2 Zhanqiang Guo et al.
computed from hessian matrix [6,7]. Combined with the features extracted by
the rules formulated artificially, some other traditional methods are also used for
vessel segmentation. Yang et al. [8] presented a geodesic activate contour model
to segment blood vessels, which adaptively configures parameters. Zhao et al.
[9] proposed a likelihood model based on level set, achieving good results for
segmentation of vascular network. Lv et al. [10] proposed a parallel algorithm
based on heterogeneous Markov random field to segment vessels. However, these
methods depend heavily on domain knowledge which may be inaccurate, and
thus are not robust to image quality.
Recently, deep learning methods are widely used in the field of medical image
processing. The segmentation algorithms based on convolutional neural network
have been shown to produce state of the art results in various medical segmenta-
tion tasks [11,12,13,14]. One of the most notable methods is 3DUnet [15]. Similar
to it, Fausto et al. [16] used convolution instead of max-pooling and residual con-
nections to improve performance. Inspired by the inception model [17], Pedro et
al. [18] proposed Uception for vascular segmentation, which increases the net-
work size to have a better representation. To reduce computational burden and
memory consumption in 3D segmentation, 2D orthogonal cross-hair filters were
formulated in DeepVesselNet [19]. Zhang et al. [20] proposed RENet to remove
redundant features and retain edge information in shallow features, and reported
good results in segmentation of cerebral vessels. Based on Multiple-U-Net, Guo
et al. [21] proposed a novel network for vessel segmentation. Aimed for CTA
images, Fu et al. [22] proposed a framework based 3D convolutional neural net-
work for segmenting cerebrovascular networks. However, these methods fail to
explicitly consider the peculiarities of the vascular structure, namely, blood ves-
sels are curved and elongated tubular structure. It is difficult and unpredictable
to rely solely on network training to learn these characteristics of vessels from
training data, especially when the size of training set is limited, which is typical
in medical image analysis.
In response to the problems mentioned above, we propose a Vessel Oriented
Filtering Network (VOF-Net) that combines domain knowledge and deep learn-
ing method. First, we propose a vessel orientation estimation network to calcu-
late the orientation field of blood vessels, through which vessel oriented filters are
designed. Then, we feed the extracted vessel features to a 3DUnet based vessel
segmentation network, which is trained to combine information from features
extracted by oriented filters. Experiments on CTA and MRA datasets show that
our proposed method yields better result than other popular vascular segmen-
tation methods.
2 Methodology
Our proposed system, as shown in Fig. 1, consists of three modules: Orientation
Estimation Network, Oriented Filtering Module, and Segmentation Network.