Scatter radiation severely degrades the image quality. Measurement-based scatter correction methods sample the scatter signal at sparsely distributed points, from which the scatter profile is estimated and deterministically removed from the projection image. The estimation of the scatter profile is generally done through a spline interpolation and the resulting scatter profile is quite smooth. Consequently, the noise is intact and the signal-to-noise ratio is reduced in the projection image after scatter correction, leading to image artifacts and increased noise in the reconstruction images. We propose a simple and effective method, referred to as filtered scatter-to-primary ratio (f-SPR) estimation, to estimate the scatter profile using the sparsely sampled scatter signal. Using the primary sampling device and the stationary digital tomosynthesis systems previously developed in our lab, we evaluated and compared the f-SPR method in comparison with existing methods in terms of contrast ratio, signal difference-to-noise ratio, and modulation transfer function. A significant improvement in image quality is observed in both the projection and the reconstruction images using the proposed method.
Proc. SPIE. 10132, Medical Imaging 2017: Physics of Medical Imaging
KEYWORDS: Signal to noise ratio, Breast, Photovoltaics, Imaging systems, Signal attenuation, Image processing, X-ray sources, Diagnostics, Iodine, Reconstruction algorithms, Spatial resolution, Dual energy imaging, Digital breast tomosynthesis, Carbon nanotubes
Digital breast tomosynthesis (DBT) captures some depth information and thereby improves the conspicuity of breast lesions, compared to standard mammography. Using contrast during DBT may also help distinguish malignant from benign sites. However, adequate visualization of the low iodine signal requires a subtraction step to remove background signal and increase lesion contrast. Additionally, attention to factors that limit contrast, including scatter, noise, and artifact, are important during the image acquisition and post-acquisition processing steps. Stationary DBT (sDBT) is an emerging technology that offers a higher spatial and temporal resolution than conventional DBT. This phantom-based study explored contrast-enhanced sDBT (CE sDBT) across a range of clinically-appropriate iodine concentrations, lesion sizes, and breast thicknesses. The protocol included an effective scatter correction method and an iterative reconstruction technique that is unique to the sDBT system. The study demonstrated the ability of this CE sDBT system to collect projection images adequate for both temporal subtraction (TS) and dual-energy subtraction (DES). Additionally, the reconstruction approach preserved the improved contrast-to-noise ratio (CNR) achieved in the subtraction step. Finally, scatter correction increased the iodine signal and CNR of iodine-containing regions in projection views and reconstructed image slices during both TS and DES. These findings support the ongoing study of sDBT as a potentially useful tool for contrast-enhanced breast imaging and also highlight the significant effect that scatter has on image quality during DBT.
We have developed a clinically ready first generation stationary breast tomosynthesis system (s-DBT). In the s-DBT system, focal spot blur associated with x-ray source motion is completely eliminated, allowing for rapid acquisition of projection images over a larger angular span without changing the acquisition time.
In the phantom studies the 1st generation s‐DBT system has demonstrated 30% higher spatial resolution than the corresponding continuous motion DBT systems. The system is currently being evaluated for its diagnostic performance in 100 patient clinical evaluation against FFDM. Initial results indicate that the s‐DBT system can produce increased lesion conspicuity and comparable MC visibility. However due to x‐ray flux limitations, certain large size patients have to be excluded. Recent studies have shown that increasing the angular span beyond 30° can be beneficial for enhanced depth resolution. We report the preliminary characterization of the 2nd generation s-DBT system with a new CNT x-ray source array, increased tube flux and a larger angular span. Increasing x‐ray tube flux allows for a larger patient population and dual energy imaging. Results indicate that the system delivers more than twice the flux, allowing for imaging of all size patients with acquisition time of 2‐4 seconds. A 7° increase in angular span over 1st generation decreased the ASF by 37%. Additionally, the 2nd generation s‐DBT system utilizing a specific AFVR reconstruction method resulted in a 92% increase in the in plane resolution over CM DBT system, and a 37% increase in spatial resolution over the 1st generation s-‐DBT system.
Digital breast tomosynthesis (DBT) provides 3D images which remove tissue overlapping and enables better cancer detection. Stationary DBT (s-DBT) uses a fixed X-ray source array to eliminate image blur associated with the x-ray tube motion and provides better image quality as well as faster scanning speed. For limited angle tomography, it is known that iterative reconstructions generally produces better images with fewer artifacts. However classical iterative tomosynthesis reconstruction methods are considerably slower than the filtered back-projection (FBP) reconstruction. The linear x-ray source array used in s-DBT enables a computationally more efficient volume reconstruction using adapted fan beam slice sampling, which transforms the 3-D cone beam reconstruction to a series of 2-D fan beam slice reconstructions. In this paper, we report the first results of the adapted fan-beam volume reconstruction (AFVR) for the s-DBT system currently undergoing clinical trial at UNC, using a simultaneous algebraic reconstruction technique (SART). An analytic breast phantom is used to quantitatively analyze the performance of the AFVR. Image quality of a CIRS biopsy phantom reconstructed using the AFVR method are compared to that using FBP algorithm with a commercial package. Our results show a significant reduction in memory usage and an order of magnitude speed increase in reconstructing speed using AFVR compared to that of classical 3-D cone beam reconstruction. We also observed that images reconstructed by AFVR with SART had a better sharpness and contrast compared to that using FBP. Preliminary results on patient images demonstrates the improved detectability of the s-DBT system over the mammography. By utilizing parallel computing with graphics processing unit (GPU), it is expected that the AFVR method will enable iterative reconstruction technique to be practical for clinical applications.
Full field digital mammography (FFDM) has been the gold standard for mammography. It detects the presence, distribution, and morphology of microcalcifications (MCs), helping predict malignancy. Digital breast tomosynthesis (DBT) has overcome some limitations of FFDM such as poor sensitivity, specificity, and positive predictive values, due to superimposition of tissue, especially in dense breasts. Current DBT systems move an x-ray tube in either continuous (CM), or step-and-shoot motion (SSM). These systems are less effective than FFDM in MC detection due to lower spatial resolution. Motion of the x-ray source and system mechanical instability cause image blur. The image quality is further affected by patient motion due to the relatively long scan time. We developed a stationary DBT (s-DBT) system using a carbon nanotube (CNT) X-ray source array. The CNT array is electronically controlled, rapidly acquiring projection images over a large angular span, with zero tube motion. No source motion, coupled with a large angular span, results in improved in-plane and depth resolution. Using physical phantoms and human specimens, this system demonstrated higher spatial resolution than CM DBT. The objective of this study is to compare the diagnostic clinical performance of s-DBT to that of FFDM. Under UNC’s IRB regulations, 100 patients with breast lesions are being recruited and imaged with both modalities. A reader study will compare the diagnostic accuracy of the modalities. We have successfully imaged the first 30 patients. Initial results indicate that s-DBT alone produces comparable MC sharpness, and increased lesion conspicuity compared to FFDM.
Current digital breast tomosynthesis (DBT) systems have been shown to have diminished microcalcification (MC)
visibility compared to 2D mammography systems. Rotating gantry DBT systems require mechanical motion of the
X-ray source which causes motion blurring of the focal spot, thus reducing spatial resolution. We have developed a
stationary DBT (s-DBT) technology that uses a carbon nanotube (CNT) based X-ray source array in order to acquire
all the projections images without any mechanical motion. It is capable of producing full tomosynthesis datasets
with zero motion blur. It has been shown to have significantly higher spatial resolution than continuous motion
DBT systems. An s-DBT system also allows for a wider angular span without increasing the acquisition time. A
larger angular span covers a larger portion of the Fourier domain, thus decreasing the tissue overlap. In this study,
we compare tomosynthesis imaging of MCs, in lumpectomy specimens, between an s-DBT system and a rotating
gantry DBT system. Results show that s-DBT produces better MC sharpness and reduced tissue overlap compared
to continuous motion DBT systems.