790 research outputs found
Robust Non-Rigid Registration with Reweighted Position and Transformation Sparsity
Non-rigid registration is challenging because it is ill-posed with high
degrees of freedom and is thus sensitive to noise and outliers. We propose a
robust non-rigid registration method using reweighted sparsities on position
and transformation to estimate the deformations between 3-D shapes. We
formulate the energy function with position and transformation sparsity on both
the data term and the smoothness term, and define the smoothness constraint
using local rigidity. The double sparsity based non-rigid registration model is
enhanced with a reweighting scheme, and solved by transferring the model into
four alternately-optimized subproblems which have exact solutions and
guaranteed convergence. Experimental results on both public datasets and real
scanned datasets show that our method outperforms the state-of-the-art methods
and is more robust to noise and outliers than conventional non-rigid
registration methods.Comment: IEEE Transactions on Visualization and Computer Graphic
ํด๋ถํ์ ์ ๋ PET ์ฌ๊ตฌ์ฑ: ๋งค๋๋ฝ์ง ์์ ์ฌ์ ํจ์๋ถํฐ ๋ฅ๋ฌ๋ ์ ๊ทผ๊น์ง
ํ์๋
ผ๋ฌธ (๋ฐ์ฌ) -- ์์ธ๋ํ๊ต ๋ํ์ : ์๊ณผ๋ํ ์๊ณผํ๊ณผ, 2021. 2. ์ด์ฌ์ฑ.Advances in simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) technology have led to an active investigation of the anatomy-guided regularized PET image reconstruction algorithm based on MR images. Among the various priors proposed for anatomy-guided regularized PET image reconstruction, Bowsherโs method based on second-order smoothing priors sometimes suffers from over-smoothing of detailed structures. Therefore, in this study, we propose a Bowsher prior based on the l1 norm and an iteratively reweighting scheme to overcome the limitation of the original Bowsher method. In addition, we have derived a closed solution for iterative image reconstruction based on this non-smooth prior. A comparison study between the original l2 and proposed l1 Bowsher priors were conducted using computer simulation and real human data. In the simulation and real data application, small lesions with abnormal PET uptake were better detected by the proposed l1 Bowsher prior methods than the original Bowsher prior. The original l2 Bowsher leads to a decreased PET intensity in small lesions when there is no clear separation between the lesions and surrounding tissue in the anatomical prior. However, the proposed l1 Bowsher prior methods showed better contrast between the tumors and surrounding tissues owing to the intrinsic edge-preserving property of the prior which is attributed to the sparseness induced by l1 norm, especially in the iterative reweighting scheme. Besides, the proposed methods demonstrated lower bias and less hyper-parameter dependency on PET intensity estimation in the regions with matched anatomical boundaries in PET and MRI.
Moreover, based on the formulation of l1 Bowsher prior, the unrolled network containing the conventional maximum-likelihood expectation-maximization (ML-EM) module was also proposed. The convolutional layers successfully learned the distribution of anatomically-guided PET images and the EM module corrected the intermediate outputs by comparing them with sinograms. The proposed unrolled network showed better performance than ordinary U-Net, where the regional uptake is less biased and deviated. Therefore, these methods will help improve the PET image quality based on the anatomical side information.์์ ์๋ฐฉ์ถ๋จ์ธต์ดฌ์ / ์๊ธฐ๊ณต๋ช
์์ (PET/MRI) ๋์ ํ๋ ๊ธฐ์ ์ ๋ฐ์ ์ผ๋ก MR ์์์ ๊ธฐ๋ฐ์ผ๋ก ํ ํด๋ถํ์ ์ฌ์ ํจ์๋ก ์ ๊ทํ ๋ PET ์์ ์ฌ๊ตฌ์ฑ ์๊ณ ๋ฆฌ์ฆ์ ๋ํ ์ฌ๋์๋ ํ๊ฐ๊ฐ ์ด๋ฃจ์ด์ก๋ค. ํด๋ถํ ๊ธฐ๋ฐ์ผ๋ก ์ ๊ทํ ๋ PET ์ด๋ฏธ์ง ์ฌ๊ตฌ์ฑ์ ์ํด ์ ์ ๋ ๋ค์ํ ์ฌ์ ์ค 2์ฐจ ํํํ ์ฌ์ ํจ์์ ๊ธฐ๋ฐํ Bowsher์ ๋ฐฉ๋ฒ์ ๋๋๋ก ์ธ๋ถ ๊ตฌ์กฐ์ ๊ณผ๋ํ ํํํ๋ก ์ด๋ ค์์ ๊ฒช๋๋ค. ๋ฐ๋ผ์ ๋ณธ ์ฐ๊ตฌ์์๋ ์๋ Bowsher ๋ฐฉ๋ฒ์ ํ๊ณ๋ฅผ ๊ทน๋ณตํ๊ธฐ ์ํด l1 norm์ ๊ธฐ๋ฐํ Bowsher ์ฌ์ ํจ์์ ๋ฐ๋ณต์ ์ธ ์ฌ๊ฐ์ค์น ๊ธฐ๋ฒ์ ์ ์ํ๋ค. ๋ํ, ์ฐ๋ฆฌ๋ ์ด ๋งค๋๋ฝ์ง ์์ ์ฌ์ ํจ์๋ฅผ ์ด์ฉํ ๋ฐ๋ณต์ ์ด๋ฏธ์ง ์ฌ๊ตฌ์ฑ์ ๋ํด ๋ซํ ํด๋ฅผ ๋์ถํ๋ค. ์๋ l2์ ์ ์ ๋ l1 Bowsher ์ฌ์ ํจ์ ๊ฐ์ ๋น๊ต ์ฐ๊ตฌ๋ ์ปดํจํฐ ์๋ฎฌ๋ ์ด์
๊ณผ ์ค์ ๋ฐ์ดํฐ๋ฅผ ์ฌ์ฉํ์ฌ ์ํ๋์๋ค. ์๋ฎฌ๋ ์ด์
๋ฐ ์ค์ ๋ฐ์ดํฐ์์ ๋น์ ์์ ์ธ PET ํก์๋ฅผ ๊ฐ์ง ์์ ๋ณ๋ณ์ ์๋ Bowsher ์ด์ ๋ณด๋ค ์ ์ ๋ l1 Bowsher ์ฌ์ ๋ฐฉ๋ฒ์ผ๋ก ๋ ์ ๊ฐ์ง๋์๋ค. ์๋์ l2 Bowsher๋ ํด๋ถํ์ ์์์์ ๋ณ๋ณ๊ณผ ์ฃผ๋ณ ์กฐ์ง ์ฌ์ด์ ๋ช
ํํ ๋ถ๋ฆฌ๊ฐ ์์ ๋ ์์ ๋ณ๋ณ์์์ PET ๊ฐ๋๋ฅผ ๊ฐ์์ํจ๋ค. ๊ทธ๋ฌ๋ ์ ์ ๋ l1 Bowsher ์ฌ์ ๋ฐฉ๋ฒ์ ํนํ ๋ฐ๋ณต์ ์ฌ๊ฐ์ค์น ๊ธฐ๋ฒ์์ l1 ๋
ธ๋ฆ์ ์ํด ์ ๋๋ ํฌ์์ฑ์ ๊ธฐ์ธํ ํน์ฑ์ผ๋ก ์ธํด ์ข
์๊ณผ ์ฃผ๋ณ ์กฐ์ง ์ฌ์ด์ ๋ ๋์ ๋๋น๋ฅผ ๋ณด์ฌ์ฃผ์๋ค. ๋ํ ์ ์๋ ๋ฐฉ๋ฒ์ PET๊ณผ MRI์ ํด๋ถํ์ ๊ฒฝ๊ณ๊ฐ ์ผ์นํ๋ ์์ญ์์ PET ๊ฐ๋ ์ถ์ ์ ๋ํ ํธํฅ์ด ๋ ๋ฎ๊ณ ํ์ดํผ ํ๋ผ๋ฏธํฐ ์ข
์์ฑ์ด ์ ์์ ๋ณด์ฌ์ฃผ์๋ค.
๋ํ, l1Bowsher ์ฌ์ ํจ์์ ๋ซํ ํด๋ฅผ ๊ธฐ๋ฐ์ผ๋ก ๊ธฐ์กด์ ML-EM (maximum-likelihood expectation-maximization) ๋ชจ๋์ ํฌํจํ๋ ํผ์ณ์ง ๋คํธ์ํฌ๋ ์ ์๋์๋ค. ์ปจ๋ณผ๋ฃจ์
๋ ์ด์ด๋ ํด๋ถํ์ ์ผ๋ก ์ ๋ ์ฌ๊ตฌ์ฑ๋ PET ์ด๋ฏธ์ง์ ๋ถํฌ๋ฅผ ์ฑ๊ณต์ ์ผ๋ก ํ์ตํ์ผ๋ฉฐ, EM ๋ชจ๋์ ์ค๊ฐ ์ถ๋ ฅ๋ค์ ์ฌ์ด๋
ธ๊ทธ๋จ๊ณผ ๋น๊ตํ์ฌ ๊ฒฐ๊ณผ ์ด๋ฏธ์ง๊ฐ ์ ๋ค์ด๋ง๊ฒ ์์ ํ๋ค. ์ ์๋ ํผ์ณ์ง ๋คํธ์ํฌ๋ ์ง์ญ์ ํก์์ ๋์ด ๋ ํธํฅ๋๊ณ ํธ์ฐจ๊ฐ ์ ์ด, ์ผ๋ฐ U-Net๋ณด๋ค ๋ ๋์ ์ฑ๋ฅ์ ๋ณด์ฌ์ฃผ์๋ค. ๋ฐ๋ผ์ ์ด๋ฌํ ๋ฐฉ๋ฒ๋ค์ ํด๋ถํ์ ์ ๋ณด๋ฅผ ๊ธฐ๋ฐ์ผ๋ก PET ์ด๋ฏธ์ง ํ์ง์ ํฅ์์ํค๋ ๋ฐ ์ ์ฉํ ๊ฒ์ด๋ค.Chapter 1. Introduction 1
1.1. Backgrounds 1
1.1.1. Positron Emission Tomography 1
1.1.2. Maximum a Posterior Reconstruction 1
1.1.3. Anatomical Prior 2
1.1.4. Proposed l_1 Bowsher Prior 3
1.1.5. Deep Learning for MR-less Application 4
1.2. Purpose of the Research 4
Chapter 2. Anatomically-guided PET Reconstruction Using Bowsher Prior 6
2.1. Backgrounds 6
2.1.1. PET Data Model 6
2.1.2. Original Bowsher Prior 7
2.2. Methods and Materials 8
2.2.1. Proposed l_1 Bowsher Prior 8
2.2.2. Iterative Reweighting 13
2.2.3. Computer Simulations 15
2.2.4. Human Data 16
2.2.5. Image Analysis 17
2.3. Results 19
2.3.1. Simulation with Brain Phantom 19
2.3.2.Human Data 20
2.4. Discussions 25
Chapter 3. Deep Learning Approach for Anatomically-guided PET Reconstruction 31
3.1. Backgrounds 31
3.2. Methods and Materials 33
3.2.1. Douglas-Rachford Splitting 33
3.2.2. Network Architecture 34
3.2.3. Dataset and Training Details 35
3.2.4. Image Analysis 36
3.3. Results 37
3.4. Discussions 38
Chapter 4. Conclusions 40
Bibliography 41
Abstract in Korean (๊ตญ๋ฌธ ์ด๋ก) 52Docto
Image Deblurring and Super-resolution by Adaptive Sparse Domain Selection and Adaptive Regularization
As a powerful statistical image modeling technique, sparse representation has
been successfully used in various image restoration applications. The success
of sparse representation owes to the development of l1-norm optimization
techniques, and the fact that natural images are intrinsically sparse in some
domain. The image restoration quality largely depends on whether the employed
sparse domain can represent well the underlying image. Considering that the
contents can vary significantly across different images or different patches in
a single image, we propose to learn various sets of bases from a pre-collected
dataset of example image patches, and then for a given patch to be processed,
one set of bases are adaptively selected to characterize the local sparse
domain. We further introduce two adaptive regularization terms into the sparse
representation framework. First, a set of autoregressive (AR) models are
learned from the dataset of example image patches. The best fitted AR models to
a given patch are adaptively selected to regularize the image local structures.
Second, the image non-local self-similarity is introduced as another
regularization term. In addition, the sparsity regularization parameter is
adaptively estimated for better image restoration performance. Extensive
experiments on image deblurring and super-resolution validate that by using
adaptive sparse domain selection and adaptive regularization, the proposed
method achieves much better results than many state-of-the-art algorithms in
terms of both PSNR and visual perception.Comment: 35 pages. This paper is under review in IEEE TI
Remove Cosine Window from Correlation Filter-based Visual Trackers: When and How
Correlation filters (CFs) have been continuously advancing the
state-of-the-art tracking performance and have been extensively studied in the
recent few years. Most of the existing CF trackers adopt a cosine window to
spatially reweight base image to alleviate boundary discontinuity. However,
cosine window emphasizes more on the central region of base image and has the
risk of contaminating negative training samples during model learning. On the
other hand, spatial regularization deployed in many recent CF trackers plays a
similar role as cosine window by enforcing spatial penalty on CF coefficients.
Therefore, we in this paper investigate the feasibility to remove cosine window
from CF trackers with spatial regularization. When simply removing cosine
window, CF with spatial regularization still suffers from small degree of
boundary discontinuity. To tackle this issue, binary and Gaussian shaped mask
functions are further introduced for eliminating boundary discontinuity while
reweighting the estimation error of each training sample, and can be
incorporated with multiple CF trackers with spatial regularization. In
comparison to the counterparts with cosine window, our methods are effective in
handling boundary discontinuity and sample contamination, thereby benefiting
tracking performance. Extensive experiments on three benchmarks show that our
methods perform favorably against the state-of-the-art trackers using either
handcrafted or deep CNN features. The code is publicly available at
https://github.com/lifeng9472/Removing_cosine_window_from_CF_trackers.Comment: 13 pages, 7 figures, submitted to IEEE Transactions on Image
Processin
Fast Fiber Orientation Estimation in Diffusion MRI from kq-Space Sampling and Anatomical Priors
High spatio-angular resolution diffusion MRI (dMRI) has been shown to provide
accurate identification of complex fiber configurations, albeit at the cost of
long acquisition times. We propose a method to recover intra-voxel fiber
configurations at high spatio-angular resolution relying on a kq-space
under-sampling scheme to enable accelerated acquisitions. The inverse problem
for reconstruction of the fiber orientation distribution (FOD) is regularized
by a structured sparsity prior promoting simultaneously voxelwise sparsity and
spatial smoothness of fiber orientation. Prior knowledge of the spatial
distribution of white matter, gray matter and cerebrospinal fluid is also
assumed. A minimization problem is formulated and solved via a forward-backward
convex optimization algorithmic structure. Simulations and real data analysis
suggest that accurate FOD mapping can be achieved from severe kq-space
under-sampling regimes, potentially enabling high spatio-angular dMRI in the
clinical setting.Comment: 10 pages, 5 figures, Supplementary Material
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