Ali Dinler

Digital Breast Tomosynthesis imaging using compressed sensing based reconstruction for 10 radiation doses real data

Abstract Purpose Digital Breast Tomosynthesis (DBT) has recently proved promising in producing three-dimensional (3D) images of a breast. Algebraic reconstruction technique (ART), which is one of the most frequently used iterative image reconstruction techniques, has been proposed to provide satisfactory images of the breast in detecting masses and micro-calcifications. However, the greatest limitation of DBT imaging is the level of radiation dose due to the very sensitive nature of the breast. Recently, the effect of total variation (TV) minimization to enhance the image quality and to reduce the noise has been investigated in DBT imaging. Studies dealing with 3D TV minimization with ART have attracted increasing attention in the field of image reconstruction. This work investigates if iterative reconstruction techniques applied without and with TV (ART and ART + TV3D) can help reduce the level of dose in DBT imaging. Methods Projections of a realistic breast phantom (CD Pasmam 1054) were acquired with a Siemens MAMMOMAT DBT scanner at 10 different doses. The effect of dose and the methods in the reconstruction quality was assessed both quantitatively and qualitatively. Results ART + TV3D showed superior results in terms of visual assessment, contrast-to-noise ratio (CNR) and full width at half maximum (FWHM) values, and one-dimensional (1D) profiles compared with ART. CNR values were evaluated for two different regions of interest (ROIs). For instance, CNR values of ROI-1 of ART and of ART + TV3D were 46.380 and 47.675 at 63 mAs, 48.945 and 50.632 at 90 mAs, and 51.248 and 52.867 at 199 mAs, respectively. Additionally, FWHM values for ART and ART + TV3D were 2.373 and 1.758 at 63 mAs, 1.930 and 1.467 at 90 mAs, and 1.591 and 1.223 at 199 mAs, respectively. Conclusions The results suggested that a compressed sensing based iterative reconstruction method (ART + TV3D) could help decrease the radiation dose level that is one of the most critical limitations of DBT imaging.

Investigation of the Inertial Focusing Behavior in Curved Microfluidic Channels for Different Aspect Ratio

Inertial focusing has attracted a significant attention in microfluidics applications in recent years. Inertial focusing occurs only under specific flow conditions at which particles migrate across streamlines to a specific number of equilibrium positions. This behavior is mostly not sensitive to the particle size in straight channels. However, curved channels can allow sized based particle separation. In this study, curved channels with various aspect ratios have been investigated by numerical simulations. Consideration of flow regimes reveals that some conditions establish a high-quality single-particle focusing situation which is characterized by the alignment of particles within a narrow band. The outcomes of our numerical model contribute to the understanding of limitation of particle focusing and particle separation in curved microchannels.Copyright

2D versus 3D total variation minimization in digital breast tomosynthesis

Total variation (TV) minimization has become an important tool for the sparse image reconstruction. In this study a realistic 3D digital breast tomosynthesis (DBT) data was reconstructed and compared using two different forms of TV: (i) 2D reconstruction by applying TV layer by layer (ii) 3D reconstruction of the entire data. It can be assumed that a 3D reconstruction should perform better. However, in real DBT the resolution in z direction is about 10-15 times lower than the resolution in x-y plane. This study investigates the performance of the reconstruction when a TV term in z direction is added into the cost function of TV minimization.

Digital breast tomosynthesis imaging using total variation and non-local means

Digital breast tomosynthesis (DBT) generates 3D images of breast by using 2D projections taken from a limited view angle. Due to the ill-posed nature of the image reconstruction in DBT alternative image reconstruction methods have been introduced for better image quality. In this study, an efficient DBT image reconstruction algorithm has been introduced. The proposed method was formulated as combination of algebraic reconstruction technique (ART), total variation (TV) and non-local means (NLM). A real DBT data set and a commercially available 3D phantom were used for performance evaluations. Results of our study showed that ART+TV+NLM helped in obtaining better reconstructed images than those obtained by ART and ART+TV in terms of reduced background noise, out-of-plane artifacts while keeping the details well-preserved.

Velocity inversion and predicting velocity slip on curved surfaces

Couette flow between two concentric rotating cylinders is a classical fluid dynamics problem that is discussed in many textbooks. However, under certain conditions, the flow between the cylinders can exhibit a highly non-intuitive behavior. For example, when the inner cylinder is rotating and the outer cylinder is stationary, it is possible to obtain an inverted velocity profile where the velocity increases unexpectedly from the rotating inner cylinder to the stationary outer cylinder. This unusual phenomenon has often been attributed to the effects of curvature since it does not occur in the equivalent planar case of Couette flow between two parallel plates. In the present study, we investigate the mechanism of velocity inversion using the direct simulation Monte Carlo method and novel velocity slip formulae. The results demonstrate that the velocity inversion cannot be explained solely by the effects of curvature. The present study shows that velocity inversion occurs due to an anomalous acceleration of...