Calcium Carbonate Grains Research Articles

PRESERVED MEMBRANE ON DINOSAUR EGGSHELL FRAGMENTS, UPPER JURASSIC MORRISON FORMATION, EASTERN UTAH

ABSTRACT Dinosaur eggshell fragments, from the Upper Jurassic Brushy Basin Member of the Morrison Formation, Utah, were examined using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Spectroscopy, and Raman Spectroscopy. Analyses revealed that the mammillary tips on the shell interior contain carbonaceous residue. Comparison under the FESEM of these shells with modern bird shells, including some samples heated to diagenetic temperatures, indicate that the residue is degraded organic compounds (DOC). Bird egg membrane is composed of interlaced collagen fibers. Features observed on, and common to, modern bird and dinosaur egg fragments include: (1) irregular-shaped calcium carbonate grains “floating” in an organic matrix; (2) three-dimensional organic fiber matrix; (3) external calcium carbonate molds of fibers in the mammillary bodies; and in heated specimens, (4) carbonaceous residue with ovate to circular pores. However, unlike birds' eggs, the dinosaur eggs contain a calcium carbonate tube around fibrous organic material that emerges from the tube and spreads laterally in a ‘puddle-like' deposit. The sizes of circular organic matrix pores of the dinosaur egg fragments are significantly smaller than those in the bird shells. Gallus gallus domesticus eggshell membranes heated to diagenetic temperatures resulted in alteration of collagen fibers to gel-like substances. The organic matrix with ovate to circular pore openings and the puddle-like deposits in the dinosaur egg fragments are interpreted as the product of membrane thermal diagenesis. The recognition of carbonaceous residue of the shell membrane on dinosaur shell fragments opens newfound opportunities to explore DOC associated with fragmental dinosaur eggs.

Characterization of the cross-lamellar structure of Olivancillaria urceus (Gastropoda: Olividae) and its dissolution pattern

In this work, we sought to characterize the cross-lamellar microstructure of the gastropod Olivancillaria urceus (Röding, 1798) and its profile after immersion in acid medium. For crystallographic analysis, segments of the valve were removed and crushed. The powder obtained was analyzed using Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR) and X-ray Diffractometry (XRD) techniques. For microstructural analysis, eight sections were taken from the shell using a rotary saw. The face of interest of each section was polished with Saint Gobain silicon carbide abrasive powder with mesh sizes of 320, 500, 600, and 1000. The eight sections were divided into four groups of two samples. Three groups were left in 4 % glacial acetic acid solution diluted in water for intervals of 20, 40, and 60 min, respectively, and the control group was not degraded. All wafers were then analyzed in Scanning Electron Microscopy to ascertain the microstructure. The angle and thickness of the layers were determined by Image J software. As a result of the FTIR-ATR technique, a transmittance spectrum was obtained whose valleys represent the vibrational modes of the carbonate ion. The diffractogram peaks and their respective Miller indices, are characteristic of the aragonite crystallographic structure and a small fraction of calcite. The micrographs obtained exposed 3 layers of cross-lamellar microstructure, however, the third and innermost layer showed discontinuity. The angle and average thickness were (105 ± 2)° and (727 ± 5)µm for the outermost layer and (116 ± 3)° and (668 ± 6)µm for the middle layer. The tablets immersed in acid medium showed loss of orientation of the calcium carbonate grains after 40 min and 60 min. Thus, the O. urceus shell exhibits orthorhombic calcium carbonate crystallography. Three layers of cross-lamellar microstructure were identified, as well as the configuration of the structure after contact with corrosive media. These results contribute to the characterization of natural materials and serve as a basis for analysis of the preservation potential in the fossil record.

Uvigerina agglutinata n.sp. a new Holocene benthic foraminifer with an outer agglutinated layer from the central Red Sea

This paper describes a new deep-sea foraminifer which has possibly evolved a way to use sediment particles from its surroundings to increase its density. The benthic foraminifer recovered from Red Sea planktonic ooze shares some similarities with two well-established Uvigerina species Uvigerina auberiana d'Orbigny, 1826 and the extinct Uvigerina auberiana var. attenuata Cushman & Renz, 1941. However, it differs from the two species mainly by the incorporation of sediment grains into its external wall. Uvigerina agglutinata n.sp. is characterized by its initially triserial coiling, which changes to biserial in the middle part and eventually becomes uniserial in final whorl. The most diagnostic feature of this species is the incorporation of different shapes and sizes of detrital calcium carbonate grains into its outer wall.

High-resolution imaging for characterizing microcalcification detection performance in breast CT.

Purpose: To demonstrate the utility of high-resolution micro-computed tomography ( ) for determining ground-truth size and shape properties of calcium grains for evaluation of detection performance in breast CT (bCT). Approach: Calcium carbonate grains ( ) were suspended in 1% agar solution to emulate microcalcifications ( ) within a fibroglandular tissue background. Ground-truth imaging was performed on a commercial scanner and was used for assessing calcium-grain size and shape, and for generating signal profiles. Calcium grains were placed within a realistic breast-shaped phantom and imaged on a prototype bCT system at 3- and 6-mGy mean glandular dose (MGD) levels, and the non-prewhitening detectability was assessed. Additionally, the -derived signal profiles were used in conjunction with the bCT system characterization (MTF and NPS) to obtain predictions of bCT detectability. Results: Estimated detectability of the calcium grains on the bCT system ranged from 2.5 to 10.6 for 3mGy and from 3.8 to 15.3 for 6mGy with large fractions of the grains meeting the Rose criterion for visibility. Segmentation of images based on morphological operations produced accurate results in terms of segmentation boundaries and segmented region size. A regression model linking bCT detectability to parameters indicated significant effects of size and vertical position within the breast phantom. Detectability using -derived detection templates and bCT statistical properties (MTF and NPS) were in good correspondence with those measured directly from bCT ( ). Conclusions: Parameters derived from ground-truth data were shown to produce useful characterizations of detectability when compared to estimates derived directly from bCT. Signal profiles derived from imaging can be used in conjunction with measured or hypothesized statistical properties to evaluate the performance of a system, or system component, that may not currently be available.

High resolution microcalcification signal profiles for dedicated breast CT.

This study introduces a methodology for generating high resolution signal profiles of microcalcification (MC) grains for validating breast CT (bCT) systems. A physical MC phantom was constructed by suspending calcium carbonate grains in an agar solution emulating MCs in a fibroglandular tissue background. Additionally, small Teflon spheres (2.4 mm diameter) were embedded in the agar solution for the purpose of fiducial marking and assessment of segmentation accuracy. The MC phantom was imaged on a high resolution (34 μm) commercial small-bore μCT scanner at high dose, and the images were used as the gold-standard for assessing MC size and for generating high resolution signal profiles of each MC. High-dose bCT scans of the MC phantom suspended in-air were acquired using 1 × 1 binning mode (75 μm dexel pitch) by averaging three repeat scans to produce a single low-noise reconstruction of the MC phantom. The high resolution μCT volume data set was then registered with the corresponding bCT data set after correcting for the bCT system spatial resolution. Microcalcification signal profiles constructed using low-noise bCT images were found to be in good agreement with those generated using the μCT scanner with all differences < 10% within the VOI surrounding each MC. The MC signal profiles were used as detection templates for a non-prewhitening-matched-filter model observer for scans acquired in a realistic breast phantom at 3, 6, and 9 mGy mean glandular dose. MC detectability using signal templates derived from bCT were shown to be in good agreement with those generated using μCT.

Improvement of voidage prediction in liquid-solid fluidized beds by inclusion of the Froude number in effective drag relations

A novel effective drag relation for liquid-solid fluidisation is proposed, suitable for application in full-scale installations. This is achieved by presenting new insights related to the influence of the temporal-spatial heterogeneity on the effective hydrodynamic drag for large fluidised systems. While heterogeneous flow behaviour can be predicted increasingly accurately in CFD simulations that explicitly model the heterogeneous solids distribution, for the operation of many large-scale applications it is infeasible to perform such computationally intensive simulations. Therefore, there is a clear need for full-scale drag relations that effectively take into account the heterogeneous behaviour and irregular spatial particle distributions. Our new drag relation is based on a large set of experiments, which shows that the degree of overall expansion is not only dependent on the ratio of laminar-turbulent flow, but also on the amount of homogenous versus heterogeneous flow, which is not included in current full-scale drag relations. To include the effect of heterogeneity, the standard drag relation, based on the Reynolds number, is extended with a specific type of Froude number. Because fully turbulent flow regimes are rare in applications of liquid-solid fluidisation, our focus is not on the turbulent flow regime but instead on laminar and transitional flow regimes. In these regimes, three types of models are investigated. The first type is based on a theoretical similarity with terminal settling, the second is based on the semi-empirical Carman-Kozeny model, and the third is based on empirical equations using symbolic regression techniques. For all three types of models, coefficients are calibrated on experimental data with monodisperse and almost spherical glass beads. The models are validated with a series of calcium carbonate grains applied in drinking water treatment processes as well as data obtained from the literature. Using these models, we show that the voidage prediction average relative error decreases from approximately 5% (according to the best literature equations which use Reynolds number only) to 1–2% (using both Reynolds and Froude number). This implies that our new models are more suitable for operational control in full-scale fluidised bed applications, such as pellet softening in drinking water treatment processes.

Native Gammarus fossarum affects species composition of macroinvertebrate communities: evidence from laboratory, field enclosures, and natural habitat

Despite the fact that native species of amphipods have been recognized as active predators similarly to invasive species, little is known about their predatory impact on aquatic communities. In this study, we used a laboratory experiment, a field enclosure experiment, and an analysis of natural community data to demonstrate how Gammarus fossarum affects the species composition of benthic communities by imposing survival selection on its prey. Our laboratory single-prey experiment brought a clear evidence that tube-less chironomids are vulnerable prey and that the predation rate on the tube-dwelling chironomids decreases with increasing tube toughness (from the soft tubes made of detritus to the hard tubes made of sand or calcium carbonate grains). We found that the introduction of G. fossarum to field enclosures significantly changed the species composition of a macroinvertebrate community at an experimental spring fen site. The soft-bodied, slow moving, and tube-less taxa were depleted the most. It appears that the observed patterns were a result of predator’s preference rather than encounter rate. Survival selection was detected also in natural communities across a large spatial scale. In accordance with the experiments, high densities of G. fossarum limited the proportion or abundance of vulnerable prey. Our study (1) provides the first convincing evidence that biotic interactions have a structuring effect on the spring fen communities, (2) documents how the predatory effect in a community depends on an interplay between the prey handling behaviour of the predator and species-specific susceptibility of prey, and (3) shows that an omnivorous native amphipod may have a strong impact on aquatic communities despite it is regarded less aggressive than its invasive relatives.

Improvement of the Richardson-Zaki liquid-solid fluidisation model on the basis of hydraulics

One of the most popular and frequently used models for describing homogeneous liquid-solid fluidised suspensions is the model developed by Richardson & Zaki in 1954. The superficial fluid velocity and terminal settling velocity together with an index makes it possible to determine the fluid porosity in a straightforward way. The reference point for the Richardson-Zaki model is the terminal settling velocity at maximum porosity conditions. To be able to predict porosity in the proximity of minimum fluidisation conditions, either the minimum fluidisation velocity must be known or the Richardson-Zaki index must be very accurate. To maintain optimal process and control conditions in multiphase drinking water treatment processes, the porosity is kept relatively low. Unfortunately, the Richardson-Zaki index models tends to overestimate the minimum fluidisation velocity and therefore also results in less accurate predictions with respect to porosity values. We extended the Richardson-Zaki model with proven hydraulics-based models. The minimum fluidisation velocity is acquired using the model proposed by Kozeny (1927), Ergun (1952) and Carman (1937). The terminal settling velocity is obtained through the model developed by Brown & Lawler (2003), which is an improved version of the well-known model developed by Schiller & Naumann (1933). The proposed models are compared with data from expansion experiments with calcium carbonate grains, crushed calcite and garnet grains applied in drinking water softening using the fluidised bed process. With respect to porosity, prediction accuracy is improved, with the average relative error decreasing from 15% to 3% when the classic Richardson-Zaki model is extended with these hydraulics-based models. With respect to minimum fluidisation velocity, the average relative error decreases from 100% to 12%. In addition, simplified analytical equations are given for a straightforward estimation of the index n.

Multiscale characterization of carbonated wollastonite paste and application of homogenization schemes to predict its effective elastic modulus

This paper describes the multiscale characterization of the carbonated wollastonite paste using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), and statistical nanoindentation (SNI, also known as ‘grid indentation’) methods as well as micromechanical homogenization models. Wollastonite (CaSiO3) fibers are commonly used as filler in ceramics or plastics. However, wollastonite can also be regarded as non-hydraulic binder material since upon carbonation it forms a heterogeneous matrix with mechanical properties similar to those of the conventional hydrated cement pastes. Carbonation reaction of wollastonite results in the formation of two main products: calcium carbonate (CaCO3) and amorphous silica gel (SiO2). The SEM/EDS microanalysis performed on this system revealed that the average calcium to silica (Ca/Si) atomic ratio of the silica gel phase was around 0.40. Three individual carbonated wollastonite paste samples, each representing a different degree of carbonation were selected for nanoindentation tests. The obtained elastic moduli for silica gel, calcium carbonate, and unreacted wollastonite grains were, respectively, 41.7 GPa, 67.3 GPa, and 134.7 GPa. The micromechanical homogenization models were then utilized to predict the effective (also referred to as ‘homogenized’) elastic moduli of the carbonated wollastonite paste. The predicted values of the effective elastic moduli of carbonated wollastonite pastes were found to be in the range of corresponding values for hydrated high to ultra-high performance cement pastes. Additionally, the values of the effective elastic moduli of the carbonated wollastonite pastes were observed to increase with the increase in the degree of carbonation.

TU-F-18C-08: Micro-Calcification Detectability Using Spectral Breast CT Based On a Si Strip Detector

Purpose: To investigate the feasibility of micro-calcification (μCa) detectability by using an energy-resolved photon-counting Si strip detector for spectral breast computed tomography (CT). Methods: A bench-top CT system was constructed using a tungsten anode x-ray source with a focal spot size of 0.8 mm and a single line 256-pixel Si strip photon counting detector with a pixel pitch of 100 μm. The slice thickness was 0.5 mm. Five different size groups of calcium carbonate grains, from 105 to 215 μm in diameter, were embedded in a cylindrical resin phantom with a diameter of 16 mm to simulate μCas. The phantoms were imaged at 65 kVp with an Entrance Skin Air Kerma (ESAK) of 1.2, 3, 6, and 8 mGy. The images were reconstructed using a standard filtered back projection (FBP) with a ramp filter. A total of 200 μCa images (5 different sizes of μCas × 4 different doses × 10 images for each setting) were combined with another 200 control images without μCas, to ultimately form 400 images for the reader study. The images were displayed in random order to three blinded observers, who were asked to give a binary score on each image regarding the presence of μCas.more » The μCa detectability for each image was evaluated in terms of binary decision theory metrics. The sensitivity, specificity, and accuracy were calculated to study the size and dose-dependence for μCa detectability. Additionally, the influence of the partial volume effect on the μCa detectability was investigated by simulation. Results: For a μCa larger than 140 μm in diameter, detection accuracy of above 90 % was achieved with the investigated prototype spectral CT system at ESAK of 1.2 mGy. Conclusion: The proposed Si strip detector is expected to offer superior image quality with the capability to detect μCas for low dose breast imaging.« less

Cone beam breast CT with a high pitch (75 μm), thick (500 μm) scintillator CMOS flat panel detector: visibility of simulated microcalcifications.

To measure and investigate the improvement of microcalcification (MC) visibility in cone beam breast CT with a high pitch (75 μm), thick (500 μm) scintillator CMOS/CsI flat panel detector (Dexela 2923, Perkin Elmer). Aluminum wires and calcium carbonate grains of various sizes were embedded in a paraffin cylinder to simulate imaging of calcifications in a breast. Phantoms were imaged with a benchtop experimental cone beam CT system at various exposure levels. In addition to the Dexela detector, a high pitch (50 μm), thin (150 μm) scintillator CMOS/CsI flat panel detector (C7921CA-09, Hamamatsu Corporation, Hamamatsu City, Japan) and a widely used low pitch (194 μm), thick (600 μm) scintillator aSi/CsI flat panel detector (PaxScan 4030CB, Varian Medical Systems) were also used in scanning for comparison. The images were independently reviewed by six readers (imaging physicists). The MC visibility was quantified as the fraction of visible MCs and measured as a function of the estimated mean glandular dose (MGD) level for various MC sizes and detectors. The modulation transfer functions (MTFs) and detective quantum efficiencies (DQEs) were also measured and compared for the three detectors used. The authors have demonstrated that the use of a high pitch (75 μm) CMOS detector coupled with a thick (500 μm) CsI scintillator helped make the smaller 150-160, 160-180, and 180-200 μm MC groups more visible at MGDs up to 10.8, 9, and 10.8 mGy, respectively. It also made the larger 200-212 and 212-224 μm MC groups more visible at MGDs up to 7.2 mGy. No performance improvement was observed for 224-250 μm or larger size groups. With the higher spatial resolution of the Dexela detector based system, the apparent dimensions and shapes of MCs were more accurately rendered. The results show that with the aforementioned detector, a 73% visibility could be achieved in imaging 160-180 μm MCs as compared to 28% visibility achieved by the low pitch (194 μm) aSi/CsI flat panel detector. The measurements confirm that the Hamamatsu detector has the highest MTF, followed by the Dexel detector, and then the Varian detector. However, the Dexela detector, with its thick (500 μm) CsI scintillator and low noise level, has the highest DQE at all frequencies, followed by the Varian detector, and then the Hamamatsu detector. The findings on the MC visibility correlated well with the differences in MTFs, noise power spectra, and DQEs measured for these three detectors. The authors have demonstrated that the use of the CMOS type Dexela detector with its high pitch (75 μm) and thick (500 μm) CsI scintillator could help improve the MC visibility. However, the improvement depended on the exposure level and the MC size. For imaging larger MCs or scanning at high exposure levels, there was little advantage in using the Dexela detector as compared to the aSi type Varian detector. These findings correlate well with the higher measured DQEs of the Dexela detector, especially at higher frequencies.

The Characterization Of CaCO3 in a Geothermal Environment: A Sem/Tem-Eels Study

AbstractMineralization of microbial biomass is a common phenomenon in geothermal habitats, but knowledge of the structure of the minerals formed in these environments is limited. A combination of spectroscopic, microscopic, and stable isotopic methods, as well as the chemical analysis of spring water, were employed in the present study to characterize calcium carbonate minerals deposited in filamentous cyanobacterial mats in different locations of La Duke hot spring, a circumneutral thermal feature near the north entrance of Yellowstone National Park, Montana, USA. Calcite was the primary crystalline mineral phase associated with biofilm-containing deposits closest to the source of the spring and the suspended microbial biomass in a pool further from the source. The carbonate minerals at all sites occurred as aggregated granules, ~2 μm in diameter, in close association with the microbial biomass. Only in the deposits closest to the source were the granules organized as laminated structures interspersed with microbial biomass. The calcium carbonate grains contained two distinct regions: a dense monolithic calcite core and a porous dendritic periphery containing organic matter (OM). Electron energy loss spectroscopy (EELS) indicated that the voids were infilled with OM and carbonates. The EELS technique was employed to distinguish the source of carbon in the organic matter and carbonate mixture. The studies of carbon isotope compositions of the calcium carbonates and the saturation indices for calcite in the spring waters suggest that processes (abiotic vs. biotic) controlling the carbonate formation may vary among the sampling sites.

Investigation into Permeability and Bearing Strength of Plugging Zone Formed by Lost Circulation Materials

Mud loss while drilling fractured formations is a major problem for drilling operating. It is a key to successful temporary sealing technology that lost circulation materials (LCM) can quickly form the plugging zone in the fractures. The permeability of plugged zone influences its bearing strength, as drilling fluid can penetrate and break it, causing it destabilizing and then failure of lost circulation controlling. With the soap film flowmeter, designing different LCM under variable confining pressures, considering the matching relationship of grain diameters and fracture width is (0.5～1):1, analyzing the permeability of plugging zones with different materials. The results indicated that permeability of plugging zone with peanut grains is lower than that of calcium carbonate, but its bearing strength is not as good as that of calcium carbonate, while using merely single LCM. Comparing other materials, the ideal plugging zone is formed with the mixture of peanut grains and calcium carbonate, which has the lowest permeability as well as the bearing strength. The mixture of matching calcium carbonate and smaller peanut grains, comparing to the width of fracture could stands 5 MPa of pressure difference at normal temperature, and 3.9 MPa at 80°C temperature in laboratory. To some extent, it can meet the needs of temporary sealing technology and successfully deal with lost circulation, which demands plugged tightly and bilateral pressurization.

TU-E-217BCD-06: Cone Beam Breast CT with a High Resolution Flat Panel Detector-Improvement of Calcification Visibility.

To investigate the advantage of a high resolution flat panel detector for improving the visibility of microcalcifications (MCs) in cone beam breast CT Methods: A paraffin cylinder was used to simulate a 100% adipose breast. Calcium carbonate grains, ranging from 125-140 μm to 224 - 250 μm in size, were used to simulate the MCs. Groups of 25 same size MCs were embedded at the phantom center. The phantom was scanned with a bench-top CBCT system at various exposure levels. A 75μm pitch flat panel detector (Dexela 2923, Perkin Elmer) with 500μm thick CsI scintillator plate was used as the high resolution detector. A 194 μm pitch detector (Paxscan 4030CB, Varian Medical Systems) was used for reference. 300 projection images were acquired over 360° and reconstructed. The images were reviewed by 6 readers. The MC visibility was quantified as the fraction of visible MCs and averaged for comparison. The visibility was plotted as a function of the estimated dose level for various MC sizes and detectors. The MTFs and DQEs were measured and compared. For imaging small (200 μm and smaller) MCs, the visibility achieved with the 75μm pitch detector was found to be significantly higher than those achieved with the 194μm pitch detector. For imaging larger MCs, there was little advantage in using the 75μm pitch detector. Using the 75μm pitch detector, MCs as small as 180 μm could be imaged to achieve a visibility of 78% with an isocenter tissue dose of ∼20 mGys versus 62% achieved with the 194 μm pitch detector at the same dose level. It was found that a high pitch flat panel detector had the advantages of extending its imaging capability to higher frequencies thus helping improve the visibility when used to image small MCs. This work was supported in part by grants CA104759, CA13852 and CA124585 from NIH-NCI, a grant EB00117 from NIH-NIBIB, and a subcontract from NIST-ATP.

TU-A-301-01: Microcalcifications Visibility in Cone Beam Breast CT with Various Flat Panel Detectors

Purpose: To investigate the visibility of microcalcifications (MCs) in cone beam breast CT using various flat panel detectors. Methods: We investigated the visibility of MCs in cone beam CT(CBCT) breast imaging using various flat panel detectors, including PaxScan 4030CB (aSi/CsI) by Varian MedicalSystems, FPD14 (aSi/aSe) by Anrad, C4742 (CCD/GdO2S:Tb) and C7921 (CMOS/CsI) detectors by Hamamatsu. A paraffin cylinder with a diameter of 135 mm and a thickness of 40 mm was used to simulate a 100% adipose breast. Calcium carbonate grains, from 125 – 140 μm to 224 – 250 μm in various size groups, were used to simulate the MCs. Groups of 25 same size MCs were arranged into 5 × 5 clusters. Each cluster was embedded at the center of a 15 mm diameter cylindrical paraffin phantom, which as inserted into a hole at the center of the breast phantom. The breast phantom with the simulated MCs was scanned on a bench top CBCTsystem at various exposure levels for each detector. The reconstructed images were reviewed by 6 readers independently. The MCvisibility was quantified as the fraction of visible MCs and averaged over all readers for analysis. The visibility was plotted as a function of the estimated dose level and image signal‐to‐noise ratio (SNR) for various scans and detectors. The relative detector DQEs were compared among the four detectors. Results: It was found the relationship between the visibility and size can be fitted with a Boltzmann function for all the detectors. The Varian detector has the best MCvisibility among all the detectors at the same dose level. Conclusions: The visibility of MCs increased with the isocenter dose and image SNR for all detectors.Detector with better DQE could achieve the same MCvisibility with lower radiation dose. This work was supported in part by grants CA104759, CA13852 and CA1245 85 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.

SU‐E‐I‐17: Evaluation of Cone Beam Breast CT (CBCT) System: Detection of Randomly Distributed Micro‐Calcification and the Effect of Beam Hardening Filter

Purpose: Detectability of micro‐calcification is very important for breast imaging. The purpose of this study is to evaluate the breast CBCT system through its detectability of randomly distributed micro‐calcifications under different mean glandular dose (MGD) and with or without different thickness copper filters. Methods: Calcium carbonate grains of various sizes (Three size groups: 224–250μm, 250–280μm, 280–300μm) were used to simulate calcifications. A breast shaped plastic container filled with paraffin was used to simulate a fatty breast; the top half of the phantom was cylindrical with 12.5cm diameter and the total height of the phantom is 14.5cm. The phantom was imaged with a CBCT system in our lab. The system consists of a conventional tungsten target x‐ray tube (G‐1592) and an a‐Si:H/CsI flat panel detector (Paxscan 4030CB). The source to image detector and source to iso‐center distances were 152 and 100 cm, respectively, resulting in a magnification factor of 1.52 at the iso‐center. All the scans were conducted at 80 kVp. The experiment was conducted under MGD equal to 2.5, 4, 6, 8 mGy. With each MGD setting, the scan was conducted without filter, with 0.002″ copper filter or with 0.004″ copper filter. Feldkamp algorithm with a ramp filter was used for image reconstruction of all scans. Results: Our CBCT system is capable of imaging calcifications as small as 224–250μm with 6mGy MGD or 250–280μm with 4mGy MGD if set 50% visibility as threshold. To all three size groups, filtering improves visibility of micro‐calcification when the dose is between invisible and high visible settings. Conclusions: Filtering improves detectability of micro‐calcification for low dose image.This work was supported in part by grants CA104759, CA124585 and CA13852 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.

WE-A-201B-02: Calcification Visibility in Cone Beam Breast CT: Effects of Under-Sampling and Limited Angle Scans

Purpose: To investigate the effects of under‐sampled and limited angle‐sampled projections on microcalcification visibility in cone beam breast CT.Materials and Methods: Different sizes of calciumcarbonate grains were embedded in a gelatin cylinder to simulate microcalcifications in dense breasts. The phantom was then imaged at 80 kVp with a bench‐top CBCTsystem, which employs a‐Si/CsI based flat panel detector with a pixel size of 194 microns operated in the non‐binning mode. For scans with under‐sampling technique, projections corresponding to 30, 50, 60, 75, 100, and 150 equally spaced views were acquired over 360 degrees with adjusted mAs per image to keep the total mAs the same. The resulting CBCTimages were compared to those obtained with 300 projections, which have been considered adequate for breast imaging. For scans with limited angle sampling technique, an angular range of 60, 72, 90, and 120 degrees were chosen to acquire projections with an increased mAs per image while a reduced mAs per image was used to acquire projections for views outside this angular range to generate a complete projection image set with the same total mAs. Feldkamp algorithm with a ramp filter was used for image reconstruction. The reconstructed images were sequentially displayed on a review workstation and reviewed by a reader at two different times. The reader was asked to indicate the visible microcalcifications, of which the ratios were calculated over all readings. Result: The visibility ratio was found to increase with the size range of the calcifications with both scanning techniques. It was found that the number of projections had no significant effect on the calcification visibility. However, the visibility ratio increased with the angular range for high exposure projections. (supported in part by research grants CA104759 and CA124585 from NCI and EB000117 from NIBIB, and a subcontract from NIST‐ATP)

SU‐FF‐I‐28: Effects of Voxel Size On Visibility of Microcalcifications in Cone Beam Breast CT

Purpose: To investigate the effects of voxel size on the visibility of simulated microcalcifications (MCs) in cone bream breast CT. Method and materials: Calcium carbonate grains (ranging from 140–150 to 200–212 μm), were used to simulate MCs. 25 MCs from same size group were arranged into a 5 × 5 cluster and embedded at the center of a 15 mm diameter paraffin rod. Rods with MCs from various size groups were constructed and scanned with a bench top experimental CBCT system. A CCD detector (C4742‐56‐12ER, Hamamatsu Photonics K.K) operated in 2×2 binning mode was used to acquire 300 projection images with a pixel size of 48 μm over 360°. Imaging geometry was configured with a magnification factor of 1.16 to result in a voxel size of 42 μm to match the spatial resolution limit. The acquired images were further binned into image sets of larger pixels (96, 144, 192, 240 and 288 μm). The image sets were then reconstructed with Feldkamp's backprojection algorithm using a ramp filter. The reconstructed image sets were reviewed by 6 readers independently. The visibility, computed as the ratio of visible MCs and averaged over all readers, was plotted as the function of voxel size to quantify the effects of voxel size on the visibility of MCs. Results: Based on the visibility versus voxel size plot, 90% visibility was achieved for 200 – 212, 180 – 200, 160 – 180, 150 – 160 and 140 – 150 μm calcifications at a voxel size of 249, 249, 206, 166 and 125 μm, respectively. The visibility versus voxel size plot may be used to determine the minimum pixel size required to achieve a specific visibility level for MCs of certain sizes. Conclusions: We have demonstrated that the minimum voxel size required to achieve a specific visibility level decreased with the MC size.

SU‐FF‐I‐20: Visibility of Simulated Microcalcifications with An ASi/aSe Flat Panel Detector Based Cone Beam CT System

Purpose: To investigate the visibility of microcalcifications (MCs) with an aSi/aSe flat panel detector (FPD14, Anrad Corporation) based cone beam CT (CBCT) system. Method and materials: A bench top experimental CBCT system was configured for breast imaging and used to image a breast phantom with embedded simulated MCs of various sizes. A paraffin cylinder with a diameter of 135 mm and a height of 40 mm was used to simulate a 100% adipose breast. Calcium carbonate grains, ranging from 125 to 425 μm in size, were used to simulate the microcalcifications. 25 MCs from same size group were arranged into a 5 × 5 cluster and embedded at the center of a 15 mm diameter paraffin rod to make an MC insert, which may be inserted into a hole at the center of the breast phantom for imaging. The breast phantom with MCs was scanned at various exposure levels. 300 projection images were acquired over 360° and reconstructed with Feldkamp's backprojection algorithm using a ramp filter. The images were reviewed by 6 readers. The ratios of visible MCs, averaged over all readers, were plotted as the function of the square root of measured dose level and image signal‐to‐noise ratio (SNR). Results: It was found that 90% visibility was achieved for 224 – 250 μm calcifications at an SNR of 16.8 or an isocenter dose of 5.2 mGys. 70% visibility was achieved for 224 – 250, 212 – 224, 200 – 212, 180 – 200, 160 – 180, 150 – 160 and 124 – 140 μm calcifications at an SNR of 16.8, 16.8, 25.1, 25.1, 44.5, 44.5 and 52.6, respectively. Conclusions: Percentage of visible MCs increased with the image SNR and isocenter dose. Higher SNRs and isocenter dose are required for imaging smaller MCs.

SU‐FF‐I‐29: Comparison of Dedicated Cone‐Beam Breast CT with Conventional CT for Detection of Micro‐Calcification

Purpose: To compare the visibility of micro‐calcifications in cone‐beam breast CT with that in conventional CT. Material and method: Calcium Carbonate grains (ranging from 180–200 to 250–280 microns) were used to simulate calcifications. Two bowl shaped plastic containers filled with paraffin were used to simulate a breast. The phantom was scanned with a bench‐top experimental CBCT system, configured for breast imaging. The system consists of a conventional tungsten target x‐ray tube (G‐1592) and an a‐Si:H/CsI flat panel detector (Paxscan 4030CB). The source to image and source to iso‐center distances are 100 and 75 cm, corresponding to a magnification factor of 1.33 at the iso‐center. A conventional CT system (GE Discovery STE PET/CT Scanner) was used to scan one phantom by itself and with two phantoms on an anthropomorphic chest phantom. Result: The visibility of the calcifications in CBCT images was found to be significantly better than that in the conventional CT images. Calcifications as small as 180–200μm were visible in the CBCT images. While calcifications of 212–224μm were visible in the conventional CT images when only breast phantom was scanned. None of the calcifications studied (280 μm or smaller) were visible when the two breast phantoms were placed on the anthropomorphic chest phantom for scan. Conclusion: Our results indicated that CBCT is capable of imaging calcifications as small as 180 μm. This is due to the intrinsic high spatial resolution of the detector used and the pendant geometry used which allowed the breast to be scanned and imaged by itself. The conventional CT is intrinsically lower in spatial resolution. An important disadvantage is the inclusion of the entire chest in the scan which results in degraded spatial resolution as well as overall higher radiation dose to the patient.