bluuebunny/crossref_metadata_2025_split huggingface dataset:
Noise texture and signal detectability in propagation‐based x‐ray phase‐contrast tomography
Authors: Chou Cheng‐Ying , Anastasio Mark A. 
Published: December 2009

PurposeX‐ray phase‐contrast tomography (PCT) is a rapidly emerging imaging modality for reconstructing estimates of an object's three‐dimensional x‐ray refractive index distribution. Unlike conventional x‐ray computed tomography methods, the statistical properties of the reconstructed images in PCT remain unexplored. The purpose of this work is to quantitatively investigate noise propagation in PCT image reconstruction.MethodsThe authors derived explicit expressions for the autocovariance of the reconstructed absorption and refractive index images to characterize noise texture and understand how the noise properties are influenced by the imaging geometry. Concepts from statistical detection theory were employed to understand how the imaging geometry‐dependent statistical properties affect the signal detection performance in a signal‐known‐exactly/background‐known‐exactly task.ResultsThe analytical formulas for the phase and absorption autocovariance functions were implemented numerically and compared to the corresponding empirical values, and excellent agreement was found. They observed that the reconstructed refractive images are highly spatially correlated, while the absorption images are not. The numerical results confirm that the strength of the covariance is scaled by the detector spacing. Signal detection studies were conducted, employing a numerical observer. The detection performance was found to monotonically increase as the detector‐plane spacing was increased.ConclusionsThe authors have conducted the first quantitative investigation of noise propagation in PCT image reconstruction. The reconstructed refractive images were found to be highly spatially correlated, while absorption images were not. This is due to the presence of a Fourier space singularity in the reconstruction formula for the refraction images. The statistical analysis may facilitate the use of task‐based image quality measures to further develop and optimize this emerging modality for specific applications.
Monte Carlo dosimetry for and eye plaque brachytherapy with various seed models
Authors: Thomson R. M. , Rogers D. W. O. 
Published: December 2009

PurposeDose distributions are calculated for various models of and seeds in the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). The sensitivity to seed model of dose distributions and dose distributions relative to TG‐43 are investigated.MethodsMonte Carlo simulations are carried out with the EGSnrc user‐code BrachyDose. Brachytherapy seeds and eye plaques are fully modeled. Simulations of one seed in the central slot of a 20 mm Modulay (gold alloy) plaque backing with and without the Silastic (silicone polymer) insert and of a 16 mm fully loaded Modulay/Silastic plaque are performed. Dose distributions are compared to those calculated under TG‐43 assumptions, i.e., ignoring the effects of the plaque backing and insert and interseed attenuation. Three‐dimensional dose distributions for different and seed models are compared via depth‐dose curves, isodose contours, and tabulation of doses at points of interest in the eye. Results are compared to those of our recent BrachyDose study for COMS plaques containing model 6711 or 200 seeds [R. M. Thomson et al., Med. Phys. 35, 5530–5543 (2008)].ResultsAlong the central axis of a plaque containing one seed, variations of less than 1% are seen in the effect of the Modulay backing alone for different seed models; for the Modulay/Silastic combination, variations are 2%. For a 16 mm plaque fully loaded with seeds, dose decreases relative to TG‐43 doses are 11%–12% (19%–20%) and 14%–15% (20%) at distances of 0.5 and 1 cm from the inner sclera along the plaque's central axis, respectively. For the same prescription dose, doses at points of interest vary by up to 8% with seed model. Doses to critical normal structures are lower for all seed models than for with the possible exception of the sclera adjacent to the plaque; scleral doses vary with seed model and are not always higher for than for .ConclusionsDose decreases relative to doses calculated under TG‐43 assumptions vary slightly with seed model (for each radionuclide). Dose distributions are sensitive to seed model; however, variations are generally no larger than the magnitudes of other systematic uncertainties in eye plaque therapy.
Dosimetric verification of IMAT delivery with a conventional EPID system and a commercial portal dose image prediction tool
Authors: Iori Mauro , Cagni Elisabetta , Paiusco Marta , Munro Peter , Nahum Alan E. 
Published: December 2009

PurposeThe electronic portal imaging device (EPID) is a system for checking the patient setup; as a result of its integration with the linear accelerator and software customized for dosimetry, it is increasingly used for verification of the delivery of fixed‐field intensity‐modulated radiation therapy (IMRT). In order to extend such an approach to intensity‐modulated arc therapy (IMAT), the combined use of an EPID system and a portal dose image prediction (PDIP) tool has been investigated.MethodsThe dosimetric behavior of an EPID system, mechanically reinforced to maintain its positional stability during the accelerator gantry rotation, has been studied to assess its ability to measure portal dose distributions for IMAT treatment beams. In addition, the PDIP tool of a commercial treatment planning system, commonly used for static IMRT dosimetry, has been validated for simulating the PDIs of IMAT treatment fields. The method has been applied to the delivery verification of 23 treatment fields that were measured in their dual mode of IMRT and IMAT modalities.ResultsThe EPID system has proved to be appropriate for measuring the PDIs of IMAT fields; additionally the PDIP tool was able to simulate these accurately. The results are quite similar to those obtained for static IMRT treatment verification, although it was necessary to investigate the dependence of the EPID signal and of the accelerator monitor chamber response on variable dose rate.ConclusionsOur initial tests indicate that the EPID system, together with the PDIP tool, is a suitable device for the verification of IMAT plan delivery; however, additional tests are necessary to confirm these results.
Theoretical and empirical investigations of for nearly water‐equivalent radiotherapy dosimetry
Authors: Zheng Yuanshui , Han Zhaohui , Driewer Joseph P. , Low Daniel A. , Li H. Harold 
Published: December 2009

PurposeThe low effective atomic number, reusability, and other computed radiography‐related advantages make europium doped potassium chloride a promising dosimetry material. The purpose of this study is to model point dosimeters with a Monte Carlo (MC) method and, using this model, to investigate the dose responses of two‐dimensional (2D) storage phosphor films (SPFs).Methods point dosimeters were irradiated using a beam at four depths for each of five square field sizes . The dose measured by was compared to that measured by an ionization chamber to obtain the magnitude of energy dependent dose measurement artifact. The measurements were simulated using DOSXYZnrc with phase space files generated by BEAMnrcMP. Simulations were also performed for films with thicknesses ranging from . The work function of the prototype material was determined by comparing the sensitivity of a thick film to a commercial ‐based SPF with a known work function. The work function was then used to estimate the sensitivity of a thick film.ResultsThe simulated dose responses of prototype point dosimeters agree well with measurement data acquired by irradiating the dosimeters in the beam with varying field size and depth. Furthermore, simulations with films demonstrate that an ultrathin film with thickness of the order of would have nearly water‐equivalent dose response. The simulation results can be understood using classic cavity theories. Finally, preliminary experiments and theoretical calculations show that ultrathin film could provide excellent signal in a dose‐to‐water irradiation.ConclusionsIn conclusion, the authors demonstrate that ‐based dosimeters can be accurately modeled by a MC method and that 2D films of the order of thick would have minimal energy dependence. The data support the future research and development of a storage phosphor‐based system for quantitative, high‐resolution multidimensional radiation therapy dosimetry.
Particle size, magnetic field, and blood velocity effects on particle retention in magnetic drug targeting
Authors: Cherry Erica M. , Maxim Peter G. , Eaton John K. 
Published: December 2009

PurposeA physics‐based model of a general magnetic drug targeting (MDT) system was developed with the goal of realizing the practical limitations of MDT when electromagnets are the source of the magnetic field.MethodsThe simulation tracks magnetic particles subject to gravity, drag force, magnetic force, and hydrodynamic lift in specified flow fields and external magnetic field distributions. A model problem was analyzed to determine the effect of drug particle size, blood flow velocity, and magnetic field gradient strength on efficiency in holding particles stationary in a laminar Poiseuille flow modeling blood flow in a medium‐sized artery.ResultsIt was found that particle retention rate increased with increasing particle diameter and magnetic field gradient strength and decreased with increasing bulk flow velocity.ConclusionsThe results suggest that MDT systems with electromagnets are unsuitable for use in small arteries because it is difficult to control particles smaller than aboutin diameter.
Quantitative analysis of breast parenchymal patterns using 3D fibroglandular tissues segmented based on MRI
Authors: Nie Ke , Chang Daniel , Chen Jeon‐Hor , Hsu Chieh‐Chih , Nalcioglu Orhan , Su Min‐Ying 
Published: December 2009

PurposeMammographic density and breast parenchymal patterns (the relative distribution of fatty and fibroglandular tissue) have been shown to be associated with the risk of developing breast cancer. Percent breast density as determined by mammography is a well‐established risk factor, but on the other hand, studies on parenchymal pattern have been scarce, possibly due to the lack of reliable quantitative parameters that can be used to analyze parenchymal tissue distribution. In this study the morphology of fibroglandular tissue distribution was analyzed using three‐dimensional breast MRI, which is not subject to the tissue overlapping problem.MethodsFour parameters, circularity, convexity, irregularity, and compactness, which are sensitive to the shape and margin of segmented fibroglandular tissue, were analyzed for 230 patients. Cases were assigned to one of two distinct parenchymal breast patterns: Intermingled pattern with intermixed fatty and fibroglandular tissue (Type I,), and central pattern with confined fibroglandular tissue inside surrounded by fatty tissue outside (Type C, ). For each analyzed parameter, the differentiation between these two patterns was analyzed using a two‐tailed ‐test based on transformed parameters to normal distribution, as well as distribution histograms and ROC analysis.ResultsThese two groups of patients were well matched both in age ( vs ) and in fibroglandular tissue volume (Type I: vs Type C: ). Between Type I and Type C breasts, all four morphological parameters showed significant differences that could be used to differentiate between the two breast types. In the ROC analysis, among all four parameters, the “compactness” could achieve the highest area under the curve of 0.84, and when all four parameters were combined, the AUC could be further increased to 0.94.ConclusionsThe results suggest that these morphological parameters analyzed from 3D MRI can be used to distinguish between intermingled and central dense tissue distribution patterns, and hence may be used to characterize breast parenchymal pattern quantitatively. The availability of these quantitative morphological parameters may facilitate the investigation of the relationship between parenchymal pattern and breast cancer risk.
Impact of skin removal on quantitative measurement of breast density using MRI
Authors: Nie Ke , Chang Daniel , Chen Jeon‐Hor , Shih Tzu‐Ching , Hsu Chieh‐Chih , Nalcioglu Orhan , Su Min‐Ying 
Published: December 2009

PurposeIn breast MRI, skin and fibroglandular tissue commonly possess similar signal intensities, and as such, the inclusion of skin as dense tissue leads to an overestimation in the measured density. This study investigated the impact of skin to the quantitative measurement of breast density using MRI.MethodsThe analysis was performed on the normal breasts of 50 women using nonfat‐saturated (nonfat‐sat) T1 weighted MR images. The skin was segmented by using a dynamic searching algorithm, which was based on the change in signal intensities from the background air (dark), to the skin (moderate), and then to the fatty tissue (bright). Tissue with moderate intensities that fell between the two boundaries determined based on the intensity gradients (from air to skin, and from skin to fat) was categorized as skin. The percent breast density measured with and without skin exclusion was compared. Also the relationship between the skin volume and the breast volume was investigated. Then, this relationship was used to estimate the skin volume from the breast volume for skin correction.ResultsThe percentage of the skin volume normalized to the breast volume ranged from 5.0% to 15.2% (median 8.6%, ) among 50 women. The percent breast densities measured with skin and without skin were highly correlated, (, ). The relationship between the skin volume and the breast volume was analyzed based on transformed data (the square root of the skin volume vs the cube root of breast volume) using the linear regression, and yielded , . When this model was used to estimate the skin volume for correction in the density analysis, it provided a better fit to the measured density with skin exclusion (with adjusted , and root mean square ) compared to the correction done by using a fixed cutoff value of 8% (adjusted , root mean square ).ConclusionsThe authors have shown that the skin volume is related to the breast volume, and this relationship may be used to correct for the skin effect in the MRI‐based density measurement. A reliable quantitative density analysis method will aid in clinical investigation to evaluate the role of breast density for cancer risk assessment or for prediction of the efficacy of risk‐modifying drugs using hormonal therapy.
Dynamic multiple thresholding breast boundary detection algorithm for mammograms
Authors: Wu Yi‐Ta , Zhou Chuan , Chan Heang‐Ping , Paramagul Chintana , Hadjiiski Lubomir M. , Daly Caroline Plowden , Douglas Julie A. , Zhang Yiheng , Sahiner Berkman , Shi Jiazheng , Wei Jun 
Published: December 2009

PurposeAutomated detection of breast boundary is one of the fundamental steps for computer‐aided analysis of mammograms. In this study, the authors developed a new dynamic multiple thresholding based breast boundary (MTBB) detection method for digitized mammograms.MethodsA large data set of 716 screen‐film mammograms (442 CC view and 274 MLO view) obtained from consecutive cases of an Institutional Review Board approved project were used. An experienced breast radiologist manually traced the breast boundary on each digitized image using a graphical interface to provide a reference standard. The initial breast boundary (MTBB‐Initial) was obtained by dynamically adapting the threshold to the gray level range in local regions of the breast periphery. The initial breast boundary was then refined by using gradient information from horizontal and vertical Sobel filtering to obtain the final breast boundary (MTBB‐Final). The accuracy of the breast boundary detection algorithm was evaluated by comparison with the reference standard using three performance metrics: The Hausdorff distance (HDist), the average minimum Euclidean distance (AMinDist), and the area overlap measure (AOM).ResultsIn comparison with the authors’ previously developed gradient‐based breast boundary (GBB) algorithm, it was found that 68%, 85%, and 94% of images had HDist errors less than 6 pixels (4.8 mm) for GBB, MTBB‐Initial, and MTBB‐Final, respectively. 89%, 90%, and 96% of images had AMinDist errors less than 1.5 pixels (1.2 mm) for GBB, MTBB‐Initial, and MTBB‐Final, respectively. 96%, 98%, and 99% of images had AOM values larger than 0.9 for GBB, MTBB‐Initial, and MTBB‐Final, respectively. The improvement by the MTBB‐Final method was statistically significant for all the evaluation measures by the Wilcoxon signed rank test .ConclusionsThe MTBB approach that combined dynamic multiple thresholding and gradient information provided better performance than the breast boundary detection algorithm that mainly used gradient information.
Simulation of dose reduction in tomosynthesis
Authors: Svalkvist Angelica , Båth Magnus 
Published: December 2009

Purpose: Methods for simulating dose reduction are valuable tools in the work of optimizing radiographic examinations. Using such methods, clinical images can be simulated to have been collected at other, lower, dose levels without the need of additional patient exposure. A recent technology introduced to healthcare that needs optimization is tomosynthesis, where a number of low‐dose projection images collected at different angles is used to reconstruct section images of an imaged object. The aim of the present work was to develop a method of simulating dose reduction for digital radiographic systems, suitable for tomosynthesis.Methods: The developed method uses information about the noise power spectrum (NPS) at the original dose level and the simulated dose level to create a noise image that is added to the original image to produce an image that has the same noise properties as an image actually collected at the simulated dose level. As the detective quantum efficiency (DQE) of digital detectors operating at the low dose levels used for tomosynthesis may show a strong dependency on the dose level, it is important that a method for simulating dose reduction for tomosynthesis takes this dependency into account. By applying an experimentally determined relationship between pixel mean and pixel variance, variations in both dose and DQE in relevant dose ranges are taken into account.Results: The developed method was tested on a chest tomosynthesis system and was shown to produce NPS of simulated dose‐reduced projection images that agreed well with the NPS of images actually collected at the simulated dose level. The simulated dose reduction method was also applied to tomosynthesis examinations of an anthropomorphic chest phantom, and the obtained noise in the reconstructed section images was very similar to that of an examination actually performed at the simulated dose level.Conclusions: In conclusion, the present article describes a method for simulating dose reduction suitable for tomosynthesis. However, the method applies equally well to any digital radiographic system, although the benefits of correcting for DQE variations may be smaller.
Impact of Different Factors on the Probability of Clinical Response in Tigecycline-Treated Patients with Intra-Abdominal Infections
Authors: Bhavnani S. M. , Rubino C. M. , Ambrose P. G. , Babinchak T. J. , Korth-Bradley J. M. , Drusano G. L. 
Published: December 2009

ABSTRACT

Patients with intra-abdominal infections differ with regard to the type of infection and the severity of illness. However, the impact of these factors, together with differences in drug exposure, on clinical response is not well understood. Using phase 2 and 3 data for patients with complicated intra-abdominal infections, the relative importance of tigecycline exposure, host factors, and disease factors, alone or in combination, for the probability of clinical response was examined. Patients with complicated intra-abdominal infections who received tigecycline intravenously as a 100-mg loading dose followed by 50 mg every 12 h for 5 to 14 days and who had adequate clinical, pharmacokinetic, and response data were evaluated. Multivariable logistic regression was used to identify factors associated with clinical response. A final multivariable logistic regression model demonstrated six factors based on 123 patients to be predictive of clinical success: a weight of <94 kg (
P
= 0.026), the absence of
Pseudomonas aeruginosa
in baseline cultures (
P
= 0.021), an APACHE II score of <13 (
P
= 0.029), non-Hispanic race (
P
= 0.005), complicated appendicitis or cholecystitis (
P
= 0.004), and a ratio of the area under the concentration-time curve (AUC) to the MIC (AUC/MIC ratio) of ≥3.1 (
P
= 0.003). The average model-predicted probability of clinical success when one unfavorable factor was present was 0.940. This probability was lower (0.855) when the AUC/MIC ratio was <3.1 and the remaining five factors were set to the favorable condition. The average model-predicted probability of clinical success in the presence of two unfavorable factors was 0.594. These findings demonstrated the impact of individual and multiple factors on clinical response in the context of drug exposure.
Pharmacokinetics of Antituberculosis Drugs in Pulmonary Tuberculosis Patients with Type 2 Diabetes
Authors: Ruslami Rovina , Nijland Hanneke M. J. , Adhiarta I. Gusti N. , Kariadi Sri H. K. S. , Alisjahbana Bachti , Aarnoutse Rob E. , van Crevel Reinout 
Published: December 2009

ABSTRACT

Altered pharmacokinetics of antituberculosis drugs may contribute to an increased risk of tuberculosis treatment failure for diabetic patients. We previously found that rifampin exposure was 2-fold lower in diabetic than in nondiabetic tuberculosis patients during the continuation phase of treatment. We now examined the influence of diabetes on the pharmacokinetics of antituberculosis drugs in the intensive phase of tuberculosis treatment, and we evaluated the effect of glycemic control. For this purpose, 18 diabetic and 18 gender- and body weight-matched nondiabetic tuberculosis patients were included in an Indonesian setting. Intensive pharmacokinetic sampling was performed for rifampin, pyrazinamide, and ethambutol at steady state. The bioavailability of rifampin was determined by comparing rifampin exposure after oral versus intravenous administration. Pharmacokinetic assessments were repeated for 10 diabetic tuberculosis patients after glycemic control. No differences in the areas under the concentration-time curves of the drugs in plasma from 0 to 24 h postdose (AUC
0-24
), the maximum concentrations of the drugs in plasma (
C
max
), the times to
C
max
(
T
max
), and the half-lives of rifampin, pyrazinamide, and ethambutol were found between diabetic and nondiabetic tuberculosis patients in the intensive phase of tuberculosis treatment. For rifampin, oral bioavailability and metabolism were similar in diabetic and nondiabetic patients. The pharmacokinetic parameters of antituberculosis drugs were not correlated with blood glucose levels or glucose control. We conclude that diabetes does not alter the pharmacokinetics of antituberculosis drugs during the intensive phase of tuberculosis treatment. The reduced exposure to rifampin of diabetic patients in the continuation phase may be due to increased body weight and possible differences in hepatic induction. Further research is needed to determine the cause of increased tuberculosis treatment failure among diabetic patients.