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 practice for imaging surgical breast specimens is a single 2D magnification view on a mammography system,
but 2D imaging overlaps the tissue in different planes causing distortion of lesion margins. Digital breast tomosynthesis
(DBT) could be used as an alternative imaging modality for imaging breast specimens. DBT systems acquire multiple
low dose projection images, over a small angular span, which are then reconstructed into a partial 3D volume. The
reconstructed images can be used to increase visualization of lesion margins and extent of microcalcifications (MCs).
Current commercial DBT systems use a single rotating X-ray source, the movement of which produces motion blur.
Motion blur reduces visualization of small objects such as MCs. MCs, depending on size and structure, can be
implicative of breast cancer. We have developed a stationary DBT (s-DBT) system using a linearly distributed, CNT Xray
source array. S-DBT allows for rapid acquisition of projection images with no image degradation from X-ray source
motion. Full tomosynthesis datasets can be acquired, allowing visualize of both masses and microcalcifications. Here we
report the preliminary results of a reader study comparing breast specimen images from a 2D commercial mammography
system and an s-DBT system. Preliminary results show that s-DBT is capable of producing equivalent image quality to
2D mammography, and in some cases is superior.
A prototype stationary digital breast tomosynthesis (s-DBT) system has been developed by retrofitting a Hologic Selenia
Dimension rotating gantry tomosynthesis scanner with a spatially distributed carbon nanotube (CNT) x-ray source array.
The goal is to improve the system spatial resolution by removing the x-ray tube motion induced focal spot blurring. The
CNT x-ray source array comprises 31 individually addressable x-ray beams covering 30° angular span. Each x-ray beam
has a minimum focal spot size of 0.64×0.61mm
(full-width-at-half-maximum), a stationary W anode operating up to
50kVp, and 1mm thick Al filter. The flux from each beam is regulated and varied using dedicated control electronics.
The maximum tube current is determined by the heat load of the stationary anode and depends on the energy, pulse
width and the focal spot size used. Stable operation at 28kVp, 27mA tube current, 250msec pulse width and 38mA tube
current, 183msec pulse width per exposure was achieved with extended lifetime. The standard ACR phantom was
imaged and analyzed to evaluate the image quality. The actual scanning speed depends on the number of views and the
readout time of the x-ray detector. With the present detector, 6 second scanning time at either 15 views or 31 views can
be achieved at 100mAs total imaging dose with a detector readout time of 240msec.
KEYWORDS: Modulation transfer functions, Digital breast tomosynthesis, Imaging systems, X-ray sources, X-rays, Image quality, Signal to noise ratio, Mammography, Sensors, Carbon nanotubes
The stationary Digital Breast Tomosynthesis System (s-DBT) has the advantage over the conventional DBT systems as
there is no motion blurring in the projection images associated with the x-ray source motion. We have developed a
prototype s-DBT system by retrofitting a Hologic Selenia Dimensions rotating gantry tomosynthesis system with a
distributed carbon nanotube (CNT) x-ray source array. The linear array consists of 31 x-ray generating focal spots
distributed over a 30 degree angle. Each x-ray beam can be electronically activated allowing the flexibility and easy
implementation of novel tomosynthesis scanning with different scanning parameters and configurations. Here we report
the initial results of investigation on the imaging quality of the s-DBT system and its dependence on the acquisition
parameters including the number of projections views, the total angular span of the projection views, the dose
distribution between different projections, and the total dose. A mammography phantom is used to visually assess image
quality. The modulation transfer function (MTF) of a line wire phantom is used to evaluate the system spatial resolution.
For s-DBT the in-plan system resolution, as measured by the MTF, does not change for different configurations. This is
in contrast to rotating gantry DBT systems, where the MTF degrades for increased angular span due to increased focal
spot blurring associated with the x-ray source motion. The overall image quality factor, a composite measure of the
signal difference to noise ratio (SdNR) for mass detection and the z-axis artifact spread function for microcalcification
detection, is best for the configuration with a large angular span, an intermediate number of projection views, and an
even dose distribution. These results suggest possible directions for further improvement of s-DBT systems for high
quality breast cancer imaging.
Tomosynthesis requires projection images from different viewing angles. Using a distributed x-ray source this can be
achieved without mechanical motion of the source with the potential for faster image acquisition speed. A distributed xray
tube has been designed and manufactured specifically for breast tomosynthesis. The x-ray tube consists of 31 field
emission x-ray sources with an angular range of 30°. The total dose is up to 100mAs with an energy range between 27
and 45 kVp. We discuss the source geometry and results from the characterization of the first prototype. The x-ray tube
uses field emission cathodes based on carbon nanotubes (CNT) as electron source. Prior to the manufacturing of the
sealed x-ray tube extensive testing on the field emission cathodes has been performed to verify the requirements for
commercial tomosynthesis systems in terms of emission current, focal spot size and tube lifetime.
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