Anthropomorphic breast phantoms are used to create images that mimic aspects of clinical breast images and are useful in optimization and characterization of breast imaging systems. Here, a full-sized compressed physical breast phantom is designed and manufactured with 100 m resolution, high reproducibility and x-ray properties similar to that of breast tissues. The phantom design is based on a digital model derived from the morphology and distribution of large, medium and small scale fibroglandular and inter-glandular adipose tissue observed in clinical breast computerized tomography (bCT) images. The physical phantom consists of four slabs of a polyamide-12 component that mimics adipose tissue fabricated using selective laser sintering (SLS). The fibroglandular component is a low viscosity resin doped with a small amount of zinc oxide nanoparticles (<110 nm) to increase attenuation. The phantom was imaged on a Senographe Pristina and compared to image simulations of the virtual phantom. The power spectral parameter, β was 3.8±0.2 and 3.9±0.5 for the physical and virtual phantoms in a digital mammogram. The corresponding Laplacian fractional entropy (LFE) averaged 0.22 and 0.14 across the range 0.125–1.29 mm-1. Very good texture cancellation was obtained in contrast-enhanced spectral mammography.
Anthropomorphic breast phantoms are useful for development and characterization of breast x-ray imaging systems. Rapid prototyping (RP) opens a new way for generating complex shapes similar to real breast tissue patterns at reasonably high resolution and a high degree of reproducibility. Such a phantom should have x-ray attenuation properties similar to adipose and fibroglandular tissue across a broad x-ray energy range. However material selection is limited to those that are compatible with the printing system, which often requires adding non-organic dopants. Fortunately, there are some off-the-shelf materials that may be suitable for breast phantoms. Here a polyamide-12/water texture phantom is being investigated, which can be used for mammography, tomosynthesis and breast CT. Polyamide-12 (PA-12) is shown to have linear attenuation coefficients across an energy range of 15 – 40 keV matching adipose tissue to within 10% effective breast density. A selective laser sintering (SLS) printer is used for manufacturing the phantom. The phantom was imaged on the Senographe Pristina (GE Healthcare, Chicago, IL), while initial assessment of 3D fidelity with the original design was performed by acquiring volume images of the phantom on a micro-CT system. A root mean distance error of 0.22 mm was seen between the micro-CT volume and the original. The PA-12 structures appeared to be slightly smaller than in the original, possibly due to infiltration of the water into the PA-12 surfaces. Power spectra measurements for mammograms of the simulated and physical phantoms both demonstrated an inverse power-law spectrum shape with exponent β= 3.72 and 3.76, respectively.
KEYWORDS: Nonlinear filtering, Image filtering, Digital filtering, Image processing, Image quality, Linear filtering, Denoising, Gaussian filters, Statistical modeling, Signal to noise ratio
Non-linear image processing and reconstruction algorithms that reduced noise while preserving edge detail are currently being evaluated in medical imaging research literature. We have implemented a robust statistics analysis of four widely utilized methods. This work demonstrates consistent trends in filter impact by which such non-linear algorithms can be evaluated. We calculate observer model test statistics and propose metrics based on measured non-Gaussian distributions that can serve as image quality measures analogous to SDNR and detectability. The filter algorithms that vary significantly in their approach to noise reduction include median (MD), bilateral (BL), anisotropic diffusion (AD) and total-variance regularization (TV). It is shown that the detectability of objects limited by Poisson noise is not significantly improved after filtration. There is no benefit to the fraction of correct responses in repeated n-alternate forced choice experiments, for n=2-25. Nonetheless, multi-pixel objects with contrast above the detectability threshold appear visually to benefit from non-linear processing algorithms. In such cases, calculations on highly repeated trials show increased separation of the object-level histogram from the background-level distribution. Increased conspicuity is objectively characterized by robust statistical measures of distribution separation.
KEYWORDS: Breast, Signal attenuation, Tissues, Dual energy imaging, Breast cancer, X-ray characterization, X-rays, Calibration, Manufacturing, Medicine
Breast density is more and more considered as an important risk factor for breast cancer and several quantitative breast
density evaluation methods have been proposed. The reference material for simulation of the breast attenuation properties
of glandular and adipose breast tissues is manufactured by a single provider. In order to characterize the attenuation
properties of these materials, measurements in Hounsfield Units (HU) have been performed using a CT-scanner. Breastequivalent
plates have been imaged in different configurations (plates in and orthogonal to image planes), providing
consistent results (± 1.3 HU). Breast density equivalent plates of different nominal breast density equivalences and sizes
were measured, demonstrating both a good homogeneity within the plates (± 1.8 HU) and a good consistency between
plates of the same nominal breast density equivalence (± 1.5 HU). In addition, dual energy CT provided mono-energetic
HU from which mono-energetic linear attenuation coefficients of water and glandular and adipose equivalent materials
were computed. The values for these coefficients were found in good agreement with results from literature, respectively
direct mono-energetic measurements of breast samples, and computation by combining published breast tissue atomic
compositions and linear attenuation coefficient tables. In conclusion, CT was found effective for the verification of the
breast equivalent material, and the homogeneity and consistency of the plates were found satisfactory. Furthermore, the
most recent spectral CT technology allowed demonstrating a good agreement of the attenuation properties of breastequivalent
material plates with state-of-the-art knowledge of real breast tissue attenuation.
KEYWORDS: Digital breast tomosynthesis, Breast, 3D modeling, Tissues, Binary data, 3D image processing, Biopsy, 3D acquisition, Reconstruction algorithms, X-rays
Needle insertion planning for digital breast tomosynthesis (DBT) guided biopsy has the potential to improve patient
comfort and intervention safety. However, a relevant planning should take into account breast tissue deformation and
lesion displacement during the procedure. Deformable models, like finite elements, use the elastic characteristics of the
breast to evaluate the deformation of tissue during needle insertion. This paper presents a novel approach to locally
estimate the Young's modulus of the breast tissue directly from the DBT data. The method consists in computing the
fibroglandular percentage in each of the acquired DBT projection images, then reconstructing the density volume.
Finally, this density information is used to compute the mechanical parameters for each finite element of the deformable
mesh, obtaining a heterogeneous DBT based breast model. Preliminary experiments were performed to evaluate the
relevance of this method for needle path planning in DBT guided biopsy. The results show that the heterogeneous DBT
based breast model improves needle insertion simulation accuracy in 71% of the cases, compared to a homogeneous
model or a binary fat/fibroglandular tissue model.
KEYWORDS: Modulation transfer functions, Point spread functions, Signal to noise ratio, Interference (communication), Reconstruction algorithms, Anisotropy, Linear filtering, Data acquisition, Imaging systems, Medical imaging
In limited angular aperture tomosynthesis systems, the addition of new degrees of freedom for data
acquisition, such as angular aperture and sampling, requires specific optimizations. Typical optimization
criteria include MTF, SNR, and NEQ. However, the strong anisotropy of the sampling frequency on the zaxis
is usually neglected. Considering the signal in slices as the information contained within the volume
defined by the slice plane and the z-sampling interval, the MTF of the reconstruction is obtained by
integrating reconstruction blur within the slice. The relationship between z-sampling and aperture is
proposed in terms of preservation of the DQE.
A method for the determination of optimal operating points of digital mammography systems is described. The digital mammography equipment uses a flat panel detector and a bi-metal molybdenum/rhodium x-ray tube. An operating point is defined by the selection of the x-ray tube target material, x-ray filtration, kVp and detector entrance dose. Breast thickness and composition are estimated from a low dose pre-exposure, then used to index tables containing sets of operating points. The operating points are determined using a model of the image chain, which computes contrast to noise ratio (CNR) and average glandular dose (AGD) for all possible exposure conditions and breast thickness and composition combinations. The selected operating points are those which provide the required CNR for the lowest AGD. An AGD reduction of 30% to 50% can be achieved for comparable Image Quality, relative to current operating points. Resulting from the optimization process, the rhodium target is used in more than 75% of cases. Measurements of CNR and AGD have been performed on various tissue equivalent materials with good agreement between calculated and measured values. The proposed method provides full Image Quality benefit of digital mammography while minimizing dose to patients in a controlled and predictive way.
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