bluuebunny/crossref_metadata_2025 huggingface dataset:
Cognitive functioning in affected sibling pairs with ADHD: familial clustering and dopamine genes
Authors: Loo Sandra K. , Rich Erika Carpenter , Ishii Janeen , McGough James , McCracken James , Nelson Stanley , Smalley Susan L.
Published: July 2008

Background:  This paper examines familiality and candidate gene associations of cognitive measures as potential endophenotypes in attention‐deficit/hyperactivity disorder (ADHD).

Methods:  The sample consists of 540 participants, aged 6 to 18, who were diagnosed with ADHD from 251 families recruited for a larger genetic study of ADHD. All members of the family underwent psychiatric interviews and children were administered a large battery of cognitive tasks. Subjects were genotyped for several dopaminergic candidate genes (DAT1, DRD4, and DRD5).

Results:  Performance on measures of intelligence, working memory, and set‐shifting had the highest sibling correlations and exhibited significant familial clustering. The 7‐repeat allele of the dopamine receptor D4 (DRD4) gene was associated with poor performance on measures of intelligence, color naming, interference control, and working memory. There were no significant associations with DAT1 and DRD5.

Conclusions:  Sibling correlations, familial clustering and candidate gene associations provide strong support for verbal working memory as a candidate endophenotype for ADHD. More complex models of, and larger sample sizes for, genetic association with cognitive functions are encouraged for future study.
Psychiatric consequences for Israeli adolescents of protracted political violence: 1998–2004
Authors: Slone Michelle , Shechner Tomer
Published: July 2008

Background:  This study examined relations between Israeli adolescents’ political violence exposure and psychiatric consequences over seven years around the second Intifada and possible differential effects according to age and gender.

Methods:  Cross‐sectional data was collected from 3667 adolescents aged 10–18, constituting two age groups of early and late adolescents sampled in three different exposure periods: pre‐Intifada, Intifada peak, and Intifada recession.

Results:  The first hypothesis predicting a main effect of severity of political violence exposure on psychiatric indices was confirmed for all Brief Symptom Index scales. The second hypothesis predicting a main effect of exposure period was confirmed with higher psychopathological indices at the Intifada peak than at the pre‐Intifada and receding Intifada periods. The exploratory question of possible moderating effects in the relation between Political Life Events exposure and exposure period to psychiatric indices showed that higher levels of exposure to political violence were associated with higher rates of symptomatology for both younger and older adolescents. For both genders, a general direct relation emerged between level of severity of political violence exposure and severity of psychiatric outcome, but differently according to Intifada exposure period.

Conclusions:  Findings document the psychiatric toll paid by adolescents who grow up in protracted conflict and political violence, emphasizing the delicate interaction between individual and conflict factors.
Restoration of Midwestern U.S. Savannas: One Size Does Not Fit All
Authors: Dettman Connie L. , Mabry Catherine M. , Schulte Lisa A.
Published: July 2008

Lowland savannas are a rare variant of Midwestern United States savanna occurring on alluvial soils, for which reference information is sparse. To evaluate the appropriateness of using upland savanna as a surrogate source of reference information for lowland savanna, we studied a pre‐Euro‐American lowland savanna using original U.S. Public Land Survey data and other historical records. Historical vegetation was reconstructed and compared among upland savannas, lowland savannas, and lowland forests; we also evaluated potential disturbance dynamics maintaining these systems. We found that all three communities were dominated by members of the genusQuercusbut also had extensive representation by many other tree species, especially notable for savannas in this region. There were no clear size–density relationships for species in the genusQuercus, indicating that these historical savannas were not characterized exclusively by large, scattered oak trees but rather by trees of many oak species and nonoak species in a wide range of size classes. Both upland and lowland savannas also contained a substantial shrub component. We found no evidence that lowland savannas were maintained by flooding, although the uneven‐aged canopy structure suggested that periodic disturbance occurred. Restoration of lowland savanna in this region should include provisions for maintaining nonoak species and shrubs, with disturbance timed to maintain an uneven‐aged canopy structure. Although the appropriateness of historical data in the face of climate change may be questionable, in this region, a warmer climate may actually help promote the “oak parkland” that was present from 8,000 BP up to Euro‐American settlement.
Linking Geographical Information Systems and Observational and Experimental Studies to Determine Optimal Seedling Microsites of an Endangered Plant in a Subtropical Urban Fire‐Adapted Ecosystem
Authors: Wendelberger Kristie S. , Maschinski Joyce
Published: July 2008

Understanding microsite requirements is critical for restoring sustainable rare plant populations and creating meaningful management plans that will enhance native species’ population viability. Natural areas bordered by urban communities have restricted size and constrained management options that confound goals of preserving biodiversity. Using geographical information systems and observational and experimental studies, we determined that current microsites required for seedling establishment within existing habitat of the federally endangered Crenulate leadplant are few and spatially restricted, resulting in little wild seedling recruitment. Experimental and wild seedlings had highest germination rates in litter layers 1–2 cm in depth and survived the longest in litter 0.5–2 cm deep. Fire suppression and aggressive native and exotic plants have accumulated litter up to 33 cm near some of the wild adult Crenulate leadplant. Only 9% of habitat occupied by this taxon at its largest population is conducive to seedling establishment. Similarly, 30% is conducive to seedling establishment in the second largest population. Fire plays a critical role in South Florida ecosystem dynamics and the restoration and preservation of its landscape and biodiversity. When fire is not possible, other management is needed. Manual litter and downed debris removal are recommended at both population sites to improve the probability of Crenulate leadplant seedling establishment and population persistence.
Stillbirths in Macaca fascicularis
Authors: Sesbuppha Wacharaporn , Chantip Surachai , Dick Edward J. , Schlabritz‐Loutsevitch Natalia E. , Guardado‐Mendoza Rodolfo , Butler Stephanie D. , Frost Patrice A. , Hubbard Gene B.
Published: July 2008

Background  Stillbirths in non‐human primates are a major problem and represent failure of the maternal–fetal–placental unit to maintain normal relationships because of various endogenous, undetermined or environmental factors.

Methods  Records of 236 stillborns and their dams in a Macaca fascicularis colony during a 7‐year period were reviewed retrospectively.

Results  The 7‐year stillbirth incidence was 11.99% (236 stillbirths, 1967 live births). Most (61.02%, n = 144) were of undetermined etiology. Fetal causes included trauma (22.46%, n = 53), fetal pneumonia (0.85%, n = 2) and congenital anomalies (0.42%, n = 1). Maternal causes included dystocia (9.75%, n = 23) and uterine rupture (0.42%, n = 1). Forty‐nine placentas were available for histologic evaluation; there was placentitis in five, necrosis in five and placental abruption in two. Most stillbirths occurred close to term. First stillbirths usually occurred in 8‐ to 12‐year‐old animals during the first six pregnancies.

Conclusions  Most stillbirths were of undetermined etiology. Fetal trauma was the most common cause.
Biochemical changes in cerebrospinal fluid of Chlorocebus aethiops naturally infected with zoonotic Meningonema peruzzii
Authors: Ngure R.M. , Karanja S.M. , Mungatana N.K. , Wamae C.N. , Ngotho J.M. , Gichuki C.W.
Published: July 2008

Background  Thirty‐four wild Chlorocebus  aethiops monkeys were trapped for research purposes.

Methods  During routine quarantine check‐up, cerebrospinal fluid (CSF) and blood were microscopically examined for parasites. Estimations of CSF protein levels were made by the biuret method and the white cell counts by the hemocytometer.

Results  Seven monkeys demonstrated microfilariae in blood and CSF. This was accompanied by a two‐ and ninefold increase in CSF total protein and white cell counts, respectively. Necropsy of one of the blood and CSF microfilariae‐positive animals revealed the presence of adult worms in the brain meninges. The parasites were identified as the zoonotic filaroid nematode Meningonema peruzii.

Conclusions  Wild C. aethiops monkeys developed CSF changes resulting, most probably, from infection with M. peruzii. Moreover, the monkeys could be acting as an important reservoir. The study highlights the need for epidemiological and pathogenological studies of this parasite, which is of public health significance. Moreover, C. aethiops proved to be a useful primate model for the study of this zoonotic infection.
Non‐nutritive sucking scoring system for preterm newborns
Authors: Neiva FCB , Leone C , Leone CR
Published: July 2008

Aim: To validate a non‐nutritive sucking (NNS) scoring system for oral feeding in preterm newborns (PTNB).

Methods: A cohort study was carried out in two phases. In phase one of the study, 22 mastered speech‐language pathologists received the protocol and procedure for a NNS scoring system to evaluate the content and presentation of the form and to define the grading scale. In phase two, six speech‐language pathologists evaluated 51 PTNBs weekly, using the defined scoring system.

Setting: This study was carried out in the Nursery Annex to the Maternity at the Intensive and Neonatal Pediatrics Service, Instituto da Criança, Hospital das Clinicas, School of Medicine, University of São Paulo (FMUSP) during the period from May 2004 to May 2006.

Participants: A total of 28 speech‐language pathologist experts and 51 PTNBs.

Results: In the first phase of the study, 22 speech‐language pathologists selected the criteria, utilized in the NNS evaluation with 80% agreement. In the second phase of the study, the NNS evaluation was carried out on 51 PTNB, and a scoring system of 50 points was proposed, which corresponds to the smallest number of false positive and negative results regarding oral feeding ability.

Conclusion: An NNS evaluation system was validated that was able to indicate when oral feeding could safely begin in PTNBs with a high level of agreement among the speech‐language pathologists who have participated.
Change in leptin, body composition and other hormones around menarche – a visual representation
Authors: Bandini LG , Must A , Naumova EN , Anderson SE , Caprio S , Spadano‐Gasbarro JL , Dietz WH
Published: July 2008

Aim: To present a visual representation of changes in body composition, leptin, insulin, estradiol and follicular stimulating hormone (FSH) levels in relation to menarche in girls.

Methods: Participants were a subset of healthy girls (n = 108) enrolled in a longitudinal study of growth and development conducted at the General Clinical Research Center at the Massachusetts Institute of Technology (MIT). Participants were seen annually from before menarche until 4 years postmenarche for measures of body composition and serum levels of leptin, insulin, estradiol and FSH. Body composition was determined by bioelectrical impedance. Standardized body composition and hormone levels were smoothed and plotted relative to menarche to visualize patterns of change.

Results: At menarche, the mean percentage body fat (%BF) of girls was 24.6% (SD = 4.1%) after menarche %BF was ∼27%. Leptin levels averaged 8.4 ng/mL (SD = 4.6) at menarche and were ∼12 ng/mL after menarche. Changes in leptin levels closely paralleled changes in %BF. Insulin, estradiol and FSH levels followed expected patterns relative to menarche. Leptin began rising closer to menarche than did insulin or the other sex hormones.

Conclusion: We provide a visual presentation of hormonal and body composition changes occurring throughout the pubertal period in girls which may be useful in generating new hypotheses related to the timing of menarche.
Intermarket network externalities and competition: An application to the media industry
Authors: Ferrando Jorge , Gabszewicz Jean J. , Laussel Didier , Sonnac Nathalie
Published: July 2008

Intermarket network externalities occur when the utility of a good produced in a given industry varies with the size of the demand for a good produced in another. A particularly significant example of this phenomenon is provided by the interaction between the media and advertising industries. Media consumers vary according to their willingness to pay for a media good, which depends on the advertising volume. In the advertising market, advertisers vary according to their willingness to pay for an advertisement, which also depends positively on the audience reached. We model a situation of competition between two content providers who are rivals in both the media and advertising industries, choosing simultaneously the newspaper prices and the advertising rates. We characterize the equilibria of the game and explore how they depend on audience attitudes towards advertising. Our main finding is that two‐sided interactions may induce exit by one of the media companies from either only the advertising market or both markets.
Boom and Bust Cycle of the Stock Market, and Economic Growth in a Vintage Capital Model
Authors: Kobayashi Takeshi , Sakuragawa Masaya
Published: July 2008

We construct a growth model of overlapping generations with vintage capital. There exists an equilibrium that converges to the balanced growth path through endogenous fluctuations of investment, consumption, and output in terms of the growth rate. When the technological change arrives and a rise in productivity is embodied only in newly invested capital, the economy converges to a new balanced growth path with a higher growth rate of output, but when we interpret the price of existing old capital as the stock market capitalization, the rise in productivity is accompanied by an initial decline in the stock market. Oscillatory equilibria are supported as perfect‐foresight equilibria in the present framework with finitely lived agents and capital. Any oscillatory equilibrium is associated with the regime switch from an economy with both young and old capital in use into one with only old capital in use.
ASSESSMENT OF MICROBIAL CONTAMINANTS PRESENT ON VACUUM LOADERS IN SHELL EGG PROCESSING FACILITIES
Authors: JONES D.R. , MUSGROVE M.T.
Published: July 2008

This study was conducted to determine the pathogen prevalence on vacuum loader cup surfaces. An off‐line (birds housed off‐site) and a mixed (birds housed on‐site and eggs brought from outside production) operation shell egg processing facility were sampled three times each. Twenty vacuum loader cups were randomly rinsed with sterile saline per visit. Total aerobic microorganisms and Enterobacteriaceae were enumerated, and the prevalence of Salmonella, Campylobacter and Listeria was determined. Aerobic microorganisms were ∼5 log cfu/mL, with higher levels noted in the mixed operation. Enterobacteriaceae levels averaged 2.5 log cfu/mL but were higher in the off‐line facility. Campylobacter was detected in 1.6% of the samples. Salmonella was detected in 3.3% of the samples with isolates serotyped as Salmonella anatum and Salmonella heidelberg. There was a high prevalence of Listeria (72%). Confirmed isolates were identified as Listeria innocua (98.8%) and Listeria monocytogenes (1.2%). Identification of the populations present on the cup surfaces will allow for the development of more effective cleaning and disinfection programs.

PRACTICAL APPLICATIONS

Vacuum loaders have previously been determined to be reservoirs for microorganisms in shell egg processing plants. Assessing the prevalence of prominent foodborne pathogens (Salmonella, Campylobacter and Listeria) on the vacuum loader cup surface would allow for more targeted approaches to cleaning and sanitation. High levels of aerobic organisms and Enterobacteriaceae were detected (∼5 and 2.5 log cfu/mL, respectively). Furthermore, Campylobacter and Salmonella were also found, but at low prevalence. Listeria was detected in 72% of the samples. Cleaning and sanitation programs currently utilized in shell egg processing facilities need to be reassessed, and new technologies need to be developed to address the presence of Salmonella, Campylobacter and Listeria.
DETECTION OF YERSINIA PESTIS BY COMPARISON OF VIRULENCE PLASMID (PYV/PCD)‐ASSOCIATED PHENOTYPES IN YERSINIA SPECIES*
Authors: BHADURI SAUMYA , SOMMERS CHRISTOPHER H.
Published: July 2008

Consumption of meat contaminated with Yersinia pestis can cause oro‐pharyngeal plague in humans. Existing microbiological media designed for selective detection of Y. pestis in food are not satisfactory for that purpose. Expression of genetic determinants in Yersinia species including low calcium response (Lcr), colony size, crystal violet (CV) binding, Congo red (CR) uptake, autoagglutination (AA) and hydrophobicity (HP) were compared. Lcr and CV binding were detectable within 24 h at 37C in Yersinia enterocolitica and Yersinia pseudotuberculosis but at 48 h in Y. pestis. Colony size, AA, and HP characteristics were expressed in Y. pseudotuberculosis and Y. enterocolitica, but not in Y. pestis. CR uptake in Y. pestis was demonstrated only on calcium‐deficient CR‐magnesium oxalate (CR‐MOX) tryptic soy agar but was expressed on both CR‐MOX and low‐calcium agarose medium for Y. pseudotuberculosis and Y. enterocolitica. CR‐uptake phenotype by Y. pestis can be used for the detection of this pathogen in foods.

PRACTICAL APPLICATIONS

Yersinia pestis, Yersinia enterocolitica and Yersinia pseudotuberculosis can cause diverse human diseases. Y. enterocolitica and Y. pseudotuberculosis can cause intestinal distress when consumed in contaminated food. Y. pestis, the causative agent of bubonic plague in humans, is also found in food and can cause febrile illness in humans. Thus, food can have a significant role in the dissemination of human plague. There is a concern for risk assessors about the presence of Y. pestis in food. A virulence plasmid of 70 kb is directly involved with virulence of these pathogens. Until now, separating Y. enterocolitica and Y. pseudotuberculosis from Y. pestis required sophisticated molecular biology and immunological techniques. This problem was eliminated by analyses of virulence plasmid encoded phenotypes as simple and reliable targets for the rapid detection of Y. pestis. These classical microbiological assays should greatly assist both regulatory agencies and the food industry in the detection of Y. pestis. Further, these techniques should also greatly assist medical and public health laboratories to identify this pathogen.
Discovering Statistically Significant Periodic Gene Expression
Authors: Chen Jie , Chang Kuang‐Chao
Published: July 2008

One frequent application of microarray experiments is in the study of monitoring gene activities in a cell during cell cycle or cell division. High throughput gene expression time series data are produced from such microarray experiments. A new computational and statistical challenge for analyzing such gene expression time course data, resulting from cell cycle microarray experiments, is to discover genes that are statistically significantly periodically expressed during the cell cycle. Such a challenge occurs due to the large number of genes that are simultaneously measured, a moderate to small number of measurements per gene taken at different time points and high levels of non‐normal random noises inherited in the data. Computational and statistical approaches to discovery and validation of periodic patterns of gene expression are, however, very limited. A good method of analysis should be able to search for significant periodic genes with a controlled family‐wise error (FWE) rate or controlled false discovery rate (FDR) and any other variations of FDR, when all gene expression profiles are compared simultaneously. In this review paper, a brief summary of currently used methods in searching for periodic genes will be given. In particular, two methods will be surveyed in details. The first one is a novel statistical inference approach, the C & G Procedure that can be used to effectively detect statistically significantly periodically expressed genes when the gene expression is measured on evenly spaced time points. The second one is the Lomb–Scargle periodogram analysis, which can be used to discover periodic genes when the gene profiles are not measured on evenly spaced time points or when there are missing values in the profiles. The ultimate goal of this review paper is to give an expository of the two surveyed methods to researchers in related fields.
On the Practice of Rescaling Covariates
Authors: Sardy Sylvain
Published: July 2008

Whether doing parametric or nonparametric regression with shrinkage, thresholding, penalized likelihood, Bayesian posterior estimators (e.g.,ridge regression, lasso, principal component regression, waveshrinkorMarkov random field), it is common practice to rescale covariates by dividing by their respective standard errors ρ. The stated goal of this operation is to provide unitless covariates to compare like with like, especially when penalized likelihood or prior distributions are used. We contend that this vision is too simplistic. Instead, we propose to take into account a more essential component of the structure of the regression matrix by rescaling the covariates based on the diagonal elements of the covariance matrix Σ of the maximum‐likelihood estimator. We illustrate the differences between the standard ρ‐ and proposed Σ‐rescalings with various estimators and data sets.
SU‐DD‐A3‐02: Real‐Time Tracking of Implanted Fiducial Markers Using Combined KV and MV Imaging
Authors: Wiersma R , Mao W , Riaz N , Xing L
Published: July 2008

Purpose: In the presence of organ motion, geometric target uncertainty can hamper the benefits of highly conformal dose techniques such as IMRT. A critical step in dealing with intra‐fraction tumor motion is the real‐time monitoring of the tumor position. The aim of this study is the first time demonstration of a real‐time 3D internal fiducial tracking system based on onboard kV diagnostic imaging together with a MV electronic portal‐imaging device (EPID). Method and Materials: A Varian Trilogy radiotherapy system equipped with both kV and MV imaging systems was used in this work. A hardware frame grabber was used to capture both kV and MV video streams simultaneously at 30 fps. An in house built support vector machine (SVM) classifier tool using prior CT based knowledge was used to locate gold cylindrical markers in the kV/MV frames. Controlled kV beam switching, synced with the ‘step’ part of a step‐and‐shoot IMRT delivery, was investigated in allowing continuous 3D tracking in the presence of beam interruption. A correlation/prediction algorithm was used to buffer lost geometric marker information during kV/MV synchronization. The geometric tracking capabilities of the system were evaluated using a pelvic phantom with embedded fiducials placed on a 3D moveable stage. Results: The maximum 3D tracking speed of the kV‐MV system is approximately 9 Hz. The geometric accuracy of the system is found to be on the order of less than 1 mm in all three spatial dimensions. Synchronized kV/MV switching is found to reduce MV scatter interference on kV imaging and to reduce the overall kV diagnostic dose needed for continuous tracking. Conclusion: A real‐time 3D fiducial tracking system using combined kV and MV imaging has been successfully demonstrated for the first time. The technique is especially suitable for RT systems already equipped with on board kV and EPID imaging devices.
SU‐DD‐A3‐03: Using Treatment Beam Imaging to Monitor Prostate Motion In Near Real‐Time On a Conventional LINAC
Authors: Mao W , Riaz N , Lee K , Wiersma R , King C , Hsu A , Luxton G , Xing L
Published: July 2008

Purpose: To directly use MV treatment beam imaging to monitor tumor motion represents an ideal realm for IGRT because it does not require additional hardware and delivers no extra radiation dose to patients. Here we report a method of obtaining the positions of implanted fiducials in near real‐time from cine EPID imaging of prostate IMRT beams. Method and Materials: A Clinac 21EX is used for the study. During IMRT beam delivery, EPID imaging of the treatment MV beam is acquired in cine mode. The framed images are captured and transferred to a PC, where a fully automated marker detection algorithm is developed to extract the coordinates of the implanted fiducials on the images of IMRT apertures that include the fiducials. The automated algorithm matches cross sections of cylindrical fiducials and evaluates multiple criteria to analyze the MV images. From an EPID image, only the coordinates of a fiducial on the plane perpendicular to the beam can be derived. The position of the marker in the direction parallel to the beam is then estimated from the pre‐treatment portal images and previous treatment beam(s) at different direction(s). This novel MV image guidance procedure is evaluated by using motion phantom experiments and five prostate patients with three implanted gold fiducials. Results: The phantom study suggests that the system is capable of detecting any motion greater than 1.2 mm. The variation of all fiducials from their planned positions was calculated on every image and the maximum variation was 4 mm with a standard deviation of 1.8 mm. The 3D positions of fiducials were calculated. The standard deviations of fiducial 3D position distributions were found to be 2.2 mm or less. Conclusion: This fully automated method provides prostate position during treatment without extra costs.
SU‐EE‐A3‐02: Image‐Guided Planning Margin Determination for Concomitant Boost Treatment of 3D‐Conformal, IMRT, and Stereotactic Lung Cancer Radiotherapy
Authors: O'Daniel J , Bucci MK , Balter P
Published: July 2008

Purpose: To determine appropriate planning margins around the GTV for concomitant boost image‐guided lung cancer treatments where the GTV is prescribed a higher dose than the CTV. Method and Materials: The dosimetric impact of the GTV planning margin (pGTV) margin was investigated with 3D isotropic expansions to the GTV, and simulations of interfractional target displacements relative to bone. Seven patients (IMRT and 3D‐conformal stereotactic) were included. GTVs and their respiratory motion envelopes were contoured from 4DCT images. All patients were aligned with daily projection imaging (IMRT) or CT (SBRT); perfect bony anatomy alignment was assumed. Average residual uncertainties (tumor versus bone) were previously determined from analysis of CBCT images. A 3D displacement probability map was calculated (0.0+/−3.4mmAP, 0.8+/−3.4mmSI, and 0.5+/−2.7mmRL), assuming setup errors were normally distributed. To determine the worst‐case dose‐coverage, pGTVs were created by expanding the GTV by 6mm (95.5% probability). Cumulative dose distributions were calculated based on the 3D displacement probability map. The assumption of normally distributed displacements was not appropriate for hypo‐fractionated patients; therefore a worst‐case systematic displacement scenario was evaluated for one patient. Results: The 4mm pGTV demonstrated good dose coverage (> 90%). With the current planning techniques, the worst‐case analysis of GTV coverage showed that usually <=5% GTV would receive <95% Rx dose. Differences between the planned and cumulative dose distributions were minimal. For the hypofractionated Patient, the probabilities that the GTV will receive at least 98%, 96%, 94%, and 92% of the prescribed dose are 42%, 78%, 93%, and 95% respectively. Conclusion: Prescribing 90%–100% of the prescription dose to the GTV + 4mm planning margin should result in sufficient dosimetric coverage of the GTV for both IMRT and hypo‐fractionated stereotactic patients. When prescribing concomitant boosts a pGTV margin is required, but this need not be as great as the PTV margin around the CTV.
SU‐EE‐A3‐03: Comparison of CBCT and Electromagnetic Transponders for Prostate Localization
Authors: Tanyi J , Ku L , Wu J , Kaurin D , He T , D'Souza W , Hung A
Published: July 2008

Purpose: In prostate cancer radiotherapy, it is unknown how large the PTV margins must be to account for the isocenter correction tolerance and intrafraction motion. The risk of geographic miss can be minimized by the placement of fiducial markers in the prostate gland for daily pretreatment localization and adjustment of patient position if necessary. In this study, we assess the magnitude of interfraction and intrafraction isocenter displacement using implanted electromangnetic transponders, and validate the accuracy of interfraction localization using cone beam CT. Method and Materials: Fifteen supine prostate IMRT patients with three implanted transponders each were studied. Initial daily localization was based on three laser and skin marks. Daily localization error distribution was determined from offsets between the initial setup position and that determined by Calypso. Post setup with the Calypso system, isocenter localization was immediately independently verified by imaging the radio‐opaque transponders using an integrated cone beam CT imaging system. Both localization techniques produced lateral, longitudinal, and vertical target offsets from machine isocenter. Organ motion or patient movement during treatment was continuously monitored by the Calypso system at a 4‐mm threshold. Results: The mean interfraction displacement (± SD) in cm in the lateral, vertical, and longitudinal directions were −0.2 ± 0.6, 1.8 ± 1.3, and 0.3 ± 0.9, respectively. After any necessary isocenter corrections, the mean isocenter placement error relative to the cone beam CT (± SD) in cm in the lateral, vertical, and longitudinal directions were 0.0 ± 0.1, 0.1 ± 0.2, and 0.0 ± 0.1, respectively. Conclusion: Compared with use of skin marks, electromagnetic isocenter repositioning provides an increased degree of isocenter localization. Good agreement was observed between cone beam CT isocenter localization and electromagnetic repositioning. However, the electromagnetic technique, with real time continuous tracking, has the added advantage of threshold‐based intervention with no additional radiation dose.
SU‐EE‐A4‐03: Evaluating and Understanding Relative Phase Angle Between Fat and Water and Its Effect On Fat Quantification in the Dixon Methods
Authors: Zhou Y , Ma J
Published: July 2008

Purpose: The purpose of this study is to measure phase angle α between water and fat as a function of TE and demonstrate that uncertainties in setting the exact TE or knowing the exact a can lead to variations in the fat quantification by the Dixon methods. Method and Materials: Two phantoms were constructed. One consisted of half pure water solution and half soybean oil with a clear interface, which was used to measure the relative phase angle between water and fat as a function of TE. The other consisted of 7 vials of homogeneously mixed vegetable oil and distilled water with different oil/water volume ratios (0/100, 10/90, 20/80, 30/70, 40/60, 50/50 and 100/0). We used a 2D FSPGR sequence to acquire the images with the following parameters: TR=180ms, flip‐angle =80°. TE was varied between 2.0 and 5.5ms in 0.1ms steps. A recently‐developed 2‐point Dixon algorithm was used to generate separated water and fat images. Results: We obtained the relationship between α and TE in phantom and in vivo by experiments. The least‐squares linear fits of the experimental results for phantom and in‐vivo yield and , respectively. From these relationships, the real α can be easily derived. Also, we demonstrated that the variations of TE allowed in the clinical range may lead to variations up to 40% in the apparent fat quantification due to the deviation of α Conclusion: It is desirable to know the true relationship of α and TE in in‐ and out‐of‐phase imaging. Such a relationship can guide us to select certain parameters to obtain desired relative phase angles. The variations in TE may lead to variations in fat quantification. The systemic experimental studies on TE dependence of α are expected to help improve the use of Dixon methods and reduce the fat quantification errors.
SU‐EE‐A4‐06: Estimation of the Optimal Maximum Beam Angle and Angular Increment for Normal and Shear Strain Estimation
Authors: Rao M , Varghese T
Published: July 2008

Purpose: In current ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. Previously we had proposed a method to estimate both the axial and lateral components of a displacement vector using radiofrequency echo signal data acquired along multiple angular insonification directions of the ultrasound beam. In this study, we present error propagation through the least square fitting process for optimization of the angular increment and maximum beam steered angle. Method and Materials: Ultrasound simulations are performed to corroborate theoretical predictions of the optimal values for the maximum beam angle and angular increment. Beam steering characteristics of the linear array were simulated by selecting appropriate time delays for each element which determines the focal point and steering angle for the beam. A uniformly elastic phantom was simulated by modeling a random distribution of 50 μm polystyrene beads with an average concentration of 9.7/mm3 in a medium (to simulate Rayleigh scattering). After computing RF signals for each insonification angle, the phantom was deformed by a uniaxial compression (1% of the phantom height). The displacement of each scatterer in the phantom was calculated using the Finite Element Analysis (FEA) software ANSYS. The new scatterer positions were used for calculating the post compression echo signals at each insonification angle. Results: The theoretical prediction matches well with numerical simulations. For typical system parameters, the optimal maximum beam angle is around 10‐deg for axial strain estimation, and around 15‐deg for lateral strain estimation. The optimal angular increment is around 4∼6 deg, which indicates that only 5∼7 beam angles are required for this strain tensor estimation technique. Conclusion: The theory presented in this study is useful for choosing optimal parameters for the angular data acquisition process for strain tensor estimation.
SU‐FF‐351‐01: Science Council Open Forum
Authors: Boone J
Published: July 2008

The purpose of this meeting is to allow AAPM members to bring suggestions and comments to Science Council members, and Science Council is interested in hearing the views of AAPM members pertaining to science. This meeting has no agenda and no presentation will be made; the goal is simply to provide a channel for communication. AAPM members interested in sharing their views on science, science policy, or AAPM governance in regards to science are welcome to attend.
SU‐GG‐I‐05: Distinguish Pulmonary Nodules by Quantitative Measurement of Dynamic Contrast Enhancement From CT and 18F‐FDG Uptake From PET: A Feasibility Study
Authors: Wang Y , Wu C , Jude M , Suh R , Brown M , Goldin J , McNitt‐Gray M
Published: July 2008

Purpose: To develop and demonstrate a novel technique in differentiating the malignant pulmonary nodule from benignity by quantitative measurements of dynamic contrast enhancement from CT and ‐FDG update from PET. Method and Materials: Three patients with pulmonary nodules (one benignity, two Malignancies) were examined in this study by a hybrid scanning protocol which integrated a DCE‐CT and PET scans. The diagnostic truth was obtained by CT‐guided biopsy. The dynamic CT images were acquired at 22 time points: baseline plus 21 post‐contrast scans with high sampling rate within first blood circulation. The PET exam was performed after the CT dynamic scans. In 4DCT image data, both local feeding vessels and nodule were contoured by radiologists for all images on in‐house analysis workstation. The Arterial Input Function (AIF) and the Time Attenuation Curve (TAC) were generated for each nodule based on mean ROI density. The dynamic CT protocol with high sampling rate provides the feasibility to quantify the perfusion parameters (wash‐in & wash‐out enhancement). The SUV was also quantified from PET images. Both CT and PET quantitative measurements were analyzed for further pulmonary nodule characterization. Results: Good enhancement studies were observed in two malignant case, in which the malignant nodules showed higher wash‐in and wash‐out compared with benign nodule densitometry. The uptake extracted from PET also showed higher activities in two malignant cases than benign case. Conclusion: A feasible technique, combining both DCE‐CT and PET scan, to quantify the nodule perfusion and PET activity features in the clinical setting has been achieved. The increased perfusion and activity related to tumor angiogenesis demonstrated the expected pattern for malignancy. With further study and more patients, these techniques might be applicable in lung nodule characterization and evaluation of lung cancer response after treatment.
SU‐GG‐I‐09: Evaluation of Noise Reduction Methods On Very Low Dose CT Renal Perfusion Imaging
Authors: Liu X , Primak A , Zavaletta V , Yu L , McCollough C
Published: July 2008

Purpose: To quantify the impact of dose reduction on the image quality of time‐resolved renal perfusion CT images and to compare the performance of several noise reduction algorithms on very low‐dose perfusion images. Method and Materials: In this study, series of renal perfusion CT images were generated using a porcine model. The 3‐minute full‐dose scans were performed at 80 kVp and 160 mAs with the animal in a baseline physiological state. Dose‐reduced scans were performed 10 minutes later on the same animal and same scanner (Siemens Definition) at 80 kVp with 32 mAs or 16 mAs, respectively, with the animal still at baseline conditions. Several traditional image‐based noise‐reduction algorithms (low‐pass, median, and sigma‐filter) and the recently introduced local highly constrained back projection (HYPR‐LR) were applied to the low‐dose images. Signal‐to‐noise ratios (SNR) and time‐density curves were obtained on the full‐dose, original low‐dose, and various de‐noised low‐dose images. Results: Examination of SNR and time‐density curves from de‐noised low‐dose images shows that the SNR and time‐density curves were similar or improved at both 1/5th and 1/10th dose levels. Conclusion: The time‐density curves of low‐dose renal perfusion CT images, which provide physiological quantification of organ perfusion and function, are not compromised by use of image‐based noise‐reduction algorithms. While traditional image‐based filters provided greater noise reduction, a decrease in spatial resolution was evident. With a different noise reduction mechanism from spatial filters, HYPR processed images maintained spatial resolution, making them more suitable for applications such as time‐resolved CT angiography. Conflict of Interest: CHM and ANP: Research grants from Siemens Medical Solutions.
SU‐GG‐I‐13: Low‐Contrast Detectability for X‐Ray Computed Tomography
Authors: Hsieh J , Toth T
Published: July 2008

Low‐contrast‐detectability (LCD) is one of the important performance parameters for computed tomography (CT). Often LCD is determined by visual inspection of low‐contrast phantom images. The testing process is gated not only by limitations of existing LCD phantoms, but also by the subjective nature of the evaluation methodology. Although statistical LCD methods were proposed, these methods often unfairly favor post‐processed images, since they measure mainly the noise characteristics in uniform portion of the phantom and do not consider the impact on LCD objects.

In this paper, we present a measurement methodology that incorporates the LCD objects as part of the testing process. To overcome limited availability of low‐contrast phantoms in terms of object size and contrast level, computer simulated objects are inserted into the reconstructed uniform phantom images prior to the post‐process filtering steps. These test objects are obtained by convolving the ideal disc shaped objects with the point‐spread‐function (PSF) of the system. We also propose a LCD index that incorporates the object contrasts and noise levels of the LCD images. The index is defined as the ratio of the measured object contrast over the standard deviation of means measured over a region equal to the LCD object size. This index overcomes the shortcomings of the previously proposed statistical method in which the visibility of post‐processed low‐contrast objects are over‐estimated. Extensive phantom tests were conducted. Existing statistical‐based LCD measure was compared with the proposed LCD index, and both were judged against visual inspection of experts. Phantoms vary over different contrast, object size, scan techniques, and reconstruction kernels. Test results have shown that the proposed LCD method outperforms the existing method and correlates well with human observers. Future extension of the algorithm includes the refinement of the LCD object shape and the non‐stationary characteristics of the PSF and noise in CT systems.
SU‐GG‐I‐14: A Patient Set‐Up Protocol Based On Partially Blocked Cone‐Beam CT
Authors: Zhu L , Wang J , Xie Y , Starman J , Fahrig R , Xing L
Published: July 2008

Purpose: Three‐dimensional x‐ray cone‐beam CT (CBCT) is being increasely used in radiation therapy. Since the whole treatment course typically lasts several weeks, the repetitive x‐ray imaging results in large radiation dose delivered on the patient. In the current radiation therapy treatment, CBCT is mainly used for patient set‐up, and a rigid transformation of the CBCT data from the planning CT data is also assumed. For an accurate rigid registration, it is not necessary to acquire a full 3D image. In this paper, we propose a patient set‐up protocol based on partially blocked CBCT. Method and Materials: A sheet of lead strips is inserted between the x‐ray source and the scanned patient. From the incomplete projection data, only several axial slices are reconstructed and used in the image registration for patient set‐up. Since the radiation is partially blocked, the dose delivered onto the patient is significantly reduced, with an additional benefit of reduced scatter signals. Results: The proposed approach is validated using experiments on two anthropomorphic phantoms. As compared to registration using the regular CBCT, the registration difference using the partially blocked CBCT is less than 1mm in translation and less than 0.2 degrees in rotation. In our implementations, the proposed protocol using partially blocked CBCT reduces radiation dose by a factor of more than 6. The comparison of the reconstructed images also shows that the image quality of the illuminated slices in the partially blocked CBCT is much improved over that in the regular CBCT. Conclusion: A practical patient set‐up protocol based on partially blocked CBCT has been developed for radiation therapy. The proposed approach greatly reduces radiation dose, as well as the adverse effect of scatter photons. It should be useful to improve the clinical practice.
SU‐GG‐I‐15: An Analytical Approach to Correction for X‐Ray Scatter in Heterogeneous Medium
Authors: Yao W , Leszczynski K
Published: July 2008

Purpose: To approximately express first order Compton scatter fluence as a function of primary fluence at detector, and to develop a method for scatter correction based on the analytical approximation. Method and Materials: From the Klein‐Nishina formula for the first order Compton scatter we derive an approximate form in which the function characterizing the scattering object is separated from the known information on the imaging system, including the geometry and the source photon spectrum. Based on the strong correlation between the unknown 3‐D object function and its projection, which can be measured, we estimate the first order scatter and the primary fluence through an iterative scheme. We use a Catphan phantom to experimentally measure primary and scatter fluences, as well as simple Monte Carlo models to determine primary and any order scatter fluences through computer simulation. These experimental and Monte Carlo results are utilized to validate our analytical approach. Results: For simple object models, our approximation results are within 2% of relative error from the exact solution (obtained using the Klein‐Nishina formula and verified with from Monte Carlo simulations). For the Catphan phantom, the relative error is within 3% between the estimated and experimentally measured primary fluences. Tomographic image reconstructions from scatter corrected projections show clearly the advantages of our scatter correction scheme in improving the accuracy of CT numbers and soft‐tissue contrast. Conclusion: Our analytical scheme can estimate primary and first order scatter x‐ray fluences to high accuracy without requiring any additional imaging time and dose to the patient. It can be employed for scatter correction in a variety x‐ray transmission imaging applications, including cone beam CT at both kV and MV photon energy ranges. The correction process is also computationally efficient — it requires a few seconds of processing time per projection image.
SU‐GG‐I‐19: A New X‐Ray Scatter Estimation and Correction Method for Kilo‐Voltage Cone Beam CT Assisted by Multislice CT Scans
Authors: Rong Y , Tolakanahalli R , Tome W , Paliwal B
Published: July 2008

Purpose: To estimate and correct for the x‐ray scatter on the flat panel detector on kV cone beam CT (CBCT) image acquisition, assisted by the original 3D volumetric image set acquired using multislice (MS) CT scanner. Method and Materials: Flood field from the CBCT flat panel detector is stored on the On Board Imager (OBI) workstation. Using the flood field together with the image acquired from MSCT scanner (GE LightSpeed PET/CT) prior to any treatment, the scatter‐free cone beam projection at each projection angle is estimated. Subtracting this estimated scatter‐free projection data from the cone beam CT projection at the same angle gives us the x‐ray scatter fluence plus uncertainties due to patient positioning and organ motion. Note that scatter has majority of low frequency components with high magnitude and patient positioning and organ motion has mainly high frequency components with very small magnitude. The calculated fluence is smoothed out using a low pass filter for eliminating high frequency signals to get pure scatter fluence. For the rest of CBCT scans during treatment, subtracting the estimated scatter fluence from CBCT projections in each scan yields an estimate of scatter‐free projections for image reconstruction. Simulations were performed on mathematical phantoms. Scatter and organ motion were introduced into the projections. After applying the above algorithm, the images were reconstructed using FDK algorithm. These images were compared to the uncorrected images and percentage decrease in variance in the images was tabulated. Image quality at various aspects was analyzed. Results and Conclusion: Filtering techniques are sufficient to extract the low‐frequency components from the subtracted signal to estimate the scatter fluence. This scatter correction strategy is patient specific and provides considerable improvements in image quality, especially for correcting the cupping artifact.