Mini Das

Evaluation of a variable dose acquisition technique for microcalcification and mass detection in digital breast tomosynthesis

In this article the authors evaluate a recently proposed variable dose (VD)-digital breast tomosynthesis (DBT) acquisition technique in terms of the detection accuracy for breast masses and microcalcification (MC) clusters. With this technique, approximately half of the total dose is used for one center projection and the remaining dose is split among the other tomosynthesis projection views. This acquisition method would yield both a projection view and a reconstruction view. One of the aims of this study was to evaluate whether the center projection alone of the VD acquisition can provide equal or superior MC detection in comparison to the 3D images from uniform dose (UD)-DBT. Another aim was to compare the mass-detection capabilities of 3D reconstructions from VD-DBT and UD-DBT. In a localization receiver operating characteristic (LROC) observer study of MC detection, the authors compared the center projection of a VD acquisitioh scheme (at 2 mGy dose) with detector pixel size of 100 microm with the UD-DBT reconstruction (at 4 mGy dose) obtained with a voxel size of 100 microm. MCs with sizes of 150 and 180 microm were used in the study, with each cluster consisting of seven MCs distributed randomly within a small volume. Reconstructed images in UD-DBT were obtained from a projection set that had a total of 4 mGy dose. The current study shows that for MC detection, using the center projection alone of VD acquisition scheme performs worse with area under the LROC curve (AL) of 0.76 than when using the 3D reconstructed image using the UD acquisition scheme (AL=0.84). A 2D ANOVA found a statistically significant difference (p=0.038) at a significance level of 0.05. In the current study, although a reconstructed image was also available using the VD acquisition scheme, it was not used to assist the MC detection task which was done using the center projection alone. In the case of evaluation of detection accuracy of masses, the reconstruction with VD-DBT (AL=0.71) was compared to that obtained from the UD-DBT (AL=0.78). The authors found no statistically significant difference between the two (p-value=0.22), although all the observers performed better for UD-DBT.

Dispersion compensation in transmission using uniform long period fiber gratings

It is proposed that the high dispersion at the transmission band edges of uniform long period gratings (LPG) fabricated on relatively high Δ fibers can be used for efficient dispersion compensation. Since the transmission of LPG varies with length of the grating or refractive index modulation, we show that it is possible to tailor the transmission spectrum to obtain high transmission with constant dispersion and negligible delay ripple over a reasonable bandwidth. Since the proposed structure works in transmission it should be suitable for fiber optic communication links.

Penalized Maximum Likelihood Reconstruction for Improved Microcalcification Detection in Breast Tomosynthesis

We examined the application of an iterative penalized maximum likelihood (PML) reconstruction method for improved detectability of microcalcifications (MCs) in digital breast tomosynthesis (DBT). Localized receiver operating characteristic (LROC) psychophysical studies with human observers and 2-D image slices were conducted to evaluate the performance of this reconstruction method and to compare its performance against the commonly used Feldkamp FBP algorithm. DBT projections were generated using rigorous computer simulations that included accurate modeling of the noise and detector blur. Acquisition dose levels of 0.7, 1.0, and 1.5 mGy in a 5-cm-thick compressed breast were tested. The defined task was to localize and detect MC clusters consisting of seven MCs. The individual MC diameter was 150 μm. Compressed-breast phantoms derived from CT images of actual mastectomy specimens provided realistic background structures for the detection task. Four observers each read 98 test images for each combination of reconstruction method and acquisition dose. All observers performed better with the PML images than with the FBP images. With the acquisition dose of 0.7 mGy, the average areas under the LROC curve (AL) for the PML and FBP algorithms were 0.69 and 0.43, respectively. For the 1.0-mGy dose, the values of AL were 0.93 (PML) and 0.7 (FBP), while the 1.5-mGy dose resulted in areas of 1.0 and 0.9, respectively, for the PML and FBP algorithms. A 2-D analysis of variance applied to the individual observer areas showed statistically significant differences (at a significance level of 0.05) between the reconstruction strategies at all three dose levels. There were no significant differences in observer performance for any of the dose levels.

Characterization and simulation of long period gratings fabricated using electric discharge

Abstract We report the characterization and theoretical simulation of long period gratings fabricated using electric arc discharge in two different fibers namely, SMF-28 ( Δ =0.0036) and DSF ( Δ =0.009). We show that this technique can efficiently fabricate gratings with required strength of coupling on both fiber types by choosing appropriate arc current and duration of the arc. We compare the transmission spectra of the fabricated gratings to the theoretically simulated plots and find the equivalent refractive index modulation created in the grating. Unlike the case of UV-induced gratings, the resonance wavelength in these gratings depends only on the period and is independent of the arc current that is controlled to achieve different refractive index modulations. Thus this technique enables easy and independent control of the fiber parameters.

Wavelength-division multiplexing isolation filter using concatenated chirped long period gratings

We propose the use of concatenated chirped long period gratings as an efficient wavelength-division multiplexing (WDM) isolation filter. The proposed filter not only works in the transmission mode but also has almost equispaced pass bands with high isolation at the stop bands. The filter has negligible dispersion effects in the pass band, which should make such a device suitable for use in WDM fiber optic communication links.

Generation of voxelized breast phantoms from surgical mastectomy specimens

PURPOSE In the research and development of dedicated tomographic breast imaging systems, digital breast object models, also known as digital phantoms, are useful tools. While various digital breast phantoms do exist, the purpose of this study was to develop a realistic high-resolution model suitable for simulating three-dimensional (3D) breast imaging modalities. The primary goal was to design a model capable of producing simulations with realistic breast tissue structure. METHODS The methodology for generating an ensemble of digital breast phantoms was based on imaging surgical mastectomy specimens using a benchtop, cone-beam computed tomography system. This approach allowed low-noise, high-resolution projection views of the mastectomy specimens at each angular position. Reconstructions of these projection sets were processed using correction techniques and diffusion filtering prior to segmentation into breast tissue types in order to generate phantoms. RESULTS Eight compressed digital phantoms and 20 uncompressed phantoms from which an additional 96 pseudocompressed digital phantoms with voxel dimensions of 0.2 mm(3) were generated. Two distinct tissue classification models were used in forming breast phantoms. The binary model classified each tissue voxel as either adipose or fibroglandular. A multivalue scaled model classified each tissue voxel as percentage of adipose tissue (range 1%-99%). Power spectral analysis was performed to compare simulated reconstructions using the breast phantoms to the original breast specimen reconstruction, and fits were observed to be similar. CONCLUSIONS The digital breast phantoms developed herein provide a high-resolution anthropomorphic model of the 3D uncompressed and compressed breast that are suitable for use in evaluating and optimizing tomographic breast imaging modalities. The authors believe that other research groups might find the phantoms useful, and therefore they offer to make them available for wider use.

Using Mastectomy Specimens to Develop Breast Models for Breast Tomosynthesis and CT Breast Imaging

Dedicated x-ray computed tomography (CT) of the breast using a cone-beam flat-panel detector system is a modality under investigation by a number of research teams. As previously reported, we have fabricated a prototype, bench-top flat-panel CT breast imaging (CTBI) system and developed computer simulation software to model such a system. We are developing a methodology to use high resolution, low noise CT reconstructions of fresh mastectomy specimens for generating an ensemble of 3D digital breast phantoms that realistically model 3D compressed and uncompressed breast anatomy. These breast models can be used to simulate realistic projection data for both breast tomosynthesis (BT) and CT systems thereby providing a powerful evaluation and optimization mechanism.

Comparison of Two Methods to Develop Breast Models for Simulation of Breast Tomosynthesis and CT

Dedicated x-ray computed tomography (CT) of the breast using a cone-beam flat-panel detector system is a modality under investigation by a number of research teams. Several teams, including ours, have fabricated prototype, bench-top flat-panel CT breast imaging (CTBI) systems. We also use computer simulation software to optimize system parameters. We are developing a methodology to use high resolution, low noise CT reconstructions of fresh mastectomy specimens in order to generate an ensemble of 3D digital breast phantoms that realistically model 3D compressed and uncompressed breast anatomy. The resulting breast models can then be used to simulate realistic projection data for both Breast Tomosynthesis (BT) and Breast CT (BCT) systems thereby providing a powerful evaluation and optimization mechanism for research and development of novel breast imaging systems as well as the optimization of imaging techniques for such systems. Having the capability of using breast object models and simulation software is clinically significant because prior to a clinical trial of any prototype breast imaging system many parameter tradeoffs can be investigated in a simulation environment. This capability is worthwhile not only for the obvious benefit of improving patient safety during initial clinical trials but also because simulation prior to prototype implementation should result in reduced cost and increased speed of development. The main goal of this study is to compare results obtained using two different methods to develop breast object models in order to select the better technique for developing the entire ensemble.

Single-step absorption and phase retrieval with polychromatic x rays using a spectral detector

In this Letter, we present a single-step method to simultaneously retrieve x-ray absorption and phase images valid for a broad range of imaging energies and material properties. Our method relies on the availability of spectrally resolved intensity measurements, which is now possible using semiconductor x-ray photon counting detectors. The retrieval method is derived and presented, with results showing good agreement.

Development of an ensemble of digital breast object models

In the investigation of emerging tomographic breast imaging methods using flat-panel detectors (FPDs), digital breast object models are useful tools These models are also commonly referred to as digital phantoms We have created an ensemble of digital breast object phantoms based on CT scans of surgical mastectomy specimens Early versions of the phantoms have been used in our published research Recently we have improved some of our processing tools such as the use of 3-D anisotropic diffusion filtering (ADF) prior to segmentation, and we have evaluated breast object models generated with different methods including power spectral analysis, ROI statistics and an observation study.