bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensional microwave imaging of realistic numerical breast phantoms via a multiple‐frequency inverse scattering technique
Authors: Shea Jacob D. , Kosmas Panagiotis , Hagness Susan C. , Van Veen Barry D. 
Published: July 2010

Purpose:Breast density measurement has the potential to play an important role in individualized breast cancer risk assessment and prevention decisions. Routine evaluation of breast density will require the availability of a low‐cost, nonionizing, three‐dimensional (3‐D) tomographic imaging modality that exploits a strong properties contrast between dense fibroglandular tissue and less dense adipose tissue. The purpose of this computational study is to investigate the performance of 3‐D tomography using low‐power microwaves to reconstruct the spatial distribution of breast tissue dielectric properties and to evaluate the modality for application to breast density characterization.Methods:State‐of‐the‐art 3‐D numerical breast phantoms that are realistic in both structural and dielectric properties are employed. The test phantoms include one sample from each of four classes of mammographic breast density. Since the properties of these phantoms are known exactly, these testbeds serve as a rigorous benchmark for the imaging results. The distorted Born iterative imaging method is applied to simulated array measurements of the numerical phantoms. The forward solver in the imaging algorithm employs the finite‐difference time‐domain method of solving the time‐domain Maxwell's equations, and the dielectric profiles are estimated using an integral equation form of the Helmholtz wave equation. A multiple‐frequency, bound‐constrained, vector field inverse scattering solution is implemented that enables practical inversion of the large‐scale 3‐D problem. Knowledge of the frequency‐dependent characteristic of breast tissues at microwave frequencies is exploited to obtain a parametric reconstruction of the dispersive dielectric profile of the interior of the breast. Imaging is performed on a high‐resolution voxel basis and the solution is bounded by a known range of dielectric properties of the constituent breast tissues. The imaging method is validated using a breast phantom with a single, high‐contrast interior scattering target in an otherwise homogeneous interior. The method is then used to image a set of realistic numerical breast phantoms of varied fibroglandular tissue density.Results:Imaging results are presented for each numerical phantom and show robustness of the method relative to tissue density. In each case, the distribution of fibroglandular tissues is well represented in the resulting images. The resolution of the images at the frequencies employed is wider than the feature dimensions of the normal tissue structures, resulting in a smearing of their reconstruction.Conclusions:The results of this study support the utility of 3‐D microwave tomography for imaging the distribution of normal tissues in the breast, specifically, dense fibroglandular tissue versus less dense adipose tissue, and suggest that further investigation of its use for volumetric evaluation of breast density is warranted.
Monte Carlo simulator of realistic x‐ray beam for diagnostic applications
Authors: Bontempi Marco , Andreani Lucia , Rossi Pier Luca , Visani Andrea 
Published: July 2010

Purpose:Monte Carlo simulation is a very useful tool for radiotherapy and diagnostic radiology. Yet even with the latest PCs, simulation of photon spectra emitted by an x‐ray tube is a time‐consuming task, potentially reducing the possibility to obtain relevant data such as dose evaluations, simulation of geometric settings, or monitor detector efficiency. This study developed and validated a method to generate random numbers for realistic beams in terms of photon spectrum and intensity to simulate x‐ray tubes via Monte Carlo algorithms.Methods:Starting from literature data, the most common semiempirical models of bremsstrahlung are analyzed and implemented, adjusting their formulation to describe a large irradiation area (i.e., large field of view) and to take account of the heel effect as in common practice during patient examinations.Results:Simulation results show that Birch and Marshall's model is the fastest and most accurate for the aims of this work. Correction of the geometric size of the beam and validation of the intensity variation (heel effect) yielded excellent results with differences between experimental and simulated data of less than 6%.Conclusions:The results of validation and execution time showed that the tube simulator calculates the x‐ray photons quickly and efficiently and is perfectly capable of considering all the phenomena occurring in a real beam (total filtration, focal spot size, and heel effect), so it can be used in a wide range of applications such as industry, medical physics, or quality assurance.
Hybrid x‐ray/optical luminescence imaging: Characterization of experimental conditions
Authors: Carpenter C. M. , Sun C. , Pratx G. , Rao R. , Xing L. 
Published: July 2010

Purpose:The feasibility of x‐ray luminescence imaging is investigated using a dual‐modality imaging system that merges x‐ray and optical imaging. This modality utilizes x‐ray activated nanophosphors that luminesce when excited by ionizing photons. By doping phosphors with lanthanides, which emit light in the visible and near infrared range, the luminescence is suitable for biological applications. This study examines practical aspects of this new modality including phosphor concentration, light emission linearity, detector damage, and spectral emission characteristics. Finally, the contrast produced by these phosphors is compared to that of x‐ray fluoroscopy.Methods:Gadolinium and lanthanum oxysulfide phosphors doped with terbium (green emission) or europium (red emission) were studied. The light emission was imaged in a clinical x‐ray scanner with a cooled CCD camera and a spectrophotometer; dose measurements were determined with a calibrated dosimeter. Using these properties, in addition to luminescence efficiency values found in the literature for a similar phosphor, minimum concentration calculations are performed. Finally, a 2.5 cm agar phantom with a 1 cm diameter cylindrical phosphor‐filled inclusion (diluted at 10 mg/ml) is imaged to compare x‐ray luminescence contrast with x‐ray fluoroscopic contrast at a superficial location.Results:Dose to the CCD camera in the chosen imaging geometry was measured at less than 0.02 cGy/s. Emitted light was found to be linear with dose and concentration . Emission peaks for clinical x‐ray energies are less than 3 nm full width at half maximum, as expected from lanthanide dopants. The minimum practical concentration necessary to detect luminescent phosphors is dependent on dose; it is estimated that subpicomolar concentrations are detectable at the surface of the tissue with typical mammographic doses, with the minimum detectable concentration increasing with depth and decreasing with dose. In a reflection geometry, x‐ray luminescence had nearly a 430‐fold greater contrast to background than x‐ray fluoroscopy.Conclusions:X‐ray luminescence has the potential to be a promising new modality for enabling molecular imaging within x‐ray scanners. Although much work needs to be done to ensure biocompatibility of x‐ray exciting phosphors, the benefits of this modality, highlighted in this work, encourage further study.
Modulator design for x‐ray scatter correction using primary modulation: Material selection
Authors: Gao Hewei , Zhu Lei , Fahrig Rebecca 
Published: July 2010

Purpose: An optimal material selection for primary modulator is proposed in order to minimize beam hardening of the modulator in x‐ray cone‐beam computed tomography (CBCT). Recently, a measurement‐based scatter correction method using primary modulation has been developed and experimentally verified. In the practical implementation, beam hardening of the modulator blocker is a limiting factor because it causes inconsistency in the primary signal and therefore degrades the accuracy of scatter correction.Methods: This inconsistency can be purposely assigned to the effective transmission factor of the modulator whose variation as a function of object filtration represents the magnitude of beam hardening of the modulator. In this work, the authors show that the variation reaches a minimum when the ‐edge of the modulator material is near the mean energy of the system spectrum. Accordingly, an optimal material selection can be carried out in three steps. First, estimate and evaluate the polychromatic spectrum for a given x‐ray system including both source and detector; second, calculate the mean energy of the spectrum and decide the candidate materials whose ‐edge energies are near the mean energy; third, select the optimal material from the candidates after considering both the magnitude of beam hardening and the physical and chemical properties.Results: A tabletop x‐ray CBCT system operated at 120 kVp is used to validate the material selection method in both simulations and experiments, from which the optimal material for this x‐ray system is then chosen. With the transmission factor initially being 0.905 and 0.818, simulations show that erbium provides the least amount of variation as a function of object filtrations (maximum variations are 2.2% and 4.3%, respectively, only one‐third of that for copper). With different combinations of aluminum and copper filtrations (simulating a range of object thicknesses), measured overall variations are 2.5%, 1.0%, and 8.6% for of copper, erbium, and tungsten, respectively. With and without of copper in the beam, the measured variations for of copper, erbium, and tungsten, 1 mm of aluminum, as well as of copper, are 1.8%, 0.2%, 5.5%, 1.9%, and 7.5%, respectively.Conclusions: The spatial variation in the effective transmission factor of the modulator blocker due to beam hardening caused by the modulator itself reaches a minimum when the ‐edge of the modulator material is near the mean energy of the spectrum. An optimal modulator material selection using the ‐edge discontinuity is therefore proposed.
Effects of breast‐air and breast‐lung interfaces on the dose rate at the planning target volume of a MammoSite® catheter for Yb‐169 and Ir‐192 HDR sources
Authors: Cazeca Mario J. , Medich David C. , Munro John J. 
Published: July 2010

Purpose:To study the effects of the breast‐air and breast‐lung interfaces on the absorbed dose within the planning target volume (PTV) of a MammoSite® balloon dose delivery system as well as the effect of contrast material on the dose rate in the PTV.Methods:The Monte CarloMCNP5 code was used to simulate dose rate in the PTV of a 2 cm radius MammoSite® balloon dose delivery system. The simulations were carried out using an average female chest phantom (AFCP) and a semi‐infinite water phantom for both Yb‐169 and Ir‐192 high dose rate sources for brachytherapy application. Gastrografin was introduced at varying concentrations to study the effect of contrast material on the dose rate in the PTV.Results:The effect of the density of the materials surrounding the MammoSite® balloon containing 0% contrast material on the calculated dose rate at different radial distances in the PTV was demonstrated. Within the PTV, the ratio of the calculated dose rate for the AFCP and the semi‐infinite water phantom for the point closest to the breast‐air interface (90°) is less than that for the point closest to the breast‐lung interface (270°) by 11.4% and 4% for the HDR sources of Yb‐169 and Ir‐192, respectively. When contrast material was introduced into the 2 cm radius MammoSite® balloon at varying concentrations, (5%, 10%, 15%, and 20%), the dose rate in the AFCP at 3.0 cm radial distance at 90° was decreased by as much as 14.8% and 6.2% for Yb‐169 and Ir‐192, respectively, when compared to that of the semi‐infinite water phantom with contrast concentrations of 5%, 10%, 15%, and 20%, respectively.Conclusions:Commercially available software used to calculate dose rate in the PTV of a MammoSite® balloon needs to account for patient anatomy and density of surrounding materials in the dosimetry analyses in order to avoid patient underdose.
Enhanced epidermal dose caused by localized electron contamination from lead cutouts used in kilovoltage radiotherapy
Authors: Lye J. E. , Butler D. J. , Webb D. V. 
Published: July 2010

Purpose:To investigate and quantify electron contamination from the lead cutouts used in kilovoltage x‐ray radiotherapy.Methods:The lead cutouts were modeled with the Monte Carlo EGSnrc user codes DOSXYZnrc and DOSRZnrc for x‐ray beams ranging from 50 to. The results from the model were confirmed with Gafchromic film measurements. The model and measurements investigated the dose distribution with and without gladwrap™ shielding under the lead, and dose distributions with round, square, and serrated edge cutouts.Results:Large dose enhancement near the edges of the lead was observed due to electron contamination. At the epidermal/dermal border, there is double the dose at the edge of the lead compared to the central dose due to electron contamination for a beam and three times the dose for a beam. gladwrap™ shielding effectively removes the contaminant dose enhancement using ten and four layers for 300 and beams, respectively.Conclusions:The contaminant dose enhancement is undesirable as it could cause unnecessary erythema and hyperpigmentation at the border of the treated and untreated skin and lead to a poorer cosmetic outcome. The contamination is easily removed by gladwrap™ shielding placed under or around the lead cutout.
A novel solid‐angle tomosynthesis (SAT) scanning scheme
Authors: Zhang Jin , Yu Cedric 
Published: July 2010

Purpose:Digital tomosynthesis (DTS) recently gained extensive research interests in both diagnostic and radiation therapy fields. Conventional DTS images are generated by scanning an x‐ray source and flat‐panel detector pair on opposite sides of an object, with the scanning trajectory on a one‐dimensional curve. A novel tomosynthesis method named solid‐angle tomosynthesis (SAT) is proposed, where the x‐ray source scans on an arbitrary shaped two‐dimensional surface.Methods:An iterative algorithm in the form of total variation regulated expectation maximization is developed for SAT image reconstruction. The feasibility and effectiveness of SAT is corroborated by computer simulation studies using three‐dimensional (3D) numerical phantoms including a 3D Shepp–Logan phantom and a volumetric CT image set of a human breast.Results:SAT is able to cover more space in Fourier domain more uniformly than conventional DTS. Greater coverage and more isotropy in the frequency domain translate to fewer artifacts and more accurately restored features in the in‐plane reconstruction.Conclusions:Comparing with conventional DTS, SAT allows cone‐shaped x‐ray beams to project from more solid angles, thus provides more coverage in the spatial‐frequency domain, resulting in better quality of reconstructed image.
Adaptive learning for relevance feedback: Application to digital mammography
Authors: Oh Jung Hun , Yang Yongyi , El Naqa Issam 
Published: July 2010

Purpose:With the rapid growing volume of images in medical databases, development of efficient image retrieval systems to retrieve relevant or similar images to a query image has become an active research area. Despite many efforts to improve the performance of techniques for accurate image retrieval, its success in biomedicine thus far has been quite limited. This article presents an adaptive content‐based image retrieval (CBIR) system for improving the performance of image retrieval in mammographic databases.Methods:In this work, the authors propose a new relevance feedback approach based on incremental learning with support vector machine (SVM) regression. Also, the authors present a new local perturbation method to further improve the performance of the proposed relevance feedback system. The approaches enable efficient online learning by adapting the current trained model to changes prompted by the user's relevance feedback, avoiding the burden of retraining the CBIR system. To demonstrate the proposed image retrieval system, the authors used two mammogram data sets: A set of 76 mammograms scored based on geometrical similarity and a larger set of 200 mammograms scored by expert radiologists based on pathological findings.Results:The experimental results show that the proposed relevance feedback strategy improves the retrieval precision for both data sets while achieving high efficiency compared to offline SVM. For the data set of 200 mammograms, the authors obtained an average precision of 0.48 and an area under the precision‐recall curve of 0.79. In addition, using the same database, the authors achieved a high pathology matching rate greater than 80% between the query and the top retrieved images after relevance feedback.Conclusions:Using mammographic databases, the results demonstrate that the proposed approach is more accurate than the model without using relevance feedback not only in image retrieval but also in pathology matching while maintaining its effectiveness for online relevance feedback applications.
Balancing dose and image registration accuracy for cone beam tomosynthesis (CBTS) for breast patient setupa)
Authors: Winey B. A. , Zygmanski P. , Cormack R. A. , Lyatskaya Y. 
Published: July 2010

Purpose:To balance dose reduction and image registration accuracy in breast setup imaging. In particular, the authors demonstrate the relationship between scan angle and dose delivery for cone beam tomosynthesis (CBTS) when employed for setup verification of breast cancer patients with surgical clips.Methods:The dose measurements were performed in a female torso phantom for varying scan angles of CBTS. Setup accuracy was measured using three registration methods: Clip centroid localization accuracy and the accuracy of two semiautomatic registration algorithms. The dose to the organs outside of the ipsilateral breast and registration accuracy information were compared to determine the optimal scan angle for CBTS for breast patient setup verification. Isocenter positions at the center of the patient and at the breast‐chest wall interface were considered.Results:Image registration accuracy was within 1 mm for the CBTS scan angles above 20° for some scenarios and as large as 80° for the worst case, depending on the imaged breast and registration algorithm. Registration accuracy was highest based on clip centroid localization. For left and right breast imaging with the isocenter at the chest wall, the dose to the contralateral side of the patient was very low for all scan angles considered. For central isocenter location, the optimal scan angles were 30°–50° for the left breast imaging and 40°–50° for the right breast imaging, with the difference due to the geometric asymmetry of the current clinical imaging system.Conclusions:The optimal scan angles for CBTS imaging were found to be between 10° and 50°, depending on the isocenter location and ipsilateral breast. Use of the isocenter at the breast‐chest wall locations always resulted in greater accuracy of image registration at smaller angles (10°–20°) and at lower doses to the contralateral organs. For chest wall isocenters, doses delivered to organs outside of the target breast were much smaller than the scattered and leakage doses of the treatment beams. The complete volumetric information of all clips in the region of interest, combined with the small dose to the contralateral organs and the small scan angle, could result in an advantage for small angle CBTS with off center isocenters over simple orthogonal pairs.
Segmenting CT prostate images using population and patient‐specific statistics for radiotherapy
Authors: Feng Qianjin , Foskey Mark , Chen Wufan , Shen Dinggang 
Published: July 2010

Purpose:In the segmentation of sequential treatment‐time CT prostate images acquired in image‐guided radiotherapy, accurately capturing the intrapatient variation of the patient under therapy is more important than capturing interpatient variation. However, using the traditional deformable‐model‐based segmentation methods, it is difficult to capture intrapatient variation when the number of samples from the same patient is limited. This article presents a new deformable model, designed specifically for segmenting sequential CT images of the prostate, which leverages both population and patient‐specific statistics to accurately capture the intrapatient variation of the patient under therapy.Methods:The novelty of the proposed method is twofold:First, a weighted combination of gradient and probability distribution function (PDF) features is used to build the appearance model to guide model deformation. The strengths of each feature type are emphasized by dynamically adjusting the weight between the profile‐based gradient features and the local‐region‐based PDF features during the optimization process. An additional novel aspect of the gradient‐based features is that, to alleviate the effect of feature inconsistency in the regions of gas and bone adjacent to the prostate, the optimal profile length at each landmark is calculated by statistically investigating the intensity profile in the training set. The resulting gradient‐PDF combined feature produces more accurate and robust segmentations than general gradient features. Second, an online learning mechanism is used to build shape and appearance statistics for accurately capturing intrapatient variation.Results:The performance of the proposed method was evaluated on 306 images of the 24 patients. Compared to traditional gradient features, the proposed gradient‐PDF combination features brought 5.2% increment in the success ratio of segmentation (from 94.1% to 99.3%). To evaluate the effectiveness of online learning mechanism, the authors carried out a comparison between partial online update strategy and full online update strategy. Using the full online update strategy, the mean DSC was improved from 86.6% to 89.3% with 2.8% gain. On the basis of full online update strategy, the manual modification before online update strategy was introduced and tested, the best performance was obtained; here, the mean DSC and the mean ASD achieved 92.4% and 1.47 mm, respectively.Conclusions:The proposed prostate segmentation method provided accurate and robust segmentation results for CT images even under the situation where the samples of patient under radiotherapy were limited. A conclusion that the proposed method is suitable for clinical application can be drawn.