Yang Feng1, He Wang1, and Junbo Li1
1Philips Healthcare, shanghai, China, People's Republic of
Synopsis
The shape and position of liver is varied
through respiratory movement in DCE MR liver images. A robust 3D deformable registration was employed to define the distortion between them and compensate it. As a result, the liver and vessels will be located at the exact position with the
exact shape (include vessels) of the reference image after registration. BACKGROUND
Dynamic contrast enhancement (DCE) MRI and its
quantitative hemodynamic parameters have increasing importance in diagnostic
radiology of the liver diseases. The DCE MRI usually takes long time and the
shape and position of liver is varied because of respiratory motion. Breath-holding
can significantly get rid of the intra-phase motion. However the inter-phase non-rigid
deformations still exist.
PURPOSE
The purpose
of this study is to develop a robust
3D deformable registration method that can be employed to define the distortion
between phases of DCE MRI and compensate it. Ideally, as a result, the liver
will be located at the exact position with the exact shape (include vessels) of
the reference image after registration.
METHODS
The proposed registration technique includes
five steps (Figure 1): pre-processing, liver segmentation, vessel segmentation,
Coherent Point Drift (CPD) match and B-spline based registration. In the
pre-processing step, both reference and target data sets were re-sampled to be
isotropic and a Gaussian smooth filter was used to de-noise them in 2D level
(transverse plane). Fuzzy C-means (FCM) is a clustering technique which divides
a given set of data into different groups [1]. In this case, it was used to
distinguish liver tissues from other tissues based on their intensity
differentiation. The mathematical morphology method was then used three times
with different structural elements (shape and size) to remove irrelevant
tissues or noises [2, 3]. Vessels were segmented by de-noising the non-liver
regions inside of the corresponding liver regions using a thresholding method. The
boundaries of segmented livers and vessels in 2D images were reconstructed into
3D point clouds for the reference and target data respectively and the CPD technique
was used to find the correspondences between them [4, 5]. A B-spline based free
form deformation (FFD) method was then applied based on this match to find the
best distortions between them [6].
RESULTS
As shown in Figure 2 and 3, with appropriate
parameter settings, liver tissues and vessels inside of livers in the target
data set (end-expiratory DCE MRI) were registered and deformed based on the
information in the reference data set (end-inspiratory DCE MRI) automatically.
The SSD of manually defined boundary points of vessels and livers before and
after registration was shown in Figure 4 to assess the performance of the
proposed method. The SSD for both livers and vessels was significantly reduced
through the registration process (39.77% for liver and 54.38% for vessels by
average). And the overlap rate of liver volumes was increased from 43.19%
before registration to 93.62% after registration.
DISCUSSION
The registered results by the proposed technique
were checked in both transverse and coronal plane and it was considered to be
clinically acceptable for test data sets. In DCE MRI studies, an accurate knowledge
of the vascular signal intensity as a function of time is crucial for the
estimation of kinetic parameters. In this study, as shown in Figure 3 and 4, not
only liver volume was replaced and deformed accurately, the vessels were also
well registered.
CONCLUSION
The proposed registration method can identify
both the rigid and non-rigid differences between livers in DCE MR images taken
at different time points fully automatically. As a result, it can deform the
target data set and track the shape and position variation of livers as well as
the vessels inside of them accurately.
Acknowledgements
No acknowledgement found.References
[1] Bezdek
J C, Ehrlich R, Full W. FCM: The fuzzy c-means clustering algorithm. Computers
& Geosciences, 1984, 10(84):191-203.
[2] Serra J. Introduction to mathematical
morphology. Computer Vision Graphics & Image Processing, 1986,
35(3):283-305.
[3] Yin X Y. Edge Detection Based on
Mathematical Morphology in the Two Color Spaces. Journal of Weinan Normal
University, 2015.
[4] Myronenko A, Song X. Point Set Registration:
Coherent Point Drift. IEEE Transactions on Pattern Analysis & Machine
Intelligence, 2010, 32(12):2262-2275.
[5] Aidibe A, Tahan A. The Coherent Point Drift
Algorithm Adapted for Fixtureless Metrology of Non-rigid Parts. Procedia Cirp,
2015, 27:84–89.
[6] Hualiang Z, Ning W, Gordon J J, et al. An
adaptive MR-CT registration method for MRI-guided prostate cancer radiotherapy.
Physics in Medicine & Biology, 2015, 60:2837-2851.