bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of cortical bone by peripheral quantitative computed tomography in continuous ambulatory peritoneal dialysis patients
Authors: NEGRI Armando Luis , BARONE Roberto , LOMBAS Carola , BOGADO Cesar E. , ZANCHETTA Jose Ruben
Published: October 2006

Several studies have suggested an increased prevalence of osteopenia in dialysis. Peripheral quantitative computed tomography (pQCT) is a new technique that allows the noninvasive evaluation of trabecular and cortical bone separately. The aim of the study was: (1) to evaluate cortical bone by pQCT in continuous ambulatory peritoneal dialysis (CAPD) patients and compare the data with that obtained in healthy controls; and (2) to correlate cortical bone parameters with bone mineral density (BMD) of the lumbar spine and femoral neck and total bone mineral content (TBMC). Cortical bone parameters were obtained in 22 CAPD patients and 27 healthy individuals at the distal radius using a Stratec XCT 960 pQCT machine. In the dialysis patients, we also determined BMD and TBMC by bone densitometry. Dialysis patients, compared with controls, showed a significant reduction in volumetric cortical BMD (VcBMD) (p=0.04) and cortical thickness (cThk) (p<0.0001) with a significant increase in radial total cross‐sectional area (TA) (p=0.006), endosteal circumference (p<0.0001), and buckling ratio (p<0.0001). In CAPD patients, total time on dialysis correlated negatively with radial total BMD (p<0.01) and VcBMD (p<0.01). Age correlated positively with TA (p<0.01), endosteal (p<0.01), and periosteal circumferences (p<0.01). Serum intact parathyroid hormone (PTH) levels correlated positively with endosteal (p=0.04) and periosteal perimeter (p=0.01). Total alkaline phosphatase correlated negatively with VcBMD (p<0.01), and positively with endosteal perimeter (p=0.02). Total bone mineral content correlated significantly with radial cortical content (p<0.001), cross‐sectional cortical area (cA; p<0.001), and cThk (p<0.01) but not with total radial BMD, VcBMD, or buckling ratio. No correlations were found between radial cortical parameters and BMD measured at the lumbar spine or femoral neck. We conclude that dialysis patients show cortical osteopenia with marked cortical thinning partially mediated by PTH action on bone. Total bone mineral content correlated with various radial cortical parameters (content, area, and thickness) but not with others. No correlations were found between cortical bone parameters measured at the peripheral skeleton with areal bone density measured at the axial skeleton. These findings suggest that pQCT may be a new tool in the assessment of bone fragility in dialysis patients.
Doppler echocardiograph evaluation of pulmonary hypertension in patients undergoing hemodialysis
Authors: TARRASS Faissal , BENJELLOUN Meryem , MEDKOURI Ghislaine , HACHIM Khadija , BENGHANEM Mohamed Gharbi , RAMDANI Benyounes
Published: October 2006

Pulmonary hypertension (PH) has been reported in hemodialysis (HD) patients, but data regarding its incidence and mechanisms are scarce. The aims of this study was to evaluate the prevalence of unexplained PH in long‐term HD patients, and to examine some possible etiologic factors for its occurrence. The prevalence of PH was estimated by Doppler echocardiography in a cohort of 86 stable patients on HD via arteriovenous access for more than 12 months. All the patients underwent full clinical evaluation, chest radiography, and a standard 12‐lead echocardiograph. Laboratory investigation included a mean of 12 months (serum calcium, phosphorus, parathormone (PTH), alkaline phosphatase, lipids, and hemoglobin). Pulmonary hypertension was defined as pulmonary artery systolic pressure >35 mmHg as determined by Doppler echocardiography using the modified Bernoulli equation. Pulmonary hypertension was detected in 23 patients (26.74%). Of those with PH, left ventricular hypertrophy was seen in 13 patients (56.52%), and valvular calcifications in 6 patients (26.08%). There were no significant differences between both groups with regard to age, sex, duration of dialysis, shunt location, and all the biological parameters of the study. The presence of PH was not related to the level of PTH, or the severity of other metabolic abnormalities. This study demonstrates a high prevalence of PH among patients with ESRD receiving long‐term HD via surgical arteriovenous access. The role of the vascular access, anemia, or secondary hyperparathyroidism as the etiology of PH in HD patients did not hold in this study.
Surveillance cultures of tunneled cuffed catheter exit sites in chronic hemodialysis patients are of no benefit
Authors: ROSENBAUM Debbie , MacRAE Jennifer M. , DJURDJEV Ognjenka , LEVIN Adeera , WERB Ron , KIAII Mercedeh
Published: October 2006

Catheter‐related infections are a major cause of morbidity and mortality in hemodialysis (HD) patients. This study evaluated the utility of surveillance swab cultures (Ssc) of tunneled cuffed catheter (TCC) exit sites as a prediction and prevention strategy for infection. A 6‐month prospective‐controlled trial with 94 chronic HD patients with a TCC who received monthly Ssc and were stratified by dialysis day into topical therapy based on Ssc results (Group A) or no therapy (Group B). Outcomes were exit site infection (ESI) and catheter‐associated bacteremia (CAB). The overall monthly prevalence of positive Ssc was 14.9%. There was no difference in the number of positive Ssc (17.7% vs. 11.6%, p>0.05) or ESI (19.6% vs.16.3%, p>0.05) between Groups A and B, respectively. Catheter‐associated bacteremia was higher in Group A (17.7% vs. 4.7%, p=0.05). There were significantly more ESI in the patients treated for a positive Ssc. In Group A, the incidence of ESI was significantly higher in those treated for a positive vs. negative Ssc (55% vs. 12%, p=0.009) and CAB rates trended higher with positive Ssc (22.2% vs. 16.7%, p>0.05). The strategy of treating positive surveillance cultures is not beneficial. Positive Ssc do not predict the occurrence of catheter‐related infection, and treatment of these cultures may lead to increased infection rates.
Prevalence rate of Cryptosporidium infection in hemodialysis patients in Iran
Authors: SEYRAFIAN Shiva , PESTEHCHIAN Nader , KERDEGARI Maryam , YOUSEFI Hossein Ali , BASTANI Bahar
Published: October 2006

Cryptosporidium is one of the most common causes of diarrhea in the world, which can be severe and prolonged in immunocompromised patients. We compared the prevalence rate of Cryptosporidium infection in hemodialysis patients and 2 control groups (i.e., their healthy family members and normal population). Stool specimens of 104 adult outpatient chronic hemodialysis patients, their 91 healthy family members, and 140 healthy individuals were examined for the presence of Cryptosporidium oocysts by using a modified acid‐fast staining method. Twelve (11.5%) dialysis patients were infected with Cryptosporidium. This was significantly higher than 4 (4.4%), and 5 (3.6%) cases in the 2 control groups, respectively (p<0.05). There was no significant difference between the 2 control groups. The prevalence rate of Cryptosporidium infection did not correlate with patients' sex, age, duration of dialysis, history of kidney transplantation, or history of taking immunosuppressive drugs. However, it was significantly higher in diabetics vs. nondiabetics (19.4% vs. 8.3%, respectively, p<0.05). Our results indicate that the prevalence rate of Cryptosporidium infection is considerably higher in dialysis patients than in the general population. Moreover, dialyzed diabetic patients had the highest rate of infection. As hemodialysis patients are candidates for renal transplantation, general preventive measures against acquiring Cryptosporidium infection must be considered.
Stability of nutritional parameters during a 5‐year follow‐up in patients treated with sequential long‐hour hemodialysis
Authors: CHAZOT Charles , VO‐VAN Cyril , BLANC Corinne , HUROT Jean Marc , JEAN Guillaume , VANEL Thierry , TERRAT Jean Claude , CHARRA Bernard
Published: October 2006

Progressive nutritional impairment has been recently reported during conventional hemodialysis (HD) treatment. We studied the nutritional parameters during a 5‐year follow‐up in HD patients. Thirty‐three patients (15F/18M; 65 years old at the study start) filled out a 3‐day food questionnaire once a year between 1995 and 1999 (study group). Twenty patients, who did not fill out the food records during this period served as a control group (control group). The food record was run by the renal dietician using a dedicated software, providing daily energy and protein intakes (DEI and DPI). Serum albumin, normalized protein equivalent of nitrogen appearance (nPNA), and postdialysis body weight (BW) at the time of food record were collected in the study group and from the patient chart in the control group. The energy intake in the study group and the protein intake in both groups were close to the recommended intakes in ESRD patients. Protein intake assessed from food questionnaire or from urea kinetics were not statistically different. Using ANOVA for repeated measures, no difference along the 5 years was found for daily energy intake, daily protein intake, nPNA, and BW in the study group. The BW and nPNA remained stable in the control group. Hence, this study does not confirm the progressive nutritional impairment reported in the HEMO study, whereas the patients' age and vintage are largely higher in the present study. The role of a large dialysis dose in maintaining nutritional status in HD patients is discussed.
Prognostic implications of clinical practice guidelines among hemodialysis patients
Authors: CHANG John J. , CONCATO John , WELLS Carolyn K. , CROWLEY Susan T.
Published: October 2006

Although the National Kidney Foundation (NKF) has published clinical practice guidelines for the management of risk factors for cardiovascular disease, these guidelines have not been tested rigorously for their effectiveness. We conducted an observational study among patients with end‐stage kidney disease to examine the prognostic impact of threshold levels recommended by the NKF for blood pressure, hemoglobin, calcium‐phosphate product, parathyroid hormone, low‐density lipoprotein, and glycosylated hemoglobin. The study population (N=197) was assembled from a previously completed randomized trial examining arteriovenous graft thrombosis. Cox proportional hazard analysis was used to calculate hazard ratios for the association of levels outside guideline recommended targets and death, adjusting for age, comorbidity, race, and albumin. The proportion of patients outside guideline targets ranged from 33% to 81%, and the impact of levels outside guideline targets on mortality varied substantially. Elevated calcium‐phosphate product and glycosylated hemoglobin had harmful effects, with adjusted hazard ratios of 1.58 (95% CI 1.00–2.50; p=0.050) and 2.21 (95% CI 0.99–4.97; p=0.054), respectively. Nontarget levels for blood pressure, hemoglobin, and parathyroid hormone had little effect, with adjusted hazard ratios of 1.15 (95% CI 0.74–1.78; p=0.542), 1.04 (95% CI 0.65–1.68; p=0.866), and 0.90 (95% CI 0.50–1.61; p=0.722), respectively. Elevated low‐density lipoprotein had a paradoxically beneficial effect, with an adjusted hazard ratio of 0.48 (95% CI 0.23–1.00; p=0.049). These results suggest that the prognostic impact of current threshold levels recommended by select NKF guidelines on mortality is variable. Accordingly, the development and implementation of clinical practice guidelines should be accompanied by corresponding efforts to confirm their impact on patient outcomes. Such efforts are essential for the improvement of guidelines and to inform health policy optimally.
Antioxidant Dps protein from the thermophilic cyanobacterium Thermosynechococcus elongatus
Authors: Franceschini Stefano , Ceci Pierpaolo , Alaleona Flaminia , Chiancone Emilia , Ilari Andrea
Published: October 2006

DNA‐binding proteins from starved cells (Dps proteins) protect bacteria primarily from oxidative damage. They are composed of 12 identical subunits assembled with 23‐symmetry to form a compact cage‐like structure known to be stable at temperatures > 70 °C and over a wide pH range. Thermosynechococcus elongatus Dps thermostability is increased dramatically relative to mesophilic Dps proteins. Hydrophobic interactions at the dimeric and trimeric interfaces called Dps‐like are replaced by salt bridges and hydrogen bonds, a common strategy in thermophiles. Moreover, the buried surface area at the least‐extended Dps‐like interface is significantly increased. A peculiarity of T. elongatus Dps is the presence of a chloride ion coordinated with threefold symmetry‐related arginine residues lining the opening of the Dps‐like pore toward the internal cavity. T. elongatus Dps conserves the unusual intersubunit ferroxidase centre that allows the Dps protein family to oxidize Fe(II) with hydrogen peroxide, thereby inhibiting free radical production via Fenton chemistry. This catalytic property is of special importance in T. elongatus (which lacks the catalase gene) in the protection of DNA and photosystems I and II from hydrogen peroxide‐mediated oxidative damage.
Concerted mutation of Phe residues belonging to the β‐dystroglycan ectodomain strongly inhibits the interaction with α‐dystroglycan in vitro
Authors: Bozzi Manuela , Sciandra Francesca , Ferri Lorenzo , Torreri Paola , Pavoni Ernesto , Petrucci Tamara C. , Giardina Bruno , Brancaccio Andrea
Published: October 2006

The dystroglycan adhesion complex consists of two noncovalently interacting proteins: α‐dystroglycan, a peripheral extracellular subunit that is extensively glycosylated, and the transmembrane β‐dystroglycan, whose cytosolic tail interacts with dystrophin, thus linking the F‐actin cytoskeleton to the extracellular matrix. Dystroglycan is thought to play a crucial role in the stability of the plasmalemma, and forms strong contacts between the extracellular matrix and the cytoskeleton in a wide variety of tissues. Abnormal membrane targeting of dystroglycan subunits and/or their aberrant post‐translational modification are often associated with several pathologic conditions, ranging from neuromuscular disorders to carcinomas. A putative functional hotspot of dystroglycan is represented by its intersubunit surface, which is contributed by two amino acid stretches: approximately 30 amino acids of β‐dystroglycan (691–719), and approximately 15 amino acids of α‐dystroglycan (550–565). Exploiting alanine scanning, we have produced a panel of site‐directed mutants of our two consolidated recombinant peptides β‐dystroglycan (654–750), corresponding to the ectodomain of β‐dystroglycan, and α‐dystroglycan (485–630), spanning the C‐terminal domain of α‐dystroglycan. By solid‐phase binding assays and surface plasmon resonance, we have determined the binding affinities of mutated peptides in comparison to those of wild‐type α‐dystroglycan and β‐dystroglycan, and shown the crucial role of two β‐dystroglycan phenylalanines, namely Phe692 and Phe718, for the α–β interaction. Substitution of the α‐dystroglycan residues Trp551, Phe554 and Asn555 by Ala does not affect the interaction between dystroglycan subunits in vitro. As a preliminary analysis of the possible effects of the aforementioned mutations in vivo, detection through immunofluorescence and western blot of the two dystroglycan subunits was pursued in dystroglycan‐transfected 293‐Ebna cells.
APPLICATION OF NUCLEIC ACID SEQUENCE‐BASED AMPLIFICATION FOR THE DETECTION OF VIABLE FOODBORNE PATHOGENS: PROGRESS AND CHALLENGES
Authors: RODRÍGUEZ‐LÁZARO DAVID , HERNÁNDEZ MARTA , D’AGOSTINO MARTIN , COOK NIGEL
Published: October 2006

Nucleic acid sequence‐based amplification (NASBA) is a sensitive transcription‐based amplification system that uses a battery of three enzymes (avian myeloblastosis virus reverse transcriptase, RNase H and T7 RNA polymerase) leading to a main amplification product of single‐stranded RNA, and is specifically designed for the specific detection of RNA. NASBA is an established diagnostic tool in clinical use, with a theoretically bigger analytical sensitivity than reverse transcription‐polymerase chain reaction (RT‐PCR) for pathogen detection, but is not progressing toward implementation in food analysis. This is unfortunate, because it has a potential for detection of viable cells through selective amplification of messenger RNA, even in a background of genomic DNA, which PCR does not possess. However, in some instances, an unexpected amplification of genomic DNA has been observed using the NASBA technique. The availability of methods for rapid, sensitive and selective detection of viable microbial pathogens in foods is a goal worth pursuing, and a developmental effort to explore and capitalize on NASBA's potential in this regard could be worthwhile. We review in this work the current status and the future application of this technique in food microbiology diagnostics.
COMPARISON OF PETRIFILM AEROBIC COUNT PLATES AND DE MAN–ROGOSA–SHARPE AGAR FOR ENUMERATION OF LACTIC ACID BACTERIA
Authors: NERO LUÍS AUGUSTO , BELOTI VANERLI , DE AGUIAR FERREIRA BARROS MÁRCIA , ORTOLANI MARIA BEATRIZ TASSINARI , TAMANINI RONALDO , DE MELO FRANCO BERNADETTE DORA GOMBOSSY
Published: October 2006

This study aimed to compare Petrifilm aerobic count (AC) plates (3M Microbiology, St. Paul, MN) and de Man–Rogosa–Sharpe (MRS) agar for enumeration of lactic acid bacteria (LAB). The study was conducted with suspensions of 10 species of LAB prepared in reconstituted powdered milk. Raw milk samples, without any added bacteria, were also tested. For selective enumeration in Petrifilm AC plates, the suspensions of LAB and the raw milk samples were submitted to decimal dilutions in MRS broth prior to plating. Petrifilm AC and MRS agar plates were incubated in jars at 30C for 72 h, in microaerophilic conditions (Campygen, Oxoid, Basingstoke, U.K.). Differences in counts in the two culture media were not significant (P ≤ 0.05), regardless of the species of the LAB. Results presented high correlation indexes for both LAB suspensions (r = 0.9922, r2 = 0.9845, P = 0.00) and raw milk samples (r = 0.9841, r2 = 0.9685, P = 0.00). These results indicate that the advantages of using Petrifilm AC plates for a rapid enumeration in aerobic microorganisms can be extended for enumeration of LAB in foods. Their convenience is particularly interesting for testing fermented milk products.
COMPARISON OF CONVENTIONAL PLATING AND SIMPLATE METHODS FOR ENUMERATION OF AEROBIC MICROORGANISMS, COLIFORM AND ESCHERICHIA COLI IN FARM ENVIRONMENTAL SAMPLES
Authors: PANGLOLI PHILIPUS , JACKSON FELIX , RICHARDS HAROLD A. , MOUNT JOHN R. , DRAUGHON F. ANN
Published: October 2006

The objective of this study was to compare conventional plating to SimPlate methods for enumeration of aerobic microorganisms, coliforms and Escherichia coli in samples from farm animals and their environment. Samples evaluated included rectal swabs, fecal material, bedding, litter and feed and soil from beef and dairy cattle, swine and poultry farms. Standard method agar pour plating and conventional violet red bile agar with 4‐methylumbelliferyl β‐D‐glucuronide were compared to the SimPlate total plate count‐color indicator method for aerobic counts and the SimPlate coliform and E. coli color indicator method for total coliforms and E. coli counts, respectively. Overall, the SimPlate methods produced counts that were not significantly different (P > 0.05) from those of the conventional methods. Population counts from the SimPlate methods were highly correlated with colony‐forming unit counts from the conventional methods with r = 0.90, 0.94 and 0.94 for aerobic counts, total coliforms and E. coli, respectively. Thus, the data from this study indicate that SimPlate methods are comparable and reliable for enumeration of aerobic microorganisms, coliforms and E. coli in environmental farm samples.
A NOVEL ASSAY TO QUANTITATE IN VIVO PERFECT RECIRCULARIZATION RATE OF RESTRICTION ENZYME‐GENERATED ENDS*
Authors: OUYANG XUEZHI , MA XIAOQIAN , WANG SHULI , LI GANG , HE JIANGUO , LIU QIUYUN
Published: October 2006

A novel assay is described to precisely quantitate the in vivo perfect recircularization rate of restriction enzyme‐generated ends. Frameshift was introduced into pBluescript II vector SK– by inserting an oligonucleotide harboring a NotI restriction recognition sequence into the EcoRI site in the multiple cloning site, which rendered the N‐terminal portion of the lacZ gene inactive, hence the loss of α–complementation, thus producing white colonies on isopropyl‐beta‐D‐thiogalactopyranoside/5‐bromo‐4‐chloro‐3‐indolyl‐β‐D‐galactopyranoside (IPTG/X‐Gal) indicator plates. The insertion of the oligonucleotide created additional NotI and EcoRI sites, respectively. By digesting the resultant plasmid with either NotI or EcoRI followed by introduction into Escherichia coli cells, in vivo perfect recircularization would restore the correct open reading frame, and colonies turned back to blue. This simple assay is sensitive and highly reliable in the assessment of in vivo perfect recircularization of linear DNA fragment.
The Effect of Rural Residence on Dental Unmet Need for Children With Special Health Care Needs
Authors: Skinner Asheley Cockrell , Slifkin Rebecca T. , Mayer Michelle L.
Published: October 2006

ABSTRACT: 
Background: Unmet need for dental care is the most prevalent unmet health care need among children with special health care needs (CSHCN), even though these children are at a greater risk for dental problems. The combination of rural residence and special health care needs may leave rural CSHCN particularly vulnerable to high levels of unmet dental needs. Objective: To examine the effects of rural residence on unmet dental need for CSHCN. Methods: We use the nationally representative National Survey of CSHCN Needs. We performed logistic regression to estimate the independent effects of rural residence on the likelihood of having an unmet dental need, using a measure of unmet need based on professional society recommendations and a measure based on parental report. Results: Using either of the measures, a substantial percentage of CSHCN do not receive all needed dental care. Rural CSHCN are more likely to forgo needed dental care than their urban counterparts. Our results suggest that rural CSHCN have unmet needs for dental care due to both difficulty accessing care and because their parents do not recognize a need. Conclusion: Traditional access barriers for rural children, such as inadequate provider supply and lack of insurance, may increase unmet needs both directly and indirectly, through their effects on parents’ perceptions of need. Reducing unmet needs for dental care in rural children with special needs will require addressing both access issues and parents’ understanding of dental care need.
Rural Residence and Hispanic Ethnicity: Doubly Disadvantaged for Diabetes?
Authors: Koopman Richelle J. , Mainous Arch G. , Geesey Mark E.
Published: October 2006

ABSTRACT: 
Context: Hispanics are at increased risk for diabetes, while rural residents have historically had decreased access to care. Purpose: To determine whether living in a rural area and being Hispanic confers special risks for diagnosis and control of diabetes. Methods: We analyzed the Third National Health and Nutrition Examination Survey (1988‐1994). Hispanics and non‐Hispanic white adults were classified according to rural/urban residence to create 4 ethnicity‐residence groups. Investigated outcomes were previously diagnosed and undiagnosed diabetes. Among those with diagnosed diabetes, we investigated control of glucose, hypertension, and lipids. Findings: The prevalence of diagnosed diabetes was greatest for rural residents, especially for rural Hispanics (8.2%) versus that for urban whites (4.6%), rural whites (6.5%), or urban Hispanics (4.5%), (P < .01). However, urban Hispanics were most likely to have undiagnosed diabetes at 3.7%, versus 2.3% of rural whites, 2.8% of urban whites, and 2.7% of rural Hispanics (P = .04). Among people with diagnosed diabetes, there was no difference in glycemic control between the 4 groups. Rural Hispanics with diagnosed diabetes had the greatest prevalence of elevated systolic blood pressure at 45%, compared to 37% of urban whites, 29% of rural whites, 28% of urban Hispanics (P = .01). In regression models controlling for potential confounders, there were no differences among urban and rural whites and Hispanics in the likelihood of undiagnosed diabetes or in glycemic control for those with diagnosed diabetes. Conclusions: Initiatives that target Hispanic health, and especially diabetes, should acknowledge rural/urban Hispanic health differences.
Family Decision‐Making for Nursing Home Residents With Dementia: Rural‐Urban Differences
Authors: Gessert Charles E. , Elliott Barbara A. , Peden‐McAlpine Cynthia
Published: October 2006

ABSTRACT: 
Context: Research has demonstrated substantial differences between end‐of‐life care in rural and urban settings. As the end of life approaches, rural elders are less likely to be hospitalized, to be placed in an intensive care unit, or to have a feeding tube, compared to their urban counterparts. These differences cannot be fully explained by rural‐urban differences in access to medical services. Purpose: To describe and understand rural‐urban differences in attitudes toward death and in end‐of‐life decision making. Methods: Eight focus groups were convened in rural and urban Minnesota nursing homes. The 38 focus group participants were family members of nursing home residents with severe cognitive impairment. Findings: Most rural focus group participants voiced unqualified acceptance of death and placed few conditions on death, beyond their hope that it would be quick and peaceful. Urban respondents presented a wider range of attitudes toward death, from unambiguous acceptance of immediate death to evident discomfort with welcoming death under any circumstances. These rural‐urban differences had practical implications. Rural respondents were much less likely to endorse interventions that would impede death, compared to their urban counterparts. Conclusions: Rural respondents tended to express confidence in natural forces; death was seen as neutral or beneficent. Resistance to the approach of death was more characteristic of urban respondents, some of whom insisted upon aggressive medical care in advanced dementia.
A comparative study of limited‐angle cone‐beam reconstruction methods for breast tomosynthesis
Authors: Zhang Yiheng , Chan Heang‐Ping , Sahiner Berkman , Wei Jun , Goodsitt Mitchell M. , Hadjiiski Lubomir M. , Ge Jun , Zhou Chuan
Published: October 2006

Digital tomosynthesis mammography (DTM) is a promising new modality for breast cancer detection. In DTM, projection‐view images are acquired at a limited number of angles over a limited angular range and the imaged volume is reconstructed from the two‐dimensional projections, thus providing three‐dimensional structural information of the breast tissue. In this work, we investigated three representative reconstruction methods for this limited‐angle cone‐beam tomographic problem, including the backprojection (BP) method, the simultaneous algebraic reconstruction technique (SART) and the maximum likelihood method with the convex algorithm (ML‐convex). The SART and ML‐convex methods were both initialized with BP results to achieve efficient reconstruction. A second generation GE prototype tomosynthesis mammography system with a stationary digital detector was used for image acquisition. Projection‐view images were acquired from 21 angles in increments over a angular range. We used an American College of Radiology phantom and designed three additional phantoms to evaluate the image quality and reconstruction artifacts. In addition to visual comparison of the reconstructed images of different phantom sets, we employed the contrast‐to‐noise ratio (CNR), a line profile of features, an artifact spread function (ASF), a relative noise power spectrum (NPS), and a line object spread function (LOSF) to quantitatively evaluate the reconstruction results. It was found that for the phantoms with homogeneous background, the BP method resulted in less noisy tomosynthesized images and higher CNR values for masses than the SART and ML‐convex methods. However, the two iterative methods provided greater contrast enhancement for both masses and calcification, sharper LOSF, and reduced interplane blurring and artifacts with better ASF behaviors for masses. For a contrast‐detail phantom with heterogeneous tissue‐mimicking background, the BP method had strong blurring artifacts along the x‐ray source motion direction that obscured the contrast‐detail objects, while the other two methods can remove the superimposed breast structures and significantly improve object conspicuity. With a properly selected relaxation parameter, the SART method with one iteration can provide tomosynthesized images comparable to those obtained from the ML‐convex method with seven iterations, when BP results were used as initialization for both methods.
Signal and noise transfer properties of photoelectric interactions in diagnostic x‐ray imaging detectors
Authors: Hajdok G. , Yao J. , Battista J. J. , Cunningham I. A.
Published: October 2006

Image quality in diagnostic x‐ray imaging is ultimately limited by the statistical properties governing how, and where, x‐ray energy is deposited in a detector. This in turn depends on the physics of the underlying x‐ray interactions. In the diagnostic energy range , most of the energy deposited in a detector is through photoelectric interactions. We present a theoretical model of the photoelectric effect that specifically addresses the statistical nature of energy absorption by photoelectrons, and characteristic x rays, and Auger electrons. A cascaded‐systems approach is used that employs a complex structure of parallel cascades to describe signal and noise transfer through the photoelectric effect in terms of the modulation transfer function, Wiener noise power spectrum, and detective quantum efficiency (DQE). The model was evaluated by comparing results with Monte Carlo calculations for x‐ray converters based on amorphous selenium (‐Se) and lead (Pb), representing both low and high‐ materials. When electron transport considerations can be neglected, excellent agreement (within 3%) is obtained for each metric over the entire diagnostic energy range in both ‐Se and Pb detectors up to , the highest frequency tested. The cascaded model overstates the DQE when the electron range cannot be ignored. This occurs at approximately two cycles/mm in ‐Se at an incident photon energy of , whereas in Pb, excellent agreement is obtained for the DQE over the entire diagnostic energy range. However, within the context of mammography and micro‐computed tomography , the effects of electron transport on the DQE are negligible compared to fluorescence reabsorption, which can lead to decreases of up to 30% and 20% in ‐Se and Pb, respectively, at ; and 10% and 5%, respectively, at . It is shown that when Swank noise is identified in a Fourier model, the Swank factor must be frequency dependent. This factor decreases quickly with frequency, and in the case of ‐Se and Pb, decreases by up to a factor of 3 at five cycles/mm immediately above the edge. The frequency‐dependent Swank factor is also equivalent to what we call the “photoelectric DQE,” which describes signal and noise transfer through photoelectric interactions.
Direct aperture optimization for IMRT using Monte Carlo generated beamlets
Authors: Bergman Alanah M. , Bush Karl , Milette Marie‐Pierre , Popescu I. Antoniu , Otto Karl , Duzenli Cheryl
Published: October 2006

This work introduces an EGSnrc‐based Monte Carlo (MC) beamlet does distribution matrix into a direct aperture optimization (DAO) algorithm for IMRT inverse planning. The technique is referred to as Monte Carlo–direct aperture optimization (MC‐DAO). The goal is to assess if the combination of accurate Monte Carlo tissue inhomogeneity modeling and DAO inverse planning will improve the dose accuracy and treatment efficiency for treatment planning. Several authors have shown that the presence of small fields and/or inhomogeneous materials in IMRT treatment fields can cause dose calculation errors for algorithms that are unable to accurately model electronic disequilibrium. This issue may also affect the IMRT optimization process because the dose calculation algorithm may not properly model difficult geometries such as targets close to low‐density regions (lung, air etc.). A clinical linear accelerator head is simulated using BEAMnrc (NRC, Canada). A novel in‐house algorithm subdivides the resulting phase space into beamlets. Each beamlet is projected onto a patient‐specific phantom. The beamlet dose contribution to each voxel in a structure‐of‐interest is calculated using DOSXYZnrc. The multileaf collimator (MLC) leaf positions are linked to the location of the beamlet does distributions. The MLC shapes are optimized using direct aperture optimization (DAO). A final Monte Carlo calculation with MLC modeling is used to compute the final dose distribution. Monte Carlo simulation can generate accurate beamlet dose distributions for traditionally difficult‐to‐calculate geometries, particularly for small fields crossing regions of tissue inhomogeneity. The introduction of DAO results in an additional improvement by increasing the treatment delivery efficiency. For the examples presented in this paper the reduction in the total number of monitor units to deliver is compared to fluence‐based optimization methods.
Chord‐based image reconstruction in cone‐beam CT with a curved detector
Authors: Zuo Nianming , Xia Dan , Zou Yu , Jiang Tianzi , Pan Xiao‐Chuan
Published: October 2006

Modern computed tomography (CT) scanners use cone‐beam configurations for increasing volume coverage, improving x‐ray‐tube utilization, and yielding isotropic spatial resolution. Recently, there have been significant developments in theory and algorithms for exact image reconstruction from cone‐beam projections. In particular, algorithms have been proposed for image reconstruction on chords; and advantages over the existing algorithms offered by the chord‐based algorithms include the high flexibility of exact image reconstruction for general scanning trajectories and the capability of exact reconstruction of images within a region of interest from truncated data. These chord‐based algorithms have been developed only for flat‐panel detectors. Many cone‐beam CT scanners employ curved detectors for important practical considerations. Therefore, in this work, we have derived chord‐based algorithms for a curved detector so that they can be applied to reconstructing images directly from data acquired by use of a CT scanner with a curved detector. We have also conducted preliminary numerical studies to demonstrate and evaluate the reconstruction properties of the derived chord‐based algorithms for curved detectors.
Comparison of MR‐thermography and planning calculations in phantoms
Authors: Gellermann J. , Weihrauch M. , Cho C. H. , Wlodarczyk W. , Fähling H. , Felix R. , Budach V. , Weiser M. , Nadobny J. , Wust P.
Published: October 2006

A systematic comparison of three‐dimensional MR (magnetic resonance) thermography and planning calculations in phantoms for the hyperthermia (HT) SIGMA‐Eye applicator. We performed experiments in a homogeneous cylindrical and a heterogeneous elliptical phantom by adjusting 82 different patterns with different phase control inside an MR tomograph (Siemens Magnetom Symphony, ). For MR thermography, we employed the proton resonance frequency shift method with a drift correction based on silicon tubes. For the planning calculations, we used the finite‐difference time‐domain (FDTD) method and, in addition, modeled the antennas and the transforming network. We generated regions according to a segmentation of bones and tissue, and used an interpolation technique with a subgrid of size at the interfaces. A Gauss‐Newton solver has been developed to adapt phases and amplitudes. A qualitative agreement between the planning program and measurements was obtained, including a correct prediction of hot spot locations. The final deviation between planning and measurement is in the range of 2–, i.e., below 10%. Additional HT phase and amplitude adaptation, as well as position correction of the phantom in the SIGMA‐Eye, further improve the results. HT phase corrections in the range of 30– and HT amplitude corrections of are required for the best agreement. The deviation MR‐FDTD, and the HT phase/amplitude corrections depend on the type of phantom, certain channel groups, pattern steering, and the positioning error. Appropriate agreement between three‐dimensional specific absorption rate distributions measured by MR‐thermography and planning calculations is achieved, if the correct position and adapted feed point parameters are considered. As long as feed‐point parameters are uncertain (i.e., cannot be directly measured during therapy), a prospective planning will remain difficult. However, we can use the information of MR thermography to better predict the patterns in the future even without the knowledge of feed‐point parameters.
Calibration of multiple LDR brachytherapy sources
Authors: DeWerd Larry A. , Micka John A. , Holmes Shannon M. , Bohm Tim D.
Published: October 2006

A trend is underway toward the use of prepackaged low dose rate brachytherapy sources, which come in the form of strands, coiled line sources, preloaded needles, and sterile cartridge packs. Since the medical physicist is responsible for verification of source strength prior to patient treatment, development of prepackaged source strength verification methods is needed. Existing guidelines are reviewed to establish the situation that medical physicists find with respect to prepackaged sources. This investigation presents an experimental evaluation of the effect of some of these multiseed geometries on source strength measurements. Multiseed strands and coils, whether , , or can be measured in a chamber with a long, sensitive axial length with a uniform response. Sterile seed cartridge packs can also be measured but require a correction factor to be applied. Sources in needles, however, cannot be measured in the needle since there is too great a variation in needle composition and needle tolerance thickness. Removing these seeds from the needle into a sterile measurement insert, which maintains sterility is a practical source strength verification method, similar to those done for multiple seed configurations in a well chamber with adequate axial uniformity. Values are compared with individual air kerma strength calibrations, and correction factors, are presented where needed. In each case, care must be taken to maintain sterility as multiple seeds are measured in well chamber inserts.
Energy and integrated dose dependence of MOSFET dosimeter sensitivity for irradiation energies between and
Authors: Lavallée Marie‐Claude , Gingras Luc , Beaulieu Luc
Published: October 2006

Since metal‐oxide‐semiconductor field effect transistors (MOSFETs) medical applications in radiotherapy and radiology are gaining popularity, evaluating them under radiation of different energies is of major interest. This study aims at a characterization of MOSFET sensitivity with regard to total integrated dose. Sensitivity is expressed by the water calibration factor and allows the user to associate the voltage difference reading displayed by the device to a dose value in water at the MOSFET location. The of seven ‐type dual‐bias MOSFETs were measured for several accumulated doses. The radiation sources used were a unit , an high dose rate unit , and an orthovoltage unit providing two x‐ray energy spectra for tube voltages of and . The value diminishes with increasing threshold voltage, especially for low‐energy radiation. It was stable for irradiations, while it decreased 6%, 5%, and 15% for beam energies of , , and , respectively. The decrease rate is higher for the first half of the device lifetime. This behavior is explained by an alteration of the effective electric field applied to the MOSFET during irradiation, caused by the accumulation of holes at the interface. It is strongly dependent on the nature of the radiation, and particularly affects low x‐ray energies. A frequent calibration of the device for this radiation type is essential in order to achieve adequate measurement accuracy, especially in low‐energy applications, such as superficial therapy, brachytherapy, and diagnostic and interventional radiology.
Intraoperative cone‐beam CT for guidance of head and neck surgery: Assessment of dose and image quality using a C‐arm prototype
Authors: Daly M. J. , Siewerdsen J. H. , Moseley D. J. , Jaffray D. A. , Irish J. C.
Published: October 2006

Cone‐beam computed tomography (CBCT) with a flat‐panel detector represents a promising modality for intraoperative imaging in interventional procedures, demonstrating sub‐mm three‐dimensional (3D) spatial resolution and soft‐tissue visibility. Measurements of patient dose and in‐room exposure for CBCT‐guided head and neck surgery are reported, and the 3D imaging performance as a function of dose and other acquisition/reconstruction parameters is investigated. Measurements were performed on a mobile isocentric C‐arm (Siemens PowerMobil) modified in collaboration with Siemens Medical Solutions (Erlangen, Germany) to provide flat‐panel CBCT. Imaging dose was measured in a custom‐built cylindrical head phantom at four positions (isocenter, anterior, posterior, and lateral) as a function of kVp and C‐arm trajectory (“tube‐under” and “tube‐over” half‐rotation orbits). At , for example (“tube‐under” orbit), the imaging dose was 0.059 (isocenter), 0.022 (anterior), 0.10 (posterior), and 0.056 (lateral) mGy/mAs, with scans at and typical for visualization of bony and soft‐tissue structures, respectively. Dose to radiosensitive structures (viz., the eyes and thyroid) were considered in particular: significant dose sparing to the eyes (a factor of 5) was achieved using a “tube‐under” (rather than “tube‐over”) half‐rotation orbit; a thyroid shield ( Pb‐equivalent) gave moderate reduction in thyroid dose due to x‐ray scatter outside the primary field of view. In‐room exposure was measured at positions around the operating table and up to from isocenter. A typical CBCT scan ( to isocenter) gave in‐air exposure ranging from at from isocenter, to at from isocenter. Three‐dimensional (3D) image quality was assessed in CBCT reconstructions of an anthropomorphic head phantom containing contrast‐detail spheres and a natural human skeleton. The contrast‐to‐noise ratio (CNR) was evaluated across a broad range of dose . CNR increased as the square root of dose, with excellent visualization of bony and soft‐tissue structures achieved at and , respectively. The prototype C‐arm demonstrates CBCT image quality sufficient for guidance of head and neck procedures based on soft‐tissue and bony anatomy at dose levels low enough for repeat intraoperative imaging, with total dose over the course of the procedure comparable to or less than the effective dose of a typical diagnostic CT of the head.
Measurements of in‐air output ratios for a linear accelerator with and without the flattening filter
Authors: Zhu X. R. , Kang Y. , Gillin M. T.
Published: October 2006

The in‐air output ratio for photon beams from linear accelerators describes the change of in‐air output as a function of the collimator settings. The physical origin of the is mainly due to the change in scattered radiation that can reach the point of measurement as the geometry of the head changes. The flattening filter (FF) and primary collimator are the major sources of scattered radiation. The change in amount of backscattered radiation from the collimator into the beam‐monitoring chamber also contributes to the variation of output. In this work, we measured the and backscatter factors into the beam‐monitoring chamber for a linear accelerator with and without the FF. We measured the with a Farmer‐type chamber in a miniphantom at the depth of for 6‐ and 18‐MV x‐ray beams from a Varian Clinac 2100EX linear accelerator. The were measured with a universal pulse counter and a diode array with build‐in counting hardware and software. The head scatter component was then derived from the relationship , where was the linear fit of measured results. Significant differences were observed for with and without the FF. Within the range of experimental uncertainty, the was similar with and without the FF. The variations in differed significantly over the range of field sizes of to with and without the FF; for the 6‐MV beam, it was 8% vs 3%, and for the 18‐MV beam, 7% vs 1%. By analyzing the contributions of backscatter factor and total in‐air output ratios with and without the FF, we directly gained insight into the contributions of different components to the total variations in of a linear accelerator. , , and are basic and useful dosimetric quantities for delivery of intensity‐modulated radiation therapy using a linear accelerator operating in a mode without the FF.
Highly accelerated MRI by skipped phase encoding and edge deghosting with array coil enhancement (SPEED‐ACE)
Authors: Chang Zheng , Xiang Qing‐San
Published: October 2006

The fast MRI method of skipped phase encoding and edge deghosting (SPEED) is further developed with array coil enhancement, and thus is termed SPEED‐ACE. In SPEED‐ACE, space is sparsely sampled with skipped phase encoding at every step using a set of receiver coils simultaneously, similar to SENSE, leading to sensitivity‐weighted images with up to layers of overlapping aliasing ghosts. The ghosted images are edge enhanced by a differential filter to yield ghosted edge maps, in which the ghost overlapping layers are greatly reduced since the sparseness of edges reduces the chance of ghost overlapping. Typical ghosted edge maps can be adequately modeled with a double‐layer structure. By using data from at least three coils through least‐square‐error minimization, a deghosted edge map is obtained and inverse‐filtered into a final deghosted image. In this way, SPEED‐ACE partially samples space with a skip size of by using multiple receiver coils in parallel, and obtains a fairly good deghosted image with an undersampling factor of . SPEED‐ACE is not limited to the double‐layer ghost model, but can be generalized to include more layers of ghosts for more flexible and improved performance. As a new parallel imaging method, SPEED‐ACE was tested using in vivo data to demonstrate the possibility of achieving undersampling factors even greater than the number of receiver coils, which is so far not achievable by other parallel imaging methods.