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Experimental validation of a three-dimensional linear system model for breast tomosynthesis.

ABSTRACT: A three-dimensional (3D) linear model for digital breast tomosynthesis (DBT) was developed to investigate the effects of different imaging system parameters on the reconstructed image quality. In the present work, experimental validation of the model was performed on a prototype DBT system equipped with an amorphous selenium (a-Se) digital mammography detector and filtered back-projection (FBP) reconstruction methods. The detector can be operated in either full resolution with 85 microm pixel size or 2 x 1 pixel binning mode to reduce acquisition time. Twenty-five projection images were acquired with a nominal angular range of +/- 20 degrees. The images were reconstructed using a slice thickness of 1 mm with 0.085 x 0.085 mm in-plane pixel dimension. The imaging performance was characterized by spatial frequency-dependent parameters including a 3D noise power spectrum (NPS) and in-plane modulation transfer function (MTF). Scatter-free uniform x-ray images were acquired at four different exposure levels for noise analysis. An aluminum (Al) edge phantom with 0.2 mm thickness was imaged to measure the in-plane presampling MTF. The measured in-plane MTF and 3D NPS were both in good agreement with the model. The dependence of DBT image quality on reconstruction filters was investigated. It was found that the slice thickness (ST) filter, a Hanning window to limit the high-frequency components in the slice thickness direction, reduces noise aliasing and improves 3D DQE. An ACR phantom was imaged to investigate the effects of angular range and detector operational modes on reconstructed image quality. It was found that increasing the angular range improves the MTF at low frequencies, resulting in better detection of large-area, low-contrast mass lesions in the phantom. There is a trade-off between noise and resolution for pixel binning and full resolution modes, and the choice of detector mode will depend on radiation dose and the targeted lesion.

SUBMITTER: Zhao B

PROVIDER: S-EPMC2673665 | biostudies-other | 2009 Jan

REPOSITORIES: biostudies-other

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Project description:Previously, the authors developed a dual-energy (DE) acquisition technique for a photon-counting digital breast tomosynthesis (DBT) imaging system. Low-energy (LE) and high-energy (HE) images are acquired in a single scan by covering alternate slits of a multislit prepatient collimator with Sn and Cu, respectively. A theoretical model was used to optimize the technique. In this article, an experimental validation of this technique is presented.Experiments were performed on a prototype DBT system. LE and HE projection images were acquired sequentially; either a Sn or a Cu filter was positioned in the filter holder at the exit window of the x-ray tube. Sn filters from 0.113 to 0.242 mm thick and Cu filters from 0.103 to 0.267 mm were used. The images were acquired with a W target at 49 kV. Tomographic images, hereafter referred to as DBT images, were reconstructed using a shift-and-add algorithm. DE-DBT images were obtained by weighted logarithmic subtraction of the LE and HE images. Weighting factors w(t) that optimally cancel breast tissues with two different glandularities were assessed for 20-80 mm thick phantoms with 0%, 50%, and 100% glandularity. The mean and standard deviation in the per-pixel signal intensity (SI) were calculated in the DBT images. These data were used to calculate signal-difference-to-noise ratios (SDNRs) between iodine enhanced and nonenhanced polymethyl methacrylate backgrounds. To illustrate the feasibility of the technique, DE-DBT images of a structured phantom containing iodine disks were assessed. The experimental results were compared against the values obtained from a theoretical model of the imaging system.The average difference between theoretical and experimental w(t) was found to range from 8% to 21%. Experimental w(t) values increase with phantom thickness and Cu thickness, depend somewhat on Sn thickness, and vary more as a function of breast composition in thick breasts than in thin breasts. Theoretical and experimental mean and standard deviation in the per-pixel SI differ by -7% to 10% and by -3% to 4%. Theoretical and experimental SDNR values differ, on average, by 1.5%. Iodine concentrations can be predicted from SDNR; the relationship can be accurately fit to a quadratic. In the images of the structured phantom, iodine concentrations of 1 mg/cm2 and larger are discernable.The strong agreement between experimental and theoretical results in this article indicates that the authors' computer model is accurate.

Project description:The goal of the present study was to develop a fully three-dimensional (3D) coculture system that would allow for systematic evaluation of the interplay between activated macrophages (AMs) and chondrocytes in osteoarthritic disease progression and treatment. Toward this end, our coculture system was first validated against existing in vitro osteoarthritis models, which have generally cultured healthy normal chondrocytes (NCs)-in two-dimensional (2D) or 3D-with proinflammatory AMs in 2D. In this work, NCs and AMs were both encapsulated within poly(ethylene glycol) diacrylate hydrogels to mimic the native 3D environments of both cell types within the osteoarthritic joint. As with previous studies, increases in matrix metalloproteinases (MMPs) and proinflammatory cytokines associated with the early stages of osteoarthritis were observed during NC-AM coculture, as were decreases in protein-level Aggrecan and collagen II. Thereafter, the coculture system was extended to osteoarthritic chondrocytes (OACs) and AMs to evaluate the potential effects of AMs on pre-existing osteoarthritic phenotypes. OACs in coculture with AMs expressed significantly higher levels of MMP-1, MMP-3, MMP-9, MMP-13, IL-1β, TNF-α, IL-6, IL-8, and IFN-γ compared to OACs in mono-culture, indicating that proinflammatory macrophages may intensify the abnormal matrix degradation and cytokine secretion already associated with OACs. Likewise, AMs cocultured with OACs expressed significantly more IL-1β and VEGF-A compared to AM mono-culture controls, suggesting that OACs may intensify abnormal macrophage activation. Finally, OACs cultured in the presence of nonactivated macrophages produced lower levels of MMP-9 and proinflammatory cytokines IL-1β, TNF-α, and IFN-γ compared to OACs in the OAC-AM system, results that are consistent with anti-inflammatory agents temporarily reducing certain OA symptoms. In summary, the 3D coculture system developed herein captures several key features of inflammatory OA and may prove useful in future screening of therapeutic agents and/or assessment of disease progression mechanisms.

Project description:The structural morphology of coronary stents (e.g. stent expansion, lumen scaffolding, strut apposition, tissue protrusion, side branch jailing, strut fracture), and the local hemodynamic environment after stent deployment are key determinants of procedural success and subsequent clinical outcomes. High-resolution intracoronary imaging has the potential to enable the geometrically accurate three-dimensional (3D) reconstruction of coronary stents. The aim of this work was to present a novel algorithm for 3D stent reconstruction of coronary artery stents based on optical coherence tomography (OCT) and angiography, and test experimentally its accuracy, reproducibility, clinical feasibility, and ability to perform computational fluid dynamics (CFD) studies. Our method has the following steps: 3D lumen reconstruction based on OCT and angiography, stent strut segmentation in OCT images, packaging, rotation and straightening of the segmented struts, planar unrolling of the segmented struts, planar stent wireframe reconstruction, rolling back of the planar stent wireframe to the 3D reconstructed lumen, and final stent volume reconstruction. We tested the accuracy and reproducibility of our method in stented patient-specific silicone models using micro-computed tomography (μCT) and stereoscopy as references. The clinical feasibility and CFD studies were performed in clinically stented coronary bifurcations. The experimental and clinical studies showed that our algorithm (1) can reproduce the complex spatial stent configuration with high precision and reproducibility, (2) is feasible in 3D reconstructing stents deployed in bifurcations, and (3) enables CFD studies to assess the local hemodynamic environment within the stent. Notably, the high accuracy of our algorithm was consistent across different stent designs and diameters. Our method coupled with patient-specific CFD studies can lay the ground for optimization of stenting procedures, patient-specific computational stenting simulations, and research and development of new stent scaffolds and stenting techniques.

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Experimental validation of a three-dimensional linear system model for breast tomosynthesis.

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