Breast density has been identified to be a risk factor of developing breast cancer and an indicator of lesion diagnostic
obstruction due to masking effect. Volumetric density measurement evaluates fibro-glandular volume, breast volume,
and breast volume density measures that have potential advantages over area density measurement in risk assessment.
One class of volume density computing methods is based on the finding of the relative fibro-glandular tissue attenuation
with regards to the reference fat tissue, and the estimation of the effective x-ray tissue attenuation differences between
the fibro-glandular and fat tissue is key to volumetric breast density computing. We have modeled the effective
attenuation difference as a function of actual x-ray skin entrance spectrum, breast thickness, fibro-glandular tissue
thickness distribution, and detector efficiency. Compared to other approaches, our method has threefold advantages: (1)
avoids the system calibration-based creation of effective attenuation differences which may introduce tedious
calibrations for each imaging system and may not reflect the spectrum change and scatter induced overestimation or
underestimation of breast density; (2) obtains the system specific separate and differential attenuation values of fibroglandular
and fat for each mammographic image; and (3) further reduces the impact of breast thickness accuracy to
volumetric breast density. A quantitative breast volume phantom with a set of equivalent fibro-glandular thicknesses has
been used to evaluate the volume breast density measurement with the proposed method. The experimental results have
shown that the method has significantly improved the accuracy of estimating breast density.
We have developed dual energy (DE) iodine contrast imaging functions with a commercial mammography and
tomosynthesis system. Our system uses a tungsten target x-ray tube and selenium direct conversion detector.
Conventional low energy (LE) images were acquired with existing Rh, Ag and Al filters at the screening doses while the
high energy images (HE) were acquired with new Cu filters at half of the screening doses. In DE 2D mode, a pair of LE
and HE images was taken with one second delay time between and with anti-scatter grid. In DE 3D mode, 22 views of
alternating LE and HE were taken over 15 degrees angle in seven seconds without grid while tube was scanned
continuously. We used log-subtraction algorithm to obtain clean DE images with the subtraction factor K derived
empirically. In 3D mode, the subtraction was applied to each pair of LE and HE slices after reconstruction. The x-ray
technique optimization was done with simulation and phantom study. We performed both phantom and patient studies to
demonstrate the advantage of iodine contrast imaging. Among several new things in our work, a selenium detector
optimized for DE imaging was tested and a large dose advantage was demonstrated; 2D and 3D DE images of a breast
under same compression were acquired with a unique DE combo mode of the system, allowing direct image quality
comparison between 2D and 3D modes. Our study showed that new DE system achieved good image quality. DE
imaging is be a promising modality to detect breast cancer.
KEYWORDS: Breast, Digital breast tomosynthesis, Mammography, 3D image processing, Image processing, Sensors, Tissues, X-rays, Systems modeling, Aluminum
Breast density is known as a strong risk factor for breast cancer. Clinical assessment of breast density during screening
mammography is often done by radiologists through visual evaluation or by a computer program. Automated computer
methods offer the potential for non-subjective density assessments. With the rapid development and increased utilization
of tomosynthesis clinically, there is a practical need for systems to provide automated breast density measurements in
tomosynthesis like those available in mammography.
QuantraTM is a software package using physical modeling of mammography systems, and performs volumetric
assessment of breast tissue composition for conventional mammography. In this paper, we describe recent developments
to extend Quantra to calculate breast density using tomosynthesis projection images. Our development took advantage of
the combo imaging mode of Hologic Selenia DimensionsTM system, which allowed co-registered conventional 2D
mammogram and 3D tomosynthesis images to be acquired in a single compression. We used the Quantra results of 2D
mammograms as a reference to refine the new processing algorithm for tomosynthesis images. This paper describes
details of the new algorithm and provides some preliminary results.
Patient motion is frequently a problem in mammography, especially when the x-ray exposure is long, resulting in image
quality degradation. At present, patient motion can only be identified by inspecting the image subjectively after image
acquisition. As digital breast tomosynthesis (DBT) takes longer time to complete the data acquisition than conventional
mammography, there is more chance for patient motion to happen in DBT. Therefore it is important to understand the
potential motion problem in DBT and incorporate a design to minimize it. In this paper we present an automatic method
to detect patient motions in DBT. The method is developed based on an understanding that, features of breast should
move along predictable trajectory in a time-series of projection measurements; deviations from it are linked to patient
motion. Motion distance is estimated by analyzing skin lines and large calcifications (if exist) in all projection images
and then a motion score is derived for a DBT scan. Effectiveness and robustness of this method will be demonstrated
with clinical data, together with discussions on different motion patterns observed clinically. The impacts of this work
could be far-reaching. It allows real-time detection and objective evaluation of patient motions, applicable to all breasts.
Patient with severe motion can be re-scanned immediately before leaving the room. Data with moderate motions can go
through additional targeted image processing to minimize motion artifacts. It also enables a powerful tool to evaluate
and optimize different DBT designs to minimize the patient motion problem. Besides, this method can be extended to
other imaging modalities, e.g. breast CT, to study patient motions.
A new generation of digital breast tomosynthesis system has been designed and is commercially available outside the US.
The system has both a 2D mode and a 3D mode to do either conventional mammography or tomosynthesis. Uniquely, it
also has a fusion mode that allows both 3D and 2D images to be acquired under the same breast compression, which results in co-registered images from the two modalities. The aim of this paper is to present a technical description on the design and performance of the new system, including system details such as filter options, doses, AEC operation, 2D and 3D images co-registration and display, and the selenium detector performance. We have carried out both physical and clinical studies to evaluate the system. In this paper the focus will be mainly on technical performance results.
The performance optimization of tomosynthesis is very challenging as it involves multiple system parameters to be
optimized towards multiple figures of merit (FOM). Common approach is to take a selected few FOMs and optimize
them under more confined conditions. While this kind of study helps us to gain more insights, extra precautions are
needed when one tries to generalize the conclusions. Several reported works have shown that increasing the scan angle
improves the contrast to noise ratio (CNR), which made the authors conclude that from the CNR perspective, large scan
angle has advantages over small angle in tomosynthesis.
In this study, we investigated the dependence of CNR on the scan angle while other system parameters were fixed. We
found that improvement of CNR with large scan angle in those published studies was actually due to reconstruction
algorithm and associated filtering effect but not due to the scan angle itself. To reveal this property, we selected six
filters to cover a board range of possible shapes, and showed CNR variations with different filters. Besides, we also
studied the ML-EM and SART iterative reconstruction algorithms, and obtained their equivalent Fourier filters
numerically. The change of the equivalent filter shapes of iterative methods at different scan angle explained the
observed CNR dependence on the scan angles. We conclude that larger scan angle does not have any intrinsic CNR
advantage over small one in tomosynthesis. The observed CNR gain at large angle is an effect from the reconstruction
filters. Therefore CNR based optimization study need to be carried out without the potential bias from filters.
We studied the use of the mammography contrast detail phantom (CDMAM) with tomosynthesis to evaluate the
performance of our system as well as to explore the application of CDMAM in 3D breast imaging. The system was
Hologic's 1st generation tomosynthesis machine. CDMAM phantom plus PMMA slabs were imaged at 3 cm, 5 cm, 7
cm, and 9 cm PMMA-equivalent thickness with 11 projections per scan and the scan angle selected from 0, 15 and 28
degrees. CDMAM images were reconstructed using the back projection method, and were scored with the CDCOM
automatic analysis program. The threshold thickness of each disk size was obtained with psychometric curve fitting. We
first studied errors and variability associated with the results when different numbers of images were used in contrast
detail analysis, then studied factors that affected CDMAM results in tomosynthesis, including the x-ray dose, the scan
angle, the in-plane reconstruction pixel size, the slice-to-slice step size, the location of the CDMAM inside the PMMA
slabs, and the scatter effect. This paper will present results of CDMAM performance of our tomosynthesis system, as
well as their dependence on the various factors, and the comparison with 2D mammography. Additionally we will
discuss the novel processing and analysis methods developed during this study, and make proposals to modify the
CDMAM phantom and the CDCOM analysis program to optimize the method for 3D tomosynthesis.
We have developed a breast tomosynthesis system utilizing a selenium-based direct conversion flat panel detector. This prototype system is a modification of Selenia, Hologic’s full field digital mammography system, using an add-on breast holding device to allow 3D tomosynthetic imaging. During a tomosynthesis scan, the breast is held stationary while the x-ray source and detector mounted on a c-arm rotate continuously around the breast over an angular range up to 30 degrees. The x-ray tube is pulsed to acquire 11 projections at desired c-arm angles. Images are reconstructed in planes parallel to the breastplate using a filtered backprojection algorithm. Processing time is typically 1 minute for a 50 mm thick breast at 0.1 mm in-plane pixel size, 1 mm slice-to-slice separation. Clinical studies are in progress. Performance evaluations were carried out at the system and the subsystem levels including spatial resolution, signal-to-noise ratio, spectra optimization, imaging technique, and phantom and patient studies. Experimental results show that we have successfully built a tomosynthesis system with images showing less structure noise and revealing 3D information compared with the conventional mammogram. We introduce, for the first time, the definition of “Depth of Field” for tomosynthesis based on a spatial resolution study. This parameter is used together with Modulation Transfer Function (MTF) to evaluate 3D resolution of a tomosynthesis system as a function of system design, imaging technique, and reconstruction algorithm. Findings from the on-going clinical studies will help the design of the next generation tomosynthesis system offering improved performance.
Preliminary MTF and LCD results obtained on several volumetric computed tomography (VCT) systems, employing amorphous flat panel technology, are presented. Constructed around 20-cm x 20-cm, 200-mm pitch amorphous silicon x-ray detectors, the prototypes use standard vascular or CT x-ray sources. Data were obtained from closed-gantry, benchtop and C-arm-based topologies, over a full 360 degrees of rotation about the target object. The field of view of the devices is approximately 15 cm, with a magnification of 1.25-1.5, providing isotropic resolution at isocenter of 133-160 mm. Acquisitions have been reconstructed using the FDK algorithm, modified by motion corrections also developed by GE. Image quality data were obtained using both industry standard and custom resolution phantoms as targets. Scanner output is compared on a projection and reconstruction basis against analogous output from a dedicated simulation package, also developed at GE. Measured MTF performance is indicative of a significant advance in isotropic image resolution over commercially available systems. LCD results have been obtained, using industry standard phantoms, spanning a contrast range of 0.3-1%. Both MTF and LCD measurements agree with simulated data.
A framework for rapid and reliable design of Volumetric Computed Tomography (VCT) systems is presented. This work uses detailed system simulation tools to model standard and anthropomorphic phantoms in order to simulate the CT image and choose optimal system specifications. CT systems using small-pitch, 2-D flat area detectors, initially developed for x-ray projection imaging, have been proposed to implement Volume CT for clinical applications. Such systems offer many advantages, but there are also many trade-offs not fully understood that affect image quality. Although many of these effects have been studied in the literature for traditional CT applications, there are unique interactions for very high-resolution flat-panel detectors that are proposed for volumetric CT. To demonstrate the process we describe an example that optimizes the parameters to achieve high detectability for thin slices. The VCT system was modeled over a range of operating parameters, including: tube voltage, tube current, tube focal spot size, detector cell size, number of views, and scintillator thickness. The response surface, which captures the effects of system components on image quality, was calculated. Optimal and robust designs can be achieved by determining an operating point from the response equations, given the constraints. We verify the system design with images from standard and low contrast phantoms. Eventually this design tool could be used, in conjunction with clinical researchers, to specify VCT scanner designs, optimize imaging protocols, and quantify image accuracy and repeatability.
Gadovist, a 1.0-molar Gd contrast agent from Schering AG, Berlin, Germany, in use in clinical MRI in Europe, was evaluated as a radiography contrast agent. In a collaboration with Brookhaven National Laboratory (BNL), Schering AG is developing several such lanthanide-based contrast agents, while BNL evaluates them using different x-ray beam energy spectra. These energy spectra include a 'truly' monochromatic beam (0.2 keV energy bandwidth) from the National Synchrotron Light Source (NSLS), BNL, tuned above the Gd K-edge, and x-ray-tube beams from different kVp settings and beam filtrations. Radiographs of rabbits' kidneys were obtained with Gadovist at the NSLS. Furthermore, a clinical radiography system was used for imaging rabbits' kidneys comparing Gadovist and Conray, an iodinated contrast agent. The study, using 74 kVp and standard Al beam filter for Conray and 66 kVp and an additional 1.5 mm Cu beam filter for Gadovist, produced comparable images for Gadovist and Conray; the injection volumes were the same, while the radiation absorbed dose for Gadovist was slightly smaller. A bent-crystal silicon monochromator operating in the Laue diffraction mode was developed and tested with a conventional x-ray tube beam; it narrows the energy spectrum to about 4 keV around the anode tungsten's K' line. Preliminary beam-flux results indicate that the method could be implemented in clinical CT if x-ray tubes with approximately twice higher output become available.
A monochromatic CT for imaging the human head and neck is being developed at the National Synchrotron Light Source. We compared the performance of this system, multiple energy computed tomography (MECT), with that of a conventional CT (CCT) using phantoms. The advantage in image contrast of MECT, with its beam energy tuned just above the K-edge of contrast element, over CCT carried out at 120 kVp, was approximately equal to 3.2-fold for iodine and approximately equal to 2.2 fold for gadolinium. Image noise was compared by simulations because this comparison requires matching the spatial resolutions of the two systems. Simulations at a 3- rad dose and 3-mm slice height on an 18-cm-diameter acrylic phantom, with MECT operating at 60.5 keV, showed that image noise for MECT was 1.4 HU vs. 1.8 HU for CCT. Simulations in the dual-energy quantitative CT mode showed a two-fold advantage for MECT in image noise, as well as its superior quantification. MECT operated in the planar mode revealed fatty tissue in the body of a rat using xenon K-edge subtraction. Our initial pan for clinical application of the system is to image the composition of carotid artery plaques non-invasively, separating the plaques' main constituents: the fatty, fibrous, and calcified tissues.
The Nd3+-doped fiber ring laser consisting of a mechanically polished tunable directional coupler and the Nd3+-doped single mode fiber with 4 m long is pumped by Ti:Al2O3 tunable laser ranging from 800 nm to 840 nm in wavelength. The optimum pumping wavelength of this Nd3+-doped fiber ring laser for commercial semiconductor laser is selected. The fiber laser's output power of 5.8 mw and the single end output slope efficiency of 24% at pumping wavelength of 830 nm are also obtained.
Micro-vibration with amplitude in the range from 2 angstroms to 1150 angstroms of an object is measured by a new Fizeau-type long-gradient index rod lens interferometer with a semiconductor laser. The theoretical analysis and experimental results are given.
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