177,033 research outputs found
The use of molecular sieves to simulate hot lesions in (18)F-fluorodeoxyglucose--positron emission tomography imaging
No full textConversion factors of effective and equivalent organ doses with the air kerma area product in patients undergoing coronary angiography and percutaneous coronary interventions
No full textTo derive effective dose (E), organ dose (HT) and conversion factors with the air kerma area product (KAP) in coronary angiography (CA) and percutaneous coronary intervention (PCI) by the radial route, using the ICRP 103 tissue weighting factors. The study included 34 patients referred for CA and 31 for PCI. E and HT were derived from in-the-field KAP measurements using Montecarlo methods. Median KAP of 23.2 and 56.8Gycm2 and E of 6.9 and 20.0mSv were found for CA and PCI, respectively. Mean KAP and E were significantly higher in males than in females (52.4±40.0 vs 32.3±16.6Gycm2; p=0.02) and (16.8±13.6 vs 10.7±5.8mSv; p=0.04). KAP (r=0.39; p=0.001) and E (r=0.34; p=0.005) showed a significant correlation with the patient's weight. Conversion factors between KAP and E (E/KAP) were 0.30±0.04mSvGy-1cm-2 for CA and 0.33±0.05mSvGy-1cm-2 for PCI. No significant differences in the E/KAP between males and females were found (0.31±0.05 vs 0.33±0.05; p=0.08). Again, no significant correlation was found between E/KAP and patient's weight (r=0.23; p=0.07). The correlation between E and KAP was excellent for CA (r=0.99) and PCI (r=0.96). The correlation between HT and KAP ranged from r=0.87 to r=1 and from r=0.71 to r=0.98 for CA and PCI, respectively. A single factor, the total KAP, could be used for a specific acquisition protocol to reliably estimate E and HT without the need of a patient's specific analysis. Conversion factors might be installation, X-ray beam quality or protocol dependent
Minimum acceptable sensitivity of intraoperative gamma probes used for sentinel lymph node detection in melanoma patients
No full textThe aim of this study was to determine the suspension level for the sensitivity of an intraoperative scintillation gamma probe in the detection of the sentinel lymph node (SLN) in melanoma patients. Thirty-eight consecutive patients with melanoma were enrolled in the study during a 12-month period and underwent lymphatic scintigraphy after the peritumoral intradermal administration of about 14 MBq of (99m)Tc-nanocolloids. The SLNs were successfully removed during the surgical intervention about 4 h later. To identify and localize the SLN, a scintillation NaI(Tl) collimated probe was used. Predictably, the probe sensitivity decreased as the photopeak energy window was progressively narrowed, from 6.9 ± 0.7 counts per second (cps)/kBq (designated as the 'optimum,' or 'OPT,' sensitivity) to 2.5 ± 0.3 cps/kBq (LOW sensitivity) and to 1.4 ± 0.2 cps/kBq (VLOW sensitivity). Maximum lymph node count rates (cps) were determined for the foregoing energy windows prior to skin incision (PREOPT, PRELOW, PREVLOW, respectively) and in vivo after incision (INVOPT, INVLOW, INVVLOW). Forty-three SLNs were removed with a mean source-to-detector distance of 46 ± 24 mm (min 12 mm, max 92 mm). Four SLNs could not have been detected using PRELOW. This figure would have decreased to 34, with nine undetectable lymph nodes, with PREVLOW. One SLN could not have been identified using INVLOW and four could not have be identified using INVVLOW. In the clinical scenario of SLN detection in melanoma patients, a system sensitivity of 2.5 cps/kBq represents a suspension level, that is, a level under which the equipment must be suspended from clinical use and the poor performance must be investigated
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Estimated Radiation Exposure from Medical Imaging in Hemodialysis Patients
No full textRadiation exposure accompanying medical imaging associates with cancer risk. Patients with recurrent or chronic diseases may be especially at risk, because they may undergo more of these procedures. The aim of this study was to assess the individual cumulative effective doses (CEDs), which quantify radiation from medical imaging procedures, in a cohort of 106 hemodialysis patients during a median follow-up of 3 years. We retrospectively calculated individual radiation exposures by collecting the number and type of radiologic procedures from hospital records. We also estimated organ doses for computed tomography procedures. The mean and median annual CEDs were 21.9 and 11.7 mSv per patient-year, respectively. The mean and median total CEDs per patient during the study period were 57.7 and 27.3 mSv, respectively. By radiation dose group, we classified 22 patients as low (100 mSv, a value associated with a substantial increase in risk for cancer-related mortality. Of the total CED,s 76% was a result of CT scanning. The annual CED significantly associated with age and transplant waitlist status. In summary, this study shows that a significant fraction of surviving hemodialysis patients during a 3-year period receives estimated radiation doses that may put them at an increased risk for cancer
Estimated radiation risk of cancer from medical imaging in haemodialysis patients.
No full textBACKGROUND: In recent years the widespread use of medical procedures increased the cumulative effective doses of ionizing radiation. Although many haemodialysis patients undergo multiple examinations with high radiation exposure, no data are available characterizing their attendant potential risks of cancer.
METHODS: The radiation exposures were obtained from a retrospective study of 159 consecutive haemodialysis patients with a follow-up duration ≥ 1 year. Effective dose and organ dose were estimated on an individual basis. Radiation risk was expressed as risk of exposure-induced death (REID) (%).
RESULTS: The 159 patients (101 males) were followed for a median of 2.7 years (mean 3.0 years). A total of 486 patient-years were available for follow-up. The mean age at study entry was 65.3 years. The mean cumulative organ doses were 103, 102, 100, 99, 77 and 58 mSv for kidneys, lung, stomach, liver, colon and bone marrow, respectively. On average, computed tomography, nuclear medicine and interventional radiology accounted for 90, 4.5 and 5.5% of organ doses, respectively. The average REID was 0.99% (i.e. odds 1 in 100) and the median REID was 0.45%. At univariate analysis, increasing age and presence of diabetes were independent predictors of lower REID, whilst patients eligible for kidney transplantation were exposed to a significantly higher REID. At multivariate analysis, younger age was an independent predictor of higher REID.
CONCLUSIONS: The excess cancer risk-attributable radiation exposure in haemodialysis patients is not negligible. Particular attention should be paid to younger patients and to patients who will undergo kidney transplantation
Performance characteristics obtained for a new 3-dimensional lutetium oxyorthosilicate-based whole-body PET/CT scanner with the National Electrical Manufacturers Association NU 2-2001 standard
No full textThe effect of activity outside the field of view on image quality for a 3D LSO-based whole body PET/CT scanner
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"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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