therapy of macular diseases. These biomarkers are also
sophisticated prognostic factors for visual outcome, with IRC
representing 1 of the most important variables associated with
vision loss and SRF possibly enhancing visual prognosis.
4
Prior studies have proposed to detect or quantify macular
fluid in OCT in an automated manner.
5
However, they are
limited to only being able to detect fluid presence or
absence without measuring its extent and distribution, by
a lack of differentiation between IRC and SRF, or by
evaluation limited to 1 particular OCT device or disease.
In this study, we present a fully automated artificial intelli-
gence method to detect and quantify IRC and SRF in macular
OCT volume scans. We validate our method on a large dataset of
eyes presenting with the major relevant exudative macular dis-
eases, that is, neovasc ular age-related macular degeneration
(AMD), diabetic macular edema (DME), and macular edema
secondary to retinal vein occlusion (RVO), imaged with the
most commonly used OCT devices (Heidelberg Spectralis,
Heidelberg Engineering, Heidelberg, Germany, and Zeiss
Cirrus, Carl Zeiss Meditec, Dublin, CA).
Methods
Image Dataset
This study followed the tenets set forth in the Declaration of Helsinki,
and approval was obtained by the Ethics Committee of the Medical
University of Vienna. A total of 1200 completely anonymized OCT
volume scans of eyes affected by the major diseases typically causing
macular fluid (AMD, DME, and RVO) were extracted from the Vienna
Reading Center database. Furthermore, for each disease we selected
scans by 2 different OCT devices (Cirrus HD-OCT, Carl Zeiss Meditec,
and Spectralis OCT, Heidelberg Engineering), resulting in 6 distinct
groups (disease device) of OCT scans.
For detection of fluid, we used 1200 anonymized OCT volumes of
patients with neovascular AMD (n ¼ 400), DME (n ¼ 400), and RVO
(n ¼ 400) acquired with Cirrus (50%) or Spectralis (50%) devices. In
each disease/device group, 50% of the OCT scans showed retinal fluid.
All scans were graded for the presence of IRC and SRF in a quality-
controlled reading center setting by 2 independent readers of the Vienna
Reading Center supervised by experienced retinal specialists. The
grading was performed on full-screen, high-resolution 27-inch monitors
in validated grading software specially designed for the annotation of
these features. In questionable cases, a consensus grading of the readers
and the supervisor was performed. Only scans with a clear consensus
annotation between the readers were taken into the sample. Scans with
primarily low image quality (i.e., scans with sections cut off because of
improper positioning during image acquisition or scans with strong
motion artifacts causing misalignment and blurring of sections) were
excluded. We randomly selected 100 scans with flu id and 100 scans
without fluid per disease/device group from the OCT database, resulting
in a total of 1200 scans.
For evaluation of fluid quantification, datasets with complete
manual annotations of IRC and SRF that were available at the Vienna
Reading Center were randomly selected. For neovascular AMD, we
used a Cirrus dataset of 152 scans as reported previously
6
and a
Spectralis dataset consisting of 60 scans. For DME, we used a dataset
of 16 Cirrus scans and a dataset of 16 Spectralis scans. For RVO, we
used a Cirrus dataset of 100 scans and a Spectralis dataset consisting
of 10 scans. The procedure used for manual annotation of macular
fluid has been reported in detail by Waldstein et al.
6
Each Cirrus cube
scan consisted of 128 B-scans with a resolution of 512 1024
pixels, with the exception of Cirrus RVO data, which consisted of
200 B-scans with a resolution of 200 1024 pixels. All cube scans
acquired on the Spectralis device consisted of 49 B-scans at a
resolution of 512 496 pixels. Both machines acquire volumes
covering approximately 6 6 2mm
3
corresponding to a field of
view of 20
20
.
Description of the Automated Method
We developed a software to perform classification among IRC,
SRF, and nonfluid regions for each location (¼ pixel) in the OCT
image by using and further developing semantic segmentation,
7
a
method based on convolutional neural networks. Specifically, we
applied deep learning, a state-of-the-art machine learning tech-
nique in the field of artificial intelligence that learns the mapping
from OCT images to pixel-level class labels based on large
amounts of labeled training data. Deep learning models allow one
to learn meaningful abstract data representations. Following the
semantic segmentation approach, the neural network maps an input
image of a specific size to an image of corresponding class labels of
the same size. The proposed neural network comprises 2 pro-
cessing components, an encoder that transforms an input image
into an abstract representation and a decoder that maps the abstract
representation to an image of clinical class labels assigning each
pixel a class such as normal tissue, IRF, or SRF.
The mapping of the encoder from raw images to abstract repre-
sentations (embeddings) was not computed on the basis of pre-
specified mathematic descriptions (handcrafted features), but the
encoder parameters were automatically learned solely on the basis of
annotated data used during training. The data embedding learned was
optimized in such a way that it was optimal for the generation of a
corresponding image of class labels. The mapping of the encoder from
raw images to the data embedding needed to generate the label image,
and the mapping of the decoder from the embedding to a full input
resolution label image were learned simultaneously (end-to-end). The
encoder and the decoder comprised a set of computing blocks (layers),
where the layers of the decoder virtually inversed the operations of the
encoder conditioned by the low-dimensional embedding learned by
the encoder. A simplified overview of the encoder-decoder architec-
ture is shown in Figure 1, and a detailed description of the algorithm
appears in the Appendix (available online at www.aaojournal.org).
The runtime of the computation depended on the resolution of
OCT volumes. For Cirrus scans, the computations took approxi-
mately 70 seconds, whereas for Spectralis scans, computations
took approximately 30 seconds per volume on a TitanX graphical
processing unit (Nvidia, Santa Clara, CA) with NVIDIA Cuda
(version 6.5) and cuDNN library (version 2).
8
Python, Theano,
9
and the Lasagne library were used to train and evaluate the deep
learning model.
10
Experimental Setup
Because of differences in the appearance of Spectralis and Cirrus
scans, we trained separate classifiers for Spectralis and Cirrus
scans. We used 70 pixel-wise annotated OCT scans performing
10-fold cross-validation including 7 scans per split for training and
testing of the model on Spectralis data. We performed 4-fold cross-
validation for training and testing of the model on Cirrus data,
where we had 257 pixel-wise annotated OCT scans and used 64
and 65 scans per split. Both datasets comprised neovascular AMD
and RVO cases. When considerably fewer scans were used to train
the model, results showed that the proposed method also achieved
a similar performance. However, the achievable performance, and
at the same time the applicability for clinical routine, increased
with the number of training volumes. When the model trained on
Cirrus data was used on Spectralis data and vice versa, results on
quantifying IRC or SRF showed that the model trained on Cirrus
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