLoS ONE 9(12): e114215.
doi:10.1371/journal.pone.0114215
Editor: Tom Waigh, University of Manchester,
United Kingdom
Received: July 9, 2014
Accepted: November 4, 2014
Published: December 4, 2014
Copyright: ß2014 Huang et al. This is an open-
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and repro-
duction in any medium, provided the original author
and source are credited.
Data Availability: The authors confirm that all data
underlying the findings are fully available without
restriction. All relevant data are within the paper
and its Supporting Information files.
Funding: The research was supported by NIH/NEI
5R01EY021540-03. Yong Huang acknowledges
China Scholarship Council (CSC) for partial
support for his PhD study. The funders had no role
in study design, data collection and analysis,
decision to publish, or preparation of the manu-
script.
Competing Interests: The authors have declared
that no competing interests exist.
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 1/14
lateral resolution of the OCT to be 12.6 mm in air and 17.5 mm respectively. The
OCT has a sensitivity of 84 dB and sensitivity roll-off of 5.7 dB/mm over an imaging
range of 5 mm. Imaging with a frame rate of 36 Hz for an image size of
1000(lateral)6512(axial) pixels using a 50,000 A-lines per second swept source
was achieved. Quantitative vessel lumen patency, lumen narrowing and thrombosis
analysis were performed based on acquired structure and Doppler images.
Conclusions: A miniature handheld OCT imager that can be used for
intraoperative evaluation of microvascular anastomosis was successfully
demonstrated.
Introduction
Vascular anastomosis–the surgical connection of two blood vessels–is a common
procedure used in various surgical subspecialties. In particular, it is a critical
constituent of reconstructive microsurgery, vascular surgery, and transplant
surgery. The conventional suture-based anastomosis technique has seen many
technological advances since the introduction of the triangulation method by
Carrel [1]. The advances range from improved surgical microscopes to improved
suture material and vascular coupling devices [2], thermo-reversible poloxamers
[3], and non-suture cuff techniques [4]. However, quality assessment of surgical
outcomes depends merely on the experience of the surgeon and involves visual
inspection of the suture site as well as all tissues involved and perfused by the
vascular pedicle. Thus, despite the overall progress pushing the limits of
microsurgical possibilities, no significant clinically relevant advances have been
made allowing for the standardized postoperative evaluation of microvascular
anastomosis patency. In the field of imaging, technologies such as near-infrared
laser angiography may provide surrogate information about perfusion and
drainage by measuring the accumulation of fluorescent dyes, however an
application providing real time surgical guidance and the opportunity of
immediate postoperative microvascular anastomosis evaluation is deemed to be
the ultimate goal. In the era of super-microsurgery, there is a critical need for
devices that can evaluate the surgical outcome objectively and not solely based on
a surgeons’ subjective evaluation and accumulated experience over the years. Such
devices can also aid in training and evaluation of trainees.
Optical coherence tomography (OCT) has been successfully used in pre-clinical
and clinical applications due to its high resolution simultaneous structure and
Doppler flow imaging [5]. OCT has been demonstrated with the advantages of
fast temporal and spatial resolution compared to other medical imaging
modalities such as MRI, CT and ultrasound tomography. Our lab recently
demonstrated the capability of a real-time graphics processing units accelerated
Phase resolved Doppler OCT (PRDOCT) system for suturing guidance and
postoperative evaluation of microvascular anastomosis [6,7]. Compared to laser
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 2/14
speckle contrast blood flow imaging, PRDOCT has the advantage of simultaneous
high resolution depth-resolved structure and blood flow information [8]. While
Doppler optical microangiography imaging (DOMAG) can provide better
performance than PRDOCT, it requires more complicated system hardware
configuration [9]. Intraoperative application of OCT requires a task-oriented
OCT system optomechanical design to achieve bench-top to bed-side clinical
translation. Different approaches have been explored by researchers such as
integration of OCT to surgical microscope for vitreoretinal surgery [10]and
miniature handheld probes via fiber tip resonant vibration [5,11], scanning
mirrors combined with GRIN needles [12], endoscopic MEMS probe [13], and
MEMS mirrors-based handheld imaging instrument [14,15]. 2D MEMS mirrors
that scan in two axes as an alternative to the larger galvanometer scanner have
been used extensively to generate 3D volume images due to their low-cost,
compact size, and fast imaging speed [15]. MEMS mirror scanning is
conventional linear raster-scanning, which is uniform in spatial sampling and the
acquired image is more intuitive to understand compared to fiber tip resonant
vibration in 3D volume image generation mode. Due to the easy access of vessels
during the open anastomosis surgery, we chose to develop a handheld imager
using a 2D MEMS mirror-based scanner. The ergonomic design aim was that
surgeons can use the imager as a typical handheld surgical tool. By making the
OCT system portable and the probe miniature, the structure and Doppler OCT
imaging can be readily available for surgeons during the procedure.
In this work, we evaluated handheld OCT imager by performing the
intraoperative evaluation of microvascular anastomosis using a mouse model. The
proposed handheld MEMS scanning mirror-based imager is compact, light-
weight, and easy to manipulate. It can provide real-time simultaneous structure
and Doppler flow imaging at a speed of 36 frames per second while each frame
consists of 10006512 (lateral6axial) pixels. The Doppler flow imaging range was
characterized to be from 0.363 mm/s to 16.3 mm/s in both directions parallel to
the scanning beam.
Materials and Methods
Ethnic Statement
Johns Hopkins University Animal Care and Use Committee approved all
experiments with the approval number of MO12M348 and the animals were
handled in accordance with the Johns Hopkins University Animal Care and Use
Committee guidelines. Animals were housed under standard rodent housing
conditions (24C, 12:12 h dark/light cycle), food and water was provided ad
libitum. Analgesia with Buprenorphine (Dose: 0.05 mg/kg) was administered 1
hour prior to surgery and then at an interval of 60 min thereafter. Animals were
operated under sterile conditions and put on a heating pad to maintain body
temperature and all efforts were made to minimize suffering. Non-invasive
imaging procedures were performed immediately after the surgical procedure was
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 3/14
completed. At the end of the experiments animals were sedated with an overdose
of isoflurane inhalation anesthesia and euthanized by cervical dislocation.
Animals
Male 6–8 week old BALB/C mice with a BW of 33¡2.8 g (n52) were obtained
from Jackson Laboratories. Animals were anesthetized using oxygen and
isoflurane mixed gas and placed on a heating pad to maintain the body
temperature. In Mouse 1, femoral artery end-to-end anastomoses was performed
with a conventional suture technique. Mouse 2 received an orthotopic hind limb
transplantation surgery with a non-suture cuff-based technique for revascular-
ization. Both femoral vein and artery were anastomosed from the donor limb to
the recipient animal’s vessels.
Microvascular Anastomosis Procedures
Conventional interrupted suture technique: Supermicrovascular anastomosis was
performed in a mouse femoral artery cut and repair model using interrupted
suture technique (11-0 Nylon, S&T, Neuhausen, Switzerland). Femoral vessels
were dissected, cut and the proximal and distal stump mounted on an
approximating clamp (S&T, Neuhausen, Switzerland) to prevent blood flow and
provide optimal surgical exposure. Fig. 1(a) illustrates the procedures of suture
based vascular anastomosis. Sutures are placed in the collapsed vessel across the
full thickness of the vessel wall (adventitia, media and intima) on one end and
then from intima to adventitia in the other vessel end. Appropriate approximation
of proximal and distal vessel stumps was achieved with 6–8 sutures.
Non-suture cuff technique: Our group pioneered the non-suture-cuff
technique, which provides a rapid and reliable method for performing sub-
millimeter anastomosis [4,16]. Fig. 1(b) shows the procedures of the sutureless
cuff technique. First, a biocompatible cuff with proper diameter to fit the size of
vessel is chosen. The cuff is mounted on the distal vessel end, which is
subsequently everted and secured over the cuff using 10-0 circular ties. The distal
vessel end with the cuff is now secured in an approximating clamp to provide
optimal stability and surgical exposure. The proximal vessel is pulled over the
vessel-cuff complex providing intima-to-intima contact. Release of the approx-
imating clamp reestablished blood flow and patency could be evaluated
macroscopically.
Conventional rubber material as a background, is placed to both facilitate the
microsurgical procedure and provide optimal separation from surrounding tissue
for optimal and clear imaging conditions.
Handheld-Probe Design
Fig. 2(a) illustrated the optomechanical design of the probe. It consists of mainly
three parts: gray MEMS housing part with optical and electrical connectors
integrated to it, black lens tube part and a gray axial distance adjustment tip. To
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 4/14
Figure 1. Illustration of microvascular anastomosis procedures. (a) suture based vascular anastomosis;
(b) cuff based non-suture technique. Cuff is mounted over the vessel end and the end is everted over the cuff.
The other cut end of the vessel is then pulled over and tied to create intima-to-intima contact.
doi:10.1371/journal.pone.0114215.g001
Figure 2. Handheld probe illustration. (a) Probe compared to a quarter coin (H: height 37.24 mm, W: width
32.43 mm, L: length 136.7 mm). (b) Optics layout inside the probe. (c) Image of the probe held by hand.
doi:10.1371/journal.pone.0114215.g002
Handheld OCT Imager for Vascular Anastomosis
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achieve light weight, the probe is made of aluminum and the weight of the probe
is measured to be 88 g. An FC/APC collimator with an output beam diameter of
1.5 mm was used as the optical input of the probe. MEMS scanning mirror
(AdvancedMEMS Inc.) with a diameter of 2.4 mm was chosen to accommodate
and stir the beam to perform scanning. MEMS scanning waveforms were supplied
through the electrical input connector located besides the optical input. A folding
mirror was used to fold the beam to a five half inch lens system, which is shown in
Fig. 2(b). Four half inches achromatic doublets (Thorlabs, AC127-050-C) form a
quasi-telecentric setup with two pairs of identical achromatic lenses to minimize
spherical aberration. One half inch achromatic lens with focal length of 30 mm
(Thorlabs, AC127-030-C) is used as the objective lens to focus the imaging beam.
The first pair of two lenses was placed within the gray MEMS housing part and the
remaining three lenses were placed in the lens tube. The length of the probe is
136.7 mm with 17.2 mm axial distance adjustment range. The axial distance
adjustment tip was designed for fine-tuning the sample position relative to the
zero-delay reference. It also gives us some flexibility when later longer focal length
lens is used. The height of the probe is 37 mm and width is 32 mm at the MEMS
housing and collimator region; after that the probe is a tube structure with an
outer diameter of 23 mm. A photograph showing a normal hand holding the
probe is shown in Fig. 2(c).
Swept Source-OCT System
Fig. 3(a) presents the system configuration. The swept source laser (Axsun
Technologies, Inc.) with a central wavelength of 1310 nm, tuning range of 100 nm
(from 1260 nm to 1360 nm), and A-scan rate of 50 kHz was used. Balanced
detector (Thorlabs, PDB480C AC) is utilized to detect the interference signal to
remove the common DC background. We used a quad-core@3.0 GHz Dell
Precision T7600 workstation to host a digitizer (AlazarTech, ATS9350), a DAQ
card (National Instrument, PCI-6221), one graphics processing unit (GPU)
(NVIDIA, Geforce GTX580). A-line trigger and k-clock signal from the laser
source are routed to the specific ports of the digitizer for equal k-space A-line data
sampling. The DAQ card generates MEMS control waveforms and synchronized
digital output as frame trigger to the digitizer for the acquisition start of a frame.
GPU is used to achieve real-time signal processing and image display. All the
scanning control and synchronization, data acquisition, image processing, and
rendering were performed on a multi-thread, CPU-GPU heterogeneous
computing system. The hybrid computing system and a customized user interface
was designed and programmed through Qt 4.8.5 and C++ (Microsoft Visual
Studio, 2008). We used computer unified device architecture (CUDA) version 5.0
from NVIDIA to program the GPU for general purpose computations.
Fig. 3(b) shows the carefully designed control waveforms generated by the DAQ
to the MEMS driver and digitizer for C-mode raster scanning imaging. An
internal clock with a sampling rate of 50 kHz was used as the clock source for the
fast-moving X and slow-moving Y waveforms. Each waveform consisted of
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 6/14
252 sections while the first and the last section were used to put and return the
MEMS mirror at a global starting point in the Y direction. Each section consists of
1400 sampling points. Fast-moving X waveform is quasi-sinusoidal with the first
and last 200 points of the section serving as the lead-in and lead-out points to put
the mirror from the zero point to acquisition start point and guide the mirror
back from the acquisition end point to the zero point in X direction. A
synchronized digital output from the DAQ with a rising edge as a frame trigger
was routed to the digitizer frame start trigger input, shown as green lines in
Figure 3. Schematic system setup and MEMS mirror control waveforms. (a) system configuration (C:
circulator, PC: polarization controller, DAQ: data acquisition card.) (b) filtered and scaled waveforms
generated by DAQ to MEMS driver to control the scanning mirror.
doi:10.1371/journal.pone.0114215.g003
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 7/14
Fig. 3(b). Once the trigger is detected, the system acquires 1000 A-lines in the
linear region, which is shown as the red dots for X imaged points and yellow dots
for Y imaged points. Each A-line consists of 1024 sampling points in the spectral
domain. The waveforms are updated periodically and iteratively through these
252 sections once a section is generated. For B-mode imaging, we simply set the Y
output to be zero all the time. Scan patterns can be switched at any time with a
delay of a few tens of milliseconds from B-mode to C-mode. Since the signal
generation source clock is 50 kHz and each section consists of 1400 points, this
gives us an effective imaging speed of 36 frames per second. It needs to be pointed
out that the imaging frame rate can be further increased by reducing the designed
imaged points or reducing the linearity of the scanning region by allowing the
MEMS mirror to perform more resonant scanning.
Imaging Protocol and Data Quantification Analysis
The OCT system was running at 36 fps with each frame size of 10006512 pixels,
corresponds to 1.5 mm (fast X)65 mm (axial) at 2D scanning mode. The 3D
volume scanning mode consists of 252 frames in the slow Y axis, which took
around 7 seconds to complete. Thus 252610006512 (1.561.565mm
3
) voxels
is acquired to cover the area of interest. Postoperative manual segmentation and
image analysis was through ImageJ 1.46r (NIH). Inner lumen area, lumen patency
rate, lumen narrowing rate and thrombosis percentage were extracted.
Results and Discussion
After assembling the probe and setting up the system, we carefully evaluated the
probe performance experimentally. Prior to the evaluation we carefully matched
the dispersion of the sample and reference through hardware first. Residual
second-order dispersion matching was achieved through our real-time numerical
dispersion compensation method [12]. We first analyzed axial resolution of the
system. Fig. 4(a) shows the measured results over the imaging range. An average
axial resolution of 12.6 mmis achieved. We evaluated the lateral resolution of our
system by imaging a USAF-1951 resolution target; the result is shown in Fig. 4(a)
inset. We can resolve up to the Group 5 Element 6, which implies a lateral
resolution of 17.5 mm. This is very close to the theoretically predicted value of
16 mmusing the formula 0.61fl/D assuming a focal length of objective lens (f)
30 mm and beam diameter (D) of 1.5 mm, where lis the central wavelength of
light source (1.31 mm). The system sensitivity was measured to be 84 dB by
putting a mirror as the sample at 0.4 mm from the zero-delay line and a neutral
density filter in front of the mirror. The system sensitivity roll-off is shown in
Fig. 4(b); the average decay is 5.7 dB/mm. We compared these values to a
standard galvanometer-based scanning system using an LSM04 3X OCT scan lens,
which has a sensitivity of 98 dB and a 4.7 dB/mm sensitivity roll-off. Reduced
sensitivity is probably due to the increased signal loss in the current MEMS probe
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 8/14
compared to a scan lens-based system. Larger sensitivity decay is due to the
reduced depth of focus of the current lens that has a focal length of 30 mm
compared to 54 mm of LSM04. Therefore further optical system optimization of
the probe through customizing lens design and coating will be achieved.
To evaluate the phase stability and thus the Doppler imaging sensitivity of the
imager, we imaged a stationary mirror and extracted the phase value of the mirror
surface position. A phase histogram is plotted in Fig. 4(c). By Gaussian fitting the
experimental data, the standard deviation of the fitting curve gave us a standard
deviation of 70 mrad, which is due to the combination of the system noise, MEMS
mirror-scanning noise, and the environmental noise. The Doppler flow imaging
speed range thus is calculated to be from 0.363 mm/s to 16.3 mm/s in both
directions parallel to the scanning beam using v(axical)5lDQ/4pDt), where Dt
equals 20 ms.
To evaluate the structure and Doppler imaging capability of our system before
animal experiments, we imaged an ex-vivo cow eye cornea shown in Fig. 4(d); all
layers are clearly visualized. We also imaged an in-vivo chorioallantoic membrane
(CAM) of a 16-day-aged chick embryo. Fig. 4(e) shows the structure image of one
vessel cross-section. Fig. 4(f) shows the corresponding Doppler image. We can see
the nearly parabolic distribution of the blood flow within the vessel lumen.
Figure 4. OCT System performance evaluation. (a) measured axial resolution over the imaging range,
inset: lateral resolution image of USAF target; (b) sensitivity roll-off over the imaging range; (c) measured
phase stability of a stationary mirror. (d) 5 frames averaged cornea imaging. (e) 5 frames averaged chicken
embryo imaging. (f) 5 frames averaged corresponding Doppler flow imaging of (e) (scale bar: 500 mm, Doppler
color bar range: 216.3 mm/s to 16.3 mm/s).
doi:10.1371/journal.pone.0114215.g004
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 9/14
Consecutively, the application of the handheld OCT imager for in-vivo mouse
microvascular anastomosis evaluation is tested. To describe how the probe was
used in animal experiment, Fig. 5(a) shows the probe held by the surgeon to
investigate the experimented mouse vessel. Fig. 5(b) demonstrates how the OCT
beam scans across the surgical site with a vessel groove adapted to the vessel. Note
that the vessel groove was not implemented in current probe version and will be
incorporated into our future version. The slow scanning direction indicated by
white arrow repeats every 252 frames to acquire volumetric images of the surgical
site. Fig. 6 shows selective frames of simultaneous structure and Doppler imaging
of the surgical sites from distal (left) to proximal (right) end of the blood vessel
under investigation: Fig. 6(a) (Mouse 1 Artery Cuff, Video S1), Fig. 6(b) (Mouse 1
Vein Cuff, Video S2) and Fig. 6(c) (Mouse 2 Artery Suture, Video S3). Successful
blood flow restoration, high vessel lumen patency, minimal lumen narrowing, and
thrombosis formation are important parameters for the surgeon to predict
successful surgical outcome. To analyze these parameters, all the selected frames
were manually segmented and highlighted using ImageJ 1.46r (NIH). The white
line encloses the inner lumen of the vessel; the yellow line outlines the blood
flowing area within the inner lumen if thrombosis was detected within the lumen.
The structure and Doppler images were cropped to a size of 1.5 mm (lateral) by
2 mm (axial). From Doppler images of Fig. 6, we can see clearly that all the blood
flow was restored successfully. Strong pulsatile artery flow was clearly visualized.
As vessel lumen diameter narrows, flow turbulences were also captured at suture-
rich sites. Blood flowing area was segmented using Doppler images. For Fig. 6(a),
the area of the artery inner lumen goes from 0.21 mm
2
(left) to 0.16 mm
2
(middle) and 0.17 mm
2
(right). Using the left figure as naive reference–as there is
no surgical operation such as cuff and suture–the inner lumen narrowing can by
characterized by 23% decrease at middle image and 16% decrease at right image.
One probable reason for this inner lumen area drop is that as shown in Fig. 1(b)
Figure 5. Application of handheld probe in the mouse experiment. (a) Handheld probe investigating the
surgical site of an experimented mouse; (b) Illustration of how the beam scans across the vessel region (red
lines indicate that fast B-mode scanning beam, white arrow indicates slow beam scanning direction, yellow
circles marks vessel groove to be implemented in our future probe optimization).
doi:10.1371/journal.pone.0114215.g005
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 10 / 14
the top vessel end needs to be expanded and then attached to the bottom vessel
end, which will cause the inner lumen area increase for the top vessel. The lumen
patency was 100% at reference (left) and drops to 56% at the middle image, and
to 80% at the right image, which corresponds to 44% and 20% thrombosis
formation crossectionally, respectively. The same analysis was applied to Fig. 6(b).
Cuff-based vein inner lumen area are 0.46 mm
2
(left), 0.09 mm
2
(middle) and
0.11 mm
2
(right). The inner lumen narrowing are 80% at the middle and 76% at
the right image. This is a relatively large shrinkage in the vein. This might be an
indication for changing the cuff with a more appropriate diameter. The patency of
the left is 55% while 100% for the middle and right images. For suture-based
artery anastomosis, the inner lumen area is 0.18 mm
2
(left), 0.11 mm
2
(middle)
and 0.13 mm
2
(right), respectively. The inner lumen narrowing values are 39% at
the middle and 28% at the right. The patency was all 100% over the images. No
thrombosis was detected. Currently, there is no detailed study of correlating inner
lumen area, restenosis, and thrombosis formation percentage with long-term
Figure 6. Selective frames of simultaneous structure and Doppler imaging of the surgical sites from distal (left) to proximal (right). White lines
represent manually segmented blood vessel inner lumen, red lines represent manually segmented thrombosis, blue lines outline the blood flowing area
within the vessel inner lumen. (a) Mouse 1 artery (Video S1); (b) Mouse 1 vein (Video S2) and (c) Mouse 2 artery (Video S3). Videos were played back at 24
frames per second. Images were cropped to best fit the area of interest (scale bar: 500 mm, Doppler color bar range: 216.3 mm/s to 16.3 mm/s).
doi:10.1371/journal.pone.0114215.g006
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 11 / 1 4
surgical outcome; however, we believe that all these parameters are not only of
vital importance for immediate surgical outcome evaluation but also for long-
term anastomosis patency prediction. With detailed quantitative image analysis,
handheld OCT intraoperative imaging might also help the surgeons to optimize
their technique.
Compared to our previous imaging results using 850 nm band OCT systems,
1.3 mm central wavelength shows larger image penetration depth, which enables
us to evaluate the inner lumen structure of vessels more accurately. At current
study, the vessel inner diameter is around 0.5 mm. For larger size vessels (0.5–
1 mm), when penetration depth becomes an issue for imaging, an angular
compounding method will be used and evaluated. Currently detailed quantitative
blood flow information analysis is limited by the phase wrapping of blood flow at
high speed combined with turbulence. Proper correction methods need to be
implemented in the future to resolve this issue. Noticeably from the video images
there is hand tremor imposed on vessel imaging. A special vessel adapter, such as
V-groove on the probe tip will be fabricated so that the probe can rest on the
mouse limb without pressing the vessel. Furthermore, three-dimensional motion-
compensation algorithms will be developed and applied to remove motion
artifacts. Thus, more comprehensive volumetric information of the vessel under
investigation can be extracted.
Conclusion
We have demonstrated a compact user-friendly handheld MEMS scanning
mirror-based imager for intraoperative evaluation of microvascular anastomosis
and the proof was tested using a mouse model. It can provide real-time
simultaneous structure and Doppler flow imaging at a speed of 36 frames per
second. The imager performance was carefully characterized experimentally and
later evaluated through in-vivo mouse femoral vessel anastomosis via both suture
and non-suture cuff techniques. Parameters such as vessel inner lumen area,
lumen narrowing, and partial thrombosis formation were extracted quantitatively
from the imaging results. In conclusion, we believe that the intraoperative
application of this handheld OCT imager will greatly improve the quality of
microvascular repair and vascular patency and thereby significantly increase long
term results after microsurgical vascular repair. Additionally this application
allows for real-time performance evaluation and thus provides an optimal
platform for in situ performance evaluations in microsurgical trainees.
Supporting Information
Checklist S1. ARRIVE checklist.
doi:10.1371/journal.pone.0114215.s001 (DOCX)
Handheld OCT Imager for Vascular Anastomosis
PLOS ONE | DOI:10.1371/journal.pone.0114215 December 4, 2014 12 / 14
Video S1. Crossectional inspection of Mouse 1 Artery (using cuff technique)
over the surgical site.
doi:10.1371/journal.pone.0114215.s002 (MP4)
Video S2. Crossectional inspection of Mouse 1 Vein (using cuff technique) over
the surgical site.
doi:10.1371/journal.pone.0114215.s003 (MP4)
Video S3. Crossectional inspection of Mouse 2 Artery (using suture technique)
over the surgical site.
doi:10.1371/journal.pone.0114215.s004 (MP4)
Author Contributions
Conceived and designed the experiments: YH DT SZ WPAL GB JUK. Performed
the experiments: YH GJF. Analyzed the data: YH DT SZ GJF GB JUK.
Contributed reagents/materials/analysis tools: YH GJF. Contributed to the writing
of the manuscript: YH GJF DT SZ WPAL GB JUK.
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