Rameesha Khawaja1, Amna Ammar1, Madiha Arshad1, Faisal Najeeb1, and Hammad Omer1
1MIPRG Research Group, ECE Department, Comsats University, Islamabad, Pakistan
Synopsis
Reconstruction of cine Cardiac MRI
(CMRI) is an active research area with room for improvement in motion detection
(particularly irregular cardiac motion) and modeling in order to significantly
enhance the quality of reconstructed images. Moreover, the reduction of scan
time and image reconstruction time of cine CMRI is also a key aspect of today’s
clinical requirement. We propose a dual domain cascade of neural networks
intercalated with multi-coil data consistency layers for the reconstruction of
cardiac MR images from Variable Density under-sampled data. The results show
successful reconstruction results of our proposed method when compared with conventional
compressed sensing reconstruction.
Introduction
Cardiac
Magnetic Resonance
Imaging is a highly versatile, non-invasive and latest medical imaging technique
that provides high spatial resolution, wide field-of-view and good soft tissue
contrast of the heart. Cine CMRI is the gold standard for assessing
cardiac morphology and function3. However, the slow nature of data
acquisition makes cine CMRI sensitive to motion7. In this paper, a
combined parallel imaging and hybrid dual domain deep learning framework is
proposed that learns the image reconstruction problem in both the frequency
domain and image domain for a robust reconstruction of adaptively coil combined8
under-sampled cardiac data. Our proposed deep learning framework consists of three
components: (1) a neural network (denoted as KW-Net) operating in the k-space domain to interpolate the
missing k-space information, (2) a
neural network (denoted as IW-Net) operating in image domain to restore the
images and (3) interleaved multi-coil data consistency3 incorporating the receiver coil sensitivity maps8
to provide multi-coil reconstruction.Method
The proposed deep learning framework (Figure 1) utilizes a customized
architecture of KW-Net and IW-Net (Figure 2) to reconstruct the complex-valued
zero filled variable density (VD) under-sampled human cardiac data
(Acceleration Factor (AF=4)). The KW-Net and IW-Net combined architecture is
composed of two cascaded U-Nets5. For the proposed deep learning
algorithm, the training dataset is extracted from the fully sampled,
multi-slice, eight receiver coils human cardiac data4 of fifteen
patients. The fully sampled multi-slice eight coil human cardiac k-space data is VD under-sampled by an
AF of 4; followed by an adaptive coil combination to get the composite under-sampled
k-space data. This zero filled VD
under-sampled k-space data is used as
the input whereas the corresponding fully sampled k-space data is used as the ground truth for training the KW-Net. K-space data is complex-valued, so for
training of the KW-Net, the real and imaginary parts of the complex k-space data are concatenated along the channel
dimension.
The output of the trained KW-Net is the interpolated complex k-space data. The inverse fast Fourier
transform of the interpolated complex k-space
data provides an interpolated image. Multi-coil data consistency3 is applied on the interpolated image to
generate the corrected images which are given as an input to the IW-Net to
remove the remaining aliasing artifacts. In multi-coil data consistency3, sensitivity maps are used to apply data
consistency on the multi-coil interpolated images which are later ‘coil
combined’ to get the corrected composite images. The IW-Net is trained by using
the corrected images as an input and the corresponding fully sampled images as the
ground truth label. The multi-coil data consistency3 is applied again on the output of IW-Net to
get the final reconstructed image by taking the coil combinations of the multi
coil images, as discussed above.
In our experiments, we use
RMS prop optimizer to minimize the loss function of mean square error. The
proposed method is later tested on human cardiac data4 of five
patients obtained from a 1.5T
scanner. The reconstruction results obtained from the proposed method are
compared with the conventional Compressed Sensing reconstruction9.Results
Figure
3 shows the cardiac reconstruction results obtained from the proposed method
and compressed sensing. The Root Mean Square Error (RMSE) of the reconstructed
images obtained from the proposed method and compressed sensing are 0.0398 and 0.0415,
respectively, showing that our proposed method outperforms compressed sensing
in reconstructing the cardiac MR images from under-sampled k-space data. Moreover, visual inspection of the results
shows that the reconstruction results obtained from the proposed method are
sharper as compared to the compressed sensing reconstruction.Discussion and Conclusion
We propose a hybrid dual domain cascaded deep learning
framework to reconstruct the human cardiac images from zero filled VD under
sampled k-space data. In our proposed
method, first the KW-Net
has been used as an interpolator in k-space
domain. Once the missing k-space
information has been interpolated, it becomes easy for IW-Net to learn the
image restoration problem in the image domain. The proposed method surpasses
the conventional compressed sensing method in reconstructing the cardiac images
as indicated by their RMSE values and visual quality of the solution images.Acknowledgements
No acknowledgement found.References
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