Phase-contrast digital tomosynthesis

In-line phase-contrast breast tomosynthesis: a phantom feasibility study at a synchrotron radiation facility

The major objective is to adopt, apply and test developed in-house algorithms for volumetric breast reconstructions from projection images, obtained in in-line phase-contrast mode. Four angular sets, each consisting of 17 projection images obtained from four physical phantoms, were acquired at beamline ID17, European Synchroton Radiation Facility, Grenoble, France. The tomosynthesis arc was  ±32°. The physical phantoms differed in complexity of texture and introduced features of interest. Three of the used phantoms were in-house developed, and made of epoxy resin, polymethyl-methacrylate and paraffin wax, while the fourth phantom was the CIRS BR3D. The projection images had a pixel size of 47 µm  ×  47 µm. Tomosynthesis images were reconstructed with standard shift-and-add (SAA) and filtered backprojection (FBP) algorithms. It was found that the edge enhancement observed in planar x-ray images is preserved in tomosynthesis images from both phantoms with homogeneous and highly heterogeneous backgrounds. In case of BR3D, it was found that features not visible in the planar case were well outlined in the tomosynthesis slices. In addition, the edge enhancement index calculated for features of interest was found to be much higher in tomosynthesis images reconstructed with FBP than in planar images and tomosynthesis images reconstructed with SAA. The comparison between images reconstructed by the two reconstruction algorithms shows an advantage for the FBP method in terms of better edge enhancement. Phase-contrast breast tomosynthesis realized in in-line mode benefits the detection of suspicious areas in mammography images by adding the edge enhancement effect to the reconstructed slices.

Characterization of a high-energy in-line phase contrast tomosynthesis prototype

PURPOSE

In this research, a high-energy in-line phase contrast tomosynthesis prototype was developed and characterized through quantitative investigations and phantom studies.

METHODS

The prototype system consists of an x-ray source, a motorized rotation stage, and a CMOS detector with a pixel pitch of 0.05 mm. The x-ray source was operated at 120 kVp for this study, and the objects were mounted on the rotation stage 76.2 cm (R1) from the source and 114.3 cm (R2) from the detector. The large air gap between the object and detector guarantees sufficient phase-shift effects. The quantitative evaluation of this prototype included modulation transfer function and noise power spectrum measurements conducted under both projection mode and tomosynthesis mode. Phantom studies were performed including three custom designed phantoms with complex structures: a five-layer bubble wrap phantom, a fishbone phantom, and a chicken breast phantom with embedded fibrils and mass structures extracted from an ACR phantom. In-plane images of the phantoms were acquired to investigate their image qualities through observation, intensity profile plots, edge enhancement evaluations, and/or contrast-to-noise ratio calculations. In addition, the robust phase-attenuation duality (PAD)-based phase retrieval method was applied to tomosynthesis for the first time in this research. It was utilized as a preprocessing method to fully exhibit phase contrast on the angular projection before reconstruction.

RESULTS

The resolution and noise characteristics of this high-energy in-line phase contrast tomosynthesis prototype were successfully investigated and demonstrated. The phantom studies demonstrated that this imaging prototype can successfully remove the structure overlapping in phantom projections, obtain delineate interfaces, and achieve better contrast-to-noise ratio after applying phase retrieval to the angular projections.

CONCLUSIONS

This research successfully demonstrated a high-energy in-line phase contrast tomosynthesis prototype. In addition, the PAD-based method of phase retrieval was combined with tomosynthesis imaging for the first time, which demonstrated its capability in significantly improving the contrast-to-noise ratios in the images.

Boundary-enhancement in propagation-based x-ray phase-contrast tomosynthesis improves depth position characterization

Propagation-based x-ray phase-contrast (PB XPC) tomosynthesis combines the concepts of tomosynthesis and XPC imaging to realize the advantages of both for biological imaging applications. Tomosynthesis permits reductions in acquisition times compared with full-view tomography, while XPC imaging provides the opportunity to resolve weakly absorbing structures. In this note, an investigation of the depth resolving properties of PB XPC tomosynthesis is conducted. The results demonstrate that in-plane structures display strong boundary-enhancement while out-of-plane structures do not. This effect can facilitate the identification of in-plane structures in PB XPC tomosynthesis that could normally not be distinguished from out-of-plane structures in absorption-based tomosynthesis.

Grating-based phase contrast tomosynthesis imaging: proof-of-concept experimental studies

PURPOSE

This paper concerns the feasibility of x-ray differential phase contrast (DPC) tomosynthesis imaging using a grating-based DPC benchtop experimental system, which is equipped with a commercial digital flat-panel detector and a medical-grade rotating-anode x-ray tube. An extensive system characterization was performed to quantify its imaging performance.

METHODS

The major components of the benchtop system include a diagnostic x-ray tube with a 1.0 mm nominal focal spot size, a flat-panel detector with 96 μm pixel pitch, a sample stage that rotates within a limited angular span of ± 30°, and a Talbot-Lau interferometer with three x-ray gratings. A total of 21 projection views acquired with 3° increments were used to reconstruct three sets of tomosynthetic image volumes, including the conventional absorption contrast tomosynthesis image volume (AC-tomo) reconstructed using the filtered-backprojection (FBP) algorithm with the ramp kernel, the phase contrast tomosynthesis image volume (PC-tomo) reconstructed using FBP with a Hilbert kernel, and the differential phase contrast tomosynthesis image volume (DPC-tomo) reconstructed using the shift-and-add algorithm. Three inhouse physical phantoms containing tissue-surrogate materials were used to characterize the signal linearity, the signal difference-to-noise ratio (SDNR), the three-dimensional noise power spectrum (3D NPS), and the through-plane artifact spread function (ASF).

RESULTS

While DPC-tomo highlights edges and interfaces in the image object, PC-tomo removes the differential nature of the DPC projection data and its pixel values are linearly related to the decrement of the real part of the x-ray refractive index. The SDNR values of polyoxymethylene in water and polystyrene in oil are 1.5 and 1.0, respectively, in AC-tomo, and the values were improved to 3.0 and 2.0, respectively, in PC-tomo. PC-tomo and AC-tomo demonstrate equivalent ASF, but their noise characteristics quantified by the 3D NPS were found to be different due to the difference in the tomosynthesis image reconstruction algorithms.

CONCLUSIONS

It is feasible to simultaneously generate x-ray differential phase contrast, phase contrast, and absorption contrast tomosynthesis images using a grating-based data acquisition setup. The method shows promise in improving the visibility of several low-density materials and therefore merits further investigation.

Fast grating-based X-ray phase-contrast tomosynthesis

As an imaging technique with low radiation dose and improved contrast, digital x-ray tomosynthesis is widely used in clinical diagnoses. Based on the superior capability of x-ray phase-contrast imaging (PCI) techniques for imaging low density materials, the combination of X-ray tomosynthesis and PCI can potentially provide higher efficiency in the detection of soft tissues. The goal of this work was to develop a fast imaging method for phase-contrast tomosynthesis, called fast grating-based phase-contrast tomosynthesis (GPC-Tomo), which integrates tomosynthesis with a grating-based PCI technique. Following the interlaced phase-stepping (PS) data collection method, which is much faster than conventional PS method, we propose a novel image reconstruction method called inner-focusing (IF) reconstruction for the fast GPC-Tomo. The proposed IF reconstruction method was validated by real experiments and the results suggested its effectiveness in achieving a fast GPC-Tomo.

In-line phase shift tomosynthesis

PURPOSE

The purpose of this work is to (1) demonstrate laboratory measurements of phase shift images derived from in-line phase-contrast radiographs using the attenuation-partition based algorithm (APBA) of Yan et al. [Opt. Express 18(15), 16074-16089 (2010)], (2) verify that the APBA reconstructed images obey the linearity principle, and (3) reconstruct tomosynthesis phase shift images from a collection of angularly sampled planar phase shift images.

METHODS

An unmodified, commercially available cabinet x-ray system (Faxitron LX-60) was used in this experiment. This system contains a tungsten anode x-ray tube with a nominal focal spot size of 10 μm. The digital detector uses CsI∕CMOS with a pixel size of 50×50 μm. The phantoms used consisted of one acrylic plate, two polystyrene plates, and a habanero pepper. Tomosynthesis images were reconstructed from 51 images acquired over a ±25° arc. All phase shift images were reconstructed using the APBA.

RESULTS

Image contrast derived from the planar phase shift image of an acrylic plate of uniform thickness exceeded the contrast of the traditional attenuation image by an approximate factor of two. Comparison of the planar phase shift images from a single, uniform thickness polystyrene plate with two polystyrene plates demonstrated an approximate linearity of the estimated phase shift with plate thickness (-1600 rad vs -2970 rad). Tomographic phase shift images of the habanero pepper exhibited acceptable spatial resolution and contrast comparable to the corresponding attenuation image.

CONCLUSIONS

This work demonstrated the feasibility of laboratory-based phase shift tomosynthesis and suggests that phase shift imaging could potentially provide a new imaging biomarker. Further investigation will be needed to determine if phase shift contrast will be able to provide new tissue contrast information or improved clinical performance.

A review of breast tomosynthesis. Part II. Image reconstruction, processing and analysis, and advanced applications

Many important post-acquisition aspects of breast tomosynthesis imaging can impact its clinical performance. Chief among them is the reconstruction algorithm that generates the representation of the three-dimensional breast volume from the acquired projections. But even after reconstruction, additional processes, such as artifact reduction algorithms, computer aided detection and diagnosis, among others, can also impact the performance of breast tomosynthesis in the clinical realm. In this two part paper, a review of breast tomosynthesis research is performed, with an emphasis on its medical physics aspects. In the companion paper, the first part of this review, the research performed relevant to the image acquisition process is examined. This second part will review the research on the post-acquisition aspects, including reconstruction, image processing, and analysis, as well as the advanced applications being investigated for breast tomosynthesis.