bluuebunny/crossref_metadata_2025_split huggingface dataset:
Species Distribution Modeling
Authors: Miller Jennifer 
Published: June 2010

AbstractThe use of species distribution models (SDM) to map and monitor animal and plant distributions has become increasingly important in the context of awareness of environmental change and its ecological consequences. From their original inception as resource inventory and conservation mapping tools, SDM have evolved along with the increasing variety and availability of statistical methods, digital biological, and environmental data with which they are built in a geographic information system. Beyond predicting species distributions, these models have become an important and widely used decision‐making tool for a variety of biogeographical applications, such as studying the effects of climate change, identifying potential protected areas, determining locations potentially susceptible to invasion, and mapping vector‐borne disease spread and risk. This article outlines the steps involved in formulating an SDM and focuses on the conceptual and theoretical foundations on which it is based and identifies issues that have merited recent and will merit future research attention.
El impacto de la crisis sobre las administraciones de seguridad social: revisión de las conclusiones de la encuesta de la AISS
Authors: Orton Ian 
Published: June 2010

ResumenEste artículo examina las conclusiones de una importante encuesta que la Asociación Internacional de la Seguridad Social (AISS) llevó a cabo en el año 2009, sobre el impacto de la crisis financiera y económica en las administraciones de seguridad social. Dichas conclusiones revelan que la mayoría de las administraciones se han visto negativamente afectadas por la disminución del rendimiento de las inversiones de los fondos de la seguridad social y por la reducción del ingreso procedente de las cotizaciones, y que se ven igualmente confrontadas al aumento de los gastos por concepto de prestaciones. A pesar de ello, las conclusiones indican que las administraciones han enfrentado estos desafíos de forma activa e innovadora. Sin embargo, otros desafíos se plantean. En este sentido, los más preocupantes incluyen la posibilidad de una lenta recuperación económica que supone una prolongada crisis del mercado de trabajo, así como los problemas que generan reservas financieras agotadas y una menor libertad fiscal.
Registration of myocardial PET and SPECT for viability assessment using mutual information
Authors: Marinelli Martina , Martinez‐Möller Axel , Jensen Brian , Positano Vincenzo , Weismüller Susanne , Navab Nassir , Landini Luigi , Schwaiger Markus , Nekolla Stephan G. 
Published: June 2010

Purpose: The combination of sequentially acquired cardiac PET and SPECT data integrating metabolic and perfusion information allows the assessment of myocardial viability, a relevant clinical parameter for the management of patients who have suffered myocardial infarction and are now candidates for complex and cost intensive therapies such as bypass surgery. However, registration of cardiac functional datasets acquired on different imaging systems is limited by the difficulty to define anatomical landmarks and by the relatively poor inherent spatial resolution. In this article, the authors sought to evaluate whether it is possible to automatically register FDG‐PET and sestamibi‐SPECT cardiac data.Methods: Automatic rigid registration was implemented with the ITK framework using Mattes mutual information as the similarity measure and a quaternion to represent the rotational component. The goodness of the alignment was evaluated by computing the mean target registration error (mTRE) at the myocardial wall. The registration parameters were optimized for robustness and speed using the data from 11 cardiac patients undergoing both PET and SPECT examinations (training datasets). The optimized algorithm was applied on the PET and SPECT data from 11 further patients (evaluation datasets). Quantitative (mTRE calculation) and visual (scoring method) comparisons were performed between automatic and manual registrations. Moreover, the automatic registration was also compared to the registration implicitly defined in the standard clinical analysis.Results: The registration parameters were successfully optimized and resulted in a mean mTRE of 1.13 mm and 1.2 s average runtime on standard computer hardware for the training datasets. Automatic registration in the 11 validation datasets resulted in an average mTRE of 2.3 mm, with 7.5 mm mTRE in the worst case and an average runtime of 1.6 s. Automatic registration outperformed manual registrations both for the mTRE and for the visual assessment. Automatic registration also resulted in higher accuracy and better visual assessment as compared to the registration implicitly performed in the standard clinical analysis.Conclusions: The results demonstrate the possibility to successfully perform mutual information based registration of PET and SPECT cardiac data, allowing an improved workflow for the sequentially acquired cardiac datasets, in general, and specifically for the assessment of myocardial viability.
Comparison of film dosimetry techniques used for quality assurance of intensity modulated radiation therapy
Authors: Ju Sang Gyu , Han Youngyih , Kum Oyeon , Cheong Kwang‐Ho , Shin Eun Hyuk , Shin Jung Suk , Kim Jin Sung , Ahn Yong Chan 
Published: June 2010

PurposeAccurate dosimetry is essential to ensure the quality of advanced radiation treatments, such as intensity modulated radiation therapy (IMRT). Therefore, a comparison study was conducted to assess the accuracy of various film dosimetry techniques that are widely used in clinics.MethodsA simulated IMRT plan that produced an inverse pyramid dose distribution in a perpendicular plane of the beam axis was designed with 6 MV x rays to characterize the large contribution of scattered photons to low dose regions. Three film dosimetry techniques, EDR2, EDR2 with low‐energy photon absorption lead filters (EDR2 WF), and GafChromic®EBT, were compared to ionization chamber measurements as well as Monte Carlo (MC) simulations. The accuracy of these techniques was evaluated against the ionization chamber data. Two‐dimensional comparisons with MC simulation results were made by computing the gamma index with criteria ranging from 2% of dose difference or 2 mm of distance to agreement (2%/2 mm) to 4%/4 mm on the central vertical plane of a square solid water phantom. Depth doses and lateral profiles at depths of 5, 10, and 15 cm were examined to characterize the deviation of film measurements and MC predictions from ionization chamber measurements.ResultsIn depth dose comparisons, the deviation between the EDR2 films was 9% in the low dose region and 5% in high dose region, on average. With lead filters, the average deviation was reduced to −1.3% and −0.3% in the low dose and high dose regions, respectively. EBT film results agreed within 1.5% difference on average with ionization chamber measurements in low and high dose regions. In two‐dimensional comparisons with MC simulation, EDR2 films passed gamma tests with a 2%/2 mm criterion only in the high dose region (, total of 63.06% of the tested region). In the low dose region, EDR2 films passed gamma tests with 3%/3 mm criterion (, total of 98.4% of the tested region). For EDR2 WF and GafChromic®EBT films, gamma tests with a 2% /2 mm criterion in the tested area was 97.3% and 96.8% of the tested region, respectively.ConclusionsThe EDR2 film WF and GafChromic®EBT film achieved an average accuracy level of 1.5% against an ionization chamber. These two techniques agreed with the MC prediction in 2%/2mm criteria evaluated by the gamma index, whereas EDR2 without filters achieved an accuracy level of 3%/3 mm with the decision criteria of agreement greater than 95% of the tested region. The overall results will provide a useful quantitative reference for IMRT verifications.
Automatic segmentation of intracranial arteries and veins in four‐dimensional cerebral CT perfusion scans
Authors: Mendrik Adriënne , Vonken Evert‐jan , van Ginneken Bram , Smit Ewoud , Waaijer Annet , Bertolini Giovanna , Viergever Max A. , Prokop Mathias 
Published: June 2010

Purpose: CT angiography (CTA) scans are the current standard for vascular analysis of patients with cerebrovascular diseases, such as acute stroke and subarachnoid hemorrhage. An additional CT perfusion (CTP) scan is acquired of these patients to assess the perfusion of the cerebral tissue. The aim of this study is to extend the diagnostic yield of the CTP scans to also include vascular information.Methods: CTP scans are acquired by injecting contrast material and repeatedly scanning the head over time. Therefore, time‐intensity profiles are available for each voxel in the scanned volume, resulting in a 4D dataset. These profiles can be utilized to differentiate not only between vessels and background but also between arteries and veins. In this article, a fully automatic method is proposed for the segmentation of the intracranial arteries and veins from 4D cerebral CTP scans. Furthermore, a vessel enhanced volume is presented, in which the vasculature is highlighted and background structures are suppressed. Combining this volume with the artery/vein segmentation results in an arteriogram and a venogram, which could serve as additional means for vascular analysis in patients with cerebrovascular diseases. The artery/vein segmentation is quantitatively evaluated by comparing the results to manual segmentations by two expert observers.Results: Results (paired two‐tailed t‐test) show that the accuracies of the proposed artery/vein labeling are not significantly different from the accuracies of the expert observer manual labeling (ground truth). Moreover, sensitivity and specificity of the proposed artery/vein labeling, relative to both expert observer ground truths, were similar to the sensitivity and specificity of the expert observer labeling compared to each other.Conclusions: The proposed method for artery/vein segmentation is shown to be very accurate for arteries and veins with normal perfusion. Combining the artery/vein segmentation with the vessel enhanced volume produces an arteriogram and a venogram, which have the potential to extend the diagnostic yield of CTP scans and replace the additional CTA scan, but could also be helpful to radiologists in addition to the CTA scan.
Assessing the intrinsic precision of 3D/3D rigid image registration results for patient setup in the absence of a ground truth
Authors: Wu Jian , Murphy Martin J. 
Published: June 2010

PurposeTo assess the precision and robustness of patient setup corrections computed from 3D/3D rigid registration methods using image intensity, when no ground truth validation is possible.MethodsFifteen pairs of male pelvic CTs were rigidly registered using four different in‐house registration methods. Registration results were compared for different resolutions and image content by varying the image down‐sampling ratio and by thresholding out soft tissue to isolate bony landmarks. Intrinsic registration precision was investigated by comparing the different methods and by reversing the source and the target roles of the two images being registered.ResultsThe translational reversibility errors for successful registrations ranged from 0.0 to 1.69 mm. Rotations were less than 1°. Mutual information failed in most registrations that used only bony landmarks. The magnitude of the reversibility error was strongly correlated with the success/failure of each algorithm to find the global minimum.ConclusionsRigid image registrations have an intrinsic uncertainty and robustness that depends on the imaging modality, the registration algorithm, the image resolution, and the image content. In the absence of an absolute ground truth, the variation in the shifts calculated by several different methods provides a useful estimate of that uncertainty. The difference observed by reversing the source and target images can be used as an indication of robust convergence.
Registration between ultrasound and fluoroscopy or CT in prostate brachytherapy
Authors: Fallavollita P. , Karim Aghaloo Z. , Burdette E. C. , Song D. Y. , Abolmaesumi P. , Fichtinger G. 
Published: June 2010

PurposeIn prostate brachytherapy, transrectal ultrasound (TRUS) is used to visualize the anatomy, while implanted seeds can be visualized by fluoroscopy. Intraoperative dosimetry optimization is possible using a combination of TRUS and fluoroscopy, but requires localization of the fluoroscopy‐derived seed cloud, relative to the anatomy as seen on TRUS. The authors propose to develop a method of registration of TRUS images and the implants reconstructed from fluoroscopy.MethodsA phantom was implanted with 48 seeds then imaged with TRUS and CT. Seeds were reconstructed from CT yielding a cloud of seeds. Fiducial‐based ground‐truth registration was established between the TRUS and CT. TRUS images are filtered, compounded, and registered to the reconstructed implants by using an intensity‐based metric. The authors evaluated a volume‐to‐volume and point‐to‐volume registration scheme. In total, seven TRUS filtering techniques and three image similarity metrics were analyzed. The method was also tested on human subject data captured from a brachytherapy procedure.ResultsFor volume‐to‐volume registration, noise reduction filter and normalized correlation metrics yielded the best result: An average of seed localization error relative to ground truth. For point‐to‐volume registration, noise reduction combined with beam profile filter and mean squares metrics yielded the best result: An average of seed localization error relative to the ground truth. In human patient data, C‐arm fluoroscopy images showed 81 radioactive seeds implanted inside the prostate. A qualitative analysis showed clinically correct agreement between the seeds visible in TRUS and reconstructed from intraoperative fluoroscopy imaging. The measured registration error compared to the manually selected seed locations by the clinician was .ConclusionsFully automated registration between TRUS and the reconstructed seeds performed well in ground‐truth phantom experiments and qualitative observation showed adequate performance on early clinical patient data.
Radiation dose efficiency comparison between differential phase contrast CT and conventional absorption CT
Authors: Zambelli Joseph , Bevins Nicholas , Qi Zhihua , Chen Guang‐Hong 
Published: June 2010

PurposeThe superior radiation dose efficiency of a newly implemented differential phase contrast CT imaging method compared to the conventional absorption CT method is demonstrated.MethodsA differential phase contrast CT imaging method has recently been implemented using conventional x‐ray sources with a grating interferometer consisting of three gratings. This approach offers the possibility of simultaneous reconstruction of both attenuation contrast and phase contrast images from a single acquisition. This enables a direct comparison of radiation dose efficiency of both types of reconstructed images under identical conditions. Radiation dose efficiency was studied by measuring the change in contrast‐to‐noise ratio (CNR) with different exposure levels. A physical phantom of 28.5 mm diameter was constructed and used for measurement of CNR in both the absorption and phase contrast CT images, which were reconstructed from the same data set.ResultsFor three of the four materials studied, at any given exposure level, the CNR of the differential phase contrast CT images was superior to that of the corresponding absorption contrast CT images. The most dramatic improvement was noted in the contrast between PMMA and water, where the CNR was improved by a factor of approximately 5.5 in the differential phase contrast CT images. Additionally, the CNR of phase contrast CT is empirically shown to have the same square root dependence on exposure, as is the case for absorption contrast CT.ConclusionsThe differential phase contrast CT method provided higher CNR than conventional absorption CT at equivalent dose levels for most of the materials studied, and so may enable achievement of the same object visibility as conventional absorption CT methods at a lower exposure level.
Electron paramagnetic resonance oxygen imaging of a rabbit tumor using localized spin probe delivery
Authors: Epel Boris , Haney Chad R. , Hleihel Danielle , Wardrip Craig , Barth Eugene D. , Halpern Howard J. 
Published: June 2010

PurposeApplication ofin vivoelectron paramagnetic resonance (EPR) oxygen imaging (EPROI) to tumors larger than those of mice requires development of both instrumental and medical aspects of imaging.Methods250 MHz EPR oxygen imaging was performed using a loop‐gap resonator with a volume exceeding. The paramagnetic spin probe was injected directly into the femoral artery feeding the rabbit leg/tumor.ResultsThe authors present continuous wave and electron spin echo EPR oxygen images of a large size (4 cm) VX‐2 tumor located on the leg of a New Zealand white rabbit.ConclusionsThis study demonstrates the feasibility of continuous wave and electron spin echo oxygen imaging modalities for investigation of volumes of tumor and normal tissue relevant to large animals. The injection of the spin probe directly into the artery feeding a rabbit leg will allow one to reduce, by over one order of magnitude, the amount of spin probe used as compared to whole animal IV injection.
Verification of MLC based real‐time tumor tracking using an electronic portal imaging device
Authors: Han‐Oh Sarah , Yi Byong Yong , Lerma Fritz , Berman Barry L. , Gui Minzhi , Yu Cedric 
Published: June 2010

Purpose: The authors have developed a novel technique using an electronic portal imaging device (EPID) to verify the geometrical accuracy of delivery of dose‐rate‐regulated tracking (DRRT). This technique, called verification of real‐time tracking with EPID (VORTE), can potentially be used for both on‐line and off‐line quality assurance (QA) of MLC‐based dynamic tumor tracking.Methods: The shape and position of target as a function of time, which is assumed to be known, is projected onto the EPID plane. This projected sequence of apertures as a function of time (target motion) is then used as the reference. The accuracy of dynamic MLC tracking can then be assessed by how well the delivered beam follows this projected target motion without the use of a physical moving phantom. The beam apertures controlled by DRRT (aperture motion) is detected by the EPID as a function of time. The aperture motion is compared to the target motion to evaluate tracking error introduced by DRRT. The accuracy of VORTE was measured using film measurements of ten static fields. The VORTE for dynamic tumor tracking was tested with several target motions, including (1) rigid‐body two‐dimensional (2‐D) cyclic motion in the superior‐inferior direction with various period and amplitude; (2) the above 2‐D cyclic motion plus cyclic deformation; and (3) 2‐D cyclic motion with both deformation and rotation. For each target motion, the controlled aperture motion resulting from DRRT was acquired at using EPID in the continuous‐acquisition mode. Leaf positions in all captured frames were measured from the EPID and compared to their expected positions. The passing rate of 2 mm criteria for all leaves from all frames was calculated for each of the four patterns of tumor motion. Additionally, the root‐mean‐square (RMS) deviations of the centroid of the apertures between the designed and delivered beams were calculated for all three cases.Results: The accuracy of MLC‐leaf position determination by VORTE is 0.5 mm (1 standard deviation) by comparison to film measurements. With DRRT, the passing rates using the 2 mm criteria for all acquired frames are 100% for the 2‐D displacement, 99% for the 2‐D displacement with deformation, and 88% for the 2‐D displacement combined with both deformation and rotation. The RMS deviations are 0.6 mm for the 2‐D displacement, 1.0 mm for the 2‐D displacement with deformation, and 1.1 mm for the 2‐D displacement combined with both deformation and rotation.Conclusions: The VORTE can measure the accuracy of MLC‐based tumor tracking without the necessity of employing a moving phantom. Moreover, it can be used for complex target motion (i.e., 2‐D displacement combined with deformation and rotation) that is difficult to create with physical moving phantoms. Therefore, the VORTE and the novel QA process illustrated by this study have a great potential for verifying real‐time tumor tracking.
Harmonic phase angle as a concentration‐independent measure of nanoparticle dynamics
Authors: Rauwerdink Adam M. , Weaver John B. 
Published: June 2010

PurposeThe harmonic spectrum of magnetic nanoparticles contains valuable information about the quantity and environment of the particles. Harmonic amplitudes have been used to produce quantitative images and ratios of these amplitudes have been used to monitor changes in the particle environment. Harmonic phase angles have not yet been utilized in these pursuits. The authors explore harmonic phase angle as a concentration‐independent means of remotely monitoring the dynamic magnetization of nanoparticles.MethodsA magnetic nanoparticle spectrometer was used to explore the impacts of viscosity and excitation frequency and amplitude on the phase angle of magnetization harmonics. A dynamic model, which accounts for particle relaxation times, was used to model some results.ResultsHarmonic phase angle can undergo large changes when a nanoparticle's Brownian motion is altered. Excitation parameters and particle characteristics have a profound effect on the extent of these changes.ConclusionsPhase angle can allow for monitoring of various impacts on a nanoparticle's Brownian motion. When combined with other concentration‐independent metrics, such as ratios of harmonic amplitudes, valuable information about the particle's environment can be gathered.