Cone Beam Breast CT Research Articles

SU‐FF‐I‐26: Automatic Detection of Calcifications in Cone Beam Breast CT Images

Purpose: Microcalcifications (MCs) play an important role in early detection of breast cancer. This study is to describe a technique to automatically identify and segment the calcifications from the breast anatomy in cone beam CT (CBCT) images. Method and Materials: Projection images of mastectomy breast specimens were acquired with a bench‐top experimental CBCT system and reconstructed using FDK algorithm with a regular ramp filter. The reconstructed images were first corrected for the non‐uniform cupping artifacts due to x‐ray scatter and beam hardening. The corrected CBCT images had more uniform background but were still too noisy for threshold segmentation. To reduce the noise level, the images were processed with a noise averaging filter in z direction followed by a total variation filter to reduce the noise level while keeping the edge sharpness and contrast of calcifications. To automatically detect the calcifications with proper threshold level, a Gaussian curve fitting was used to fit the histogram of the CBCT image. Since the CT numbers of calcifications are usually significantly above those for breast tissue, cutoff point of the Gaussian curve was used as the threshold value to segment the calcifications. Results: With this method, the calcifications in the entire breast were successfully segmented from the breast tissue background. The results agreed well with those identified by visualization. Conclusion: The calcifications in CBCT breast images can be automatically detected by threshold based segmentation method with the nonuniform cupping artifacts corrected for and the noise level properly reduced.

Simulated scatter performance of an inverse‐geometry dedicated breast CT system

The purpose of this work was to quantify the effects of scatter for inverse-geometry dedicated breast CT compared to cone-beam breast CT through simulations. The inverse geometry was previously proposed as an alternative to cone-beam acquisition for volumetric CT. The inverse geometry consists of a large-area scanned-source opposite a detector array that is smaller in the transverse direction. While the gantry rotates, the x-ray beam is rapidly sequenced through an array of positions, acquiring a truncated projection image at each position. Inverse-geometry CT (IGCT) is expected to detect less scatter than cone-beam methods because only a fraction of the object is irradiated at any time and the fast detector isolates the measurements from sequential x-ray beams. An additional scatter benefit is the increased air gap due to the inverted geometry. In this study, we modeled inverse-geometry and cone-beam dedicated breast CT systems of equivalent resolution, field of view, and photon fluence. Monte Carlo simulations generated scatter and primary projections of three cylindrical phantoms of diameters 10, 14, and 18 cm composed of 50% adipose/50% glandular tissue. The scatter-to-primary ratio (SPR) was calculated for each breast diameter. Monte Carlo simulations were combined with analytical simulations to generate inverse-geometry and cone-beam images of breast phantoms embedded with tumors. Noise reprehenting the photon fluence of a realistic breast CT scan was added to the simulated projections. Cone-beam data were reconstructed with and without an ideal scatter correction. The CNR between breast tumor and background was compared for the inverse and cone-beam geometries for the three phantom diameters. Results demonstrated an order of magnitude reduction in SPR for the IGCT system compared to the cone-beam system. For example, the peak IGCT SPRs were 0.05 and 0.09 for the 14 and 18 cm phantoms, respectively, compared to 0.42 and 1 for the cone-beam system. For both geometries, the effects of scatter on contrast-to-noise ratio (CNR) were small for the 10 cm diameter phantom. The inverse-geometry improved the CNR by factors of 1.16 for the 14 cm phantom and 1.48 for the 18 cm phantom compared to a cone-beam acquisition without scatter correction. When an ideal scatter correction was applied to the cone-beam acquisition, the IGCT CNR improvements were 1.03 and 1.25 for the 14 and 18 cm phantoms. Overall, the results suggest that the inverse geometry may be advantageous for dedicated breast CT, an application that requires high-contrast resolution, spatial resolution, and dose efficiency.

Circle Plus Partial Helical Scan Scheme for a Flat Panel Detector-Based Cone Beam Breast X-Ray CT

Flat panel detector-based cone beam breast CT (CBBCT) can provide 3D image of the scanned breast with 3D isotropic spatial resolution, overcoming the disadvantage of the structure superimposition associated with X-ray projection mammography. It is very difficult for Mammography to detect a small carcinoma (a few millimeters in size) when the tumor is occult or in dense breast. CBBCT featured with circular scan might be the most desirable mode in breast imaging due to its simple geometrical configuration and potential applications in functional imaging. An inherited large cone angle in CBBCT, however, will yield artifacts in the reconstruction images when only a single circular scan is employed. These artifacts usually manifest themselves as density drop and object geometrical distortion that are more noticeable in the reconstructed image areas that are further away from the circular scanning plane. In order to combat this drawback, a circle plus partial helical scan scheme is proposed. An exact circle plus straight line scan scheme is also conducted in computer simulation for the purpose of comparison. Computer simulations using a numerical breast phantom demonstrated the practical feasibility of this new scheme and correction to those artifacts to a certain degree.

Cone Beam Breast CT noise reduction using 3D adaptive Gaussian filtering

In Cone Beam Breast CT (CBBCT) imaging, noise causes degradation of three dimensional breast images, impeding correct diagnosis of breast cancer. Within Feldkamp's cone beam reconstruction framework, applying weighted reconstruction filters to the projection images after pre-processing procedures has long been used to reduce noise and improve image quality. However, CBBCT noise is distributed across frequencies along with the useful signal. Various reconstruction filters working in the frequency domain suppress noise as well as the edge detail signal. Based on fuzzy c-means clustering and the two-dimensional histogram analysis of a large number of clinical CBBCT data, we managed to discriminate fatty stroma, glandular tissues and the transition areas between these tissues by the local mean and standard deviation values. We also proposed a three-dimensional Gaussian filtering scheme to reduce the noise in 3D reconstructed images adaptively without much blurring of detail signal.

SU‐GG‐I‐16: A Segmentation Technique to Estimate Breast Density From Cone Beam Breast CT Images

Purpose: To describe and demonstrate the use of an improved segmentation technique to estimate breast density from cone beam breast CT (BCT) images. Method and Materials: To compute the breast density, the dense tissue must be separated from the adipose tissue in the BCT images. To accomplish this task, the BCT images were first processed with a previously reported post‐reconstruction method to correct for the beam hardening and scatter induced cupping artifacts. With this method, the adipose signals were extracted from the coronal view CT image and used to form a 3‐D background map which was then subtracted from the original images for correction. The corrected data were edge enhanced and smoothed to reduce the noise levels in the images. The results were processed by threshold segmentation to separate the dense tissue from the adipose tissue and form a 3‐D dense tissue map which was then used to compute the dense tissue volume and the breast density. Results: For demonstration, the proposed technique was applied to cone beam CT images of mastectomy breast specimens to estimate the breast density. The cupping artifacts were successively corrected for and the dense tissue was successfully separated from the adipose tissue with the segmented dense tissue structures matching well with those visualized in the images. Conclusion: We have successfully implemented a method to use cone beam breast CT images to estimate the breast density. The technique was successfully demonstrated with cone beam CT images of mastectomy breast specimens. This technique lends itself to more accurate and consistent measurement of breast density which may be used an indicator for breast cancer risk.This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.

Dedicated Cone-Beam Breast CT: Feasibility Study with Surgical Mastectomy Specimens

The purpose of this study was to investigate the feasibility of diagnostic breast imaging using a flat-panel detector-based cone-beam CT system. Imaging of 12 mastectomy specimens was performed at 50-80 kVp with a voxel size of 145 or 290 microm. Our study shows that cone-beam breast CT images have exceptional tissue contrast and can potentially reduce examination time with comparable radiation dose.

Visibility of microcalcification in cone beam breast CT: Effects of x‐ray tube voltage and radiation dose

Mammography is the only technique currently used for detecting microcalcification (MC) clusters, an early indicator of breast cancer. However, mammographic images superimpose a three-dimensional compressed breast image onto two-dimensional projection views, resulting in overlapped anatomical breast structures that may obscure the detection and visualization of MCs. One possible solution to this problem is the use of cone beam computed tomography (CBCT) with a flat-panel (FP) digital detector. Although feasibility studies of CBCT techniques for breast imaging have yielded promising results, they have not shown how radiation dose and x-ray tube voltage affect the accuracy with which MCs are detected by CBCT experimentally. We therefore conducted a phantom study using a FP-based CBCT system with various mean glandular doses and kVp values. An experimental CBCT scanner was constructed with a data acquisition rate of 7.5 frames/s. 10.5 and 14.5 cm diameter breast phantoms made of gelatin were used to simulate uncompressed breasts consisting of 100% glandular tissue. Eight different MC sizes of calcium carbonate grains, ranging from 180-200 microm to 355-425 microm, were used to simulate MCs. MCs of the same size were arranged to form a 5 x 5 MC cluster and embedded in the breast phantoms. These MC clusters were positioned at 2.8 cm away from the center of the breast phantoms. The phantoms were imaged at 60, 80, and 100 kVp. With a single scan (360 degrees), 300 projection images were acquired with 0.5 x, 1x, and 2x mean glandular dose limit for 10.5 cm phantom and with 1x, 2x, and 4x for 14.5 cm phantom. A Feldkamp algorithm with a pure ramp filter was used for image reconstruction. The normalized noise level was calculated for each x-ray tube voltage and dose level. The image quality of the CBCT images was evaluated by counting the number of visible MCs for each MC cluster for various conditions. The average percentage of the visible MCs was computed and plotted as a function of the MGD, the kVp, and the average MC size. The results showed that the MC visibility increased with the MGD significantly but decreased with the breast size. The results also showed that the x-ray tube voltage affects the detection of MCs under different circumstances. With a 50% threshold, the minimum detectable MC sizes for the 10.5 cm phantom were 348(+/-2), 288(+/-7), 257(+/-2) microm at 3, 6, and 12 mGy, respectively. Those for the 14.5 cm phantom were 355 (+/-1), 307 (+/-7), 275 (+/-5) microm at 6, 12, and 24 mGy, respectively. With a 75% threshold, the minimum detectable MC sizes for the 10.5 cm phantom were 367 (+/-1), 316 (+/-7), 265 (+/-3) microm at 3, 6, and 12 mGy, respectively. Those for the 14.5 cm phantom were 377 (+/-3), 334 (+/-5), 300 (+/-2) microm at 6, 12, and 24 mGy, respectively.

TU‐C‐M100F‐04: Quantification of Dynamic Contrast Enhancement in Breast Cone‐Beam CT

Purpose: Contrast uptake behavior measured by dynamic contrast enhanced (DCE) MR has been shown to have diagnostic value for breast cancer. This paper is to show the feasibility of DCE breast cone beam CT (CBCT) for quantification of dynamic contrast uptake using a baseline and a single contrast enhanced CBCT. Method and Materials: A novel algorithm is proposed to determine the contrast uptake behavior for breast CBCT with a baseline image followed by a contrast enhanced acquisition synchronized with contrast injection. The method is based on the assumption that the contrast uptake curve in every voxel of the volume has a washin and a washout phase governed by a 3‐parameter equation, and the baseline along with the contrast enhanced projections are used to solve for these 3 parameters in each voxel. A computer simulation was performed based on functional CT data of cervix patients to evaluate the feasibility of the method to estimate different contrast uptake shapes. A phantom study was also done in a breast phantom with flow mechanism to compare the method against clinical CT for a fast washout and a plateau contrast uptake curve. Results: The computer simulation showed excellent accuracy of uptake characteristics for the new method that the DCE‐CBCT algorithm correctly determined the contrast uptake behavior in 14 out of 15 patients. Good agreement was also found in the phantom study in which both uptake curves (rapid washout and plateau) were accurately determined by the DCE‐CBCT method compared to those measured with clinical CT, although the former curves are more dispersed. Conclusions: Preliminary simulation and phantom data suggest the feasibility of the proposed method to determine different contrast uptake behavior in contrast enhanced breast CBCT which might have a potential for diagnosis of breast cancer.

WE-E-L100J-06: Simulation Studies On Contrast Enhanced Dual Energy Mammography

Purpose: Technique optimization for contrast-enhanced dual energy mammography in a breast CT scanner. Method and Materials: Using kVp accuracy and HVL measurements physically performed on the x-ray source of a dedicated cone beam breast CT system, a mathematical spectral model was calibrated to have the same spectral and output properties as the physical system. Mathematical breast phantoms were fabricated by generating random sized and randomly placed glandular spheres on an adipose background to approximate the anatomical noise of the breast. The simulated imaging geometry matched that of the breast CT system. Quantum noise was simulated using Poisson model and a validated random number generator. Contrast-enhanced dual energy mammography was optimized for parameters including kVp, x-ray spectral filtration, and mAs distribution between high and low energy images. Mean glandular dose to the breast was calculated using dose coefficients generated from previously published Monte Carlo simulations. A figure of merit of the contrast-to-noise ratio at constant mean glandular dose was chosen for the optimization task to maximize image quality at minimal radiation dose levels. Optimization was carried out over a range of breast diameters, breast compositions, and iodine concentrations. Results: Spectra study suggested the optimal kVp to be between 120kV and 140kV for the high energy image, and between 50kV and 60kV for the low energy image, for the studied ranges of breast diameters and compositions. Added copper filtration up to 1mm for the high kVp spectra continued to improve CNR at set dose levels. Iodine as diluted as 0.05% of the 350mg/mL standard solution could be detected with a 2.5mGy total dose. Optimized mAs distribution suggested a higher dose proportion for the low kVp image than for the high kVp image. Conclusion: An optimized contrast-enhanced dual energy mammography can efficiently suppress anatomical noise and significantly improve contrast detection.

WE-E-L100J-07: Breast CT with Energy Resolved Detection

Purpose: To evaluate breast CT with energy resolved detection. Methods and Materials: A new breast CT system with energy resolved x‐ray detector and Scanning Multi‐Slit (SMS) data acquisition was evaluated. The SMS CT provides efficient scatter rejection, and uses linear array of photon counting detectors. A breast CT phantom with 14 cm diameter and 50/50 adipose/glandular composition was used. The phantom included carcinoma, adipose, blood, iodine, and CaCO3 as contrast elements. The x‐ray technique was 90 kVp with 660 mR entrance exposure. Photon counting, charge (energy) integrating, and photon energy weighting CTimages were generated. The CNR improvement with photon energy weighting was calculated. The CTimages with calcium/tissue and iodine/tissue decomposition were generated with dual energy subtraction. The x‐ray spectrum was electronically split into low and high energy parts by photon counting detector to perform dual energy subtraction. Results:CNR of the energy weighting CTimages of carcinoma, blood, iodine, and CaCO3 was higher by 19.3%, 19.9%, 29.7% and 40.4%, respectively, as compared to conventional CT.Photon counting dual energy subtraction provided 61% higher CNR as compared to conventional dual kVp dual energy subtraction. CNR of the photon counting dual energy subtracted CTimages of CaCO3 was increased by 69% when photon energy weighting was applied to CT projections prior subtraction. CNR improvement of SMS CT due to scatter rejection is 32% as compared to cone beam breast CT. Combination of photon energy weighting with scatter rejecting results in 50%‐85% CNR improvement in SMS CT as compared to conventional CT.Conclusion:Photon countingCT has a potential for improved sensitivity due to higher CNR with scatter rejection, quantum limited detection, and photon energy weighting. It has a potential for improved specificity due to single kVp dual energy subtraction that enables calcium/tissue and iodine/tissue decomposition.

WE‐E‐L100J‐01: Simulation of Tomosynthesis Mammograms with Cone Beam CT Images of Mastectomy Breast Specimens

Purpose: To describe and discuss about a technique to simulate digital mammograms and tomosynthesis images with cone beam CT images of mastectomy breast specimens. Method and Materials: To allow x‐ray images to be simulated, cone beam breast CT images of a mastectomy breast specimen were acquired at 80 kVp and used to generate a 3‐D map of linear attenuation coefficients for mammographic x‐rays. The map was then deformed to generate a new map for a compressed breast. A software re‐projector was developed and used to compute projection images for a stationary detector and a linearly shifted x‐ray source. A special re‐projector was developed to preserve the contrast of microcalcifications (MCs). The resulting images were then used to reconstruct tomosynthesis mammograms using various reconstruction algorithms. Results: We have successively used cone beam CT images of mastectomy breast specimens to generate 3‐D maps of attenuation coefficients to model compressed breasts and to use them to simulate digital mammograms and tomosynthesis images. It was found that MCs clearly visible in cone beam CT images were not visible in regular mammograms but faintly visible in tomosynthesis images. The MCs were clearly visible in both MC enhanced mammograms and the tomosynthesis images reconstructed from them. Conclusions: Cone beam CT images may be used to model a compressed breast for simulating mammograms and tomosynthesis images. Cone beam CT images are superior to regular or tomosynthesis mammograms in depicting MCs within their resolution limit. MC enhanced re‐projection, however, could be useful in displaying the cone beam CT images with the more conventional appearances of regular and tomosynthesis mammograms while maintaining the contrast and visibility of MCs in the CT images.This work was supported in part by a research grant EB00117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI.

TU-FF-A4-06: Motion Blurring Correction for a Cone Beam CT System with Image Decomposition and Deconvolution Method

Purpose: To improve the image resolution of a cone beam breast CT system by correcting the image blurring caused by gantry motion for a system works under continuous fluoroscopy acquisition mode. Method and Materials: Computer simulation models were built to simulate the effects on CT system resolution from different subcomponents, including the focal spot distribution and gantry motion. The system MTF results showed that image resolution degraded from the center towards the edge of the FOV, along the azimuthal direction. The major cause of this degradation was the gantry motion during continuous fluoroscopy acquisition. Azimuthal MTF results from computer simulation were used to generate a 2-D MTF response function to model the system resolution property by fitting discrete data points into a set of 3rd order polynomials. To preserve the image resolution of CT images on the radial direction, the original CT images were converted from the Cartesian coordinates into a new orthogonal coordinate system by the following transformation: For each radial position, the image data were de-convolved with corresponding system MTF in frequency domain along the azimuthal direction (along T axis). CT Images were converted back to Cartesian coordinates after deconvolution by: Results: A full view 2D MTF function was generated from computer simulations. With the presented method, the azimuthal resolution of the CT image was improved while the radial resolution was preserved. This method was applied to simulated phantom images and clinical breast CT images, qualitative observations showed improved spatial resolution along azimuthal direction. Conclusion: The full view 2D MTF function proved to be sufficient to model the spatial resolution of a cone beam CT scanner, which is a non-isotropic, shift-variant system. The presented novel image decomposition and deconvolution method demonstrated the promising potential to correct for the spatial resolution degradation.

TU‐EE‐A4‐03: A Comparison of Anatomical Noise Properties Between Breast CT and Projection Breast Imaging

Purpose: To compare the statistical properties of the anatomical noise present in breast images. Images from a dedicated breast CT scanner are compared with mammographic projection images. Method and Materials: A dedicated breast CT (bCT) scanner was used to image the breasts of volunteers and patients. Twenty‐five of the available 105 patient datasets were selected for analysis. Noise power spectra (NPS) calculations were performed on the datasets for the right breast of the 25 patients in order to examine the statistical nature of the anatomical background of the breast. The projection images acquired at 80 kVp during the cone beam breast CT acquisition were analyzed using NPS calculations. Approximately 50 projection images and 50 bCT slice images were analyzed per patient. Three regions of interest (ROIs) were used per image. The ROIs were randomly distributed within the boundary of the breast. The 2D NPS was calculated for each ROI and the average 2D NPS was computed and averaged radially yielding a 1D NPS. A power law expression of the form αf−β was computed from the results of the projection and bCT images, and the β values were compared. Theoretical development suggests that the β for bCT should be one less than that of the projection images, i.e. β [bCT] = β [proj] − 1. Results: The β values for the bCT slice images were consistently less than those for the projection images. The difference ranged from 0.90 to 2.15, with the average difference being 1.34. The β values for projection images were consistent with the 2.8 value described by Burgess (2001). Conclusion: Lower β values from the NPS results of the bCT images could quantitatively indicate potential improvement in detection ability. More work is needed to conclusively say if this is the case.

Computer modeling of the spatial resolution properties of a dedicated breast CT system

Computer simulation methods were used to evaluate the spatial resolution properties of a dedicated cone-beam breast CT system. X-ray projection data of a 70 microm nickel-chromium wire were simulated. The modulation transfer function (MTF) was calculated from the reconstructed axial images at different radial positions from the isocenter to study the spatial dependency of the spatial resolution of the breast CT scanner. The MTF was also calculated in both the radial and azimuthal directions. Subcomponents of the cone beam CT system that affect the MTF were modeled in the computer simulation in a serial manner, including the x-ray focal spot distribution, gantry rotation under the condition of continuous fluoroscopy, detector lag, and detector spatial resolution. Comparison between the computer simulated and physically measured MTF values demonstrates reasonable accuracy in the simulation process, with a small systematic difference (approximately 9.5 +/- 6.4% difference, due to unavoidable uncertainties from physical measurement and system calibration). The intrinsic resolution in the radial direction determined by simulation was about 2.0 mm(-1) uniformly through the field of view. The intrinsic resolution in the azimuthal direction degrades from 2.0 mm(-1) at the isocenter to 1.0 mm(-1) at the periphery with 76.9 mm from the isocenter. The results elucidate the intrinsic spatial resolution properties of the prototype breast CT system, and suggest ways in which spatial resolution can be improved with system modification.

Tilted angle CZT detector for photon counting/energy weighting x-ray and CT imaging

X-ray imaging with a photon counting/energy weighting detector can provide the highest signal to noise ratio (SNR). Scanning slit/multi-slit x-ray image acquisition can provide a dose-efficient scatter rejection, which increases SNR. Use of a photon counting/energy weighting detector in a scanning slit/multi-slit acquisition geometry could provide highest possible dose efficiency in x-ray and CT imaging. Currently, the most advanced photon counting detector is the cadmium zinc telluride (CZT) detector, which, however, is suboptimal for energy resolved x-ray imaging. A tilted angle CZT detector is proposed in this work for applications in photon counting/energy weighting x-ray and CT imaging. In tilted angle configuration, the x-ray beam hits the surface of the linear array of CZT crystals at a small angle. This allows the use of CZT crystals of a small thickness while maintaining the high photon absorption. Small thickness CZT detectors allow for a significant decrease in the polarization effect in the CZT volume and an increase in count rate. The tilted angle CZT with a small thickness also provides higher spatial and energy resolution, and shorter charge collection time, which potentially enables fast energy resolving x-ray image acquisition. In this work, the major performance parameters of the tilted angle CZT detector, including its count rate, spatial resolution and energy resolution, were evaluated. It was shown that for a CZT detector with a 0.7 mm thickness and 13° tilting angle, the maximum count rate can be increased by 10.7 times, while photon absorption remains >90% at photon energies up to 120 keV. Photon counting/energy weighting x-ray imaging using a tilted angle CZT detector was simulated. SNR improvement due to optimal photon energy weighting was 23% and 14% when adipose contrast element, inserted in soft tissue with 10 cm and 20 cm thickness, respectively, was imaged using 5 energy bins and weighting factors optimized for the adipose. SNR improvement was 42% and 31% when CaCO3 contrast element, inserted in soft tissue with 10 cm and 20 cm thickness, respectively, was imaged using 5 energy bins and weighting factors optimized for CaCO3. The SNRs of the photon counting single-kVp dual-energy subtracted images of CaCO3 and adipose were higher by 2.04 and 2.74 times, respectively, as compared to currently used dual-kVp dual-energy subtracted images. Experiments with a CZT crystal with 2 mm thickness have shown significant decrease in the tailing effect of the CZT pulse spectrum at 59 keV and 122 keV photon energies, when the tilting angle configuration was used. Finally, feasibility of the tilted angle CZT detector for photon counting cone beam breast CT imaging was demonstrated.

TU‐C‐330D‐01: Advances in Breast Imaging

Despite development and advances of new modalities, x‐ray mammography remains the main screening tool for early detection of breast cancers. It also continues to play an important role in the diagnosis and management of breast cancers. X‐ray mammography has relied on the use of high resolution screen/film combinations. Such techniques, although improved over the years, have the drawbacks of all the inconveniences and inflexibility associated with the use of film for image acquisition, storage and display. Motivated by search for better image quality and a general move towards filmless radiology, various digital mammography techniques have been developed, investigated and commercialized. These techniques can be largely divided into four types: amorphous silicon and selenium flat panel detector, amorphous silicon and cesium iodide flat panel detector, CCD and cesium iodide based slot scanning system, and storage phosphor imaging technique with dual‐side image read out. Each of these systems has its unique advantages and disadvantages and achieves various degrees of clinical implementation. Typical of all digital mammography techniques is the potential compatibility with digital image archival, retrieval and distribution systems. Furthermore, the acquisition of breast images in digital format has begun to facilitate the development and investigation of many advanced imaging techniques. Among them, dual‐energy mammography techniques have been developed to quantify breast tissue composition or to separate calcifications from the overlying tissue structures. Stereo‐mammography has been developed to use two projection views to provide a 3‐D perspective of the breast tissue structures, thus reducing the problem of overlapping structures. Tomosynthesis imaging pushes the idea of 3‐D imaging further by acquiring 10–25 projection views and use them to synthesize images to depict the breast structures as a number of thick layers. More recently, cone beam breast CT has been developed and investigated to scan the breast in a dedicated manner and provide true 3‐D images of the breast. Along a different direction, the development and investigation of various contrast mammography techniques have allowed x‐ray imaging to be used to image and study breast vasculatures as possible indication of breast cancer.In this presentation, we will try to achieve the following educational objectives:1. Review the development and investigation of major digital mammography techniques.2. Review the development and investigation of various advanced breast x‐ray imaging techniques.Research sponsored by the National Cancer Institute and the National Institute of Biomedical Imaging and Bioengineering.

MO-E-I-609-02: Imaging Properties of Cone Beam Breast CT- Effects of Detector Properties and Imaging Conditions

Purpose: To investigates the effects of detector properties and imaging conditions on the imaging properties of cone‐beam breast CT with both computer simulations and imaging experiments. Method and Materials: Cone beam breast CT was simulated with the breast analytically modeled as cylinder embedded spherical shape soft tissue masses and calcifications. X‐ray spectrum, breast attenuation, geometric magnification, focal spot blurring, x‐ray detection,detector blurring, image pixelization and digitization were all incorporated in computing the projection images.Quantum noise, system noise,detector blurring were also simulated and incorporated in the model. Image filtering and reconstruction were then performed using the Feldkamp algorithm. Simulation was performed for two flat‐panel detectors, one CsI based and the other a‐Se based. Images of phantoms and breast specimens were also obtained to demonstrate the ability of our experimental cone beam breast CT system to image the 3‐D structures of the breast with embedded cancers and calcifications. Results: Our simulation results shows that the a‐Se detector performs slightly better at 30 and 40 kVp's while the CsI detector performs better at 50 or higher kVp's. ImageSNRs are optimized at 50 and 60 kVp for the s‐Se and CsI detector, respectively. Phantom images obtained with our experimental system show that with higher dose and smaller pixel size, calcifications as small as could be resolved. Images of breast specimens show excellent separation between glandular and adipose tissues. The speculated nature of the tumor masses can be clearly seen in selected projection while ambiguous in other projections or in regular mammograms. It was also found that inclusion of surgical clips (used to indicate tumor location) had caused detrimental reconstruction artifacts. Acknowledgment: This work was supported in part by a research grant EB000117 from the NIBIB and a research grant CA104759 from the NCI.

TU‐D‐I‐611‐07: A Scanning Sampled Measurement (SSM) Technique for Scatter Measurement and Correction in Cone Beam Breast CT

Purpose: To implement and investigate a scanning sampled measurement (SSM) technique used to obtain sampled scatter measurement for scatter correction in cone beam breast CT. Method and Materials: Breast phantom or specimen is mounted on the rotating stage in a stationary gantry experimental cone beam CT system. A slightly tilted 2‐D array of 1.2‐mm diameter lead beads, with the beads 1 cm apart from each other, was placed between the object and x‐ray source. A series of projection images were acquired as the phantom is rotated (1 degree per projection view) and the lead beads array shifted by 1.2‐mm from one projection view to the next. Image signals in the lead bead shadow were used to obtain sampled scatter measurements which are then interpolated to form an estimated scatter distribution. The image data in the lead bead shadows are restored by interpolating image data from the two adjacent projection views to form complete (lead bead free) projection images. The estimated scatter distribution is then subtracted from the corresponding restored projection image to obtain the scatter corrected projection images. Results: Sampled scatter measurements were successfully made in each projection image and the accuracy of scatter measurements was verified with a larger beam blocker placed between the lead beads and x‐ray source. The SPRs in the projection images of a breast phantom are found to range from 0.1 to 0.5. Using scatter distribution interpolated from scanning sampled measurements and restored projection image data, scatter correction was successfully performed on all projection images. The resulting scatter corrected projection image data resulted in more accurate reconstruction of the linear attenuation coefficients and reduced the cupping effects. This work is supported in part by a research grant EB000117 from the NIBIB & Bioengineering and a research grant CA104759 from the NCI.

MO-E-I-609-01: Evaluation of Scattered Radiation Effect On Breast Cone-Beam CT Image: A Phantom Study

Purpose: To quantify the impact of scattered radiation on CT image reconstruction. Method and Materials: A 14 cm diameter cylindrical 50/50 (50% glandular/50% adipose) tissue equivalent phantom was used to assess CT scatter conditions in a custom build cone-beam breast CT scanner. The amount of scatter was varied by controlling the vertical dimension of the collimator opening (in the cone angle direction), which ranged from 16.8 to 100.2 mm at isocenter. Four data sets were acquired for each collimation, two with a 50/50 tissue equivalent rod and two with a 100% glandular tissue equivalent rod at the center of the phantom, with a scan technique of 80 kVp, 5 mA and 16.6 s (500 views). The images were reconstructed at the exact location for all the different collimated images, and the CNR was used to assess the image quality as a function of scatter to primary ratio (SPR). Results: As the amount of scatter (collimator gap) increases, the cupping artifact in the reconstructed image increases slightly. The CNR dropped from 2.6 at 16.8 mm collimation to 2.0 at 22.5 mm collimation, and remained at about 2.0 with further increases in the gap's width. Conclusion: Based on the preliminary results presented here, the scatter radiation increased the cupping artifact in the reconstructed image and reduced the CNR. However, the reduction in CNR appears to occur most dramatically at lower SPR and does not worsen significantly as the scatter increases from moderate (SPR = 0.1) to high (SPR = 0.5) levels.