10,441 research outputs found
Application of CT in Diagnosing Carcinoma of the Maxillary Sinuses : PART 2: An Experimental Study of Pitfalls Encountered when Diagnosing Carcinoma of the Maxillary Sinuses with CT
No full text1982-03A phantom simulating the transverse section of the maxillary sinuses was constructed for experimentation with various CT scanners to study the following: (1) the occasional inability to image the very thin posterior-lateral walls which have no real bone defects, and (2) to verify whether or not the bony walls surrounding the maxillary sinuses are actually as thick as they appear on CT. The phantom was made of an acrylic cylinder containing three cavities simulating the maxillary sinuses and the nasal cavity and filled with water. The walls, made of thin aluminum and acrylic plates and placed between water and air, disappeared in some CT images. The thickness of the walls calculated from CT values was greater than the true thickness imaged by each CT scanner. The author stresses that in CT images, either experimentally or clinically, thin bony walls placed between water and air or fat tend to disappear, and that bony walls tend to appear thicker than their true thickenss.departmental bulletin pape
X-ray CT Scans of Polistes sp. (wasp)
No full textX-ray CT Scans of a paper wasp for Dr. Timothy Rowe of The University of Texas at Austin. Specimen scanned by Matthew Colbert and Philip Watson 13 December 2004.
Voxel Size X and Y = 0.01464mm, Z= 0.0322mm. Total slices = 540.
Please acknowledge The University of Texas High-Resolution X-ray CT Facility (UTCT)
Advertising value equivalence – PR’s illegitimate offspring.
No full textPublic relations measurement and evaluation have long been major practice subjects. From the late 1970s onwards they have been identified as an important issue for research and practice implementation (McElreath, 1980, 1989; Synnott & McKie, 1997, Watson & Noble 2007; Watson 2008). The evolution of public relations measurement starts much earlier, with some suggesting that media monitoring practices can be identified from the late 18th century onwards (Lamme & Miller, 2010). Although the academic approach to measurement and evaluation has mostly favoured social science methodologies (Broom & Dozier 1990, Michaelson & Stacks 2011), there has been persistent and widespread practice use of Advertising Value Equivalence (AVE) to express the value of public relations activity for decades. Recent data (Daniels & Gaunt, 2009) found that AVE was used by 35% of a large international sample of practitioners. Early significant US practitioners, including Lee and Page, instituted media monitoring of programme outputs and AT&T developed sophisticated opinion researching to guide and monitor its communication activity (Cutlip 1994). Literature in the 1930s and 1940s indicate that these practices were extant, especially basic monitoring of media coverage (Batchelor, 1938). However, there are indications that AVE was in use from the 1940s onward. Plackard and Blackmon (1947) refer to it in the US and provide an example of its calculation. In the UK, the first warning against AVE came in a 1949 edition of the IPR Journal (J. L’Etang, personal communication, January 10, 2011). Both sources thus indicate it was an established practice by mid-century, although it did not surface in professional or quasi-academic literature till the late 1960s. AVE was further operationalized by the emergence of computer based analysis, such as offered by PR Data, in the mid-1960s (Tirone, 1977). From that decade onwards, its use became widespread, as indicated by industry coverage of awards and case studies and by award case studies. Latterly, AVE has been directly challenged by the Barcelona Declaration’s Principle 5 which stated that “AVEs are Not the Value of Public Relations” (AMEC, 2010). It added that AVEs “do not measure the value of public relations and do not inform future activity; they measure the cost of media space and are rejected as a concept to value public relations.” Time will tell whether AVE is replaced by other, valid metrics. This paper investigates the evolution of AVE, which has long been damned as illegitimate, and postulates whether it arose from clippings agencies, advertising planning practices or from other influences on public relations
Patients' & Healthcare Professionals' Values Regarding True- & False-Positive Diagnosis when Colorectal Cancer Screening by CT Colonography: Discrete Choice Experiment.
No full textTo establish the relative weighting given by patients and healthcare professionals to gains in diagnostic sensitivity versus loss of specificity when using CT colonography (CTC) for colorectal cancer screening
Patient doses in ct, dental cone beam ct and projection radiography in Finland, with emphasis on paediatric patients
No full textDiagnostic radiology represents the largest man-made contribution to population radiation doses in Europe. To be able to keep the diagnostic benefit versus radiation risk ratio as high as possible, it is important to understand the quantitative relationship between the patient radiation dose and the various factors which affect the dose, such as the scan parameters, scan mode, and patient size. Paediatric patients have a higher probability for late radiation effects, since longer life expectancy is combined with the higher radiation sensitivity of the developing organs. The experience with particular paediatric examinations may be very limited and paediatric acquisition protocols may not be optimised.
The purpose of this thesis was to enhance and compare different dosimetric protocols, to promote the establishment of the paediatric diagnostic reference levels (DRLs), and to provide new data on patient doses for optimisation purposes in computed tomography (with new applications for dental imaging) and in paediatric radiography.
Large variations in radiation exposure in paediatric skull, sinus, chest, pelvic and abdominal radiography examinations were discovered in patient dose surveys. There were variations between different hospitals and examination rooms, between different sized patients, and between imaging techniques; emphasising the need for harmonisation of the examination protocols.
For computed tomography, a correction coefficient, which takes individual patient size into account in patient dosimetry, was created. The presented patient size correction method can be used for both adult and paediatric purposes. Dental cone beam CT scanners provided adequate image quality for dentomaxillofacial examinations while delivering considerably smaller effective doses to patient compared to the multi slice CT. However, large dose differences between cone beam CT scanners were not explained by differences in image quality, which indicated the lack of optimisation.
For paediatric radiography, a graphical method was created for setting the diagnostic reference levels in chest examinations, and the DRLs were given as a function of patient projection thickness. Paediatric DRLs were also given for sinus radiography. The detailed information about the patient data, exposure parameters and procedures provided tools for reducing the patient doses in paediatric radiography. The mean tissue doses presented for paediatric radiography enabled future risk assessments to be done. The calculated effective doses can be used for comparing different diagnostic procedures, as well as for comparing the use of similar technologies and procedures in different hospitals and countries.Diagnostisen röntgensäteilyn osuus ihmisen aiheuttamasta väestön keskimääräisestä säteilyannoksesta on kaikkein suurin. Jotta diagnostisen hyödyn ja säteilyhaitan välinen suhde voidaan pitää mahdollisimman suurena, on tärkeää ymmärtää kvantitatiivisesti potilaan säteilyannoksen ja siihen vaikuttavien tekijöiden, kuten kuvausarvojen, kuvausmenetelmien ja potilaiden kokojen välinen suhde. Lapsipotilailla on aikuisia suurempi riski säteilyn myöhäisiin haittavaikutuksiin, mikä on seurausta pitkästä odotettavissa olevasta eliniästä sekä kehittyvien elinten korkeasta säteilyherkkyydestä. Henkilökunnan kokemus tietyissä lasten tutkimuksissa voi olla rajallinen eikä lasten kuvausmenetelmiä välttämättä ole optimoitu.
Työn tarkoituksena oli kehittää ja vertailla eri annosmittausmenetelmiä tietokonetomografiatutkimuksissa (TT) ja lasten natiiviröntgentutkimuksissa, edistää lasten vertailutasojen käyttöönottoa sekä tuottaa uutta potilasannostietoa röntgentutkimusten optimointia varten.
Potilasannoskartoituksissa todettiin suuria vaihteluita kuvaustekniikoissa eri sairaaloiden, tutkimushuoneiden ja eri kokoisten potilaiden välillä. Tutkimustekniikoiden vaihtelusta aiheutuneet erot potilasannoksissa osoittivat tarvetta kuvausmenetelmien optimoinnille sekä kansallisella, että kansainvälisellä tasolla.
Tietokonetomografiatutkimuksia varten kehitettiin korjauskerroin, joka ottaa potilaan koon huomioon aikuisten ja lasten potilasannoksia määritettäessä. Tietokonetomografiatutkimuksissa lapset, naiset ja pienikokoiset potilaat absorboivat säteilyä suhteellisesti isokokoisia potilaita voimakkaammin. Hampaiston kuvantamisessa käytettävien rajoitetun kartiokeilan TT-laitteiden kuvanlaatu todettiin riittäväksi potilasannosten ollessa oleellisesti pienempiä kuin monileike-TT-laitteilla. Eri kartiokeila-TT-laitteiden potilasannoksissa oli kuitenkin suuria eroja kuvanlaadusta riippumatta, mikä osoitti tarvetta kuvaustekniikoiden jatkokehitykselle.
Lasten keuhkokuvauksia varten annettiin graafiset vertailutasot, joiden avulla sairaalat voivat suoraan verrata eri kokoisten potilaiden säteilyannoksia vertailutasoon. Vertailutasot annettiin myös lasten nenän sivuontelokuvauksia varten. Yksityiskohtaiset tiedot kerätystä aineistosta, kuvausarvoista ja -menetelmistä antoivat työkalut potilasannosten vähentämiseksi lasten natiiviröntgentutkimuksissa. Kudoksiin absorboituvien annosten määrittäminen mahdollistaa jatkossa potilaskohtaiset riskiarvioinnit. Määritettyjä efektiivisiä annoksia voidaan käyttää diagnostisten menetelmien ja kuvaustekniikoiden vertailuun eri sairaaloiden ja valtioiden välillä.ei saavutettav
Use of CT Colonography in the English Bowel Cancer Screening Programme
No full textObjective: To examine use of CT colonography (CTC) in the English Bowel Cancer Screening Programme (BCSP) and investigate detection rates.
Design: Retrospective analysis of routinely coded BCSP
data. Guaiac faecal occult blood test (gFOBt)-positive
screenees undergoing CTC from June 2006 to July 2012
as their first-line colonic investigation were included.
Abnormalities found at CTC, subsequent polyp, adenoma
and cancer detection and positive predictive value (PPV)
were calculated. Detection rates were compared with
those observed in gFOBt-positive screenees investigated
by colonoscopy. Multilevel logistic regression was used
to examine factors associated with variable detection.
Results: 2731 screenees underwent CTC. Colorectal
cancer (CRC) or polyps were suspected in 1027
individuals (37.6%; 95% CI 33.8% to 41.4%); 911 of
these underwent confirmatory testing. 124 screenees
had CRC (4.5%) and 533 had polyps (19.5%), 468
adenomatous (17.1%). Overall detection was 24.1%
(95% CI 21.5% to 26.6%) for CRC or polyps and
21.7% (95% CI 19.2% to 24.1%) for CRC or adenoma.
Advanced neoplasia was detected in 504 screenees
(18.5%; 95% CI 16.1% to 20.8%). PPV for CRC or
polyp was 72.1% (95% CI 66.6% to 77.6%). By
comparison, 9.0% of 72 817 screenees undergoing
colonoscopy had cancer and 50.6% had polyps;
advanced neoplasia was detected in 32.7%. CTC
detection rates and PPV were higher at centres with
experienced radiologists (>1000 examinations) and at
high-volume centres (>175 cases/radiologist/annum).
Centres using three-dimensional interpretation detected
more neoplasia.
Conclusions: In the BCSP, detection rates after positive
gFOBt are lower for CTC than colonoscopy, although
populations undergoing the two tests are different.
Centres with more experienced radiologists have higher
detection and accuracy. Rigorous quality assurance of
BCSP radiology is needed
An approach to increasing the resolution of industrial CT images based on an aperture collimator
No full textThe spatial resolution of CT images is dominated by the focal spot size when it is large relative to the detector cells. We propose an approach to increase the spatial resolution by utilizing an aperture collimator. The aperture collimator is specially designed and placed in front of the X-ray source so that the rays penetrating the collimator form a set of narrow fan beams. Then an iterative algorithm is introduced to reconstruct CT images from the data obtained by scanning the narrow fan beams. Numerical experiments show that the proposed approach could significantly increase the resolution of the CT images. Furthermore, this approach is also robust against some challenging cases, such as the examination of low contrast object, reconstruction based on multi-energy data and perturbation of geometric errors in CT systems. (C) 2013 Optical Society of AmericaOpticsSCI(E)EI1ARTICLE2327946-279632
Author Co-Citation Analysis (ACA): a powerful tool for representing implicit knowledge of scholar knowledge workers
No full textIn the last decade, knowledge has emerged as one of the most important and valuable organizational assets. Gradually this importance caused to emergence of new discipline entitled ―knowledge management‖. However one of the major challenges of knowledge management is conversion implicit or tacit knowledge to explicit knowledge. Thus Making knowledge visible so that it can be better accessed, discussed, valued or generally managed is a long-standing objective in knowledge management. Accordingly in this paper author co- citation analysis (ACA) will be proposed as an efficient technique of knowledge visualization in academia (Scholar knowledge workers)
Verbeterde beeldreconstructie bij CT-scanners
No full textDe CT-scanner heeft een belangrijke rol in de medische wereld. Helaas gebruikt de CT-scanner voor het opstellen van een scan schadelijke straling. In dit onderzoek is nagegaan of er een betere beeldreconstructietechniek te vinden is voor het opstellen van een CT-afbeelding met gebruik van minder straling.De standaard voor het opstellen van een CT-afbeelding is het gebruik van de 2-norm. Vergelijken we de CT-afbeeldingen geconstrueerd met de 2-norm met CT-afbeeldingen geconstrueerd met de 1-norm en 0.5-norm dan zien we dat de 1-norm visueel het beste resultaat oplevert.Naast het vergelijken van de verschillende normen hebben we ook verschillende epsilon-regularisatiemethodes bekeken. De numerieke experimenten met de verschillende epsilon-regularisatiemethodes hebben we uitgevoerd op een systeem met 0%, 3% en 10% ruis, om te onderzoeken welke methode het beste toepasbaar is in de praktijk. Van de door ons geteste epsilon-regularisatiemethodes bleek de epsilon-regularisatie met epsilon := epsilon/2 met startwaarde epsilon = 10^(-8) en gebruik van de 1-norm de meest geschikte methode om een onderbepaald CT-probleem op te lossen
MRI-based synthetic CT in the detection of knee osteoarthritis: Comparison with CT
No full textMagnetic resonance Imaging is the gold standard for assessment of soft tissues; however, X-ray-based techniques are required for evaluating bone-related pathologies. This study evaluated the performance of synthetic computed tomography (sCT), a novel MRI-based bone visualization technique, compared with CT, for the scoring of knee osteoarthritis. sCT images were generated from the 3T T1-weighted gradient-echo MR images using a trained machine learning algorithm. Two readers scored the severity of osteoarthritis in tibiofemoral and patellofemoral joints according to OACT, which enables the evaluation of osteoarthritis, from its characteristics of joint space narrowing, osteophytes, cysts and sclerosis in CT (and sCT) images. Cohen's κ was used to assess the interreader agreement for each modality, and intermodality agreement of CT- and sCT-based scores for each reader. We also compared the confidence level of readers for grading CT and sCT images using confidence scores collected during grading. Inter-reader agreement for tibiofemoral and patellofemoral joints were almost-perfect for both modalities (κ = 0.83–0.88). The intermodality agreement of osteoarthritis scores between CT and sCT was substantial to almost-perfect for tibiofemoral (κ = 0.63 and 0.84 for the two readers) and patellofemoral joints (κ = 0.78 and 0.81 for the two readers). The analysis of diagnosis confidence scores showed comparable visual quality of the two modalities, where both are showing acceptable confidence levels for scoring OA. In conclusion, in this single-center study, sCT and CT were comparable for the scoring of knee OA.</p
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