Browsing by Subject "Alternating direction method of multipliers"

Now showing 1 - 7 of 7

Open Access
ADMM based mainlobe power constrained phase-only sidelobe supression
(IEEE, 2014) Alp, Yaşar Kemal; Arıkan, Orhan
A novel sidelobe suppression technique is proposed for phased arrays, where only the phases of the array elements are adjusted to suppress the gain in the direction of interest while keeping the mainlobe power at a certain level. Mainlobe power constrained sidelobe suppression is formulated as a convex RSDP (Relaxed Semidefinite Program). Solution to resultant RSDP is obtained by ADMM (Alternating Direction Method of Multipliers) technique, which can handle designs for arrays with number of elements is significantly larger than that can be handled by other convex solvers such as CVX. In addition, although the available convex solvers can not provide a rank-1 solution matrix, a rank-1 solution matrix is obtained by modifying the ADMM iterations. In the conducted experiments, it is observed that proposed ADMM based method can achieve more than 10dB improvement in sidelobe levels compared to alternative techniques.
Open Access
Coded scenes for fast system calibration in magnetic particle imaging
(IEEE, 2018) Ilbey, S.; Top, C. B.; Güngör, A.; Sarıtaş, Emine Ülkü; Güven, E.
Magnetic nanoparticle (MNP) agents have a wide range of clinical application areas for both imaging and therapy. MNP distribution inside the body can be imaged using Magnetic Particle Imaging (MPI). For MPI image reconstruction with the system function matrix (SFM) approach, a calibration scan is necessary, in which a single MNP sample is placed and scanned inside the full field of view (FOV), which is a very time consuming task. In this study, we propose the use of coded scenes that include MNP samples at multiple positions inside the FOV, and reconstruct the SFM using compressed sensing techniques. We used simulations to analyze the effect of number of coded scenes on the image quality, and compare the results with standard sparse reconstruction using single MNP sample scan. The results show that with the proposed method, the required number of measurements is decreased substantially, enabling a fast system calibration procedure.
Open Access
Compressed multi-contrast magnetic resonance image reconstruction using Augmented Lagrangian Method
(IEEE, 2016) Güngör, A.; Kopanoğlu, E.; Çukur, Tolga; Güven, H. E.
In this paper, a Multi-Channel/Multi-Contrast image reconstruction algorithm is proposed. The method, which is based on the Augmented Lagrangian Method uses joint convex objective functions to utilize the mutual information in the data from multiple channels to improve reconstruction quality. For this purpose, color total variation and group sparsity are used. To evaluate the performance of the method, the algorithm is compared in terms of convergence speed and image quality using Magnetic Resonance Imaging data to FCSA-MT, an alternative approach on reconstructing multi-contrast MRI data.
Open Access
Fast system calibration with coded calibration scenes for magnetic particle imaging
(IEEE, 2019) İlbey, Serhat; Top, C. B.; Güngör, Alper; Çukur, Tolga; Sarıtaş, Emine Ülkü; Güven, H. Emre
Magnetic particle imaging (MPI) is a relatively new medical imaging modality, which detects the nonlinear response of magnetic nanoparticles (MNPs) that are exposed to external magnetic fields. The system matrix (SM) method for MPI image reconstruction requires a time consuming system calibration scan prior to image acquisition, where a single MNP sample is measured at each voxel position in the field-of-view (FOV). The scanned sample has the maximum size of a voxel so that the calibration measurements have relatively poor signal-to-noise ratio (SNR). In this paper, we present the coded calibration scene (CCS) framework, where we place multiple MNP samples inside the FOV in a random or pseudo-random fashion. Taking advantage of the sparsity of the SM, we reconstruct the SM by solving a convex optimization problem with alternating direction method of multipliers using CCS measurements. We analyze the effects of filling rate, number of measurements, and SNR on the SM reconstruction using simulations and demonstrate different implementations of CCS for practical realization. We also compare the imaging performance of the proposed framework with that of a standard compressed sensing SM reconstruction that utilizes a subset of calibration measurements from a single MNP sample. The results show that CCS significantly reduces calibration time while increasing both the SM reconstruction and image reconstruction performances.
Open Access
Image reconstruction for Magnetic Particle Imaging using an Augmented Lagrangian Method
(IEEE, 2017) Ilbey S.; Top C.B.; Çukur, Tolga; Sarıtaş, Emine Ülkü; Guven H.E.
Magnetic particle imaging (MPI) is a relatively new imaging modality that images the spatial distribution of superparamagnetic iron oxide nanoparticles administered to the body. In this study, we use a new method based on Alternating Direction Method of Multipliers (a subset of Augmented Lagrangian Methods, ADMM) with total variation and l1 norm minimization, to reconstruct MPI images. We demonstrate this method on data simulated for a field free line MPI system, and compare its performance against the conventional Algebraic Reconstruction Technique. The ADMM improves image quality as indicated by a higher structural similarity, for low signal-to-noise ratio datasets, and it significantly reduces computation time. © 2017 IEEE.
Open Access
Real-time three-dimensional image reconstruction using alternating direction method of multipliers for magnetic particle imaging
(IEEE, 2018) İlbey, Serhat; Güngör, A.; Top, C. B.; Sarıtaş, Emine Ülkü; Güven, H. E.
Manyetik Parçacık Görüntüleme (MPG), süperparamanyetik demiroksit nanoparçacıklarının uzamsal dağılımını tespit etmekte kullanılan görece yeni bir medikal görüntüleme yöntemidir. MPG’de görüntü geriçatımı için kullanılan yöntemlerden biri sistem matrisi yaklaşımıdır. Bu yöntemde öncelikle kalibrasyon ölçümleri yapılarak sistem matrisi elde edilir. Daha sonra, sistem matrisi ve görüntülenen objeden alınan veri ile bir doğrusal denklem sistemi oluşturulur ve görüntülenen alandaki manyetik parçacık dağılımı yinelemeli düzenlileştirme veya eniyileme algoritmaları ile çözülür. Bu çalışmada, grafik işlemciler kullanılarak yön degiştiren çarpanlar yöntemi ile üç boyutlu bir görüntüleme uzayında gerçek zamanlı görüntü geriçatımı yapılabileceği gösterilmiştir.
Open Access
A synthesis-based approach to compressive multi-contrast magnetic resonance imaging
(IEEE, 2017) Güngör, A.; Kopanoğlu, E.; Çukur, Tolga; Güven, H. E.
In this study, we deal with the problem of image reconstruction from compressive measurements of multi-contrast magnetic resonance imaging (MRI). We propose a synthesis based approach for image reconstruction to better exploit mutual information across contrasts, while retaining individual features of each contrast image. For fast recovery, we propose an augmented Lagrangian based algorithm, using Alternating Direction Method of Multipliers (ADMM). We then compare the proposed algorithm to the state-of-the-art Compressive Sensing-MRI algorithms, and show that the proposed method results in better quality images in shorter computation time.