1,720,968 research outputs found
Agreement between left ventricular ejection fraction assessed in patients with gated IQ-SPECT and conventional imaging
No full textBACKGROUND:
The aim of the study was to assess the agreement between the left ventricular ejection fraction (LVEF) values obtained with IQ-SPECT and those obtained with a conventional gamma camera equipped with low-energy high-resolution (LEHR), considered as the method of reference.
METHODS:
Gated-stress MPI using 99mTc-tetrofosmin was performed in 55 consecutive patients. The patients underwent two sequential acquisitions (Method A and B) performed on Symbia-IQ SPECT with different acquisition times and one (Method C) on a Ecam SPECT equipped with LEHR collimators. The values of the different datasets were compared using the Bland-Altman analysis method: the bias and the limits of agreement (LA) were estimated in a head-to-head comparison of the three protocols.
RESULTS:
In the (Method A-Method C) comparison for LVEF, the bias was 3.8% and the LAs ranged from - 9.3% to 16.8%. The agreement was still lower between Method B and C, whilst only slightly improved when Methods A and B were compared.
CONCLUSIONS:
The wide amplitude in LA intervals of about 30% indicates that IQ and LEHR GSPECT are not interchangeable. The values obtained with IQ-SPECT should only be used with caution when evaluating the functional state of the heart
The role of activity, scan duration and patient's body mass index in the optimization of FDG imaging protocols on a TOF-PET/CT scanner
No full textBACKGROUND: Time-of-flight (TOF) PET technology determines a reduction in the noise and improves the reconstructed image quality in low count acquisitions, such as in overweight patients, allowing a reduction of administered activity and/or imaging time. However, international guidelines and recommendations on the 18F-fluoro-2-deoxyglucose (FDG) activity administration scheme are old or only partially account for TOF technology and advanced reconstruction modalities. The aim of this study was to optimize FDG whole-body studies on a TOF-PET/CT scanner by using a multivariate approach to quantify how physical figures of merit related to image quality change with acquisition/reconstruction/patient-dependent parameters in a phantom experiment.METHODS: The NEMA-IQ phantom was used to evaluate contrast recovery coefficient (CRC), background variability (BV) and contrast-to-noise ratio (CNR) as a function of changing emission scan duration (ESD), activity concentration (AC), target internal diameter (ID), target-background activity ratio (TBR) and body mass index (BMI). The phantom was filled with an average concentration of 5.3kBq/ml of FDG solution and the spheres with TBR of 21.2, 8.8 and 5.0 in 3 different sessions. Images were acquired at varying background activity concentration from 5.1 to 1.3kBq/ml, and images were reconstructed for ESD of 30-151s per bed position with and without point spread function (PSF) correction. The parameters were all considered in a single analysis using multiple linear regression methods.RESULTS: As expected, CRC depended only on sphere ID and on PSF application, while BV depended on sphere ID, ESD, AC and BMI of the phantom, in order of decreasing relevance. Noteworthy, ESD and AC resulted as the most significant predictors of CNR variability with a similar relevance, followed by the BMI of the patient and TBR of the lesion.CONCLUSIONS: AC and ESD proved to be effective tools in modulating CNR. ESD could be increased rather than AC to improve image quality in overweight/obese patients to fulfil ALARA principles
Patients undergoing multiphase CT scans and receiving a cumulative effective dose of ≥ 100 mSv in a single episode of care
No full textOBJECTIVES: To estimate the number of patients who receive a cumulative effective dose (CED) of ≥100mSv from computed tomography (CT) in a single day or episode of care.METHODS: We examined 28,870 patients who underwent 49,834 CT examinations in a tertiary care centre in Italy in 2.5years. Radiation exposures were retrieved from the hospital's automatic exposure monitoring system. Two cohorts were identified as those who received a CED of ≥100mSv in a single day and within a month starting from the first examination. Organ doses were estimated for the first cohort.RESULTS: Among the 1765 (6.1%) patients who received CED ≥100mSv in the observation period, 427 received a CED of ≥100mSv within a month (and 70 patients in a single day). This group represented 1.5% of all patients who underwent CT exams and 24% of those who received CED ≥100mSv in the observation period. The clinical indication for referral included cancer in 132 patients (31%) and non-oncological indications in 295 patients (69%). In 68/70 patients with CED>100mSv in a single day, at least one organ/tissue received a dose of ≥100mGy.CONCLUSIONS: The finding of a sizeable percentage of patients undergoing CT exams and receiving CED ≥100mSv in a single episode of care points toward the need of imaging appropriateness criteria, to revise the routine protocols, to replace older machines, and to provide to the radiologist the patient's prior radiation history to facilitate an appropriate decision-making process.KEY POINTS: Patients can receive effective doses greater than 100mSv in a single CT or in multiple CT examinations performed in a single episode of care in 1.5% of patients in a 2.5-year period. In this study, the clinical indication for CT referral was non-oncological in 69% of patients. The patient's prior radiation history should be provided to the referring physicians and the radiological medical practitioner to facilitate an appropriate decision-making process
Radiation exposure from medical imaging in dialyzed patients undergoing renal pre-transplant evaluation
No full textBACKGROUND AND AIM:
Ionizing radiation exposure from medical procedures is rising sharply-the per-capita annual effective dose in the US is 3.0 millisieverts (mSv). Hemodialyzed and kidney transplanted patients receive still higher doses of ionizing radiation due to the presence of multiple comorbidities. The aim of this study was to assess the cumulative effective dose (CED) among dialyzed patients undergoing renal pre-transplant evaluation.
PATIENTS AND METHODS:
We evaluated 70 hemodialysis patients between June 2009 and December 2014, aged 46.4 ± 12.0 years. The number and type of radiologic procedures were collected through the Radiology Information System. CED was expressed as total mSv/patient and annual CED (mSv/patient/year).
RESULTS:
A total of 744 radiologic procedures were performed, accounting for 3869 mSv of ionizing radiation: conventional radiology, computed tomography and nuclear medicine accounted for 78, 14 and 8 % of the procedures, but they represented, respectively, 8, 83 and 9 % of the total CED. The mean (median) annual CED was 35 (7) mSv/patient/year, while total CED was 72 (32) mSv/patient. Thirty-seven patients were active waitlisted and received 47 (10) mSv during the pre-transplant evaluation and 36 (5) mSv during the waiting phase to maintain active status. Concerning cancer risk, 4 (7 %) patients were classified at low risk (<3 mSv/year), 19 (35 %) at moderate risk (3 to <20 mSv/year), 8 (15 %) at high risk (20 to <50 mSv/year), and 23 (43 %) at very high risk (≥50 mSv/year).
CONCLUSIONS:
Our study demonstrated that during renal pre-transplant evaluation, dialyzed patients receive a high dose of ionizing radiation. Considering that transplanted individuals have a high incidence of cancer due to multifactorial etiology, it is mandatory to reduce the ionizing radiation imaging
Conversion factors for effective dose and organ doses with the air kerma area product in patients undergoing percutaneous transhepatic biliary drainage and trans arterial chemoembolization
No full textConversion factors used to estimate effective (E) and organ doses (HT) from air Kerma area product (KAP) are required to estimate population doses in percutaneous transhepatic biliary drainage (PTBD) and trans arterial chemoembolization (TACE) interventional procedures.
In this study, E and HT for ten critical organs/tissues, were derived in 64 PTBD and 48 TACE procedures and in 14,540 irradiation events from dosimetric, technical and geometrical information included in the radiation dose structured report using the PCXMC Monte Carlo model, and the ICRP 103 organ weighting factors. Conversion factors of: 0.13; 0.19; 0.26 and 0.32 mSv Gy−1 cm−2 were established for irradiation events characterized by a Cu filtration of 0.0; 0.1; 0.4 and 0.9 mm, respectively. While a single coefficient of conversion is not able to provide estimates of E with enough accuracy, a high agreement is obtained between E estimated through Monte Carlo methods and E estimated through E/KAP conversion factors accounting separately for the different modes of fluoroscopy and the fluorography component of the procedures.
An algorithm for the estimation of effective and organ doses from KAP has been established in biliary procedures which considers the Cu filtration in the X-ray irradiation events. A similar algorithm could be easily extended to other interventional procedures and incorporated in radiation dose monitoring systems to provide dosimetric estimates automatically with enough accuracy to assess population doses
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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